ETCHING METHOD AND ETCHING DEVICE
An etching method and etching device are provided, enabling uniform rendering of the thickness of a film for processing on a wafer regardless of the film thickness profile thereof, and thereby enabling global planarizing of the wafer surface. In an etching method, the film thickness profile of the film for processing formed on the wafer is ascertained in advance, and wet etching is performed by discharging an etchant liquid L1 at a thick portion of the film for processing; simultaneously with the discharge of the etchant liquid L1, a diluting liquid L2 for the etchant liquid L1 is discharged at a thin portion of the film for processing.
This application is divisional of U.S. patent application Ser. No. 10/839,404, filed May 5, 2004, which is incorporated herein by reference to the extent permitted by law. This application claims the benefit of priority to Japanese Patent Application No. JP 2003-132764 filed in the Japanese Patent Office on May 12, 2003, which also is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION1. Field of the Invention
This invention relates to an etching method to planarize the surface shape of a wafer, and an etching device employing this method.
2. Description of the Related Art
The rising integration levels in semiconductor devices in recent years have been accompanied by advances in the miniaturization and multilayer design of elements and wiring. Pattern formation for fine wiring may also rely on thin film fabrication techniques and lithography, but with the adoption of multilayer designs, a planarized base surface is indispensable for the precise formation of fine patterns.
For example, in reducing the size of a gate electrode, much depends on the performance of the exposure equipment used in lithography processes; however where miniaturization of device isolation regions and reduction of distances from other gate electrodes are concerned, techniques to planarize the base surface using shallow trench isolation (hereafter abbreviated “STI”) are also attracting attention in addition to advanced lithographic techniques.
In this state, if CMP (chemical-mechanical polishing) is performed to planarize the buried insulating film 5, a global step existing at the surface of the initial buried insulating film 5 remains at the surface of the buried insulating film 5 even after polishing.
Hence as shown in
Accordingly, buried insulating film the thickness of which is greater at the periphery of the silicon substrate than at the center (0) becomes such that the film thickness at the periphery and near the center (0) is the same, as shown by the profile of
Further, in STI formation, when by the above-described etching the thickness of the buried insulating film 5 is rendered uniform as shown in
However, when using the above-described etching method, the film thickness profiles of the film for processing which can be corrected are limited; for example, the film thickness of a film for processing with a large film thickness near the center (0) of the wafer, as shown in
In the STI formation process, planarizing by CMP is performed on the buried insulating film (film for processing) subjected to such etching. Consequently, as shown in
Further, if in order to avoid the above adverse effects CMP polishing is performed so as to expose the stopper layer 3 at the center of the wafer as shown in
In light of the above, this invention has as an object of providing an etching method and etching device, in which the film thickness of a film to be processed having any film thickness profile can be uniform, regardless of the film thickness profile of the film to be processed on the wafer, and global planarizing of the wafer surface can be obtained.
SUMMARY OF THE INVENTIONIn order to attain this object, an etching method of this invention is the etching method in which the film thickness profile of a film for processing formed on a wafer is ascertained in advance and an etchant liquid is discharged onto thick portions of the film for processing to perform wet etching, and simultaneously with the discharge of etchant liquid, a diluting liquid for the etchant liquid is discharged onto thin portions of the film for processing.
By means of this etching method, if the etchant liquid discharged onto thick portions of the film for processing spreads to thin portions of the film for processing, the etchant liquid is diluted by the diluting liquid discharged at the thin portions. Accordingly, the effect of etching of the film for processing by the etchant liquid is weakened at thin portions. Hence etching of the film for processing proceeds further at thick portions of the film than at thin portions, and the film thickness distribution of the film for processing can be rendered uniform.
Further, an etching device of this invention includes a spin chuck which holds and rotate a wafer, a liquid-discharging nozzle to supply etchant liquid to a predetermined position on the wafer held by the spin chuck, and a diluting liquid-discharging nozzle to discharge a diluting liquid for the etchant liquid on the outside of the position where etchant liquid is discharged on the wafer held by the spin chuck.
In an etching device of this configuration, etchant liquid is discharged from a liquid-discharging nozzle at a predetermined position in the radial direction of a wafer held and rotated on the spin chuck, and a diluting liquid is discharged from the diluting liquid-discharging nozzle on the outside of this predetermined position. Hence although the etchant liquid flows and is supplied on the outside of the position where etchant liquid is discharged due to centrifugal force resulting from the wafer rotation, the etchant liquid is diluted by the diluting liquid, and the rate of etching can be reduced. On the other hand, on the inside of the position where etchant liquid is discharged, the centrifugal force due to wafer rotation prevents the flowing-in of etchant liquid, so that etching by the etchant liquid can be suppressed. Consequently the etching rate can be made highest at the position where etchant liquid is discharged, and etching progress can be suppressed in the outer and inner radial directions from this discharge position.
