Abrasive free polishing in copper damascene applications

Abstract

An abrasive free wafer polishing device utilizing an abrasive free chemical solution includes a workpiece fixture (11), a brush assembly (12) and a high flow rate fluid dispenser (13). The fluid dispenser (13) dispenses an abrasive free chemical solution to an interface at which the workpiece and the brush assembly come into contact with a flow rate of at least 50 ml/min. The abrasive free chemical solution and brush assembly (12) operate to chemically react with a metal (e.g. copper) on the workpiece and abrade away the reacted copper during a polishing process.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to chemical mechanical planarization (CMP) tools, and more particularly, to polishing devices for use in CMP tools.

BACKGROUND

[0002] CMP tools are typically used to planarize the surface of a semiconductor wafer, to remove the upper portion of a layer formed on the semiconductor wafer (e.g., damascene processes), or to remove a barrier layer formed on the semiconductor wafer. Some conventional CMP tools include a carrier, which may or may not have a polishing motion imparted, to hold a wafer and a platen or table with a polish pad. The CMP tool causes the polish pad and the wafer surface to come into contact, typically applying a specified pressure between the polish pad and the wafer surface. In addition, the CMP tool typically introduces slurry at the interface between the polish pad and the wafer surface. The slurry can have abrasive particles suspended in a chemical solution that reacts with selected materials on the wafer surface. The pressure, abrasive particles, chemical solution, and polishing motion effect the polishing.

[0003] There are several shortcomings of conventional CMP tools in polishing copper on a semiconductor wafer. For example, standard CMP slurries typically contain abrasive particles. These abrasive particles can cause unacceptable amounts of pitting of metal and micro scratching oxide when applied to remove copper. Further, abrasive particles from the slurry can possibly cause contamination problems in a clean room environment. Therefore, there is a need for a simple and inexpensive alternative process for abrasive free polishing which will reduce the load on the clean room environment with an acceptable removal rate while significantly reducing pitting and micro scratching.

SUMMARY

[0004] In accordance with aspects of the present invention, an abrasive free polishing (AFP) device for metal damascene applications is provided. In one aspect of the present invention, the AFP device includes a controller, a workpiece fixture, a brush assembly, and a high flow rate fluid dispenser that dispense an AFP chemical solution. Unlike conventional slurries, the AFP chemical solution contains no abrasive particles. The high flow rate fluid dispenser applies the AFP chemical solution to the interface where the brush assembly contacts the surface of the workpiece to be polished (also referred to herein as the active area) with a sufficient volume to achieve a desired removal rate.

[0005] During the AFP process, the workpiece is loaded into the AFP device and positioned by the workpiece fixture so that the surface to be polished is in contact with the brush assembly. The AFP device imparts a polishing motion between the workpiece and the brush assembly, while the fluid dispenser applies the AFP chemical solution to the active area. This aspect of the invention advantageously eliminates abrasive particles in polishing a workpiece, thereby reducing oxide erosion, micro scratching of the oxide layer and pitting of the metal layer during damascene applications. The workpiece is polished because of the AFP chemical solution reacting with the metal layer in conjunction with the brush assembly abrading away the reacted portions of the metal layer from the workpiece. In accordance with this aspect of the present invention, the AFP device controls the volume of AFP chemical solution introduced to the active area to achieve a desired removal rate. In one embodiment, the fluid dispenser provides the AFP chemical solution at a rate of about 300 ml/min to achieve a removal rate of greater than about 5000 Å/min.

[0006] In further aspect of the present invention, the AFP device includes a platen with multiple through-holes for providing the AFP chemical solution directly to the active area (i.e., interface where the brush assembly contacts the surface of the workpiece to be polished). The through-holes more easily provide the AFP chemical solution directly to the active area and, moreover, allow the fluid dispenser to provide the AFP chemical solution directly to the active area at a relatively high flow rate.

[0007] In a still further aspect of the present invention, the AFP device controls the temperature of the AFP process. While AFP can be performed over a large temperature range, there is a preferred temperature zone in which the AFP process achieves an optimal removal rate. In one embodiment, the AFP chemical solution itself is used to assist in controlling the temperature of the process. Further, in this embodiment, the chemical solution can be used to flush away and/or react with debris that have accumulated on the workpiece, as well as to assist in keeping the reaction temperature within a specified temperature range.

[0008] In another aspect of the present invention, the metal layer deposited on the workpiece can be made up of copper, silver or tantalum. In still another aspect of the present invention, the device includes a tank to hold the AFP chemical solution. In this aspect, the workpiece fixture rotatably positions the workpiece in a vertical position. In a further refinement, at least a portion of the workpiece is submerged in the AFP chemical solution, whereby the workpiece rotates through the fluid during the AFP process. This aspect allows a high volume of AFP chemical solution to be provided to the active area, as well as assist in control of the reaction temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a simplified block diagram illustrating an AFP device, according to one embodiment of the present invention.

