A heater for wafer processing, such as thin film deposition, includes a first heating unit and a second heating unit. The first heating unit includes a substrate with a top surface for supporting a wafer thereon and a back surface. The second heating unit is disposed proximate the back surface of the substrate and is preferably disposed inside an inner space of a shaft supporting the first heating unit in a processing chamber. The first heating unit and the second heating unit are independently controlled. The second heating unit is designed based on the actual temperature profile and heat loss on the top surface. Therefore, the second heating unit can more effectively compensate the heat loss to achieve a more uniform temperature profile on the top surface.