Thermal Etching

Summary

The thermal etching process works in the temperature range where the chemisorption curve of the reactants and desorption curves of the reaction products overlap. This region represents the process window for a thermal etching process. The rate for thermal etching is limited by the elementary step with the lowest rate. Flow uniformity across the wafer is extremely critical to achieve good etching rate nonuniformity. The intrinsic selectivity of thermal etching processes is typically very high. Thermal etching is an isotropic etching process because reactants and reaction products move with thermal energies and in random direction. Aspect ratio dependent etching can be effectively reduced by increasing pressure. Archetypical applications of thermal etching are etching of silicon with fluorine and etching of SiO₂ with HF. Both applications are used in the manufacturing of micro‐electromechanical systems devices where high etch rates are needed for undercutting etching processes.