Patent ID: 7358197

Claim:
A method for forming a polysilicon film on a dielectric layer, said method comprising: providing a semiconductor substrate having a dielectric layer thereon in a reaction chamber; injecting a first silicon source gas at a first flow rate into said reaction chamber to form a first polysilicon film with a first surface over said dielectric layer; injecting a second silicon source gas at a second flow rate into said reaction chamber to form a second polysilicon film with a second surface having a higher flatness compared to said first surface over said first polysilicon film, wherein said second silicon source gas has a different growth rate than said first silicon source gas; patterning said second polysilicon film and said first polysilicon film by removing a region of said second polysilicon film and a part of said first polysilicon layer located thereunder so that a remaining part of the first polysilicon film forms a third surface flatter than said first surface; and removing said remaining part of the first polysilicon film until said dielectric layer is exposed.