Effect of sample doping level during etching of silicon by fluorine atoms

The rate of silicon etching by XeF₂ is dependent on the type of dopant and the doping level. Soft-x-ray photoemission was used in an effort to elucidate the mechanism responsible for this phenomenon. Si(111) samples were subjected to sufficient XeF₂ to reach the steady-state etching regime, and spectra were collected of the fluorosilyl reaction intermediate species that form on the surface. Samples that were lightly doped (10¹⁷ cm^-3) showed virtually no difference between p and n doping, while heavily doped samples (10²⁰ cm^-3) showed a marked difference. The heavily doped n-type sample had a slightly thinner reaction layer than did the lightly doped samples, while the heavily doped p-type sample had a much thicker layer, in which the composition of the layer was also changed. These results are discussed in terms of possible reaction mechanisms.