Apparatus for transporting wafer to and from polishing head

Abstract: Apparatus for transporting a wafer into position against the pressure head of apparatus for polishing the wafer. The transport apparatus includes a dolly for positioning a wafer over a transport head assembly. The transport head assembly removes the wafer from the dolly and positions the wafer against the pressure head. When the transport head assembly removes the wafer from the dolly and positions the wafer against the pressure head, the transport head assembly only contacts the wafer at selected points at the periphery of the wafer.

Description: This invention relates to polishing apparatus of the general type as described by the features of the pre-characterizing portion of claim 1. More particularly, the invention relates to apparatus for polishing a side of a thin, flat wafer of a semiconductor material, the apparatus including a polishing head which receives the wafer at a wafer load station, which carries the wafer to a wetted polishing surface under pressure, and which rotates and oscillates the wafer over the polishing surface. In a further respect, the invention relates to apparatus of the type described which includes apparatus for transporting a wafer to the load station for pickup by the polishing head while preventing dust particles and other impurities from contacting the wafer during its transport to the load station. Apparatus for polishing thin, flat semiconductor wafers is well known in the art. See, for example, U. S. Patent Nos. 3,841,031 to Walsh and 4,193,226 to Gill, Jr. et al. and the published European Patent Application No. EP-A-0 284 343 to Gill, Jr. Such apparatus includes a polishing head which receives a wafer at a wafer load station and carries the wafer to a wetted polishing station. The polishing head presses the wafer downwardly against the wetted polishing surface. The polishing head can rotate and oscillate the wafer over the polishing surface. A particular problem encountered in transporting the wafer to the load station for pickup by the polishing head is preventing contaminants from contacting the wafer. Accordingly, it would be highly desirable to provide improved semiconductor polishing apparatus of the general type described which would permit the ready transportation of a wafer to a wafer load station for pickup by the polishing head and which would prevent contaminants from contacting the wafer during its transport to the load station. Therefore, it is a principal object of the invention to provide improved apparatus for polishing a surface of a flat semiconducteur wafer. The solution of this problem is defined by the terms of claim 1. Advantageous further developments of the invention are subject of the subclaims. These and other, further and more specific objects and advantages of the invention will be apparent to those skilled in the art from the following detailed description thereof, taken in conjunction with the drawings, in which: Fig. 1 is an exploded assembly view of a wafer transport head assembly utilized to remove a wafer from a dolly and transport the wafer to the polishing head; Fig. 2 is an exploded assembly view of a wafer water track assembly utilized to carry a polished wafer from the polishing head to a storage cassette; Fig. 3 is an assembly view of a wafer dolly and track utilized to transfer a wafer from a wafer cassette to the wafer transport head assembly; Fig. 4. is a perspective view of the wafer transport dolly; Fig. 5 is an elevation view illustrating use of the wafer dolly to transport a wafer from a wafer cassette to the wafer transport head assembly; Fig. 6 is a perspective view of a wafer cassette; Fig. 7 is a section view illustrating operation of the wafer water track assembly to transport a wafer from the polishing head to a wafer cassette; and, Figs. 8A to 8E illustrate operation of the wafer transport head assembly to remove a wafer from the wafer dolly and position the wafer adjacent the polishing head. Briefly, in accordance with our invention, we provide apparatus for transporting a wafer into position against the pressure head of apparatus for polishing the wafer. The transport apparatus includes a dolly for positioning a wafer over a transport head assembly. The transport head assembly removes the wafer from the dolly and positions the wafer against the pressure head. When the transport head assembly removes the wafer from the dolly and positions the wafer against the pressure head, the transport head assembly only contacts the wafer at selected points at the periphery of the wafer. Turning now to the drawings, which depict the presently preferred embodiments of the invention for the purpose of illustrating the practice thereof and not by way of limitation of the scope of the invention, and in which like reference characters refer to corresponding elements throughout the several views, Figs. 1 to 8 depict apparatus for transporting a wafer to and from a pressure or polishing head. In order to facilitate the understanding