Power switching system for esc with array of thermal control elements

A method of etching a semiconductor substrate in a plasma processing chamber, the plasma processing chamber having an electrostatic chuck assembly for supporting the substrate during plasma processing, the electrostatic chuck assembly including a baseplate and a heater array comprising thermal control elements operable to tune a spatial temperature profile on the semiconductor substrate, the thermal control elements defining heater zones each of which is powered by two or more power supply lines and two or more power return lines wherein each power supply line is connected to at least two of the heater zones and each power return line is connected to at least two of the heater zones, the electrostatic chuck assembly being mated to a power distribution assembly via the baseplate, the power distribution assembly including a power distribution circuit connected to each power supply line and power return line of the heater array and a power switching device connected to the power distribution circuit, the method comprising:

• independently supplying power to each one of the heater zones via one of power supply lines and one of power return lines to provide time-averaged power to each of the heater zones by time-divisional multiplexing of a plurality of switches of the power switching device.