WO2012128761A1

WO2012128761A1 - Fluid filled template for use in chemical mechanical planarization

Info

Publication number: WO2012128761A1
Application number: PCT/US2011/029539
Authority: WO
Inventors: Leonard Borucki
Original assignee: Araca, Inc.
Priority date: 2011-03-23
Filing date: 2011-03-23
Publication date: 2012-09-27

Abstract

A method of chemical mechanical planarization (CMP) wherein a wafer-holding template is placed on a polishing head of a CMP polishing tool wherein template contains a central fixed volume chamber into which fluid has been placed.

Description

FLUID FILLED TEMPLATE FOR USE IN CHEMICAL MECHANICAL PLANARIZATION

BACKGROUND OF THE INVENTION

[0001 ] Embodiments of the present invention relate to a method of CMP wherein a wafer-holding template is placed on the polishing head of a CMP polishing tool which template contains a central fixed volume chamber in which a fluid has been placed, the volume of which may be controlled to impart a distortion to the flat surface underlying the wafer to which the wafer surface then conforms and by these means characteristic radial non-uniformities in polishing rate of the wafer may be altered, decreased and improved.

Field of the Invention

[0002] When integrated circuits (ICs) are constructed in the semiconductor industry and related industries, a process called chemical-mechanical planarization, or CMP, is typically used numerous times during manufacturing to planarize the wafer surface on which the circuits are being built. Planarization is essential for the construction of the wiring, or interconnects, that are used in circuits, and it also can be an important step in forming transistors and other electronic components. Non-planar surfaces present difficulties for the application of lithographic tools, which are used to create patterns on the wafer and which have a limited depth of focus. CMP in the last 20 years has in fact become a key enabling technology that has made possible essentially unlimited complexity in integrated circuit design. IC fabrication facilities therefore typically have large numbers of CMP tools and incur substantial costs running them. [0003] In a conventional CMP process, a silicon or other semiconductor material wafer with integrated circuit chips under construction is held upside down in a rotating wafer carrier and is pressed with a controlled force against a large rotating polishing platen. The platen is covered with a thin polyurethane polishing pad, typically up to a meter in diameter and 1 -2 mm thick. Microscopic protuberances on the pad surface, also known as asperities or summits, make contact with the wafer, and, with the assistance of pol ishing slurry containing chem istry and abrasive particles, effect the removal of material from the wafer surface The polishing slurry is usually applied at a slow, continuous rate to the pad in the vicinity of the wafer using a drip or spray system.

[0004] Diamond conditioner disks serve the purpose of continual and consistent roughening of the polishing pad and are suspended from an arm or a bridge, platform or similar structure of the polishing tool so that they are pressed diamond bearing face down into the polishing pad. Diamonds on the conditioner disk surface cut and roughen the pad during CMP operation. This is necessary because the action of the slurry on the wafer and pad quickly smoothen the pad otherwise greatly dim inishing its effectiveness and the rate of removal of the wafer surface during polishing. The diamond conditioner disk sits under a load on the polishing pad and is both rotated and moved back and for the between the center of the pad to ensure an even dispersal of roughening over the polishing pad.

[0005] The wafer polishing head consists of an apparatus for holding and rotating the wafer and is suspended from a supporting arm, bridge, platform or similar structure of the polishing tool and holds the wafer rotating face down against the top of the rotating polishing pad. [0006] Depending upon the type of wafer to be polished and the specific objectives of the operator, a variety of loads, head and platen rotation rates and, in the case of the diamond conditioner disk, motions across the polishing pad surface may be employed. Likewise, the type, quantity and concentration of slurry may be varied to obtain different results.

[0007] The wafer polishing head itself is a structure that is attached to a shaft that may be further attached to a bridge or platform that is typically part of the framework of the CMP polishing tool. The wafer polishing head is suspended above the polishing pad except during polishing when it is lowered onto and placed into contact with the rotating polishing pad under a load that is controlled by the operator.

[0008] The bottom side of the wafer polishing head typically incorporates a rubber or polymer membrane, a thin, soft partially porous polymer sheet or backing film, or a flat metal or ceramic surface, and this bottom-side structure holds the wafer to itself by any suitable means. For example, the bottom surface of the wafer polishing head may be equipped with a large number of small holes or perforations passing through it for the purpose of supplying a vacuum or negative (sub-ambient) pressure to the back side of the wafer to hold it in place during handling. The same holes may also be used to apply localized positive pressures to the backside of the wafer during polishing that are in addition to the main load applied by the wafer polishing head. Such backside air pressure can be used to modulate the polish rate uniformity on the wafer front surface. Wafer polishing head designs that incorporate a rubber or polymer membrane are typically designed so that air pressure can be applied selectively in circular or annular zones constructed behind the membrane. Pressures applied in these zones allow the operator to affect the polish rate uniformity in the corresponding zones on the wafer front side. There are also presently available ceramic-faced vacuum equipped wafer polishing heads for the polishing of silicon or other semiconductor material wafers. However, for silicon oxide and copper clad wafers in particular, this method of polishing has exhibited problems in regard to the achievable polish rate uniformity.

