PHILIPOSSIAN, Ara (2550 East River Road, Tucson, AZ, 85178, US)
SAMPURNO, Yasa (8476 N. Moonfire Drive, Tucson, AZ, 85743, US)
PHILIPOSSIAN, Ara (2550 East River Road, Tucson, AZ, 85178, US)
| What is claimed is: 1. An apparatus comprising a series of projections at intervals corresponding to the width between grooves in CMP polishing pads having concentric grooves, said projections being the width and depth of the grooves or less joined on a structure that swerves as a support and spacer for the projections, said structure in turn attached to the frame of the CMP polisher by appropriate structural support means0 2. An apparatus according to claim 1 comprising a series of projections or brushes set in or on a sheet or shape suspended above the polishing pad in CMP positioned so that they enter the grooves in the said polishing pad and during operation of CMP expel spent slurry from the grooves. 3. An apparatus according to claim 1 wherein the body of the device is a sheet. 4. An apparatus according to claim 1 wherein the body of the device is a geometric shape. 5. An apparatus according to claim 1 wherein the material from which the projections are made are selected from among peek, polycarbonate, polyamide and polyacetal. 6. An apparatus according to claim 1 wherein the projections comprise one or more brush bristles or filaments. 7. An apparatus according to claim 6 wherein the said apparatus is used in tandem with a slurry injector. 8. A method for removing spent slurry from the grooves of a polishing pad during CMP using an apparatus comprising a series of projections at intervals corresponding to the width between grooves in CMP polishing pads having concentric grooves, said projections being the width and depth of the grooves or less joined on a structure that swerves as a support and spacer for the projections, said structure in turn attached to the frame of the CMP polisher by appropriate structural support means. 9. A method for removing spent slurry from the grooves of a polishing pad during CMP according to claim 8 wherein the said apparatus is used in tandem with a slurry injector. 10. An apparatus according to claim 1 wherein there is additionally a means of removing the said spent and contaminated slurry from the land areas of the pad as well as the grooves. 1 1. An apparatus according to Claim 10 wherein the said means of removing said spent slurry comprises a scraping edge, a scraper or a series of projections or bristles, significantly shorter than those entering the grooves. 12. An apparatus according to Claim 11 wherein the angle of the apparatus is such that motion of the polishing pad will induce spent slurry to move in an outward direction where it may be properly disposed of. 13. An apparatus according to claim 10 wherein the edge of the present invention has a clearance of 1mm or less. 14. An apparatus according to claim 10 wherein brush bristles may be used to provide spent slurry removal from the surface and grooves of such non-concentrically grooved polishing pads as an XY type polishing pad or a K type polishing pad. |
FIELD OF THE INVENTION
[0001] The present invention relates to an apparatus for cleaning spent slurry, pad debris, conditioner debris and any spent chemicals from surface and the grooves of a CMP polishing pad during CMP operation comprising a means of forcing the spent slurry and pad debris by a scraping or pushing means and a series of projections at intervals corresponding to the width between grooves, said projections being the width and depth of the grooves or less joined on a structure that swerves as a support and spacer for the projections, said structure in turn attached to the frame of the CMP polisher by appropriate structural support means. The present relates more specifically to an apparatus for cleaning the grooves of a CMP polishing pad during CMP operation comprising a series of projections at intervals corresponding to the width between grooves, said projections being the width and depth of the grooves or less joined on a structure that swerves as a support and spacer for the projections, said structure in turn attached to the front of a slurry injector so that it serves the purpose both of clearing old slurry from the grooves before the new slurry is injected and providing a guide to maintain the injector on a true course in regard to the grooves and lands on the CMP polishing pad between grooves.
BACKGROUND 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 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 polishing slurry containing chemistry 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 discs 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 disc 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 diminishing 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 head consists of the wafer and the apparatus for supporting and rotating the wafer, depends from a 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 wafer head itself is a structure attached to a shaft in the wafer head housing that depends from the apparatus and may be attached thereto by a bridge or platform that is typically part of the framework of the CMP polishing tool. The wafer 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 wafer 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 wafer head by means of a retaining ring with an inner diameter slightly larger than the outer diameter of the wafer. The leading surface of the retaining ring closest to the polishing pad is in very close to the same vertical position to and the surface is parallel with to the face of the wafer that contacts the polishing pad (the leading face of the wafer).
[0009] The function of the slurry is to deliver continuously the mechanical abrasive particles and chemical components to the surface of the wafer and to provide a means of removing reaction products and wafer debris from the polishing surface. There are several varieties of slurry of varying effectiveness and properties known to the art.
[0010] At present, for the most common type of CMP tool, the rotary polisher, slurry is applied at a constant flow rate onto the rotating polishing pad using a simple delivery tube, nozzle or spray bar. Fresh slurry flows away from the application point(s) under the influence of gravity and centripetal acceleration and becomes mixed with used slurry or slurry that has passed between the polishing pad and wafer and been involved in polishing.
[0011] Old slurry, besides being somewhat chemically "spent," additionally contains the debris from wafer, conditioner and pad which, if the old slurry re-enters the gap between the wafer and polishing pad, are exposed to the wafer surface and can lead to increases in contamination and increases in defectivity. It is therefore important to remove the debris of polishing, and by extension used slurry, from the polishing pad quickly after it is generated and to the greatest extent possible not reintroduce it under the wafer.
