Doping reaction of PH₃ and B₂H₆ with Si(100)

Abstract

The reaction of phosphine PH3 and diborane B2H 6 on Si(100) surfaces was studied by surface analytical techniques in relation to the in situ doping process in the chemical vapor deposition of silicon. Phosphine chemisorbs readily either nondissociatively at room temperature or dissociatively with the formation of silicon-hydrogen bonds at higher temperatures. Hydrogen can be desorbed at temperatures above 400°C to generate a phosphorus layer. Phosphorus is not effective in shifting the Fermi level until the coverage reaches 2×1014/cm 2. A maximum shift of 0.45 eV toward the conduction band was observed. In contrast, diborane has a very small sticking coefficient and the way to deposit boron is to decompose diborane directly on the silicon surface at temperatures above 600°C. Boron at coverages less than 2×10 14/cm2 is very effective in shifting the Fermi level toward the valence band and a maximum change of 0.4 eV was observed.