Apparatus and method for temperature control of workpieces in vacuum

Abstract

A flat workpiece is placed in contact with a flat platen in a vacuum chamber, and is held by a uniformly-distributed force while a small mass flow of gas is introduced along a contour to form a uniform pressure region between the flat workpiece and the platen. Separation of the two surfaces due to aplanarity or surface roughness is less than the gas mean free path, and high rates of heat transfer are obtained uniformly over the area of the workpiece. A scavenging port, located outwardly of the gas introduction contour is differentially pumped to reduce the rate of gas leakage into the chamber. Preferably, pressure is provided by an electrostatic clamp (for non-insulating substrates) or other clamping arrangement which does not occlude the front surface of the workpiece. In the electrostatic clamp, the voltage activation sequence prevents workpiece vibration, while a clamping current sensor immediately detects degree of contact, e.g., due to debris on the platen, and initiates a suitable warning or control. High cooling rates, freedom from bowing or stress, and full utilization of front surface area are all achieved.