| 摘要 |
Electric characteristics of a thin film transistor including a channel formation region including a microcrystalline semiconductor are improved. The thin film transistor includes a gate electrode, a gate insulating film formed over the gate electrode, a microcrystalline semiconductor layer formed over the gate insulating film, a semiconductor layer which is formed over the microcrystalline semiconductor layer and includes an amorphous semiconductor, and a source region and a drain region which are formed over the semiconductor layer. A channel is formed in the microcrystalline semiconductor layer when the thin film transistor is placed in an on state, and the microcrystalline semiconductor layer includes an impurity element for functioning as an acceptor. The microcrystalline semiconductor layer is formed by a plasma-enhanced chemical vapor deposition method. In forming the microcrystalline semiconductor layer, a process gas is excited with two or more kinds of high-frequency electric power with different frequencies. |