[0012] Eventually the rotation of the pad brings the slurry into contact with the leading edge of the wafer or the leading edge of a wafer retaining ring, where it forms a bow wave. Some of the fresh slurry at this point is advected into the narrow 10 to 25 micron gap between the wafer and polishing pad and is utilized for polishing. The gap exists because the surface of the pad is rough, the surface of the wafer is relatively smooth and the wafer contacts only the high points of the pad surface. However, most of the fresh slurry remains in the bow wave and is carried to the edge of the pad by the combined rotation of the polishing head and pad. The slurry is then lost over the edge of the pad. Thus, actual slurry utilization, the percentage of new slurry applied that enters the gap between the rough pad surface and the wafer of total slurry applied, is universally quite low in such rotary CMP tools. This is a significant problem because slurry consumption and waste disposal account for a large share of the cost of ownership and operation of a CMP tool.
[0013] An additional influence is exerted polishing removal rate from the wafer and uniformity arise because when wafers are polished it is the practice in the art to wash used slurry off of the CMP polishing pad between wafers by application of deionized water to the polishing pad, typically this water is added to the center of the pad. The time between removing one wafer and replacing it with a second is short and invariably a large quantity of water remains on the pad when polishing of the new wafer begins.
[0014] This water is not uniformly distributed and as a result it dilutes the newly added slurry in a non-uniform manner causing both a general decrease in removal rate by the diluted slurry and lack of uniformity in removal rate due to variations in slurry concentration on different parts of the pad. Since this effect lasts several seconds it can exert a significant negative effect on anywhere from 25 percent to 50 percent of the time during which the wafer is polished and this in turn can result in a significant and costly reduction in process effectiveness and product quality.
[0015] To facilitate the advection or entry of the slurry under the wafer, the practitioners of the prior art have used grooves in the CMP pad. This was effective in making sure that some slurry reached the pad-wafer interface but, unfortunately, still allowed most of the slurry to be cast off of the pad without ever having been used. Slurry is expensive and devices, equipment and procedures for providing and removing large amounts of slurry must be included in the CMP process which both complicates and encumbers that process.
[0016] Methods available for substantially reducing the amount of slurry used or making sure that most of the slurry introduced to the pad during CMP is actually introduced between the pad and the wafer and utilized as intended before being cast off of the pad solve these problems to date have, as stated above, consisted of placing grooves in the surface of the CMP pad to conduct some portion of the slurry under the wafer during CMP polishing have been introduced into the prior art. In U.S. Patent No. 5,216,843 (Breivogel et al filing date 24 September 1992)
(incorporated herein by reference) "an apparatus for polishing a thin film" ... "said apparatus comprising" ... "a pad covering said table, said pad having an upper surface into which have been formed a plurality of preformed grooves, said preformed grooves facilitating the polishing process by creating a corresponding plurality of point contacts at the pad substrate interface." and a "means for providing a plurality of micro channel grooves into said upper surface of said pad while polishing said substrate wherein said micro channel grooves aid in facilitating said polishing process by channelling said slurry between said substrate and said pad." Still in U.S. Patent No. 7, 175,510 (Skyopec et al. filing date 19 April 2005 incorporated herein by reference) a method of polishing wherein "The polishing pad has grooves that channels (sic) slurry between the wafer and polishing pad and rids excess material from the wafer, allowing an efficient polishing of the surface of the wafer." is described. Even as recently as Skyopec et al, the preferred method for maximizing the amount of slurry that was introduced between the pad and the wafer was preparation of the grooves in the polishing pad surface and the efforts of practitioners of the art were limited to ensuring that these "micro-channels" were regenerated or maintained in a suitable fashion.
[0017] In US-2007/0224920 (incorporated herein by reference) these grooves are enhanced by holes in the pad made in sizes and shapes appropriate to optimize the amount of slurry conducted under the wafer by the grooves. However this does not solve the basic problem of waste of new slurry due to slurry accumulation in the bow wave or the problem of consistent rate of removal polishing.
[0018] Moreover, Novellus Systems, Inc. has addressed the slurry utilization problem by means of orbital polishers (U.S. Patent No. 6,500,055 incorporated herein by reference) in which the slurry is injected through the polishing pad directly under the wafer (U.S. Patent No. 5,554,064 (incorporated herein by reference). This guarantees high slurry utilization but requires a complex platen and custom pad to accommodate the slurry distribution system and a specialized polishing tool to take advantage of the injection method. Similarly in US-2007/0281592 (incorporated herein by reference) slurries and other conditioning chemicals are introduced and removed through apertures in the diamond conditioning disk for the purpose of facilitating multistep CMP processes but this is not intended to and does not effectively improve the utilization of slurry by directing a larger fraction between the wafer and the CMP pad.
[0019) Also in the prior art are U.S. Patent No. 5,964,413, (incorporated herein by reference) which teaches an Apparatus for dispensing slurry. This is a device for spraying slurry on to the pad rather than pumping it in specific positions at the pad wafer interface.
[0020] In addition, U.S. Patent No. 6,929,533 (incorporated herein by reference), teaches methods for enhancing within-wafer CMP uniformity. This patent describes methods for enhancing the polish rate uniformity of rotary and linear polishers using slurry dispense bars with multiple nozzles to distribute the slurry over the entire wafer track. The slurry dispenser bars sit above the pad and do not contact it.