[0010] FIG. 2 is an overview flow diagram illustrating the operation of the AFP device illustrated in FIG. 1, according to one embodiment of the present invention.

[0011] FIG. 2A is a flow diagram illustrating a method to determine if a workpiece is in an AFP device, according to one embodiment of the invention.

[0012] FIG. 3 is a diagram illustrating one embodiment of the AFP device in FIG. 1.

[0013] FIG. 3A is a diagram illustrating another embodiment of the AFP device illustrated in FIG. 1.

[0014] FIG. 4 is a diagram illustrating another embodiment of the AFP device illustrated in FIG. 1.

[0015] FIG. 5 is a diagram illustrating yet another embodiment of the AFP device illustrated in FIG. 1.

[0016] FIG. 6 is a schematic partial side view in cross section of a CMP apparatus using the ceramic platen of the invention.

[0017] FIG. 7 is a schematic partial side view in cross section of another apparatus using the ceramic platen.

[0018] FIG. 8 is a perspective view of the apparatus of FIG. 7 required to impart oscillatory motion to an orbiting ceramic platen of the invention.

[0019] FIG. 9 is a schematic partially exploded view showing mechanical stop details of a CMP tool of FIG. 8 for providing oscillatory motion to orbiting ceramic platen of the invention.

[0020] FIG. 10 is a schematic illustration showing a side view, in partial cross-section to show details of an alternative CMP tool, wherein a wafer carrier is equipped to both oscillate and orbit, to rotate and orbit, against a polishing pad mounted to a ceramic platen of the invention that is either stationary or rotating.

[0021] FIG. 11 is a diagram illustrating the operational flow of an AFP device, according to one embodiment of the present invention.

[0022] FIG. 12 is a diagram illustrating the layout of an AFP device, according to one embodiment of the present invention.

DETAILED DESCRIPTION

[0023] The present invention in one aspect uses a chemical solution, applied at a high rate to the active area, in conjunction with a brush assembly to achieve abrasive free polishing (AFP) of a bulk metal layer (e.g. copper) formed on a workpiece with an increased removal rate relative to conventional CMP tools using a slurry without abrasives. Unlike traditional CMP polishing, AFP does not follow standard kinematics during the polishing process, because its reaction is chemically based. CMP polishing tools follow a standard Preston type relationship. This relationship is defined as an increase in pressure or velocity resulting in a corresponding and linear increase in removal rate. Conversely, AFP is kinematically insensitive resulting in a substantial decrease in the requirement for precise control of motion or contact. However, the removal rate of AFP can be relatively low compared to CMP. The inventors of the present invention have appreciated that by providing a high flow rate of AFP chemical solution to the active area (i.e., the interface at which the surface of the workpiece to be polished contacts the brush assembly), the removal rate is significantly increased. Further, dripping solution onto a portion of the polish pad left uncovered by workpiece as in some other AFP systems cannot easily provide the high flow rate to the active area that achieves removal rates of about 4000 Å/min and higher (after threshold pressure of 3 PSI is exceeded).

[0024] Additionally, AFP is temperature dependent and will be affected by temperature increases resulting from friction between the workpiece and the brush assembly of the AFP device. The desired reaction temperature can be achieved by using a low thermal mass brush assembly in conjunction with the volume or flow rate of the AFP chemical solution applied to the active area. Further, the temperature of the AFP chemical solution itself can be controlled to aid in controlling the reaction temperature.

[0025] FIG. 1 illustrates an AFP device 10 for polishing a copper layer formed on a workpiece (e.g., a semiconductor wafer), according to one embodiment of the present invention. This embodiment includes a workpiece fixture 11, a brush assembly 12, a high flow rate fluid dispenser 13 (hereinafter fluid dispenser 13), and a controller 14. Workpiece fixture 11 is used to manipulate and/or position the workpiece during the AFP process. Brush assembly 12 provides an abrading surface. Fluid dispenser 13 is configured to provide AFP chemical solution during the AFP process to the active area (which, as previously described is the interface at which the abrading surface of the brush assembly contacts the surface of the workpiece to be polished). Still further, fluid dispenser 13 is configured to provide the AFP chemical solution to the active area with a relatively high flow rate. Controller 14 is connected to the workpiece fixture 11, brush assembly 12, and fluid dispenser 13 and is configurable to provide control signals to workpiece fixture 11, brush assembly 12 and fluid dispenser 13. Although only one fluid dispenser 13 and workpiece fixture 11 are shown, several fluid dispensers or workpiece fixtures may be used depending on the application.

[0026] In one embodiment, the chemical solution includes an organic acid, a copper complex former agent, and an oxidizer, which promotes the copper reacting process. The organic acid can be, for example, oxalic acid. The copper complex former agent can be, for example, quinaldic acid. The oxidizer can be, for example, hydrogen peroxide. For metals other than copper, a different metallic complex former agent may be used. An example of a copper AFP solution is HSC 430 produced by Hitachi Chemical. Other acceptable chemical solutions include RS3125 available from Rodel, Phoenix, Ariz.

