In this paper, we address issues of the power consumption of the lamps, temperature uniformity across wafer, and the grating temperature measurements, for a large diameter wafer process. The optimum design of the lamp separation and the distance between the lamp arrays and wafer surface can be obtained with uniform radiation and the minimum lamp power. Based on a simplified radiation thermal model, the transient and steady state non-uniformity of temperature on the wafer edge can be predicted. The wafer emissivity as a function of temperature and wavelength is exactly modeled. The effect of a multi-layer grown on Si was also included. A grating temperature measurement was demonstrated in the RTP process. We used the laser ablation technique to fabricate a Si grating. To increase the sensitivity of measurements, a large angle diffracted beam was used.