| abstract |
(57) [Summary] (with correction) [PROBLEMS] To improve the operating characteristics and reliability of a semiconductor device by making the structure of a TFT arranged in various circuits appropriate according to the function of the circuit, In addition, power consumption is reduced, the number of steps is reduced, and manufacturing cost is reduced and yield is improved. SOLUTION: A concentration gradient is provided such that the concentration of an impurity element for controlling conductivity gradually increases as an LDD region of a TFT approaches a drain region. In order to form the LDD region 211 having such an impurity element concentration gradient, in the present invention, the gate electrode 119 having a tapered portion is formed. And a method is used in which the ionized impurity element for controlling the conductivity type is accelerated by an electric field, passes through the gate electrode 119 and the gate insulating film 130, and is added to the semiconductor layer. |