JP2005079465A - Membrane for supporting head of chemical mechanical polishing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate problems arising from tensile stress generated in a membrane mounted on a supporting plate. <P>SOLUTION: The fitting property of a projection 270 at the end of a membrane 118 is improved. Concretely, the membrane has a circular bottom 201, a wall 202 rising from the outer edge of the circular bottom, an annular part 203 extending from the upper end of the wall to the central direction of a circle and the projection 270 located at the terminal end of the annular part, and the cross section of the projection is U-shaped having a straight line 272 at the tip thereof. Since the fitting property to a groove 262 formed on a supporting plate 170 is thereby improved, the projection hardly comes off from the groove even if tensile stress is applied to it and a malfunction caused by the contact of the supporting plate with a holding ring 110 due to a mounting failure can be avoided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates generally to a chemical mechanical polishing apparatus for semiconductor wafers, and more particularly to a membrane used in a support head of a chemical mechanical polishing apparatus.

  Integrated circuits are usually formed on a substrate, in particular a silicon wafer, by successively depositing a conductor layer, a semiconductor layer or an insulating layer. After each layer is deposited, the layer is etched to create a circuit structure. As the series of layers are successively deposited and etched, the top surface of the wafer, ie the exposed surface of the substrate, becomes increasingly non-planar. If the exposed surface is non-planar, there is a problem in the photolithographic process of the integrated circuit fabrication process. Therefore, it is necessary to periodically planarize the wafer surface.

One of the planarization methods is chemical mechanical polishing (CMP). In this flattening method, it is usually necessary to attach the wafer to a support head (polishing head) as described in, for example, Patent Document 1 below. A wafer mounting portion of the support head includes a support plate having a plurality of through holes, and generally a thin flexible membrane is mounted on the side of the support plate where the wafer is mounted. When a fluid is sucked from the through hole of the support plate, a low-pressure pocket or suction cup is formed between the back surface of the wafer and the membrane, and the support head holds the wafer by suction by the suction cup. Subsequently, the support head applies pressure to the wafer and presses the exposed surface of the wafer against the rotating polishing pad.
Japanese Patent Laid-Open No. 10-180627

  FIG. 3 is a diagram illustrating a method of assembling a support plate and a membrane according to the prior art. A protrusion 6 is provided at the end of the membrane 4. The protrusion 6 is fitted into the groove 5 on the upper surface of the support plate 2 and assembled to the support plate. As described above, since the support head adsorbs the wafer by sucking the fluid, the membrane is generally assembled on the lower surface of the support plate with a tensile stress.

  In this case, the protrusion 6 is easily detached from the groove 5 due to the tension of the membrane. When the support head is assembled with the membrane detached, the corners of the membrane 4 come into contact with the holding ring 8 as shown in FIG.

  Also, the lower surface of the membrane may not be flat due to tensile stress. In this case, since the pressure applied to the wafer is not uniform, the polishing amount may be non-uniform.

  Accordingly, an object of the present invention is to eliminate problems caused by tensile stress generated in a membrane attached to a support plate.

  In the present invention, the protruding portion at the end of the membrane has a better fit. Specifically, the membrane of the present invention has a circular bottom portion, a wall portion standing up from an outer edge of the circular bottom portion, an annular portion extending in the center direction of the circle from the upper end of the wall portion, and protruding at the end of the annular portion. The protrusion has a U-shaped cross section with a straight portion at the tip.

  With the above configuration, the fitting property with the groove formed on the upper surface of the support plate is improved, so that it is difficult to come off from the groove even when subjected to tensile stress, and contact with the holding ring due to poor mounting and thus malfunction can be avoided. In addition, the membrane can be easily adjusted and the working efficiency can be improved. The membrane is manufactured by molding a rubber material such as elastomer, silicone, EPDM rubber, etc., and preferably chloroprene rubber.

  Furthermore, since the length from the inner side of the wall portion to the protruding portion is smaller than the length from the outer periphery of the support plate to the groove, the membrane is caused by contact between the membrane and the holding ring due to poor mounting in combination with the protruding portion. Malfunctions can be avoided.

