We present a first-principles study on the dissociative reaction of mono(alkylamino)silane precursors with different sizes of alkylamino ligands on a hydroxylated SiO₂ (001) surface. The adsorption energies (ΔE_AD), reaction energy barriers (ΔE_a), and desorption energies (ΔE_DE) of by-products for the six chosen precursors were compared and their ALD windows of temperature were estimated. The results indicate that the dissociative reactions of all six precursors are energetically favorable and DMAS, DEAS, DPAS, DIPAS and DSBAS are appropriate for low temperature deposition with relatively wide ALD windows. In addition, the analysis of reaction rate constants suggests that DMAS, DEAS, DPAS and DIPAS can be used to grow SiO₂ thin films with a high deposition rate. Due to the higher reaction rate constants and wider ALD windows of DPAS and DIPAS, they are the most appropriate precursors for ALD at low temperature. These findings underscore the important role of substitution groups in the precursors and suggest ways for designing better precursors for deposition of conformal, dense, and high-purity thin films via ALD processes.