of the invention, like reference characters herein and in European Patent Application No. EP-A-0 284 343 to Gill, Jr. also refer to corresponding elements. Consequently, the apparatus in Figs. 1 to 8 can be used to transport a wafer to and from a layer 120 in the pressure head of Fig. 2B of European Patent Application No. EP-A-0 284 343. Further, as illustrated in Fig. 1 of European Patent Application No. EP-A-0 284 343, and as is well known in the art, elongate carrier means 13 is provided to move the pressure head between a first operative position over the wafer transport apparatus of Figs. 1 to 8 herein and a second operative position over a polishing surface. The pressure head maintains the wafer against the polishing surface to polish the wafer. Fig. 1 illustrates a transport head assembly including a base 200, alignment cup 201, support piston 202, legs 203 to 205, and pins 206 to 208. Apertures 210 open at and extend downwardly from circular rim surface 211. Apertures 210 are generally formed at equal intervals around rim surface 211. Although only four apertures 210 are visible in Fig. 1, there actually six apertures 210 formed in rim surface 211. Three of the pins 206 to 208 and springs 209 are omitted from Fig. 1 for the sake of clarity. Each aperture 210 is, however, intended to be provided with a spring 209 and pin 206 to 208. Each pin 206 to 208 is identical in shape and dimension. Indents 212 to 214 each receive the upper arm 216 of a leg 203 to 205. The bottom arm 217 of each leg 203 to 205 is attached to base 200 with bolts 218. Legs 203 to 205 press alignment cup 201 against springs 219. The lower end of each spring 219 rests in a detent 220 formed in base 200. The upper end of each spring 219 rests in a similar detent (not visible) formed in cup 201. Support piston 202 is slidably received by cylindrical aperture 221 formed in cup 201. Springs 222 provide support for piston 202. The lower ends of springs 222 are received by detents 223. The upper ends of springs 222 are received by similar detents 224 formed in the bottom of piston 202. The upper tip 225 of each pin 206 to 208 is tapered in a truncated conical shape. Piston 202 includes cylindrical outer surfaces 226 which slidably contact surface 221. Arcuate lips or support surfaces 227 and 228 are above planer floor portions 229 and 230. The wafer storage cassette 232 shown in Fig. 6 includes a plurality of opposed, spaced apart pairs 223A, 223B and 234A, 234B of support ledges. Each ledge pair supports selected peripheral edge portions of a wafer 10. Wafer 10 includes spaced apart top 10A and bottom 10B surfaces. Surfaces 10A and 10B each terminate at edge 10C. The wafer dolly 236 is utilized to transport wafers from cassette 232 to the transport head assembly of Fig. 1. Dolly 236 includes rectangular base 237. Pin 238 is fixedly attached to base 237 and maintains roller 239 in position adjacent base 237. Elongate pin 240 is fixedly attached to base 237. Spring 241 is positioned around pin 240. Ends 242A and 242B of spring 241 bear against pin 243 fixedly attached to base 237. Spring 241 functions to bias dolly 236 so that roller 239 will travel along a track 244 (Fig. 3) in the manner described below. Tongue 245 of dolly 236 is connected to neck 246. Neck 246 is attached to base 237. Upper planer surface 248 of tongue 245 is bounded at either end by arcuate outwardly sloping or diverging surfaces 247 and 249. Surfaces 247 and 249 contact the lower linear circular portion 10D of edge 10C and prevent the bottom 10B of wafer 10 from contacting upper surface 248 of dolly 236. The operation of the wafer dolly 236 of Fig. 4 is explained with reference to Fig. 3. In Fig. 3, the tongue 245, neck 246 and base 237 of dolly 236 are shown in ghost outline for the sake of clarity. During operation, roller 239 of dolly 236 moves along edge of track 244 of plate 262. Track 244 is, except for a jog 244A at the center of the track, linear. Jog 244A enables the orientation of tongue 245 to be altered by 180 degrees. The lower portion of pin 240 is pivotally connected to plate 250. Motive power means (not shown) are provided for moving plate 250 in directions 251 and 252 along cylindrical rod 253. Cylindrical aperture 254 in plate 250 slidably moves along rod 253. When plate 250 is at the midpoint illustrated in Fig. 3, tongue 245 is in the orientation indicated by dashed lines 245. When plate 250 is moved in the direction of arrow 252, tongue 245, base 237, and neck 246 pivot 90° in the direction indicated by arrow 256. Consequently, base 237 assumes the orientation indicated by dashed lines 237A. Conversely, if plate 250 moves from the center position illustrated in Fig. 3 in the direction of arrow 251, the tongue 245, neck 246, and base 237 are rotated 90° in the direction of arrow 257 and base 237 assumes the orientation illustrated by dashed lines 237B. In Fig. 3, dashed lines 259 generally indicate the position of a wafer cassette 232 and of means for raising and lowering cassette 232. Dashed lines 260 generally indicate