WO2012082115A1

WO2012082115A1 - Polishing head retaining ring

Info

Publication number: WO2012082115A1
Application number: PCT/US2010/060330
Authority: WO
Inventors: Ara Philipossian; Michael Goldstein; Yasa Sampurno
Original assignee: Araca, Inc.
Priority date: 2010-12-14
Filing date: 2010-12-14
Publication date: 2012-06-21

Abstract

A retaining ring for the polishing head in chemical mechanical polishing that in an embodiment distributes heat evenly by a heat exchanger means embedded within or on the lower surface of the ring that reduces the discrepancy in the temperature about different points of the lower surface of the ring in contact with or facing the polishing pad during chemical mechanical polishing.

Description

Polishing Head Retaining Ring

Background of the Invention

[0001] The present invention relates to a retaining ring for the polishing head in chemical mechanical polishing that distributes heat evenly by a heat exchanger means embedded within or on the lower surface of the ring that reduces the discrepancy in the temperature about different points of the lower surface of the ring in contact with or facing the polishing pad during chemical mechanical polishing. The present invention further relates to a method of chemical mechanical polishing using a retaining ring in which a heat exchanger means is embedded within or on the lower surface of the retaining ring that reduces the discrepancy of the temperature about different points of the lower surface of the ring in contact with or facing the polishing pad during chemical mechanical polishing.

Field of the Invention

[0002] When integrated circuits (ICs) are manufactured in the semiconductor industry and related industries, a process called chemical-mechanical planarization, or CMP, is typically used one or more times during manufacturing to planarize the wafer surface on which the circuits are being built. Planarization is ess ential 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 wafer with integrated circuit chips under construction is held upside down on a rotating polishing head and is pressed with a controlled force against a large rotating polishing platen. The platen is covered with a polishing pad made of polyurethane resin or other suitable material, typically up to a meter in diameter and 1 to 4 mm in thickness. Microscopic protuberances on the pad surface, also known as asperities or summits, make contact with the wafer, and, with the assistance of polishing slurry containing chemicals 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 polishing pad in the vicinity of the wafer using a drip or spray system.

[0004] A diamond conditioner disc serves the purpose of continual and consistent roughening of the polishing pad and is typically suspended from an arm or a bridge, platform or similar structure of the polishing tool. The diamond conditioner disc sits under a load on the polishing pad and is both rotated and moved back and forth or oscillated between the center of the polishing pad and the edge to ensure an even dispersal of roughening over the surface of the polishing pad. Diamonds on the conditioner disc surface cut and roughen the pad during CMP operation. This is necessary because the action of the slurry on the wafer and polishing pad quickly smoothen the polishing pad, greatly diminishing the rate of removal of the wafer surface during polishing.

[0005] The polishing head consists of the apparati for supporting and rotating the wafer, depends from the aforesaid supporting arm, bridge, platform or similar structure of the polishing tool and holds the wafer rotating face down onto the face 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, respective rotation rates and, in the case of the diamond conditioner disc, 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 polishing head is suspended above the polishing pad except during polishing when it is rotated at between 20 and 100 RPM and lowered onto and placed into contact with the rotating polishing pad under a load that may be controlled by the operator.

[0008] The surface of the polishing head facing the polishing pad holds the wafer by a number of different means and the wafer is maintained in a constant position centered on the axis of rotation of the polishing head by means of a retaining ring made of a durable chemically stable material such as engineering plastic like PEEK. The inner diameter of the ring is essentially the same as or slightly larger than the outer diameter of the wafer. The retaining ring or at least a part of the retaining ring is fixed to the polishing head by a number of means, including, for example but without limitation, by bolting it to the polishing head and consequently the retaining ring rotates at the same rate as the wafer and is essentially stationary with respect to it. The leading surface of the retaining ring facing the polishing pad, from the standpoint of the direction of rotation of the polishing pad, is very close to and parallel with the face of the wafer that contacts the polishing pad (the contact face of the wafer).

[0009] Retaining rings in CMP take various forms including, without limitation, rings consisting of a single part bolted or otherwise securely affixed directly to the polishing head and rings consisting of composites of more than one part, but particularly common are forms where the ring is a composite of two rings, one, made of a structurally and dimensionally stable material such as metal, ceramic or certain filled engineering plastics and the like, which is bolted or otherwise securely affixed to the polishing head and provides the dimensional stability essential to the proper function of the retaining ring and the other, the part of the retaining ring that contacts the polishing pad, is made from a more flexible materials such as engineering plastic material including polycarbonate, polyacetal, PEEK or carbon fiber reinforced (CFR) peek and the like. The two parts comprise two rings with the same internal diameter and typically a very close if not necessarily always identical external diameter. Where at least a two component ring is used, the vertical dimensions (thickness) of the structurally more stable portion of the retaining ring attached to the polishing head are whatever is necessary to bring the leading surface of the remaining part of the retaining ring just into contact with the slurry and polishing pad. The thickness of the said remaining part of the retaining ring is typically between 200 and 400 mils (l/5^th to 2/5^th inch) and it is bonded or otherwise securely but relatively easily removably affixed to the other part of the ring by suitable methods including, without limitation, quick curing adhesives known to be stable in CMP environments. The function of the retaining ring is to keep the wafer from slipping laterally as polishing proceeds as well as to achieve a more uniform removal rate, especially at the wafer periphery, by extending the polishing interface to the outside of the substrate. Slanting grooves may be made in the surface of the retaining ring facing the polishing pad to moderate slurry flow as it approaches the wafer.