  In another aspect, the membrane of the present invention includes a circular bottom portion, a wall portion standing up from an outer edge of the circular bottom portion, an annular portion extending in the center direction of the circle from the upper end of the wall portion, and an end portion of the annular portion. The joint portion between the circular bottom portion and the wall portion of the membrane has a shape that prevents downward swelling when the circular bottom portion receives tensile stress in the center direction of the circle. Even when subjected to tensile stress by this configuration, the lower surface of the membrane becomes flat and pressure is uniformly applied to the wafer, so that uniform polishing can be performed.

  The anti-swelling shape is preferably R, but may be chamfered or other shapes.

  It is more preferable that the R is R in which the thickness of the membrane is the same as that of the place other than the joining portion. The R is more preferably R centering on the inner vertex.

  According to the present invention, since the fitting property between the protruding portion of the membrane and the groove formed on the upper surface of the support plate is improved, it is difficult to come off from the groove even when subjected to tensile stress, and the contact with the holding ring due to poor mounting and operation Defects can be avoided.

  Hereinafter, an embodiment of the present invention will be described.

  FIG. 1 shows a chemical mechanical polishing (CMP) apparatus 20 for polishing one or more wafers 10. The CMP apparatus 20 includes a lower machine base 22 provided with a table top 23 and a removable upper outer cover (not shown). The table top 23 supports polishing stations 25a, 25b, and 25c and a transfer station 27 that receives a wafer from a loading device (not shown) and loads the wafer onto a support head. The polishing stations 25a, 25b, and 25c and the transfer station 27 are arranged so as to be located at the apex of a substantially square.

  Each polishing station 25a, 25b, 25c includes a rotatable platen 30 with a polishing pad 32 placed thereon. The polishing pad 32 is made of a composite material having a rough polishing surface. If the wafer 10 is a disk having a diameter of 8 inches (200 mm) or 12 inches (300 mm), the diameters of the platen 30 and the polishing pad 32 are about 20 inches and 30 inches, respectively. The platen 30 is connected to a platen drive motor (not shown) in the machine base 22. Each polishing station 25a-25c may further include a pad conditioner 40.

  On the surface of the polishing pad 32, a reaction material (for example, deionized water for polishing an oxide), abrasive particles (for example, silicon dioxide for polishing an oxide), and a chemical reaction catalyst (for example, for polishing an oxide). Slurry 50 containing potassium hydroxide) is supplied by a slurry / rinse supply arm 52. Typically, a slurry is provided that covers the entire polishing pad 32 and is sufficiently wetted. The slurry / rinse arm 52 includes a plurality of spray nozzles (not shown) that provide a high pressure rinse to the polishing pad at the end of each polishing / conditioning cycle.

  Above the lower machine base 22, a rotatable multi-head carousel 60 including a carousel support plate 66 and a cover 68 is disposed. The carousel support plate 66 is supported by the center post 62 and is rotated around the carousel shaft 64 by a carousel motor assembly disposed in the machine base 22. The multi-head carousel 60 includes four support head systems 70a-70d. The support head systems 70a-70d are attached to the carousel support plate 66 at equiangular intervals around the carousel shaft 64. The carousel motor rotates the carousel support plate 66 to pivot the support head systems 70a-70d and the wafers attached thereto around the carousel axis 64 between the polishing station and the transfer station. Three of the support head systems 70a-70d hold the wafer and polish it against the polishing pad 32 of the polishing stations 25a-25c. One of the support head systems 70a-70d receives the wafer from the transfer station 27 and passes the wafer to the transfer station.

  Each support head system 70 a-70 d includes a support head 100. Each support head 100 independently rotates about its central axis. The support drive shaft 74 extends through a radial slot 72 formed in the carousel support plate 66, and connects the support head 100 and the support head rotation motor 76 (a part of the cover 68 is shown). Each support head has one support drive shaft and a support head rotation motor. Each drive shaft and motor are supported by a slider (not shown). As the slider is driven along the slot 72 by a radial drive motor (not shown), the support head 100 moves in the lateral direction.