[0027] In one embodiment, brush assembly 12 includes brushes manufactured of a material with enough rigidity to apply the needed pressure to abrade the reacted metallic layer without scratching the oxide layer. Poly-vinyl-acrylic (PVA) and Polyurethane are two such materials, but other embodiments may use any material having rigidity and abrading properties suitable for the application. A further advantage of this type of material is that brush assembly 12 can be made as a relatively inexpensive and lightweight device.

[0028] In a further refinement, the brushes of brush assembly 12 have low thermal mass characteristics. As previously described, the reaction of the AFP chemical solution and the metal, together with the friction between the brushes of brush assembly 12 and the surface of the workpiece can increase the reaction temperature and undesirably reduce the removal rate. The contact area between the workpiece and the brushes of brush assembly 12, combined with volume and/or flow rate of the AFP chemical solution to the active area, is designed so the reaction temperature will remain at a desired level. This temperature level can range from 5 to 40° C., but preferably ranges between 10 and 30° C.

[0029] FIG. 2 illustrates the operation of AFP device 10 (FIG. 1), according to one embodiment of the present invention. Referring to FIGS. 1 and 2, AFP device 10 operates as follows. During an operation 20, a workpiece, having a bulk copper layer in need of polishing (for example, a damascene process application), is loaded into AFP device 10. The loading can be achieved by any number of methods including but not limited to loading via robotic arm, by human assistance, or some combination thereof. The workpiece is transferred to workpiece fixture 11 which positions at least a portion of the workpiece to be in contact with the abrading surface of brush assembly 12. In this embodiment, the workpiece is a semiconductor wafer.

[0030] During an operation 21, controller 14 causes fluid dispenser 13 to provide an AFP chemical solution to the active area. In one embodiment, controller 14 causes fluid dispenser 13 to provide the AFP chemical solution at a predetermined flow rate to achieve a desired reaction temperature and removal rate. For example, increasing the flow rate tends to allow more of the abrasive free chemical solution to reach the active area and thereby react with the copper being polished. Moreover, increasing the flow rate would also tend to remove more of the heat generated during the polishing process, thereby controlling the reaction temperature. In one embodiment, fluid dispenser 13 provides the AFP solution at a flow rate of greater than about >300 ml/min.

[0031] During an operation 22, controller 14 causes the workpiece and brush assembly 12 to come into contact with a desired pressure. In addition, controller 14 causes AFP device 10 to impart a polishing motion between the workpiece and the abrading surface of brush assembly 12. The polishing motion imparted can be rotational, orbital, oscillating, linear, combination thereof, or any other motion that can help achieve a desired polishing profile.

[0032] Although operations 21 and 22 are described sequentially, those skilled in the art of CMP tools will appreciate after reviewing the present disclosure that operations 21 and 22 can be performed concurrently, in different orders, or in combination with other operations. Still further, the polishing motion and speed, the pressure, the AFP chemical solution and the flow rate of the AFP chemical solution can be optimized for particular brush types and AFP applications. For example, these parameters can be changed one or more times in an optimized manner during a single polishing operation, depending on the application.

[0033] The process performs an operation 23 in which the AFP process is terminated. In one embodiment, operation 23 is performed after the workpiece has been subjected to the AFP process for approximately 180 seconds. Generally, the duration of a polishing process is determined as the sum of the time needed to reach the end point (i.e., the end point time) and the time that the polishing process is continued past the end point time (i.e., the over-polish time). However, the AFP process allows for the use of up to twice the over-polish time of standard CMP processes without the copper dishing and oxide erosion that could occur using standard CMP processes. The duration of the AFP process may vary in other embodiments, depending on the type of brushes used and their accompanying thermal mass, the AFP chemical solution used, the polishing motion and speed, the workpiece surface material, the mean temperature throughout the process, the flow rate of the AFP chemical solution, etc.

[0034] As previously described, the relatively high flow rate of AFP chemical solution to the active area advantageously increases the removal rate to one more suitable for a production environment. Further, this embodiment advantageously reduces micro scratching, erosion of the oxide layer, and pitting of the copper layer because there are no abrasive particles in the process. Additionally, unlike conventional systems that use slurries, an AFP device according to the present invention reduces the risk of clean room contamination because there are no abrasive particles in the AFP chemical solution.

[0035] FIG. 2A illustrates one embodiment of operation 20 (FIG. 2). During operation 20, an operation 24 is performed in which AFP device 10 checks whether a workpiece is loaded in AFP device 10. This operation can be performed visually by the user, or by using a sensor device (not shown) configured to provide a signal to controller 14 (see FIG. 1). In view of this disclosure, those skilled in the art of CMP tools can implement a suitable sensor without undue experimentation. If a workpiece is present in AFP device 10, an operation 25 is performed in which the cleaning operation is aborted. Alternatively, operation 25 removes the workpiece from AFP device 10 instead of aborting the process. If AFP device 10 is empty or an operation 25 has been performed, then an operation 26 is performed. During operation 26 a workpiece is loaded into the workpiece fixture.

