RTP temperature measurements using Si grating prepared by laser ablation for large diameter wafer applications

Although a resolution of 1 °C of the grating temperature measurements has been demonstrated in RTP process, the conventional etching process to fabricate gratings on large diameter wafers makes it impractical for the production purpose. We, therefore, used the laser ablation technique to fabricate such Si gratings without any lithography and etching process. To increase the sensitivity of measurements, a large-angle diffracted beam was used by optimizing the incident angle and the grating period. As a result, an improvement of sensitivity could be obtained. The Si gratings were fabricated by the interference of two high power laser beams with the wavelength of 266 nm. The grating period was determined by interference condition, and could be varied from 180 to 550 nm, which would be beneficial to increase the measurement sensitivity. HeNe laser was used as the light source to measure the thermal expansion of grating periods for the temperature measurements. The temperature measurement of Si wafer from room temperature to 800 °C was demonstrated.