[0009] To overcome this problem, Fujikoshi Machinery Corporation developed a disk, or wafer polishing template, made of a single piece of PVC and machined it so that there was a raised ring around the upward-facing circumference of the disk of a half centimetre to a centimetre or so in width so that the diameter of the inner edge of the ring is the same or slightly more than the diameter of the ceramic plate on the bottom side of the head. The height of the ring is two or three millimeters. This ring prevents the plastic PVC wafer polishing template from slipping off of the ceramic plate as a result of the horizontal frictional shear force that occurs when the wafer is polished. The ring also helps to prevent slurry from seeping behind the wafer polishing template when vacuum is applied though the holes in the ceramic plate. The silicon dioxide or other non-silicon type wafers to be polished are affixed to the front of the disk using a soft, semi-porous polymer wafer backing film with a retaining ring. The wafer backing film has an adhesive on one side by means of which it is affixed to the wafer polishing template. The retaining ring prevents the wafer from slipping out from under the wafer polishing template due to frictional shear forces. The wafer itself is attached to the wafer backing film during handling by wetting the soft semi-porous polymer film and using the liquid capillary force to hold the wafer in place. This PVC disk with retaining ring and wafer backing film design has the further advantage that it is easily removable from the polishing head and allows quick and efficient removal of and attachment of different wafers to the polishing tool resulting in a very considerable time savings and increase in process cost effectiveness.

[0010] However, these disks possessed the problem of being unable to deliver uniformity of polishing primarily due to the non-uniform thickness of the PVC material used. The PVC was machined into the desired shape using a lathe or a mill, which tended to result in slightly prominent disk centers that in turn applied excess pressure to the wafer surface at the center as it is pressed against the polishing pad leading to unacceptable levels of radial polishing non-uniformity and a significantly flawed final polished wafer product. US patent application 12 261540, hereby incorporated by reference, teaches the use of a flat disk-like template prepared from a stable and initially very flat material such as polycarbonate sheet which maintains a very smooth surface and precise thickness even under the conditions of CMP polishing and maintains the position of the wafer on the lower downward facing surface of the template of an embodiment of the present invention by means of a backing film. Further, under this application without the need for machining, the surface of the said template facing the pad may be polished to assure even better radial removal rate uniformity. The said template is held in place by a ring with outer diameter equal to that of the template and inner diameter equal or slightly larger than that of the ceramic disk used in the head, said ring being held to the template by adhesive or other suitable means.

BRIEF SUMMARY OF THE INVENTION

[001 1 ] Although the wafer template of US Patent Application 12261540 considerably increased the level of radial uniformity of the material removal rate and the convenience of the Fujikoshi design, considerable radial non-uniformity of the material removal rate remained to a problematic extent in many cases in the polishing of wafers. Although the polishing pad facing surface of the template was near perfectly flat when manufactured, during use the dynamics of contact with an also moving polishing pad on a possibly non-planar platen under load during operation and the motion of slurry near the edges and center of the wafer still resulted in a problematically higher rate of material removal in the center of the wafer than at the edges. The inventors of the present invention, in order to overcome the problems of the prior art, specifically a higher rate of material removal at the center of the wafer and other non-uniform cutting patterns observed with the use of the templates of the prior art, while at the same time retaining both convenience and cost effectiveness, engaged in various studies and research and as a result of extensive, careful and detailed study of the problem have conceived and developed the present invention.

[0012] An embodiment of the present invention comprises a wafer polishing template as described in US application 12261540. This wafer polishing template is a planar template for a CMP polishing tool wafer polishing head possessing a means of securing a wafer in CMP polishing wherein the back surface of the said template is held to the polishing head by retaining means. An embodiment of the invention relates more particularly to such a planar template wherein the size of the template is the same size or larger than the size of the wafer backing film, the means of holding the wafer comprises a wafer backing film, the material from which the template is made is polycarbonate sheet, the retaining means is a vacuum, and a retaining ring is also affixed around the edge of the said template on the face toward the polishing head to secure the template in place. The said wafer polishing template is placed on the wafer polishing head that relies upon vacuum to hold the wafer or the wafer template. In the embodiment of the invention, the template further contains a central chamber filled completely which an incompressible fluid, the volume of which may be controlled to impart a distortion to the flexible surface or membrane forming one side of the chamber and underlying the wafer to which the wafer surface then conforms and a method for using the same. The embodiment of the invention overcomes the problem of radial non- uniformity of polishing rate by using an incompressible fluid within the chamber behind the flexible membrane to redistribute pressure non-uniformities on the wafer surface, from whatever cause, so that the pressure non-uniformities are minimized. For example, if variations of the platen surface shape or the pad thickness momentarily produce a larger displacement of one area of the wafer compared with another, and thus a momentarily larger pressure, then the membrane behind the wafer will flex locally in response, and the incompressible fluid in the cavity, by having a constant pressure throughout, will insure that the membrane will adjust so that the pressures on the backside of the wafer are constant and therefore that the contact pressures on the front side are nearly constant; ie, the wafer will deflect locally due to the presence of the flexible membrane and the fluid behind it in such a way as to minimize pressure differences across the wafer surface.

