Ion Beam Etching of Silicon, Refractory Metals, and Refractory Metal Silicides Using a Chemistry Assisted Technique

The etching characteristics of silicon and two refractory metals (Ti, Mo) and four refractory metal silicides (TiSi₂, TaSi₂, MoSi₂, PtSi) are described using a technique called chemically assisted ion beam etching (CAIBE). In this technique, reactive Cl₂ gas is introduced into a sample chamber in conjunction with, and relatively independent of, a broad beam of Ar⁺ ions. Incremental increases in the Cl₂ partial pressure caused linearly increasing etch rates for all materials investigated, except for Si0₂. In the case of silicon, correlation between broad beam CAIBE and ultrahigh vacuum (UHV) etching studies was made. The relative etch rate increase of the refractory metals and silicides investigated were found to be related to the vapor pressures of the reaction products. Additional studies have shown that various residual gas contaminants such as hydrogen, oxygen, and H₂0 can influence etching mechanisms by reducing the reactive Cl₂ flux or by forming stable oxides. Linewidths with dimensions below 0.6 μm have been obtained in polycide (a stacked silicide/polysilicon) structures with an etch selectivity >9:1 between the film layers and SiO₂ using CAIBE.