Patent ID: 6893503

Claim:
A method of manufacturing a semiconductor device including at least a thin film transistor, said method comprising the steps of: forming an amorphous semiconductor film comprising silicon over a substrate having an insulating surface; providing the amorphous semiconductor film with an element which promotes crystallization of the amorphous semiconductor film; crystallizing the amorphous semiconductor film by a first heat treatment to form a crystalline semiconductor film; introducing an impurity element belonging to Group 15 into a first portion of the crystalline semiconductor film by using a mask while a second portion of the crystalline semiconductor film below the mask is not provided with the impurity element; wherein the first and second portions of the crystalline semiconductor film are in contact with the insulating surface over the substrate; performing a second heat treatment for gettering so that the element contained in the second portion is moved to the first portion in a direction parallel to the insulating surface; and patterning the crystallized semiconductor film to form a crystalline semiconductor island in the second portion thereby removing the first portion of the crystalline semiconductor film; forming an active layer of the thin film transistor using the crystalline semiconductor island; wherein the second heat treatment is performed in a temperature range not exceeding a glass transition point of the substrate.