EP0835723A1 - A carrier head with a layer of conformable material for a chemical mechanical polishing system - Google Patents

Abstract

The disclosure relates to a carrier head (100)for a chemical mechanical polishing apparatus. Alayer of conformable material (308) is disposed in arecess of the carrier head to provide a mountingsurface for a substrate (10). The conformablematerial may be elastic and undergo normal strain inresponse to an applied load. The carrier head mayalso include a support fixture (352) detachablyconnected to a backing fixture (350), a retaining ring(362) connected directly to the conformable material,and a shield ring (360) which projects over a portionof the layer of conformable material.

Description

The present invention relates generally to chemicalmechanical polishing of substrates, and more particularlyto a carrier head for a chemical mechanical polishingsystem. Reference should be made to the Applicants' US Patent SpecificationNo. 5 643 053.

Integrated circuits are typically formed onsubstrates, particularly silicon wafers, by thesequential deposition of conductive, semiconductive orinsulative layers. After each layer is deposited, thelayer is etched to create circuitry features. As aseries of layers are sequentially deposited and etched,the outer or uppermost surface of the substrate, i.e.,the exposed surface of the substrate, becomesincreasingly more non-planar. This non-planar outer surface presents a problem for the integrated circuitmanufacturer. If the outer surface of the substrate isnon-planar, then a photoresist layer placed thereon isalso non-planar. A photoresist layer is typicallypatterned by a photolithographic apparatus that focusesa light image onto the photoresist. If the outer surfaceof the substrate is sufficiently non-planar, then themaximum height difference between the peaks and valleysof the outer surface may exceed the depth of focus of theimaging apparatus, and it will be impossible to properlyfocus the light image onto the outer substrate surface.

It may be prohibitively expensive to design newphotolithographic devices having an improved depth offocus. In addition, as the feature size used inintegrated circuits becomes smaller, shorter wavelengthsof light must be used, resulting in further reduction ofthe available depth of focus. Therefore, there is a needto periodically planarize the substrate surface toprovide a substantially planar layer surface.

Chemical mechanical polishing (CMP) is one acceptedmethod of planarization. This planarization methodtypically requires that the substrate be mounted to acarrier or polishing head. The exposed surface of thesubstrate is then placed against a rotating polishingpad: The carrier provides a controllable load, i.e.,pressure, on the substrate to push it against thepolishing pad. In addition, the carrier may rotate toprovide additional motion between the substrate andpolishing pad. A polishing slurry, including an abrasive and at least one chemically-reactive agent, isdistributed over the polishing pad to provide an abrasivechemical solution at the interface between the pad andsubstrate. A CMP process is fairly complex, and differsfrom simple wet sanding. In a CMP process the reactiveagent in the slurry reacts with the outer surface of thesubstrate to form reactive sites. The interaction of thepolishing pad and abrasive particles with the reactivesites results in polishing.

An effective CMP process has a high polishing rateand generates a substrate surface which is finished(lacks small-scale roughness) and flat (lacks large-scaletopography). The polishing rate, finish and flatness aredetermined by the pad and slurry combination, therelative speed between the substrate and pad, and theforce pressing the substrate against the pad. Becauseinadequate flatness and finish can create defectivesubstrates, the selection of a polishing pad and slurrycombination is usually dictated by the required finishand flatness. Given these constraints, the polishingrate sets the maximum throughput of the polishingapparatus.

The polishing rate depends upon the force pressingthe substrate against the pad. Specifically, the greaterthis force, the higher the polishing rate. If thecarrier head applies a non-uniform load, i.e., if thecarrier applies more force to one region of the substratethan to another, then the high pressure regions will bepolished faster than the lower pressure regions. Therefore, a non-uniform load may result in non-uniformpolishing of the substrate.

An additional consideration in the production ofintegrated circuits is process and product stability. Toachieve a high yield, i.e., a low defect rate, eachsuccessive substrate should be polished undersubstantially similar conditions. Each substrate shouldbe polished by approximately the same amount so that eachintegrated circuit is substantially identical.

In view of the foregoing, there is a need for achemical mechanical polishing apparatus which optimizespolishing throughput, while providing the desiredflatness and finish. Specifically, the chemicalmechanical polishing apparatus should have a carrier headwhich applies a substantially uniform load to thesubstrate.

In one aspect, the invention is directed to acarrier for positioning a substrate on a polishingsurface in a chemical mechanical polishing apparatus.The carrier comprises a housing and a containmentassembly connected to the housing to hold a layer ofconformable material. The layer of conformable materialprovides a mounting surface for a substrate.

Implementations of the invention may include thefollowing. The containment assembly may include aflexible membrane defining an enclosed volume, with theconformable material disposed within the enclosed volume.The flexible membrane may be attached to a backingmember, and a flexible connector may connect the backingmember to the housing. The flexible connecter may forma pressure chamber between the housing and the backingmember. The flexible membrane may include a firstflexible membrane portion defining a first enclosedvolume and a second flexible membrane portion defining asecond enclosed volume, and the conformable material mayinclude a first conformable material having a first viscosity disposed in the first enclosed volume and asecond conformable material having a second viscositydisposed in the second enclosed volume. The conformablematerial may be a viscoelastic material such as silicone,gelatin, or urethane. The conformable material may havea durometer measurement, such as between about twenty-fiveand thirty-five, selected to provide both elasticityand normal strain in response to an applied load. Thecontainment assembly may include a base member with arecess, and the layer of conformable material may bedisposed in the recess to provide the mounting surface.The base member may be detachably connected to thecarrier head. A retaining ring having approximately thesame thickness as the substrate may be connected to themounting surface. A shield which is thinner than theretaining ring may be connected to the base member andproject over a portion of the layer of conformablematerial to surround the retaining ring. The shield maybe positioned to prevent the conformable material fromextruding when the substrate is pressed against thepolishing surface. The carrier may further comprise achucking mechanism to attach the substrate to the mounting surface. The chucking mechanism may include apassageway formed through the layer of conformablematerial to the mounting surface, and a pump may beconnected to the passageway to suction the substrate tothe mounting surface. The passageway may have a diametersuch that the passageway does not collapse if the pumpapplies suction to the passageway. The chuckingmechanism may include a pocket between the substrate andthe layer of conformable material to suction thesubstrate to the mounting surface.