A Problem Solved

[0010] Since most of slurry used in a polishing process may be thermally activated, the temperature distribution of the wafer affects the removal rate across the surface of the wafer non-uniformly. It has been observed that as wafer size and consequently retaining ring size in CMP increase, the temperature distribution about the ring becomes increasingly uneven with a particular running hot spot at a position on the leading edge of the retaining ring surface facing the wafer at commonly used rotation rates of 30 to 60 RPM¹. The largest temperature increase occurs on the part of retaining ring near the polishing pad center where cooling by fresh slurry is minimal. In general, the retaining ring exhibits a higher temperature than the polished wafer partly due to the pressure and the coefficient of friction, which are larger for retaining ring (made for example from PEEK) than for the wafer. At the periphery of the wafer, there is a suggestion of wafer edge heating due to heat transfer from the ring. The effect is observed to increase as the size of wafers increases, and is predicted to increase further with further increases in wafer size and exerts a significant effect on the thermally sensitive reaction rate of the slurry as it acts upon the wafer adjacent to the hot spot. Since this is at the periphery of the wafer, the result is a non-uniformity in polishing rate between the center and periphery of the wafer that increases with increasing wafer and retaining ring size. Non-uniformity in polishing rate in turn renders increasingly large areas of the polished wafer unusable which is a considerable waste of materials and expense.

[001 1] The appearance of a higher temperature area or hot spot on the retaining ring is a transient phenomenon. The retaining ring is hotter on the surface of the part nearest the polishing pad center and on the leading edge from the standpoint of polishing pad rotation than parts nearer the pad edge. Secondly, there is also a temperature gradient corresponding to inner vs. outer edges of the retaining ring itself. The effect appears to be related in large part to the thermal conductivity of the materials, PEEK in particular, used to make the retaining ring or, in composite rings, the part of the retaining ring contacting the polishing pad. However, the flexibility, wear properties and durability of PEEK and other suitable retaining ring materials are all optimal for retaining ring construction and use and so a solution to the problem of hot spots where these materials may continue to be used in retaining ring construction is desired.

Summary of the Invention

[0012] The inventors of the present invention, in order to overcome the problems of the prior art, specifically the appearance of a temperature differential or hot spot in the retaining ring during CMP that results increasingly in wafer non-uniformity as the size of the wafer and retaining ring increase, while seeking at the same time to retain both convenience and cost effectiveness in the manufacture and use of retaining rings, engaged in various studies and

' Solid State Technology, December 2009, p. 13 Figure 3. incorporated by reference and

made a part hereof research and as a result of extensive, careful and detailed study of the problem have conceived and developed the present invention.

How the Present Invention Overcomes Problems of the Prior Art

[0013] The present invention comprises a retaining ring for the wafer in chemical mechanical polishing that distributes heat evenly by a heat transfer means embedded within or on the retaining ring or attached to the lower surface of the retaining ring that reduces the difference in the temperature about different points of the lower surface of the retaining ring in contact with the polishing pad to approach and ideally achieve uniform temperature on the retaining ring surface facing the polishing pad during chemical mechanical polishing. The present invention further relates to a method of chemical mechanical polishing using a retaining ring in which a heat transfer means is embedded within or on the retaining ring or attached to the lower surface of the retaining ring that reduces the difference in temperature about different points of the lower surface of the retaining ring in contact with the polishing pad to approach and ideally achieve uniform temperature on the retaining ring surface facing the polishing pad during chemical mechanical polishing.

[0014] The invention operates by allowing accelerated dissipation of heat from the structural material of the retaining ring in contact with the slurry and polishing pad into a material with substantially greater heat transfer properties that distributes the heat rapidly to cooler areas of the ring. The heat, thus dissipated, is no longer, as a practical matter, sufficient to raise the temperature of the structural material of the retaining ring locally and thereby influence negatively the removal rate at the periphery of the wafer.

Brief Description of the Drawings

[0015] Figure 1 is a top view cross section of the flexible lower portion of the three layer retaining ring of the present invention.

[0016] Figure 2 is a lateral cross sectional view of the flexible lower portion of the three layer retaining ring of the present invention.

[0017] Figure 3 is a lateral cross sectional view of the three layer retaining ring and wafer attached to the polishing head with a circulation pump attached to the retaining ring of the present invention. [0018] Figure 4 is a lateral cross sectional view of the two layer retaining ring of the present invention.

[0019] Figure 5 is a lateral cross sectional view of the one layer retaining ring of the present invention in the embodiment where the channel or chamber is in the retaining ring itself.

[0020] Figure 6 is a lateral cross sectional view of the one layer retaining ring of the present invention in the embodiment where the channel or chamber is in the polishing head.

Detailed Description of the Invention

[0021] The apparati and methods of the present invention have 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 wafer non-uniformity (WIW U) in the wafer due to the generation of localized temperature differences or hot spots in the retaining ring during CMP. Thus it is an overall objective of the present invention to provide an apparatus and method for CMP that achieves significant reduction in the said hots spots and consequently in the level of non-uniformity of the semiconductor wafer and of the inconvenience, inefficiency and process waste to the CMP process due to the generation of such localized temperature differences in the retaining ring during CMP.

[0022] The purpose of the apparatus and method of the present invention is to allow the consistent and efficient production of a significantly higher quality of semiconductor wafer product for lower cost.

[0023] Through application of the apparatus and method of the present invention, the consistent and efficient production of a significantly higher quality of semiconductor wafer product with lower expense or difficulty of operation of the CMP process is achieved.

