Gate Oxide Thinning at the Isolation Oxide Wall

Abstract

Transmission electron micrographs of cross sections of MOS devices have shown thinning of the gate oxide at the isolation oxide wall. It is shown that the thinning is related to the slope of that wall which is in turn affected by the time of overetch in BHF during window photolithography. A 7 min overetch produces a thinning of ∼25% and cases of 30% thinning have been found in device samples. The thinning is caused by the wall acting as a partial barrier to local oxidation at that site.