Improve hot phosphoric process robustness in 300 mm nitride strip wet bench

Selectivity between thermally grown oxide and LPCVD nitride during hot phosphoric process is a well known key point of shallow trench isolation (STI) module integration. The main challenges are to control the step height and the pad oxide remaining thickness. Actually, following the technology shrinks from 120 nm to 65 nm, these parameters become critical for the lithography steps sensitivity regarding previous patterning and for the Sac On Pad integration. The process robustness is improved by saturating the initial chemical and by refreshing the phosphoric acid during the bath lifetime. The highlights are a process stability improvement, a H₃PO₄ filter lifetime increase and an overall better tool availability.