Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• a driver circuit including a first n-channel TFT and a p-channel TFT, and a pixel portion including a second n-channel TFT;
• the first n-channel TFT including a first semiconductor layer, a gate insulating film over the first semiconductor layer, and a first gate electrode over the gate insulating film, wherein the first semiconductor layer contains a first channel forming region, a pair of first impurity regions, a pair of second impurity regions, and a pair of third impurity regions;
• the p-channel TFT including a second semiconductor layer, the gate insulating film over the second semiconductor layer, and a second gate electrode over the gate insulating film, wherein the second semiconductor layer contains a second channel forming region, and a pair of fourth impurity regions;
• the second n-channel TFT including a third semiconductor layer, the gate insulating film over the third semiconductor layer, and a third gate electrode over the gate insulating film, wherein the third semiconductor layer contains a third channel forming region, a pair of fifth impurity regions, and a pair of sixth impurity regions,
• wherein each of the first gate electrode, the second gate electrode, and the third gate electrode has a tapered side surface,
• wherein the pair of first impurity regions are overlapped with the tapered side surface of the first gate electrode,
• wherein the pair of second impurity regions are not overlapped with the first gate electrode,
• wherein the pair of fifth impurity regions are not overlapped with the third gate electrode,
• wherein the pair of third impurity regions contain an impurity imparting n-type at a higher concentration than that of the pair of first impurity regions and the pair of second impurity regions, and
• wherein the pair of sixth impurity regions contain an impurity imparting n-type at a higher concentration than that of the pair of fifth impurity regions.