Patent ID: 8608900

Claim:
A plasma reactor, comprising: a reactor chamber and an electrostatic chuck having a surface for holding a workpiece inside said chamber; a backside gas pressure source coupled to said electrostatic chuck for applying a thermally conductive gas under a selected pressure into a workpiece-surface interface formed whenever a workpiece is held on said surface; thermal control apparatus thermally coupled to said electrostatic chuck and a valve for controlling flow of coolant through said thermal control apparatus; a chuck temperature sensor in said electrostatic chuck; a workpiece temperature sensor at said surface of said electrostatic chuck configured to measure a temperature of said workpiece; a memory storing a schedule of changes in RF power or workpiece temperature; and a thermal model coupled to receive inputs from both of said workpiece and chuck temperature sensors and configured to simulate heat transfer between said thermal control apparatus and said surface based upon contemporaneous measurements from said chuck temperature sensor and said workpiece temperature sensor during processing of said workpiece; a first control processor coupled to said thermal model and to said memory and governing said backside gas pressure source in response to a prediction from said thermal model of a change in said selected pressure that would compensate for an effect of a next scheduled change in RF power on the temperature of said workpiece in accordance with a desired workpiece temperature.