Method for fabricating P-wells and N-wells having optimized field and active regions

摘要

A method forms, in a CMOS semiconductor substrate, P- and N-wells having independently optimized field regions and active regions. In one embodiment, P- and N-wells are formed by (i) creating in successive steps the field regions of the P- and N-wells; (ii) creating an oxide layer over the field regions, (iii) creating in successive steps the active regions. The method achieves the P- and N-wells without increasing the number of photoresist masking steps. In addition, optical alignment targets (OATs) are optionally formed simultaneously with these P- and N-wells without increasing the total number of process steps.