[0013] An embodiment of the invention operates by means of a central rounded cavity within the wafer polishing template. This cavity is may be cylindrical, ovoid curving in the vertical direction, or may be lens shaped and is typically radially symmetrical, preferably circular, about the center of rotation of the wafer polishing template though that is not required. The outermost extension of the cavity is typically near the edge of the wafer though depending upon the sort of surface displacement desired this dimension may be greater or less than the outer diameter of the wafer. The wall of the cavity on the wafer side is sufficiently thin that when water or some other suitable incompressible fluid is introduced into the cavity through a small inlet in the side of the cavity or the side of the cavity furthest from the face of the wafer being polished, and when air has been completely removed, the wall facing the wafer is either planar, convex or concave, depending on whether the volume of water equals the volume of the cavity, exceeds it, or is less than it. Since the wafer is also attached to the leading face of the wafer polishing template by means of a wafer backing film and capillary forces, the wafer bends accordingly with the center distortion more prominent than that of the outer edges. If the volume of fluid in the cavity equals or exceeds the cavity volume, so that the wafer is flat or convex, then when the wafer is polished, the membrane and fluid redistribute the contact pressure in such a way as to minimize pressure variations over most of the wafer surface. If the cavity is filled in excess, then near the edges of the membrane where the membrane is constrained by the template, the wafer contact pressure and thus the material removal rate will decrease, thereby providing a means of controlling the wafer edge polish rate. If the volume of fluid in the cavity is less than the cavity volume, then the wafer near the edge will have higher contact pressures and so the edge will have a higher material removal rate. An area about the wafer center will in this case also have contact pressures with minimal variation but the mean contact pressure in the wafer center will be lower than at the wafer edge due to mechanical support by the membrane at the edge.

[0014] It is possible that should non-uniformity of other forms - for example as yet reported non-uniformity of removal rate characterized by greater removal rate at the center than the edges of the wafer - be observed, adjustment of the shape or thickness of the cavity and of the pressure may be used to achieve uniformity of material removal rate in these situations as well so long as the said non-uniformity is radial in distribution. By adjusting the volume of fluid in the cavity and then making profilometric, interferometric or other surface measurement of the polished wafer, the volume of the fluid in the cavity may be adjusted to achieve optimal, uniform results. In this way, the apparatus and method of an embodiment of the invention are able to significantly reduce or even eliminate the non-uniformity observed in removal rates of CMP wafers in the prior art.

DESCRIPTION OF FIGURES

[0015] Figure 1 is a top view of the apparatus of the an embodiment of the invention

[0016] Figure 2 is a side cross sectional view of the apparatus of an embodiment of the invention.

[0017] Figure 3 is a cross sectional side view showing the apparatus of an embodiment of the invention attached to the wafer polishing head of a Fujikoshi Machinery Corp. APD-800 or APD-500 CMP tool. [0018] Figure 4 is a graph showing the profilometric measurement of the surface of a wafer polished using an embodiment of the invention.

[0019] Figure 5 is a graph showing the profilometric measurement of the surface of a wafer polished with a polycarbonate template that did not incorporate a fluid filled central chamber.

DETAILED DESCRIPTION OF INVENTION

[0020] The method of an embodiment of the invention has been developed in response to the present state of the art, and, in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available CMP methods for reducing the level of defects to the semiconductor wafer and inconvenience, inefficiency and process waste to the CMP process caused by radial non-uniformity of material removal rate in the wafer. Thus it is an overall objective of an embodiment of the invention to provide a method for CMP that achieves significant reduction in the level of defects to the semiconductor wafer and inconvenience, inefficiency and process waste to the CMP process caused by the radial non-uniformity of cutting rate.

[0021 ] The purpose of the method is to facilitate the consistent production of a high quality of semiconductor wafer product.

[0022] Through application of the method of an embodiment of the invention, the consistent production of a significantly higher quality of semiconductor wafer product has been achieved, in particular, the embodiment of the invention improves the uniformity of wafer polishing. [0023] All dimensions of an embodiment of the invention are based on a polishing pad size or as the case may be counter face size of about 20" to 30" in diameter and a wafer size of between 8" and 12" in diameter and may be altered as needed in proportion to changes in the size of the polishing pad and wafer used. The specific dimensions given herein are in no way limiting but are by way of example to demonstrate an effective embodiment of the invention. For the avoidance of doubt, dimensions include, without limitation, dimensions of parts, flow rates, measurement of damage, rates of rotation and velocities.

[0024] The wafer template apparatus of an embodiment of the invention is not particularly limited but may resemble the wafer template apparatus described in US Application 12 12261540 in terms of the external diameter, overall shape and manner of attachment to the wafer polishing head of the CMP tool. That is to say it may comprise a planar template for a CMP polishing tool wafer polishing head possessing a means of securing a wafer in CMP polishing wherein the back surface of the said template is held to the polishing head by retaining means. More particularly, an embodiment of the invention relates to such a planar template wherein the size of the template is the same size or larger than the size of the wafer backing film, the means of holding the wafer comprises a wafer backing film, the material from which the template is made is polycarbonate sheet, the retaining means is a vacuum, and a retaining ring is also affixed around the edge of the said template on the face toward the polishing ring to secure the template in place. It should be observed that an embodiment of the invention may be applicable with polishers that use means other than vacuum to secure the wafer or wafer template to the wafer polishing head. However, in the preferred embodiment, the said wafer polishing template is placed on the wafer polishing head that holds wafers or wafer templates by means of a vacuum applied through the wafer polishing head. In an embodiment of the invention, the template further contains a central chamber with a fluid, the volume of which may be controlled to impart a distortion to the flat surface or membrane underlying the wafer to which the wafer surface then conforms and a method for using the same. A feature of embodiments of the invention that was not present in the wafer templates of the prior art is that there is a central cavity within the wafer having a diameter of from 4 millimeters larger to 2 millimeters smaller than the diameter of the wafer. Embodiments of the invention overcome the problem of radial non- uniformity of material removal rate by using the incompressible fluid to minimize differences in nominal contact pressures across the wafer surface.

