Patent ID: 6743649
Filing Date: 2004-06-01
Classification: G02F,H01L

Abstract:
A method for forming a semiconductor device which comprises a pixel TFT disposed in a pixel section and a driver circuit comprising a p-channel TFT and an n-channel TFT disposed in a periphery of the pixel section over a substrate, comprising the steps of:forming a semiconductor layer which contains crystalline structure over the substrate; forming a plurality of island semiconductor layers by selectively etching the semiconductor layer which contains crystalline structure; forming a gate insulating film in contact with the island semiconductor layers; forming a conductive layer comprising a heat resistant conductive material over the gate insulating film; forming a gate electrode which has a tapered portion by selectively etching the conductive layer; forming a first impurity region which has gradient in a concentration of an impurity element that imparts n-type in a direction parallel to the substrate, at least in an island semiconductor layer of the n-channel TFT of the driver circuit and the pixel TFT, by adding an impurity element that imparts n-type through the tapered portion of the gate electrode and the gate insulating film; forming a second impurity region in the island semiconductor layers that form the n-channel TFT of the driver circuit and the pixel TFT, by forming a mask over the gate electrodes and a region adjacent to the gate electrodes and by adding an impurity element which imparts n-type; forming in an island semiconductor layer which forms the p-channel TFT of the driver circuit, at the same time a third impurity region which has gradient in a concentration of an impurity element imparting p-type in a direction parallel to the substrate by adding the impurity element imparting p-type through the tapered portion of the gate electrode and the gate insulating film; and a fourth impurity region by adding the impurity element imparting p-type without using the tapered portion of the gate electrode; forming a first interlayer insulating film comprising an inorganic insulating material over the n-channel TFT and the p-channel TFT of the driver circuit and the pixel TFT; forming a second interlayer insulating film comprising an organic insulating material in contact with the first interlayer insulating film; and forming a pixel electrode which is connected to the pixel TFT and has a light reflective surface, over the second interlayer insulating film.