[0021] U.S. Patent No. 6,283,840 (incorporated herein by reference) teaches a cleaning and slurry distribution system assembly for use in chemical mechanical polishing apparatus. This apparatus has "an outlet to distribute slurry to the enclosed region to form a reservoir of slurry in the enclosed region, wherein the slurry is distributed to a region not enclosed by the retainer by travelling between the polishing surface and the lower surface of the retainer." However, the application of the slurry to specific land areas where it is needed is not taught and in fact most slurry is lost through grooves between the land areas which generally exceed the land areas in cross sectional area between the wafer and the polishing pad. This apparatus also fails to teach or accomplish control over flow as a function of radius from the center of the polishing pad and there is no teaching or reported effect of separation of the old spent slurry, dilution water or polishing wastes from the newly applied slurry whether in the grooves or on the land area of the polishing pad.
[0022] The main function that the apparatus accomplishes is to keep spray from the slurry or from cleaning agents from depositing on the polisher, where the residue can become a source of defect-causing contamination. This is mentioned several times in the description. The background mentions reducing slurry consumption in passing in the last paragraph, but the patent contains no teaching that the apparatus accomplishes this or indeed how it would be accomplished nor any discussion of slurry might be removed from the grooves in the polishing pad.
[0023] U.S. Patent No. 5,997,392, teaches a slurry injection technique for chemical-mechanical polishing. The slurry application method involves spraying the slurry onto the pad under pressure from a multiplicity of nozzles, however, this invention suffers from the same drawbacks as U.S. Patent No. 6,929,533 in that lack of precision in the placement and form of the slurry substantially decreases its effectiveness and no removal method for old slurry is contemplated either from grooves or lands other than what was already in existence.
[0024] U.S. Patent No. 3,342,652 (incorporated herein by reference) teaches a process for chemically polishing a semiconductor substrate and a slurry solution is applied to the surface of the pad in bursts as a stream forming a liquid layer between the cloth and the wafers to be polished. The solution is applied from a dispensing bottle and is applied tangentially to the wafer-plate assembly so as to provide maximum washing of the polishing cloth in order to remove waste etching products however there is no teaching as to how to obtain removal of spent slurry from the grooves in the polishing cloth where it may accumulate.
[0025] In U.S. Patent No. 6,284,092 (incorporated herein by reference), CMP teaches a slurry atomization slurry dispense system in which "... a polishing slurry dispenser device disposed to dispense the slurry toward the pad preferably as a stream or more preferably drops toward the pad surface and a curtain of air to intersect the slurry at or near the polishing pad surface. The wafer is polished using less slurry than a conventional polishing apparatus while still maintaining the polishing rates and polishing uniformity of the prior art polishing apparatus. A preferred dispenser is an elongated housing having a slurry tube and air tube therein each tube having a plurality of spaced apart slurry openings and air openings along its longitudinal axis which tube is preferably positioned radially over at least one-half the diameter of the polishing pad. Once again, however removal from the grooves of spent slurry is not addressed
[0026] A polishing slurry is directed from the slurry tube toward the surface of the pad, preferably in the form of drops, and the air from the air tube forms an air curtain, with the air curtain intersecting the slurry drops preferably at or slightly above the pad surface to atomize the slurry."
[0027] U.S. Patent No. 6,429,131 (incorporated herein by reference) concerns CMP cut rate uniformity and teaches improved CMP uniformity achieved by providing improved control of the slurry distribution. Improved slurry distribution is accomplished by, for example, the use of a slurry dispenser that dispenses slurry from a plurality of dispensing points. Providing a squeeze bar between the slurry dispenser and wafer to redistribute the slurry also improves the slurry distribution. This invention can distribute slurry evenly over the pad but does not provide a uniform layer of slurry the thickness of the gap or efficient removal of spent slurry from the grooves.
[0028] Finally in U.S. Patent Application No. 12/262,579 (Incorporated herein by reference) a method and device for injecting slurry between the wafer and the polishing pad comprising a solid crescent shaped injector the concave trailing edge of which is fitted to the size and shape of leading edge of the polishing head with a gap of between 0 and 1 inches, which rests on the pad with a light load, the bottom surface facing the pad, and through which CMP slurry or components thereof are introduced through one or more openings in the top of the injector and travel through a channel or reservoir the length of the device to the bottom where it or they exit multiple openings in the bottom of the injector and are, are spread into a thin film, and are introduced at the junction of the surface of the polishing pad and the wafer along the leading edge of the wafer in quantities small enough that all or most of the slurry is introduced between the wafer and the polishing pad. This solves the problem of introducing slurry that is relatively uncontaminated by spent slurry, excessive diluent water or polishing debris into the gap between the wafer and the pad but does not address the specific problem of removal of spent slurry and polishing debris that accumulates in the grooves during CMP operation.