Advantages of the invention include the following.The carrier provides uniform loading of the backside ofthe substrate to evenly polish the substrate. Theconformable material deforms and redistributes its massif the polishing pad is tilted, the substrate is warped,or there are irregularities on the backside of thesubstrate or the underside of the rigid surface. Theconformable layer is chemically inert vis-a-vis thepolishing process. The carrier head is also able tovacuum chuck the substrate to lift the substrate off thepolishing pad.

Additional advantages of the invention will be setforth in the description which follows, and in part willbe obvious from the description, or may be learned bypractice of the invention. The advantages of theinvention may be realized by means of theinstrumentalities and combinations particularly pointedout in the claims.

The accompanying drawings, which are incorporated inand constitute a part of the specification, schematicallyillustrate the present invention, and together with thegeneral description given above and the detaileddescription given below, serve to explain the principlesof the invention.

FIG. 1 is a schematic perspective view of a chemicalmechanical polishing apparatus.

FIG. 2 is a cross-sectional view of the supportassembly, carrier head and polishing pad of the chemicalmechanical apparatus of FIG. 1.

FIG. 3A is a schematic cross-sectional view of thecarrier head and polishing pad of the chemical mechanicalapparatus of FIG. 1.

FIG. 3B is a schematic cross-sectional view of analternate carrier head.

FIG. 4 is a schematic cross-sectional view of acarrier head having multiple enclosed volumes filled witha conformable material.

FIG. 5 is a schematic cross-sectional view of acarrier head having a loading mechanism.

FIG. 6 is an exploded perspective view of a chemicalmechanical polishing apparatus.

FIG. 7 is a schematic top view of a carousel, withthe upper housing removed.

FIG. 8 is a cross-sectional view of the carousel ofFIG. 7 along line 8-8.

FIG. 9A is a schematic cross-sectional view of acarrier head including bellows and a layer of conformablematerial in accordance with the present invention.

FIG. 9B is a view of the carrier head of FIG. 9A inwhich the bellows are replaced by a flexible membrane.

FIG. 10 is an exaggerated cross-sectional view of asubstrate in contact with the layer of conformablematerial of the carrier head of FIG. 9A or FIG. 9B.

FIG. 11A is a schematic cross-sectional view of acarrier head according to the present inventionillustrating vacuum chucking lines in the layer ofconformable material.

FIG. 11B is a view of the carrier head of FIG. llAin which the vacuum chucking lines are closed byapplication of a load to the carrier head.

FIG. 12A is a schematic cross-sectional view of acarrier head according to the present inventionincorporating a vertically-movable cylinder for forminga vacuum pocket.

FIG. 12B is view of the carrier head of FIG. 12A inwhich the vertically-movable cylinder has been positionedto form a vacuum pocket.

FIG. 13 is a schematic cross-section view of anotherembodiment of a carrier head according to the presentinvention.

Referring to FIGS. 1 and 2, a chemical mechanicalpolishing (CMP)apparatus 30 generally includes a base 32which supports arotatable platen 40 and apolishing pad42. TheCMP apparatus 30 further includes a carrier orcarrier head 100 which receives asubstrate 10 andpositions the substrate on the polishing pad. Asupportassembly 60 connectscarrier head 100 tobase 32. Thecarrier head is positioned against the surface of thepolishing pad bysupport assembly 60.

Ifsubstrate 10 is an eight-inch (200 mm) diameterdisk, then platen 40 and polishingpad 42 will be abouttwenty inches in diameter.Platen 40 is preferably arotatable aluminum or stainless steel plate connected bya drive shaft (not shown) to a drive mechanism (also notshown). The drive shaft may also be stainless steel.The drive mechanism, such as a motor and gear assembly,is positioned inside the base to rotate the platen and the polishing pad. The platen may be supported on thebase by bearings, or the drive mechanism may support theplaten. For most polishing processes, the drivemechanism rotatesplaten 40 at thirty to two-hundredrevolutions per minute, although lower or higherrotational speeds may be used.

Referring to FIG. 3A, polishingpad 42 may be a hardcomposite material having a roughened polishingsurface44. Thepolishing pad 42 may be attached to platen 40 bya pressure-sensitive adhesive layer 49.Polishing pad 42may have a fifty mil thick hardupper layer 46 and afifty mil thick softerlower layer 48.Upper layer 46 ispreferably a material composed of polyurethane mixed withother fillers.Lower layer 48 is preferably a materialcomposed of compressed felt fibers leached with urethane.A common two-layer polishing pad, with the upper layercomposed of IC-1000 and the lower layer composed of SUBA-4,is available from Rodel, Inc., Newark, Delaware (IC-1000and SUBA-4 are product names of Rodel, Inc.).

Referring to FIG. 1, a slurry 50 containing areactive agent (e.g., deionized water for oxidepolishing), abrasive particles (e.g., silicon dioxide foroxide polishing) and a chemically reactive catalyzer(e.g., potassium hydroxide for oxide polishing) issupplied to the surface of polishingpad 42. A slurrysupply tube orport 52 distributes or otherwise metersthe slurry onto the polishing pad. The slurry may alsobe pumped through passages (not shown) inplaten 40 andpolishingpad 42 to the underside ofsubstrate 10.

To properly position the carrier head with respectto the polishing pad,support assembly 60 includes acrossbar 62 that extends over the polishing pad.Crossbar 62 is positioned above the polishing pad by apair of opposedupright members 64a, 64b and 66, and abiasing piston 68. One end ofcrossbar 62 is connectedtoupright members 64a and 64b by means of ahinge 65.The other end ofcrossbar 62 is connected to thebiasingpiston 68. The biasing piston may lower and raisecrossbar 62 in order to control the vertical position ofthe carrier head. Thesecond upright member 66 ispositioned adjacent to thebiasing piston 68 to providea vertical stop which limits the downward motion of thecrossbar.

To place a substrate oncarrier head 100, thecrossbar is disconnected from the biasing piston, and thecrossbar is rotated abouthinge 65 to liftcarrier head100 off the polishing pad. The substrate is then placedin the carrier head, and the carrier head is lowered toplacesubstrate 10 against polishing surface 44 (see FIG.3A).