BRIEF DESCRIPTION OF THE DRAWINGS
Hereinafter, embodiments of etching methods and etching devices to which this invention are applied are explained in detail, referring to the drawings.
[Etching Device]
Of these, the liquid-discharging nozzle 103 in particular discharges etchant liquid L1 at a predetermined position on a wafer held by the spin chuck 101. This liquid-discharging nozzle 103 is freely moveable in the radial direction from the center of rotation of the wafer 1 held by the spin chuck 101, in a configuration enabling movement of the position of discharging the etchant liquid L1. The liquid-discharging nozzle 103 may have a plurality of discharge apertures to discharge the etchant liquid L1 at a plurality of positions in the radial direction on the wafer 1 held by the spin chuck 101.
The diluting liquid-discharging nozzle 105 discharges diluting liquid L2 for the etchant liquid L1, at a predetermined position on the wafer 1 held by the spin chuck 101. This diluting liquid-discharging nozzle 105 is provided so as to discharge diluting liquid L2 on the outside from the position where etchant liquid L1 is discharged by the liquid-discharging nozzle 103, with respect to the rotation center of the spin chuck 101. Further, the diluting liquid-discharging nozzle 105 is freely moveable in the radial direction on the wafer 1 held by the spin chuck 101, in a configuration enabling movement of the position where the diluting liquid L2 is discharged. Note that the diluting liquid-discharging nozzle 105 may have a plurality of discharge apertures to discharge the diluting liquid L2 at a plurality of positions in the radial direction on the wafer 1 held by the spin chuck 101.
In the etching device 100 with such a configuration, etchant liquid L1 is discharged from the liquid-discharging nozzle 103 at a predetermined position in the radial direction of the wafer 1 held and rotated on the spin chuck 101, and diluting liquid L2 is discharged from the diluting liquid-discharging nozzle 105 on the outside from this predetermined position. Accordingly, although the etchant liquid L1 flows and is supplied to the outside of the position where the etchant liquid L1 is discharged through the centrifugal force due to the rotation of the wafer 1, the etchant liquid L1 is diluted by the diluting liquid L2, so that the etching rate can be lowered. On the other hand, on the inside of the position where the etchant liquid L1 is discharged, inflow of the etchant liquid L1 is prevented by the centrifugal force due to the rotation of the wafer 1, so that progress of etching by the etchant liquid L1 can be suppressed. Hence etching can be performed such that the etching effect is greatest at the position where the etchant liquid L1 is discharged, and the etching effect is suppressed on the outside and inside thereof.
Since the liquid-discharging nozzle 103 is moveable in the radial direction, by moving the position of discharge of etchant liquid L1 in the radial direction together with supply of the etchant liquid L1 from the liquid-discharging nozzle 103, the amount of etchant liquid L1 supplied can be increased at positions further toward the outside. Accordingly, the effect of etching by the etchant liquid L1 can be increased to the extent that the position of discharge of the etchant liquid L1 is toward the outside. This is similarly the case even when the liquid-discharging nozzle 103 has a plurality of discharge apertures in the radial direction of the wafer 1, with etchant liquid L1 discharged from each discharge aperture.
Further, since the diluting liquid-discharging nozzle 105 is moveable in the radial direction, by moving the position of discharge of diluting liquid L2 in the radial direction together with the supply of diluting liquid L2 from the diluting liquid-discharging nozzle 105, the amount of diluting liquid L2 supplied can be increased at positions further toward the outside. Hence to the extent that the position of discharge of the diluting liquid L2 is toward the outside, the rate of dilution of the etchant liquid L1 can be increased, and the etching rate can be lowered. This is similarly the case even when the diluting liquid-discharging nozzle 105 has a plurality of discharge apertures in the radial direction of the wafer 1, with diluting liquid L2 discharged from each discharge aperture.
[Etching Method]
Next, an embodiment of an etching method of this invention employing an etching device with the above configuration is explained, based on the above
As the basic concept underlying an etching method of this invention, the film thickness profile of the film for processing is ascertained in advance, etchant liquid L1 is discharged only onto portions with poor compatibility with the processing means, such as for example portions in which the film thickness is larger, and diluting liquid L2 is discharged onto portions where the film thickness is small to perform etching. An etching device with the configuration explained in
In order to perform etching only at the thick portions of the above film, etchant liquid L1 is discharged at a position where the thickness of the film for processing is large in the radial direction of the wafer 1, based on position information in the radial direction for the wafer 1 and film thickness profile information about the film for processing formed on the wafer 1, and simultaneously with this, diluting liquid L2 for the etchant liquid L1 is discharged at a thin portion of the film on the outside of the position of discharge of the etchant liquid L1.