  At the time of polishing, three of the support heads 100, for example, the support heads of the support head systems 70a to 70c are arranged above the polishing stations 25a to 25c, respectively. Each support head 100 lowers the held wafer to contact the polishing pad 32. In general, the support head 100 keeps the wafer in contact with the polishing pad and applies a downward pressure uniformly on the entire back surface of the wafer. The support head 100 also transmits torque from the drive shaft 74 to the wafer to prevent the wafer from jumping out from under the support head 100 during polishing.

  Next, the structure of the support head will be described with reference to FIGS.

  FIG. 2 is a cross-sectional view of the support head 100. The support head 100 includes a housing 102, a base 104, a gimbal mechanism 106, a load chamber 108, a retaining ring 110, and a wafer packing assembly 112.

  The housing 102 has a substantially circular shape. The housing 102 is connected to a drive shaft 74 and rotates about a rotation axis 107 substantially perpendicular to the surface of the polishing pad during wafer polishing. Two passages 126 and 128 pass through the housing 102 for the fluid that controls the support head. A vertical bore 124 is further passed through the housing, and a cylindrical bush 122 is fitted therein.

  The base 104 is a ring-shaped object disposed under the housing 102. Base 104 is preferably formed from a rigid material such as aluminum, stainless steel, or FRP.

  Between the housing 102 and the base 104 is a rotating diaphragm 160 which is typically a ring-shaped 60 mi1 (about 1.52 mm) thick silicon film. One end on the inner diameter side of the rotary diaphragm 160 is clamped to the housing 102 by the internal clamp ring 162, and one end on the outer diameter side is clamped to the base 104 by the outer clamp ring 164. A space between the housing 102 and the base 104 is sealed by the rotating diaphragm 160 to define the load chamber 108. A first pump (not shown) is connected to the load chamber 108 via a path 126. A fluid, preferably a gas such as air, is pumped into or discharged from the load chamber 108 to control the downward load on the base 104. That is, the vertical position of the base 104 with respect to the polishing pad 32 is controlled by the load chamber 108.

  The retaining ring 110 is generally an annular body fixed at the outer end of the base 104. When the fluid is pumped into the aforementioned load chamber 108 and the base 104 is pushed down, the retaining ring 110 is also pushed down to load the polishing pad 32.

  The gimbal mechanism 106 includes a gimbal rod 150 that fits into a path 154 by a cylindrical bush 122 and a flexure ring 152 that is fixed to the base 104. Since the gimbal rod 150 can slide vertically along the path 154, the base 104 can move vertically but not radially. Accordingly, the gimbal mechanism 106 pivots the base 104 with respect to the housing 102 so that the base 104 can remain substantially parallel to the surface of the polishing pad.

  An elastic film 140 is bonded to the lower surface of the base 104 by a clamp ring 142 to form a bag-like bladder 144. A path 130 passes through the base 104, and attachment tools 134 and 132 are attached to one end of the path 130 and the end of the path 128 of the housing 102, respectively. A flexible tube is connected between the fixtures 132 and 134. A second pump (not shown) is connected to the bladder 144 via a path 128, a tube, and a path 130. When the pump forces a fluid, preferably a gas such as air, the bladder 144 expands downward. On the other hand, when the pump discharges the fluid under reduced pressure, the bladder 144 contracts. The bladder 144 can be used to apply a downward pressure to the support structure 114 and the membrane 118 described later.

  Wafer backing assembly 112 includes a support structure 114, flexure diaphragm 116, and membrane 118. The membrane 118 is attached to the support structure 114.

  The support structure 114 is disposed below the base 104 and includes a support plate 170, an annular lower clamp 172, and an annular upper clamp 174.

  FIG. 4B is a simplified view of the support plate 170 and the membrane 118. Hereinafter, the support structure 114 will be described with reference to both FIG. 2 and FIG.

  The support plate 170 is a disc body having a lip 258 protruding downward at an outer end portion thereof and having a substantially flat lower surface 256. A plurality of through holes 176 are formed in the support plate 170. An annular groove 262 is formed on the upper surface of the support plate. The support plate 170 is preferably formed of aluminum or stainless steel. When the aforementioned bladder 144 expands and pushes the upper clamp 174, the support structure 114 is pushed down.