Support assembly 60 includes atransfer case 70which is suspended fromcrossbar 62 to controllably orbitand rotate the substrate about the polishing pad. Thetransfer case 70 includes adrive shaft 72 and ahousing74. Thehousing 74 includes a fixedinner hub 76 and anouter hub 78. The fixedinner hub 76 is rigidly securedto the underside ofcrossbar 62, for example by aplurality of bolts (not shown). The rotatableouter hub 78 is journalled to fixedinner hub 76 by upper and lowertapered bearings 77. These bearings provide verticalsupport to rotatableouter hub 78, while allowing it torotate with respect to the fixed inner hub. Thedriveshaft 72 extends through fixedinner hub 76 and is alsovertically supported bytapered bearings 79 which allowthedrive shaft 72 to rotate with respect to the fixedinner hub 76.

As discussed in aforementioned U.S. PatentApplication Serial No. 08/173,846, a first motor andgearassembly 80 is connected to driveshaft 72 to control theorbital motion of the carrier head, and a second motorandgear assembly 84 is connected by means of apulley 85anddrive belts 86 and 87 to rotatableouter hub 78 tocontrol the rotational motion of the carrier head. Oneend of ahorizontal cross arm 88 is connected to thelower end ofdrive shaft 72. The other end ofcrossarm88 is connected to the top of a secondaryvertical driveshaft 90. The bottom ofsecondary drive shaft 90 fitsinto acylindrical depression 112 in the carrier head.Thus, whendrive shaft 72 rotates, it sweepssecondarydrive shaft 90 andcarrier head 100 in an orbital path.

Support assembly 60 also includes a rotationalcompensation assembly to control the rotational speed ofcarrier head 100. The compensation assembly includes aring gear 94 which is connected to the bottom ofrotatableouter hub 78 ofhousing 74, and apinion gear96 connected tosecondary drive shaft 90 immediatelybelowcross arm 88.Ring gear 94 has an inner toothed surface, and thepinion gear 96 includes an outer toothedsurface which engages the inner toothed surface ofringgear 94. Ascross arm 88 pivots, it sweepspinion gear96 around the inner periphery ofring gear 94. A pair ofdowel pins 98 extend from thepinion gear 96 into a pairof mating dowel pin holes 114 in the carrier head torotationally fix the pinion gear with respect to thecarrier head. Thus, the rotational motion of rotatableouter hub 78 is transferred tocarrier head 100 throughring gear 94,pinion gear 96, and pins 98.

The compensation assembly allows the user ofCMPapparatus 30 to vary both the rotational and orbitalcomponents of motion of the carrier head, and therebycontrol the rotation and orbit ofsubstrate 10. Byrotating rotatableouter hub 78 while simultaneouslyrotatingdrive shaft 72, the effective rotational motionofcarrier head 100 may be controlled.Carrier head 100andsubstrate 10 may be caused to rotate, orbit, orrotate and orbit. The carrier head rotates or orbits atabout thirty to two-hundred revolutions per minute (rpm).

As the substrate orbits, the polishing pad may berotated. Preferably, the orbital radius is no greaterthan one inch, and the polishing pad rotates at arelatively slow speed, e.g., less than ten rpm and morepreferably at less than five rpm. The orbit of thesubstrate and the rotation of the polishing pad combineto provide a nominal speed at the surface of thesubstrate of 1800 to 4800 centimeters per minute.

A substrate is typically subjected to multiplepolishing steps including a main polishing step and afinal polishing step. For the main polishing step,carrier head 100 applies a force of approximately four toten pounds per square inch (psi) tosubstrate 10,althoughcarrier head 100 may apply more or less force.For a final polishing step,carrier head 100 may applyabout three psi.

Generally,carrier head 100 transfers torque fromthe drive shaft to the substrate, uniformly loads thesubstrate against the polishing surface and prevents thesubstrate from slipping out from beneath the carrier headduring polishing operations.

As shown in more detail in FIG. 3A,carrier head 100includes three major assemblies: ahousing assembly 102,asubstrate loading assembly 104, and a retainingringassembly 106.

Thehousing assembly 102 is generally circular so asto match the circular configuration of the substrate tobe polished. Thehousing assembly 102 may be machinedaluminum. The top surface ofhousing assembly 102includes acylindrical hub 110 havingcylindrical recess112 for receivingsecondary drive shaft 90. At least onepassageway 116 connectsrecess 112 to the bottom ofhousing assembly 102.

As shown in FIG. 2, driveshaft 72 includes one ormore channels 150 andsecondary drive shaft 90 includesone ormore channels 152, to provide fluid or electricalconnections to the carrier head. Arotary coupling 154 at the top ofdrive shaft 72 couples channel(s) 150 toone or more fluid orelectrical lines 156. For instance,one oflines 156 may be a conformable material supplyline as described below. Another rotary coupling (notshown) incross arm 88 connects channel(s) 150 indriveshaft 72 to channel(s) 152 insecondary drive shaft 90.As shown,passageway 116 passes throughhousing assembly102 to connect to channel 152 tosubstrate loadingassembly 104.

As the polishing pad rotates, it tends to pull thesubstrate out from beneath the carrier head. Therefore,carrier head 100 includes a retainingring assembly 106which projects downwardly fromhousing assembly 102 andextends circumferentially around the outer perimeter ofthe substrate. The retainingring assembly 106 may beattached with a key-and-keyway assembly 120 tohousingassembly 102 so that the retaining ring assembly rests onthe polishing pad and is free to adjust to variations inthe height of the polishingsurface 44. Aninner edge122 of retainingring assembly 106 captures the substrateso that the polishing pad cannot pull the substrate frombeneath the carrier head. Retainingring assembly 106may be made of a rigid plastic material.

Substrate loading assembly 104 is located beneathhousing assembly 102 in the recess formed by retainingring assembly 106.Substrate loading assembly 104 mayinclude aremovable carrier plate 124, amembrane 134which defines anenclosed volume 126, and aremovablecarrier film 128.Enclosed volume 126 may be located in the cylindrical recess surrounded by retainingringassembly 106.

Theremovable carrier plate 124 may be a circularstainless-steel disk of approximately the same diameteras the substrate. The lower surface of the carrierplate, or the lower surface of the housing if the carrierplate is not present, provides aface 130 to whichmembrane 134 may be adhesively attached.

