Temperature measurement method and heat treatment apparatus

A heat treatment apparatus for irradiating a substrate with light to heat the substrate, comprising:

• a chamber for receiving said substrate therein;
• a susceptor for placing and holding said substrate thereon within said chamber;
• first radiation thermometer and a second radiation thermometer provided obliquely above or obliquely below said susceptor and for detecting a brightness temperature of said substrate;
• an input parameter calculation part for calculating at least two input parameters from said brightness temperature detected by said first radiation thermometer and said second radiation thermometer, said at least two input parameters including a first input parameter corresponding to an emissivity ratio between a first emissivity of said first radiation thermometer and a second emissivity of said second radiation thermometer and a second input parameter corresponding to said brightness temperature of said substrate;
• an output parameter estimation part for estimating an output parameter from said first input parameter and said second input parameter, said output parameter being a ratio between a logarithm of said first emissivity and a logarithm of said second emissivity;
• and
• a temperature calculation part for calculating the temperature of said substrate from said output parameter estimated by said output parameter estimation part and said brightness temperature detected by said first radiation thermometer and said second radiation thermometer,
• wherein said output parameter estimation part estimates said output parameter based on a correlation between said first input parameter and said output parameter, said correlation being specified as different according to said second input parameter.