Initial Surface Reaction of Di-Isopropylaminosilane on a Fully Hydroxyl-Terminated Si (001) Surface

We studied the interaction of di-isopropylaminosilane (SiH3N(C3H7)2, DIPAS) molecules with a fully hydroxyl-terminated Si (001) surface for SiO2 thin-film growth by using density functional theory. The amino group consisting of DIPAS was chosen in order to obtain a high adsorption energy because its lone-pair electrons in the N atom would help in the adsorption of DIPAS. The absolute value of the adsorption energy (0.67 eV) of DIPAS was higher than its reaction energy barrier of 0.38 eV. Thus, DIPAS could react with the surface without desorption. The reaction between DIPAS and the surface produced a silyl group (-SiH3) as a primary product and di-isopropylamine (NH(C3H7)2, DIPA) as a by-product. A second DIPAS, which was adsorbed near the pre-adsorbed DIPAS or -SiH3 with DIPA, required higher reaction energy barriers of 3.91 or 1.92 eV, respectively, because of its interaction with the first DIPAS or DIPA. However, when the second DIPAS was adsorbed near -SiH3 without DIPA, a low reaction energy barrier of 0.42 eV was required, indicating a negligible effect of -SiH3 on the second DIPAS reaction. Therefore, to obtain a highly dense Si layer, DIPA must desorb from the surface. DIPA requires a relatively high desorption energy of 0.40 eV because the lone-pair electrons in the N atom of DIPA also enhance its adsorption on the surface. The high desorption energy could reduce the process window of atomic layer deposition.