Wafer holder, heater unit having the wafer holder, and wafer prober having the heater unit
A wafer holder hardly deformable under high load and capable of effectively preventing a contact failure with a wafer and further capable of preventing temperature increase of a driving system of a wafer prober is provided. In a wafer holder having a chuck top and a supporter, variation in thickness of the chuck top from a wafer-mounting surface to a contact surface with the supporter, and variation in thickness of the supporter from a bottom surface to a contact surface with the chuck top are both set to at most 50 μm. When the supporter is of a structure having a circular tube portion and a base portion separate from each other, variation in thickness of the circular tube portion from a contact surface with the chuck top to a contact surface with the base portion, and variation in thickness of the base portion from a bottom surface to a contact surface with the circular tube portion are preferably both set to at most 25 μm.
1. Field of the Invention
The present invention relates to a wafer holder used for a wafer prober for inspecting electric characteristics of a semiconductor wafer by mounting and fixing the wafer on a wafer-mounting surface and pressing a probe card on the wafer, as well as to a heater unit including the wafer holder and a wafer prober including the heater unit.
2. Description of the Background Art
Conventionally, in a process for inspecting a semiconductor wafer, a semiconductor wafer (wafer) as an object of processing has been subjected to heat treatment (that is, burn-in). Specifically, by heating the wafer to a temperature higher than the normal temperature of use, degradation of a possibly defective semiconductor chip is accelerated and the defective chip is removed, in order to prevent defects after shipment. In the burn-in process, after semiconductor circuits are formed on the semiconductor wafer and before the wafer is cut into individual chips, electrical characteristics of each semiconductor chip are measured while the semiconductor wafer is heated and defective ones are removed. In the burn-in process, reduction of process time is strongly desired in order to improve throughput.
In the burn-in process as such, a chuck top for holding a semiconductor substrate and containing a heater for heating the wafer is used. As the conventional heater, one formed of metal has been used, because it is necessary to have the entire rear surface of the wafer in contact with the ground electrode. On a flat plate heater formed of metal, the wafer having the circuits formed thereon is mounted and heated by the heater provided inside, while a probe card having a number of electrode pins for electric conduction is pressed on the wafer for inspecting the electric characteristics of the wafer chip. At this time, an operation of moving a wafer holder on which the chuck top is mounted to a prescribed position by a driving system and pressing the wafer to a probe referred to as a probe card having a number of electrode pins for electric conduction is repeated. In the burn-in process, reduction of process time is strongly desired in order to improve throughput.
As described above, the wafer mounted on the chuck top is pressed to the probe card with a strong force of several tens to several hundreds kgf, and therefore, when the heater is thin, the heater would possibly be deformed, resulting in contact failure between the wafer and the ground electrode. Therefore, it has been necessary to use a thick metal plate having the thickness of at least 15 mm for the conventional chuck top formed of metal, for maintaining rigidity of the chuck top and the wafer holder. As a result, it takes long time to increase and decrease the temperature of the heater contained in the chuck top, which is a significant drawback in improving the throughput.
In the burn-in process, the chip is electrically conducted and electric characteristics are measured. As recent chips come to have higher outputs, it is possible that a chip generates considerable heat during measurement of electric characteristics, and in some situations, the chip might be broken by self-heating. Therefore, after measurement, rapid cooling is required. During measurement, heating as uniform as possible is required. In view of the foregoing, copper (Cu) having thermal conductivity as high as 403 W/mK has been used as the metal material.
In consideration of such problems, Japanese Patent Laying-Open No. 2001-033484 proposes a wafer prober using a ceramic substrate that is thin but having high rigidity and is not susceptible to deformation with a thin metal conductive layer formed on its surface, in place of the thick metal plate. It is described that the chuck top having the metal conductive layer formed on the surface of the ceramic substrate has high rigidity and not much susceptible to deformation, and therefore, it does not cause contact failure, and in addition, it has small thermal capacity and hence allows heating and cooling in a short period of time. It is described that as a support base for mounting the chuck top, an aluminum alloy or stainless steel is used.
The wafer prober described in Japanese Patent Laying-Open No. 2001-033484 above has high rigidity and hardly deforms, as a ceramic substrate is used.
As described in Japanese Patent Laying-Open No. 2001-033484, however, when the wafer prober is supported only by the outermost circumference, the wafer may warp when pressed by the probe card, and therefore, it has been necessary to devise measures, such as providing a number of pillars.
Further, recently, as the semiconductor processes have come to be miniaturized, the load applied per unit area at the time of probing has been increased, and high accuracy of registration between the probe card and the prober comes to be required. The prober typically repeats an operation of heating the wafer to a prescribed temperature, moving to a prescribed position at the time of probing, and pressing the probe card. At this time, in order to move the prober to the prescribed position, driving system thereof is also required of high positional accuracy.
There is a problem, however, that when the wafer is heated to a prescribed temperature, that is, to about 100 to 200° C., the heat is transferred to the driving system, and metal components forming the driving system thermally expand, degrading positional accuracy. This is a cause of a contact failure made more likely during an inspection of a semiconductor chip having a particularly minute circuitry. Further, along with the increase in load at the time of probing, rigidity of the prober itself mounting the wafer has come to be required. Specifically, when the wafer prober itself deforms because of the load at the time of probing, uniform contact of the pins of probe card with the wafer would fail and inspection becomes impossible, or in the worst case, the wafer would be broken. In order to suppress deformation of the prober, the prober has been made larger and its weight has been increased, posing a problem that the increased weight adversely influences the accuracy of the driving system. Further, as the prober is made larger, the time for heating and cooling the prober becomes extremely long, posing another problem of lower throughput.
Further, in order to improve throughput, it is often the case that a cooling mechanism is provided for improving the heating/cooling rate of the prober. Conventionally, however, the cooling mechanism has been air-cooling as described in Japanese Patent Laying-Open No. 2001-033484, or a cooling plate has been provided immediately below the heater formed of metal. The former approach has a problem that cooling rate is slow, as it is air-cooling. The latter approach also has a problem that, as the cooling plate is metal and the pressure of the probe card directly acts on the cooling plate at the time of probing, it is susceptible to deformation.
Further, in the prober, stress generated at the time of probing results in a load on the chuck top, causing deformation. When the deformation involves large deflection, state of contact between the large number of probe pins attached to the probe card and the wafer may vary and errors may possibly occur at the time of measurement, posing a problem that accurate evaluation becomes impossible.
SUMMARY OF THE INVENTIONIn view of the situations of the conventional art as described above, an object of the present invention is to provide a wafer holder capable of effectively preventing contact failure with a wafer, with deformation of a chuck top being small even under high load. A further object is to provide a wafer holder capable of preventing temperature increase in a driving system of the wafer holder, when a semiconductor wafer having minute circuitry requiring particularly high accuracy is mounted on a chuck top and heated. A still further object is to provide a heater unit including the wafer holder described above and a wafer prober including the heater unit.
In order to attain the above-described objects, the wafer holder provided by the present invention is characterized in that the wafer holder has a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting the chuck top, wherein variation in thickness of the chuck top from the wafer-mounting surface to a contact surface with the supporter is at most 50 μm, and variation in thickness of the supporter from a bottom surface to a contact surface with the chuck top is at most 50 μm.
Preferably, in the wafer holder described above, the supporter has a structure including a circular tube portion in contact with the chuck top and a base portion supporting the circular tube portion, with the circular tube portion and the base portion separated, variation in thickness of the circular tube portion from a contact surface with the chuck top to a contact surface with the base portion is at most 25 μm, and variation in thickness of the base portion from a bottom surface to a contact surface with the circular tube portion is at most 25 μm.
More preferably, in the wafer holder described above, variation in thickness of the chuck top from the wafer-mounting surface to the contact surface with the supporter, variation in thickness of the supporter from the bottom surface to the contact surface with the chuck top, variation in thickness of the circular tube portion from the contact surface with the chuck top to the contact surface with the base portion, and variation in thickness of the base portion from the bottom surface to the contact surface with the circular tube portion are all at most 10 μm.
Preferably, in the wafer holder described above, ratio of the maximum diameter to the maximum thickness of the chuck top, that is, ratio of the maximum diameter to the maximum thickness (diameter/thickness) is at least 5 and at most 100. Further, it is preferred that the ratio described above is at least 10 and at most 50.
Preferably, in the wafer holder described above, the material of the chuck top is a composite of metal and ceramics, and more preferably, it is a composite of aluminum and silicon carbide, or a composite of silicon and silicon carbide. Alternatively, the material of the chuck top may be ceramics.
Preferably, in the wafer holder described above, the material of the supporter is ceramics or a composite of two or more ceramics, and more preferably, it is any of alumina, silicon nitride, mullite, and a composite of alumina and mullite.
Preferably, in the wafer holder described above, the supporter is formed of a circular tube portion in contact with the chuck top and a base portion supporting the circular tube portion, thickness of the circular tube portion is at least 0.1 and at most 5.0 with thickness of the chuck top being 1.0, and thickness of the base portion is at least 0.5 and at most 10.0 with thickness of the chuck top being 1.0. Further, it is preferred that the circular tube portion and the base portion are formed integrally.
Preferably, the wafer holder described above has a pillar between the circular tube portion and the base portion or between the circular tube portion and the chuck top, and a sum of thickness of the pillar and the circular tube portion is at least 0.1 and at most 5.0 with thickness of the chuck top being 1.0.
The present invention is also directed to a wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting the chuck top, wherein ratio of the maximum diameter to the maximum thickness of the chuck top is at least 5 and at most 100.
Preferably, in the wafer holder described above, the ratio of the maximum diameter to the maximum thickness of the chuck top is at least 10 and at most 50.
Preferably, in the wafer holder described above, the material of the chuck top is a composite of metal and ceramics.
Preferably, in the wafer holder described above, the material of the chuck top is a composite of aluminum and silicon carbide, or a composite of silicon and silicon carbide.
Preferably, in the wafer holder described above, the material of the chuck top is ceramics.
Preferably, in the wafer holder described above, the material of the supporter is ceramics or a composite of two or more ceramics.
Preferably, in the wafer holder described above, the material of the supporter is any of alumina, silicon nitride, mullite, and a composite of alumina and mullite.
The present invention is also directed to a wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting the chuck top, wherein the supporter is formed of a circular tube portion in contact with the chuck top and a base portion supporting the circular tube portion, thickness of the circular tube portion is at least 0.1 and at most 5.0 with thickness of the chuck top being 1.0, and thickness of the base portion is at least 0.5 and at most 10.0 with thickness of the chuck top being 1.0.
Preferably, in the wafer holder described above, the circular tube portion and the base portion are formed integrally.