[0029] Although the creation and maintenance of grooves and micro-channels are essential for the operation of CMP polishing, they still do not afford an efficient means of introduction of slurry between the pad and the wafer whereby most or even a substantial portion of the slurry introduced onto the pad is actually introduced between the pad and the wafer and as noted, they have the additional defect of allowing a significant accumulation of spent slurry and polishing debris during CMP operation which is difficult to remove and which detracts significantly from the improvements made in the prior art in application of slurry to the lands accurately between the wafer and the polishing pad. Most of the slurry that continues to accumulate in the grooves continues rotation after rotation to come into contact with the pad continuing to be the source of defectivity and un-uniformity in reaction rate at the wafer surface.
SUMMARY OF THE PRESENT INVENTION
[0030] The present invention relates to an apparatus for cleaning the grooves of a CMP polishing pad during CMP operation comprising a series of projections at intervals corresponding to the width between grooves, said projections being the width and depth of the grooves or less joined on a structure that swerves as a support and spacer for the projections, said structure in turn attached to the frame of the CMP polisher by appropriate structural support means and a method for using the same. The present relates more specifically to an apparatus for cleaning the grooves of a CMP polishing pad during CMP operation comprising a series of projections at intervals corresponding to the width between grooves, said projections being the width and depth of the grooves or less joined on a structure that swerves as a support and spacer for the projections, said structure in turn attached to the front of a slurry injector so that it serves the purpose both of clearing old slurry from the grooves before the new slurry is injected and providing a guide to maintain the injector on a true course in regard to the grooves and lands on the CMP polishing pad between grooves and a method for using the same. BRIEF DESCRIPTION OF THE DRAWINGS
[0031J FIG. 1 is frontal view of the apparatus of the present invention.
[0032] FIG. 2 is a cross section lateral view of the apparatus of the present invention.
[0033] FIG. 3 is an overview of the present invention used with a slurry injector
[0034] FIG. 4 is a side view of the present invention used with a slurry injector.
[0035] FIG. 5 is a drawing describing the determination of the appropriate distance between projections in a non-perpendicular application of the apparatus.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0036] The inventor of the present invention, seeking to solve the problem of the prior art whereby slurry accumulating in the grooves of the polishing pad during operation have has devised a method of removing slurry from the grooves in the said polishing pad by means of an apparatus comprising a series of projections at intervals corresponding to the width between grooves, said projections being the width and depth of the grooves or less joined on a structure that serves as a support and spacer for the projections, said structure in turn attached to the frame of the CMP polisher by appropriate structural support means and a method for using the same.
[0037] The apparatus and method of the present 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 slurry supply and removal systems for CMP tools. Thus, it is an overall objective of the present invention to provide spent CMP slurry and polishing debris removal methods that remedy the shortcomings of the prior art.
[0038] The purpose of this apparatus and method is to allow more effective removal of spent slurry and polishing debris from the grooves in the surface of the polishing pad. It is an additional purpose of this invention to remove or assist in the removal of spent slurry and polishing debris from the polishing pad more quickly so that it will not interfere with CMP or re-enter the grooves. CMP slurry should be fresh slurry so that it is more able to remove and planarize the metal surface of wafers for such semiconductor wafers as silicon wafers or silicon compound wafers that have been plated with copper or tungsten or other materials and thereafter to planarize the semiconductor surface itself. In principle when old slurry or water are allowed to mix with new slurry in large and uncontrolled amounts and much of this mixture is allowed to be disposed of from the polishing pad without ever having been used under the wafer, there is substantial waste of slurry.
[0039] Manufacturers and users of CMP pads need to minimize slurry waste not only from premature removal of unused fresh slurry but from contamination of much fresh slurry by admixture with residual spent slurry to obtain the most cost effective and high quality polishing of wafers and consequently to obtain as good a uniformity of removal rate across the wafer with as low a defectivity rate as is reasonably possible.
[0040] The present invention overcomes the problems of the prior art by selectively ejecting inaccessible but problematic used slurry from the grooves in the surface of the polishing pad where it may be swept away with other spent slurry in the bow wave before the leading edge of the wafer or a slurry injector, as the case may be, where much if not most of said spent slurry would be sloughed off of the edge of the polishing pad by centripetal forces without ever having been used and by ensuring that uncontaminated slurry is thus delivered to the wafer in quantities and locations along its leading edge that are conducive to uniform polishing of the wafer surface.
[0041] Through the use of the apparatus of the present invention, less contamination of fresh slurry, more effective and efficient use of fresh slurry and the greater uniformity of removal rate can be achieved easily with together with resulting improved polished wafer quality.
[0042] Another purpose of the apparatus and method of the present invention, at least in embodiments corresponding to polishing pads with relatively large concentric ring type grooves is to provide additional alignment for slurry injectors and similar devices where the sheet or shape of the present invention is attached to them. As long as the positions of the projections and the slurry outlets for the slurry injector are properly set with respect to one another so that the slurry outlets are between the projections, the projections will enter the grooves of such concentric ringed polishing pads holding the slurry outlets over the areas of the pad between the grooves, the "land" areas of the polishing pad, during CMP operation.
[0043] All dimensions for parts in the present invention follow are based on a pad 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.
