The gas-phase etching of SiO2 was examined using HF and methanol vapor at low temperature below 0 °C and at low pressure. The etching rate of SiO2 increased with decreasing temperature and showed a maximum around –30 °C. The obtained etching rate was maximum 40 nm/min at plasma-enhansed CVD SiO2. The etching rate of SiN examined for comparison was less than 10 times smaller than that of SiO2 in this condition. As a result, the etching selectivity of SiO2 to SiN was found to be over 20 at –40 °C. Utilizing low temperature less than –30 °C, gas-phase etching of SiO2 which shows high etching rate and selectivity was achieved.
This paper describes iterative methods for the high frequency electromagnetic analysis using the finite element method of Maxwell equations including displacement current. The conjugate orthogonal conjugate gradient method has been widely used to solve a complex symmetric system. However, the conventional method suffers from oscillating convergence histories in large-scale analysis. In this paper, to solve large-scale complex symmetric systems arising from the formulation of the E method, an iterative substructuring method like the minimal residual method is presented, and the performance of the convergence of the method is evaluated by numerical results. As the result, the proposed method shows a stable convergence behavior and a fast convergence rate compared to other iterative methods.
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