  The flexure diaphragm 116 is generally a flat annular body. An end on the inner diameter side of the flexure diaphragm 116 is clamped between the lower clamp 172 and the upper clamp 174, and one end on the outer diameter side is clamped between the base 104 and the holding ring 110. The support structure 114 and the membrane 118 are suspended from the base 104 by the flexure diaphragm 116, and the support structure 114 and the membrane 118 are fitted in a space formed by the base 104 and the holding ring 110. The flexure diaphragm 116 is made of a moderately flexible material and is slightly bent in the vertical direction but rigid in the radial direction.

  The membrane 118 is generally formed of a flexible material such as chloroprene or ethylene propylene rubber, and has a bottom 201 in the shape of a circular sheet. The portion (wall portion) 202 of the membrane 118 standing up from the outer edge of the circular bottom 120 extends around the bottom surface of the support plate 170 at the position of the lip 258 and reaches the top surface of the support plate 170 for further support. Extends inwardly along the upper surface 264 of the plate. At the tip of the annular portion 203 of the membrane 118 extending along the upper surface 264, there is an outer end portion (protruding portion) 270 protruding downward (in the direction of the bottom portion 201), and a groove 262 on the upper surface of the support plate 170 is provided. Is fitted. The end of the annular portion 203 of the membrane 118 is clamped between the support plate 170 and the lower clamp 172.

  The sealed space surrounded by the membrane 118, the support structure 114, the flexure diaphragm 116, the base 104 and the gimbal mechanism 106 defines a compression chamber 190. A third pump (not shown) is connected to the chamber 190 via a passage 196. When the third pump forcibly supplies a fluid, preferably a gas such as air, into the chamber 190, the volume of the chamber increases and the membrane 118 is pushed downward. On the other hand, when the pump exhausts air from the fluid chamber, the volume of the chamber decreases and the membrane is pushed up. Since gas is more compressible, it is preferable to use gas rather than liquid.

  A wafer is attached to the lower surface 120 of the membrane 118. The inner surface 188 of the retaining ring 110, together with the lower surface 120, defines a recess 192 for receiving the wafer. During polishing, the wafer 10 is placed in the recess 192 with the back side of the wafer in contact with the lower surface 120. The edge of the wafer contacts the lip 258 of the support plate 170 through the membrane 118.

  The retaining ring 110 functions to prevent the wafer from coming out of the recess, and transmits a lateral load from the wafer to the base 104. By pumping fluid out of the chamber 190, the central portion of the membrane 118 is bent inward and the central portion of the membrane 118 is pulled upward. When the wafer is in contact with the lower surface 120, if the membrane 118 holds upward, a low-pressure pocket is generated between the circular bottom 201 of the membrane 118 and the wafer. The low-pressure pocket holds the wafer on the support head, and the wafer can be detached from the support head by returning to atmospheric pressure. Using this operation, the support head transports the wafer between the polishing station and the transfer station.

  The membrane 118 is attached to the support plate 170 in a state of receiving a tensile stress in the radial direction so that the membrane 118 is not bent at atmospheric pressure. Specifically, the diameter of the support plate 170 is set larger than the inner diameter of the membrane 118 (the inner diameter of the wall portion 202) before mounting. Accordingly, a force that contracts toward the inner diameter side is generated in the membrane 118 after being mounted, so that there is a problem that the upper surface portion or the annular portion 203 of the membrane 118 is easily lifted from the support plate.

  In the conventional membrane shown in FIG. 4 (a), since the cross section of the protrusion is semicircular, there is a problem that the protrusion is likely to be detached from the groove before the upper surface of the membrane is pressed by the lower clamp. If assembly to the support head 100 is performed while the protruding portion is out of the groove, the side surface portion of the membrane, that is, the wall portion, and the inner surface of the retaining ring may come into contact with each other, causing malfunction.

  In the present embodiment shown in FIG. 4B, the cross section of the protrusion 270 is U-shaped having a straight portion 272. The presence of the straight portion 272 increases the frictional force and has a size that can resist the tensile stress. Therefore, the protrusion 270 is less likely to be detached from the groove 262, and the work efficiency is improved.

  Further, in the prior art, as shown in FIG. 4 (a), the length of the upper surface portion (annular portion) of the membrane is longer than the length of the corresponding upper surface portion of the support plate, so even if the protruding portion does not come off the groove. Depending on the manner of assembly, the side surface of the membrane and the inner surface of the retaining ring may come into contact with each other.