[0025] As shown in Figure 1 , the template (8) of an embodiment of the invention comprises a hard flat sheet of material ( 10). The material that may be used is not particularly limited but it should be hard, dimensionally stable under the conditions of operation of CMP and resistant to the chemical composition of the slurries used in CMP. Any hard material may be used as the material for the sheet (10) of embodiment of the invention but hard plastic is preferred. Any hard plastic sheet such as acrylic, polyurethane or polycarbonate sheet may be used but polycarbonate sheet is preferred for its availability, cost effectiveness, flatness and dimensional stability.

[0026] The thickness of this material is not particularly limited but it is preferably between 0.01 inch and 1/2 inch and more preferably between 0.093 inch and 1 /2 inch. The outer shape and dimensions of the sheet ( 1 0) are not particularly limited and any sheet dimensions and shape that do not interfere with the normal operation of the wafer head may be used but a circular shape is preferred and the diameter thereof should be sufficiently large to encompass the outer dimensions of the ceramic plate at the bottom of the wafer polishing head by at least about 1 /8 inch and more preferably by ¼ inch or more. It is preferred that the diameter of the sheet( l O) not exceed the diameter of the template by more than 2 inches.

[0027] The sheet may be a single layer or in multiple layers held together by any suitable means. The sheets may be the same thickness or the thickness may be varied. The means of binding multiple sheets together are not particularly limited and any suitable means including bolting, pinning, lamination with adhesive or mechanical attachment may be used but secure attachment by a series of pins (34) in recessed openings (not shown) in the outermost sheets (36) supplied for this purpose is preferred, combinations of methods of attachment may be used, and the use of adhesive between the outermost sheets (10) in addition to bolting or pinning is more preferred. If pins are used any number of pins may be used but between 10 and 20 stainless steel pins are preferred.

[0028] The adhesive used to hold the multiple sheets together in embodiments of the invention is not particularly limited but adhesives that are durable and not reactive and will not quickly degrade in the presence of the compounds contained in commercially available CMP slurries are preferred.

[0029] Around the circumference (12) of the sheet (10) on the upward facing face of the sheet (10) is attached the retaining means. The retaining means is not particularly limited and may comprise a series of architectural supports around the circumference of the sheet placed so as to prevent the template from slipping during CMP polishing or a complete retaining ring with an inner diameter equal to or no more than 1 /8 inch larger than the diameter of the ceramic plate on the lower face of the wafer head but a retaining ring ( 14) is preferred. The retaining ring ( 14) may be made of any hard material but hard plastic is preferred. Any hard plastic sheet such as acrylic, polyurethane or polycarbonate sheet may be used but polycarbonate sheet is preferred. The sheet or sheets (10) and the retaining ring (14) may be individually of the same or different material and the use of the same material is preferred. The degree of flatness of the sheet ( 10) is not particularly limited. However, polycarbonate sheets with a tolerance of 1 mil (25 micrometer) are commercially available.

[0030] The wafer is secured to the sheet by means of a backing film (22) with a ring (24) for securing the lateral edges of the wafer. Any suitable backing film commercially available for CMP polishing may be used for this purpose.

[003 1 ] The dimensions of the retaining ring (14) are not particularly limited but it is preferred that the outer edge ( 16) of the retaining ring be concentric with the sheet ( 10) where the sheet (10) is circular in shape and it is also preferred that the said outer edge (16) be the same diameter as the outer edge ( 18) of the sheet. The inner edge (20) of the retaining ring (14) should be concentric with the center of the sheet ( 10) and should be the same diameter as the wafer polishing head or up to about 1/8 inch in diameter larger and a diameter as close in size as possible to the size of the plate on the lower face of the wafer head is preferred. The thickness of the retaining ring in embodiments of the invention is not particularly limited but should be sufficient to allow the retaining ring to hold against the sides of the wafer polishing head securely and is preferably at least the same thickness as the sheet ( 10), more preferably at least twice the thickness of the sheet (10) and is further preferably between 1/16¹ and ½ inches in thickness and more preferably between 1 /8 and ¼ inches in thickness.

[0032] The means of attaching the retaining ring (14) to the sheet (10), in an embodiment of the invention, is not particularly limited and any suitable means including bolting, pinning, lamination with adhesive or mechanical attachment may be used but secure attachment by a series of pins (34) in recessed openings (36) in both the retaining ring (14) and the sheet ( 1 0) supplied for this purpose is preferred, combinations of methods of attachment may be used, and the use of adhesive between the retaining ring ( 14) and the sheet ( 10) in addition to bolting or pinning is more preferred. If pins is used any number of pins may be used but between 1 0 and 20 stainless steel pins are preferred.

[0033] Figure 3 shows the ceramic plate (26) on the lower face of the wafer polishing head (28) and the affixation of the template (8) thereto. The side of the template (8) possessing the retaining means (24) is placed on the wafer polishing head (28) so that the sheet (10) face contacts the face of the ceramic plate (26). The wafer (30) is attached to the backing film (22).. The securing means of the wafer or wafer template in embodiments of the invention is not particularly limited and any suitable means may be used that may be effectively used to secure the wafer in CMP. However, the use of vacuum is preferred. Vacuum is introduced through the multiple small openings (not shown) in the surface of the ceramic plate (26) equipped for that purpose and the template is affixed and ready to commence CMP polishing on the CMP polishing pad (not shown). To remove the template, maintenance of the vacuum to the ceramic plate (26) is discontinued after the completion of polishing operations and the template (8) with the wafer (30) attached by means of the backing film (22) and the ring (24) for securing the wafer is removed from the CMP polisher.

