Two-element plasma resistant lightpipe assembly

Abstract

A plasma resistant lightpipe is used in a pyrometric temperature measurement system to measure the temperature of a substrate in a reaction chamber. The plasma resistant lightpipe includes two lightpipe elements. The first lightpipe element, which may be a sapphire rod or aluminum nitride rod, is positioned within a backside gas delivery path to the chamber. The first lightpipe element is resistant to etching caused by reactive plasmas or gases used within the chamber, such as fluorine. The second lightpipe, which is a quartz rod, is positioned beneath the first lightpipe element such that the two lightpipe elements are optically coupled. The first lightpipe element may be directly mounted in the base plate or electrostatic chuck of the pedestal assembly or directly mounted in a plug, which is then positioned within the base plate or electrostatic chuck. The first lightpipe element is securely mounted into the base plate, electrostatic chuck, or the plug by shrink and/or interference fitting, by spring pins or set screws. In one embodiment, the interface between the first lightpipe element and the second lightpipe element is set in a plane defined by the top surface of the seal plate. Thus, there is little danger of damaging the lightpipe elements during the removal of the electrostatic chuck and base plate.