Preferably, the wafer holder described above has a pillar between the circular tube portion and the base portion or between the circular tube portion and the chuck top, and a sum of thickness of the pillar and the circular tube portion is at least 0.1 and at most 5.0 with thickness of the chuck top being 1.0.
Further, the present invention also provides a heater unit for a wafer prober characterized in that it includes any of the wafer holders in accordance with the present invention described above, and a wafer prober characterized in that it includes the heater unit.
According to the present invention, in a wafer holder having a chuck top mounting and fixing a wafer and a supporter supporting the chuck top, variation in thickness of the chuck top from the wafer-mounting surface to the contact surface with the supporter, and variation in thickness of the supporter from the bottom surface to the contact surface with the chuck top are both set to at most 50 μm, and therefore, when electric characteristics of a wafer are measured in the burn-in process, the chuck top deformation is small even when high load is applied, and contact failure with the wafer can effectively be prevented. Further, at the measurement of a semiconductor wafer having minute circuitry that requires particularly high accuracy, temperature increase in the driving system of the wafer holder is prevented when the wafer is mounted on the chuck top and heated, and therefore, positional accuracy between the wafer and the probe card can be improved.
Further, in the present invention, when the ratio of the maximum diameter to the maximum thickness of the chuck top is set to at least 5 and at most 100, deformation (deflection) of the chuck top can be reduced, and therefore, a wafer prober capable of accurately measuring electric characteristics of the wafer without damaging the wafer can be provided.
In the present invention, when the supporter is formed of a circular tube portion in contact with the chuck top and a base portion supporting the circular tube portion, the thickness of the circular tube portion is at least 0.1 and at most 5.0 with the thickness of the chuck top being 1.0, and the thickness of the base portion is at least 0.5 and at most 10.0 with the thickness of the chuck top being 1.0, a wafer holder having high rigidity and superior heat insulating effect can be provided. In this case, the chuck top deformation is small even when a high load is applied, and contact failure with the wafer can effectively be prevented. Further, at the measurement of a semiconductor wafer having minute circuitry that requires particularly high accuracy, temperature increase in the driving system of the wafer holder is prevented when the wafer is mounted on the chuck top and heated, and therefore, positional accuracy between the wafer and the probe card can be improved.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 17 to 22 are schematic cross-sectional views showing examples of the wafer holder in accordance with the present invention.
FIGS. 24 to 29 are schematic cross-sectional views showing examples of the wafer holder in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific, basic example of a wafer holder in accordance with the present invention will be described with reference to
In wafer prober 100 of the present invention, variation in thickness of chuck top 2 from the wafer-mounting surface (when chuck top conductive layer 3 is provided on chuck top 2, from the surface of chuck top conductive layer, same in the following) to the contact surface between chuck top 2 and supporter 4 is set to at most 50 μm, and variation in thickness of supporter 4 from the bottom surface to the contact surface between supporter 4 and chuck top 2, that is, variation in thickness of chuck top 2 and supporter 4, is set to at most 50 μm. With the variation in thickness of chuck top 2 and supporter 4 adjusted to be at most 50 μm, deformation and rattling of chuck top 2 can effectively curbed, and contact failure between chuck top 2 and the wafer can be prevented, when load is applied by the probe card at the time of measurement.
In the present invention, the ratio of the maximum diameter to the maximum thickness (diameter/thickness) of chuck top 2 may be at least 5 and at most 100. In that case, deformation (deflection) of the chuck top can be reduced, and therefore, a wafer prober capable of accurately measuring electric characteristics of the wafer without damaging the wafer can be provided.
When the ratio mentioned above exceeds 100, chuck top 2 deflects because of the load laid by probing, and flatness and parallelism of the upper surface of chuck top 2 would possibly be degraded significantly. In such a situation, accurate measurement might be impossible, because of contact failure of a probe pin. When the ratio mentioned above is smaller than 5, there would be thermal influence from a side surface of chuck top 2. Specifically, when the area of an outer circumferential surface is too large as compared with the areas of the upper and lower surfaces of chuck top 2, dependent on the heat balance of the upper and lower surfaces, good temperature control tends to be difficult. In such a situation, thermal uniformity of the wafer-mounting surface of chuck top 2 deteriorates, and accurate measurement might be impossible. The ratio of the maximum diameter to the maximum thickness mentioned above is, more preferably, at least 10 and at most 50. Particularly when Young's modulus of the material used for chuck top 2 is 250 GPa or higher, it is effective to control the ratio of the maximum diameter to the maximum thickness within the range described above. In the structure having a space 5 described above, deflection of chuck top 2 is more likely because of the applied load, and control of the ratio of the maximum diameter to the maximum thickness is more important.
In the present invention, Young's modulus may be measured, for example, by the pulse method or the flexural resonance method.
Further, it is preferred that the thickness of chuck top 2 except for the thickness of chuck top conductive layer 3 is at least 8 mm. When the thickness is smaller than 8 mm, chuck top 2 much deforms when load is applied at the time of inspection and flatness and parallelism of chuck top 2 are deteriorated significantly, causing contact failure of a probe pin and accurate measurement would be impossible. Further, the wafer might be damaged. The thickness of at least 10 mm is more preferable, as the possibility of contact failure can further be reduced.
As other specific examples of the structure of wafer holder in accordance with the present invention, structures shown in
In supporter 4 of the present invention, base portion 41 and circular tube portion 42 may be formed integrally. Here, “formed integrally” means that there would be no slip or gap between base portion 41 and circular tube portion 42 when supporter 4 bears load. By way of example, a solid cylindrical member may be hollowed out to form base portion 41 and circular tube portion 42 integrally. In that case, there is no interface between base portion 41 and circular tube portion 42. Alternatively, a disk-shaped member for forming base portion 41 and a hollow cylindrical member for forming circular tube portion 42 may be fabricated separately and thereafter the two members may be bonded by glass, ceramic paste or the like, to form base portion 41 and circular tube portion 42 integrally. The integrally formed state does not include bodies that are mechanically joined, for example, by screws or clamping. Integral formation of base portion 41 and circular tube portion 42 is preferred as deformation of supporter 4 is less likely.
When space 5 is formed in the wafer holder of the present invention, the shape of space 5 is not specifically limited, and any shape may be available that minimizes the amount of transfer of cold air or heat generated at chuck top 2 to supporter 4. It is preferred that supporter 4 is adapted to have the hollow cylindrical shape with a bottom, as the contact area between chuck top 2 and supporter 4 can be made small and space 5 can be formed easily. When such space 5 is formed, what lies between chuck top 2 and supporter 4 is mostly an air layer, and hence, an efficient heat insulating structure can be formed.
In the present invention, when the thickness of chuck top 2 is set to 1.0, the thickness of circular tube portion 42 of supporter 4 may be at least 0.1 and at most 5.0. When the thickness of circular tube portion 42 is smaller than 0.1 with the thickness of the chuck top being 1.0, the heat when the wafer is heated may be transferred to the driving system, possibly resulting in thermal expansion of metal components in the driving system. When the thickness of circular tube portion 42 is larger than 5.0 with the thickness of the chuck top being 1.0, circular portion 42 tends to be deformed more easily.
Further, when the thickness of chuck top 2 is set to 1.0, the thickness of base portion 41 of supporter 4 may be at least 0.5 and at most 10.0. When the thickness of base portion 41 is smaller than 0.5 with the thickness of the chuck top 2 being 1.0, base portion 41 tends to be deformed more easily. When the thickness of base portion 41 is larger than 10.0 with the thickness of the chuck top being 1.0, heat capacitance of base portion 41 increases as compared with chuck top 2, and therefore, temperature controllability of chuck top 2 would possibly be lowered and, at the same time, heating/cooling of the heater would take longer time, decreasing throughput.
Specifically, when the thickness of circular tube portion 42 is set to at least 0.1 and at most 5.0 and the thickness of base portion 41 is set to at least 0.5 to at most 10.0 with the thickness of the chuck top being 1.0, a wafer holder having high rigidity and superior heat insulating effect can be provided, in which chuck top deformation is small even under high load and contact failure with the wafer can be prevented and which can enhance positional accuracy between the wafer and the probe card as temperature increase in the driving system of the wafer holder is prevented when the wafer is mounted on the chuck top and heated.
Preferably, the radial thickness of circular tube portion 42 of supporter 4 is at most 20 mm. When the radial thickness exceeds 20 mm, the amount of heat transferred from chuck top 2 through supporter 4 to the driving system of wafer holder may possibly increase. When the radial thickness of the hollow cylindrical portion is smaller than 1 mm, supporter 4 tends to be deformed or damaged more easily by the pressure when the probe card is pressed to the wafer, that is, load of the probe card, at the time of wafer inspection, and therefore, the radial thickness should preferably be at least 1 mm. The most preferable radial thickness of circular tube portion 42 is 10 to 15 mm. Further, the radial thickness of circular tube portion at a portion in contact with chuck top 2 should preferably be 2 to 5 mm. In that case, good balance between the strength and heat insulating characteristic of supporter 4 can be attained.
Further, preferably, the height of circular tube portion 42 is at least 10 mm. When the height is lower than 10 mm, the pressure from probe card acts on chuck top 2 at the time of wafer inspection, and the pressure further propagates to supporter 4. As a result, the bottom portion of supporter 4 would deflect, possibly degrading flatness of chuck top 2. Further, the amount of heat transferred from chuck top 2 through supporter 4 to the driving system of wafer holder may be increased. Further, it is preferred that the thickness of base portion 41 is at least 10 mm. When the thickness is smaller than 10 mm, the pressure from the probe card acts on chuck top 2 at the time of wafer inspection, and the pressure further propagates to supporter 4. As a result, the bottom portion of supporter 4 would deflect, possibly degrading flatness of chuck top 2. Further, it is possible that supporter 4 itself is deformed or damaged by the load of probe card. It is more preferable that the thickness of base portion 41 of supporter 4 is 10 mm to 35 mm. The thickness of 35 mm or smaller is suitable, as the wafer holder can be reduced in size.
