Journal of Applied Physics vol:72 issue:12 pages:5867-5875
The influence of temperature and roughness on the backside emissivity of Si wafers was studied. In situ measurements were done in two commercial rapid thermal processing systems. An experimental setup was built for in situ emissivity measurements of wafers with a polished or nonpolished backside. The emissivity of double-side polished wafers was measured for temperatures ranging from 300 to 700-degrees-C and at wavelengths of 1.7 and 3.4 mum. It was found that the absorption coefficient alpha of lightly doped silicon is described by the equation alpha=4.15 X 10(-5)lambda1.51T2.95 exp(-7000/T) cm-1, for wavelengths lambda ranging from 1.5 to 5 mum and temperatures T ranging from 673 to 973 K (lambda in mum, T in K). The backside emissivity of Si wafers with different roughnesses was measured. At temperatures above 600-700-degrees-C the wafers are opaque and the emissivity is only slightly dependent on backside roughness. At lower temperatures the wafers are partially transparent and the emissivity is strongly dependent on the backside roughness of the wafer due to light trapping in the bulk of the wafer. For the latter case a new model was developed to simulate the emissivity of wafers with a rough backside at low temperatures.