Theoretical approach to the optimal preheating temperature for cw CO2 laser annealing of semiconductors

Using the classical and semiclassical theory, we first give the precise formula of the light absorptance β(T) in semiconductors. As an example, the results for p-type Si wafers are calculated numerically. The absorptance β(T), the absorption coefficient α(T), and the reflectance R(T) of a cw CO2 laser in p-type Si wafers are shown as a function of temperature. By using these relations some important results are found: (1) The optimal preheating temperature range for cw CO2 laser annealing is determined; (2) a conclusion is reached that annealing efficiency is higher for laser irradiation from the back surface, in agreement with experimental observations; and (3) it is shown that to discuss the problem of light absorption by means of the light-absorption coefficient is not sufficient. In this paper a theoretical method of determining the optimal preheating temperature for cw CO2 laser annealing of semiconductors is proposed.