[0044] Referring to Figures 1 and 2, The apparatus of the present invention comprises a structure, that is to say a sheet or a solid geometric structure or shape (10) that is attached either directly to the CMP tool by suitable connection means or indirectly through some other device such as a slurry injector. The shape of the structure (10) is not particularly limited and it may be a sheet or a block or other three dimensional shape but a rectilinear block or sheet is preferred and a sheet is more preferred. The bottom surface or edge (12) of the shape facing the polishing pad (14) and upon which the projections are located is not particularly limited, provided it must be linear in some orientation so that when the apparatus is in use it may be laid on top or suspended a short distance of between about l/64th inch and about 1/2 inch and more preferably about l/32nd inch and l/4th inch above the rotating CMP pad surface. The gap (16) between the said edge and surface (12) may vary throughout the length of the surface facing the polishing pad (14) but a uniform gap (16) distance is preferred.
[0045] The thickness of the sheet (10) of the present invention is not particularly limited, however a thickness of between l/16th inch and 1/2 inch is preferred and between l/16th and l/4th inch is more preferred. The thickness of the sheet may depend to some extent upon the material from which it is made with structurally more stable rigid materials usable in thinner sheets. The material from which the sheet of the present invention may be made is not particularly limited and metal, glass, ceramic or hard plastic sheets may all be used and hard plastic sheets are preferred. The said hard plastics used in the sheet of the present invention are not particularly limited but polycarbonate, acrylic and peek sheets may all be used and polycarbonate or peek sheets or reinforced compounds of the same are preferred. The sheet of the present invention may be reinforced by sheets of more durable material such as aluminium (24).
[0046] The height of the sheet of the present invention is not particularly limited but it should not be so great as to be unwieldy or interfere with the smooth operation of CMP and a dimension of 4 inches or less is preferred.
[0047] The preferred orientation of the sheet of the present invention is vertical, in which case the direction of the projections (18) of the present invention are substantially parallel to the plane of the sheet, but it may be any orientation that is permitted by the durability of the material of the sheet and a sheet the plane of which is parallel to the polishing pad may be used. Typically, when the sheet is vertical or at least not horizontal the projections (18) must be lined up along the edge of the sheet facing the polishing pad (14) but when the sheet is in a horizontal and parallel orientation with respect to the polishing pad (14), the projections (18), which in this case should be perpendicular to or very near to perpendicular to the surface of the sheet parallel to the polishing pad (14). In this case the sheet (10) should be thicker, preferably between l/4th and 1/2 inch to support provide proper support to the projections. In the case of a horizontal sheet, also, the gap (16) may be reduced so that the sheet in effect rides upon the polishing pad.
[0048] The sheet (10) in its vertical orientation may be entirely planar or it may be curved or contain one or more angles and of these non-planar orientations an evenly curved sheet is preferred. A curved sheet or otherwise non-linear sheet may be applicable to connection to another device such as an injector (34). Insofar as the sheet (10) is not horizontal, the projections (18) should be lined up along the edge or surface facing the polishing pad (12). Generally a vertical or a horizontal sheet are preferred to other angular orientations for the sake of facility of maintaining the position of the sheet (10) with respect to the polishing pad (14) and the width of the gap (16). [0049] Where the orientation of the sheet (10) is horizontal, there is no particular limitation as to the positioning of the projections (18) except that they may be so positioned as to fit within the grooves (20) when the apparatus is engaged and CMP is being carried out.
[0050J As shown in Figures 3 and 4, in the case where a shape other than a sheet (10) is involved, the conditions for positioning the shape with respect to the polishing pad (14) are essentially the same as for the sheet (10). There is no particular limitation on the size or shape of the shape provided that it should not be so large as to impede smooth operation of CMP or so heavy as to sag and cause the projections (18) to be forced further into the grooves (20) in the polishing pad (14) than intended. Typically on the shape of the apparatus of the present invention, the part of the shape closest to the polishing pad (18) will be either a flat surface or plane or an edge (12). The edge may be linear, curved or may correspond to the apex of a curved surface. If the former, the orientation and alignment of the projections (18) should correspond to the preferred orientation of projections for a horizontal sheet and if the latter then to the preferred orientations of projections for a vertical sheet. It is essential, however, that whatever the shape or the type of surface, the distance of the surface or edge of the shape at the point where the projections (18) are attached should maintain a constant gap (16) with the polishing pad (14).
[0051] The projections (18) of the present invention correspond in number and position to the grooves (20) of the polishing pad (14). These projections may be of the same material as the sheet (10) or shape or they may be of a different material. If they are of a different material from the sheet (10) or shape or are of the same material as the sheet or shape (10) but are attached they must be so securely fastened to the sheet or shape (10) and be able to bear the prolonged and repeated drag of contact with the polishing pad (14) under CMP operation conditions. Methods of attachment in this case are not limited but may include adhesives or incorporation into the sheet or shape during molding by such means as injection molding or the application of thermosetting resin and in this case incorporation during injection molding would be preferred, particularly for materials different from those used in the sheet or shape (10). Since considerable stress is involved it may be desirable to drill small holes into the sheet or shape (10) and add pegs, the externally exposed portions of which constitute the projections and secure these with adhesives or by melting under pressure (molding). Where the projections (18) are made from the same material and are part of the sheet or shape (10), they may be prepared either by molding of the sheet or shape or machining the sheet or shape or some combination of these methods.
