First Principles Study of Phosphine Adsorption and Decomposition on Si(100)-2x1

Michael Mysinger, Stanford University

Phosphine has significant potential as a precursor in chemical vapor deposition to form in situ phosphorus-doped epitaxial and polycrystalline silicon films. Due to this potential, we study phosphine's interaction with the Si(100)-2x1 surface. We characterize the potential energy surfaces of various mechanisms for adsorption and decomposition of phosphine using ab initio quantum chemical calculations. We find molecular adsorption occurs on the lower silicon atom in the tilted Si-Si dimer structure, with a binding energy of 16 kcal/mol. The molecular adsorption of phosphine is followed by dissociation to PH2(a) + H(a), which occurs by three competing pathways. The most thermodynamically favored pathway involves hydrogen loss to the same dimer, which is exothermic by 48 kcal/mol relative to PH3(g). The lowest energy barrier for hydrogen loss, however, involves hydrogen loss across the trench with an energy barrier 5 kcal/mol below the PH3(g) state. The final pathway involves hydrogen loss to a neighboring dimer in the same row, whose energy barrier and thermodynamic stability lie in between those of the other two pathways.

Abstract Author(s): Michael Mysinger and Charles Musgrave