An 18O Study of the Oxidation Mechanism of Silicon in Dry Oxygen

The mechanism of thermal oxidation of silicon in dry oxygen was studied using 18 O as a tracer. layers first grown in natural oxygen were grown further in 18 O‐enriched oxygen up to thicknesses ranging from 5 to 26 nm at 930°C. 18 O profiling was carried out using the nuclear reaction microanalysis. Fixed 18 O is found near the interface ( 18 O FNI) and near the external surface of the oxide ( 18 O FNES). In this work we studied: ( i ) the possible origins of 18 O fixation near the external surface of the oxide ( 18 O FNES) and ( ii ) the possible growth mechanisms of films of thicknesses ranging from 260 to 5 nm. It was shown that 18 O FNES does not seem to be due to some interfering phenomena (network oxygen exchange with water vapor traces or effects connected with the experimental procedure) and is not due to a growth mechanism by Si transport. A step‐by‐step motion of network oxygen atoms seems to be the more likely to explain 18 O FNES. The amount of 18 O FNES becomes more important as the original thickness of the film becomes smaller. Even for thicknesses under 20 nm we always found large amounts of 18 O fixed near the interface, which corresponds to growth by oxygen species migrating through the oxide network and without measurable interaction with it (very likely molecules for thick oxide samples). However for ∼5 nm thickness films, the amounts of 18 O FNES can reach 50% and 80% of the total amount of 18 O at pressures equal to 10 torr and 10 −1 torr, respectively.