[0052] Where the projection (18) is composed of a different material from the sheet or shape, the material used is not particularly limited provided that it should have at least the same durability as the materials used in the sheet or shape and metals, plastic or ceramic coated metals, ceramic, or engineering plastics such as peek, polycarbonate, polyamide and polyacetal, mixtures of the same or reinforced compounds of any of these may be used. The projections may also be of the same material either as a unit or added to the sheet or shape of the present invention but be coated with another material to impart properties such as durability or wettability or the like.
[0053] In the case where a sheet is used as the sheet or shape (10) of the present invention, the projections (18) may be prepared by carefully measuring the difference between grooves (20) and machining the space between them to the desired depth leaving projections (18) of the desired width and position. These may be then further shaped, buffed, coated or otherwise prepared.
[0054] The positioning of the projections (18) of the present invention is not particularly limited except that the distance between then must be such that they are able to fit within the grooves (20) of the particular polishing pad (14) being used for CMP. The simplest case is of a flat planar sheet placed perpendicular to the direction of motion of the polishing pad (14) at the point of contact. The distance between the centers of the projections (18) should be the radial distance between grooves along the same line. If the sheet or the line of projections (18) is not perpendicular to the direction of motion of the polishing pad (14) for all or part of its length, then the distance between two consecutive projections (18) in the chosen orientation is according to the following law of cosines formula:
2 2 2
A = ri + Γ2 - ri r 2 cosine Θ
As shown in Figure 5. where A is the distance between the two projections (18) being considered, Θ is the angle from the center of the polishing pad (18) between points where the two projections in question contact the polishing pad (14), the is the distance from the center of the polishing pad (14) to the inner of the two grooves occupied by one of the two projections in question and r 2 is the distance from the center of the polishing pad to the outer of the two grooves occupied by one of the two projections. This rule will also apply where the sheet (or line of projections) is not merely at a uniform angle but is curved or possesses some other nonlinear order but the calculation must then be made as between any two projections along the line of projections (18) on the sheet or shape (10) of the present invention. It is of critical importance that the correct distance between projections be determined. If the direction or angle of the line of projections is not radial, as long as the distance between projections is uniform, to some extent an adjustment can be made to fit the projections in the grooves by adjusting the angle of the line of projections. However, if the distance between the projections (18) is not entirely uniform, particularly where the sheet or shape (10) of the present invention has been curved, this is not possible and care must be taken to ensure that at whatever angle the sheet or shape (10) of the present invention is set to the radial direction from the center of the polishing pad (14), the distance between the projections (18) is such that when the apparatus is set in place, the projections will be in a position to enter the grooves (20) of the polishing pad. (14)
[0055] The number of projections (18) of the present invention is not particularly limited. It is preferred that the number of projections (20) equal the number of grooves (20) in the polishing pad (14). If there are fewer projections (18) than grooves (20), it is preferred that the projections (18) all contact grooves (20) that pass under the wafer (30) during CMP.
[0056] The lengths of the projections (18) of the present invention are not particularly limited. However, the projections (18) should neither be so short that they fail to remove a significant amount of spent slurry from the groove (20) nor so long that they drag on the polishing pad (14) causing damage, disruption of the motion of the polishing wheel or, where the apparatus of the present invention is attached to a slurry injector (34) or other CMP process device, the unwanted alteration of the position or function of the said injector (34) or other CMP device. A length of between 1/4 and 3/4 of the depth of the groove (20) in the polishing pad (14) is preferred and between 3/8 and 2/3 is more preferred.
[0057] The thickness of the projection (18) of the present invention is not particularly limited. At its thickest diameter the projection (18) of the present invention should be thick enough to support the projection along its remaining length but at the same time thin enough to avoid causing damage to the polishing pad (14), disruption of the motion of the polishing wheel or, where the apparatus of the present invention is attached to a slurry injector (34) or other CMP process device, the unwanted alteration of the position or function of the said injector (34) or other CMP device. A thickness of between 1/2 and 7/8 of the width of the groove (20) in the polishing pad (14) is preferred.
[0058] The shape of the projection (18) is not particularly limited and depends upon the dimensions of the groove in the polishing pad (14) and the properties of the material from which the projection is made. A conical or triangular projection (18) with the apex at just over half the deepest point in the groove (20) is preferred. Other shapes depending upon the workability and durability of the material include for example but without limitation, cones, cylinders, rods, or tabs, or convex lens shapes with the sides of the convex shape fore and aft to the direction of the rotation of the polishing pad (14), with or without rounded ends, though rounded ends are preferred, The front surface of the projection (18) may be flat or rounded and if flat or if rounded and convex may be set at a slight angle away from parallel with the direction of motion of the polishing pad (14) so as to prefer ejection of the slurry from the groove (20) in the direction of the edge of the polishing pad (14). [0059] The surface of the projection (18) may be rough or smooth and a smooth surface is preferred. The smooth surface can either be prepared by initially using materials with smooth surfaces or, where the surface is rough initially, by machining, polishing or buffing the projections to obtain a smooth surface without rough edges or sharp points that might cause damage to the polishing pad (14), disruption of the motion of the polishing wheel or, where the apparatus of the present invention is attached to a slurry injector or other CMP process device, the unwanted alteration of the position or function of the said injector or other CMP device.
[0060] The clearance or gap (16) of the sheet (10) or shape of the present invention from the polishing pad (14) is not particularly limited. However, the clearance should be at least as large as the gap between the pad and the wafer and preferably l/32nd inch or more above the surface of the polishing pad.
