Optical techniques for measuring parameters such as temperature across a surface

Abstract

A sensor of a parameter such as temperature includes an indicator encapsulated within a rigid enclosure, wherein the sensor has a characteristic that varies with the parameter that is detectable upon illumination with electromagnetic radiation through a window of the enclosure that is transparent to the radiation. In a specific example, the indicator changes an optical characteristic such as its color as a function of its temperature, and may be of an irreversible type in order to indicate the peak temperature reached. The sensor may include a pattern of such indicators that have different peak temperatures to which they respond, so that the sensor gives a unique visual pattern at each temperature within its measurement range. This pattern may be viewed directly or processed by computer to compare the pattern with those which indicate known temperatures. The sensor and system utilizing it have particular advantages for operation in a vacuum, and/or under ion bombardment, such occurs in plasma etching and deposition machines, and/or within a strong electromagnetic field, such as within the radio frequency and microwave frequency ranges. An array of such sensors positioned across a surface of a thermally conductive substrate is especially useful for measuring a temperature distribution occurring across semiconductor wafers in wafer processing machinery.