[0024] All dimensions in the present 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 temperatures, effects or damage, and rates of rotation and the like.

[0025] The retaining ring of the present invention is not particularly limited. Any retaining ring commercially available for use in CMP may be used in the present invention, and new rings may be designed and prepared either for existing CMP tools or for CMP tools designed to polish larger wafer sizes than are currently polished in industry may be used as the retaining ring of the present invention whether of unified or composite construction.

[0026] It is being the case that retaining rings of the existing art are very often constructed of two or more parts: the part nearest the wafer being a consumable part made of PEEK, polyacetal or polycarbonate resin or other suitable retaining ring materials and the upper part being a structurally more durable layer that is typically bolted to the CMP tool, although many other methods of attachment including, but not limited to, magnetic, and adhesive attachment are known to the art and many are currently in use. The following description of the emplacement of the heat exchanging means of the present invention refers to emplacement in the said consumable portion of the retaining ring. By analogy where the ring is a single component ring attached directly to the polishing head and is therefore entirely "consumable" the following structures or similar structures may be prepared therein accordingly. Suitable structures for practicing the present invention achievable in the non- consumable portion of a composite ring will be discussed in a subsequent section below.

[0027] The heat exchanging means of the present invention, is not particularly limited and any heat exchange means compatible with CMP and the dimensions of the retaining ring may be used, however, heat conduction or heat convection means that transfer heat at a rate substantially greater than the material in which they are placed are preferred. In particular, as the heat conduction means of the present invention, strips or wires of highly conductive metals, such as copper, silver or aluminium, or alloys or other suitable materials may be used, and strips of copper are preferred. The dimensions of the strip of conductive material are not particularly limited. In particular, the width of the strip is not particularly limited, however a strip, the width of which is between half and nine tenths of the width of the retaining ring surface that contacts the polishing pad is preferred. The thickness of the strip is also not particularly limited; however a thickness sufficient to conduct heat at a rate adequate to significantly reduce or prevent the formation of a hot spot on the surface of the retaining ring is necessary. A thickness of between 1/16^th inch and 1/2 ^ inch is preferred and a thickness of between 1 /8 and 3/8 inch is more preferred. The strip may be continuous or discontinous but a strip continuous about the entire circumference of the retaining ring of the present invention is preferred. The dimensions of the strip may be uniform throughout the circumference of the ring or they may vary, however, dimensions uniform throughout the circumference of the strip are preferred. Though the orientation of the strip to the surface of the retaining ring facing the polishing pad is not particularly limited, a parallel orientation of the upper and lower surfaces with the said contact surface of the retaining ring is preferred.

[0028] The wires used as the heat conducting means of the present invention are not particularly limited, however, they may be made from the same materials as used in the strips of the present invention and like the said strips should be continuous around the circumference of the retaining ring. The size of the wires is not particularly limited, and wires having a diameter of between l/64^th of an inch and l/8^th of an inch are preferred. Wires of a larger diameter may be run parallel around the circumference of the retaining ring where more than one wire are used. They may be embedded at any vertical distance relative to the surface of the retaining ring facing the polishing pad but it is preferred that they be in a plane parallel to the surface of the retaining ring facing the polishing pad. The number of wires is not particularly limited and one or more wires may be used. The smaller the diameter of the wires, larger numbers of wires are preferred. The dimensions of space within the retaining ring occupied by the wires are not particularly limited and may be the same or similar to the dimensions of the space occupied by the metal strips of the present invention. When larger numbers of smaller diameter wires are used they may be used in the form of mesh, netting, or a bundle or bundles to optimize heat conductivity.

[0029] The strip or wire of the present invention are embedded or placed in a chamber or chambers on or in the retaining ring of the present invention sufficiently spacious to contain them. The chamber or chambers of the present invention is not limited in shape but a chamber or chambers that run around the circumference of the retaining ring at a constant inner and outer diameter are preferred. The chamber or chambers may be prepared by any suitable means, however, molding or stamping them into the ring at the time of the manufacture of the ring or placement in the retaining ring by machining or cutting are preferred. To maintain the structural integrity of the retaining ring after incorporation of the said chamber, the strips or wires of the present invention should be covered by a layer of the same material as the surface of the retaining ring is made of. This material should then be secured either in the construction of the retaining ring and this material may be further secured by molding or sealing or by other suitable means such as adhesive. Where the strip or wires are not embedded during the molding of the retaining ring itself, they may be secured in the channel or chamber prepared for them by adhesive, conductive paste or thermosetting resin. Although, it is not required, however, it is preferable that the area proximate to the strip or wires of the present invention that is to be closed be composed of the same materials as the consumable part of the ring itself,

[0030] The depth of the strip or wires of the present invention behind the surface of the present invention is not particularly limited; however the depth should not be so small that the said strip or wires become easily exposed during use of the retaining ring or so small that the structural integrity of the retaining ring and hence its performance are in any way impaired nor so great that heat exchange with the surface becomes impractical. In rings with no surface grooves, although the depth is not particularly limited and should depend upon the strength of the retaining ring material and the structure of the ring, the depth of the said strip or wire is preferably least 1 /16* inch and more preferably l/8^th inch behind the surface of the retaining ring facing the polishing pads. In grooved retaining rings, the depth of the strip or wires of the present invention, though not particularly limited, is preferably at least 1/16^th inch below the surface of the deepest groove.

[0031] Although less effective than an actual conductive strip, a channel or chamber satisfying the aforestated limitations and filled with commercially available thermally conductive paste or its equivalent may be used as the heat exchanging means of the present invention.

