Method of cooling a wafer support at a uniform temperature in a capacitively coupled plasma reactor

A method of transferring heat from or to a workpiece support and a workpiece supported on a top surface of the workpiece support in an RF coupled plasma reactor, comprising:

• electrostatically clamping the workpiece onto the top surface of the workpiece support;
• initiating an RF plasma over the workpiece;
• transferring heat from or to a coolant by circulating said coolant through a refrigeration loop in which an internal flow channel located inside of said workpiece support constitutes an evaporator of the refrigeration loop having an evaporator inlet and an evaporator outlet, the refrigeration loop further comprising:
• a compressor in fluid communication with said evaporator outlet;
• a condenser in fluid communication with an outlet of said compressor;
• an expansion valve between an output of said condenser and said evaporator inlet;
• and
• a bypass valve between said outlet of said compressor and said evaporator inlet;
• and
• maintaining thermal conditions of the coolant inside said evaporator within a range in which heat exchange between said workpiece support and said coolant is primarily or exclusively through the latent heat of vaporization of said coolant,
• wherein transferring and maintaining comprise controlling said expansion valve and said bypass valve.