Method for real-time semiconductor wafer temperature measurement based on a surface roughness characteristic of the wafer

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

• generating a first laser beam at a first wavelength;
• generating a second laser beam at a second wavelength;
• simultaneously reflecting the first and second laser beams off the wafer while said wafer is at a reference temperature;
• modulating the wavelengths of the first and second laser beams while said wafer is at said reference temperature;
• measuring first and second rates of change in specular reflectance of the water as functions of wavelength corresponding to the first and second modulated laser beam wavelengths while the wafer is at said reference temperature;
• determining a surface roughness characteristic of the wafer at the reference temperature by use of said first and second rates of change in specular reflectance at said reference temperature;
• simultaneously reflecting the first and second laser beams off the wafer while the wafer is at an unknown temperature;
• simultaneously modulating the wavelengths of the first and second laser beams while said wafer is at said unknown temperature;
• again measuring first and second rates of change in specular reflectance of the water as functions of wavelength corresponding to the first and second modulated laser beam wavelengths while the wafer is at the unknown temperature;
• and
• determining the unknown temperature from the measured surface roughness characteristic of the wafer at the reference temperature and the first and second rates of change in specular reflectance of the wafer at the unknown temperature.