Abstract:
A vacuum chuck for holding a semiconductor wafer during high pressure processing comprises a wafer platen, first through third lift pins, and an actuator mechanism. The wafer platen comprises a smooth surface, first through third lift pin holes, and a vacuum opening. In use, the vacuum opening applies vacuum to a surface of a semiconductor wafer, which chucks the semiconductor wafer to the wafer platen. The first through third lift pins mount within the first through third lift pin holes, respectively. The actuator mechanism couples the first through third lifting pins to the wafer platen. The actuator mechanism operates to extend the first through third lift pins in unison above the smooth surface of the wafer platen. The actuator mechanism operates to retract the first through third lift pins in unison to at least flush with the smooth surface of the wafer platen.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of high pressure processing. More particularly, this invention relates to the field of high pressure processing of a semiconductor wafer. 
     BACKGROUND OF THE INVENTION 
     Processing of semiconductor wafers presents unique problems not associated with processing of other workpieces. Typically, the semiconductor processing begins with a silicon wafer. The semiconductor processing starts with doping of the silicon wafer to produce transistors. Next, the semiconductor processing continues with deposition of metal and dielectric layers interspersed with etching of lines and vias to produce transistor contacts and interconnect structures. Ultimately in the semiconductor processing, the transistors, the transistor contacts, and the interconnects form integrated circuits. 
     A critical processing requirement for the processing of the semiconductor wafer is cleanliness. Much of semiconductor processing takes place in vacuum, which is an inherently clean environment. Other semiconductor processing takes place in a wet process at atmospheric pressure, which because of a rinsing nature of the wet process is an inherently clean process. For example, removal of photoresist and photoresist residue subsequent to etching of the lines and the vias uses plasma ashing, a vacuum process, followed by stripping in a stripper bath, a wet process. 
     Other critical processing requirements for the processing of the semiconductor wafers include throughput and reliability. Production processing of the semiconductor wafers takes place in a semiconductor fabrication facility. The semiconductor fabrication facility requires a large capital outlay for processing equipment, for the facility itself, and for a staff to run it. In order to recoup these expenses and generate a sufficient income from the facility, the processing equipment requires a throughput of a sufficient number of the wafers in a period of time. The processing equipment must also promote a reliable process in order to ensure continued revenue from the facility. 
     Until recently, the plasma ashing and the stripper bath were found sufficient for the removal of the photoresist and the photoresist residue in the semiconductor processing. However, recent advancements for the integrated circuits have made the plasma ashing and the stripper bath untenable for highly advanced integrated circuits. These recent advancements include small critical dimensions for etch features and low dielectric constant materials for insulators. The small critical dimensions for the etch features result in insufficient structure for lines to withstand the stripper bath leading to a need for a replacement for the stripper bath. Many of the low dielectric constant materials cannot withstand an oxygen environment of the plasma ashing leading to a need for a replacement for the plasma ashing. 
     Recently, interest has developed in replacing the plasma ashing and the stripper bath for the removal of the photoresist and the photoresist residue with a supercritical process. However, high pressure processing chambers of existing supercritical processing systems are not appropriate to meet the unique needs of the semiconductor processing. In particular, high pressure chambers of existing supercritical processing systems do not provide a mechanism for handling the semiconductor wafer during loading and unloading nor for holding the semiconductor during e supercritical processing. It is critical that the mechanism provides handling and holding of the semiconductor wafers without breaking or otherwise damaging the semiconductor wafers. 
     What is needed is a mechanism for handling semiconductor wafers during loading and unloading of the semiconductor wafers into and out of a supercritical processing chamber and for holding the semiconductor wafers during the supercritical processing which promotes cleanliness, which is economical, which is efficient, and which does not break the semiconductor wafers. 
     SUMMARY OF THE INVENTION 
     The present invention is a vacuum chuck for holding a semiconductor wafer during high pressure processing. The vacuum chuck comprises a wafer platen, first through third lift pins, and an actuator mechanism. The wafer platen comprises a smooth surface, first through third lift pin holes, and a vacuum opening. In use, the vacuum opening applies vacuum to a surface of a semiconductor wafer, which chucks the semiconductor wafer to the wafer platen. The first through third lift pins mount within the first through third lift pin holes, respectively. The actuator mechanism couples the first through third lifting pins to the wafer platen. The actuator mechanism operates to extend the first through third lift pins in unison above the smooth surface of the wafer platen. The actuator mechanism operates to retract the first through third lift pins in unison to at least flush with the smooth surface of the wafer platen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the preferred vacuum chuck of the present invention. 
