PURPOSE: To enable a thin film semiconductor to rise enough in temperature by a method wherein a first layer which contains impurity is formed on a semiconductor thin film and a second layer which absorbs incoherent light rays of a transparent substrate penetrating wavelength band is formed thereon, and then impurity is diffused into the semiconductor thin film through the irradiation with incoherent light rays.

CONSTITUTION: An SiO2 film 2 is deposited on a transparent insulating substrate 1 through an LPCVD method. Then, poly-Si is deposited thereon and patterned for the formation of an active layer 3. An gate insulating film 4 and a gate electrode 5 serving as a gate of a transistor are formed of poly-Si through thermal oxidation and an LPCVD method and patterned into a gate. In succession, a coat-type impurity diffusing agent layer 6 is applied thereon through a spin coating and baked, and then an a-Si layer 7 is formed thereon through a plasma CVD method. The a-Si layer serves as a layer to improve an incoherent light absorbing efficiency. After the a-Si layer 7 has been deposited, the substrate 1 is irradiated with incoherent light rays of a tungsten resistor halogen lamp from both the sides.