The etching reaction of silicon with CF₄ was studied in a home-made ECR（electron cyclotron resonance） plasma etching system. Experimental data for the etch rates of p-Si(100) and n-Si(100) were measured and analyzed with varying etch time, etching pressure, CF₄ flow rate, the partial pressure of O₂ and etching temperature to investigate the characteristics of the etching system. The etch rates were almost the same for both p- and n-type Si(100) and increased with the increases in etching pressure and CF₄ flow rate, while the etch rate decreased because polymer film was formed on the Si surface at high pressure and reactive species were pumped away at high flow rate of CF₄. The etch rate became maximum when the amount of O₂ added to CF₄ was about 15% and showed uniformity. The etching profile showed anisotropic etching at low pressure and isotropic etching at high pressure.