DESIGN AND CONSTRUCTION OF VACUUM SYSTEMS FOR LARGE AREA CuIn<sub>1-x</sub>Ga<sub>x</sub>Se<sub>1-y</sub>S<sub>y</sub> THIN FILM SOLAR CELL FABRICATION
Two large-area vacuum systems have been designed, fabricated and installed to serve as a nucleus of a pilot plant for preparation of CIGS thin films solar cells. The chambers are pumped with cryopumps and rotary mechanical pump. The cryopumps are attached directly to the chambers through short tubulations and three-position gate valves because the cryopumps can operate in any orientation. The pumping speeds were chosen to obtain vacuum in the range of 10-5 Torr and 10-7 Torr in 5 minutes and 10 hours respectively. A graphical process has been developed and employed for representation of the variation of the rates of outgassing, throughput of vacuum pumps and the pressure with time. The vacuum chambers are fitted with five 10 cm x 30 cm magnetron sputtering sources for deposition of Mo, In, CuGa, ZnO, and ZnO:Al. Thickness uniformity over a large area (10 x 15 cm2) was improved through adjustment of magnetic field by preferentially removing nickel-coated soft iron strips in the versatile magnetic array provided specifically for that purpose at the rear of the magnetron sputtering sources and by boosting the magnetic field at the extremities. CIGS Solar cells are being prepared routinely using these vacuum systems.
