MANUFACTURE OF MOS THIN FILM TRANSISTOR

PURPOSE:To obtain a MOS transistor in which the spread of the depletion layer of a channel region is eliminated by a method wherein impurity-doped polycrystalline silicon films and non-doped polycrystalline silicon films are built up and the films are subjected to thermal annealing. CONSTITUTION:A phosphorus-doped polycrystalline silicon film 2 is formed on a quartz glass substrate 1. A non-doped polycrystalline silicon film 3 is formed on the silicon film 2. The films 2 and 3 are patterned and a cap layer 4 is applied to them. A boron-doped polycrystalline silicon film 5 is formed and a non-doped polycrystalline silicon film 6 is formed on the film 5. The films 5 and 6 are patterned and the cap layer 4 is removed. By subjecting the films to annealing in an N2 atmosphere, phosphorus in the silicon film 2 and boron in the silicon film 5 are diffused into the silicon film 3 and the silicon film 6 respectively. With this constitution, a MOS transistor in which the spread of the depletion layer of a channel region is eliminated can be obtained.