First, as one example of the etching method, a case is illustrated in which a film for processing is formed on a wafer having a film thickness profile in which the film is thick in the center (0) portion and gradually becomes thinner toward the outer periphery, as shown
In this case, first the wafer 1 is held and rotated by the spin chuck 101 in a state in which the rotation center of the spin chuck 101 is made to coincide with the center of the wafer. Then, by discharging etchant liquid L1 from the liquid-discharging nozzle 103 at the center (0) of the wafer, which is the portion where the thickness of the film for processing is greatest, the film for processing on the wafer 1 is etched.
Then, when etchant liquid L1 is discharged from the liquid-discharging nozzle 103 while rotating the wafer W, centrifugal force causes the etchant liquid L1 to flow in the outward radial direction, similarly to a so-called spin coater or other equipment. Accordingly, etching by the etchant liquid L1 occurs at the outer periphery of the wafer W as well.
Simultaneously with discharge of the etchant liquid L1 from the liquid-discharging nozzle 103, diluting liquid L2 for the etchant liquid L1 is discharged from the diluting liquid-discharging nozzle 105 at a position on the outside from the position where the etchant liquid L1 is discharged. As this diluting liquid L2, the solvent component of the etchant liquid L1, or else a chemical which neutralizes the etchant component in the etchant liquid L1, is used. As a result, the etchant liquid L1 is diluted (neutralized) by the diluting liquid L2 at the outer periphery, where the film for processing is thinner, compared with the center portion of the wafer W, so that the effect of etching of the film for processing by the etchant liquid L1 is weakened.
At this time, if the diluting liquid-discharging nozzle 105 discharges diluting liquid L2 while moving in the radial direction of the wafer 1 on the outside of the liquid-discharging nozzle 103, the time of supply of diluting liquid L2 is longer on moving to the outside. Therefore, the further toward the outside, the higher is the rate of dilution, and so the smaller is the effect of etching by the etchant liquid L1. If the diluting liquid-discharging nozzle 105 includes a plurality of discharge apertures in the radial direction, the amount of diluting liquid L2 supplied increases toward the outside, and toward the outside the rate of dilution of the etchant liquid L1 rises. Hence there is no need to cause the diluting liquid-discharging nozzle 105 to move in the radial direction of the wafer 1.
Accordingly, the difference in thickness of the film for processing at the center (0) of the wafer 1 and at the outside thereof can be alleviated, as shown in the film thickness profile in
Next, as a second example of an etching method, a case is illustrated in which a film for processing is formed having a film thickness profile in which the film is thin in the center (0) portion and gradually becomes thicker toward the outer periphery, as shown in
In this case, first the wafer 1 is held and rotated by the spin chuck 101 in a state in which the rotation center of the spin chuck 101 is made to coincide with the center of the wafer. Then, etchant liquid L1 is discharged while moving the liquid-discharging nozzle 103 in the radial direction of the wafer W, from the position Pin on the inside in the radial direction from the position Pmax, at which the film is thickest, to this position Pmax. Here the position Pin is taken to be the position at which the film thickness changes from the smallest value to become thick. As a result, etchant liquid L1 is supplied from the position Pin toward the outside through the action of centrifugal force, but the time of supply of etchant liquid L1 becomes longer in moving from the position Pin toward the outside, and the time of supply of etchant liquid is longest at the outer periphery including the position Pmax. Hence from the position Pin to the position Pmax, etching by etchant liquid L1 proceeds further in moving toward the outer periphery, so that the amount of etching of the film for processing increases.
When in this way etchant liquid L1 is discharged from the liquid-discharging nozzle 103 while rotating the wafer W, the etchant liquid L1 flows in the outward direction from the position of discharge due to centrifugal force, so that etching by the etchant liquid L1 proceeds further at the outer periphery at Pmax, the portion at which the film is thickest. Accordingly, on the outside of the position Pmax, diluting liquid L2 is discharged while moving the diluting liquid-discharging nozzle 105 in the radial direction of the wafer W, similarly to the above first example. Consequently, the rate of dilution of the etchant liquid L1 rises in moving to the outer periphery beyond the position Pmax, and the effect of etching by the etchant liquid L1 is reduced.
