A semiconductor display device which includes the polycrystalline silicon TFTs
is constructed by a pixel region and a peripheral circuit and TFT characteristics
required for each circuit are different. For example, an LDD structure TFT having
a large off-current suppressing effect is suitable for the pixel region. Also,
a GOLD structure TFT having a large hot carrier resistance is suitable for the
peripheral circuit. When the performance of the semiconductor display device is
improved, it is suitable that difference TFT structures are used for each circuit.
In the case where the GOLD structure TFT having both Lov regions and Loff regions
is formed, ion implantation into the Lov regions is independently performed using
a negative resist pattern formed in a self alignment by a rear surface exposure
method as a mask, and thus impurity concentrations of the Lov regions and the Loff
regions can be independently controlled. Therefore, the GOLD structure TFT having
both the hot carrier resistance and the off-current suppressing effect can be formed
and the simplification of a manufacturing process of the semiconductor display
device and the improvement of performance thereof are compatible with each other.
