Mechanism of surface selectivity in aluminum chemical vapor deposition

Abstract

The pyrolysis of triisobutylaluminum occurs much more readily on the surface of Al than on the surface of an oxide. This propensity allows Al to be grown selectively on a wafer and may simplify certain metallization steps in integrated circuit manufacture. In this study, ab initio molecular orbital techniques have been used to elucidate how the transition state energy for beta-hydride elimination of the alkyl ligand varies for Al atoms in different chemical environments. Elementary considerations of the nature of the four-center transition state suggest that the energetics of promoting an electron to the empty pπ-orbital on Al determines the energy of the transition state. Molecular cluster calculations are then used to show that the energy of this electron promotion increases substantially when comparing an Al atom bonded to other Al atoms versus O atoms, explaining the observed surface selectivity.