Atomic layer deposition of diisopropylaminosilane on WO₃(001) and W(110): a density functional theory study

The decomposition reactions of the Si precursor, diisopropylaminosilane (DIPAS), on W(110) and hydroxylated WO₃(001) surfaces are investigated to elucidate the initial reaction mechanism of the atomic layer deposition (ALD) process using density functional theory (DFT) calculations combined with ab initio molecular dynamics (AIMD) simulations. The decomposition reaction of DIPAS on WO₃(001) consists of two steps: Si-N dissociative chemisorption and decomposition of SiH₃*. It is found that the Si-N bond cleavage of DIPAS is facile on WO₃(001) due to hydrogen bonding between the surface OH group and the N atom of DIPAS. The rate-determining step of DIPAS decomposition on WO₃(001) is found to be the Si-H dissociation reaction of the SiH₃* reaction intermediate which has an activation barrier of 1.19 eV. On the contrary, sequential Si-H dissociation reactions first occur on W(110) and then the Si-N dissociation reaction of the C₅H₇NSi* reaction intermediate is found to be the rate-determining step, which has an activation barrier of 1.06 eV. As a result, the final products in the DIPAS decomposition reaction on WO₃(001) are Si* and SiH*, whereas Si* atoms remain with carbon impurities on W(110), which imply that the hydroxylated WO₃ surface is more efficient for the ALD process.