Fabrication of integrated circuit having twin tubs

摘要

A twin tub process is disclosed. After a thermal oxide is grown 21 over an already-formed p-tub 13, an n-tub 27 is formed by ion implantation. Then a layer of protective material 25, illustratively PETEOS, is formed over the oxides which cover the n-tub and p-tub. The protective layer of PETEOS helps to prevent ambient boron from contaminating the n-tub 27. Use of the protective PETEOS layer 25 permits the use of thinner thermal oxides over the tubs, thereby reducing the height difference at the tub boundary. <IMAGE>