Abstract: A method for improving the uniformity of wafer-to-wafer film thicknesses. Before depositing films, shower heads in a PECVD system is heated to production temperature to make the entire system (including the shower heads) reach a stable temperature in coordination with heating of a heater block. Subsequently, a gas source, output via the shower heads, is provided, and then a plasma of the gas source is generated to form a film on the wafer due to the temperatures of the shower heads remain constant during wafers deposition. Therefore, the problem of the uneven thicknesses of films among wafers is resolved. Moreover, if the heating of the shower heads by use of a plasma (which can also be used to heat the heater block) and the heater block is concurrently performed after the preventive maintenance (PM) or open chamber cleaning of the PECVD system, the heating time of the heater block can be further shortened.