[0032] Alternatively, the heat exchanging means of the present invention may be a fluid comprising a liquid or a gas emplaced within a channel or chamber about the circumference of the retaining ring. The gas of the present invention could be any available chemically inert gas such as air or nitrogen. Though either liquid or gas may be utilized, a liquid is preferred because liquids tend to have much greater heat capacity and therefore effectiveness in stabilizing the temperature around the retaining ring and eliminating or reducing hot spots during CMP operation. Conversely, the greater ability of a chilled gas to flow more quickly through a narrow channel or chamber may be more suitable in some applications. Although the liquid of the present invention is not particularly limited, preferably, the liquid of the present invention is any safe and chemically stable liquid capable of reasonably efficient heat transfer. For example, Water, aqueous solutions of organic or inorganic salts (brines), non volatile organic or inorganic solvents or mercury may be used as the liquid heat exchanging means of the present invention. However, mercury raises certain volatility and safety concerns as do most organic and non-aqueous inorganic solvents. Unless the circulation system that conducts these liquids is entirely sealed and there is no danger of an elevated pressure induced rupture of the channel or chamber during operation, water or aqueous solutions of salts are preferred and water is more preferred.

[0033] The means of circulation of the gas or liquid heat exchange means of the present invention may be either neglected, relying on natural convection in the case of gasses, or forced by the acceleration resulting from the rotation of the ring in the case of liquids, or, in the case of either gases or liquids, by the use of a pump or other high pressure source. In the case of gases, given the low likely rates of natural heat exchange or flow induced by acceleration, pumping is clearly preferred. Pumping may be either closed circuit or open circuit but since the maintenance of a consistent temperature about the ring is preferred, closed circuit pumping of the gas of the present invention is preferred. The gas may be at atmospheric or elevated pressure but elevated pressures may create problems of ease of application so to the extent effective results may be obtained for a particular gas, a pressure at or near atmospheric pressure is preferred.

[0034] Where the heat conduction means is a liquid such as water or mercury, the acceleration of the rotation of the retaining ring may be used to force the circulation of the said liquid through the channel or chamber around the retaining ring of the present invention. Since mercury has a much greater density than water and is not easily pumped, and given safety concerns, this method is preferred for mercury circulated in a closed system. Any metallic alloy that is stable and a liquid at temperatures used in CMP operation may be used in place of mercury. However, because water has a substantially lower density and heat conductivity than mercury and the rotation rate of the retaining ring is not so large - between 30 and 60 rpm - pumping is preferred for water and aqueous solutions of salts (brines).

[0035] Where mercury is the liquid heat transfer means of the present invention, the closed system used to contain the mercury is not particularly limited, provided, however, that it is chemically stable with respect to mercury and not permeable thereto and is mechanically sound under CMP wafer rotation operation conditions. Glass is preferred, however, whatever material is chosen should additionally itself have a high heat conductivity to allow heat to pass from the retaining ring material to the said liquid rapidly. This closed system would typically consist of a closed loop of tubing, made of such material placed in a channel, or multiple loops place in a large chamber or multiple channels running concentrically around the circumference of the ring. The positioning of the loop or loops and the emplacement and fixation within the material of the retaining ring would be carried out in the same manner as was the case for wires stated above. The desirable aspect of this system is the high mobility of mercury which would transfer the heat absorbed much more quickly than the stationary strip. The less preferred aspects of this embodiment are that the system necessary to contain the mercury would impede the transfer of heat, and mercury and the system to contain it would be relatively expensive to be adding to a consumable piece of equipment. The amount of mercury envisioned in this embodiment would be somewhat less than sufficient to fill the channel or system for holding it but would more likely be merely a slug that would travel rapidly around the circumference of the ring absorbing and radiating heat in turn. In the case of a non-continuous slug of mercury however, it would be desirable to adjust the rate of rotation to optimize the equilibration of the temperature. However, this would restrict the ability of the operator to vary the rotation rate of the polishing head which could have other implications for production. For that reason, a continuous slug of mercury, where feasible, in spite of safety and cost concerns is preferred. It may be that embodiments using mercury utilize a very thin consumable part and with the part attached to the polishing head containing the mercury and its containment system. In this case the amount of mercury use could be larger and more suitable materials such as metals could be used in the part of the mercury containment system used to transfer heat from the part of the retaining ring facing the polishing pad.

[0036] Where the liquid heat exchanging means of the present invention is water, an acceleration powered passive circulation may be used. In this case, there is no need for a separate closed system to contain the water. The water may be placed directly into the channel or chamber prepared within the retaining ring. Moreover, in contrast to the mercury, though the amount of water or brine placed in the channel is not particularly limited, the channel or chamber may be filled or nearly filled to maximize the benefit of the heat exchanging properties and circulation of the water or brine. The size of the channel may likewise be large enough to maximize the amount of water present provided that the structural integrity of the retaining ring is maintained. The dimensions for water channels of the present invention where acceleration powers the movement of the water are not particularly limited but the depth should be as reported above for the depth of the channel prepared for the strip of the present invention and the width of the channel should be between about ¼ inch to about 80 percent of the width of the retaining ring and 2/3 the thickness between the surface of the retaining ring facing the polishing pad or the bottom of the groove in that surface, where the surface is grooved, and the top surface of the retaining ring or the retaining ring consumable portion attached to the structurally stable non-consumable portion of the retaining ring or the polishing head as the case may be.

[0037] Since water requires no special containment system, the above embodiment is relatively cost effective. The consumable portion of the ring may easily be disposed of when worn and consumed sufficiently through use in CMP.

