Influence of Water Adsorption/Desorption Processes on the Selectivity of Vapor HF Etching

Abstract

We studied the etching mechanisms of thermal oxide and borophosphosilicate glass (BPSG) under various etching conditions. It was found that a high etch selectivity of BPSG over thermal oxide can be obtained by suppressing the adsorption of on thermal oxide. Adsorption of at the thermal oxide surface can be limited by increasing the substrate temperature or by reducing the vapor partial pressure. On the other hand, adsorption of at the BPSG surface is not significantly influenced by the substrate temperature and the partial pressure, because an liquid layer is formed on the BPSG surface, even at a substrate temperature of 65°C. The etch rate of oxides in vapor strongly depends on the amount of adsorbed at the oxide surface. The BPSG etch selectivity over thermal oxide can therefore significantly be improved by reducing adsorption on the thermal oxide surface via an increased substrate temperature or a reduced vapor partial pressure. In addition, the influence of the substrate temperature and the vapor partial pressure on the particle generation during the etch process was studied. It was found that particles are generated in the case of etching at elevated substrate temperatures in combination with high pressure under the influence of reaction by‐products.