The role of chemisorption in plasma etching

Abstract

It is shown that the sticking probability (i.e., the probability for dissociative chemisorption plus the probability for nondissociative chemisorption where E≳20 kcal/mole) for CF₄, CF₃H, and CF₃Cl on polycrystalline films of SiO₂, Si₃N₄, and silicon is less than 10⁻⁷. The sticking probability for CF₂Cl₂ and CCl₄ is detectable on some of these surfaces but still less than 10⁻⁶. Electron collisions with nondissociatively adsorbed molecules (E≳20 kcal/mole) are shown to result in the rapid buildup of adsorbed carbon and chlorine which will then remain on the surface indefinitely. It is further shown that CF_x radicals have sticking probabilities between 0.08 and 0.75 on clean silicon. Based on these results, it is concluded that the dissociative chemisorption of stable gases is probably not important in plasma etching while radiation‐induced‐dissociative chemisorption and the chemisorption of CF_x radicals are expected to play an important role.