Substrate carrier using a proportional thermal fluid delivery system

A method for processing a workpiece comprising:

• generating a plasma containing gas ions in a plasma chamber;
• applying the plasma to a workpiece on a workpiece holder;
• regulating a temperature of the workpiece through a thermal fluid channel of the workpiece holder, using a heat exchanger to provide a thermal fluid to the fluid channel and to receive the thermal fluid from the fluid channel, the thermal fluid in the fluid channel to control the temperature of the workpiece carrier during substrate processing using a proportional valve to control the flow rate of the thermal fluid from the heat exchanger to the fluid channel and a temperature controller to receive a measured temperature from a thermal sensor of the workpiece holder and to control the proportional valve in response to the measured temperature to adjust the flow rate of the thermal fluid.