In this paper, amorphous semiconductor and insulator thin film are etched using reactive ion etcher. At that time, we experiment in various RIE conditions (chamber pressure, gas flow rate, rf power, temperature) that have effects on quality of thin film. The using gases are $CF_4,;CF_4+O_2,;CCl_2F_2,;CHF_3$ gases. The etching of a-Si:H thin film use $CF_4,;CF_4+O_2$ gases and the etching of $a-SiO_2,;a-SiN_x$ thin film use $CCl_2F_2,;CHF_3$ gases. The $CCl_2F_2$ gas is particularly excellent because the selectivity of between a-Si:H thin film and $a-SiN_x$ thin film is 6:1. We made precise condition on dry etching with uniformity of 5%. If this dry etching condition is used, that process can acquire high yield and can cut down process cost.