A study of phosphorus adsorption and desorption kinetics on silicon (111) surfaces

Abstract

Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) methods were used to characterize the (111) surface of Si wafers before and after the deposition of P 2 molecules. Before deposition, the well-known Si(111)-7 LEED pattern was easily obtained by thermal cleaning at 1200 °C. Cleaning was done by electron bombardment in a vacuum chamber with a base pressure of ∼ 10 -10 Torr. After cleaning, AES showed that about 10 -2 atomic layer of carbon was the only surface contaminant. The sensitivity of our cylindrical AES apparatus for phosphorus was about 10 -3 atomic layer. We found that ∼5×10 -2 atomic layer of phosphorus deposited on a Si(111) surface caused the fractional order spots to dissappear from the LEED pattern, so that a sharp Si(111)-1 pattern remained. The kinetics of phosphorus desorption from the Si(111) surface was investigated with AES and mass spectrometry. P 2 was found to be the main desorption procuct. The desorption process obeyed second order kinetics. The activation energy for the desorption of P 2 was 68.6 ± 0.8 kcal mole -1 for phosphorus coverages between 0.1 and 0.5 atomic layer.