Title of Invention

A CMP (CHEMICAL MECHANICAL PLANARIZATION) PROCESS

Abstract

ABSTRACT IN/PCT/2002/00498/CHE A CMP (chemical mechanical planarization) process The present invention relates to a CMP (chemical mechanical planarization) process which comprises polishing a substrate comprising a metal and a non-conductive material using an abrasive that comprises an alumina powder in which the alumina particles of the powder have a silica coating and in which the powder has a BET surface area of at least 50m /gm, an alumina content of at least 90% by weight and an alpha alumina content of at least 90% by weight and wherein at least 90% of the alumina particles have ultimate particle widths of not more than 50 nanometers with less than 10% having ultimate particle sizes greater than lOOnm.

Full Text

This invention relates to CMP (chemicals mechanical planarizatitHi") poxes and specifically to CMP materials comprising as the abrasive alpha alumina powders. CMP is a process that is used to -products of great importance in a wide range of Electra placations. Semiconductor devices are ‘icily made by depositing a metal such as copper in spaces between non-conductive structures and then removing the metal layer until the non-conductive structure is eiqxtsed and the spaces between remain occupied by the metal. The demands placed on the abrasive are in many ways in conflict It must remove the metal but preferably not the non-conductive material. It must remove efficiently but not so quickly that the process caroms be terminated whey the desired level of rational has been reached The CMP process can be carried out using a slurry of the abrasive in a liquid medium and it is typical to include in the slunk, in addition to the abrasive, other additives including oxidiL2mg agents, (such as hydnagen peroxide, ferric nitrate, potassium iodated and the like); corrosion inhibitors such as benzotriazole; cleaning ‘ents and surface active agents. It can also however be canned using a fixed abrasive in which the abrasive particles are dispersed in and held within a cured resin material which can optionally be given a profiled surface. The CMP process can be applied to any layered device comprising metal and insulator layers each of which is in turn deposited on a substrate in quantities that need to be reduced to a uniform thickness and a highly uniform surface routines (Ra) level. CMP is the process of reducing the deposit layer to the required thickness and planarity. The problem is that the best material removal abrasives leave a rather unacceptably rough surface or achieve the material removal so aridly that the desired termination point is often overshot. Those abrasives that remove material at a moderate rate may lack selectivity or leave a poor surface. In the past these ctmflictirig demands have been optimised by the use of relatively soft abrasives such as gamma alumina and silica. These slow down the rate of removal but are not very discrimination’ as between metal and non-conductive material. Alpha alumina with an average particle size of ‘bait 100 nanometers has been proposed and this is found to be very discriminating in preferentially removing metal rather than non-conductive material. Unfortunately however it is also very aggressive such that it is very difficult to avoid "dishing" which is the formation of a depression in a metal layer lying between adjacent non-conductive material structures. Dishing adversely affects the performance of the semi-conductor and is therefore considered to be very undesirable. A need therefore exists for an abrasive that can be presented to a substrate in a CMP application that will remove metal selectively and relatively slowly such that dishing can be minimized. Fine alumina powder coated with silica has been desorbed in the context of polishing ‘placations in EP 0 554 908 Al and ceramic materials made from alumina and silica are described in WO-A-974 9647. CMP formulations comprising silica and/or alumina are described in USP 5,693,239. Description of the Invention The present invention provides a CMP process which comprises polishing a substrate comprising a metal and a non-conductive material using an abrasive that comprises an alumina powder in which the alumina particles of the powder have a silica coating and in which the powder has a BET surface area of at least SOm’/gm, an alumina content of at least 90% by weight and an alpha alumina content of at least 90% and preferably 95% by weight and wherein at least 90% of the particles have ultimate particle widths of not more than 50, for example from 20 to 50, nanometers with no more than 10% having ultimate particle sizes greater than lOOnm. Such alumina powders with this particle size range and surface area are sometimes referred to hereafter as "nano-alumina" powders or particles for convenience and brevity. The alumina powder particles are provided with a silica