     FIG. 2 further illustrates the preferred vacuum chuck of the present invention. 
     FIG. 3 illustrates an exploded view of the preferred vacuum chuck of the present invention. 
     FIG. 4 illustrates a cross-section of the preferred vacuum chuck of the present invention. 
     FIG. 5 illustrates a pressure vessel incorporating the preferred vacuum chuck of the present invention. 
     FIG. 6 illustrates a pressure chamber frame of the present invention. 
     FIGS. 7A through 7C illustrate an upper platen of the preferred vacuum chuck of the present invention. 
     FIG. 8 illustrates a first lift pin of the present invention. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The preferred vacuum chuck of the present invention is illustrated in FIG.  1 . The preferred vacuum chuck  10  comprises a wafer platen assembly  12  and a lift mechanism. Preferably, the wafer platen assembly  12  comprises an upper platen  12 A and a lower platen  12 B. Alternatively, the wafer platen assembly comprises a single piece platen. The upper platen  12 A preferably comprises first and second vacuum grooves,  14  and  16 . Alternatively, the upper platen  12 A comprises the first vacuum groove  14 . The lift mechanism comprises a cylinder support  18 , an air cylinder (not shown), a pin support (not shown), and first through third lift pins,  20  . . .  22 . 
     A side view of the preferred vacuum chuck  10  is illustrated in FIG.  2 . Preferably, a plurality of threaded fasteners  24  couple the cylinder support  18  to the lower platen  12 B. 
     An exploded view of the preferred vacuum chuck  10  is illustrated in FIG.  3 . The preferred vacuum chuck comprises the wafer platen assembly  12  and the lift mechanism  26 . The wafer platen assembly  12  preferably comprises the upper platen  12 A, the lower platen  12 B, first and second threaded fasteners,  25  and  27 , and first through third nylon inserts,  42  . . .  44 . The upper platen  12 A comprises the first and second vacuum grooves,  14  and  16 , first through third upper lift pin holes,  28 A . . .  30 A, and an o-ring groove  32 . The lower platen comprises first through third lower lift pin holes,  28 B . . .  30 B. 
     When assembled, the first and second threaded fasteners,  25  and  27 , couple the upper platen  12 A to the lower platen  12 B. Further, when assembled, the first upper and lower lift pin holes,  28 A and  28 B, form a first lift pin hole, the second upper and lower lift pin holes,  29 A and  29 B, form a second lift pin hole, and the third upper and lower lift pin holes,  30 A and  30 B form a third lift pin hole. Preferably, the first through nylon inserts,  42  . . .  44 , couple to top ends of the first through third lower lift pin holes,  28 B . . .  30 B, respectively. Alternatively, the first through third nylon inserts,  42  . . .  44 , couple elsewhere along the first through third lift pin holes. Further alternatively, the first through third nylon inserts,  42  . . .  44 , are not included in the wafer platen assembly  12 . 
     The lift mechanism comprises the cylinder support  18 , the air cylinder  34 , the pin support  36 , and the first through third lift pins,  20  . . .  22 . The first through third lift pins,  20  . . .  22 , couple to the pin support  36 . Preferably, the first through third lift pins,  20  . . .  22 , include threaded ends  38  which thread into threaded holes  40  in the pin support  36 . The pin support  36  couples to the air cylinder  34 . The air cylinder  34  couples to the cylinder support  18 . The cylinder support  18  couples to the wafer platen assembly  12 . 
     It will be readily apparent to one skilled in the art that the air cylinder may be replaced by another drive mechanism such as an alternative fluid drive mechanism or an electro-mechanical drive mechanism. 
     A cross-section of the preferred vacuum chuck  10  of the present invention is illustrated in FIG.  4 . The preferred vacuum chuck  10  includes a first vacuum passage  46  in the upper platen  12 A coupling the first and second vacuum grooves,  14  and  16 , to a second vacuum passage  48  in the lower platen  12 B. In use, the second vacuum passage  48  couples to a vacuum pump (not shown) which provides vacuum to the first and second vacuum grooves,  14  and  16 , which chuck a semiconductor wafer (not shown) to the upper platen  12 A. 
