We studied the interaction of Bis-diethylaminosilane (SiH₂[N(C₂H₅)₂]₂, BDEAS) with a hydroxylized Si (001) surface for SiO₂ thin-film growth using density functional theory (DFT). BDEAS was adsorbed on the Si surface and reacted with the H atom of hydroxyl (-OH) to produce thedi-ethylaminosilane (-SiH₂[N(C₂H₅)₂], DEAS) group and di-ethylamine (NH(C₂H₅)₂, DEA). Then, DEAS was able to react with another H atom of -OH to produce DEA and to form the O-(SiH₂)-O bond at the inter-dimer, inter-row, or intra-dimer site. Among the three different sites, the intra-dimer site was the most probable when it came to forming the O-(SiH₂)-O bond.