the location of the transport head assembly. Operation of the wafer dolly 236 is further illustrated in Fig. 5. When plate 250 moves in the direction of arrow 252 (Fig. 3) such that the base of dolly 236 arrives at the position indicated by dashed lines 237A, the dolly 236 is in the position indicated in the right hand portion of Fig. 5 with tongue 245 extending into cassette 232 beneath a wafer 10. Means 260 is operated to lower cassette 232 while tongue 245 remains in fixed position. Lowering cassette 232 causes portions of the peripheral edge portion 10D to contact arcuate outwardly sloped surfaces 247 and 249 to lift wafer 10 off of ledge pair 233B (not visible in Fig. 5) and 233A. After wafer 10 is so positioned on surfaces 247 and 249, plate 250 is moved in the direction of arrow 251 to move roller 239 along edge 44 through jog 44A and to a point where base 237 is in the position indicated by dashed lines 237B in Fig. 3. When the base is in the position indicated by dashed lines 237B, dolly 236 is in the position indicated by the left hand portion of Fig. 5 with tongue 245 above the transport head assembly 264. Once tongue 245 is positioned over transport head assembly 264, assembly 264 is operated in the manner described in Figs. 8A to 8E to remove the wafer 10 from tongue 245 and position wafer 10 adjacent the pressure head. In Fig. 8A, the transport head assembly 264 and tongue 245 are in the position illustrated in the left hand portion of Fig. 5. In Fig. 8B, means 261 has been activated to upwardly displace base 200 and assembly 264 in the direction of arrow 270 while dolly 236 and tongue 245 remain stationary. As shown in Fig. 4, portions of edge 10C of wafer 10 extend outwardly away from and free of contact with or support by tongue 245. When transport assembly 264 is displaced in the direction of arrow 270 in Fig. 8B, selected points of these free portions contact the tapered upper ends 225 of the six spaced apart pins extending upwardly from surface 211. Tapered ends 225 guide wafer 10 downwardly intermediate the pins onto support surface 227. While transport head assembly 264 rises in Fig. 8B, portions of walls 221, 226 and 263 move upwardly past tongue 245. Both the distance between parallel opposed walls 226 and 263 and the area circumscribed by wall 221 are sufficient to permit tongue 245 to fit therein when transport head assembly 264 rises in the direction of arrow 270. In Fig. 8B, tongue 245 is shown separated from wafer 10 even though wafer 10 has not completely settled onto support surface 227. This is done for the sake of clarity. Normally wafer 10 will not be lifted and separated from stationary tongue 245 until wafer 10 is contacting support surface 227 and tongue 245 is beneath surface 227. The transport head assembly 264 rises when means 261 applies an upward force (acting in the direction of arrow 270) against base 200. A pneumatic cylinder, hydraulic cylinder or any other mechanical, electrical, manual etc. prior art means may be utilized to raise, and lower, base 200 and transport head assembly 264. After wafer 10 is resting on circular planer support surface 227, the pressure head 265 is lowered to a position adjacent alignment cup 201. Dolly 226 can remain in fixed position or can be removed from assembly 264 in the direction of arrow 252 (Fig. 3). In Figs. 8C to 8E, dolly 236 is assumed to have been removed from assembly 264. After wafer 10 has settled onto support surface 227, the upward movement of transport head assembly 264 is halted and pressure head 265 is positioned adjacent alignment cup 201 in the manner illustrated in Fig. 8C. Means 266 are used to position pressure head 265 over alignment cup 201. The positioning means 266 can comprise the counterbalanced apparatus of Fig. 1 of European Patent Application EP-A-0 284 343 or can comprise any other appropriate prior art positioning apparatus. When pressure head 265 is positioned adjacent alignment cup 201 as illustrated in Fig. 8C, water is squirted through apertures (see apertures 90 in Fig. 2B of European Patent Application EP-A-0 284 343) formed in polishing head 265 to wet wafer 10. The flow of water through the apertures is then discontinued and a suction is applied to the apertures. While pressure head 265 is maintained in a fixed position, means 261 is utilized to resume the movement of base 200 and transport head assembly 264 in the direction of arrow 270. As transport head assembly 264 continues to rise, the bottom circular planer surface 272 of lip 72A contacts the six pins (including pins 206 to 208) in apertures 210. Surface 272 downwardly forces the six pins into apertures 210, compressing springs 209. The upward movement of alignment cup 201 halts when the lower circular planer surface 272 of lip 72A is contacted by circular surface 211 in the manner illustrated in Fig. 8D. After surface 211 contacts surface 272, means 261 is utilized to continue to upwardly displace base 200, compressing springs 219 and 222. While springs 219 are being compressed, pressure head 265 