coating but it is understood that the tenn "silica" as used herein includes, besides silicon dioxide, complex oxid’ of sihca with metal oxides such as muUite; alkali metal aluminosihcates and borosilicates; alkaline earth metal silicates and the like. Thus a recited pax:entage of "silica" may in fact also comprise other components besides silicon dioxide. The ‘mina content of ties nano-alumina powder is at least 90% and the alpha alumina content is at least 90%, and preferably at least 95%. The balance is provided by silica and nun or amounts of other phase’ of alumina which are intermediates in the conversion of boehmite to the alpha phase. They are the result of inconplete conversion during the firing process which is minimized to ensure that the particles are not excessively agglomerated and therefore more difficult to separate. In discussing the "width" of such nano-alumina particles hereafter it is to be understood that, except wha’ the context clearly indicates the oHitraiy, it is intended to refer to the number average value of the largest dimension perpendicular to the longest dimension of a particle. In practice it is found that the nano-alumina particles have a somewhat blocky ‘pearance such that the particle often appear to be equated. The measurement technique is based on the use of a scanning, or a transmissitm, electron microscope such as a JEOL 2000SX instrument. Alpha alumina is the hard’ and densest form of alumina and is fcamed by heating otho' fcsms of alununa or hydrated alumina at elevated temperatures. It is ftierefore Ihe form of alumina that is best ad’>ted to abrasive applications. Alpha alumina is conventionally fomied by a fiision process in which an alumina hydrate is heated to above about 2000°C and then cooled and crushed. Heating at these high temperatures causes the ciystals of alpha alumina to grow to several microns and to sinter togetho- to produce an extremely hard material. The high density and the hardness of the alumina particles produced in this w’ make the cmshing process veiy difficult To get small particles, it is necessaiy to break the sinter bonds and, if even smaller particles are needed, peihaps of the order of a few microns or less in size, even to crush the primary aystals themselves. This is of course an extremely difScult task requiring much e)q>aiditure of aiergy. While the sinter bonds are veiy difficult to break, especially when sintering to essentially theoretical density has occurred, the fracture of the ultimate ciystals themselves is even harder. Recently the development of sol-gel, and particular’ seeded sol-gel, processes have permitted the production of alumina with a microcrystalline structure in which the size of the ultimate crystals, (often called micK)ci}’tallites), is of the order of 0.1 micrometer or 100 nanometers. Such seeded processes incorporate seed particles that are cqiable of nucleating the conversion of boehmite, {alpha alumina monohydrate), to the alpha alumina phase at relatively low temperatures. The nature of the seed particle in terms of its ayslal shqw and lattice dimensions should be as close as possible to that of the target mataial for the nucleation to be efBcient so that the logical choice is alpha alumina itself Virtually as soon as the alpha phase is generated, in the form of particles comprising microcrysKdIites of alpha alumina less fhaa cme micron in size, there is a taidency for the particles to sinter together where they ctaitact CHK another. This tendeaicy accelerates with ino’asing tempoHture, Keqiing the temperature of fcffmatiwi of the iUpha phase low therefore minimizes the degree to which the particles are sintCTed together and thus makes crushing to the ultimate particles size somewhat easier. In U.S. Patent 4,657,754, Bauer et al. teach firing a dried seeded sol-gel alumina to convert at least a portion to the alpha phase and then crushing the dried product to a powder of alpha particles, taking care not to cause excessive sintering or particle grow’ during tiie firing. Tliis ensures that little sintering will have taken place. Thus the crushing will need to break only a few sinter bonds and no ultimate particles. Firing to complete the conversion can then be undertaken with the product already in its powder form. This is still a difScult and ejqiensive operation however and limited essentially by the size of the ultimate particles of alpha alumina in the product, (lOOnm). Such particles are however much larger than the nano-alumina particles to which tiiis Application pertains. Fine alpha alumina powder is widely used as a polishing, or lapping abrasive. In such lapping applications, the fina- and more uniform the particle size of the powder, the better the finish that can be attained. However for CMP applications such fine alpha alumina as is produced by tiie Bauer jMDcess referred to above is extremely aggressive and readily results in dishing. The