Light irradiation type heat treatment method

A method of irradiating a substrate with light to heat the substrate, said method comprising the steps of:

• (a) sequentially transporting multiple dummy wafers into a chamber and placing the dummy wafers on a susceptor before a substrate to be treated is transported into said chamber;
• (b) irradiating a back surface of each dummy wafer in a first group among said multiple dummy wafers with light from a continuous lighting lamp to heat each dummy wafer in the first group to a first heating temperature, and thereafter irradiating a front surface of each dummy wafer in the first group with a flash of light from a flash lamp to heat each dummy wafer in the first group;
• (c) measuring, as a judgment temperature, a predetermined temperature at a time when a predetermined time period has elapsed since turning off of said continuous lighting lamp and said flash lamp upon completion of heating of each dummy wafer in the first group;
• and
• (d) irradiating a back surface of each dummy wafer in a second group among said multiple dummy wafers with light from said continuous lighting lamp to heat each dummy wafer in the second group to a second heating temperature lower than said first heating temperature, and thereafter irradiating a front surface of each dummy wafer in the second group with a flash of light from said flash lamp to heat each dummy wafer in the second group, said step (d) being started after said judgment temperature falls within a predetermined range with respect to a target temperature,
• wherein said judgment temperature is a temperature of the back surface of each dummy wafer in the first group or an atmosphere temperature in said chamber.