Theenclosed volume 126 is filled with aconformablematerial 132. Theconformable material 132 is a non-gaseousmaterial which undergoes viscous, elastic, orviscoelastic deformation under pressure. Preferably,conformable material 132 is a viscoelastic material, suchas a silicon, a gelatin, or another substantiallyresilient yet viscous substance which will redistributeits mass under pressure. The pressure applied duringpolishing is substantially uniformly distributed acrosssubstrate 10 by means of the conformable material inenclosed volume 126.

As shown in FIG. 3A,membrane 134 definesenclosedvolume 126. The membrane is comprised of a flexible,stretchable and compressible material such as rubber.Membrane 134 may entirely encapsulateconformablematerial 132. Anupper surface 136 ofmembrane 134 isplaced againstface 130. Alternately, as shown in FIG.3B, the enclosed volume may be formed by extending themembrane across the recess beneathface 130 and fillingthe enclosed volume withconformable material 132.

Carrier film 128 may be attached to alower surface138 ofmembrane 134.Carrier film 128 is formed of athin circular layer of a porous material such asurethane.Carrier film 128, if used, is sufficientlythin and flexible that it substantially conforms to thesurface ofsubstrate 10.Carrier film 128 provides amountingsurface 142 to whichsubstrate 10 is releasablyadhered by surface tension. Alternately, if the carrierfilm is not used, the lower surface ofmembrane 134 maybe porous to accomplish the same thing (see FIG. 5).Carrier film 128 is sufficiently thin and flexible sothat it substantially conforms to the surface ofsubstrate 10.

The space defined by retainingring assembly 106 andmountingsurface 142 provides asubstrate receivingrecess 140. The substrate is placed against mountingsurface 142, causingconformable material 132 andcarrierfilm 128, if present, to deform to contact the substrateacross its entire backside.Carrier head 100 is thenlowered to bring the substrate into contact withpolishingsurface 44. The load applied to the substrateis transferred throughconformable material 132.

The polishingsurface 44 may be non-planar; e.g., itmay have sloping contours.Carrier plate 124 and theunderside orsurface 141 ofhousing assembly 102 may alsobe non-planar. The polishing pad may be tilted relativeto the carrier head. In addition, the backside ofsubstrate 10 may have surface irregularities. Thesubstrate could also be warped. Theconformable material 132 ensures a uniform distribution of the carrier load onthe substrate for both large scale effects (e.g., atilted polishing pad) and small scale effects (e.g.,surface irregularities on the backside of the substrate).Conformable material 132 conforms to the substratesurface as well as to face 130. That is, the conformablematerial insidemembrane 134 redistributes its mass toconform to surface irregularities on the backside of thesubstrate andface 130. Because the conformable materialcontacts substrate across its entire back surface, andbecause the conformable material has a uniform density,it ensures a uniform load across the backside of thesubstrate. In addition,conformable material 132 mayflow and deform. This permits the substrate to tilt withrespect tohousing assembly 102 to follow the contours ofthe polishing pad. In summary, the conformable materialensures thatcarrier head 100 uniformly loads thesubstrate against the polishingsurface 44.

Whencarrier head 100 rotates at high speeds,centrifugal force will tend to push the conformablematerial in the enclosed volume outwardly toward the edgeof the carrier head. This tends to increase the densityof the conformable material near the perimeter ofenclosed volume. Consequently, the conformable materialnear the edge of the enclosed volume will tend to becomeless compressible than the center, and a non-uniform loadmay be applied to the substrate.

To prevent this non-uniform load,enclosed volume126 is connected bypassageway 116,channels 150 and 152, and conformablematerial supply line 156 to asupply 158.Supply 158 can provide conformable material at a constantpressure toenclosed volume 126. Consequently, whencarrier head 100 rotates andconformable material 132 isforced toward the edge of the enclosed volume,supply 158provides additional conformable material to the center ofthe enclosed volume and maintains the conformablematerial at a substantially uniform distributionthroughoutenclosed volume 126. This uniformdistribution of conformable material ensures uniformpolishing at the center and edges of the substrate.

Supply 158 may also be used to control the viscosityofconformable material 132. By increasing the pressureon the conformable material, the density ofconformablematerial 132 can be increased. If the density ofconformable material 132 increases, its viscosity willdecrease.

The minimum pressure fromsupply 158 must overcomethe load applied by the carrier head to the substrate;otherwise, this load will force the conformable materialback throughpassageway 116. When the carrier head stopsrotating, the conformable material is uniformly redistributedthroughoutmembrane 134. The excessconformable material then flows back throughpassageways116, 150 and 152 to supply 158.

In another implementation,conformable material 132may be a material, such as rubber, which is sufficientlyrigid that it does not flow under the influence ofcentrifugal forces. In this implementation, the distribution ofconformable material 132 does not changesignificantly whencarrier head 100 rotates. Thus,conformable material supply 158 is not required.

As shown in FIG. 4,substrate loading assembly 104may include multiple compartments or enclosedvolumes 160and 162. Theenclosed volumes 160 and 162 are defined bytwo or more membrane portions. The membrane portions maybe separate, discrete membranes, or they may be differentportions of a single membrane.Enclosed volume 160 maybe a circular disk, located above the center of mountingsurface 142, andenclosed volume 162 may be an annularring surroundingenclosed volume 160. Theenclosedvolumes 160 and 162 containconformable materials 164 and166, respectively.Conformable materials 164 and 166have different viscosities. By selecting the relativeviscosities ofconformable materials 164 and 166, over-polishingof the substrate edge may be avoided and moreuniform polishing of the substrate may be achieved. Eachenclosed volume may be connected by apassageway 168 toa supply (not shown).

Referring to FIG. 5,carrier head 100 may be held ina vertically-fixed position by support assembly 60 (seeFIG. 3A), and a force may be applied tosubstrate 10 bythe carrier head. In this embodiment, theloadingassembly 104 includes a flexible connector, such as abellows 170. The bellows 170 connects asubstratebacking member 174 to abottom surface 173 ofhousingassembly 102. The bellows 170 is expandable so thatsubstrate backing member 174 can move vertically relative tohousing assembly 102. The interior ofbellows 170forms apressure chamber 176.Pressure chamber 176 canbe pressurized negatively or positively by a pressure orvacuum source (not shown) which is connected to pressurechamber 176 by aconduit 178.Membrane 134 is attachedto the bottom face ofsubstrate backing member 174. Bypressurizingchamber 176, a force is exerted onconformable material 132 to press the substrate againstthe polishing pad. Thus,flexible connector 170 acts asa loading mechanism, and replaces thebiasing piston 68.