[0036] FIG. 3 illustrates AFP device 10 (FIG. 1) according to an embodiment of the present invention. In this embodiment, brush assembly 12 includes a wave generator 31, a brush pad 32 and through-holes 33, and workpiece fixture 11 includes carrier assemblies 34 and 34a. Wave generator 31 is used to impart orbital kinematic motion to the polishing pad in the range of about 100 to about 1000 RPM with orbit radius ranging from about 0.25 to about 1.00 inches and provides an AFP chemical solution dispenser. Carrier assemblies 34 and 34a are configured to hold individual workpieces 35 and 35a, respectively. Brush assembly 12 is attached to wave generator 31. Through-holes 33 are distributed in brush pad 32 of brush assembly 12 and allow for transfer of the AFP chemical solution from the wave generator 31 to the surface of brush assembly 12. This embodiment advantageously allows the AFP chemical solution to be directly applied at the desired location (i.e. the active areas or interfaces between the workpieces 35 and 35a and brush pad 32).

[0037] In one embodiment, the brushes of brush assembly 12 contact the workpiece with a pressure of about 1.0 psi. In other embodiments, the pressure can range from 0.5 psi to 5 psi or more, depending on the application. Further, in this embodiment, workpieces 35 and 35A are rotated at a speed between 10 and 200 rpm while brush pad 33 is rotated at a speed between 100 and 1000 rpm. Although the polishing motion can assist in removal of reacted material, the heat generated by friction between brush pad 32 and workpieces 35 and 35A tends to increase the reaction temperature and thereby reduce the removal rate as previously described. However, the AFP chemical solution is provided directly to the active areas via through-holes 33 at a relatively high flow rate to remove this heat. Further, unlike conventional systems that drip a solution on top of the polish pad at a location that is uncovered by the workpiece, through-holes 33 allow the AFP chemical solution to be provided directly to the active area at a relatively high flow rate. In addition, the relatively high flow rate of the AFP chemical solution maintains a more uniform concentration of the reactants in the AFP chemical solution in the active areas, thereby maximizing the removal rate. That is, a relatively low flow rate that would tend to allow the concentration of reactants in the AFP chemical solution in the active areas to decrease as the reactants react with the copper layer, thereby tending to decrease the removal rate.

[0038] In other embodiments of the present invention, metals other than copper can be subjected to this process. Examples of these metals include tantalum and silver, although these different metals may require different AFP chemical solutions to react with them. Different metals may require alternate complexing chemistries and oxidizers in order to be polished by AFP. It is desirable that the material form a complex when immersed in the AFP solution that is softer than the polyurethane pad. AFP should be possible with the above-mentioned metals since they can form complexes and oxides.

[0039] Additionally, other embodiments of the present invention allow the platen to apply varying motions (see FIGS. 6-10 and accompanying discussion) in conjunction with a rotating carrier. For example, the platen could orbit, the platen could oscillate, or the platen could orbit and oscillate in combination with a rotating or non-rotating carrier, or in combination with several differing types of motion of the carrier so as to achieve the desired polishing profile.

[0040] FIG. 3A illustrates AFP device 10 (FIG. 1) according to another embodiment of the present invention. This embodiment is similar to the embodiment of FIG. 3, with the addition of a temperature control system. In this embodiment, a cooling fluid is circulated through a platen 39 of brush assembly 12 via cooling channels 36. Cooling fluid enters cooling channel 36 through inlet 37 and exits through outlet 38. This embodiment allows for temperature control in addition to the methods previously mentioned. Any fluid can be used for cooling of brush assembly 12 so long as the fluid is suitable for the heat exchanging process and does damage the materials comprising the brush assembly. In one embodiment, the cooling fluid is de-ionized water.

[0041] FIG. 4 illustrates AFP device 10 according to another embodiment. In this embodiment brush assembly 12 includes pancake shaped brushes 41 and 41a. Brushes 41 and 41a are configured vertically with workpiece 35 being disposed between them. Workpiece fixture 11 is implemented as a freely rotating support member 43 and is positioned below and between brushes 41 and 41a. Although only one support member 43 is shown, several support members may be used to rotatably support the workpiece. This vertical configuration potentially reduces clean room costs by reducing valuable floor space requirements (also referred to herein as footprint) as compared to standard horizontal CMP devices. In this embodiment of the present invention, AFP device 10 can include a tank 42 to hold the AFP chemical solution, with at least a portion of workpiece 35 being submerged so that workpiece 35 will rotate through the AFP chemical solution. Rotating workpiece 35 through the AFP solution in effect exposes the surfaces of workpiece 35 to a high rate of shear with respect to the AFP chemical solution. As previously described, a high flow rate of AFP chemical solution to the active area tends to increase the removal rate and remove heat generated by friction and the chemical reaction of the AFP solution with the metal being polished. Vertical configuration allows for a high volume of AFP chemical solution to be applied between the workpiece 35 and the brushes 41 and 41a in addition to the AFP chemical solution applied as the workpiece 35 rotates through the tank 42. An application of a high volume of AFP chemical solution will result in a desired polishing profile being obtained.