[0061] The means of attaching the sheet or shape of the present invention to the CMP tool are not particularly limited and for sheets or shapes used independently, an adjustable arm (22) from the CMP apparatus ending in a plate fixture (24) to which the sheet or shape (10) may be attached is preferred. The means of attachment of the sheet or shape (10) of the present invention to the adjustable arm is not particularly limited and sliding, snapping and bolt on or fastening means may all be used without limitation; however bolting (28) the upper part of the sheet or shape of the present invention to a plate (24) attached to the said adjustable arm is preferred. Additionally, by creating a slot (26) in the sheet or shape (10) so that the bolt (28) may be loosened and slid vertically it may be possible to more precisely position the sheet or shape above the polishing pad (14). In addition a suitable means of adjustment may be incorporated into the design or configuration of the adjustable arm (22) to which the said sheet or shape (10) is attached for both vertical and horizontal alignment with the concentric grooves (20) of the polishing pad (14).
[0062] Where the sheet or shape of the present invention is attached to a slurry injector (34) or other CMP device, the means of attachment is not particularly limited. However it may be bolted (28) or screwed on, snapped on by preparing mated structures (48) for that purpose on the slurry injector (34) or other device and the sheet (10) or shape of the present invention or by adhesive or the like and of these methods bolting is preferred.
[0063] The sheet (10) type apparatus of the present invention may be prepared by taking a sheet of the chosen material, cutting it in length and height to dimensions that correspond to the size of polishing pad (14) being used and at the same time will permit its use above a CMP polishing pad (14). In the case of a linear or flat sheet placed in the radial direction from the center of the polishing pad, the determination of the distance between central points of consecutive projections must be measured and the edge of the sheet to face the polishing pad machined to leave the projections. The projections are further carefully machined to obtain the desired length, thickness, shape and surface characteristics. The means of attachment is prepared and the apparatus is attached to a CMP tool with a polishing pad (14) on the platen. The polishing pad is rotated very slowly, perhaps 1 - 5 rpm, to allow confirmation that the projections fit within the grooves of the pad and will remain there throughout the rotation cycle.
[0064] Where a shape is used in place of a sheet or where the sheet is curved or at an angle with respect to the polishing pad (14) the positions of the projections (18) must be carefully determined and the projections (18) carefully prepared when machining them from the sheet or shape or attaching them. As a practical matter, where a shape (10) is used, attachment of projections may be preferred. Subsequently alteration of the shape and surface of the projections (18) may be then carried out. The same alignment test is applied here as for the sheet referred to earlier.
[0065] For polishing pads with very small concentric grooves of less than half a millimetre in width, it may be necessary to use projections comprising one or a very small number of bristles or filaments of a material sufficiently stiff to force the filament at least partially into the groove during CMP operation. The material that may be used for the bristles or filaments of the present invention is not particularly limited and, without limitation, natural or synthetic materials may be used but synthetic materials are preferred. The synthetic materials that may be used are not particularly limited but must be able to withstand the chemical environment of CMP operation and must at the same time maintain both adequate stiffness to enter the groove simultaneous with adequate durability and resistance to shear force to ensure prolonged use during CMP operation and bristles or filaments made of plastic resins are preferred. The type of plastic resin used in the bristles or filaments of the present invention is not particularly limited but nylons and polyester resins are preferred. Effectively this means of providing a groove cleaner also inherently provides the means for sweeping the spent slurry and debris from the surface of the polishing pad. This means may be entirely brush like or may be any suitable combination of brush like projections and solid scraper like structures that can effectively force the spent slurry and debris from the pad. This is particularly useful for polishing pads with X-Y configuration grooves and other non concentric forms. Given the importance of cleaning the grooves, at least a partial presence of brush like structures in the slurry removal means is preferred.
EMBODIMENTS
[0066] The following descriptions of specific embodiments of the present invention are for the purpose of clarification only and in no way limit the scope of the present invention.
EMBODIMENT FOR AMAT GROOVE POLISHING PAD 200MM WAFER: FREE [0067] A sheet of 0.093 inch thick Lexan® polycarbonate is cut in rectangular dimensions of 9 inches by 1.5 inch. Two vertical grooves 1/8* inch in width and 3/4 th inch in length are cut at 7.5 inches inches apart at equal distances from the center of the length of the sheet and centered half way up the width of the sheet. Two 1 l/4 th inch by 8 inch metal plates of aluminium l/8 th inch thickness with corresponding groove cut through them are fixed with adhesive to either side of the sheet. The edge of the sheet to be designated the lower or contact edge is machined in 2.6 mm segments to a depth of 2 mm leaving behind 0.4 mm thickness or less projections the centers of which are 3mm apart. These are then gently machined to remove rough edges. An arm suitable for the CMP tool to be used with a plate and bolts is prepared and the sheet of the present embodiment is loosely bolted to it. Utilizing the lateral range of motion of the arm, the sheet is placed over the polishing pad so that the sheet is placed in a radial orientation with respect to the center of the polishing pad and projections line up precisely with the grooves. The bolts are loosened and the sheet is lowered onto the pad so that it just fails to contact the pad and the projections just enter the grooves by about ½ millimetre or so. The bolts are tightened and CMP operation is carried out normally.
