MANUFACTURE OF SEMICONDUCTOR DEVICE

PURPOSE:To diffused an impurity in low concentration with good controllability by employing coating type thermal diffusion type in a step of channel doping at the time of manufacturing a MOS transistor. CONSTITUTION:A patterned semiconductor layer 2 is formed on an insulation substrate 1. It is coated by a spinner or the like with coating type diffusion agent 11. After coating, it is prebaked in two steps in an inert gas atmosphere 201, and further heat treated in the atmosphere 201. Then, in order to control dose with good controllability, the inert gas is replaced with O2 gas 202. Thereafter, the O2 gas is stopped, and it is returned to the presence of the inert gas. A thin oxide film is formed on the surface of the silicon layer by exposing it with the O2 gas atmosphere, and diffusion is stopped. Accordingly, the controllability of diffusing at a low temperature can be enhanced.