[0034] The central chamber (40) of embodiments of the invention is not particularly limited. It can be fashioned within one layer of hard material ( 10) however this method requires extensive machining or perhaps molding and is not preferred. If two or more sheets of hard material ( 10) are used a chamber may be prepared by machining a depression in inward faces of either or both sheets. If more than two sheets are used, the chamber (40) may be cut out of the central sheet or sheets. In this case the outermost sheets may be machined or not as is optimal for operation conditions.

[0035] Although the number of sheets ( 10) used is not limited, given the complexity of preparation and structure, an apparatus comprising 2 sheets the inner faces of one or more of which are machined is preferred and an apparatus comprising 2 sheets the inner face of the sheet ( 10) nearest the wafer is machine is more preferred.

[0036] The shape of the chamber (40) is not particularly limited. However, it is preferred that it be the shape of the wafer (30) and between two millimeters greater in diameter to 4 millimeters less in diameter than the wafer and a diameter of between 1.5 millimeters less than and 1 millimeter more the wafer is preferred. A chamber (40) with a diameter of between 1 millimeter more than the diameter of the wafer to 1 millimeter less than the diameter of the wafer (30) is preferred.

[0037] The thickness of the chamber (40) is not particularly limited but should be sufficient that the flow of fluid through the chamber is not impeded but yet not so thin that the opposing walls touch during normal operation. Rather than the thickness of the chamber itself, the thinnest portion of the machined areas, particularly a machined area on the sheet (10) facing the wafer should not be less than 0.010 inch and preferably not less than 0.030 inch. This thickness may be constant or it may increase or decrease by about l/32^nd of an inch or less between the center of rotation of the wafer template and the edge of the chamber.

[0038] The form of the chamber (40) is not particularly limited and may be a cylinder with flat upper and lower walls parallel to the surface of the sheets(l O). It could also be a cylindrical shape in which the two ends were shaped in lenticular curves, either convex or concave with convex being preferred. Or, the shape of the chamber (40) could be ovoid with no flat walls or hemispherical with one flat wall. Cylindrical chambers (40) are preferred.

[0039] The chamber is equipped with at least one small channel (50) prepared from the side of template though which fluid may be introduced unless fluid is introduced from the back of the template in embodiments where the chamber (40) is created between the back surface of the template and the wafer head (28) and liquid may be introduced through channels (not shown) in the wafer head (28) in which case such a channel through the side of the template, though it may still be used is not essential. Where channels (50) are used, two or more channels (50) are preferred at least one being an inlet and another an outlet and two channels are more preferred.

[0040] The channels may be equipped with small opening and closing means (52) so that when fluid is added, the loss of air or fluid though the egress channel may be controlled. The opening and closing means (52) are not particularly limited, and any means that can selectively allow or not allow motion of fluid or air may be used, but cap screws with screws and valves are preferred and cap screws with screws are more preferred. In the case of the use of cap screws, each entry channel possesses one cap screw. The length of the cap screw is not particularly limited and any cap screws that are of suitable dimensions to fit within the dimensions of the template of the embodiment of the invention may be used but 2-56 cap screws that are about 0.5 inches in length are preferred. Tightening the cap screws seals the channel. Sealing occurs in part because of the large number of threads. A small amount of Teflon paste on the threads will improve the effectiveness of the seal. Within each channel in this case there may also be a PEEK tube between the cap screw and the chamber and this channel is of an outer diameter corresponding to the inner diameter of the channel. When the cap screw is fully closed, the tip of the cap screw impacts upon the aperture at the outer end of the PEEK tube and may create a second seal. The need for at least two channels (50) arises because one channel (50) is needed to place fluid in the chamber (40) and a different channel (50) is needed to allow for the egress or purging of air from the chamber (40). The size of the channels (40) is not particularly limited but if the channels (50) are too small flow is unduly restricted and if they are too large, the channel will not fit within the thickness of the wafer template (8). A channel (50) diameter of between l/64^th inch and 0.133 inch is preferred and l/20^th inch and 0.125 inch is more preferred. The angle of separation between the inlet and purging lines (50) are not particularly limited but an angle of between 10 and 90 degrees is preferred.

[0041 ] The channels (50) are equipped with means of conveying fluid into the chamber (40) from a source outside the wafer template (8). These means are not particularly limited however, plastic or metallic tubing with a pump connected to a reservoir are preferred. The size of the tubing is not particularly limited but tubing w ith a size approximately the same as the diameter of the respective channel is preferred. Valves should be attached to the tubing outside of the apparatus to control egress of fluid from the chamber once the air has been replaced. Valves can be manually or electronically controlled and electronic control is preferred. Cap screws are set within the template material itself and require additional machining to create a widening at the beginning of the channel (50) having the same dimensions as the outer diameter and length of the cap screw as described above. The means of inducing the fluid into the chamber (40) used in an embodiment of the invention are not particularly limited, however, pumps and syringes may be used.

[0042] The fluid of an embodiment of the invention is not particularly limited and any fluid suitable for hydraulic pressure apparatuses may be used including different organic oils, solvents, inorganic solvents and liquids, aqueous solutions or water so long as they do not react with or significantly change the template material or cause the adhesive holding the sheets together, when adhesive is used, to degrade resulting in delaminating of the apparatus. Water is preferred as the hydraulic fluid of an embodiment of the invention.

