Silicon oxide has been grown in a low pressure furnace using N 2 O. An atomically flat SiO 2 (N 2 O)/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 Å. The thickness variation of a 20 Å N 2 O-oxide, grown on a 4 in. substrate <1 Å. The excellent uniformity is attributed to the increased mean-free path of N 2 O molecules in the low pressure environment. Since only one Si plane was distorted beneath the N 2 O-oxide/Si interface, this suggests that thermal stress is not the limiting factor for obtaining an atomically smooth interface.