Self-catalysis by aminosilanes and strong surface oxidation by O2 plasma in plasma-enhanced atomic layer deposition of high-quality SiO2

Abstract

Plasma-enhanced atomic layer deposition (PE-ALD) has been applied to prepare high-quality ultrathin films for microelectronics, catalysis, and energy applications. The possible pathways for SiO₂ PE-ALD using aminosilanes and O₂ plasma have been investigated by density functional theory calculations. The silane half-reaction between SiH₄ and surface –OH is very difficult and requires a high activation free energy of 57.8 kcal mol⁻¹. The introduction of an aminosilane, such as BDMAS, can reduce the activation free energy to 11.0 kcal mol⁻¹ and the aminosilane plays the role of a self-catalyst in Si–O formation through the relevant half-reaction. Among the various species generated in O₂ plasma, ³O₂ is inactive towards surface silane groups, similar to ordinary oxygen gas. The other three species, ¹O₂, ¹O, and ³O, can strongly oxidize surface silane groups through one-step or stepwise pathways. In the ³O pathway, the triplet must be converted into the singlet and follow the ¹O pathway. Meanwhile, both ¹O and ³O can decay to ¹O₂ and enter into the relevant oxidation pathway. The concept of self-catalysis of aminosilanes may be invoked to design and prepare more effective Si precursors for SiO₂ ALD. At the same time, the mechanism of strong surface oxidation by O₂ plasma may be exploited in the PE-ALD preparation of other oxides, such as Al₂O₃, HfO₂, ZrO₂, and TiO₂.