Method of etching an oxide layer

Abstract

A method of etching openings in oxide layers is disclosed. A hard mask layer is formed on the oxide layer. The hard mask layer is then patterned by a photoresist layer and an etch is performed to form openings in the hard mask. Next, the patterning layer may be removed and an etch is performed to remove the oxide in the regions defined by the hard mask layer openings. The etch with hard mask has minimized aspect ratio dependency, so that openings of different sizes may be formed simultaneously. An etch that may be carried out with Freon 134a (C.sub.2 H.sub.2 F.sub.4) to provide superior oxide:nitride selectivity is also disclosed. Additionally, the etch may be carried out at high temperature for improved wall profile without loss of selectivity. For deep openings, a two step etch process is disclosed, with a polymer clean step between the etches to remove polymer build up from first etch, and allow the etch to proceed to an increased depth.