[0043] The CMP polisher of an embodiment of the invention with a wafer polishing head (28) that is equipped with vacuum to hold a wafer (30) directly or a disk during polishing (not shown) is not particularly limited and CMP polishing tools such as polishers manufactured by Fujikoshi Machinery in which the means of securing the wafer or wafer template to the wafer polishing head employs vacuum and related polishers such as the Araca APD-500 or APD-800 may be used. [0044] As the method for the use of an embodiment of the invention, after a template has been prepared as described above, a wafer (30) is attached to the face of the wafer template (8) that will face the polishing pad by a moist wafer backing film. The wafer template (8) and wafer (30) are attached to the CMP tool as shown in Figure 3. Prior to this, tubes or other means are attached firmly to the channels (50) and the chamber (40) is filled with fluid. The inlet and egress cap screws or valves (52) are closed and a set volume is maintained on the fluid in the chamber. The volume of the fluid may be equal to, slightly more than or slightly less than the designed geometric volume of the chamber, slightly larger or smaller volumes being accommodated by the flexing of the wafer-side chamber membrane. After placement of the wafer template (8) and the wafer (30) on the wafer polishing head (28), polishing is carried out. Ellipsometers, reflectometers, 4-points probes or other suitable metrological means are used to determine the material removal rate on the wafer (30) at different points and consequently the uniformity of the said material removal rate and after several more polishing trials are conducted on near identical wafers varying the volume placed in the chamber (40) incrementally, a volume is selected for the type of disk and conditions being used that results in the most uniform radial cutting rate.

[0045] In a preferred embodiment of the present invention, the opening and closing means (52) of the fluid addition and air purging lines are accomplished as follows: as described above, tubes, made typically of PEEK or other similar suitable material, are inserted into channels, machined or otherwise prepared in the facing sheet surfaces of two template sheets which have a diameter equal to the said external diameter of the tubes as far as the inner chamber. The tubes are affixed to stainless steel or other suitable material cap screw sleeves with an external diameter of 0.133 inches and the internal diameter of the cap screw sleeve into which the PEEK tube is placed determines the external diameter of the tube. The screw cap sleeves are about 1 inch in length and they are affixed to channels prepared in the facing surfaces of the template disks with adhesives such as super glue or DAP. To the screw cap initially are attached screw adapters. The adapter or adapters to be used for liquid inlet additionally are equipped with further PEEK tubing that extends to a syringe. Fluid, typically water, is added using the syringe until all of the air is removed from the central chamber. (40). Then the purging line is stopped by screwing in securely a screw cap to the screw cap sleeve or sleeves used for purging of air.

[0046] One this has been done, the volume inside the chamber (40) may be increased or decreased slightly by addition or removal of fluid, typically water, using the syringe until the desired convex or concave modification of the surface of the template (28) is obtained. Then the screw cap tube adapter is removed from the screw cap sleeve and a screw cap is crewed in securely to the fluid inlet line or lines as was done with the air purging lines earlier. The device may then be used in this condition. After test runs are conducted on identical test wafers, and non-uniformity of cutting rate is determined, the volume in the chamber is further increased or decreased opening and shutting the inlet screw cap and attaching and removing the syringe line as needed to improve uniformity of cut rate until an optimal result is obtained. Then the screw cap is again reset and CMP is conducted normally.

[0047] Another aspect of an embodiment of the invention is the prevention of leaks from the central chamber (40) where two or more sheets are attached together to create the template. The means of determining such leaks in an embodiment of the invention is not particularly limited, however, addition of brightly dyed fluid that would exhibit lines of color along the path of any appreciable leak is preferred. Before filling the central chamber (40) with water it may be leak tested though there is nothing to prevent the user of an embodiment of the invention from using the same colored fluid for practice of the present invention as is used to verify the absence of leaks. This method of leak detection of course requires that the sheets used be transparent so that the color lines created by leaks from the central chamber may be observed visually.

EXAMPLES

[0048] Example 1 .

A template for an ARACA APD-800 polisher was prepared by cutting 2 polycarbonate sheets (Lexan 0.093 inches thick) into circular disks having a diameter of 14.563 inches. The outer face of the "upper disk" - the one contacting the CMP polisher - was machined so that there was a circular step with inner diameter 14.208 inches, and a vertical depth of 0.028 inches centered on the center of the disk. A ring was prepared from another sheet of Lexan of 14.563 inches outer diameter, 14.208 inches inner diameter and 0.093 inches thickness. This was placed on the step, which it just fitted in size, the upper disk was placed evenly on the lower disk and 18 0.125 inch diameter holes set equidistantly apart about the ring and centered halfway between the inner and outer diameters of the ring were drilled through the ring, the upper disk and to a depth of about halfway (0.046 inches) through the bottom disk. In practice these holes are drilled to a depth sufficient that the top of the dowel to be inserted rests even with the top surface of the ring or is slightly recessed. [0049] The disks were again separated and a circular cylindrical depression of diameter 7.874 inches and depth about 0.053 inches centered on the center of the bottom disk was machined into the bottom disk. The cylinder ended up being about 204 mm in diameter or about 4 mm wider than the wafer with which it was to be concentric. The sides of this chamber were vertical and the bottom was as smooth and even as it could be made.

[0050] Finally two radial channels about 0.0625 inches in diameter were machined and cut in the bottom sheet from the chamber to the outer edge of the disk and in the top sheet from where the chamber wall would contact the inner face of the upper sheet to the outer edge of the upper sheet at an angle of about 20 degrees apart. Roughly half of the diameter of the channel was cut into the top sheet and half into the bottom. The outermost one inch of the channel was expanded by again attaching and clamping the sheets together and drilling along the channels with a #39 0.099 inch drill to a depth of 1 inch. A small horizontal slot about 0.099 or 0.133 inch thick, about 0.375 inches long and about 0.1 inches deep was machined at the mouth of each of these expanded channels to provide a space for the anti-rotation tabs of the screw cap sleeves and the plates were again separated.