In wafer holder 200 having such a structure as shown in
In the present invention, when base portion 41 and circular tube portion 42 are formed integrally, the contact surface between circular tube portion 42 and base portion 41 is considered to mean the portion corresponding to the contact surface between base portion 41 and circular tube portion 42 shown in
Further, when every variation in thickness described above is set to at most 10 μm, deformation and rattling of chuck top 2 can further be reduced. Specifically, in wafer holder 100 of
In the step of inspecting a semiconductor wafer, heating of a wafer mounted and fixed on the wafer-mounting surface of chuck top 2 is not required in some cases. Recently, however, it is more often the case that heating to about 100 to 200° C. is required. Therefore, it is preferred that the wafer holder of the present invention includes a heater body 6 as shown, for example, in
When heater body 6 for heating chuck top 2 is provided and transfer of heat from heater body 6 to supporter 4 can not be prevented, the heat would be transferred to the driving system provided below supporter 4 in the wafer prober mounting the wafer holder of the present invention, and because of difference in thermal expansion coefficient among components, machine accuracy would be deviated, possibly causing significant deterioration in flatness and parallelism of the wafer-mounting surface (upper surface) of chuck top 2. It is preferred that the wafer holder of the present invention has a heat insulating structure such as cavity 51 or space 5 described above, because significant deterioration of flatness and parallelism of chuck top 2 can be avoided. Further, it is advantageous that the wafer holder of the present invention has a hollow structure with space 5, as weight can be reduced than in an example having supporter 4 of solid cylindrical shape.
As the above-described heater body 6, one formed by sandwiching a resistance heater body 61 with an insulator 62 as shown in
Insulator 62 sandwiching resistance heater body 61 is not specifically limited, and any heat-resistant insulator may be used. By way of example, mica, silicone resin, epoxy resin, phenol resin or the like may be used. When insulator 62 is resin, filler may be dispersed in the resin, in order to increase thermal conductivity of insulator 62 and to transfer the heat generated in heater body 6 more smooth to the chuck top. The filler dispersed in the resin serves to increase thermal conductivity of the resin. Filler material is not specifically limited, provided that it does not have reactivity to the resin, and a substance such as boron nitride, aluminum nitride, alumina, silica or the like may be available.
As to the method of forming the heater body or the resistance heater body, other then etching metal foil described above, a method is available in which heater body 6 is provided by forming an insulating layer by thermal spraying or screen printing on a surface opposite to the wafer-mounting surface of chuck top 2, and forming a resistance heater body layer in a prescribed pattern thereon by screen printing or vapor deposition. Heater body 6 formed of metal foil may be fixed by a mechanical method such as screw fixing, on chuck top 2.
When chuck top 2 is heated by heater body 6 and wafer is inspected, for example, at 200° C., it is preferred that the temperature at a bottom surface of supporter 4 of the wafer holder is at most 100° C. When the temperature at the bottom surface of supporter 4 exceeds 100° C., the driving system of the wafer holder is distorted because of difference in thermal expansion coefficient, and the accuracy would be degraded, possibly causing contact failure, due to positional deviation at the time of probing, warp or biased contact of the probe caused by lower parallelism. Further, when measurement is to be done at a room temperature after the inspection at 200° C., cooling takes long time and hence, throughput would be decreased.
As an exemplary structure around the portion feeding power to heater body 6 of the wafer holder in accordance with the present invention, a portion surrounded by a circle in
A support surface of supporter 4 supporting chuck top 2 should preferably have a heat-insulating structure. The heat-insulating structure may be made by forming a notch in supporter 4 to reduce contact area between chuck top 2 and supporter 4. It is also possible to form the heat-insulating structure by forming a notch in chuck top 2. In that case, it is preferred that chuck top 2 has Young's modulus of at least 250 GPa. Specifically, as the pressure of probe card is applied to chuck top 2, the amount of deformation would inevitably increase if a notch is formed and the material thereof has low Young's modulus. Large amount of deformation possibly leads to damage to the wafer or damage to chuck top 2 itself. Formation of the notch in supporter 4 is preferred, because such a problem can be avoided. As for the shape of the notch, it may be formed as concentrical trench 21 such as shown in
In the wafer holder of the present invention, supporter 4 may include a plurality of pillars in addition to the circular tube portion. By way of example, preferably, a plurality of pillars 23, 43 may be arranged between chuck top 2 and circular tube portion 42 of wafer holder 500, and supporter 4 may be formed by combining pillars 23, 43 and circular tube portion 42 as shown, for example, in
In the present invention, a plurality of pillars 43 may be provided between circular tube portion 42 and base portion 41 of wafer holder 600 as shown in
It is preferred that pillars 23, 43 are in uniform, concentrical arrangement or in a similar arrangement, and that the number is at least 8. Recently, wafer size has come to be increased to 8 to 12 inches, and therefore, if the number is smaller than 8, distance between pillars 23, 43 to each other would be long, and when the pins of the probe card are pressed to the wafer mounted on chuck top 2, deflection would be more likely between the pillars. When the example in which pillars 23, 43 are provided is compared with the example in which chuck top 2 and supporter 4 are integral, provided that the contact area with chuck top 2 is the same, two interfaces can be formed, that is, between chuck top 2 and pillar member 23, 43 and between pillar member 23, 43 and supporter 4 when pillars 23, 43 are provided. These interfaces serve as the heat resistant layers, and hence, heat resistance layers can be increased twice as much, whereby the heat generated in chuck top 2 can more effectively be insulated. The shape of the pillars 23, 43 is not specifically limited, and it may be a cylinder or it may be a triangle pole, a quadrangular pole or a polygonal pole with any polygon as a bottom surface. No matter what shape, by inserting pillars 23, 43 as described above, the heat from chuck top 2 to supporter 4 can be insulated. It is noted, however, that regardless of the shape of pillars 23, 43, pillars 23, 43 should be arranged in symmetry on supporter 4. If the arrangement of pillars 23, 43 is asymmetrical, it becomes impossible to uniformly disperse the pressure applied to chuck top 2, possibly leading to deformation or damage to chuck top 2.
When pillars are provided in the present invention, it is preferred that the sum of thickness of pillar 23, 24 and circular tube portion 42 is at least 0.1 and at most 5.0, with the thickness of chuck top 2 being 1.0. When the sum of thickness of pillar 23, 24 and circular tube portion 42 with the thickness of chuck top being 1.0 is smaller than 0.1, the heat when the wafer is heated would be transferred to the driving system, possibly resulting in thermal expansion of the metal components of the driving system. When the sum of thickness of pillar 23, 24 and circular tube portion 42 with the thickness of chuck top being 1.0 is larger than 5.0, circular tube portion 42 tends to deform more easily.
It is preferred that the thermal conductivity of pillars 23, 43 described above is at most 30 W/mK. When the thermal conductivity is higher than 30 W/mK, the effect of heat insulation would possibly be degraded. As the material of pillars 23 and 43, silicon nitride (Si3N4), mullite, mullite-alumina composite, steatite, cordierite, stainless steel, glass (fiber), heat resistant resin such as polyimide, epoxy or phenol, and a composite thereof may be used.
In the present invention, the thermal conductivity may be measured by a method such as laser flash method, using pelletized samples.
Perpendicularity between an outer circumferential portion of circular tube portion 42 and the contact surface of supporter 4 with chuck top 2 when supporter 4 is formed of base portion 41 and circular tube portion 42, or between the outer circumferential portion of circular tube portion 42 and the contact surface of pillars 23, 43 with the chuck top 2 when pillars 23, 43 are provided, should preferably be at most 10 mm, with the measured length converted to 100 mm. For instance, with perpendicularity exceeding 10 mm, it is possible that when the pressure applied from chuck top 2 acts on pillars 23, 43 or circular tube portion 42, pillars 23, 43 or circular tube portion 42 itself tends to deform more easily.
Further, in the wafer holder of the present invention, it is preferred that a support rod 8 is provided near the central portion of circular tube portion 42 of supporter 4 of wafer holder 700, as shown in
As to the size of support rod 8 described above, it is preferred that the cross-sectional area in the radial direction is 0.1 to 100 cm2. When the cross-sectional area is smaller than 0.1 cm2, satisfactory supporting effect would not be attained, and support rod 8 tends to deform. When the cross-sectional area of support rod 8 exceeds 100 cm2, the amount of heat transferred to the driving system increases, it becomes necessary to reduce the size of a cooling module 9 to be inserted in the hollow cylindrical portion of supporter 4 as will be described later, and hence, efficiency of cooling would decrease. The cross-sectional shape of support rod 8 is not specifically limited, and it may be a cylinder, triangle pole, a quadrangular pole or the like. The method of fixing support rod 8 to supporter 4 is not specifically limited, and methods such as brazing with an active metal, glass fixing, or screw fixing may be used, and among these methods, screw fixing is particularly preferred. Screw fixing of support rod 8 to base portion 41 facilitates attachment/detachment, and as heat treatment is not involved at the time of fixing, deformation of supporter 4 or support rod 8 by the heat treatment can be avoided.
In the wafer holder in accordance with the present invention, supporter 4 preferably has Young's modulus of at least 200 GPa. When supporter 4 has Young's modulus of at least 200 GPa, deformation of supporter 4 can be made small, and hence, it becomes possible to support chuck top 2 mounted on supporter 4 and to effectively suppress deformation thereof. When Young's modulus of supporter 4 is smaller than 200 GPa, thickness of the bottom portion of supporter 4 cannot be made thin, and therefore, it is difficult to ensure volume of the space, and hence it tends to be difficult to attain the heat insulating effect. Further, it tends to be difficult to ensure a space for mounting the cooling module, which will be described later. More preferable Young's modulus of supporter 4 is at least 300 GPa. Use of supporter 4 having Young's modulus of 300 GPa or higher is particularly preferred, as the deformation of supporter 4 can significantly be reduced, allowing further reduction in size and weight of supporter 4.
When supporter 4 includes base portion 41 and circular tube portion 42, it is preferred that base portion 41 and circular tube portion 42 each have Young's modulus of at least 200 GPa. When Young's modulus of base portion 41 is smaller than 200 GPa, it is difficult to reduce the thickness of base portion 41, and it is difficult to satisfactorily ensure the volume of space 5, and hence, it is difficult to expect good heat insulating effect. Further, when the wafer holder of the present invention has the cooling module, which will be described later, mounted thereon, it tends to be difficult to satisfactorily ensure the space therefor. It is preferred that base portion 41 and circular tube portion 42 each have Young's modulus of at least 300 GPa, as the deformation of supporter 4 can significantly be reduced, allowing further reduction in size and weight of supporter 4.
Supporter 4 preferably has thermal conductivity of at most 40 W/mK. When the thermal conductivity of supporter 4 is set to at most 40 W/mK, the amount of heat transferred from chuck top 2 through supporter 4 to the driving system of the wafer holder can further be reduced, and temperature increase of the driving system can effectively be prevented, so that accuracy of the driving system is not affected.
Recently, a temperature as high as 150° C. is required at the time of probing, and therefore, it is particularly preferred that supporter 4 has thermal conductivity of at most 10 W/mK. More preferable thermal conductivity is at most 5 W/mK. With the thermal conductivity of this range, amount of heat transfer from supporter 4 to the driving system decreases significantly.
