Novel applications of ion implantation to LSI processing

Ion implantation has been successfully utilized to simplify the fabrication of a 1024 bit IGFET random access memory array ina novel manner. IGFET integrated circuits Often require enhanced surface doping to suppress unwanted spurious channels between devices. Using conventional diffusion technology, an extra masking level is required to form these regions. A technique has been developed which eliminates this extra mask by uniformly increasing the doping in the surface layer of the silicon and then controllably compensating the enchanced doping in the windows patterned to form gate oxide regions. Threshold voltage control is excellent, mobilities are normal and no undesirable effects have been observed if care is exercised in controlling the implanted doses.