Process for selectively etching a layer of silicon dioxide on an underlying stop layer of silicon nitride

A process for using an etchant material for plasma etching a multilayer structure to form a etched pattern therein, comprising:

• providing a fluorinated chemical etchant system including an etchant material and an additive material, said additive material comprising at least one of CH.sub.2 F.sub.2 or CH.sub.3 F;
• providing a multilayer structure having a plurality of structural layers, one of the outer structural layers of the multilayer structure comprising a silicon dioxide outer layer on an underlying silicon nitride stop layer;
• forming on the top surface of the multilayer structure a chemical etchant resistant layer having a pattern of openings therein and thereby exposing areas of the silicon dioxide outer layer corresponding to the pattern of openings;
• and
• etching the exposed areas of the silicon dioxide outer layer to the silicon nitride stop layer, at a high SiO.sub.2 etch rate, and at a high level of selectivity of said SiO.sub.2 etch rate with respect to said Si.sub.3 N.sub.4 etch rate, with a fluorinated chemical etchant system including an etchant material and an additive material, said additive material comprising a fluorocarbon material in which the number of hydrogen atoms is equal to or greater than the number of fluorine atoms, ad said etching step forming an etch pattern in the silicon dioxide outer layer in which the contact sidewalls of sad SiO.sub.2 outer layer are perpendicular to the multilayer structure layers.

A dry etching process for a multilayer semiconductor wafer, comprising:

• a) providing a silicon-dioxide layer;
• b) providing a silicon-nitride layer, located under the silicon-dioxide layer;
• and
• c) using a plasma,
• having an etchant, and a fluorocarbon additive gas in which the number of hydrogen atoms are greater than the number of fluorine atoms,
• to etch through the silicon-dioxide layer down to the top surface of the silicon-nitride layer.