Heat treatment method and heat treatment apparatus for heating substrate by irradiating substrate with light
First irradiation which causes an emission output from a flash lamp to reach its maximum value over a time period in the range of 1 to 20 milliseconds is performed to increase the temperature of a front surface of a semiconductor wafer from a preheating temperature to a target temperature for a time period in the range of 1 to 20 milliseconds. This achieves the activation of the impurities. Subsequently, second irradiation which gradually decreases the emission output from the maximum value over a time period in the range of 3 to 50 milliseconds is performed to maintain the temperature of the front surface within a ±25° C. range around the target temperature for a time period in the range of 3 to 50 milliseconds. This prevents the occurrence of process-induced damage while suppressing the diffusion of the impurities.
1. A method of heating a substrate by irradiating the substrate with light, the method comprising the steps of:
(a) heating a substrate to a predetermined preheating temperature;
(b) irradiating a first surface of said substrate with a flash of light from a flash lamp to keep increasing the temperature of said first surface of said substrate from said preheating temperature to a maximum target temperature over a time period longer than the time required for heat conduction from said first surface to a second surface of said substrate which is a surface opposite from said first surface, wherein an emission output of said flash lamp keeps increasing until a temperature of said first surface reaches said maximum target temperature in said step (b); and
(c) irradiating said first surface of said substrate with a flash of light from said flash lamp to maintain the temperature of said first surface of said substrate within a ±25° C. range around said maximum target temperature for not less than 5 milliseconds, said step (c) being performed after said step (b), wherein said maximum target temperature is the highest temperature reached by said substrate throughout said heating method, except that it may exceed same during said irradiating step (c) but not more than by 25° C.
2. The method according to claim 1 , wherein the rate of increase in the temperature of said first surface in said step (b) is not less than 1000° C./sec.
3. The method according to claim 1 , wherein said substrate is a semiconductor wafer of silicon.
4. The method according to claim 1 , including using a switching element to intermittently supplying electrical charges from a capacitor to said flash lamp to control an emission output from said flash lamp in said step (b) and in said step (c).