[0042] FIG. 5 illustrates AFP device 10 according to still another embodiment. In this embodiment, brush assembly 12 is implemented with cylindrical brushes 51 and 51a with wafer 35 being disposed between them. FIG. 5 is a side view taken along the longitudinal axes of cylindrical brushes 51 and 51a. Cylindrical brushes 51 and 51a rotate about their longitudinal axes, thereby polishing both the top and bottom surfaces of the workpiece. This embodiment allows for a high volume of AFP chemical solution to be applied to the surface of the workpiece 35, thus allowing for a desirable removal resulting in a preferred polishing profile.

[0043] Other embodiments can be implemented by suitably modifying commercially available buffer units or wafer cleaning units. In one embodiment, a buff unit for an AvantGaard 676 CMP tool is modified to have a suitable brush pad and AFP chemical solution dispenser. In particular, the unit is modified to provide a polishing pressure of 1-3 psi and dispense AFP chemical solution with a flow rate of about 100-300 ml/min. Other modifications may include changing the type of brushes and/or the fluid dispenser to be compatible with chemical makeup of the AFP chemical solution. These embodiments are carrierless, which are generally less complex and less costly than systems that use carriers. The reduced cost of carrierless AFP devices makes practical a system using several such carrierless AFP devices in a continuous process. Material removal rates are a strong function of local solution chemical activity. Each AFP roller set removes a finite amount of material proportional to the flow rate of AFP solution to brush.

[0044] The AFP chemical solution of the invention is useful in a wide range of CMP tools, including but not limited to orbital polishers, for example, U.S. Pat. No. 5,554,064 entitled “Orbital Motion Chemical-Mechanical Polishing Apparatus and Method of Fabrication,” discloses an orbital chemical-mechanical polishing apparatus, and is hereby incorporated by reference to the extent pertinent. An improved CMP machine disclosed in our copending U.S. Ser. No. 09/153,993, filed Sep. 17, 1998 adds an additional type of motion to the polishing pad of the apparatus: namely, rotation or oscillation achieved by rotating the platen with its polishing pad, in the preferred embodiment, in alternating clockwise and counterclockwise directions. These rotations or oscillations of the platen with its polishing pad during CMP enhance the polished wafer surface by reducing polish variations as compared to a surface obtained using orbital motion only.

[0045] Polishing pads, as referred to in FIGS. 6-10, can be manufactured from materials such as Poly-vinyl-acrylic (PVA) and Polyurethane, but any material exhibiting the desired rigidity and abrading properties suitable for the application can be used. Preferably, the polishing pads have a type of abrading surface that allows a high volume of AFP chemical solution to reach the active area (i.e., the interface at which the polishing pad contacts the surface of the workpiece).

[0046] The platen used in this embodiment can be of a solid type as shown in FIG. 6 (platen 102) or, more preferably, of a type as shown in FIG. 3 (brush assembly 32) which allows AFP chemical solution to be applied in a high volume to the surface of the workpiece via through-bores 33 to achieve the desired polishing profile.

[0047] An oscillating orbital CMP apparatus is shown in FIG. 6, and is modified by addition of an AFP chemical solution and dispenser. Thus the apparatus includes a frame 100 of the present invention onto which is mounted a platen 102 that is equipped with a polishing pad 104. The apparatus includes a pair of rotary bearings, an upper rotary bearing 106 is fixedly mounted to an underside of platen 102, and a rotatable wave generator 110 that includes a substantially cylindrical sleeve 111 extending downward under platen 102. A first central axis Co of upper rotary bearing 106 of wave generator 110 is offset from a second central axis Cc of a lower rotary bearing 108. Lower rotary bearing 108 is fixedly mounted to the lower portion of sleeve 111, and to frame 100 of the apparatus. Thus, when wave generator 110 is brought into rotational motion, first central axis Co of upper rotary being 106 is equal to the parallel offset between first central axis Co and second central axis Cc. This causes platen 102 and polishing pad 104 to orbit. As indicated in FIG. 6, rotary motion is imparted to wave generator 110 by means of a drive belt 112 that embraces sleeve 111 and that extends over a pulley 114 coupled to a drive motor 116. More detail about the orbital motion is found in U.S. Pat. No. 5,554,064 previously incorporated by reference.

[0048] A shaft 118 extends from an underside of platen 102 where it is fixedly attached, through the annular space of sleeve 111 of wave generator 110 downward to a mechanism for imparting rotary or oscillatory motion to platen 102. Shaft 118 includes an upper pedestal 120 fixedly attached to the underside of platen 102. Extending downward from upper pedestal 120, shaft 118 includes an upper universal joint 122a and a lower universal joint 122b, spaced from upper universal joint 122a.