  In the present embodiment, the length of the upper surface portion (annular portion) 203 of the membrane 118 in an unloaded state (more specifically, the length from the inner surface of the wall portion 202 to the outer surface of the protruding portion 270) is determined. Since the length of the corresponding upper surface portion (more specifically, the length from the outer periphery of the support plate 170 to the outer wall surface of the groove 262) is set to be equal to or less, the mounting failure of the membrane 118 is prevented, and thus the protruding portion 270 is formed into the groove. If it does not deviate from 262, the membrane 118 and the inner surface of the retaining ring 110 will not contact each other.

  FIG. 5A is a diagram for explaining another problem in the membrane of the prior art.

  In the conventional membrane 40 shown in FIG. 5A, the corner 41 on the lower surface side shifts to the inner diameter side due to the force that contracts toward the inner diameter side when mounted. As a result, there is a problem that the thickness on the lower surface side of the membrane partially increases, and the stress 43 applied to the wafer becomes non-uniform when the wafer 42 is pressed, and therefore the polishing amount of the wafer becomes non-uniform. As a result, the wafer becomes unsuitable for the production of integrated circuits and the yield decreases.

  In this embodiment shown in FIG. 5B, R51 is provided at the corner on the lower surface side of the membrane 50. R51 shown in the figure has a radius equal to the thickness of the other part of the membrane 50 with the inner vertex 54 as the center. Since R51 is provided in this way, the amount of change in the thickness of the membrane 50 is small even when a force that contracts toward the inner diameter is applied. As a result, the distribution of the stress 53 applied to the wafer 52 is uniform, and the polishing amount is uniform. This R is experimentally determined so that the change in the wall thickness becomes minute. The shape is not limited to R as long as the circular bottom portion of the membrane 50 receives a tensile stress toward the center of the circle, and prevents the downward bulging, in other words, the shape that does not change the wall thickness. It may be missing.

  As mentioned above, although this invention was demonstrated about some embodiment, this invention is not limited to these.

It is a disassembled perspective view of a chemical mechanical polishing apparatus. It is a schematic sectional drawing of a support head. It is a figure which shows the membrane attachment method of a prior art. (A) represents the conventional membrane, (b) is a figure showing the membrane of one Embodiment of this invention. (A) represents the contact state of the conventional membrane and a wafer, (b) is a figure showing the contact state of the membrane and wafer of one Embodiment of this invention.

Explanation of symbols

  20 ... CMP apparatus, 32 ... polishing pad, 50 ... membrane, 51 ... R, 100 ... support head, 114 ... support structure, 118 ... membrane, 170 ... support plate, 201 ... circular bottom, 202 ... wall, 203 ... Annular part, 270 ... projecting part, 272 ... straight line part.

Claims (6)

A circular bottom,
A wall standing up from the outer edge of the circular bottom;
An annular portion extending in the center direction of the circle from the upper end of the wall portion;
A flexible membrane having a protrusion located at the end of the annular portion,
A membrane for a support head of a chemical mechanical polishing system, wherein a cross section of the protruding portion is a U-shape having a linear portion at a tip. The membrane according to claim 1, wherein the membrane is attached to a disk-shaped support plate having an annular groove that fits into the protrusion.
The support head membrane, wherein a length from the inside of the wall portion to the protruding portion is smaller than a length from the outer periphery of the support plate to the groove. A circular bottom,
A wall standing up from the outer edge of the circular bottom;
An annular portion extending in the center direction of the circle from the upper end of the wall portion;
A flexible membrane having a protrusion located at the end of the annular portion,
A membrane for a support head of a chemical mechanical polishing system, wherein a joint portion between the circular bottom portion and the wall portion has a shape that prevents downward swelling when the circular bottom portion receives a tensile stress in the center direction of the circle. The support head membrane according to claim 3, wherein the anti-swelling shape is R. The support head membrane according to claim 4, wherein the R is a R having a thickness equal to that of a portion other than the joining portion. The support head membrane according to claim 4, wherein R is R centering on an inner vertex.

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