Anisotropic elective etch of nitride.

摘要

A gas mixture for use in the selective dry etching of a nitride insulator layer (16) relative to an oxide insulator layer (12) formed on a silicium substrate (10) comprising: a gas mixture containing chlorine and oxygen. The oxygen in this gas mixture must comprise 15% or less by volume. In a preferred process embodiment for etching Si3N4 and leaving a layer of SiO2 therebelow, Cl2 gas may be used in combination with 12% or less oxygen by volume. Etch selectivity of greater than five to one is achieved with this gas mixture when a plasma RF frequency of less than 1 MHz is utilized. When a high frequency RF component in the range of 10 - 27 MHz is added to the RF excitation signal, then an etch uniformity of better than 3% is achieved.