EMBODIMENT FOR AMAT GROOVE POLISHING PAD ATTACHED TO SLURRY
INJECTOR
[0068J An injector according to U.S. Patent Application No. 12/262,579 was prepared and two triangular notches were cut at either end of the leading edge of the injector to a depth of 1/2 inches. A block of PC corresponding in dimension approximately to the length of the injector X 2 inches X 1 1/2 inches was machined so that one face matches the leading edge of the injector and so that triangular projections having dimensions mating them to the triangular notches cut in the leading edge of the injector remain. The depth of the triangular projections is such that the surface of the shape contacting the polishing pad will ride evenly about one half to two millimetres above the polishing pad as desired. The height of the shape should be such that it is greater than the height of the face of the injector by at least about 1/4* inch or so that a "shelf may be allowed to remain on top of the injector. This shelf may be bolted to the injector to ensure greater stability of contact between the two apparati during operation. The leading face of the "shape" may then be cut as desired to create an optimal bow wave. On the bottom face of the shape along a line corresponding to a radius of the polishing pad small holes are drilled at intervals corresponding to the interval of the grooves on the polishing pad and positioned so that when attached to the slurry injector they fall between the slurry outlets that are intended to ride of the land areas of the polishing pad. The holes are about 1mm in diameter or a little less and small rods or filaments of nylon with rounded ends - for brush use is preferred - are placed in the holes and secured with adhesive so that they protrude from the surface between 1 and 2 mm and so that when the apparatus is in place they are able to enter into the grooves of the polishing pad by between 0.5 and 0.8 mm. The shape is affixed to the injector, the bolts tightened, the position of the groove cleaner injector combination adjusted so that the projections aligned with and enter the grooves and CMP operation is carried out normally.
EMBODIMENT FOR K GROOVE POLISHING PAD AND FOR NON CONCENTRIC
RING PADS
[0069] A sheet is prepared as in the embodiment for the M groove pad above except that instead of machining the contact face, small 0.5-1 mm holes are drilled at 1.5 mm intervals and using an optical microscope 3 toothbrush filaments are placed into the holes and fixed with adhesive. The nylon brash filaments should protrude no more than 0.5 mm from the polishing pad facing edge of the sheet. The sheet may then be affixed to the CMP tool in the same manner as with the sheet for the M polishing pad and CMP operation carried out.
DETAILED DESCRIPTION OF THE DRAWINGS
[0070] FIG. 1 is a frontal view of the AMAT groove apparatus of the present invention.
[0071] 10 is the sheet of the present invention
[0072] 12 is the bottom or contact surface of the sheet
[0073] 14 is the polishing pad
[0074] 16 is the gap between the contact surface of the sheet and the polishing pad
[0075] 18 are the projections
[0076] 20 are the grooves in the polishing pad.
[0077] 22 is the arm supporting the apparatus of the present invention from the CMP tool.
[0078] 24 is the metal plates attached beside the sheet or shape of the present invention.
[0079] 26 is the groove through which the bolt may be moved to adjust groove cleaner height above the polishing pad.
[0080] 28 are bolts.
[0081] FIG. 2 is a cross section lateral view of the apparatus of the present invention.
[0082] The numbering is the same as for FIG. 1.
[0083] FIG. 3 is an overview of the apparatus of the present invention used in conjunction with a slurry injector.
[0084] 30 is the wafer.
[0085] 32 is the gap between the wafer and slurry injector.
[0086] 34 is the slurry injector.
[0087] 36 is the slurry channel in the slurry injector. [0088] 40 is the shape of the present invention.
[0089] 42 is the connection between the slurry injector (34) and the supporting arm (22).
[0090] 44 is the slurry input.
[0091] 48 is the shelf and cut and mated shape of groove cleaner and slurry injector (34) or related device that is used to snap and hold the shape of the present invention to the slurry injector.
[0092] 50 is the bolt to bolt the upper shelf of the shape to the injector (34).
[0093] 52 is the shelf of the shape overlapping the top of the injector and bolted thereto.
[0094] FIG. 4 is a lateral view of the apparatus of the present invention used in conjunction with a slurry injector. Note that this view is taken along cut A to B in FIG. 3.
[0095] FIG. 5 elucidates the determination of the appropriate distance between projections in a non-perpendicular application of the apparatus
EFFECTS OF THE PRESENT INVENTION
[0096] The present invention removes partially spent slurry the grooves of concentric polishing pads in CMP once each revolution before the spent slurry in the grooves has the opportunity to contact the pad a second time. This improves the effectiveness of the slurry used and reduces the quantity of slurry required. This is particularly important because the cost of slurry constitutes a significant part of the cost of CMP operation. It additionally can reduce substantially the number of defects and non-uniformity in the wafer caused by reuse of spent slurry and the presence in spent slurry of impurities and contaminants, many of which are antithetical to effective CMP operation. In the case of the polishing pads with larger concentric grooves the present invention has the added positive feature of helping maintain the slurry outlets directly above the land areas of the polishing pad between the grooves. The design of the invention is also flexible enough to allow application to a variety of polishing pads and slurry injector configurations.
Next Patent: SWITCHABLE FEEDBACK DAMPING OF DROP-ON-DEMAND PIEZOELECTRIC FLUID-EJECTION MECHANISM