[0049] A variety of mechanisms that may be used to impart rotational or oscillatory motion will become clear to one of skill in the art that has read and understood this disclosure. In the preferred embodiment of FIG. 6, a drive shaft 124 is coupled to lower universal joint 122b at one of its ends, and to a gear box 126 at its other end. The axis of drive shaft 124 is along the same axis of rotation of second center axis Cc of lower rotary bearing 108. A step motor 136 that is controlled by a motor controller 138 drives gearbox 126. Motor controller 138 controls the degree of rotation imparted by motor 136 to shaft 124. Thus, by adjusting motor controller 138, the arc may by varied within the range from about −360 to about +360 degrees for oscillatory motion. For rotational motion, the motor may be allowed to continuously rotate shaft 124 thereby causing continuous rotation of polishing pad 104.

[0050] Other mechanisms may also be utilized to impart oscillatory (partial rotational movement) or rotational movement to polishing pad 104. For example, in the alternative embodiment of the invention shown in FIG. 7, oscillatory motion is produced by a combination of a drive motor and mechanical and electrical stops that cause the shaft to move in alternate counterclockwise and clockwise motion, limited by the mechanical stop. Thus, referring to FIGS. 6, 8, 9 and 10, a substantially vertical shaft 124 is coupled to and extends downward from below lower universal joint 112b, and into a hard stop box 140. As shown, shaft 124 has a radial leg 128 that sweeps the interior of a surrounding cap 142 when shaft 124 is rotated. To limit rotation of shaft 124, one or more mechanical stops are placed in cap 142 to arrest rotational movement of shaft 124 by blocking movement of radial leg 128. A pair of electrical sensors or stops (not shown) is located on the outside of each side of a mechanical stop 130 so that radial leg 128 will encounter the electrical stops before being blocked by the mechanical stop.

[0051] A motor 136, able to impart rotary motion, is mounted to supporting frame 100 of the apparatus, and is mechanically coupled to gear box 126. Thus, motor 136, through gear box 126, rotates shaft 124 and, hence, shaft 118 counterclockwise, thereby causing platen 102 to rotate in the same direction until radial leg 128 of shaft 124 is stopped by mechanical stop 130. Then, due to electrical contact with an electrical sensor 132, direction of the rotation is reversed to a clockwise direction. Again, shaft 118 and platen 102 also rotate clockwise until radial leg 128 of shaft 124 is limited by mechanical stop 130. Contact with the other electrical stop 132 causes reversal of the rotational movement, as described above. Thus, the apparatus provides clockwise and counterclockwise oscillatory movement in an arc determined by the location of the mechanical stop.

[0052] The pad is simultaneously subject to at least partial rotational movement and orbital movement. For complete rotational movement the AFP chemical solution supply lines (and other supply lines) should be supplied with rotatable couplings so that the supply lines do not twist around the shaft. Obviously, for partial rotational movement or oscillation, such rotational couplings may not be needed, as long as the supply lines are of adequate length.

[0053] In an embodiment, developed for polishing standard 8 and 12-inch wafers, the platen and pad orbit such that the locus of the center of the pad describes a circle with a diameter from about ½ of the wafer diameter to about 0.1 inches (2.54 mm) with the preferred orbit diameter of 1.25 inches (31.75 mm). The center of orbit of the carrier is offset from the center of the orbit of the platen by from about 0 to about 1 inch (25.4 mm) with a preferred offset of about 0.375 inches (9.54 mm).

[0054] Typically, the pad and platen orbit at speeds of at least 300 revolutions per minute, more preferably in the range 300-600 revolutions per minute, but the range can be as much as 200-2000 revolutions per minute. The wafer carrier 150 may rotate or oscillate about its axis or remain stationary.

[0055] The polishing pad may be rotated or oscillated an integral number of times during each polish cycle. The duration of a polish cycle depends upon several factors, and typically varies in the range from about one to about four minutes. It is preferred to have from about 1 to about 20 complete oscillations per polish cycle, preferably about 6 to 10 sweeps per polish-minute.

[0056] While the arc through which polishing pad 104 rotates or oscillates may vary, it is preferred to oscillate continuously. It should preferable be able to oscillate through the range from about −180 degrees (counterclockwise) to about +180 degrees (clockwise). Oscillatory motion in the region from about −135 degrees to about +135 degrees is useful, but lesser or greater angular rotation may also be beneficial.

[0057] It will be readily apparent that in the above CMP tool, the surface of a semiconductor substrate being polished may be subjected to a combination of several kinds of motion, depending upon mode of operation of the apparatus, in addition to the application of a high volume of AFP chemical solution. For example, when the platen both orbits and oscillates, and the wafer carrier rotates, the wafer surface is subjected to orbital, rotational and oscillating polishing movement. On the other hand, when the platen orbits and rotates, while the wafer carrier rotates, the wafer surface is subjected to orbital polishing movement along with two kinds of rotational polishing movement. When the wafer carrier is stationary, the wafer surface is subjected to either orbital and rotational polishing movement, or orbital and oscillating polishing movement, depending upon mode of operation of the apparatus.

