Patent ID: 8012304

Claim:
A plasma reactor, comprising: a reactor chamber and an electrostatic chuck having a surface for holding a workpiece inside said chamber and having respective inner and outer zones; inner and outer zone backside gas pressure sources coupled to said electrostatic chuck for applying a thermally conductive gas under respective pressures to respective inner and outer zones of a workpiece-surface interface formed by a workpiece held on said surface; inner and outer zone heat exchangers coupled to said respective inner and outer zones of said electrostatic chuck; inner and outer zone temperature sensors coupled to inner and outer zones of said electrostatic chuck; a memory storing a schedule of changes in RF power; a thermal model capable of simulating heat transfer through said inner and outer zones, respectively, to said surface based upon measurements from said inner and outer temperature sensors, respectively; inner and outer zone first control processors coupled to said thermal model and governing said inner and outer zone backside gas pressure sources, respectively, in response to predictions from said model of changes in said respective pressures that would compensate for the effect of the next scheduled change in RF power in each respective one of said zones.