Enclosed volume 126 may be connected to a supply asshown in the embodiment of FIG. 2. Aflexible conduit182, which may be a plastic tubing, connects apassageway180 insubstrate backing member 174 topassageway 116 inhousing assembly 102 for this purpose. The points atwhichflexible conduit 182 is connected topassageways180 and 116 may be sealed by appropriate fittings topreventconformable material 132 from leaking intopressure chamber 176.

Referring to FIG. 6, in another embodiment, one ormore substrates 10 are polished by a chemical mechanicalpolishing (CMP)apparatus 220. A complete description ofCMP apparatus 220 may be found in EP-A-0774323, the entire disclosure ofwhich is hereby incorporated by reference.

TheCMP apparatus 220 includes alower machine base222 with a table top 223 mounted thereon and removableupper outer cover (not shown). Table top 223 supports aseries of polishingstations 225a, 225b and 225c, and atransfer station 227.Transfer station 227 forms agenerally square arrangement with the three polishingstations 225a, 225b and 225c.Transfer station 227serves multiple functions of receivingindividualsubstrates 10 from a loading apparatus (not shown),washing the substrates, loading the substrates intocarrier heads (to be described below), receiving thesubstrates from the carrier heads, washing the substratesagain, and finally transferring the substrates back tothe loading apparatus.

Each polishingstation 225a-225c includes arotatable platen 230 on which is placed apolishing pad232. Ifsubstrate 10 is an eight-inch (200 mm) diameterdisk, then platen 230 and polishingpad 232 will be abouttwenty inches in diameter.Platen 230 is preferably arotatable aluminum or stainless steel plate connected bystainless steel platen drive shaft (not shown) to aplaten drive motor (not shown). For most polishingprocesses, the drive motor rotatesplaten 230 at thirtyto two-hundred revolutions per minute, although lower orhigher rotational speeds may be used.

Referring to FIG. 10, polishingpad 232 is acomposite material with a roughened polishing surface234.Polishing pad 232 may be attached to platen 230 bya pressure-sensitive adhesive layer 239.Polishing pad 232 may have a fifty mil thick hardupper layer 236 anda fifty mil thick softerlower layer 238.Upper layer236 is preferably a material composed of polyurethanemixed with other fillers.Lower layer 238 is preferablya material composed of compressed felt fibers leachedwith urethane. A common two-layer polishing pad, withthe upper layer composed of IC-1000 and the lower layercomposed of SUBA-4, is available from Rodel, Inc.,located in Newark, Delaware (IC-1000 and SUBA-4 areproduct names of Rodel, Inc.).

Returning to FIG. 6, each polishingstation 225a-225cmay further include an associatedpad conditionerapparatus 240. Eachpad conditioner apparatus 240 has arotatable arm 242 holding an independently rotatingconditioner head 244 and an associatedwashing basin 246.The conditioner apparatus maintains the condition of thepolishing pad so it will effectively polish any substratepressed against it while it is rotating.

Aslurry 250 containing a reactive agent (e.g.,deionized water for oxide polishing), abrasive particles(e.g., silicon dioxide for oxide polishing) and achemically reactive catalyzer (e.g., potassium hydroxidefor oxide polishing), is supplied to the surface ofpolishingpad 232 by aslurry supply tube 252.Sufficient slurry is provided to cover and wet theentirepolishing pad 232. Two or more intermediate washingstations 255a and 255b are positioned between neighboringpolishingstations 225a, 225b and 225c. The washing stations rinse the substrates as they pass from onepolishing station to another.

A rotatablemulti-head carousel 260 is positionedabovelower machine base 222.Carousel 260 is supportedby acenter post 262 and rotated thereon about acarouselaxis 264 by a carousel motor assembly located withinbase222.Center post 262 supports acarousel support plate266 and acover 268.Multi-head carousel 260 includesfourcarrier head systems 270a, 270b, 270c, and 270d.Three of the carrier head systems receive and holdsubstrates, and polish them by pressing them against thepolishing pad 232 onplaten 230 of polishingstations225a-225c. One of the carrier head systems receives asubstrate from and delivers the substrate to transferstation 227.

The fourcarrier head systems 270a-270d are mountedoncarousel support plate 266 at equal angular intervalsaboutcarousel axis 264.Center post 262 allows thecarousel motor to rotate thecarousel support plate 266and to orbit thecarrier head systems 270a-270d, and thesubstrates attached thereto, aboutcarousel axis 264.

Eachcarrier head system 270a-270d includes apolishing orcarrier head 300. Eachcarrier head 300independently rotates about its own axis, andindependently laterally oscillates in aradial slot 272formed incarousel support plate 266. Acarrier driveshaft 274 connects a carrierhead rotation motor 276 tocarrier head 300 (shown by the removal of one-quarter of cover 268). There is one carrier drive shaft and motorfor each head.

Referring to FIG. 7, in which cover 268 ofcarousel260 has been removed,carousel support plate 266 supportsthe fourcarrier head systems 270a-270d. Carouselsupport plate includes fourradial slots 272, generallyextending radially and oriented 90° apart.Radial slots272 may either be close-ended (as shown) or open-ended.The top of support plate supports four slotted carrierhead support slides 280. Eachslide 280 aligns along oneof theradial slots 272 and moves freely along a radialpath with respect tocarousel support plate 266. Twolinear bearing assemblies bracket eachradial slot 272 tosupport eachslide 280.

As shown in FIGS. 7 and 8, each linear bearingassembly includes arail 282 fixed tocarousel supportplate 266, and two hands 283 (only one of which isillustrated in FIG. 8) fixed to slide 280 to grasp therail. Two bearings 284 separate eachhand 283 fromrail282 to provide free and smooth movement therebetween.Thus, the linear bearing assemblies permit theslides 280to move freely alongradial slots 272.

Abearing stop 285 anchored to the outer end one oftherails 282 preventsslide 280 from accidentally comingoff the end of the rails. One of the arms of eachslide280 contains an unillustrated threaded receiving cavityor nut fixed to the slide near its distal end. Thethreaded cavity or nut receives a worm-gear lead screw286 driven by a slideradial oscillator motor 287 mounted oncarousel support plate 266. Whenmotor 287 turnsleadscrew 286, slide 280 moves radially. The fourmotors 287are independently operable to independently move the fourslides along theradial slots 272 incarousel supportplate 266.

