Influence of Carbon Addition on the Electrical and Structural Properties of Phosphorus and Boron Doped Silicon Layers

Phosphorus and boron doped polycrystalline silicon layers grown by chemical vapor deposition were additionally doped with carbon via the introduction of C2H ~ in the gas phase. Addition of carbon to n-type and p-type polycrystalline silicon gives rise to characteristic differences in resistivity vs. P c~H2 input pressures, at least at small input pressures of C2H~. The difference in resistivity can be explained by a donor activity of carbon or silicon-carbon complexes or by an asymmet-rical energy distribution of grain boundary traps, both at the grain boundaries. It is also shown that the addition of carbon has a strong influence onthe morphology of the growing silicon layer. With increasing values ofP c~2, the size of the grains in the layer decreases, under certain circumstances even amorphous ilicon is formed, and this effect is stronger at the lowest temperatures. The decomposition kinetics of C2H2 has also been discussed. It is concluded that at high input pres-sures of C~H2 the deposition rate of carbon is gas phase diffusion controlled. At lower Pc~H2 values and temperatures above 850 ~ the formation of Si-C nuclei is rate-limiting as far as the introduction of carbon is concerned. Polycrystal l ine sil icon layers are used extensively for the fabrication of integrated circuits (1), e.g., gate material in MOS field effect transistors and lateral diodes (2). The electrical propert ies of chemical ly de