Three-step nitride etching process for better critical dimension and better vertical sidewall profile

Abstract

This invention describes a three-step process for etching a layer of silicon nitride over a thin layer of silicon dioxide on a semiconductor substrate for producing silicon nitride pattern with nearly vertical sidewalls, very small critical dimension bias and no trenching in the silicon dioxide, comprising a first step of a highly anisotropic etch process with a high etch rate, achieved by adding CHF.sub.3 to the gaseous mixture of SF.sub.6 and He, carried out at a relatively high power and low pressure, used to etch the bulk of the silicon nitride layer, a second step of lower etch anisotropy and etch rate, achieved by replacing CHF.sub.3 with HBr, carried out at higher pressure and lower power, used to etch out the remainder of the nitride layer with a small over-etch beyond the end point, a third step of high Si.sub.3 N.sub.4 /SiO.sub.2 etch selectivity, achieved by adding an oxidant to the reactive gas mixture, used to remove any remaining silicon nitride residues.

Dependencies are inferred from the claim text.