is maintained in fixed position, which causes alignment cup 201 to also remain in fixed position. Consequently, while base 200 continues to move upwardly and while alignment cup 201 remains stationary while springs 219 are further compressed, the continued compression of springs 222 causes piston 202 to be upwardly displaced in the direction of arrow 270 to press wafer 10 against layer 120. Once wafer 10 is positioned by piston 202 immediately adjacent or contacting layer 120, the suction through apertures 90 maintains the wafer against layer 120. Fig. 8E illustrates the position of piston 202 and springs 219, 222 after means 261 have been utilized to upwardly displace base 200 to cause piston 202 to move upwardly and press wafer 10 against layer 120. Once wafer 10 is pressed against layer 120, means 266 can be utilized to lift pressure head 265 up away from the transport head assembly and means 261 can be utilized to lower the transport head assembly back to the position of Fig. 8A. Means 266 is then utilized to move pressure head 265 to a polishing station to polish wafer 10. After the wafer 10 is polished to within selected tolerances, pressure head 265 is positioned over the water track illustrated in Figs. 2 and 7. The water track of Figs. 2 and 7 includes an elongate rectangular housing 271 having a circular reservoir formed therein to receive a wafer ejected from pressure head 265. The wafer 10 is separated from layer 120 by discontinuing the suction through apertures 90 and by directing water flow outwardly through apertures 90. The circular reservoir in housing 271 has a floor 274 and upwardly extending outwardly sloped circular walls 273 and 275. Vertically oriented cylindrical wall 293 interconnects walls 273 and 275. An elongate channel having a floor 276 is in fluid communication with the circular reservoir. Floors 274 and 276 are co-planar. The elongate channel includes a pair of elongate, opposed spaced apart sloped side wafer-guide surfaces 277 and 278 extending upwardly and outwardly away from floor 276. Each sloped wafer-guide surface 278, 279 terminates at a vertical side wall 280 and 279, respectively. A liquid or a mixture of a liquid and gas flows into the circular reservoir and elongate channel in the direction of arrows 281 through orifice 282. Since orifice 282 injects fluid 281 to the side of the center of a wafer in the reservoir, the flow 281 of fluid imparts a rotational force on the wafer, causing it to rotate as it travels from the reservoir down the elongate channel. Gas can be included in the fluid flowing from orifice 282, or can be bubbled through apertures formed in floors 274 and 276. The admixture of gas to fluid flowing through the reservoir and channel facilitates the travel of a wafer 10 down the water track because the air bubbles function like ball bearings intermediate wafer 10 and floors 274 and 276. The lower linear circular portion 10D of edge 10C contacts sloped wall 273 while the wafer is in the circular reservoir and contacts sloped, parallel opposed walls 277 and 278 while the wafer travels down the elongate channel. Accordingly, wall 273 is sized and walls 277, 278 are spaced apart such that the bottom 10B of wafer 10 does not contact floors 174, 176 while moving down the water track. The level of water in the track is ordinarily sufficient to keep a wafer 10 in the track covered, or at least coated, with water. When a wafer moving along the water track approaches the dispensing end 285 of the elongate channel, sloped ceiling 286 of member 287 gradually constricts the size of the channel through which water in the track can flow, tending to increase the velocity of water moving through the channel and facilitating movement of the wafer out of the dispensing end 285 into a cassette 232 positioned adjacent end 275. A stream of water directed through orifice 288 in the direction of arrow 289 flows against a wafer 10 moving through the channel toward dispensing end 285. The water imparts a downward force against the wafer 10 and also imparts a force in the direction of travel of wafer 10 which assists movement of the wafer 10 along the channel and out of end 185. The downward force produced by fluid flowing through orifice 288 is important because it prevents wafer 10 from tipping or tilting after it leaves end 285 and before the wafer 10 has moved completely into its storage slot 233A, 233B in cassette 232. Water or other fluid flowing out of the dispensing end 285 of the water track is collected in a reservoir 290. Water from the reservoir 290 can be recycled by pump means 291 back to orifices 282, 283, 284. After a wafer 10 travels down the water track and out of dispensing end 285 into a storage slot 233A, 233B in cassette 232, means 260 lowers (or raises) cassette 232 to position another storage slot to receive a wafer 10 from the water track. When the cassette is filled, as would be the cassette in Fig. 6 after it receives a wafer 10 in slot 233A, 233B, the cassette is removed and an empty cassette installed in the reservoir.