[0038] Because water has a lower density than mercury, there may be difficulties depending upon the temperature generated at the leading edge of the ring in equalizing the temperature around the ring at the velocity generated by simple acceleration. For this reasona preferred embodiment of the present invention is that in which the channel or channels or chamber or chambers containing the water or brine heat exchanging means are connected to a circulatory pump that forces the water through the channel or chamber at an adequate velocity to equilibrate the temperature or reduce the variation thereof on the surface of the retaining ring facing the polishing pad during CMP operation. All other conditions may remain the same as when acceleration was used to force the movement of water through the channel or chambers provided, however, that the channel should be smaller to make better use of the pump in generating a suitable velocity, and in this case dimensions of between 1/5 inches and 2/5 inches by 2/5 inches and 3/5 inches are preferred with the depth behind the retaining ring surface facing the polishing pad being the same as for the other embodiments. The flow rate generated by the pump is not particularly limited, but a rate of at least 20 ml per minute is preferred a rate of at least 50 ml per minute is more preferred and a rate of 100 ml per minute is even more preferred.

[0039] The use of brine as the heat conduction means of the present invention is the same as the use of water except that brine may be considerably heavier than water and its heat conductivity and heat capacity may be slightly different. The practitioner of the present invention using a pump and brine thus has at least two ways of optimizing the effectiveness of the heat conduction means of the present invention: first by adjusting the pump flow rate and second by adjusting the brine concentration. [0040] The channel or chamber of the present invention is made in the dimensions specified above and may be made by molding the material of the retaining ring into an upper and lower half which, when placed together, form the consumable portion of the ring with the channel or chamber of the present invention between them. In the case of strips, wires, closed systems or acceleration driven water or brine systems this may be sufficient. The heat transfer medium or system is placed between the two halves of the retaining ring and the retaining ring is sealed together by suitable means such as heat fusion or adhesive with adhesive being preferred. The preferred adhesive is the quick setting super glue type adhesives used to hold the consumable portion of the ring to the non-consumable portion of the ring in the prior art.

[0041] In the alternative, sheets of the material from which the retaining ring is made may be cut into 3 rings having the diameter of the retaining ring desired and a channel may be cut top down partially into or entirely through the middle sheet to create the channel or chamber. A means of adding fluid or water and draining water and purging air may added through the middle layer. This fluid adding means may also have a means for sealing such as a screw sleeve into which screws or bolts may be added to seal the channel to the outside. In the alternative, where a circulation pump is used, the ingress and egress lines leading to the pump are machined through either the top face of the outer part of the middle layer, the inner face of the top layer or both. The size of these lines are not particularly limited, but a diameter of between 1/16^th and 3/8^th inch are preferred. A plastic tube adapter (90 degree elbow bend is preferred) may be placed in and fixed by adhesive to each line so that flexible pump lines may be attached during operation. In the case where a pump is used a small separation wall should bisect the chamber between ingress and egress lines so that water from the said lines is kept separate and the integrity of the channel maintained. This wall can be accomplished by leaving a wall crossing the channel between the ingress and egress lines during machining or later adding a wall and fixing it by means of adhesives or other suitable methods. Leaving a wall in the sheet or sheets when cutting the channel during machining is preferred. The thickness of the wall is not particularly limited but to minimize the thermally non-conductive effect of such a wall and the potential for a hot spot appearing there and defeating the aim of the invention, a thickness of ½ inch or less is preferred.

[0042] The advantage to machining all the way through the middle layer to prepare the channel is that the channel may then have a smooth roof and floor, consisting of the lower and upper surfaces of the upper and lower sheets respectively, conducive to less hindered more rapid circulation of the water or fluid of the present invention. Moreover, the fluid or water is thus closer to the surface from which heat must be conducted than it would be if the channel were not cut all the way through the middle layer. The advantage to only machining partly through the middle layer is better structural integrity of the resulting ring and less potential for leakage.

[0043] As to the thickness of the layers, though the thickness is not particularly limited, said thickness of the various layers may be equal and uniform at between 50 and 150 mils or one or more of the layers may have a different thickness. A system where the bottom layer - into which the grooves are to be cut - is about 200 mils and the remaining layers are about 100 mils each is preferred. Where a flat ungrooved surface is used for the bottom layer, a thinner bottom layer is preferred. The total thickness is not particularly limited and should be adjusted for optimal application the CMP tool used, however a thickness of between 200 and 600 mills is preferred, which includes the thickness of prior art retaining rings (consumable portion). The retaining ring is sealed with the adhesive of the present invention, and tests with colored fluids may be conducted to determine whether leaks are present or not. This would work both for systems using a gas or a liquid as heat transfer medium. Once the ring has been fabricated and leak tested it should be fixed to the more stable portion of the retaining ring by prior art methods such as adhesives and forced tightly against this portion to assure that there are minimal structural anomalies. Where an acceleration driven water or brine system is used, water or brine may be introduced and after all of the air is purged out the system may then be sealed and made ready for use. Where a pump driven gas or water brine system is used the tubes leading from the pumps may be attached to the attachments for ingress and egress of gas or fluid.

