Effect of thermally induced stresses on the rapid-thermal oxidation of silicon
During rapid-thermal processing (RTP), radiative losses from the edge of silicon wafers which are heated by uniform irradiation create a radial temperature gradient. This temperature gradient induces a stress distribution which is compressive at the center and tensile towards the edge of the wafer. This thermally induced stress affects oxidation kinetics during the rapid-thermal oxidation (RTO) of silicon. The tensile stress enhances the oxidation towards the edge of the wafer, which is opposite to the effect of the radial temperature gradient. For a radially symmetric temperature distribution, the resolved stress and its effect on oxidation are largest along specific crystal directions, namely, the slip directions on slip planes. The stress effect on oxidation is largest at low temperatures and for short times. The temperature dependence relates to the magnitude of the temperature gradient and yield strength of silicon at different temperatures. As the oxidation proceeds, the influence of the thermally induced stress on RTO kinetics diminishes as the effects of the intrinsic stress and the viscous properties of the oxide increase. These observations have implications for RTP temperature measurement and RTO process uniformity.
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