Atomic layer deposition (ALD) was used to deposit SiO2 films in the temperature range of 50-400 o C. H2Si[N(C2H5)2]2 and an O2 plasma were used as Si precursor and oxidant, respectively. The growth process was characterized in detail, using various in situ diagnostics. Ultrashort precursor doses (~50 ms) were found to be sufficient to reach self-limiting ALD growth with a growth-percycle of ~1 A. The films exhibited a refractive index of 1.46 ± 0.02, a mass density of 2.0 ± 0.1 g/cm 3 , and an O/Si ratio of 2.1 ± 0.1, virtually independent of the substrate temperature. The results therefore demonstrate an efficient ALD process for the conformal and uniform deposition of SiO2 at low substrate temperatures. Also the surface chemistry during the plasma ALD process and surface passivation performance of the ALD SiO2 films on crystalline silicon surfaces are briefly addressed.