[0044] The pumps of the present invention are not particularly limited and any hydraulic or air pumps that can maintain sufficient pressure to force the gas or liquid of the present invention through the channels or chamber of the present invention at a pressure adequate to maintain a sufficient gas or liquid velocity to allow for heat exchange to occur at a rate sufficient to effectively reduce the difference in the temperature between different parts of the ring during CMP operation may be used. The size of the pumps of the present invention is not particularly limited but it is preferred that they be sufficiently small to be attachable to the polishing head and to rotate with the head without otherwise interfering with the CMP process. The cross-sectional area of the pump outlet is not particularly limited and may differ in size from the cross sectional area at the inlet of the channel or chamber of the present invention, however pumps having an outlet cross sectional area that are between 50% larger or smaller than cross sectional area of the channel or chamber inlet of the present invention are preferred and pumps having an outlet cross sectional area the same as the cross sectional area of the channel or chamber inlet of the present invention are more preferred. Pumps, the output flow rate of which may be adjusted at the operator's discretion, are preferred.

[0045] The output of the hydraulic pump of the present invention is not particularly limited, however, a pump that is capable of inducing a minimum flow of 1 ml per second over the course of the channel or chamber is preferred, a pump that is capable of maintaining a minimum flow of 5 ml per second over the course of the channel or chamber is more preferred and a pump that is capable of maintaining a minimum flow of 10 ml per second over the course of the channel or chamber is even more preferred.

[0046] The output of the air or gas pump of the present invention is not particularly limited, however, a pump that is capable of inducing a minimum flow of 5 ml per second over the course of the channel or chamber is preferred, a pump that is capable of maintaining a minimum flow of 10 ml per second over the course of the channel or chamber is more preferred and a pump that is capable of maintaining a minimum flow of 20 ml per second over the course of the channel or chamber is even more preferred.

[0047] The means used to connect the pump of the present invention to the channel or chamber of the present invention is not particularly limited, however, tygon tubing or other plastic tubing may be used and aluminium or other metallic tubing or the like may also be used. In any case, the material should be low friction and should be sufficiently durable to withstand the pressures used in the channel or chamber of the present invention without leaking.

[0048] The point of contact between the pump connecting means and the channel or chamber of the present invention depends upon the particular embodiment and is not particularly limited. Where the embodiment comprises a single component ring and the channel or chamber is embedded in the contact surface of the polishing head, the said tube may be connected to a tube connector plated in a hole leading through the polishing head into the channel or chamber of the present invention. In this case, the said tube connector may be sealed with adhesive or other suitable substance to the polishing head. Alternatively, in this case or where the embodiment comprises a single component retaining ring bolted to a flat polishing head surface wherein the channel or chamber of the present invention is placed in the upper surface of the said retaining ring, the said point of contact may either comprise a side channel from the outside of the upper surface of the retaining ring to the channel or chamber of the present invention. This side channel may be equipped with a tube connector and may be sealed thereto as in the preceding embodiment. Alternatively the said side channel may be made in the same manner as in the proceeding embodiment, provided however that the said side channel bends or turns inside the polishing head to open into the top of the channel or chamber of the present invention.

[0049] In the multilayer retaining rings of the present invention, the side channel may be located so that it either traverses the layer in which the channel or chamber of the present invention is located or traverses the superseding layer and then bends and opens in the top of the said channel or chamber. In this case, the tube connector is equipped and sealed in the same manner as in the immediately preceding embodiment.

EXAMPLES

[0050] The invention having now been generally described, it may be more readily understood by reference to the following examples and figures which are included merely for purposes of illustration of certain aspects and embodiments of the present invention and are not to limit the invention.

Example 1. Three large sheets of Peek polymer 350mm X 350mm, two of 100 mil thickness and the third of 200 mil thickness are aligned, laid one atop the other, secured and cut together so that 3 rings of identical inner and outer diameter of 301mm and [350mm] are produced. Referring to Figures 1 and 2, the "upper" ring or top layer (32) having a 100 mil thickness and the bottom layer (40) having a 200 mil thickness are set aside and a ring of inner diameter 310 mm and [340mm] is cut from the middle layer (36) of 100 mil thickness to create two concentric rings, the smaller one having inner and outer diameters respectively of 301mm and 310mm and the larger one having inner and outer diameters of 340mm and [350mm] respectively. These are set aside and the bottom layer (40) is scored with grooves spaced 1 cm and 100 mil deep at 45 degrees angles to the radii of the retaining ring with the leading end of the groove (in the direction of the rotation of the retaining ring) on the outer edge of the retaining ring and the trailing end of the groove on the inner edge of the retaining ring (not shown). The two middle rings of the middle layer (36) are fixed to the bottom layer (40) by an acrylonitrile adhesive with the inner diameters of the smaller ring and the bottom layer (40) aligned and the outer diameters of the bottom layer (40) and the larger ring aligned. A PEEK dam approximately (22) 1 cm wide, 30m m long and 100 mil thick is fixed with adhesives to a point in the resulting channel (10).

[0051 ] On either side of the dam (22), the middle layer (36) and part of the bottom layer (40) are cut away to a width of about 150 mils and a depth of about 150 mils. Into these two channels (14) are fixed pumpline adapters (on one end these are tubes about 1/4 inch in diameter and on the other end these are flattened to about 150 mil thickness and 150 mill width) (26) and these are fixed with adhesives to the openings (14) in the bottom (40) and middle layers (36) in front of and trailing the dam (22).

[0052] Notches 50 mil deep corresponding to these cuts are prepared in the top layer (32) and the face with these notches is affixed with adhesives to the middle layer (36) so these notches match the position of the adapters (26) and the rings fit smoothly together. Cracks or holes between the tube adapters and the retaining ring material were filled with adhesive or a suitable filler. The top layer (32) is then affixed with adhesive to the middle layer (36) and rivets or bolts (not shown) may be affixed in recesses in the top (32) and bottom layers (40) through parts of the middle layer (36) other than the channel at intervals around the circumference of the rings to secure the layers.

