cassette and place them onto a wafer mounting surface
SYSTEMS AND METHODS FOR WAFER in an item of processing equipment or into a special
HANDLING IN SEMICONDUCTOR PROCESS cassette for loading into a wafer processing system in
EQUD?MENT herently involves risk of wafer contamination and
5 breakage. As the industry has progressed, the demand BACKGROUND OF THE INVENTION for automated handling of wafers during loading of This invention relates generally to systems and meth- process equipment has also grown, ods for handling semiconductor wafers in semiconduc- This invention is particularly directed to meeting tor process equipment and, more specifically, to systems performance challenges involved automated wafer hanand methods for conveying wafers in standard plastic 10 dling and loading of high current ion implantation syswafer cassettes to a wafer transfer station, for receiving tems. However, this is just one case of the application of wafers into a vacuum load lock system and conveying the invention to automation of wafer handling. High the wafers to a wafer transfer station, and for batch current ion implantation machines, in the parlance of handling of semiconductor wafers in wafer processing the current state of the art, are considered to be masituations where full batch processing is required and 15 chines which generate useful boron ion beam currents dummy wafers may have to be used due to missing 0f 2-3 milliamperes (mA) and about 10-12 mA of arwafers in a plastic wafer cassette. senic ion beam current. The expense of high current ion DISCUSSION OF BACKGROUND AND PRIOR implanters demands that effective automation of wafer ART 20 handing be provided, but systems currently on the _ , „ , , . ... market do not adequately meet the advancing needs of The manufacture of large scale integrated circuit ^ industry (LSIC) chips has become one of the most important Jo ... eyen manufacturing efficiency, industries in the world over the last ten or fifteen years. ,, . . . r * • • J * • i t • This technology has produced the dramatic improve- *e semiconductor manufacturing industry is looking to mentin performance/cost of both mainframe andI mini- 25 develop even higher beam current ion implantation computer systems and the microcomputer systems systems t0'grease wafer throughput for high dose which are proliferating in the home computer and pro- mpknts. A. copending and commonly assigned U.S. fessional office computer field. LSIC technology has Patent application of Derek Aitken entitled APPARAalso made significant advances in performance and cost TUS AND METHODS FOR ION IMPLANTAreduction in telecommunications and real time control 30 TION, U.S. patent application Ser. No. 641,027, filed systems for industrial processes and equpment. To un- Aug. 15,1984, now U.S. Pat. No. 4,578,589, issued Mar. derstand the importance of this invention in the LSIC 25, 1986, discloses ion beam line technology capable of field, some background information on integrated cir- generating useful ion beam currents several times cuit (IC) manufacture will be helpful. greater in magnitude than current commercial state of TT„„ „^ . . „TM. TM , „T 35 the art technology. More specifically, boron ion beam
Very great improvements in the scale of integration novel ion optics technology and ion beam line compoof semiconductor devices on IC chips and the speed of nent technology disclosed in the Aitken application, operation of such devices have been achieved over the 40 This technology will herein be referred to as the Aitken past several years. These improvements have been very high current beam technology. Ion beam currents made possible by a number of advances in IC manufac- wju at these levels result in a new generation of ion turing equipment as well as improvements in the materi- implantation apparatus which will dramatically imals and methods utilized in processing virgin semicon- prove wafer throughput especially for high dose imductor wafers into IC chips. The most dramatic ad- 45 lants Effective automation of wafer handling is even vances in manufacturing equipment have been im- more in high throughput machines and improved apparatus for lithography and etching.and im- ]anters which m oriented toward performance capa. proved systems for implanting ions of conductivity bmties which make duction of advanced semiconmodifymg impunties into semiconductor wafers. ... ... mQre ... Qn j manufacturmg
The density of integrated circuits and their speed of 50 i -m. j • j * t C Um- *
.. j jiii *u J scale. The desired features m a wafer handling system
operation are dependent largely upon the accuracy ^nd . u- u ±u u * • ■ 'i * * *t.
resolution of the lithography and etching systems used f\ a h,Sh throuShPut lon lmPlanter sVstem the
to form patterns of circuit elements in masking layers on , ,. ,
the semiconductor wafer. However, density and speed W Batch loading of wafers onto the wafer scanning
are also dependent upon tight control of the profile of 55 svstem ln the vacuum environment of the main wafer
doped regions in the wafer, i.e., regions to which sub- Process chamber without breaking the vacuum between
stantial concentrations of conductivity modifying impu- batch loadmS and unloading.
rities have been added. Tight control of wafer doping (2) Ability to use the standard plastic wafer cassette in
can best be achieved using ion implantation techniques the wafer handling system so that standard cassette to
and equipment. 60 special cassette transfer can be avoided.
The semiconductor processing industry is highly (3) Provision of dummy wafers to substitute for missoriented toward batch processing of semiconductor »ng wafers in the cassette since the scan wheel must be wafers. In the infancy of the industry, almost all pro- fulty loaded.
cessing of wafers involved hand manipulation of the (4) Multiple cassette handling in a separate load lock
wafers. Wafers are almost universally carried from one 65 vacuum chamber for implantation of multicassette
item of process equipment to another in plastic wafer batches without breaking vacuum so that critical parts
cassettes which carry twenty five wafers. Manual han- in the wafer process chamber and post-acceleration
dling of wafers to remove them from the plastic wafer tube are not exposed to air between batches.