Radiation-enhanced diffusion during high-temperature ion implantation

To investigate the influence of elevated temperatures during ion implantation on the resulting profile shapes of implanted ions and generated defects, our Varian 350D implanter has been equipped with a lamp heater. The wafers can be heaten up to 1100degreeC. As one application we have investigated the high- temperature implantation of boron in the temperature range from 500 to 1000degreeC. The resulting profiles have been measured by SIMS. All profiles show a very marked enhancement of the diffusion coefficient which can be attributed to the defects generated during ion implantation. The apparent diffusion coefficient has the maximum at 800degreeC and is about 43000 times larger than the intrinsic diffusion coefficient. The activation energy of the apparent diffusion coefficient is negative at temperatures above 800degreeC. This behaviour can be interpreted by assuming that the generated point defects recombine faster at higher temperatures so that at lower temperatures more of them ca n act as diffusion vehicles. Further investigations hace shown that the apparent diffusion coefficient is proportional to the square root of the dose rate.