[0053] Additional bolt fixtures or other suitable fixtures are prepared and placed in the portion of the ring not occupied by the channel (10) so that the ring may be affixed to the non-consumable portion (52) of a commercially available ring or to a CMP polisher polishing head (44) as the case may be.

[0054] The ring may then be affixed to the other non-consumable portion (52) of a ring on a CMP polisher polishing head or as the case may be to a polishing head directly by the aforesaid bolt or other suitable fixtures. In this case the ring was attached to the polishing head. Pump lines (18) were attached to the adapters so that the flow of water is against the direction of rotation of the retaining ring and the pump lines (18) are affixed on the other end to an LTC series 650 mL/pm liquid free flow pump (48) fixed by being bolted to the polishing head (44). Water was added through the pump until the channel (10), pump lines (18) and pump (48) are full and the pump (48) was started. A flow of about 10 ml/sec initially was used but this was adjusted upward as far was possible preserving the integrity of the seals of the channel.

[0055] Example 2

A retaining ring according to the present invention or the consumable portion thereof as the case may be is prepared according to Example 1 except that instead of 3 layers there are only 2 layers, the middle (36) and bottom layer (40) being combined into a layer 300 mils thick in this example, and the channel was cut 100 mils deep and about an inch wide around the center of this middle layer (36) and the inlet and outlet (14) are cut 150 mils deep and 150 mils wide in ahead of and behind the dam (22). Polishing of the surface was carried out to smoothen the bottom of the channel (10). The dam (22) was left in the matrix of the material when the channel (10) cut as opposed to being added as was the case in Example 1.

[0056] Example 3

As shown in Figure 4, a retaining ring according to the present invention or the consumable portion thereof was prepared based on Example 2 except that the channel (10), dam (22) and inlet and outlet (18) were heat pressed into the retaining ring. This could also have been the lower consumable part of the ring as the case may be.

[0057] Example 4

A retaining ring and CMP tool according to the present invention wherein the ring is a standard retaining ring that does not possess the channel for holding the heat exchanging means of the present invention affixed in any suitable way to the polishing head (44) and the channel (10), dam (22), inlets and outlets (18) of the present invention prepared by modification of the polishing head (44) contacting the retaining ring either as part of a template addition or as part of the original CMP tool as shown in Figure 5

[0058] Example 5

A retaining ring prepared according to any of the preceding examples where instead of water, air or nitrogen are used as the head exchange medium. In this case a correspondingly higher flow rate for the heat exchanging means than is used with a liquid was used. Moreover, instead of a water pump, a Parker BTC miniature diaphragm air pump with a brushless motor was affixed to the polishing head and utilized to supply the gas pressure.

[0059] Example 6

A retaining ring prepared according to any of the previous examples where instead of a fluid, a series of bundles of copper wires of 20 gauge with 50 wires to a bundle filling the channel (10). More than 80% of the space of the channel was occupied by the said bundles. The bundles were embedded in conductive paste. In this case obviously the pump (48), pump lines (48), dam (22), inlet and outlet (18) of the present invention were unnecessary and the channel was closed.

[0060] Example 7

A retaining ring or polishing head (44) as the case may be prepared according to any of the previous examples except that it was not quipped with a pump (48) or dam (22), and where the channel (10) was filled to 80% with water and the acceleration force due to the rotation of the ring and inertial effects was relied upon to generate fluid circulation around the channel (10).

[006\]Figure 1 is a top view cross section of the flexible lower portion of the three layer retaining ring embodiment of the present invention, wherein 10 is the channel or chamber, 14 is the pump inlet or outlet fixture, 18 are the pump lines, 22 is the dam, and 26 are the openings/adapter to the channel or chamber.

[0062] Figure 2 is a lateral cross sectional view of the flexible lower portion of the three layer retaining ring embodiment of the present invention, wherein 32 is the top layer, 36 is the middle layer, and 40 is the bottom layer.

[0063] Figure 3 is a lateral view of the three layer retaining ring embodiment of the present invention and the wafer attached to the polishing head with a circulating pump attached to the retaining ring of the present invention wherein 44 is the polishing head, 48 is the pump, 52 is the non consumable portion of the ring, 56 is the adhesive backing paper for the wafer and 60 is the wafer.

[0064] Figure 4 is a lateral cross sectional view of the two layer retaining ring embodiment of the present invention. [0065] Figure 5 is a lateral cross sectional view of the one layer retaining ring embodiment of the present invention in the embodiment where the channel or chamber is in the retaining ring itself.

[0066] Figure 6 is a lateral cross sectional view of the one layer retaining ring embodiment of the present invention where the channel or chamber is in the polishing head.

EFFECTS OF THE INVENTION

[0067] The present invention is a retaining ring for the polishing head in chemical mechanical polishing and a method for using the same that distributes heat in the said retaining ring evenly by a heat exchanger means embedded within or on the lower surface of the ring that induces the temperature about different points of the lower surface of the ring in contact with the polishing pad to remain uniform during chemical mechanical polishing. By maintaining a more even temperature distribution about the ring, the present invention is capable of substantially improving the uniformity of cutting in CMP.

Claims

CLAIMS What is claimed is:

1. A retaining ring for chemical mechanical polishing that reduces differences in temperature over its surface in contact with the polishing pad by a heat exchanging means contained within it.

2. A retaining ring for chemical mechanical polishing according to claim 1 wherein the heat exchanging means is a channel or chamber within the ring around its circumference in which a heat exchange medium conducts heat from areas of relatively high temperature to areas of relatively low temperature.