[00 1 ] A transparent and quick drying DAP adhesive was carefully applied to the inner faces of the lower plate in amounts sufficient to ensure sealing between the plates but not so much that any significant excess would exude into the chamber. Two PEEK tubes (1/16^th inch capillary tubing outer diameter 1/16^th inch, inner diameter 0.010 inch PEEK capillary tubing by Professional plastics) attached with super glue or other similar adhesive to 2-56 screw cap sleeves were placed in the channels in the lower sheet and the anti rotation tabs were oriented with the recessed groves made to accommodate them. Care was taken to avoid adhesive covering either the ends of the tubes or the opening of the screw cap sleeves. The lower and upper sheets were placed together with dowel holes matching. Stainless steel dowels obtained in the dimensions of the dowel holes were placed in the dowel holes. The same adhesive was applied to the step area of the outer face of the upper plate, the ring was laid atop this again with dowel holes matching the position of the dowels and the sheets were clamped and left to dry to obtain the template in an embodiment of the invention.

[0052] Once the adhesive had dried, an open screw cap, or as the case may be an unthreaded fitting, with dimensions matching that of inner diameter of the sleeve and sufficiently long to be easily manipulated across the residual recess made for anti rotation tabs was attached to 1/16^th inch peek capillary tubing (about 5 inches length, outer diameter 0.062 inches, inner diameter 0.010 inches) in turn attached to a 100 μ 1 syringe (With Removable needle compression fitting 1/16^th inch Hamilton Company Part Number 55751 -01). Screw caps threaded to match the screw cap sleeves were prepared.

[0053] Water with a bright red colored opaque dye was introduced to the central chamber by means of the syringe and PEEK tubing until all of the air had been purged from the central chamber. Then the purge line was capped securely with the screw cap and a soft washer and a slight positive excess volume was introduced into the central chamber, the syringe was removed and the screw cap applied to the inlet line with a soft washer. An hour was allowed to pass to verify that none of the dyed water was leaking through the adhesive seal. One of the ports was then opened and excess water was allowed to drip out of the purge line naturally. When the dripping had stopped, the purge line was again sealed with a crew cap and a soft washer. The syringe was then used to add or remove a small amount of water to adjust the surface geometry in response to results of polishing trials.

[0054] A retaining ring and wafer backing film were applied to the lower outer surface of the template and a 200 mm blanket copper wafer was polished on an ARACA, Inc. APD 800 CMP polisher. The slurry used was Copper -1 which was 7 parts by volume of HS 2H635- 12 slurry, 7 parts by volume of deionized water and 6 parts by volume of deionized hydrogen peroxide. The slurry flow rate was 150 ml/minute and an Araca slurry injector (US patent application 12 262579, incorporated herein by reference in its entirety) was used to introduce the slurry. Note that the use of the injector though desirable is not essential to the practice of an embodiment of the invention. The polishing pad used was a 31 inch 1C1020 M-groove pad with a Suba IV Sub-pad. The pad was conditioned using a 3M A 165 full face diamond conditioner rotating at 95 RPM and sweeping at 10 times per minute. The conditioning was in situ at 5.8 lb_f. The wafer polishing pressure was 1 .5 psi, the sliding velocity was 1 .2 m/s (platen/head rotation rates of 51/49 RPM) and polishing time was set at one minute. A controlled rinse was performed with de- ionized water at a flow rate of 2000 ml/minute for 30 seconds. The platen rotation rate during the rinse was 42 RPM.

[0055] Upon completion of polishing of the aforesaid wafer under the aforesaid conditions, the wafer was removed and measured along two separate diameters using profilometry and removal rate was calculated based on surface measurement and the results, including the average removal rate are shown in Figure 4. [0056] Comparative Experiment. Except that in place of the template in an embodiment of the invention, a standard polycarbonate wafer template with no central chamber as was described in US Application 12261540 a 200 mm blanket copper wafer was polished in the same manner as described in Example 1. The results obtained are shown in Figure 5.

[0057] Figure 1 is a top view of the apparatus of an embodiment of the invention where 8 is the wafer template, 10 is the sheet of hard material, and 12 is the circumference of the wafer template (8).

[0058] Figure 2 is a side cross sectional view of the apparatus of an embodiment of the invention.

[0059] Figure 3: a cross sectional side view showing the apparatus of an embodiment of the invention attached to the wafer head of an Araca APD 800 CMP tool where, 14 is the retaining ring, 16 is the outer edge of the retaining ring, 18 is the outer edge of the sheet, 20 is the inner edge of the retaining ring, 22 is the backing film, 24 is the ring for securing the lateral edges of the wafer, 26 is the ceramic plate of the polishing head, 28 is the polishing head, 30 is the wafer, 34 are the bolts, 36 is the recessed opening for the bolts, 40 is the chamber within the template, 50 is the channel from the edge of the wafer template (8) to the chamber (40), and 52 is the opening and closing means of the channel (50).

[0060] Figure 4 is a graph showing the profilometric measurement of the surface of a wafer polished using an embodiment of the invention. [0061 ] Figure 5 is a graph showing the profilometric measurement of the surface of a wafer polished with a polycarbonate template that did not possess a fluid filled central chamber.

