Method of cooling a wafer support at a uniform temperature in a capacitively coupled plasma reactor
View Patent ↗A method of controlling the temperature of a workpiece on a workpiece support in a plasma reactor includes placing coolant in a flow channel thermally coupled to the workpiece support, supporting a thermally conductive gas between the workpiece and the workpiece support to establish a backside gas pressure, providing sensors to measure the temperature of the workpiece support and the workpiece, and determining whether the rate of change in workpiece temperature is less or more than a rate limited by a thermal mass of the workpiece support. If the rate is less or equal, the thermal conditions of the coolant in the flow channel are changed to reduce a difference between the measured workpiece support temperature and a target workpiece support temperature. If the rate is more, the pressure of the thermally conductive gas is changed to reduce a difference between the measured workpiece temperature and a target workpiece temperature.
1. A method of controlling the temperature of a workpiece supported on a top surface of a workpiece support in an RF coupled plasma reactor, comprising:
placing coolant in a flow channel that is thermally coupled to said workpiece support;
supplying a thermally conductive gas between the backside of said workpiece and the workpiece support top surface to establish a backside gas pressure;
providing a first temperature sensor thermally coupled to said workpiece support and a second temperature sensor thermally coupled to said workpiece;
determining whether a change in thermal condition of said workpiece is a first type of change having a first rate of change not exceeding a rate limited by a thermal mass of said workpiece support or a second type of change having a second rate of change exceeding said first rate of change;
causing or responding to said first type of change in thermal condition of said workpiece by monitoring a temperature of said workpiece support through said first temperature sensor, and changing the thermal conditions of said coolant in said flow channel so as to reduce a difference between the output of said first temperature sensor and a target workpiece support temperature;
causing or responding to said second type of change in thermal condition of said workpiece by monitoring the temperature of said workpiece through said second temperature sensor, and changing the pressure of said thermally conductive gas so as to reduce a difference between the output of said second temperature sensor and a target workpiece temperature.
2. The method of claim 1 wherein:
said second type of change in thermal conditions corresponds to a change in workpiece temperature lying in a range limited by an RF heat load on the workpiece and a present temperature of said workpiece support;
said first type of change in thermal conditions corresponds to a change in workpiece temperature exceeding said range.
3. The method of claim 2 wherein:
said target workpiece support temperature corresponds to said first type of change in thermal condition of said workpiece;
said target workpiece temperature corresponds to said second type of change in thermal condition of said workpiece.
4. In an RF coupled plasma reactor, a method of transferring heat between a workpiece support and a workpiece supported on a top surface of the workpiece support with an at least nearly uniform temperature across the workpiece support, comprising:
placing coolant in a flow channel that is thermally coupled to said workpiece support;
coupling RF power into a processing zone of said reactor;
supplying a thermally conductive gas between the backside of said workpiece and the workpiece support top surface to establish a backside gas pressure;
providing a first temperature sensor thermally coupled to said workpiece support and a second temperature sensor thermally coupled to said workpiece;
determining whether a change in RF heat load on the workpiece is one change in RF heat load having a first rate of change not exceeding a rate limited by a thermal mass of said workpiece support or an other change in RF heat load having a second rate of change exceeding said first rate of change;
responding to said one change in RF heat load on said workpiece by monitoring a temperature of said workpiece support through said first temperature sensor, and changing the thermal conditions of said coolant in said flow channel so as to reduce a difference between the output of said first temperature sensor and a target workpiece support temperature;
responding to said other change in RF heat load on said workpiece by monitoring the temperature of said workpiece through said second temperature sensor, and changing the pressure of said thermally conductive gas so as to reduce a difference between the output of said second temperature sensor and a target workpiece temperature.
5. The method of claim 4 wherein:
the other change in RF heat load on the workpiece corresponds to a change in workpiece temperature lying in a range limited by an RF heat load on the workpiece and a current temperature of said workpiece support;
the one change in RF heat load on the workpiece corresponds to a change in workpiece temperature exceeding said range.
6. The method of claim 5 wherein:
said target workpiece support temperature is determined in accordance with said one change in RF heat load on said workpiece;
said target workpiece temperature is determined in accordance with the other change in RF heat load on said workpiece.