Etching method

Abstract

The described embodiments of the present invention provide a trench etching technique having a high level of control over the sidewall profile of the trench and a high degree of selectivity to the etch mask. The described embodiments are for etching silicon and tungsten, but the invention is suitable for etching a wide variety of materials. A silicon etchant such as HBr, the combination of HBr/SF.sub.6, BCl.sub.3, SICl.sub.4 or other etchant is combined with a passivant such as carbon monoxide or nitrogen. The passivant gases include an interactive .pi. bonding system and/or paired electrons not involved in bonding. These passivant gases create a weak adductive bond to the dangling bonds or radicals generated during etching. The passivant gases also create a weak adductive bond to the sides of the trench being etched and are not removed due to the oblique angle of the sidewalls relative to the reactive ion flux vector corresponding to the trench etch. In this manner, general and subtle profile control is achieved. The more complex molecules of the etch mask (using silicon dioxide or photoresist as used in the described embodiments) create more dangling bonds or surface radical states and bond tighter than silicon to the passivant gas. Thus, the selectivity to the mask material of the etch is enhanced.