present invention addresses this problem by providing an alpha alumina-containing abrasive with smaller particle sizes, (the nano-alumina particles), and that results in less aggressive cutting. Suiprisii’y enough it is also selective enough to be used conveniently in CMP applications. The nano-alumina abrasive powder can be used in the form of a slurry which is ‘lied to the surface to be polished at the same time as a polishing pad is moved over the surface. Thus according to one embodimait, the invention conprises a CMP jwocess in which a defOTmable polishing pad is moved in contact with a surface to be polished while a slurry comprising a nano-alumina powder in which the alumina particles of the powder have a silica coating and in which the powder has a BET surfece area of at least 50m’/gm, an alumina content of at least 92% by weight and an alpha alumina content of at least 90% by weight and wherein at least 95% of the particles have ultimate particle widths of fiom 20 to 50 nanometers with less than 5% having ultimate particle sizes greater than 1 OOnm. According to an alternative embodiment the alpha alumina powder is presented to the surface to be given a CMP treatment using a fixed abrasive comprising a nano-alumina powder in which the alumina particle of the powder have a silica coating and in wliich the powder has a BET surface area of at least 50m’/gm, an alumina amtent of at least 92% by weight and an alpha alumina amtent of at least 90% by weight and vidierein at least 95% of the particles have ultimate particle widths of from 20 to 50 nanometers, with less than 5% having ultimate particle sizes greater than I OOnm, dispersed in a cured binder. The binder/abrasive can be present as a coating on the outer portion of a wheel, for example the rim, or it may be deposited as a coating on a planar surface of a flexible sheet material such as a cover, disc or belt before the binder is cured to give an abrasive tool. The surface of the binder/ab:asive layer can be smooth or it may be given a surface stmcture comprising a plurality of shsqies in random or rqieating order before the binda: is cured. Such surfaces are said to be "engineered" since they can be pre-detemiined or sh’ied to have any configuration demanded by the application and the substrate surface to which it is to be applied. Production of Nano-Alumina A suitable process by wiiich the nano-alumina particles can be made comprises dispersing in a boehmite gel a material, particularly silica, that forms a barriea- around the boehmite particles, at a temperature below that at which boehmite converts to alpha alumina, said material being incorporated in an amount sufficient to inhibit particle size growth after fomiation of alpha alumina from the boehmite, then drying and firing the gel at a temp’ature to convert at least the major proportion of the alumina to the alpha phase in the form of loose aggregates of ultimate particles with sizes from about 20 to about 50 nanometers. These aggregates are described as "loose" by which is meant that they can be relatively easily comminuted to recover the primary particles which have a width tiiat is less than about 50 nanometers. The firing should not be at a terr’Krature to cause significant growth or over-sintering of the particles, (which would of course cause them to be extranely dtfi&cult, if not impcssible, to separate to the primary particles), hi feet the barrio- coating makes the sintering of such products occur only at an elevated temperature of about 1400°C or higher and the usual firing temperature employed is preferably below 1300°C. The barrier material is believed to fcMHi a very thin coating around the particles of boehmite in the gel wiiich inhibits migration of alumina across the particle boundaiy and thus prevents, or at least significantly inhibits, growtii of the particle as it is converted to the alpha phase. The result is tiierefore the foiraation of alpha alumina particles with sizes of the order of those in the originating boehmite gel. The preferred glass forming barrier material is most convenientiy silica but other glass fomiing materials enable of acting in the above way are within the purview of the present invention. These could include boron containing materials such as borosilicates and the like. For the purposes of this description, the primary enmhasis will be on the most readily available and easily usable materials based on silica. When silica is used as the barrier material, the amount incorporated is preferably from about 0.5 to about 10% by weight based on the weight of the alumina in the gel. It is usually preferred to disperse tiie silica in a sol or a gel of the boehmite so as to maximize the intimacy of the dispersion between the components. The boehmite can be ar’ of those currently available which have dispersed particle sizes of the order of a few tens of nanometers or less. Clearly the boehmites with