Claims: Apparatus for polishing a wafer (10) including a transport apparatus for transporting the wafer into position against a pressure head (265), said wafer having a top surface (10A), a bottom surface (10B) and a peripheral edge (10C) circumscribing said wafer, the polishing apparatus further including at least one station having a polishing surface, a frame, and carrier means mounted on said frame to move said pressure head (265) between at least two operative positions, a first operative position with said pressure head positioned over said transport apparatus, and a second operative position with said pressure head (265) positioned over said station, being characterized in that said transport apparatus comprises (a) a transport head assembly (264); (b) displacement means (261) for upwardly displacing said transport head assembly (264); (c) a wafer dolly (236) having an elongate tongue (245) to support a portion of the wafer (10) such that selected portions of said peripheral edge extend outwardly away from and free of said tongue (245); (d) means for positioning a wafer (10) on said tongue (245) such that said selected portions of said peripheral edge extend outwardly away from and free of said tongue; (e) means for positioning said wafer dolly (236) with said elongate tongue extending over and in a selected position above said transport head assembly (264), said transport head assembly including (i) a base (200), (ii) an alignment member (202) mounted on said base and having a support surface (227) shaped and dimensioned to receive and support said selected peripheral edge portions of said wafer (10) to support said wafer in a selected orientation,and a wall structure defining a central opening formed in said alignment member (202) intermediate and extending downwardly from said support surface and shaped and dimensioned to receive said tongue (245), (iii) a plurality of spaced apart upstanding pins (206,207,208) for contacting said selected peripheral areas of said wafer (10) to guide said wafer when said wafer slides intermediate said pins downwardly toward said support surface (227), said pins circumscribing said central opening and said support surface, said central opening, support surface (227) and pins (206,207,208) being shaped and dimensioned such that when said tongue (245) is in said selected operative position over said transport head assembly and when said displacement means (261) upwardly displaces said transport head assembly (264) toward said tongue (245), said wafer slides intermediate said pins (206) onto said support surface (227) while said wall structure and support surface (227) move upwardly past said tongue; and (iv) means (261) for upwardly displacing said alignment member (202) to position said wafer (10) adjacent a lower portion (120) of said pressure head (265) when said pressure head is in said first operative position over said transport head assembly (264). Apparatus as claimed in claim 1 being characterized by a cassette (232) for storing wafers, out of which a wafer can be transported on said tongue (245) of said wafer dolly (236) into said position above said transport head assembly (264). Apparatus as claimed in claim 2, characterized by means (266) for moving said pressure head (265) from said polishing station to and over a fluid housing apparatus for transporting a polished wafer into said cassette (232) for storing wafers, said fluid housing apparatus including (a) a housing (271); (b) a reservoir formed in said housing to receive the wafer released from said pressure head when said pressure head (265) is in said first operative position, said reservoir including (i) a floor (274), and (ii) sloped side surfaces (273) extending upwardly away from said floor (274) to receive and contact at least selected portions of said peripheral edge of said wafer to prevent said bottom surface (10B) from contacting said floor of said reservoir; (c) an elongate channel formed in said housing (271) in fluid communication with said reservoir to receive a wafer (10) therefrom, said channel including (i) a floor (276), (ii) elongate, opposed, spaced apart sloped side surfaces (277,278) extending upwardly away from said floor (276) of said channel to receive and contact portions of said peripheral edge of said wafer to prevent said bottom surface (10B) from contacting said floor of said channel when said wafer moves along said channel, and (iii) a wafer-dispensing end (285); (d) orifice means (282,283,284) formed in said housing (271) to direct fluid under pressure into said reservoir to flow through said reservoir, through said elongate channel, and out of said wafer-dispensing end (285) of said channel, said fluid flow carrying said wafer from said reservoir to and out of said wafer-dispensing end; (e) a second reservoir (290) to receive fluid flowing out of said wafer-dispensing end (285) of said channel; (f) said cassette (232) being positioned in said second reservoir (290) to receive a wafer moving out of said dispensing end (285) toward said cassette, said cassette including surfaces (233) for slidably receiving portions of said peripheral edge (10C) of said wafer. Apparatus as claimed in claim 3, characterized by means (288) for directing a stream of fluid against said wafer when said wafer is adjacent said dispensing end (285) of said channel to generate fluid flow forces against said wafer which (a) downwardly press portions of said peripheral edge (10C) of said wafer against said sloped surfaces (277,278) of said channel; and, (b) assist movement of said wafer along said channel toward and out of said dispensing end (285) into said cassette (232).

Inventors: GILL GERALD L JR, HYDE THOMAS C, GILL, GERALD L., JR., HYDE, THOMAS C.
Applicants: WESTECH SYSTEMS INC, WESTECH SYSTEMS, INC.
Application year: 1989
Main classification: H01L21
IPC codes: B24B41, B65G49, B24B37, H01L21