A carrier head assembly or system, each including acarrier head 300, acarrier drive shaft 274, acarriermotor 276, and a surrounding non-rotating shaft housing278, is fixed to each of the four slides. Drive shafthousing 278 holdsdrive shaft 274 by paired sets oflowerring bearings 288 and a set ofupper ring bearings 289.Each carrier head assembly can be assembled away frompolishingapparatus 220, slid in its untightened stateintoradial slot 272 incarousel support plate 266 andbetween the arms ofslide 280, and there tightened tograsp the slide.

Arotary coupling 290 at the top ofdrive motor 286couples two or more fluid orelectrical lines 292 intotwo ormore channels 294 indrive shaft 274.Channels294 are used, as described in more detail below, topneumaticallypower carrier head 300, to vacuum-chuck thesubstrate to the bottom of the carrier head and toactuate a retaining ring against the polishing pad.

During actual polishing, three of the carrier heads,e.g., those ofcarrier head systems 270a-70c, arepositioned at and above respective polishingstations225a-225c.Carrier head 300 lowers a substrate intocontact with polishingpad 232, andslurry 250 acts asthe media for chemical mechanical polishing of the substrate or wafer. Thecarrier head 300 uniformly loadsthe substrate against the polishing pad.

The substrate is typically subjected to multiplepolishing steps, including a main polishing step and afinal polishing step. For the main polishing step,usually performed atstation 225a,carrier head 300applies a force of approximately four to ten pounds persquare inch (psi) tosubstrate 10. At subsequentstations, carriedhead 300 may apply more or less force.For example, for a final polishing step, usuallyperformed at station 225c,carrier head 300 may apply aforce of about three psi.Carrier motor 76 rotatescarrier head 300 at about thirty to two-hundredrevolutions per minute.Platen 230 andcarrier head 300may rotate at substantially the same rate.

Generally,carrier head 300 holds the substrateagainst the polishing pad and evenly distributes adownward pressure across the back surface of thesubstrate. The carrier head also transfers torque fromthe drive shaft to the substrate and ensures that thesubstrate does not slip from beneath the carrier headduring polishing.

Referring to FIG. 9A,carrier head 300 includes ahousing assembly 302, aloading mechanism 304 and abaseassembly 306. Thedrive shaft 274 is connected tohousing assembly 302.Loading mechanism 304 connectshousing assembly 302 tobase assembly 306. The loadingmechanism applied a load, i.e., a downward pressure, tobase assembly 306. Thebase assembly 306 transfers the downward pressure fromloading mechanism 304 tosubstrate10 to push the substrate against the polishing pad.Baseassembly 306 includes aconformable layer 308 to evenlydistribute the downward pressure across the back surfaceof the substrate. Each of these components will bedescribed in greater detail below.

Housing assembly 302 may be formed of aluminum orstainless steel. The housing assembly is generallycircular in shape to correspond the circularconfiguration of the substrate to be polished. The topsurface of the housing assembly may include acylindricalhub 320 having a threadedneck 322. To connectdriveshaft 274 tocarrier head 300, twodowel pins 324 may beinserted into matching dowel pin holes inhub 320 and aflange 296. Then, a threadedperimeter nut 298 isscrewed onto threadedneck 322 to firmly attachcarrierhead 300 to driveshaft 274. Whendrive shaft 274rotates, dowel pins 324 transfer torque tohousingassembly 302 to rotate the carrier head about the sameaxis as the drive shaft.

At least twoconduits 326 and 328 extend throughhub320. There may be one conduit for eachchannel 294 indrive shaft 274. Whencarrier head 300 is attached todriveshaft 274, the dowel pins align the carrier head sothatconduits 326 and 328 connect tochannels 294. O-rings(not shown) may be positioned inhub 320surrounding eachconduit 326 and 328 to form a fluid-tightseal between the conduits to the channels.

Loading mechanism 304 forms a vertically-movableseal betweenhousing assembly 302 andbase assembly 306and defines apressure chamber 330. A gas, such as air,is pumped into and out ofpressure chamber 330 throughconduit 326 to control the load applied tobase assembly306. When air is pumped intopressure chamber 330,baseassembly 306 is forced downwardly to bringsubstrate 10into contact with polishingpad 232. When air is pumpedout ofpressure chamber 330, base assembly is liftedupwardly to remove the substrate from polishingpad 232.

Loading mechanism 304 may include a cylindricalbellows 332 which is bolted or fixed tohousing assembly302 andbase assembly 306 to formpressure chamber 330.Bellows 332 may be a stainless steel cylinder whichexpands or contracts depending upon whether a gas issupplied to or removed frompressure chamber 330.Bellows 332 may include upper andlower support plates334 and 336 which are bolted or otherwise secured tohousing assembly 302 and abase assembly 306,respectively. Acylindrical seal 338 may fit into acircumferential groove 312 onrim 310 ofhousing 302 andin acircumferential groove 339 in an upwardly-extendingwall portion 318 of,base assembly 306. Theseal 338surrounds and protectsbellows 332 from the corrosiveeffects ofslurry 250. Whenhousing assembly 302 isrotated, bellows 332 transfers torque from the housingassembly to the base assembly, causing it to also rotate.However, because the bellows are flexible,base assembly 306 can pivot with respect to the housing assembly aboutan axis parallel to the surface of the polishing pad toremain substantially parallel to the polishing padsurface.

Base assembly 306 includes a rigid backing fixtureorplate 350 and adetachable module 352 which isattached to the underside ofbacking plate 350. Backingplate 350 may be generally disk-shaped to match theconfiguration ofsubstrate 30, and may be formed of ametal such as aluminum or stainless steel.Module 352includes a rigid support fixture orcup 354,conformablelayer 308, anannular shield ring 360, and anannularretaining ring 362. Each of these elements will bediscussed in detail below.

Module 352 may be removably attached tobackingplate 350 by various attachment mechanisms, such asbolts, screws, key and key slot combination, vacuumchucking, or magnets. As such,module 352 can bedetached and replaced if it is damaged or worn out. Inaddition, it may be replaced to change the polishingparameters. For example, different modules mayincorporate conformable layers with different durometermeasurements. The different modules may also havedifferent retaining ring widths or retaining ringheights. The height and width of the retaining ringaffects the polishing rate near the edge of thesubstrate. These module features can be selected toprovide an optimal polishing performance.

