The need for low temperature processes in VLSI CMOS technology has led to increasing interest in fully implanted wells. In comparison with diffused wells the advantages are good control of the doping profile, low lateral distribution and self-immunity to latch-up.
The technique using a medium energy machine with multiple charged ions is not viable in a production context and only high energy machines can be improved to meet the high throughputs required.
We have performed boron and phosphorus in the 1 to 3 MeV range on tandem and Van de Graaff machines to prove their effectiveness. Spreading resistance for boron and phosphorus and SIMS for boron are the characterizatton methods uped. The agreement with expected profiles for doses in the 1013 to 1014 /cm2 range is good. We checked the compatibility with a N-well CMOS process: - low doping level at the surface to ensure low capitances and no disturbance of the channel region - high doping level at one micrometer under the surface to lower punchthrough and latch-up effects. The efficiency of masking materials such as Si02 and photoresists is experimentally measured detecting residual doping underneath various thicknesses of the masking pattern. The application to C-MOS technology is discussed.