     A cross-section of a pressure chamber incorporating the preferred vacuum chuck  10  of the present invention is illustrated in FIG.  5 . The pressure chamber  50  comprises a pressure chamber frame  52 , a chamber lid  54 , the preferred vacuum chuck  10 , a sealing plate  56 , a piston  58 , first and second guide pins,  60  and  62 , an interface ring  64 , and an upper cavity plate/injection ring  66 . 
     The pressure chamber frame  52  of the present invention is illustrated isometrically in FIG.  6 . The pressure chamber frame  52  comprises a pressure chamber housing portion  72 , a hydraulic actuation portion  74 , a wafer slit  76 , windows  78 , posts  79 , a top opening  80 , and bolt holes  82 . The wafer slit  76  is preferably sized for a 300 mm wafer. Alternatively, the wafer slit  76  is sized for a larger or a smaller wafer. Further alternatively, the wafer slit  76  is sized for a semiconductor substrate other than a wafer, such as a puck. 
     The hydraulic actuation portion  74  of the pressure chamber frame  52  includes the windows  78 , which provide access for assembly and disassembly of the pressure chamber  50  (FIG.  5 ). Preferably, there are four of the windows  78 , which are located on sides of the pressure chamber frame  52 . Preferably, each of the windows  78  are framed on their sides by two of the posts  79 , on their top by the pressure chamber housing portion  72 , and on their bottom by a base  73 . The bolt holes  82  receive bolts (not shown), which fasten the chamber lid  54  (FIG. 5) to the pressure chamber frame  52 . 
     Referring to FIG. 5, the first and second guide pins,  60  and  62 , couple to the pressure chamber frame  52 . The piston  58  couples to the pressure chamber frame  52  and to the first and second guide pins,  60  and  62 . The piston  58  and the pressure chamber frame  52  form a hydraulic cavity  84 . The sealing plate  56  couples to the pressure chamber frame  52  and to a neck portion  68  of the piston  58 , which forms a pneumatic cavity  86 . The neck portion  68  of the piston  58  couples to the interface ring  64 . The preferred vacuum chuck  10  couples to the interface ring  64 . The upper cavity plate/injection ring  66  couples to the pressure chamber frame  52 . The chamber lid  54  couples to the pressure chamber frame  52  and upper cavity plate/injection ring  66 . 
     It will be readily apparent to one skilled in the art that fasteners couple the preferred vacuum chuck  10  to the interface ring  64 , couple the interface ring  64  to the neck portion  68  of the piston  58 , and couple the sealing plate  56  to the pressure chamber frame  52 . 
     FIG. 5 illustrates the pressure chamber  50  in a closed configuration. In the closed configuration, an o-ring in the o-ring groove  32  seals the upper platen  12 A to the upper cavity plate/injection ring  66 , which forms a wafer cavity  88  for a semiconductor wafer  90 . 
     Referring to FIGS. 4 and 5, operation of the preferred vacuum chuck  10  and the pressure chamber  50  of the present invention begins with the pressure chamber  50  in the closed configuration and with the wafer cavity  88  not holding the semiconductor wafer  90 . In a first step, a hydraulic system (not shown) releases hydraulic pressure to the hydraulic cavity  84  and a pneumatic system pressurizes the pneumatic cavity  86 . This causes the piston  58  and, consequently, the preferred vacuum chuck  10  to move away from the upper cavity plate/injection ring  66  and it causes an upper surface of the upper platen  12 A to come to rest at or below the wafer slit  76 . 
     In a second step, a robot paddle (not shown) inserts the semiconductor wafer  90  through the wafer slit  76 . In a third step, the air cylinder  34 , which is driven by the pneumatic system, raises the pin support  36  and, consequently, the first through third lift pins,  20  . . .  22 . This raises the semiconductor wafer  90  off the robot paddle. In a sixth step, the robot paddle retracts. In a seventh step, the air cylinder  34  lowers the pin support  36 , the first through third lift pins,  20  . . .  22 , and the semiconductor wafer  90  until the semiconductor wafer  90  rests upon the upper platen  12 A. In an eighth step, a vacuum applied via the first and second vacuum passages,  46  and  48 , clamps the semiconductor wafer  90  to the preferred vacuum chuck  10 . 
     In a ninth step, the pneumatic system releases the pneumatic pressure to the pneumatic cavity  86  and the hydraulic system pressurizes the hydraulic cavity  84 . This causes the piston  58  and, consequently, the preferred vacuum chuck  10  to rise. It also causes the o-ring in the o-ring groove of the upper platen  12 A to seal to the upper cavity plate/injection ring  66 , which forms the wafer cavity  88  for high pressure processing of the semiconductor wafer  90 . 