When supporter 4 includes base portion 41 and circular tube portion 42, it is preferred that base portion 41 and circular tube portion 42 each have thermal conductivity of at most 40 W/mK. When either base portion 41 or circular tube portion 42 has thermal conductivity exceeding 40 W/mK, the heat transferred to chuck top 2 is easily transferred to supporter 4, possibly affecting the accuracy of the driving system. Recently, a temperature as high as 150° C. is required at the time of probing, and therefore, it is particularly preferred that base portion 41 and circular tube portion 42 each have thermal conductivity of at most 10 W/mK, and thermal conductivity of at most 5 W/mK is particularly preferred as the amount of heat transfer from supporter 4 to the driving system decreases significantly.
As the material for supporter 4 having Young's modulus and thermal conductivity as described above, various ceramics or a composite of two or more ceramics may be used. Among these, considering processability and cost, mullite, silicon nitride, alumina or mullite-alumina composite is preferred as the material for supporter 4. Particularly, mullite is preferred as it has low thermal conductivity and attains high heat insulating effect, and alumina is preferred as it has high Young's modulus and high rigidity, respectively. Mullite-alumina composite is generally preferred as the thermal conductivity is lower than alumina and Young's modulus is higher than mullite.
In the wafer holder of the present invention, it is preferred that chuck top 2 has Young's modulus of at least 250 GPa. If Young's modulus of chuck top 2 is smaller than 250 GPa, chuck top 2 would be significantly deformed when load is applied at the time of inspection, and flatness and parallelism of the wafer-mounting surface of chuck top 2 would possibly be degraded significantly. In that case, contact failure occurs and accurate inspection becomes impossible, and further, the wafer might possibly be damaged. Young's modulus of at least 300 GPa is more preferable, as the possibility of contact failure can further be reduced.
Chuck top 2 preferably has thermal conductivity of at least 15 W/mK. When the thermal conductivity of chuck top 2 is lower than 15 W/mK, temperature uniformity of the wafer mounted on chuck top 2 would be deteriorated. When the thermal conductivity is not lower than 15 W/mK, thermal uniformity having no adverse influence on inspection can be attained. Thermal conductivity of 170 W/mK or higher is more preferable, as the thermal uniformity of the wafer can further be improved.
It is preferred that warp of chuck top 2 is at most 30 μm. When the warp exceeds 30 μm, contact with a needle of the prober may possibly be biased at the time of probing, and evaluation of characteristics would fail, or erroneous determination of defects would be made because of the contact failure. Thus, it is possible that production yield is evaluated lower beyond necessity.
Further, the parallelism between the surface of the chuck top conductive layer 3 and the rear surface at the bottom portion of supporter 4 is preferably at most 30 μm. If the parallelism exceeds 30 μm, the contact failure describe above possibly occurs. Even when the warp and parallelism of chuck top 2 are at most 30 μm and satisfactory at a room temperature, it is not preferred from the same reasons as described above that the warp and parallelism exceed 30 μm at the time of probing at 200° C. It is not preferred either, from the same reasons as described above that the warp and parallelism exceed 30 μm at the time of probing at −70° C. Specifically, it is preferred that at least one of warp and parallelism is at most 30 μm in the entire temperature range of probing, and further, it is preferred that warp and parallelism are at most 30 μm in the entire temperature range of probing.
The warp and parallelism may be measured using, for example, a three-dimensional measuring apparatus.
It is preferred that chuck top 2 deflects at most by 30 μm when a load of 3.1 MPa is applied to chuck top 2. A large number of pins for inspecting the wafer press the wafer from the probe card to the chuck top 2, and therefore, the pressure also acts on chuck top 2, and chuck top 2 deflects to no small extent. When the amount of deflection at this time exceeds 30 μm, it becomes impossible to press the pins of the probe card uniformly onto the wafer, and inspection of the wafer might fail. More preferably, the amount of deflection when the load of 3.1 MPa is applied to chuck top 2 is at most 10 μm.
As the material for chuck top 2 having such Young's modulus and thermal conductivity as described above, various ceramics, metal and metal-ceramics composite materials may be available. Preferred metal-ceramics composite material include, by way of example, composite material of aluminum and silicon carbide and composite material of silicon and silicon carbide, which have relatively high thermal conductivity and easily realize thermal uniformity when the wafer is heated. Of these, composite of silicon and silicon carbide (Si—SiC) is particularly preferred, as it has high thermal conductivity of 170 W/mK to 220 W/mK and high Young's modulus.
As regards the method of forming heater body 6 when a conductive material such as metal or metal-ceramic composite is used as the material for chuck top 2, heater body 6 may be formed by forming an insulating layer through a method of thermal spraying or screen printing on a surface opposite to the wafer-mounting surface of chuck top 2, and by screen printing the conductive layer thereon, or by forming the conductive layer in a prescribed shape through a method such as vapor deposition.
Alternatively, metal foil of stainless steel, nickel, silver, molybdenum, tungsten, chromium and an alloy of these may be etched to form a prescribed pattern of heater body, to provide the heater body 6. In this method, insulation from chuck top 2 may be attained by the method similar to that described above, or an insulating sheet may be inserted between chuck top 2 and the heater body 6. This is preferable, as the insulating layer can be formed at considerably lower cost and in a simpler manner than the method described above. Resin available for this purpose includes, from the viewpoint of heat resistance, mica sheet, epoxy resin, polyimide resin, phenol resin and silicone resin. Among these, mica is particularly preferable, as it has superior heat resistance and electric insulation, allows easy processing and is inexpensive.
Use of ceramics as the material for chuck top 2 is advantageous in that formation of an insulating layer between chuck top 2 and heater body 6 is unnecessary. As the method of forming heater body 6 in this case, methods similar to those described above may be adopted. Among ceramics, alumina, aluminum nitride, silicon nitride, mullite, and a composite material of alumina and mullite are preferred as they have relatively high Young's modulus and hence, not much deformed by the load of the probe card. Of these, aluminum nitride (having thermal conductivity of 170 W/mK) and Si—SiC composite (having thermal conductivity of 170 W/mK to 220 W/mK) are preferred, as they have particularly high thermal conductivity and allow formation of chuck top 2 of superior thermal uniformity.
Alternatively, when a metal is used as the material for chuck top 2, tungsten, molybdenum and an alloy of these having high Young's modulus may be used. Specific examples of the alloy are an alloy of tungsten and copper, and an alloy of molybdenum and copper. These alloys can be produced by impregnating tungsten or molybdenum with copper. Similar to the ceramics-metal composite described above, such metal is a conductor, and therefore, by forming chuck top conductive layer 3 and forming heater body 6 by the method similar to that described above, chuck top 2 for use is obtained.
In the wafer holder of the present invention, chuck top 2 may have on its surface a chuck top conductive layer 3. In this case, the surface of chuck top conductive layer 3 may form the wafer-mounting surface. When chuck top 2 is an insulator, chuck top conductive layer 3 has a function of a ground electrode. In addition to the function above, chuck top conductive layer 3 has a function of earthing that intercepts electromagnetic noise from heater body 6 and the like, and the function of protecting chuck top 2 from corrosive gas, acid, alkali chemical, organic solvent or water. Possible material for chuck top conductive layer 3 includes copper, titanium, nickel, noble metal, tungsten, molybdenum and the like.
Possible methods of forming chuck top conductive layer 3 include a method in which a conductive paste is applied by screen printing and then fired, vapor deposition or sputtering, thermal spraying and plating. Among these, thermal spraying and plating are particularly preferred. Thermal spraying and plating do not involve heat treatment at the time of forming chuck top conductive layer 3, and therefore, warp of chuck top 2 caused by heat treatment can be avoided and chuck top conductive layer 3 can be formed at a low cost.
Particularly, a method of forming chuck top conductive layer 3 by forming a thermally sprayed film and then forming a plating film further thereon is preferred. The material thermally sprayed (aluminum, nickel or the like) forms some oxide, nitride or oxynitride at the time of thermal spraying, and such compound reacts to the surface of chuck top 2, realizing firm contact between the thermally sprayed film and chuck top 2. The thermally sprayed film, however, has low electric conductivity because it contains the compound mentioned above. In contrast, though contact strength of a plated film with the surface of chuck top 2 is not as high as that of the thermally sprayed film, plating forms an almost pure metal film, and therefore, a conductive layer of superior electric conductivity can be formed. The thermally sprayed film and the plating film both contain metal as the main component and, therefore, contact strength therebetween is high. Therefore, by forming the thermally sprayed film as a base and forming plating film thereon, chuck top conductive layer 3 having both high contact strength and high electric conductivity can be provided.
When the material of chuck top 2 is metal, chuck top 2 itself has electric conductivity even when chuck top conductive layer 3 is not formed. Chuck top conductive layer 3, however, may be newly formed on the wafer-mounting surface of chuck top 2, if it is the case that chuck top 2 is much susceptible to oxidation or alteration, or it does not have sufficiently high electric conductivity. As the method of forming chuck top conductive layer 3 in this case, vapor deposition, sputtering, thermal spraying or plating may be used as in the foregoing. Specifically, a method of applying oxidation resistant plating such as nickel, or a method of forming chuck top conductive layer 3 by the combination of thermal spraying and plating and polishing the surface as the wafer-mounting surface may be used.
Chuck top conductive layer 3 preferably has the surface roughness Ra of at most 0.1 μm. When the surface roughness Ra exceeds 0.1 μm, the heat generated from a wafer having a high calorific value during inspection of the wafer could not be radiated from chuck top 2, and the wafer might be heated and possibly be broken by the heat. The surface roughness Ra of chuck top conductive layer 3 should more preferably be at most 0.02 μm, as more efficient heat radiation becomes possible.
Surface roughness Ra of a contact surface between supporter 4 and chuck top 2 is preferably at least 0.1 μm, both at supporter 4 and chuck top 2. When the surface roughness Ra mentioned above of supporter 4 and chuck top 2 at the contact surface is at least 0.1 μm, increase in contact area between supporter 4 and chuck top 2 and relative decrease in gap between supporter 4 and chuck top 2 are prevented, and heat resistance at the contact surface increases. Therefore, the amount of heat transferred to the driving system of the wafer holder can be reduced. The upper limit of surface roughness Ra is not specifically limited. When the surface roughness Ra exceeds 5 μm, however, the cost for surface processing tends to increase, and therefore, surface roughness Ra of at most 5 μm is preferred. As for the method of realizing surface roughness Ra of at least 0.1 μm, polishing process or sand blasting may be performed. In that case, conditions for polishing or sand blasting must be optimized to maintain surface roughness Ra of at least 0.1 μm.