[0058] In accordance with term usage of this document, “an oscillating polishing movement: refers to movement of the device (carrier or platen) and not the actual movement experienced (or traced) by a locus on the wafer surface; the same applies to “linear”, “rotational”, “sweeping” and “orbital polishing movements”.

[0059] It will be readily apparent to one of skill in the art who has read this disclosure, that a platen similar to the platen in FIG. 3 in use herein would allow for distribution of AFP chemical solution to the workpiece surface and, that the mode of movement of the carrier and platen can be reversed, i.e., the wafer carrier may be equipped with mechanical means to generate orbital and either oscillating or rotational movement; while the platen may be retained stationary or may rotate. Accordingly, the platen can also be used in an apparatus for carrying out this “reverse” application of polishing movement, through the embodiment illustrated in FIG. 10. Since many of the component parts of the apparatus are similar to that of the above-described embodiment, the same numerals are used for simplicity. In this instance, a wafer carrier 150 is linked to a wave generator 110, that is similar to the wave generator described above in that it is comprised of two bearings 106 and 108, spaced vertically from each other, and with centers of rotation offset. The lower bearing 108 is mounted to a support structure, such as the housing 154, which is in turn supported by a support structure 156. One end of the wave generator has a cylindrical sleeve 111, which is driven by a belt 112 that passes over a drive pulley 114 of an electrical motor 116, which preferably has speed control. Once again, a central shaft 118 extends in the annular space of the wave generator and the pedestal 120 at its lower end is mounted to the upper surface of the wafer carrier 150. The shaft 118 is equipped with at least two universal joints, 122a and 122b, one at each of its ends. A drive shaft 124 is mounted to an upper end of the shaft 118, above the upper universal joint 122b, and is driven through gear box 126 by motor 136, which is in turn controlled by motor controller 138. Thus, the apparatus for imparting orbital and rotational or oscillating movement to the wafer carrier 150 is similar to the apparatus described above for imparting such motion to the polishing pad platen of the invention.

[0060] In this instance, the wafer carrier, when it contains a wafer 152, is brought into contact with the pad 160, which is supported on platen 166, which may rotate or which may be held stationary. When the platen rotates, the pad sweeps across the face of the wafer being polished in a “sweeping motion.” At the same time, operation of the above-described apparatus imparts an orbital motion to the wafer carrier (and hence to the wafer) along with either complete rotation of the carrier around its central axis, or oscillation about that access. Thus, in addition to AFP chemical solution being applied to the workpiece surface, the apparatus provides for several permutations of polishing movement on the surface of the wafer: (1) orbital, rotational and sweeping polishing movement; (2) orbital, oscillation and sweeping polishing movement; (3) orbital and oscillating polishing movement; and (4) orbital and rotational polishing movement.

[0061] FIG. 11 illustrates a flow process of an AFP system according to one embodiment of the present invention. This embodiment consists of three AFP devices 61, 62, and 63, which remove the bulk metal layer and feed a CMP device 64. CMP device 64 removes the barrier layer. The barrier layer is a layer (e.g. tantalum) that is typically formed between the bulk metal layer and the oxide layer. The workpieces next are sent to a cleaner 65 and then on to a SRD (Spin/Rinse/Dry) module 66. This embodiment is advantageously used when the AFP process has a duration that is about three times that of CMP device 64. In this way, the combined throughput of AFP devices 61-63 would match the throughput of CMP device 64. In light of the present disclosure, one skilled in the art can implement any number of other workable combinations of these modules to achieve a desired effective removal rate, throughput and cost, without undue experimentation.

[0062] FIG. 12 illustrates a layout of an AFP device 70, according to one embodiment of the present invention. In this embodiment, three AFP units 71, 72, and 73 remove portions of the bulk metal layer and feed a CMP unit 74, which is used to remove portions of the barrier layer. The workpieces would next be sent to a cleaner/SRD (Spin/Rinse/Dry) module 75. A robot wafer transport 76 is used to move workpieces to and from units 71-74 of the system. In light of the present disclosure, one skilled in the art of CMP tools can implement any number of other workable combinations to achieve a desired effective removal rate, throughput and cost.

[0063] As used herein, a workpiece may be semiconductor wafer, a semiconductor substrate with or without active devices or circuitry, a partially processed wafer, a silicon or insulator structure, a hybrid assembly, a flat panel display, a micro electromechanical structure (MEMS), a disk for a hard drive memory, or any other material that has a bulk metal layer that would benefit from planarization.

[0064] The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Because many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Claims

1. A process for polishing a metal layer of a workpiece, the process comprising:

loading a workpiece into a polishing tool;

providing an abrasive free chemical solution to the metal layer of the workpiece at a flow rate of about 50 cc/min to about 500 cc/min; and

polishing the metal layer on the workpiece.

2. The process of claim 1 wherein the abrasive free chemical solution is provided to an interface between the workpiece and an abrading surface via through-holes in the abrading surface.