the mtst consistently fine particles sizes are preferred since these do not have the hard-to-disperse agglomerates that characterize some of the other commercial products. It ‘jpears that the silica interacts with the surfece of the boehmite particles, probably by f(»mati(Mi of a glass, and this slows the conversion to alpha alumina and the subsequent growth of these alpha particles. Because of this particle growth suppression mechanism there is little reason to keep the tanperalure low. Thus more r’id conversion can be obtained using higher temperatures without adverse effect on the alpha crystal size. Addition of the silica to a boehmite sol and the gelation of the sol nuxture obtained is an important preferred feature of the present invention since diis permits a complete and uniform dispersion to be achieved. In addition the silica becomes attached to the essentially colloidal sized boehmite particles which are inhibited fixim significant further growth. When the conversion to alpha has occurred the particles are in the form of loose agglomerates of primaiy particles with a width of about 50 nanometers or less and may qipear under a scanning electron microscope to have the fomi of a series of rod-shq’ed or cluster agglomerates, or sometimes a rou’ networic of elements comprising the primary particles. These loose agglomerates or aggregates are relatively easily broken down to the individual particles, for example by wet or dry milling. They are relatively easily brokai up because of the formation of a silica-containing barrier phase at the crystal boundaries vMch inhibits the fonnation of a sinter bond between alpha alumina ultimate particle. This results in a nano-alumina product with a number avenge particle width of less than about 50 nanometers. A wet milling process can often lead to the formation of a minor amount of hydrated alumina, for example alumina trihydrate, by surface hydrolysis of the alpha alumina. Such hydrates will revert to alpha alumina upon firing of course and for the purposes of tins specification, such surfece modified alpha alumina is not distinguished from unmodified alpha alumina. The process leads to the production of alpha alumina particles of a fine, uniform particle si’. Prior art alpha alumina powders milled to give a high BET surfece area are found to comprise a wide range of particle sizes to the extent that these oftoi appear to be in a bimodal the predominant alumina phase. The process therefore also provides a fine alumina powder havir’ a BET surface area of at least 50 m /gm. and preferably at least 100 m /gm., in which at least at least 90% of the total alumina phase weight is provided by particles of miaxxaystalline alpha alumina, and wherein at least 90% of the particles have widths of fiom not greater than 50, and preferably fiom 20 to 50, nanometers and less than 10% have ultimate particle widths greater than 100 nanometers. Tlie flection of these large particles is measured by electron, (scanning or transmissioi), microscope analysis of an ultramicrotomed sample and an assessment of the percentage of the total field occupied by particles, occiqsied by particles having ultimate particle widths greater than 100 nanometers. The balance of the powder wei’t is largely provided by the barrier material which, as indicated above, can be any material enable of inhibiting particle growth and/or sintering during the conversion to alpha alumina Where the barrier comprises a silica-containing material such as a mullite this can represent as much as 15% by weight of the total weight or even more. Usually however, opiating with the preferred minor amounts of silica sol specified above, the alumina represents about 95% of the weight of the powder. It is also possible that the non-alpha alumina in the alumina phase of the nano-alumina powder may be provided by alumina phases intermediate between the bodiraite and alpha phases, such as gamma alumina or theta alumina. The amount of silica present diould be carefijlfy controlled because if too much is added there will be a tendency to react with the bulk of the alumina and much of the final product will have the relatively useless chemical composition of mullite or other silica-containing phase. On the otiier hand too little will not be effective to limit alpha particle growth. In practice it is found that an amount fix)m about 0.5 to about 8, and preferabfy fix)m about I to about 5 wt. % of the solids content of the gel should be silica. Generally it is preferred that the amount of silica in the final product ‘ould be less than about 10 wt% and preferabty should be less than about 8, and most preferably less than about 5 wt%. The silica can be added in the fomi of colloidal silica, a silica sol or a compound that under the reaction ccHiditions will liberate such a colloid or sol and fomi a glassy coating around the alumina particles. Such compounds could include