The Electronic Structure and Deposition Kinetics of Arsenic on the Silicon Surface.

In this work the interaction of arsenic with silicon surfaces was investigated. As well as being of considerable theoretical interest, the results provide a basis for understanding the properties of dopants segregated at grain boundaries in polycrystalline silicon, used in silicon integrated circuit technology. The molecular character of arsenic adsorbed on the Si(100) surface was investigated using thermal desorption spectroscopy. A loosely bound, As(,4) surface species is adsorbed from solid evaporation sources and desorbs at about 350(DEGREES)C. A high desorption temperature (900 C) tightly bound, As(,2) species is also observed. Its behavior suggests that the adsorbed arsenic exists as monomers on the surface, and recombines prior to desorption. The deposition kinetics of tightly bound arsenic from arsine gas was also examined with Auger electron spectroscopy. A quantitative model was developed to describe the observed reduction in deposition rate due to coadsorbed hydrogen evolved from arsine decomposition. Changes in the silicon electronic structure due to arsenic deposition from arsine gas were studied with ultra-violet photoemission spectroscopy. The adsorbed arsenic reduces the density of the midgap silicon surface states and increases the emission intensity at 2 eV below the Fermi level. The Fermi pinning energy at the surface is unchanged by the submonolayer quantity of adsorbed arsenic. Arsenic was also incorporated within a few atomic layers of the surface by thermal annealing in an arsine ambient. The incorporated arsenic type converts the subsurface region and shifts the silicon valence band maximum away from the Fermi level just beneath the surface without changing the Fermi pinning energy at the surface. Type conversion of the subsurface region without modification of the Fermi pinning energy at the surface was also observed in the case of boron deposited on n-type silicon.