Equilibrium and kinetics in the chemical vapour deposition of silicon

Abstract

In the growth of silicon layers on various substrates it appears that the growth rate is not uniquely determined by substrate temperature and input parameters of the gases used. An analysis of this situation is given and essential points in the chain reaction of steps in the growth process will be indicated. Differences in growth rate reported for different experimental situations can be explained on the basis of this analysis where the temperature gradient normal to the growing interface will appear to be of special importance. Some examples are given of resulting surface morphology as a function of growth and etch conditions. Another point of interest in the growth process is the incorporation of dopant which determines the electrical properties of the layers. Here also equilibrium and kinetics show an interplay. For low growth rates there appears to be a good correlation between the concentration of impurities in the solid and the partial pressure of dopant in the gas phase. For growth rates exceeding a critical-value kinetic effects can be expected as those found in liquid phase epitaxy. It appears that an n-type dopant as phosphorus shows this effect. In this case the surface concentration of ionized donors exceeds the bulk concentration of these centres and trapping occurs at higher growth rates.