When the supporter is formed of base portion 41 and circular tube portion 42, it is preferred that surface roughness Ra at a contact surface between circular tube portion 42 and chuck top 2 or pillar 23, 43 is at least 0.1 μm. When the surface roughness Ra is smaller than 0.1 μm, contact area between circular tube portion 42 and chuck top 2 or pillar 23, 43 increases, and the gap therebetween becomes relatively smaller. Therefore, as compared with the case where surface roughness Ra is 0.1 μm or larger, the amount of heat transfer possibly increases. Though the upper limit of surface roughness Ra is not specifically limited, when the surface roughness Ra exceeds 5 μm, the cost for surface processing tends to increase, and therefore, surface roughness Ra of at most 5 μm is preferred.
It is preferred that, other than the contact surface between supporter 4 and chuck top 2, the surface roughness Ra is similarly set to be at least 0.1 μm at the contact surface between the bottom surface of supporter 4 and the driving system, the contact surface between base portion 41 of supporter 4 and circular tube portion 42, and the contact surface between circular tube portion 42 and the plurality of pillars 23, 43 when circular tube portion 42 and the plurality of pillars 23, 43 are used in combination, as the heat resistance is increased and the amount of heat transferred to the driving system of the wafer holder can be reduced.
Specifically, when the surface roughness Ra of the contact surface between the bottom portion of supporter 4, that is, the bottom surface of supporter 4 and the driving system is at least 0.1 μm, the amount of heat transferred to the driving system can also be reduced. Further, as for the surface roughness Ra at the contact surface between base portion 41 and circular tube portion 42, it is preferred that at least one of base portion 41 and circular tube portion 42 has surface roughness Ra of at least 0.1 μm. At the contact surface, if base portion 41 and circular tube portion 42 both have surface roughness Ra smaller than 0.1 μm, the effect of cutting heat from circular tube portion 42 to base portion 41 of supporter 4 would possibly be reduced. Reduction in heat quantity transferred to the driving system, attained by the increased thermal resistance, leads to reduction of power supply to the heater body 6.
When base portion 41 and circular tube portion 42 are formed integrally in supporter 4 and pillars 23, 43 are provided between supporter 4 and chuck top 2, it is also preferred that the surface roughness Ra at the contact surface between pillar 23, 43 and supporter 4 and at the contact surface between pillar 23, 43 and chuck top 2 is at least 0.1 μm as described above. By making larger the surface roughness Ra also at pillars 23, 43, transfer of heat to supporter 4 can be reduced. As described above, by forming interfaces between various members and setting surface roughness Ra of the interfaces to at least 0.1 μm, the amount of heat transferred to the bottom portion of supporter 4 can be reduced, and as a result, power supply to the heater body 6 can be reduced.
In the present invention, surface roughness Ra represents arithmetic mean deviation, of which detailed definition can be found, for example, in JIS B 0601.
In the wafer holder of the present invention, when supporter 4 has a hollow cylindrical shape with a bottom and whereby space 5 is formed, it is preferred that a metal layer is formed on the surface of supporter 4 as an electromagnetic shield layer, utilizing the space inside the supporter 4. The electromagnetic wave generated by heater body 6 for heating chuck top 2 may affect wafer inspection as noise, and when a metal layer is formed on supporter 4, it is possible to intercept (shield) the electromagnetic wave.
The method of forming the metal layer (electromagnetic shield layer) is not specifically limited, and by way of example, a conductive paste prepared by adding glass frit to metal powder of silver, gold, nickel or copper may be applied using a brush and burned, metal such as aluminum or nickel may be thermally sprayed, or the layer may be formed by plating. Combination of these methods is also possible and, by way of example, metal such as nickel or the like may be plated after burning the conductive paste, or plating may be done after thermal spraying. Among these methods, plating is preferred, as it has high contact strength and is highly reliable. Further, thermal spraying is preferred as it allows formation of the metal film at a relatively low cost.
As another method of forming the metal layer (electromagnetic shield layer), a conductor may be provided on at least a part of the surface of supporter 4. Specifically, a conductor having a circular tube shape may be attached on a side surface of supporter 4. The material used here is not specifically limited, as long as it is a conductor. By way of example, metal foil or a metal plate of stainless steel, nickel, aluminum or the like may be used. Metal foil of the material mentioned above is formed to have a circular tube shape of a size larger than the outer diameter of supporter 4, and it may be attached on the side surface of supporter 4.
Further, at the bottom surface portion of supporter 4, metal foil or a metal plate may be attached, and by connecting this to the metal foil or metal plate attached to the side surface, the effect of shielding the electromagnetic wave can be enhanced.
When the wafer holder of the present invention has space 5, the metal foil or metal plate may be attached inside the space 5, and by connecting this to the metal foil or metal plate attached to the side surface and the bottom surface of supporter 4, the effect of shielding the electromagnetic wave can be enhanced. By adopting the method of attaching metal foil or a metal plate, the electromagnetic wave can be shielded at a lower cost than when plating is provided or a conductive paste is applied. Though the method of fixing the metal foil or the metal plate to supporter 4 is not specifically limited, it may be attached using, for example, metal screws. Further, the metal foil or the metal plates on the bottom surface and on the side surface may be integrated beforehand and then fixed on supporter 4.
It is preferred that a metal layer (electromagnetic shield layer) for shielding the electromagnetic wave is also formed between heater body 6 heating chuck top 2 and chuck top 2. The electromagnetic shield layer has a function of cutting off noise such as electromagnetic wave or electric field generated at heater body 6 and the like that may influence probing of the wafer. Though the noise does not have much influence on the measurement of common electric characteristics, it has particularly significant influence on the measurement of high-frequency characteristics of the wafer. The electromagnetic shield layer may be formed, for example, by inserting metal foil between heater body 6 and chuck top 2. It is preferred that the electromagnetic shield layer is insulated from chuck top 2 and heater body 6. Though the metal foil to be used here is not specifically limited, foil of stainless steel, nickel or aluminum is preferred, as heater body 6 is heated to the temperature of about 200° C. For forming the electromagnetic shield layer, a method similar to the method of forming a meal layer on the side surface of supporter 4 described above may be used, and as another example, metal foil may be inserted between heater body 6 and chuck top 2.
Further, it is preferred that an insulating layer is provided between the electromagnetic shield layer and chuck top 2. The insulating layer serves to cut off noise that affects inspection of the wafer, such as the electromagnetic wave or electric field generated at heater body 6 and the like. The noise particularly has significant influence on measurement of high-frequency characteristics of the wafer, and the noise does not have much influence on the measurement of normal electric characteristics. Though most of the noise generated at the heater body 6 is shielded by the electromagnetic shield layer, in terms of electric circuit, a capacitor is formed between chuck top conductive layer 3 formed on the wafer-mounting surface of chuck top 2 and the electromagnetic shield layer when chuck top 2 is an insulator, or between chuck top 2 itself and heater body 6 when chuck top 2 is a conductor, and the capacitor may have an influence as a noise at the time of inspecting the wafer. In order to reduce the influence, it is preferred to form the insulating layer between the electromagnetic shield layer and chuck top 2.
By controlling the resistance value, dielectric constant and capacitance of the insulating layer, the noise at the time of inspection can significantly be reduced. Specifically, it is preferred that the resistance value of the insulating layer is at least 1×107Ω. When the resistance value is smaller than 1×107Ω, small current flows to chuck top conductive layer 3 because of the influence of heater body 6, which small current possibly becomes noise and affects inspection. When the resistance value is at least 1×107Ω, the small current can sufficiently be reduced not to affect inspection. Recently, circuit patterns formed on wafers have been miniaturized, and therefore, it is necessary to reduce such noise as much as possible. In order to further improve reliability, it is preferred to set the resistance value of the insulating layer to at least 1×1010Ω.
Further, when chuck top 2 is an insulator, capacitance between chuck top conductive layer 3 and the electromagnetic shield layer, or when chuck top 2 is a conductor, the capacitance between chuck top 2 itself and the electromagnetic shield layer, should preferably be at most 5000 pF. When the capacitance exceeds 5000 pF, the influence of the insulating layer as a capacitor would be too large, possibly causing noise and affecting inspection. Capacitance of at most 1000 pF is particularly preferred, as it enables inspection free of noise influence of even a miniaturized circuitry.
Further, it is preferred that the dielectric constant of the insulating layer is at most 10. When the dielectric constant of the insulating layer exceeds 10, charges tend to be stored more easily between the electromagnetic shield layer sandwiching the insulating layer and chuck top 2, which might possibly be a cause of noise generation. Particularly, as the wafer circuits have been much miniaturized in these days, it is preferable to reduce noise, and therefore, dielectric constant should preferably be at most 4 and more preferably at most 2. Setting small the dielectric constant of the insulating layer is preferred, as the thickness of the insulating layer necessary for ensuring the resistance value and the capacitance described above can be made thinner, and hence, thermal resistance posed by the insulating layer can be reduced.
The thickness of the insulating layer should preferably be at least 0.2 mm. In order to reduce the size of the device and to maintain good heat conduction from heater body 6 to chuck top 2, the thickness of the insulating layer should be small. When the thickness of the insulating layer becomes smaller than 0.2 mm, however, defects in the insulating layer itself or problems in durability would be generated. It is more preferred that the thickness of the insulating layer is at least 1 mm, because such a thickness prevents the problem of durability and ensures good heat conduction from the heater body 6. Though there is no specific upper limit of the thickness of the insulating layer, preferably it is at most 10 μm. When the thickness exceeds 10 mm, though the noise cutting effect is good, the time of conduction of heat generated by heater body 6 to chuck top 2 and to the wafer becomes too long, and hence, it possibly becomes difficult to control the heating temperature. Though it depends on the conditions of inspection, the thickness of the insulating layer of at most 5 mm is preferred, as temperature control is relatively easy.
The thermal conductivity of the insulating layer is preferably at least 0.5 W/mK, in order to realize good heat conduction from heater body 6 as described above. Thermal conductivity of at least 1 W/mK is preferred, as heat conduction is further improved. It is preferred that the diameter of the insulating layer, that is, the area for forming the insulating layer, is the same or larger than the area for forming the electromagnetic shield layer or heater body 6. When the diameter of the insulating layer is smaller than the area for forming the electromagnetic shield layer or heater body 6, noise may possibly enter from a portion not covered with the insulating layer.
The material for the insulating layer has only to satisfy the characteristics described above and have heat resistance sufficient to withstand the inspection temperature, and ceramics or resin may be used. Of these, resin such as silicone resin or the resin having filler dispersed therein, and ceramics such as alumina, may suitably be used. The filler dispersed in the resin serves to improve heat conduction of the resin. Any material having no reactivity to the resin may be used as the filler, and by way of example, substances such as boron nitride, aluminum nitride, alumina and silica may be available.