organosilanes such as tetraethyl orthosilicate, and certain metal silicates. Generalfy alkali metal silicates are less preferred. The form of the silica in the sol should preferably be of a particle size that is at least similar to, or preferabfy smaller than, that of tiie boehmite, that is, of the order of a few nanometers at most. Adding the silica in the fonn of a sol to the boehmite sol aisures the most uniform and effective dislribution of the silica such a minimum amount can be used. The gel may be dried at lower ten’’eratures before it is calcined, which is commonly done at a temperature of about 700°C, over a period of several hours. The calcination drives off the water in the gel, prcffnotes formation of the gla’ surfece barrier and be’ns convasion of the boehmite to the gamma alumina phase. The calcinatiai pnxess can however be carried out under other conditions with higher or IOWCT temperatures if desired, tr even omitted altogether. Firing of the dried gel can occur under any cmditions that will bring about phase conversion to alpha alumina. Generally unseeded boehmite will ccaivert to the alpha phase at temperatures of from about 1000 to 1300°C with ttie time to accon:y>lish Uie conversion decreasing with increasing tempaature. In the present invention the prefored firing tempCTature is fixim about UOO°C to I250°C and the time taken at that tenperature will be somewhat longer than would be usual for such aluminas due to the presence of the silica. The firing may require as much as 40 houi’ at the lower end of the temperature range and as little as one minute at the upper aid of this range. Firing at the lower end of the range such as fix)m about 1100 to about 125(fC minimizes the tendency for flie particles to form aggregates. In this temperature range, a time at the firing temperature of fiom about 1 minute to about 40 hours is needed to reach the desired level of conversion to alpha alumina without fomuitionofexcessive amounts ofintractable (as o’iposedto loose), agglomerates. In firing, the time at the firing temperature is very inporlant. A slow ramp-up to the firing temperature may dictate the use of a shorter time at the firing temperature and this ramp-up is often a Junction of the equipment used. Generally a rotary furnace needs a much shorter time to reach the desired t’nperature while a box furnace can take a significantly longa- time. Thus for reasons of control and reproducibility it m’ often be preferred to use a rotaiy fiimace. In addition a large sample will need longer to reach a uniform bo’ temperature than a smaller one. The temperatur&'time schedule actuaUy used will tha’fore be dictated by the circumstances, with the above considerations in mind. Comminution can be accomplished in a mill using conventional techniques such as wet or dry ball milling or the like. Alternatively it is possible to take advantage of presence of mullite or other aluminosilicate phases at the particle boundaries within the E’onKrates to raaks, comminution easier. Such phases will usually have different thermal expansion properties fix)m alpha alumina and it is often possible to nature such boundary layers by cyclmg tfie product through high and low temperatures to create expansion stresses. Such stresses may sometimes themselves be adequate to bring about comminution. It m’ also be possible to subject these silica-containing boundaries to chemical stresses by a hydrothermal treatment or by treating the product with a base or an acid. More commonly however such thermal or chemical comminution will need to be followed by some sort of physical coniminidm to complete the breakdown to a powder with a number average particle widlii of less Ihan 50 nanometers. The voy fine particle sizes obtained by tiie process are believed to be unique in that they combine a high surface area in excess of 50, and more often 120 m’/gm. with a particle size distribution such that less than about 10% by weight of the particles have an ultimate particle size greater than 100 nm. Since milling is typicalfy done using low purity alpha alumina media, it is believed that a si’ficant proportion of the 100 nm+ particles obsCTved are more likely derived from attrition of the media and not fix)m alpha alumina obtained by the conversion of the boehmite. By contrast products obtained by milling larger alpha alumina particles ‘ically have a much wider spread of particle sizes with large number of particles ‘‘eater than 100 nm in size. It is preferred that the final milling used to separate the nano-alumina particles is perfomied using low-pun’ alpha alumina, {about 88% alpha alumina), or zirconia media. "Zirconia" media is understood to include media made from a zirconia stabilized by additives such as yttria, rare earth metal oxides, magnesia, calcia and the like. This is thought to be possibly due to the way in which high-pwri’ alumina media break down during milling to pK>duce quite