[0062] As may be clearly understood from the example, there is a dramatic, significant and industrially very meaningful improvement in the uniformity and precision of the radial polish rate obtained using embodiments of the invention over the radial polish rate obtainable using the prior art. This improvement by means of embodiments of the invention is obtained at nominal cost and minimal loss of convenience and operation time for the operators of CMP polishers.

Claims

CLAIMS What is claimed is:

1. A planar template for holding a wafer in chemical mechanical polishing wherein by adjusting the volume by a volume or pressure adjusting means within a fluid filled chamber within the template small adjustments to the geometry of the surface of the template may be made selectively to optimize the radial uniformity of the material removal rate.

2. A planar template for holding a wafer in chemical mechanical polishing according to claim 1 . wherein the chamber is prepared by altering one or more of the surfaces of two or more sheets and then fixing the sheets together by a fixing means.

3. A planar template for holding a wafer in chemical mechanical polishing according to claim 1 wherein the chamber is in the shape of a cylinder.

4. A planar template for holding a wafer in chemical mechanical polishing according to claim 2 wherein the chamber is made by altering the surface of one sheet.

5. A planar template for holding a wafer in chemical mechanical polishing according to claim 1 wherein the volume or pressure adjusting means is a detachable fluid supply means attached to the central chamber by channels with flow control means.

6. A planar template for holding a wafer in chemical mechanical polishing according to claim 5. wherein the flow control means is a valve.

7. A planar template for holding a wafer in chemical mechanical polishing according to claim 5 wherein the flow control means is a cap screw.

8. A planar template for holding a wafer in chemical mechanical polishing according to claim 5 wherein the fluid control means is a syringe.

9. A planar template for holding a wafer in chemical mechanical polishing according to claim 5 wherein the fluid control means is a pump.

1 0. A planar template for holding a wafer in chemical mechanical polishing according to claim 2 wherein the fixing means is an adhesive.

1 1 . A planar template for holding a wafer in chemical mechanical polishing according to claim 10 wherein the adhesive fixing means is supplemented by dowels or pegs between layers of the planar template.

1 2. A planar template for holding a wafer in chemical mechanical polishing according to claim 1 wherein the material from which the template is made is polycarbonate.

1 3. A planar template for holding a wafer in chemical mechanical polishing according to claim 2 wherein the sheets are polycarbonate sheets.

14. A planar template for holding a wafer in chemical mechanical polishing according to claim 2 wherein the thickness of the polycarbonate sheet to which the wafer is attached is between 0.01 and 0.8 inches.

15. A planar template for holding a wafer in chemical mechanical polishing according to claim 2 wherein the diameter of the polycarbonate sheet to which the wafer is between 0.1 mm and 5 cm larger than the diameter of the attached wafer.

16. A planar template for holding a wafer in chemical mechanical polishing according to claim 15 wherein the diameter of the polycarbonate sheet to which the wafer is attached is between 2 mm smaller and 6 mm larger than the diameter of the attached wafer.

17. A planar template for holding a wafer in chemical mechanical polishing according to claim 2 wherein the thickness of the polycarbonate sheet to which the wafer is attached is between 0.01 and 0.8 inches.

18. A planar template for holding a wafer in chemical mechanical polishing according to claim 1 wherein the template comprises two polycarbonate sheets, the inner surface furthest from the wafer of the sheet to which the wafer is attached is altered to create a cylindrical chamber, the thickness of the polycarbonate sheet to which the wafer is attached is between 0.01 and 0.8 inches, the diameter of the polycarbonate sheet to which the wafer is attached is between 2mm and 6 mm larger than the diameter of the attached wafer, the two sheets are bonded together with adhesive and dowels, the chamber is filled with fluid and the volume or pressure of the fluid is changed to alter the surface geometry of the polycarbonate surface underlying the wafer to improve the radial uniformity of material removal rate on the wafer surface during chemical mechanical polishing.

19. A method of chemical mechanical polishing wherein a planar template for holding a wafer in chemical mechanical polishing in which by adjusting the pressure by a pressure adjusting means within a fluid filled chamber within the template small adjustments to the geometry of the surface of the template may be made selectively to optimize the radial uniformity of the cutting rate.

20. A method of chemical mechanical polishing according to claim 19 wherein the chamber is prepared by altering one or more of the surfaces of two or more plastic sheets and then fixing the sheets together by a fixing means.

21. A method of chemical mechanical polishing according to claim 19 wherein a the wafer is held by a planar template for holding a wafer in chemical mechanical polishing in which the template comprises two polycarbonate sheets, the inner surface furthest from the wafer of the sheet to which the wafer is attached is altered to create a cylindrical chamber, the thickness of the polycarbonate sheet to which the wafer is attached is between 0.01 and 0.8 inches, the diameter of the polycarbonate sheet to which the wafer is attached is between 2 mm smaller and 6 mm larger than the diameter of the attached wafer, the two sheets are bonded together with adhesive and dowels, the chamber is filled with fluid and the pressure of the fluid is changed to alter the surface geometry of the polycarbonate surface underlying the wafer to improve the radial uniformity of cutting rate on the wafer surface during chemical mechanical polishing.

22. A method according to claim 19 wherein an increase in pressure in the chamber is used to induce a convex geometry upon the surface of the sheet beneath the wafer. A method according to claim 19 wherein a reduction in pressure in the chamber is used to induce a convex geometry upon the surface of the sheet beneath the wafer.

A method according to claim 19 wherein a neither a reduction in nor in increase in pressure is applied to the chamber resulting in a flat geometry upon the surface of the sheet beneath the wafer.