Using Ellipsometry for Assessment of TiN Surface Roughness after Plasma Etch

Abstract

Titanium nitride (TiN) is widely used in metal gate applications. Exposing TiN to a plasma results in pronounced surface roughness that can be easily characterized by ellipsometry. The ellipsometric angle Δ is proportional to the roughness if the roughness does not exceed . It is possible to plot a “roughness diagram” where a border can be drawn between the smooth and rough etch surfaces depending on the etch conditions. This diagram could be used for gate-etch process optimization. In our case, the roughness could be overcome by increasing HBr content and/or substrate bias during the etching.