Reaction mechanisms for atomic layer deposition of aluminum oxide on semiconductor substrates

Abstract

In this work, we have studied the TMA/H2O (TMA = Al(CH3)3) atomic layer deposition (ALD) of Al2O3 on hydroxyl (OH) and thiol (SH) terminated semiconductor substrates. Total reflection x-ray fluorescence reveals a complex growth-per-cycle evolution during the early ALD reaction cycles. OH and SH terminated surfaces demonstrate growth inhibition from the second reaction cycle on. Theoretical calculations, based on density functional theory, are performed on cluster models to investigate the first TMA/H2O reaction cycle. Based on the theoretical results, we discuss possible mechanisms for the growth inhibition from the second reaction cycle on. In addition, our calculations show that AlCH3 groups are hydrolyzed by a H2O molecule adsorbed on a neighboring Al atom, independent of the type of backbonds (Si-O, Ge-O, or Ge-S) of AlCH3. The coordination of Al remains four-fold after the first TMA/H2O reaction cycle.