A specific example of the insulating layer will be described in the following. First, as the material, silicone resin having boron nitride dispersed therein is used. The material has thermal conductivity of about 5 W/mK, and dielectric constant of 2. When the silicone resin with boron nitride dispersed is inserted as the insulating layer between the electromagnetic shield layer and chuck top 2, and chuck top 2 corresponds to a 12-inch wafer, it may be formed, for example, to have the diameter of 300 mm. The thickness of the insulating layer may be selected dependent on the conditions of probing, and when the thickness of the insulating layer is set to 0.25 mm, capacitance of 5000 pF can be attained and when the thickness is set to 1.25 mm or more, capacitance of 1000 pF or lower can be attained. Volume resistivity of the insulating layer is 9×1015 Ω·cm, and therefore, when the diameter is 300 mm and the thickness is made at least 0.8 mm, the resistance value of at least 1×1012 Ω can be attained. Therefore, when the thickness of the insulating layer is made at least 1.25 mm, an insulating layer having sufficiently low capacitance and sufficiently high resistance value can be obtained.
Further, it is preferred that a guard electrode layer is provided between chuck top 2 and the electromagnetic shield electrode layer, with an insulating layer interposed. By connecting the guard electrode layer to the metal member formed on supporter 4, the noise that affects measurement of the high-frequency characteristics of the wafer can further be reduced. Specifically, in the present invention, by covering supporter 4 as a whole including heater body 6 with a conductor, the influence of noise at the time of measuring the characteristics of the wafer at a high frequency can be reduced.
Here, it is preferred that the resistance value of each of the insulating layers between heater body 6 and the electromagnetic layer, between the electromagnetic layer and the guard electrode layer and between the guard electrode layer and chuck top 2 is at least 1×107Ω. When the resistance value is smaller than 1×107Ω, small current flows to chuck top conductive layer 3 because of the influence of heater body 6, which small current possibly becomes noise and affects inspection. The resistance value of at least 1×107Ω is preferred, as the small current can sufficiently be reduced not to affect inspection. Recently, circuit patterns formed on wafers have been miniaturized, and therefore, it is necessary to reduce such noise as much as possible. When the resistance value of the insulating layer is set to at least 1×1010Ω, a structure of higher reliability can be realized.
Further, when chuck top 2 is an insulator, capacitance between chuck top conductive layer 3 and the guard electrode layer, and between chuck top conductive layer 3 and the electromagnetic shield layer, or when chuck top 2 is a conductor, the capacitance between chuck top 2 itself and the guard electrode layer, and between chuck top 2 and the electromagnetic shield electrode layer, should preferably be at most 5000 pF. When the capacitance exceeds 5000 pF, the influence of the insulating layer as a capacitor would be too large, possibly becoming noise and affecting inspection. As the wafer circuits have been miniaturized as described above, capacitance of at most 1000 pF is particularly preferred, as it enables good probing.
A more specific example for forming the guard electrode layer in accordance with the present invention will be described. By way of example, as the insulating layer, silicone resin having boron nitride dispersed therein is used as the insulating layer. The insulating layer has the dielectric constant of 2. When the silicone resin with boron nitride dispersed is inserted as the insulating layer between the electromagnetic shield layer and the guard electrode layer, or between the guard electrode layer and chuck top 2, and the chuck top corresponds to a 12-inch wafer, it may be formed, for example, to have the diameter of 300 mm. Here, when the thickness of the insulating layer is set to 0.25 mm, capacitance of 5000 pF can be attained. When the thickness is set to at least 1.25 mm, capacitance of 1000 pF or lower can be attained. Volume resistivity of the insulating layer is 9×1015 Ω·cm, and therefore, when the diameter is 300 mm and the thickness is made at least 0.8 mm, the resistance value of about 1×1012Ω can be attained. Though the thickness of the insulating layer may be selected dependent on the conditions of probing, the insulating layer has thermal conductivity of about 5 W/mK and, therefore, when the thickness of the insulating layer is made at least 1.25 mm, good capacitance and good resistance value can both be attained.
When the wafer holder in accordance with the present invention has space 5, a cooling module 9 may be provided in space 5 inside supporter 4 of wafer holder 800 as shown in
As the material of cooling module 9, aluminum, copper and an alloy of these are preferred, because they have high thermal conductivity and capable of removing heat quickly from chuck top 2. It is also possible to use stainless steel, magnesium alloy, nickel or other metal materials. On a surface of cooling module 9, a metal film formed of a material such as nickel, gold, silver or the like may be formed by a method of plating, thermal spraying or the like, to add oxidation resistance. Among these materials, nickel-plated aluminum or nickel-plated copper is particularly preferred as cooling module 9, as it has superior oxidation resistance and high thermal conductivity and is relatively inexpensive.
Alternatively, ceramics may be used as the material for cooling module 9. Among ceramics, aluminum nitride and silicon carbide are preferred as they have high thermal conductivity and are capable of removing heat quickly from chuck top 2. Further, silicon nitride and aluminum oxynitride are preferred, as they have high mechanical strength and superior durability. Oxide ceramics such as alumina, cordierite and steatite are preferred as they are relatively inexpensive. The material for cooling module 9 may be arbitrarily selected in consideration of intended use, cost and the like.
A coolant may be caused to flow in cooling module 9. Causing the coolant flow is preferred, as the heat transferred from chuck top 2 to cooling module 9 can quickly be removed and the cooling rate of chuck top 2 can be improved. Types of the coolant may be liquid such as water, Fluorinert or Galden, or gas such as nitrogen, air or helium. When the temperature of use is always 0° C. or higher, water is preferred considering magnitude of specific heat and cost, and when it is cooled below zero, Galden is preferred considering specific heat.
As the method of forming the passage for the coolant flow, two plates may be prepared, for example, and the passage may be formed by machine processing on one or both of the plates. Specifically, flow passages are formed on the surfaces of two cooling plates formed of aluminum, for example, and in order to improve corrosion resistance and oxidation resistance, entire surfaces are nickel-plated, and thereafter, the two plates are joined by means of screws or welding. At this time, a sealing member such as an O-ring may preferably be inserted around the joined portion of the passage, to prevent leakage of the coolant.
As another method of forming the flow passage, a pipe through which the coolant flows may be attached to a cooling plate formed of aluminum or copper. Here, in order to increase contact area between the cooling plate and the pipe, it is preferred that the cooling plate is processed to have a counter-sunk trench of an approximately the same cross-sectional shape as the pipe and the pipe is arranged in the trench, or a flat-shaped portion is formed on a portion of the side surface of the pipe along the longitudinal direction and that flat portion is fixed on the cooling plate. By these methods, the pipe can be in close contact on the cooling plate, and therefore, cooling efficiency can further be enhanced. As to the method of fixing the metal plate and the pipe, screw fixing using a metal band, welding or brazing may be available. A deformable substance such as resin may be inserted between the cooling plate and the pipe. Then, tight contact between the two is attained and cooling efficiency can be enhanced.
Specifically, two copper plates (oxygen-free copper) are prepared as the cooling plates, and the passage through which water as a coolant flows is formed by machine processing or the like on one of the copper plates. The other copper plate and a pipe formed of stainless steel at an inlet of the coolant are simultaneously joined by brazing. In order to improve corrosion resistance and oxidation resistance of the joined cooling plates, the entire surface is nickel-plated, and thus, cooling module 9 is formed.
As another approach, a pipe through which the coolant flows is attached to a cooling plate such as an aluminum plate or copper plate, whereby cooling module 9 may be formed. In this case, by forming a counter-sunk trench having a shape close to the cross-sectional shape of the pipe to realize close contact with the pipe, cooling efficiency can further be increased. Further, in order to improve tight contact between the cooling pipe and the cooling plate, thermally conductive resin, ceramics or the like may be inserted as an intervening layer.
At the time of heating chuck top 2, if cooling module 9 can be separated from chuck top 2, efficient temperature elevation of chuck top 2 becomes possible, and from the viewpoint of higher rate of temperature increase, it is preferred that cooling module 9 is movable. As a method of realizing mobile cooling module 9, an elevating mechanism 10 such as an air cylinder may be used as shown in
On the other hand, when the cooling rate of chuck top 2 is of high importance, cooling module 9 may be fixed on chuck top 2. Specifically, as shown in
No matter in which arrangement the cooling module 9 is formed, the method of fixing cooling module 9 is not specifically limited and, by way of example, it may be fixed by a mechanical method such as screw fixing or clamping. When chuck top 2, cooling module 9 and heater body 6, and further an insulated heater, if any is provided, are to be fixed together by screws, three or more screws are preferred as tight contact between each of the members can be improved, and six or more screws are more preferable.
Further, in the structure described above, cooling module 9 may be mounted inside the space 5 of supporter 4, or cooling module 9 may be mounted on supporter 4 and chuck top 2 may be mounted thereon. No matter which method is adopted, cooling rate can be increased as compared with the example having mobile cooling module 9, as chuck top 2 and cooling module 9 are fixed together. Further, as cooling module 9 is mounted on supporter 4, contact area of cooling module 9 with chuck top 2 is increased, and hence, the chuck top can more rapidly be cooled.
When cooling module 9 fixed on chuck top 2 can be cooled by a coolant, it is preferred that the flow of coolant to cooling module 9 is stopped when the temperature of chuck top 2 is increased or when it is kept at a high temperature. In that case, the heat generated by heater body 6 is not removed by the coolant, and whereby efficient temperature increase or maintenance of high temperature of chuck top 2 becomes possible. Naturally, chuck top 2 can be cooled efficiently by causing the coolant to flow again at the time of cooling.
Further, chuck top 2 itself may be formed as the cooling module, by providing a passage through which the coolant flows inside chuck top 2 and whereby integrating the chuck top and the cooling module. In that case, the time for cooling can further be reduced than when cooling module 9 is fixed on chuck top 2. As a structure of chuck top 2 for this approach, the following example may be available. Namely, chuck top conductive layer 3 is formed on one surface of one of two members to provide the wafer-mounting surface, a passage for the coolant flow is formed on the opposite surface, and the other one of the members is integrated by brazing, glass fixing or screw fixing, on the surface having the passage formed thereon, whereby chuck top 2 is completed. Alternatively, a passage may be formed on one surface of said the other member, and the member may be integrated with said one member on the surface having the passage formed thereon, or passages may be made both on the one and the other members, and the members may be integrated on the surfaces having the passages formed thereon. It is preferred that the difference in thermal conductivity of the one and the other members is as small as possible, and ideally, the members are preferably formed of the same material.