large fi-’ments. By contrast low-purity alumina media typically produce micron-sized particles and zirconia media are so tough they ‘pear to produce almost no fragments at all. Use of Nano-Alumina in CMP Slurrv One embodiment of the present invention is directed to slurries of nano-alumina that are usefiol in CMP processes and to CMP processes employing nano-alumina abrasive powders. CMP (chemical-mechanical polishing) slurries usually axiprise the abrasive in an oxidizing liquid medium which is often a solution of hydrogen peroxide in deicHiized water. The sluny often contains in addition a complexing agent such benzotriazole. When the nano-alumina is present in such a sluny the concentration is typically fiom 1 to 15%, and preferable Gxxn 2 to 10% by wei’t of the total sluny weight. The sluny is used in conjunction with a pad that moves over the surface to be polished as the slurry is fed on to the surface of the workpiece. Use of Nano-Alumina in Fixed Abrasives for CMP Applications In recent times howler there has beai a move to replace the conventional sluny/pad combination with a fixed abrasive in which the abrasive is in the fomi of a composite with the particles of abrasive being held in an easily erodable binder matrix. This composite can for example provide die grinding surfece of an ateasive wheel. It can also take the form of a layer dqxjsited on and adhered to a flexible substrate, to wWch a regular pattern has been ‘iplied for example by a molding or embossing process. These latter are often referred to as "engineered" abrasives. The fixed abrasives are then moved relative to the surfece to be treated ralho- as a pad would be in the conventional CMP process. However in place of the sluny the liquid fed to the surfiice is deionized water or an aqueous oxidizing solidon. This is still a tme CMP q)eration as the term is used herein and the results are the same. Such proc’ses are however potentially much more efficient in the use ofabrasive and Ihe ease of treatment or disposal of the waste. Description of the Drawings Figure 1 shows a nano-alumina powder usefiil in the CMP [rocesses of the invention. As can be seen it comprises liighly uniform 20-50 nm particles with very few larger than 50 nm in widtii. Some appear to be loosely agglomerated but the individual particle structure is clearly visible. Figure 2 shows the X-Ray diffraction trace for a nano-alumina useful in the production of CMP products according to the invention. Description of Preferred Embodiments The invention is now fijrther described with reference to the following Examples wWch are intended for the purposes of illusti’ffli only and should not be taken as implying any necessary limitation on the essential scope of the invention. Testing for CMP Suitability In manufacturing semicaiductor components it is conventicMial to deposit on a silicon wafer substrate a number of layers of different conductive and non-conductive materials. As deposited the layers are often uneven and need to be "planarized" to give a surfece with as low an R’, {a measure of surface roughness), as possible. In a typical CMP operation, the task is to remove material efficiently while at the same time leaving as unblemished a surface as possible. While efficiency is important, control is even more significant since the thickness of the layers deposited is measured in Angstroms and too aggressive a removal rate can make it difficult to stop exactly when the desired thickness of the layer has been achieved. Thus steady but controlled removal is the goal. This steadiness is also significant when the deposited material overlies a previously deposited layer on which a pattern, such as a circuit, has been etched. When the ove-lying layer has been removed to tfie level of the previously deposited etched l’er, it is important that the erosion does not continue such that the filled area between ranaining etched stmctures of the previous layer is not fiirther eroded, a process known as "dishing". If the selectivi’ of ranoval betweai the prior and the ova-lying layers is mariced and the rate of removal of tfie overlying layer is high, Ihe potential for dishing is great and this of course results in a highly non-planar surface upon which a subsequent layer may be deposited. hi evaluating the CMP potaitial of a particular abrasive therefOTe we set up two types of test. The first was intaided to evaluate the selectivity of removal and the second was intended to evaluate the potential for dishing. The selectivity tests were carried out on san’les having a surfece to be planarized that was made of either copper or an insulating k’er of silicon dioxide, (hereinafter referred to the "oxide" layer). The samples were made by depositing a 10,000 A (10 x 10"'m) layer of the oxide on a soniconductor grade silicon wafer that had been thoroughly cleaned. This provided the oxide sample for evaluation or removal rate. Planarized