Cup 354 may be formed of aluminum or stainless steeland may have an outer lip or rim 356 which projectsdownwardly to surround a recess. Theconformable layer308 is disposed within the recess so that the bottomsurface of the conformable layer is substantially flushwith the bottom surface ofrim 356. The recess may beapproximately one-eighth to one-quarter inch deep.

Theconformable layer 308 is made of a visco-elasticmaterial that has a substantially homogeneous density.Conformable layer 308 is elastic; i.e., it will return toits original shape when an applied load is removed.Conformable layer 308 is slightly compressible. Inaddition,conformable layer 308 undergoes normal strain;i.e., it will redistribute its mass in directions normalto an applied load. The durometer measurement of theconformable layer must be carefully selected. If thedurometer measurement is too low, the material will lackelasticity. On the other hand, if the durometermeasurement is too high, the material will not undergonormal strain.Conformable layer 308 may have adurometer measurement of between approximately fifteen totwenty-five on the Shore scale. Preferably,conformablelayer 308 has a durometer measurement of about twenty-oneon the Shore scale. The conformable material may have anadhesive surface so that it adheres to the walls ofcup354. In addition, it should be resistant to heat and bechemically inert vis-a-vis the polishing process. Anappropriate conformable material is a urethane materialavailable from Pittsburgh Plastics of Zelienopal, Pennsylvania.Module 352 may be manufactured by pouringliquid urethane intocup 354 and curing it to form layer309.

Referring to FIG. 10,conformable layer 308permitssubstrate 10 to shift or pivot to accommodate changes inthe surface of the polishing pad.Conformable layer 308deforms to match the back side ofsubstrate 10 and evenlydistribute the load fromloading mechanism 304 to thesubstrate. For example, ifsubstrate 10 is warped,conformable layer 308 will, in effect, conform to thecontours of the warped substrate.

Athin sheet 358 of a low-friction material may belaminated to the outer surface ofconformable layer 308to provide a low-frictionsubstrate mounting surface 364.Thesheet 358 may be a seven mil thick film of urethanehaving a durometer measurement of approximately eighty-threeon the Shore scale.Sheet 358 permits theconformable material layer 308 to closely conform to theback side ofsubstrate 10 but prevents the substrate fromadhering to the conformable material.Sheet 358 issufficiently thin thatsubstrate 10 may be considered tobe in direct contact withconformable layer 308.

Referring to FIG. 9A,module 352, as previouslynoted, also includesshield ring 360 and retainingring362.Shield ring 360 is formed of a rigid material suchas aluminum or stainless steel and is positioned belowcomformable layer 308 to be substantially flush with thebottom surface ofrim 356 and the conformable layer.Shield ring 360 holdsconformable layer 308 with the recess ofcup 354 when a load is applied tosubstrate 10.Shield ring 360 may be appropriately secured torim 356such as by screws or bolts (not shown).

Retainingring 362 is an annular rigid ring,positioned within the circumference ofshield ring 360.Retainingring 362 may be adhesively attached directly toconformable layer 308. Retainingring 362 may be formedof a hard plastic or ceramic material. Retainingring362 is separated fromshield ring 360 by a small gap "r"so that the retaining ring may shift or pivot toaccommodate variations in the vertical height of thesurface of polishingpad 232. In operation,substrate 10fits into a circular recess defined by retainingring 362and abuts mountingsurface 364 of the conformable layer.Retainingring 362 andsubstrate 10 have substantiallythe same thickness, so that retainingring 362 alsocontacts polishing pad 232. The shear force created bythe relative velocity betweensubstrate 10 andpolishingpad 232 tends to push the substrate from beneathcarrierhead 300. Retainingring 362 preventssubstrate 10 frommoving from beneathbase assembly 306.

Referring to FIG. 9B, in another embodiment, inwhich similar parts are referred to with primed numbers,loading mechanism 304' may include aflexible membrane340 instead of a bellows.Flexible membrane 340 may bean annular sheet of silicone approximately sixty milsthick, with inner andouter edges 342 and 344. Theinneredge 342 is clamped between aninner clamp ring 346 andbase assembly 306', whereasouter edge 344 is clamped between anouter clamp ring 348 and housing assembly302'. The clamp rings attach the flexible membrane tothe housing assembly and the base assembly to formpressure chamber 330'.Flexible membrane 340 acts as adiaphragm which rolls or unrolls, depending upon thevertical distance across pressure chamber 330'.

Housing assembly 302' includes two opposingflanges314 which project downwardly fromrim 310. Eachflange314 may have arectangular slot 315. Atorque pin 316extends through eachrectangular slot 315 and is securedin a receivingrecess 317 in upward-extending wallportion 318' ofbacking plate 350 of base assembly 306'.The width ofrectangular slot 315 is comparable to thewidth oftorque pin 316 so that the pin cannot movehorizontally in the slot. Whendrive shaft 274 rotateshousing assembly 302', torque pins 316 transfer torquefrom the housing assembly to the base assembly. Theheight ofrectangular slot 315 is greater than the heightoftorque pin 316 so that the pin can move vertically inthe slot. Thus, base assembly 306' must rotate withhousing assembly 302', but it is free to move verticallywith respect to the housing assembly.

As discussed above,carrier head 300 may liftsubstrate 10 away from polishingpad 232 in order to movethe substrate from one polishing station to another. Inaddition, the substrate may be ejected fromcarrier head300 to return the substrate to transfer station 227 (seeFIG. 6). Specifically,carrier head 300 may vacuum-chuck or pressure-eject the substrate to or from mountingsurface 364, as explained in more detail below.

The carrier head includes several fluid lines whichpermit a gas, such as air, to flow into and out ofbaseassembly 306 to vacuum-chuck or pressure-eject thesubstrate. Becausebase assembly 306 andhousingassembly 302 can move vertically relative to each other,flexible fluid conduits are used to linkconduit 328 toapassageway 370 inbacking plate 350. As shown in FIG.9A, the flexible fluid conduit may be a metal bellows372. The metal bellows can expand and contract to matchthe distance acrosschamber 330. Alternately, as shownin FIG. 9B, the flexible fluid conduit may be aplastictubing 374 positioned within chamber 330'. The plastictubing may, for example, be wrapped in a half, a three-quarter,a full turn. When base assembly 306' movesrelative to the housing assembly, the tubing coils oruncoils to match the distance across chamber 330'.