3. The process of claim 1 wherein the process is performed at a temperature between about 5 to about 40° C.

4. The process of claim 1 wherein the process is performed at a temperature from about 10 to about 30° C.

5. The process of claim 1 where the polishing is performed with low thermal weight brushes.

6. The process of claim 1 wherein the metal layer comprises copper.

7. The process of claim 1 wherein the metal layer comprises silver.

8. The process of claim 1 wherein the metal layer comprises tantalum.

9. The process of claim 1 performed with the workpiece in a substantially vertical orientation.

10. The process of claim 1 further comprising controlling a temperature at which the abrasive free chemical solution reacts with metal of the metal layer.

11. The process of claim 1 wherein the abrasive free chemical solution comprises an organic acid, a metallic complex forming agent, and an oxidizer.

12. The process of claim 11 wherein the organic acid comprises oxalic acid.

13. The process of claim 11 wherein the metallic complex forming agent comprises quinaldic acid.

14. The process of claim 11 wherein the oxidizer comprises hydrogen peroxide.

15. An apparatus for polishing a metal layer formed on a workpiece, the apparatus comprising:

means for loading a workpiece into the apparatus;

means for providing an abrasive free chemical solution to the metal layer of the workpiece at a flow rate of about 50 cc/min to about 500 cc/min; and

means for polishing the metal layer on the workpiece.

16. The apparatus of claim 15, wherein the means for polishing includes an abrading surface with through-holes, and wherein the means for providing provides the abrasive free chemical solution to an interface between the abrading surface and the workpiece via the through-holes.

17. The apparatus of claim 15, wherein the means for polishing comprises means for orienting the workpiece in a substantially vertical position.

18. The apparatus of claim 15 further comprising means for controlling a temperature at which the abrasive free chemical solution reacts with metal of the metal layer.

19. The apparatus of claim 15 wherein the abrasive free chemical solution comprises an organic acid, a metallic complex forming agent, and an oxidizer.

20. The apparatus of claim 15 wherein the means for polishing rotates the workpiece through a reservoir of abrasive free chemical solution.

21. The apparatus of claim 15 wherein the means for polishing includes a pair of pancake-shaped pads, the workpiece being disposed between the pancake-shaped pads during a polishing operation.

22. The apparatus of claim 15 wherein the means for polishing provides an orbital motion and an oscillating motion.

23. A polishing device for polishing a metal layer formed on a surface of a workpiece, the polishing device comprising:

a workpiece fixture;

a brush assembly;

a fluid dispenser configured to store and dispense an abrasive free chemical solution; and

a controller coupled to the workpiece fixture, brush assembly, and fluid dispenser, wherein during a workpiece polishing operation the controller is configured to cause:

the fluid dispenser to provide an abrasive free chemical solution to an interface between the brush assembly and a workpiece at a rate of about 50 cc/min to about 500 cc/min,

the workpiece to contact the brush assembly, and

a polishing motion to be imparted between the workpiece and the brush assembly.

24. The polishing device of claim 23, wherein the brush assembly further comprises a platen, the platen having a cooling channel.

25. The polishing device of claim 23, wherein the workpiece fixture comprises a support member.

26. The polishing device of claim 25, wherein the support member is configured to rotatably support a workpiece in a vertical position.

27. The polishing device of claim 23, wherein the workpiece fixture comprises a carrier.

28. The polishing device of claim 23 further comprising a platen, the platen having a through-hole extending through the platen.

29. The polishing device of claim 23, wherein the abrasive free chemical solution comprises an organic acid, a metallic complex forming agent, and an oxidizer.

30. A polishing device for polishing a metal layer formed on a surface of a workpiece, the polishing device comprising:

a workpiece fixture;

a brush assembly;

a fluid dispenser configured to store and dispense an abrasive free chemical solution;

a wafer carrier adapted for securely holding at least one semiconductor substrate to expose a frontal surface of the substrate to be polished on an side of the carrier facing a polishing pad on the platen; and

a controller coupled to the workpiece fixture, brush assembly, and fluid dispenser, wherein during a workpiece polishing operation the controller is configured to cause:

the fluid dispenser to dispense abrasive free chemical solution to an interface between the brush assembly and a workpiece at a rate of about 50 cc/min to about 500 cc/min,

the workpiece to contact the brush assembly, and

a polishing motion to be imparted between the workpiece and the brush assembly.

31. The polishing device of claim 30, wherein the brush assembly further comprises a platen having a cooling channel configured to conduct a cooling fluid.

32. The polishing device of claim 30 further comprising a platen, the platen having a through-hole extending through the platen and configured to conduct abrasive free chemical solution.

33. The polishing device of claim 30 further comprising a tank configured to contain abrasive free chemical solution, wherein the brush assembly is configured to rotate the workpiece through the abrasive free chemical solution contained in the tank.

34. The polishing device of claim 30 wherein the brush assembly includes a pair of pancake-shaped pads, the workpiece being disposed between the pancake-shaped pads during a polishing operation.