versions of these oxide layer samples were then given a 400 angstrom (4 x IO"*m) layer of a titanium adhesion layer followed by a 10,000 A (lOx 10"‘m)I’er of copper. This copper surface was used to evaluate the rate of removal of copper. The dishing tests were carried out on siliccm wafer samples thai had been given the above oxide layer but to a depth of 16,000 A (16 x 10"V). The oxide layer was planarized and then etched to give a pattem that was 2,200 A (2.2 x 10"'m) de’. Over this etched layer was deposited a 10,000 A (10 X 10' m) layer of ccpper. fliis copper surface was then planarized until the oxide surface was ejqwsed and the depth of dishing that resulted was assessed. Example 1 - Selectivi’ Evaluation A CMP sluny acceding to ‘e inventicMi vras evaluated ag’nst two commercial alumina slurries in the removal of copper and oxide on samples made using the procedures outlined above. In each case 2000gm of an alumina slurty contMiing 10% solids by weight was mixed with 250 ml of 30% hydrogen peroxide solution and 4 gm of benzotriazole (botii purchased from VWR Scientific Products). Deicmized water was added to make a final slurry weight of 4000gm. The three resulting slurries were then evaluated on a laboratoiy scale polisher. A Rodel IC1400 stacked perforated polislung pad was used for tiie polishing tests. A polishing pressure of 34.5 Kpa, (5 psi), a relative surface speed of die woriqiiece of appn)ximately 1.2 m/sec, and a slurry flow rate of 100 ml/minute were used. The material removal rate (MRR) was measured using a balance with a repeatability of +/- 10 micrograms and was craiverted into A/min (m/min). The removal rates obtained with the fliree mat’als was as follows: ALUMINA SOURCE Cu REMOVAL Oxide REMOVAL SELECTIVITY COMP-1 640 A/Min (6.4xlCf*nvhiin) 90 A/Min (9.0 X lO'‘nVinin) 7 COMP-2 590 A/Min (5.9xl0’mtain) 340 A/Min (34xl0’mtein) 1,7 INVENnON-1 360 A/Min (3.6xl0*intain) 50 A/Min (S.OxlO’nVmin) 7 The alumina used in Comp-1 was obtained fix)m Saint-Gobain Industrial Ceramics, Inc. undCT the product code SL 9245. The particle size was of the order of 100 nanometers or so with a wide particle size range. It was obtained by the Bauer process described above. The Comp-2 alumina was "Product Code Masteiprep" purchased fix>m Buehler Limited. It is believed to be predominantly gamma alumina. The alumina used in Invention-1 is shown in Figure 1 and was obtained by the process described above for Ihe production of nano-alumina. Tlie X-Ray diffraction trace of (he nano-alumina is shown in Figure 2 which indicates that the alpha alumina content is in excess of 80%. The actual level is difficult to assess accurately because the peak associated with the theta-alumina transitiraial form is not readily separated from two adjacent alpha alumina peaks. The nano-alumina comprised 2% by weight of silica as a coating around the particles. The silica was added to a boehmite dispersicai and the silica-coated boehmite particles woe fired at 1150-1200°C for 10 hours, after which Ihe particle were cooled to room ten’ierature and milled using zirconia metha for 27 hours in a polyurethane-Iined Sweco mill. The data shows that the rate of removal is reduced by comparison with the larger particle size alpha alumina as a result of the smaller particle size but the selectivity is fiilly maintained. Thus whm removing material to the point at which the underlying layer is revealed, it become possible to identify the endpoint accurately and terminate the planarization sqjpropriately. TTie gamma alumina product had fest removal rates but hardly any selectivity as between the copper and the oxide materials. The nano-alumina product was the only one that pCTnitted controlled, steady oxide removal while retaining selectivity. Example 2 - Dishing evaluation The same three aluminas that were evaluated in Example 1 were then evaluated for dishing in the manner described above. The test format was exactly that described m Example 1 except that the material tested was the layered product described above and the end-point was the first point at which both metal and insulating oxide material were visible. Measurements of "dishing" made using a profilometer obtained fiwm Tencor Craporation. Tlie measurements were made of the depth of dishing between adjacent features of varying heights from 5 to 45 micrometere in height. The depth ofdishing for each sample was averaged. The results obtained were as follows: COMP-1 220 A (22xl0’m) COMP-2 200 A (lOxlO’m) INVENTION-] 120 A (UxlO’m) From this it is clear that the dishing is fer less severe with the nano-alumina than with the other aluminas of the prior art. Example 3 In this Example the products evaluated in Example 1 were-evaiuated in a CMP sluny in which the sluny comprised 97 gm of ferric nitrate and 0.5 gm of benzotriazole dissolved in 2000 gm of deionized water. To this soluticai were added 2000 gm of a 10% alumina dispersion