APPARATUS AND METHOD FOR TEMPERATURE CONTROL OF WOAPPARATUS AND METHOD FOR TEMPERATURE CONTROL OF WORKPIECES IN VACUUM RKPIECES IN VACUUM

摘要

A flat workpiece (2) 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 (203) to form a uniform pressure region between the flat workpiece (201) and the platen (2). Separation of the two surfaces due to 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 (2). A scavenging port (207), located outwardly of the gas introduction contour (203) is differentially pumped to reduce the rate of gas leakage into the chamber. Pressure is provided by an electrostatic clamp (250) where the voltage activation sequence prevents workpiece vibration. A clamping current sensor immediately detects degree of contact, e.g., due to debris on the platen, and initiates a suitable warning or control.