The role of gas phase reactions, electron impact, and collisional energy transfer processes relevant to plasma etching of polysilicon with H2 and Cl2

Abstract

Plasma etching of silicon with H2 and Cl2 was simulated with mixtures of H2, Cl2, and SiCl4. The gas phase chemistry was elucidated by varying power and pressure. The cross sections for production of H (3p2P) atoms were probed through the emission response to pressure variations. Addition of rare gases to a hydrogen plasma identified qualitatively major energy transfer paths between the rare gas metastables and the H2/H system. We conclude that dissociation of hydrogen molecules and excitation of hydrogen atoms are separate electron impact collisional events that constitute the main excitation route in a hydrogen plasma. We find further that the role of metastable H atoms in the 2s2S state at 10.19 eV is minor, and that the direct dissociative excitation in a single electron impact at 16.57 eV is insignificant. The occurrence of state specific collisional energy exchange has limiting consequences for any actinometric method.