Silicon oxide has been grown in a low pressure furnace using N2O. An atomically fiat SiO2 (N2O)/Si interface, as determined by high resolution transmission electron microscopy, has been achieved by desorbing the native oxide in situ for oxide thicknesses 11 to 38 Angstrom. The thickness variation of a 20 Angstrom N2O-oxide, grown on a 4 in. substrate <1 Angstrom. The excellent uniformity is attributed to the increased mean-free path of N2O molecules in the low pressure environment. Since only one Si plane was distorted beneath the N2O-oxide/Si interface, this suggests that thermal stress is not the limiting factor for obtaining an atomically smooth interface.