ESTIMATION OF EFFECTIVE DIFFUSION TIME IN A RAPID THERMAL-DIFFUSION USING A SOLID DIFFUSION SOURCE

Abstract

Two-step rapid thermal diffusion (RTD) of phosphorus and boron using a solid diffusion source is described. In the case of phosphorus diffusion, the profiles measured by SIMS show two distinct regions, i.e., a constant concentration region near the surface and an exponentially decaying region forming the diffusion tail. For the quantitative analysis of the RTD process, two correction terms for the effective diffusion time have been introduced. The first correction term incorporates the temperature transient cycle, and the second term is due to the finite point defect lifetime during the cooling. From the Boltzmann-Matano analysis, it has been found that the increment of effective diffusion time due to the finite point defect lifetime (t(def)) is about 3 s. A simple mathematical modeling shows that one can regard t(def) as the lifetime of point defects. In the case of the boron diffusion, borodisc is used for the diffusion source. The boron profiles show existence of a boron-rich layer at the surface. The correction term in the effective diffusion time has a strong dependence on temperature. This has been explained to be due to the initial growth of the boron-rich layer during the first RTD step. The maximum value of t(def) for boron diffusion has been found to be less than for the phosphorus diffusion case. The introduction of the additional correction terms to the effective diffusion time makes it possible to treat the RTD process similarly to the normal diffusion.