Metal film protection of CMOS wafers against KOH

This paper reports a new protection for the front side of fully processed CMOS wafers against KOH etching solutions. The protection is based on thin TiW and Au films and is fully CMOS compatible. No mechanical fixture is required during the anisotropic etching step. Therefore, the new method is excellently suited for batch micromachining. Up to 100% of all chips on 6 inch wafers were fully operational after 4 hours KOH etching. The membrane yield after KOH etching was 100% and nearly 90% after the not yet optimized removal of the protection films. Thus, this protection fulfils the requirements of inexpensive and reliable sensor production.