     After high pressure processing of the semiconductor wafer  90  in the wafer cavity  88 , the semiconductor wafer  90  is removed in an unloading operation. The unloading operation is a reverse of the loading operation. 
     The upper platen  12 A of the present invention is further illustrated in FIGS. 7A through 7C. FIG. 7A illustrates a wafer bearing surface  92 , which in use supports the semiconductor wafer  90  (FIG.  5 ). The wafer bearing surface  92  includes the first and second vacuum grooves,  14  and  16 , the first through third upper lift pin holes,  28 A . . .  30 A, and the first o-ring groove  32 . Preferably, the upper platen  12 A accommodates a 300 mm wafer. In order to protect most of a back side of the 300 mm wafer, the first and second vacuum grooves,  14  and  16 , have a diameter slightly less than 300 mm. Alternatively, the upper platen  12 A accommodates a different size wafer. Preferably, the wafer bearing surface  92 , in the region that accommodates the 300 mm wafer, has a surface with no perturbations larger than about 0.0002 in. Alternatively, the wafer bearing surface  92 , in the region that accommodates the 300 mm wafer has a surface with no perturbations larger that about 0.00015 in. Preferably, the wafer bearing surface  92  is fabricated by grinding and polishing to an 8 μin. finish. Alternatively, the wafer bearing surface  92  is fabricated by grinding and polishing to a 4 μin. finish. 
     FIG. 7B illustrates a partial cross-section  94  of the upper platen  12 A. The partial cross-section  94  includes the first and second vacuum grooves,  14  and  16 , the first upper lift pin hole  28 A, the o-ring groove  32 , and the first vacuum passage  46 . Preferably, a width of the first and second vacuum grooves,  14  and  16 , is not greater than about 0.060 in. Alternatively, the width of the first and second vacuum grooves,  14  and  16 , is not greater than about 0.065 in. Preferably, a diameter of the first through third lift pin holes,  28  . . .  30 , is not greater than about 0.060 in. Alternatively, the diameter of the first through third lift pin holes,  28  . . .  30 , is not greater than about 0.065 in. 
     It has been found that 0.070 in. is a critical dimension for the preferred vacuum chuck. When the width of the first and second vacuum grooves,  14  and  16 , and the diameter of the first through third lift pin holes,  28  . . .  30 , are at or below about 0.100 in., the semiconductor wafer  90  (FIG. 5) does not break when exposed to thermodynamic conditions for supercritical carbon dioxide (pressure in excess of 1,073 psi and temperature in excess of 31° C.). If the width of the first or second vacuum groove,  14  or  16 , or the diameter of the first, second, or third lift pin hole,  28 ,  29 , or  30 , exceeds about 0.100 in., the semiconductor wafer  90  breaks when exposed to the thermodynamic conditions of the supercritical carbon dioxide. By fabricating the width of the first and second vacuum grooves,  14  and  16 , and the diameter of the first through third lift pin holes at about 0.060 in., a reasonable margin of safety is maintained in order to avoid breaking semiconductor wafers. 
     FIG. 7C illustrates a back side  96  of the upper platen  12 A showing the first vacuum passage  46  and a heating element groove  98 . Preferably, when assembled, the heating element groove  98  holds a heating element, which heats the semiconductor wafer  90  during processing. 
     The first lift pin  20  is illustrated in FIG.  8 . (It is noted that the first lift pin  20  is illustrative of the first through third lift pins  20  . . .  22 .) The first lift pin  20  includes a shaft section  100 , a shoulder section  102 , and the threaded end  38 . Preferably, the shaft section  100  has a diameter of 0.50 in., which fits in the first lift pin hole having the 0.060 in. diameter with a reasonable allowance. Preferably, the first lift pin  28  is fabricated of stainless steel. Preferably, the shaft section is machined by grinding. Alternatively, another method is used to fabricate the shaft section. 
     Operation of the pressure chamber  50  is taught in U.S. patent application Ser. No. 10/121,791, filed on Apr. 10, 2002, which is incorporated by reference in its entirety. 
     It will be readily apparent to one skilled in the art that other various modifications may be made to the preferred embodiment without departing from the spirit and scope of the invention as defined by the appended claims.