Effect of temperature on deposition layer formation in HBr/N2/fluorocarbon-based plasma

The effects of wafer temperature on etching rate and surface composition were investigated to clarify the surface reaction mechanism under HBr/N-2/fluorocarbon-based gas plasma for developing a process for three-dimensional NAND flash devices. The etching rates of both polycrystalline silicon (poly-Si) and SiO2 were found to increase at a wafer temperature of 20 degrees C as compared with those at 60 degrees C. Comparing the gas combination of fluorocarbon/N-2 and HBr/N-2 mixtures, the temperature dependence of SiO2 etching rates was considered to relevant to the sticking probability of fluorocarbon polymers. To determine the cause of the temperature dependence of the poly-Si etching rate, surface composition was evaluated by thermal-desorption-spectroscopy and laser-sputtered-neutral-mass-spectrometry analyses. Ammonium bromide was confirmed in the deposition film at a wafer temperature of 20 degrees C. The observed increase in poly-Si etching rate at lower temperatures was possibly caused by increased amounts of nitrogen, hydrogen, and bromine fixed to the surface with the formation of ammonium bromide. (C) 2017 The Japan Society of Applied Physics