Method and apparatus for precise temperature measurement

A method for determining the temperature of a semiconductor wafer comprising the steps of:

• heating said wafer with a modulated heat source such that the temperature of at least one error source is modulated with a selected modulation depth and the temperature of said wafer is substantially unmodulated;
• detecting the radiance of said wafer along with the radiance of said at least one error source;
• and
• determining the temperature of said wafer by calculating the contribution of said at least one error source based upon said modulation depth.

A method for measuring the temperature of a first heated object in the presence of a second radiating object, comprising the steps of:

• heating said first and second objects with a power source such that said first and second objects emit radiation with partially overlapping spectral bands;
• detecting said radiation emitted by said first and second objects;
• modulating said power source to a selected modulation depth and frequency such that the temperature of said second object varies with said selected modulation depth and frequency and the temperature of said first object remains substantially unmodulated;
• determining the fraction of radiation emitted by said second object which was detected based upon said modulation depth and frequency;
• and
• calculating the temperature of said first object.

A system for measuring the emissivity of a first object in the presence of a second object, comprising:

• a power source for energizing said first and second objects such that said first and second objects emit radiation in a selected spectral band;
• a first detector for detecting radiation power emitted by said first and second objects, said radiation power depending upon the temperature of said first and second objects;
• a second detector for detecting said radiation emitted by said second object, said second detector isolated from the radiation emitted by said first object;
• a modulation source for modulating said heater to a selected modulation depth and frequency such that the temperature of said second object varies with said selected modulation depth and frequency and has an AC component and a DC component and a modulation depth and the temperature of said first object remains substantially unmodulated;
• circuitry to determine the magnitude of the AC component of the radiation detected in said first detector;
• circuitry to determine the magnitude the AC component of the radiation detected in said second detector;
• and
• circuitry to find the ratio of the AC component of the radiation detected in said first detector and the AC component of the radiation detected in said second detector.