Patent ID: 7432138

Claim:
A method of manufacturing a thin film transistor substrate, comprising the steps of: (a) forming a bottom gate electrode above a substrate; (b) forming a first gate insulating film above the substrate so as to cover the bottom gate electrode (c) forming a plurality of island-shaped semiconductor films above the first gate insulating film, one of the island-shaped semiconductor films intersects with the bottom gate electrode; the step (c) including the sub-steps of: (c-1) depositing an amorphous semiconductor film; (c-2) polycrystallizing the amorphous semiconductor film by irradiation of laser beam; and (c-3) patterning a polycrystallized semiconductor film obtained from the amorphous semiconductor film in the sub-step (c-2), (d) forming a second gate insulating film above the first gate insulating film with a smaller thickness than the first gate insulating film, so as to cover the plurality of island-shaped semiconductor films; (e) forming a top gate electrode above the second gate insulating film so that the top gate electrode intersects with one of the plurality of island-shaped semiconductor films which does not intersect with the bottom gate electrode; (f) forming a source/drain region by injecting a first conductive type impurity into an upper plane of (i) the island-shaped semiconductor film intersecting with the bottom gate electrode and into an upper plane of (ii) the island-shaped semiconductor film intersecting with the top gate electrode, the source/drain region being formed on either side of the bottom gate electrode or the top gate electrode; and (g) forming an LDD region by injecting a first conductive type impurity into an upper plane of the island-shaped semiconductor film above the bottom gate electrode, the LDD region being formed on a portion more inside than the source/drain region and partially covering the bottom gate electrode excluding a channel region which resides above the bottom gate electrode, the LDD region being lower in impurity concentration than the source/drain region.