When chuck top 2 integrated with the cooling module is used, as the material for chuck top 2, ceramics or metal-ceramics composite may be used, or metal may be used. Metal is advantageous in that it is inexpensive as compared with ceramics or metal-ceramics composite, and it allows easy processing and hence the passage can be formed easily. When the chuck top of metal is used, however, it is preferred to provide a plate 11 for preventing deformation as shown in wafer holder 1100 of
It is preferred that the plate 11 for preventing deformation has Young's modulus of at least 250 GPa, similar to ceramics or metal-ceramics composite material used as the material for chuck top 2. Plate 11 for preventing deformation may be inserted between chuck top 2 and supporter 4 of wafer holder 1100 as shown in
In a structure in which the cooling module is integrated within chuck top 2, the electromagnetic shield layer or the guard electrode layer may be formed as needed, as in the example in which chuck top 2 and cooling module 9 are formed as separate members. In this case, insulated heater body 6 may be covered with metal, a guard electrode layer may be formed with an insulating layer interposed, and between the guard electrode layer and chuck top 2, an insulating layer may be formed.
Further, when chuck top 2 formed of metal is used and plate 11 for preventing deformation is arranged on chuck top 2, again, it is possible to form the electromagnetic shield layer or the guard electrode layer. By way of example, on a surface opposite to the wafer-mounting surface of chuck top 2, insulated heater body 6 is arranged, heater body 6 is covered by a metal layer (electromagnetic shield layer), and thereafter, plate 11 for preventing deformation is arranged, and heater body 6, the electromagnetic shield layer and plate 11 for preventing deformation may be fixed integrally on chuck top 2. When the guard electrode is to be formed, the insulated heater body 6 described above is covered with metal, the guard electrode is formed with an insulating layer interposed, an insulating layer is formed between the guard electrode and chuck top 2, and plate 11 for preventing deformation is formed, and the heater body 6, the electromagnetic shield layer, the guard electrode and plate 11 for preventing deformation may be fixed integrally to chuck top 2.
As for the method of mounting chuck top 2 integrated with the cooling module on supporter 4, the cooling module portion 9 may be place in the space formed in supporter 4, or as in the case in which chuck top 2 and cooling module 9 are fixed by screws, it may have a structure that is arranged at the cooling module portion on supporter 4.
Next, an example in which the base portion and the circular tube portion of supporter 4 are formed integrally will be described with reference to FIGS. 22 to 29. Wafer holder 1300 has chuck top 2 having chuck top conductive layer 3, and supporter 4 supporting chuck top 2, and has space 5 at a portion between chuck top 2 and supporter 4. In wafer holder 1300, supporter 4 has a structure in which the base portion and the circular tube portion are formed integrally. As it has space 5, the heat insulating effect can be enhanced.
Even when supporter 4 has a structure having the base portion and the circular tube portion formed integrally, the structure near the electrode portion such as shown in
Further, it is also possible to provide cooling module 9 such as shown in wafer holder 1500 of
Further, by providing plate 11 for preventing deformation as shown in wafer holder 1800 of
The wafer holder in accordance with the present invention may be arranged in a container formed of stainless steel or the like, to be a heater unit. The heater unit may suitably be used as a wafer prober for inspecting electric characteristics of a wafer, and on the wafer prober, a driving system for moving the wafer holder may be provided. When the wafer holder of the present invention has characteristics such as high rigidity and high thermal conductivity, it may be applied, for example, to a handler apparatus or a tester apparatus, in addition to the wafer prober. In any application, use of the wafer holder in accordance with the present invention enables inspection of high accuracy without causing contact failure to a semiconductor having minute circuitry.
EXAMPLES As wafer holders, samples having the supporter of integral type basic shape (such as shown in
A wafer holder 300 having the structure shown in
Next, as supporter 4, a cylindrical plate of mullite-alumina composite having the diameter of 310 mm and the height of 40 mm was prepared. The contact surface with chuck top 2 and the bottom surface of supporter 4 were polished to have the variation in thickness of 46 μm from the bottom surface to the contact surface with chuck top 2, and thereafter, the contact surface with chuck top 2 was counter-bored to the inner diameter of 290 mm and the depth of 3 mm, to form a cavity 51 for arranging heater body 6.
On chuck top 2 above, stainless steel foil insulated by mica was attached as the electromagnetic shield layer, and further, heater body 6 sandwiched by mica was attached. Heater body 6 was formed by etching stainless steel foil in a prescribed pattern, and the electromagnetic shield layer and heater body 6 were arranged at a position to be housed in cavity 51 provided in supporter 4. In supporter 4, a through hole was formed in the similar manner as that shown in
On supporter 4 described above, chuck top 2 having heater 6 and the electromagnetic shield layer attached was mounted, and thus, wafer holder 300 for a wafer prober having integral type supporter 4 shown in
Wafer holder 300 having integral type supporter 4 shown in
Wafer holder 300 having integral type supporter 4 shown in
Wafer holder 300 having integral type supporter 4 shown in
A wafer holder 400 having a separate type supporter 4 with base portion 41 and circular tube portion 42 such as shown in
Further, as components of supporter 4, a circular tube portion formed of a mullite-alumina composite having the diameter of 310 mm, radial thickness of 10 mm and height of 30 mm, and a base portion formed of a mullite-alumina composite having the diameter of 310 mm and thickness of 15 mm were prepared. The circular tube portion and the base portion were polished and finished such that the variation in thickness of circular tube portion 42 from the contact surface with the chuck top 2 to the contact surface with the base portion 41 attained to 22 μm, and the variation in thickness of base portion 41 from the bottom surface to the contact surface with circular tube portion 42 attained to 23 μm. Circular tube portion 42 and base portion 41 were combined and supporter 4 was obtained.
Wafer holder 400 having separate type supporter 4 shown in
A wafer holder 400 having a separate type supporter 4 with base portion 41 and circular tube portion 42 such as shown in
The obtained wafer holder was mounted on a wafer prober, and semiconductor wafers were inspected continuously for 10 hours, under three different inspection conditions shown in Table 2 below, with the results also shown in Table 2. Table 1 below collectively shows the variation in thickness of the chuck top from the wafer-mounting surface to the contact surface with the supporter (that is, variation in thickness of the chuck top), the variation in thickness of the supporter from the bottom surface to the contact surface with the chuck top (that is, variation in thickness of the supporter), the variation in thickness of the circular tube portion from the contact surface with the chuck top to the contact surface with the base portion (that is, the variation in thickness of the circular tube portion), and the variation in thickness of the base portion from the bottom surface to the contact surface with the circular tube portion (that is, the variation in thickness of the base portion) of the supporters in accordance with Examples 1A to 3A and Comparative Examples 1A to 3A described above.
As can be seen from the results shown above, when the variation in thickness of the chuck top and the variation in thickness of the supporter were both adjusted to be at most 50 μm and the variation in thickness of the circular tube portion and the variation in thickness of the base portion were both adjusted to be at most 25 μm for the supporter having the circular tube portion, deformation of the wafer holder was not observed even when high load was applied, and contact failure at the time of inspection could be avoided. Particularly, when the variation in thickness of the circular tube portion and the variation in thickness of the base portion were both adjusted to be at most 10 μm for the supporter having the circular tube portion, deformation of the wafer holder was not observed and contact failure at the time of inspection could be avoided under severer inspection conditions.
Example 1BAlumina substrates having the purity of 99.5%, diameter of 305 mm and the thickness shown in Table 3 were prepared. On the wafer-mounting surface of each alumina substrate, concentrical trench for vacuum chucking and a through hole were formed, and the wafer-mounting surface was nickel-plated, to form the chuck top conductive layer. Thereafter, the chuck top conductive layer was polished, the amount of warp of the entire body was set to 10>m, surface roughness Ra was set to 0.02 μm, and the variation in thickness from the wafer-mounting surface to the contact surface with the supporter was set to 10 μm, and thus a chuck top was obtained.
Next, a mullite-alumina composite of a cylindrical shape having the diameter of 305 mm and the thickness of 40 mm was prepared.
The contact surface with the chuck top and the bottom surface of the supporter were polished and finished such that the variation in thickness from the bottom surface to the contact surface with the chuck top attained to 3 μm, and then, the contact surface with the chuck top was counter-bored to the inner diameter of 285 mm and the thickness of 20 mm. On each chuck top, stainless steel foil insulated by mica was attached as the electromagnetic shield layer, and further, the heater body sandwiched by mica was attached. The heater body was formed by etching stainless steel foil in a prescribed pattern. In the supporter, a through hole for connecting an electrode for power feeding to the heater body was formed. Then, a metal layer was formed by thermal spraying of aluminum, on the side surface and the bottom surface of the supporter.
Next, the chuck top having the heater body and the electromagnetic shield layer attached was mounted on the supporter, and thus, a wafer holder for a wafer prober was completed.
By applying electric power to the heater of wafer holder for the wafer prober described above, the wafer was heated to 150° C., and probing was done continuously. The results are as shown in Table 3. Samples of which ratio of diameter to thickness was at least 5 and at most 100 had no problem after continuous probing for 10 hours. Samples having the ratio smaller than 5 had the chuck top warped after two hours, contact with a probe pin was biased, and probing failed. In samples having the ratio of diameter to thickness exceeding 100, thermal uniformity of the wafer-mounting surface of the chuck top was unsatisfactory and accurate measurement was impossible.
Further, at the position of the diameter of 275 mm of the chuck top of wafer holder for the wafer prober described above, a load (100 kg) was applied by using a load sensor having the diameter of 20 mm, and the magnitude of deflection was measured. The results are as shown in Table 3.
As can be seen from Table 3, when the ratio of diameter to thickness exceeded 100, the amount of deflection increased and accurate measurement was impossible.
Example 2BUsing the wafer holder for the wafer prober similar to sample No. 5 of Example 1B except that the metal layer on the supporter was provided not by thermal spraying but by fixing metal foil of stainless steel with screws, probing was done at a heated temperature of 150° C. as in Example 1B, and there was no problem after continuous probing for 10 hours.
For comparison, the metal layer on the supporter was removed and probing was done. Under the conditions of Example 1B, there was no problem after continuous probing for 10 hours. However, probing related to high frequency was affected by noise, and sometimes probing was not successful. Further, probing was done with the electromagnetic shield layer removed. Then, because of the influence of noise that seemed to be generated from the heater body, wafer characteristics could not be measured.
Example 3BSi—SiC substrates having the diameter of 305 mm or 205 mm and the thickness shown in Table 4 were prepared. On the wafer-mounting surface of each Si—SiC substrate, concentrical trench for vacuum chucking and a through hole were formed, and the wafer-mounting surface was nickel-plated, to form the chuck top conductive layer. Thereafter, the chuck top conductive layer was polished and finished such that the amount of warp of the entire body was set to 10 μm, surface roughness Ra was set to 0.02 μm, and the variation in thickness from the wafer-mounting surface to the contact surface with the supporter was set to 10 μm, and thus a chuck top was obtained.