3. A retaining ring for chemical mechanical polishing according to claim 2 wherein the said heat exchange means is a mesh or bundle of wires comprising a heat conducting substance.

4. A retaining ring for chemical mechanical polishing according to claim 3 wherein the said heat conducting substance is a metal.

5. A retaining ring for chemical mechanical polishing according to claim 4 wherein the metal is copper or aluminium.

6. A retaining ring for chemical mechanical polishing according to claim 3 wherein the heat exchanging means is embedded in a channel in a conductive paste.

7. A retaining ring for chemical mechanical polishing according to claim 2 wherein the heat exchange means is conductive paste.

8. A retaining ring for chemical mechanical polishing according to claim 2 wherein the channel or chamber is filled with a fluid as the heat exchange means.

9. A retaining ring for chemical mechanical polishing according to claim 8 wherein the said fluid is a gas.

10. A retaining ring for chemical mechanical polishing according to claim 9 wherein the said gas is forced through the chamber or channel.

1 1. A retaining ring for chemical mechanical polishing according to claim 10 wherein the means for forcing the gas through the chamber or channel is a pump.

12. A retaining ring for chemical mechanical polishing according to claim 9 wherein the said gas is air or nitrogen.

13. A retaining ring for chemical mechanical polishing according to claim 8 wherein the said fluid is a liquid.

14. A retaining ring for chemical mechanical polishing according to claim 13 wherein the liquid is forced through the chamber or channel.

15. A retaining ring for chemical mechanical polishing according to claim 14 wherein the means for forcing the liquid through the channel or chamber is a pump.

16. A retaining ring for chemical mechanical polishing according to claim 13 wherein the said liquid is water.

17. A retaining ring for chemical mechanical polishing according to claim 13 wherein the liquid is not forced to move through the chamber or channel by artificial means.

18. A retaining ring for chemical mechanical polishing according to claim 1 comprising a single layer equipped with a chamber or channel in which a heat exchange means has been placed.

19. A retaining ring for chemical mechanical polishing according to claim 1 comprising multiple layers with a chamber or channel in which a heat exchange medium has been placed.

20. A retaining ring for chemical mechanical polishing according to claim 19 comprising a single non-consumable layer and one or more consumable layers.

21. A retaining ring for chemical mechanical polishing according to claim 19 wherein the channel is wholly or partially in the non-consumable layer or the polishing head.

22. A retaining ring for chemical mechanical polishing according to claim 19 wherein the channel is in the consumable layers.

23. A retaining ring for chemical mechanical polishing according to claim 18 wherein the chamber or channel is partially in the polishing head

24. A retaining ring for chemical polishing according to claim 18 wherein the chamber or channel is within the polishing head but all or part of the bottom surface of which comprises the retaining ring.

25. A retaining ring for chemical mechanical polishing according to claim 20 wherein the number of layers in the consumable part of the retaining ring is 3.

26. A retaining ring for chemical mechanical polishing according to claim 20 wherein the number of layers in the consumable part of the retaining ring is 2.

27. A retaining ring for chemical mechanical polishing according to claim 20 wherein the number of layers in the consumable part of the retaining ring is 1.

28. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing that reduces differences in temperature over its surface in contact with the polishing pad by a heat exchanging means contained within it.

29. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 28 wherein the heat exchanging means is a channel or chamber within the ring around its circumference in which a heat exchange medium conducts heat from areas of relatively high temperature to areas of relatively low temperature.

30. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 29 wherein the said heat exchange means is a mesh or bundle of wires comprising a heat conducting substance.

31. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 30 wherein the said heat conducting substance is a metal.

32. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 31 wherein the metal is copper or aluminium.

33. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 30 wherein the heat exchanging means is embedded in a channel in a conductive paste.

34. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 29 wherein the heat exchange means is conductive paste.

35. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 29 wherein the channel or chamber is filled with a fluid as the heat exchange means.

36. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 35 wherein the said fluid is a gas.

37. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 36 wherein the said gas is forced through the chamber or channel.

38. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 37 wherein the means for forcing the gas through the chamber or channel is a pump.

39. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 36 wherein the said gas is air or nitrogen.

40. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 35 wherein the said fluid is a liquid.

41. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 40 wherein the liquid is forced through the chamber or channel.

42. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 41 wherein the means for forcing the liquid through the channel or chamber is a pump.

43. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 40 wherein the said liquid is water.

44. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 40 wherein the liquid is not forced to move through the chamber or channel by artificial means.

45. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 28 comprising a single layer equipped with a chamber or channel in which a heat exchange means has been placed.

46. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 28 comprising multiple layers with a chamber or channel in which a heat exchange medium has been placed.

47. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 46 comprising a single non-consumable layer and one or more consumable layers.

48. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 46 wherein the channel is partially in the non-consumable layer or the polishing head.

49. A method for chemical mechanical polishing using a retaining ring for chemical polishing according to claim 46 wherein the chamber or channel is within the polishing head but all or part of the bottom surface of which comprises the retaining ring

50. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 48 wherein the chamber or channel is in the consumable layers.

51. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 46 wherein the chamber or channel is wholly or partially in the polishing head.

52. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 48 wherein the number of layers in the consumable part of the retaining ring is 3.

53. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 48 wherein the number of layers in the consumable part of the retaining ring is 2.

54. A method for chemical mechanical polishing using a retaining ring for chemical mechanical polishing according to claim 48 wherein the number of layers in the consumable part of the retaining ring is 1.