Characterization of Ammonium Silicate Residue during Polysilazane (PSZ) Dry Etching in NF_3/H_2O Gas Chemistry

摘要

In high aspect ratio (HAR) structure in semiconductor devices, the removal of silicon oxide (SiO_2) layer is one of the critical and difficult steps. Because, it represents a possible source of high contact resistance and a decrease in gate oxide reliability. In the present study, we have employed plasma dry etching by using NF3 and H_2O mixtures to find the effect of the gas chemistry on the oxide etching. Etch rates of SiO_2 were reported as a function of H_2O ratio, substrate temperature, and pressure. Polysilazane oxide (PSZ) was chosen in this study. PSZ processing generates ammonium hexafluorosilicate ((NH_4)_2SiF_6) as a by-product. Therefore, there is an optimization need for high etch rate and selectivity without by-product formation.