Next, mullite-alumina composite bodies of cylindrical shape having the diameter of 305 mm and 205 mm and the thickness of 40 mm were prepared. The contact surface with the chuck top and the bottom surface of the supporter were polished, so that the variation in thickness from the bottom surface to the contact surface with the chuck top was finished to 3 μm, and then, the bodies were counter-bored to the inner diameters of 285 mm and 185 mm and the depth of 20 mm. On each chuck top, stainless steel foil insulated by mica was attached as the electromagnetic shield layer, and further, the heater body sandwiched by mica was attached. The heater body was formed by etching stainless steel foil in a prescribed pattern. In the supporter, a through hole for connecting an electrode for power feeding to the heater body was formed. Then, a metal layer was formed by thermal spraying of aluminum, on the side surface and the bottom surface of the supporter.
Next, the chuck top having the heater body and the electromagnetic shield layer attached was mounted on the supporter, and thus, a wafer holder for a wafer prober was completed.
By applying electric power to the heater of wafer holder for the wafer prober described above, the wafer was heated to 150° C., and probing was done continuously. The results are as shown in Table 4. Samples of which ratio of diameter to thickness was at least 5 and at most 100 had no problem after continuous probing for 10 hours. Samples having the ratio smaller than 5 had the chuck top warped after two hours, and contact with a probe pin was biased, and probing failed. In samples having the ratio of diameter to thickness exceeding 100, thermal uniformity of the wafer-mounting surface of the chuck top was unsatisfactory and accurate measurement was impossible.
Further, at a position of the diameter of 275 mm or 175 mm of the chuck top of wafer holder for the wafer prober described above, a load (100 kg) was applied by using a load sensor having the diameter of 20 mm, and the magnitude of deflection was measured. The results are as shown in Table 4.
As can be seen from Table 4, when the ratio of diameter to thickness exceeded 100, the amount of deflection increased and accurate measurement was impossible.
Example 4BUsing the wafer holder for the wafer prober similar to sample No. 9 of Example 3B except that the metal layer on the supporter was provided not by thermal spraying but by fixing metal foil of stainless steel with screws, probing was done at a heated temperature of 150° C. as in Example 3B, and there was no problem after continuous probing for 10 hours.
For comparison, the metal layer on the supporter was removed and probing was done. Under the conditions of Example 3B, there was no problem after continuous probing for 10 hours. However, probing related to high frequency was affected by noise, and sometimes probing was not successful. Further, probing was done with the electromagnetic shield layer removed. Then, because of the influence of noise that seemed to be generated from the heater body, wafer characteristics could not be measured.
Example 1CA substrate formed of a composite of silicon and silicon carbide (Si—SiC) having the purity of 99.5%, diameter of 310 mm and the thickness of 10 mm was prepared. On the wafer-mounting surface of the Si—SiC substrate, concentrical trench for vacuum chucking and a through hole were formed, and the wafer-mounting surface was nickel-plated, to form the chuck top conductive layer. Thereafter, the chuck top conductive layer was polished, the amount of warp of the entire body was set to 10 μm, surface roughness Ra was set to 0.02 μm, and the variation in thickness from the wafer-mounting surface to the contact surface with the supporter was set to 10 μm, and thus a chuck top was obtained.
Next, as the circular tube portion of the supporter, samples 1 to 8 of mullite-alumina composite, having the diameter of 310 mm, inner diameter of 290 mm (that is, radial thickness of 10 mm), and the thickness shown in Table 5 were prepared. Further, as the base portion of the supporter, mullite-alumina composite bodies having the diameter of 310 mm and the thickness shown in Table 5 were prepared. These circular tube portions and the base portions were fixed by screws, and supporter samples 1 to 8 were obtained. The contact surface with the chuck top and the bottom surface of the supporters were polished and finished until the variation in thickness from the bottom surface to the contact surface with the chuck top attained to 5 μm.
On the chuck top, stainless foil insulated by mica was attached as the guard electrode on the surface opposite to the wafer-mounting surface, and further, the heater body sandwiched by mica was attached. The heater body was formed by etching stainless steel foil in a prescribed pattern. The guard electrode and the heater body were arranged at a position to be housed in the circular tube portion of the supporter. In the circular tube portion of the supporter, a through hole for connecting an electrode for power feeding to the heater body was formed as shown in
On the supporter thus obtained, the chuck top having the heater body and the electromagnetic shield layer attached was mounted, and the wafer holder for the wafer prober shown in
A mullite-alumina composite body of cylindrical shape having the diameter of 310 mm and the thickness of 60 mm was prepared. Portions to be the contact surface with the chuck top and the bottom surface of the supporter were polished, so that the variation in thickness from the bottom surface to the contact surface with the chuck top was finished to 5 μm, and then the surface was counter-bored to have the diameter of 290 mm and the depth of 30 mm, whereby a circular tube shape with a bottom was obtained. Thus, a supporter of sample 9, which has the circular tube portion having the thickness of 30 mm and the base portion having the thickness of 30 mm integrated and inseparable was formed.
The wafer holder of sample 9 was completed in the similar manner as Example 1C except for the supporter described above. The wafer holder was mounted on the wafer prober, and a semiconductor was inspected continuously for 10 hours under three different conditions of inspection as shown in Table 6 below. The results are also shown in Table 6.
Example 3C Sixteen pillars formed of alumina-mullite composite having the diameter of 10 mm and thickness of 5 mm were prepared. These 16 pillars were arranged uniformly as shown in
The wafer holder of sample 10 was completed in the similar manner as Example 1C except that 16 pillars described above were provided in the supporter. The wafer holder was mounted on the wafer prober, and semiconductors were inspected continuously for 10 hours under three different conditions of inspection as shown in Table 6 below. The results are also shown in Table 6.
(Note)
In the Table, samples with * represent comparative examples
(Note)
In the Table, samples with * represent comparative examples
As can be seen from the results above, with the thickness of the chuck top t1 being 1.0, when the thickness t2 of the circular tube portion of the supporter was set to at least 0.1 and at most 5.0 and the thickness t3 of the base portion was set to at least 0.5 and at most 10.0 with respect to the thickness t1, the wafer holder did not deform even under high load, and contact failure could be avoided. Further, in the example in which the pillars were provided, contact failure could be avoided even under the load of 200 kgf at 200° C., when the sum of thickness t4 of the pillar and thickness t2 of the circular tube portion was set to at least 0.1 and at most 5.0 with the thickness t1 of the chuck top being 1.0
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.
Claims
1. A wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting said chuck top, wherein variation in thickness of said chuck top from said wafer-mounting surface to a contact surface with said supporter is at most 50 μm, and variation in thickness of said supporter from a bottom surface to a contact surface with said chuck top is at most 50 μm.
2. The wafer holder according to claim 1, wherein said supporter has a structure including a circular tube portion in contact with said chuck top and a base portion supporting said circular tube portion, with said circular tube portion and said base portion separated, and variation in thickness of said circular tube portion from a contact surface with said chuck top to a contact surface with said base portion is at most 25 μm, and variation in thickness of said base portion from a bottom surface to a contact surface with said circular tube portion is at most 25 μm.
3. The wafer holder according to claim 1, wherein variation in thickness of said chuck top from said wafer-mounting surface to the contact surface with said supporter, variation in thickness of said supporter from the bottom surface to the contact surface with said chuck top, variation in thickness of said circular tube portion from the contact surface with said chuck top to the contact surface with said base portion, and variation in thickness of said base portion from the bottom surface to the contact surface with said circular tube portion are at most 10 μm.
4. The wafer holder according to claim 1, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 5 and at most 100.
5. The wafer holder according to claim 1, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 10 and at most 50.
6. The wafer holder according to claim 1, wherein material of said chuck top is a composite of metal and ceramics.
7. The wafer holder according to claim 1, wherein material of said chuck top is a composite of aluminum and silicon carbide, or a composite of silicon and silicon carbide.
8. The wafer holder according to claim 1, wherein material of said chuck top is ceramics.
9. The wafer holder according to claim 1, wherein material of said supporter is ceramics or a composite of two or more ceramics.
10. The wafer holder according to claim 9, wherein material of said supporter is any of alumina, silicon nitride, mullite, and a composite of alumina and mullite.
11. The wafer holder according to claim 1, wherein said supporter is formed of a circular tube portion in contact with said chuck top and a base portion supporting said circular tube portion, thickness of said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0, and thickness of said base portion is at least 0.5 and at most 10.0 with thickness of said chuck top being 1.0.
12. The wafer holder according to claim 1, wherein said circular tube portion and said base portion are formed integrally.
13. The wafer holder according to claim 1, having a pillar between said circular tube portion and said base portion or between said circular tube portion and said chuck top, and a sum of thickness of said pillar and said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0.
14. A wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting said chuck top, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 5 and at most 100.
15. The wafer holder according to claim 14, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 10 and at most 50.
16. The wafer holder according to claim 14, wherein material of said chuck top is a composite of metal and ceramics.
17. The wafer holder according to claim 14, wherein material of said chuck top is a composite of aluminum and silicon carbide, or a composite of silicon and silicon carbide.
18. The wafer holder according to claim 14, wherein material of said chuck top is ceramics.
19. The wafer holder according to claim 14, wherein material of said supporter is ceramics or a composite of two or more ceramics.
20. The wafer holder according to claim 19, wherein material of said supporter is any of alumina, silicon nitride, mullite, and a composite of alumina and mullite.
21. A wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting said chuck top, wherein said supporter is formed of a circular tube portion in contact with said chuck top and a base portion supporting said circular tube portion, thickness of said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0, and thickness of said base portion is at least 0.5 and at most 10.0 with thickness of said chuck top being 1.0.
22. The wafer holder according to claim 21, wherein said circular tube portion and said base portion are formed integrally.
23. The wafer holder according to claim 21, having a pillar between said circular tube portion and said base portion or between said circular tube portion and said chuck top, and a sum of thickness of said pillar and said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0.
24. A heater unit for a wafer prober, comprising the wafer holder according to claim 1.
25. A heater unit for a wafer prober, comprising the wafer holder according to claim 14.
26. A heater unit for a wafer prober, comprising the wafer holder according to claim 21.
27. A wafer prober, comprising the heater unit according to claim 1.
28. A wafer prober, comprising the heater unit according to claim 14.
29. A wafer prober, comprising the heater unit according to claim 21.
Type: Application
Filed: Jul 25, 2006
Publication Date: Feb 1, 2007
Inventors: Katsuhira Itakura (Itami-shi), Masuhiro Natsuhara (Itami-shi), Tomoyuki Awazu (Itami-shi), Hirohiko Nakata (Itami-shi), Kenji Shinma (Itami-shi)
Application Number: 11/492,223
International Classification: B65D 85/00 (20060101);
