Thermal processing is used in various stages of microelectronics fabrication. One of the heating processes may be rapid thermal processing (RTP), which involves high temperatures and heating rates, and short durations. Temperature control and uniformity within a few degrees is a requirement in RTP. Prediction, measurement, and control of wafer temperatures during RTP have been a challenge due to the highly non-linear radiative properties of the wafers. These properties are functions of temperature, wavelengths, doping level, surface patterns, and thin-film structures. A numerical model has been developed to determine the wafer radiative properties, taking into account bandgap, free carrier, and lattice absorption effects, as well as thin-film interference near the surface and partial transparency within the wafer thickness. Experimental measurements of spectral reflectivity of different pattern sizes were made for SiO2 stripes on Si wafer. Results indicate that the radiative properties of patterned wafers for pattern sizes down to 4 μm can be adequately predicted by the average reflectivity of Si and SiO2, weighted according to their relative areas. This was found to be true regardless of the diffractive effects seen visually. The numerically determined radiative properties were used in a model of radiantively heated patterned wafer to find the temperature distribution at steady-state. For the model wafer having 2550 Å SiO2 film on Si, with SiO2 and Si stripe patterns, the patterns created regions of high and low temperatures on the wafer, which can lead to significant thermal stresses and defects in the wafer.

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