Patent ID: 8030146

Claim:
A method of forming a polysilicon channel layer, comprising: providing a substrate having a first polysilicon layer and a second polysilicon layer disposed thereon; covering the substrate by a first mask, wherein the first mask has a first opening and a second opening for respectively exposing the first polysilicon layer and the second polysilicon layer; doping a first dopant atom not selected from the IIIA group and the VA group inside the first polysilicon layer and the second polysilicon layer to respectively form a first polysilicon channel layer and a second polysilicon channel layer, wherein the doping concentration of the first dopant atom in the first polysilicon channel layer is the same with the doping concentration of the first dopant atom in the second polysilicon channel layer; removing the first mask and covering the substrate by a second mask, wherein the second mask has a third opening for exposing the first polysilicon channel layer; and doping a second dopant atom inside the first polysilicon channel layer to form a third polysilicon channel layer, wherein the total doping concentration of the first dopant atom and the second dopant atom in the third polysilicon channel layer is larger than the doping concentration of the first dopant atom in the second polysilicon channel layer.