From the above, as shown by the film thickness profile of
Next, as a third example of an etching method, a case is illustrated in which a film for processing is formed on a wafer 1, when the film thickness profile has two peaks, at the center (0) in the radial direction and at the outer periphery in the radial direction, as shown in
First, similarly to the first example explained using
As a result, the central peak is planarized by etching, as shown in
Hence in such a state, by performing treatment similar to that of the second example explained using
In the above third example, a procedure was explained in which, after planarizing the peak at the center by the method of the first example, the method of the second example is used to planarize the peak at the outer periphery. However, this procedure may be reversed to perform similar planarizing. In addition, if the etching device includes two sets of a liquid-discharging nozzle and a diluting liquid-discharging nozzle, the method of the first example and the method of the second example can be performed simultaneously, to accomplish similar planarizing. In this case, the two sets of a liquid-discharging nozzle and diluting liquid-discharging nozzle are positioned in the order, from the center of the spin chuck to the outer periphery, of liquid-discharging nozzle, diluting liquid-discharging nozzle, liquid-discharging nozzle, diluting liquid-discharging nozzle.
As explained in the above first through third examples, by means of an etching method of this invention, the film thickness can be rendered uniform regardless of the film thickness profile.
Also, in the etching methods explained in the above first through third examples, it is preferable that a kind of chemical capable of etching a film for processing in a lower rate be used as the etchant liquid L1, enabling the amount of etching to be controlled easily and the thickness of a film being reliably uniform.
Further, in the above etching methods it is preferable that the discharge amounts and discharge times of the liquids L1 and L2, as well as the wafer rotation rate, be set such that the etchant liquid L1 and diluting etchant liquid L2 do not flow from the respective discharge positions to the center position. By this means, the etching rate (etching effect) in the wafer radial direction can be controlled more reliably.
In the above etching methods, the temperature of the etchant liquid L1 may be made high (30° C. or higher, and preferably 40° C. to 60° C.), such that the etching amount is suppressed through the cooling effect when the etchant liquid L1 flows to the wafer periphery. The etching rate is higher for higher temperatures of the etchant liquid L1. Hence when high-temperature etchant liquid L1 is discharged from the liquid-discharging nozzle 103, the etching rate is high in the vicinity of the discharge position, but as the etchant liquid L1 flows to the outer periphery the temperature of the etchant liquid L1 falls, and the etching rate also falls. Hence together with the decline in etching rate due to dilution of the etchant liquid L1 through the supply of diluting liquid L2, the etching rate can also be lowered through the reduced temperature, so that excessive etching at peripheral positions of the wafer 1 is prevented.
When adopting such a method, in order to promote cooling of the etchant liquid L1, it is more effective to provide the spin chuck 101 with a function for lowering the temperature of the peripheral portion of the wafer 1. As a mechanism to provide such a function to lower the temperature, for example, a coolant such as N2 or similar can be discharged only onto the rear surface of the peripheral portion of the wafer 1 to cause cooling, or other means can be used.
As another method to reduce the effect of etching by the etchant L1 on the outside compared with the position where the etchant liquid L1 is discharged, a method may be employed in which the flow rate of the etchant liquid L1 toward the outer periphery is increased by spraying an inert gas on the outer side of the position where the etchant liquid L1 is discharged. In this case, the inert gas is sprayed from obliquely above the wafer 1 toward the outer periphery of the wafer 1 on the outer side of the position of discharge of the etchant liquid L1. In this way, by increasing the speed of flow of the etchant liquid L1, the time of supplying the etchant liquid L1 is shortened at the outer periphery compared with the position of discharge of the etchant liquid L1. As a result, using this method also, the etching rate (etching effect) can be reduced at the outer periphery compared with the position where the etchant liquid L1 is discharged.
When performing etching accompanied by such spraying of an inert gas, a gas supply nozzle to spray an inert gas toward the outer periphery of the wafer 1 is provided in the etching device explained using
Here, an embodiment in which an etching method of this invention is applied to an STI process in semiconductor device manufacturing is explained.
The sample used in this example has the structure shown in
The profile prior to etching previously shown in
With a buried insulating film 15 having such a film thickness profile as the film for processing, etching was performed so as to eliminate the excess thickness in the center portion. 1) As an etchant liquid enabling wet etching of the buried insulating film 15 which is the film for processing, diluted hydrofluoric acid (DHF) was adopted. 2) As the diluting liquid to dilute the etchant liquid, water was adopted. 3) The center of the silicon substrate 11 serving as the wafer was set as the rotation center, and the liquid-discharging nozzle 103 was fixed such that the position where the etchant liquid L1 was discharged was this center. 4) The diluting liquid-discharging nozzle 105 was moved from a position 20 mm in the outward direction from the center (0) of the silicon substrate 11 to a position 50 mm distant in 5 mm intervals, and the diluting liquid L2 was discharged, with the discharge flow rate at the low flow rate of 1 liter/minute or less, at each position for three seconds.