Referring to FIG. 11A, in one implementation,passageway 370 is connected to one ormore passages 376ofcup 354. In addition, vacuum-chuckingpassages 380extend throughconformable layer 308 frompassages 376 incup 354 to mountingsurface 364. Eachvacuum chuckingpassage 380 is simply a hole in the conformable layer.The-hole is large enough so that it does not collapsewhen a vacuum is applied but small enough so that it doescollapse when a load is applied to the substrate.

Apump 382 is connected viafluid line 292,channel294,conduit 328,conduit 372,passageway 370,passages 376, and vacuum-chuckingpassages 380 to mountingsurface364. If a vacuum is applied topassages 380 bypump 382,substrate 10 will be vacuum-chucked to mountingsurface364. If air is forced intopassages 380 bypump 382,substrate 10 will be ejected from mountingsurface 364.

Referring to FIG. 11B, whensubstrate 10 ispositioned against polishingpad 232 and a load isapplied,conformable layer 308 will be compressed andvacuum-chuckingpassages 380 will collapse. Thus, thepassages do not significantly affect the distribution ofthe load across the backside of the substrate. When theload is removed,conformable layer 308 will return to itsnormal state and vacuum-chuckingpassages 380 willreopen. Each vacuum-chuckingpassage 380 should bebetween approximately one-eighth and one-quarter of aninch in diameter.

Referring to FIGS. 12A and 12B, in anotherimplementation,substrate 10 is vacuum-chucked tocarrierhead 300 by the formation of a vacuum pocket. As shownin FIG. 12A,module 352 may include a vertically-movabledisk 390.Conformable layer 308 may be adhesivelyattached todisk 390.Disk 390 has a diameter less thanthat of the substrate, and it may be connected to theactivating mechanism of anair cylinder 392.Aircylinder 392 may be positioned incup portion 354, and it392 may be powered by apump 382. The pump is connectedto the air cylinder by the flexible conduit,passageway370, andpassages 376. The actuating mechanism ofair cylinder 392 may movedisk 390 between a first positionin which the disk is flush with abottom surface 394 ofbase 378 of cup 354 (see FIG. 12A) and a second positionin which the disk has been drawn upwardly away from thesubstrate. In the second position, the portion ofconformable layer 308 beneath the disk will be pulledupwardly. Since the edges ofconformable layer 308remain in contact withsubstrate 10, whereas the centerofconformable layer 308 is drawn away from the center ofsubstrate 10, avacuum pocket 398 is formed between thesubstrate and the conformable layer. This vacuum pocketvacuum-chucks the substrate to the carrier head.A conformable layer in accordance with the presentinvention may be incorporated into various other carrierhead designs, such as the one described in JP-A-322071, the entire disclosure ofwhich is hereby incorporated by reference.

Referring specifically to FIG. 13, such acarrierhead 400 includes a housing assembly 402, abase assembly404 and a retainingring assembly 406. Aconformablelayer 408, similar in composition and structure to theconformable layer described above, may be adhered orattached to asurface 418 ofbase assembly 404 to provideasubstrate mounting surface 410.

The present invention has been described in terms ofa preferred embodiment. The invention however, is not limited to the embodiment depicted and described.Rather, the scope of the invention is defined by theappended claims.

Claims (22)

1. A carrier for positioning a substrate on apolishing surface in a chemical mechanical polishingapparatus, comprising:

   a housing; and

   a containment assembly connected to the housing tohold a layer of conformable material, the layer ofconformable material providing a mounting surface for asubstrate.
2. The carrier of claim 1 wherein the containmentassembly includes a flexible membrane defining anenclosed volume, and the conformable material is disposedwithin the enclosed volume.
3. The carrier of claim 2 wherein the flexiblemembrane is attached to a backing member, and wherein aflexible connector connects the backing member to thehousing.
4. The carrier head of claim 3 wherein theflexible connecter forms a pressure chamber between thehousing and the backing member.
5. The carrier head of claim 2 wherein theflexible membrane includes a first flexible membraneportion defining a first enclosed volume and a secondflexible membrane portion defining a second enclosedvolume, and the conformable material includes a firstconformable material having a first viscosity disposed inthe first enclosed volume and a second conformablematerial having a second viscosity disposed in the secondenclosed volume.
6. The carrier of claim 1 wherein the conformablematerial is a viscoelastic material.
7. The carrier head of claim 6 wherein theconformable material is selected from the groupconsisting of silicone and gelatin.
8. The carrier of claim 6 the conformable materialhas a durometer measurement selected to provide bothelasticity and normal strain in response to an appliedload.
9. The carrier of claim 8 wherein the conformablematerial has a durometer measurement between abouttwenty-five and thirty-five.
10. The carrier of claim 9 wherein the conformablematerial is substantially pure urethane.
11. The carrier of claim 1 wherein the containmentassembly includes a base member with a recess, and thelayer of conformable material is disposed in the recessto provide the mounting surface.
12. The carrier of claim 11, wherein the basemember is detachably connected to the carrier head.
13. The carrier of claim 11 further comprising aretaining ring connected to the mounting surface.
14. The carrier of claim 13 wherein the retainingring has approximately the same thickness as thesubstrate.
15. The carrier of claim 14 further comprising ashield connected to the base member and projecting overa portion of the layer of conformable material tosurround the retaining ring.
16. The carrier of claim 15 wherein the shield isthinner than the retaining ring.
17. The carrier of claim 11 further comprising ashield ring connected to the base member and projectingover a portion of the layer of conformable material.
18. The carrier of claim 17 wherein the shield ispositioned to prevent the conformable material fromextruding when the substrate is pressed against thepolishing surface.
19. The carrier of claim 1 further comprising achucking mechanism to attach the substrate to themounting surface.
20. The carrier of claim 19 wherein the chuckingmechanism includes a passageway formed through the layerof conformable material to the mounting surface, andwherein a pump is connected to the passageway to suctionthe substrate to the mounting surface.
21. The carrier of claim 20 wherein the passagewayhas a diameter such that the passageway does not collapseif the pump applies suction to the passageway.
22. The carrier of claim 21 wherein the chuckingmechanism includes a pocket between the substrate and the layer of conformable material to suction the substrate tothe mounting surface.

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