BORON AUTODOPING DURING SILANE EPITAXY

In order to calculate the redistribution of boron in silicon by both diffusion and autodoping during epitaxial growth, certain materials parameters must be known as a function of temperature. The parameters are the diffusion coefficient of boron, the evaporation coefficient of boron from silicon, and the silicon evaporation rate in a hydrogen ambient. The value of the diffusion coefficient of boron is already well known while the values for the other two parameters have not been determined over the temperature range usually used for epitaxial growth. The evaporation coefficient of boron in silicon in a hydrogen ambient was experimentally determined to be where is in microns per minute, the energy is expressed in electron volts, and temperature is in degrees Kelvin. The evaporation rate of silicon in a hydrogen ambient was measured as in a hydrogen ambient. These results were obtained in the temperature range from 1190° to 1380°C. These results allowed the accurate prediction of boron back surface "autodoping" effects during epitaxial growth using a numerical solution to Fick's second law. Radial as well as in‐depth concentration vs. distance plots were experimentally determined illustrating boron autodoping for both lightly and heavily doped substrates. Reduction of boron autodoping was obtained by the addition of to the ambient during epitaxial growth, permitting the growth of lightly doped layers on heavily boron‐doped substrates.