Upon measuring the thickness of the buried insulating film 15 on the stopper layer 13 in the radial direction of the silicon substrate 11 after performing the above etching, the film thickness was reduced in the center portion and the film was finished to approximately the same thickness from the center to the outer periphery, as shown by the profile after etching of
From this state, CMP was used to polish and remove the entirety of the buried insulating film 15 on the stopper layer 13, as shown in
The sample used in this example has the structure shown in
The profile before etching previously shown in
With an inter-layer insulating film 23 having such a film thickness profile as the film for processing, etching similar to that of Embodiment 1 described above was performed so as to eliminate the excess thickness in the center portion.
The shape of the inter-layer insulating film 23 after performing this etching is as shown in
The result of etch-back treatment by RIE, CMP polishing or other planarizing of the inter-layer insulating film 23 following this appears in
In the above-described Embodiments 1 and 2, examples were disclosed in which a film for processing formed on a wafer (silicon substrate), such as a buried insulating film or an inter-layer insulating film, was subjected to treatment to modify the shape of the film for processing prior to processing; however, the film for processing may be the wafer itself, and a method of this invention may be used to perform planarizing in the case where, for example, the wafer thickness differs at the wafer center and periphery.
In the above, cases of performing etching based on a film thickness profile were explained. However, etching methods of this invention may be employed to perform etching based on a topmost-surface height position profile on a wafer, which is a global difference in the wafer surface and is not local differences due to formation of trenches, wiring or similar. In this case, the above mentions of thicker film portions and similar should be replaced by terms referencing portions at higher surface positions.
As explained above, in an etching method of this invention, by diluting etchant liquid, discharged onto a thick portion of a film for processing which has spread to a thin portion of the film for processing, with a diluting liquid discharged onto the thin portion of the film, the effect of etching of the film for processing by the etchant liquid is weakened at the thin portion of the film, and the etching rate at film portions thicker than the thin portion can be increased. Consequently the film thickness can be rendered uniform regardless of the film thickness profile of the film for processing, and consequently global planarizing of the wafer surface becomes possible.
In an etching device of this invention, by providing a liquid-discharging nozzle which discharges etchant liquid at a predetermined position in the radial direction of a wafer held and rotated on a spin chuck and a diluting liquid-discharging nozzle which discharges diluting liquid on the outside of the above predetermined position, the etchant liquid flowing outward from the position of discharge of etchant liquid due to centrifugal force is diluted and the etching effect thereof diminished, and in addition the inflow of etchant liquid on the inside of the position of discharge of etchant liquid is prevented so that etching can be suppressed. Hence etching can be performed in which the etching effect is greatest at the position of discharge of the etchant liquid, and the etching effect is suppressed on the outside and inside of the above position.
Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications could be effected therein by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.
Claims
1. An etching device, comprising:
- a spin chuck to hold and rotate a wafer;
- a liquid-discharging nozzle to discharge etchant liquid at a predetermined position on the wafer held by said spin chuck; and
- a diluting liquid-discharging nozzle to discharge diluting liquid for said etchant liquid on the outer side of the position where said etchant liquid is discharged on the wafer held by said spin chuck.
2. The etching device according to claim 1, wherein said diluting liquid-discharging nozzle has a plurality of discharge apertures to discharge said diluting liquid at a plurality of positions in the radial direction on the wafer held by said spin chuck.
3. The etching device according to claim 1, wherein said diluting liquid-discharging nozzle moves the position where said diluting liquid is discharged in the radial direction on the wafer held by said spin chuck.
4. The etching device according to claim 1, wherein said liquid-discharging nozzle has a plurality of discharge apertures to discharge said etchant liquid at a plurality of positions in the radial direction on the wafer held by said spin chuck.
5. The etching device according to claim 1, wherein said liquid-discharging nozzle moves the position where said etchant liquid is discharged in the radial direction on the wafer held by said spin chuck.
6. The etching device according to claim 1, wherein a gas supply nozzle is provided on the outer side from the position where said etchant liquid is discharged on the wafer held by said spin chuck, to spray inert gas toward the outer periphery.
Type: Application
Filed: Jul 13, 2006
Publication Date: Nov 2, 2006
Inventors: Hayato Iwamoto (Kanagawa), Kei Kinoshita (Villach), Hajime Ugajin (Kanagawa)
Application Number: 11/457,289
International Classification: H01L 29/76 (20060101); H01L 29/94 (20060101); H01L 31/00 (20060101);