in deionized water. The aluminas are described below. ALUMINA SOURCE Cu REMOVAL Oxide REMOVAL SELECTIVITY COMP-3 14180 A/Min (1418xl0’mtain) 31 A/Min (31xlff'°mAim) 457.4 COMP-4 13471 A/Min (1.3471 X10* m’nin) 30 A/Min (30x Iff'‘'mAnin) 449 INVENnON-2 1175 A/Min (1.175xia-'mAnin) 8 A/Min (Sxlff'‘mAnin) 147 The alumina used in Comp-3 was obtained from Saint-Gobain Industrial Ceramics, Inc. under the product code SL 9245. The particle size was of the (deer of 100 nanometers or so with a wide particle size range. It was obtained by flue Bauer fsocessdesaibed above. It was thus the same as was used in Comp-1. The Comp-4 alumina was 'Product Code Masterprep" purchased from Buehler Limited. It is believed to be predaninantly gamma alumina. This was the alumina used in Comp-2 above. The nano-alumina used is similar to the one used in and was obtained by the process described above for the production of the nano-alumina used in Invention-1. It aspired however ‘‘proximately 5% by weight of silica as a coating around the particles. The silica was added to a bemire dispersion and the silica-coated boehmite particles were fired at 1150-1200°C for 10 hours, after which the particles were cooled to room temperature and milled use’ zirconium media in a Drays mill with a polyurethane lining till the powder had a BET surface area of >80 m’/gm. The data shows that the rate of removal is reduced by comparison with the larger particle size alpha alumina or the gamma alumina product, (which were virtually identical), as a result of the smaller particle size. An adequate selectivity was however fairy maintained. Thus when removing material to the pre-determined point, for example one at which an undCTlying layer is revealed, it becomes possible to identify the eloping accurately and terminate the planarization appropriately. WE CLAIM: 1. A CMP (chemical mechanical planarization) process which comprises pushing a substrate comprising a metal and a non conductive material using an abrasive that comprises an alumina powder in which the alumina particles of the powder have a silica coating and in which the powder has a BET surface area of at least 50m /gm, an alumina content of at least 90% by weight and an alpha alumina content of at least 90% by weight and wherein at least 90% of the alumina particles have ultimate particle widths of not more than 50 nanometers with less than 10% having ultimate particle sizes greater than lOOnm. 2. The CMP process as claimed in claim 1 in which the alpha alumina content of the alumina powder is at least 95%. 3. The CMP process as claimed in claim 1 in. which the silica content of the alumina abrasive is from I to 8 wt%. 4. The CMP process as claimed in claim 1 in which the alumina abrasive is presented to a workpiece in the form of a slurry comprising from 2 to 7 wt% of the alumina. 5. The CMP process as claimed in claim I in which the alumina abrasive is presented to the workpiece in the form of a fixed abrasive comprising the abrasive dispersed in a cured resin matrix. 6. The CMP process as claimed in claim 5 in which the fixed abrasive has a profiled surface comprising a plurality of shaped structures. 7. A CMP slurry that comprises an alumina powder in which the alumina particles of the powder have a silica coating and in which the powder has a BET surface area of at least 50m /gm, an alumina content of at least 90% by weight and an alpha alumina content of at least 90% by weight and wherein at least 90% of the particles have ultimate particle widths of from 20 to 50 nanometers with less than 10% having uhimate particle sizes greater than lOOnm. 8. An engineered abrasive suitable for use in CMP applications comprising a working surface which itself comprises a plurality of shaped structures obtained by curing a dispersion of alumina abrasive particles in a curable resin wherein the alumina abrasive particles have a silica coating, a BET surface area of at least 50m /gm, an alumina content of at least 90% by weight and an alpha alumina content of at least 90% by weight and wherein at least 90% of the particles have ultimate particle widths of from 20 to 50 nanometers with less than 10% having ultimate particle sizes greater than lOOnm.

Documents:

in-pct-2002-0498-che abstract-duplicate.pdf

in-pct-2002-0498-che abstract.pdf

in-pct-2002-0498-che claims-duplicate.pdf

in-pct-2002-0498-che claims.pdf

in-pct-2002-0498-che correspondence-others.pdf

in-pct-2002-0498-che correspondence-po.pdf

in-pct-2002-0498-che description (complete)-duplicate.pdf

in-pct-2002-0498-che description (complete).pdf

in-pct-2002-0498-che drawings-duplicate.pdf

in-pct-2002-0498-che drawings.pdf

in-pct-2002-0498-che form-1.pdf

in-pct-2002-0498-che form-19.pdf

in-pct-2002-0498-che form-26.pdf

in-pct-2002-0498-che form-3.pdf

in-pct-2002-0498-che form-5.pdf

in-pct-2002-0498-che others.pdf

in-pct-2002-0498-che pct.pdf

in-pct-2002-0498-che petition.pdf