Stoichiometry reversal in the growth of thin oxynitride films on Si(100) surfaces

Synchrotron-based O 1s and N 1s photoabsorption spectroscopy, O 1s, N 1s, Si 2p, and valence-band photoelectron spectroscopy (PES), and medium energy ion scattering (MEIS) have been used to determine the composition and thickness of oxynitride films grown in N2O on a Si(100) surface. Core-level photoabsorption spectroscopy is shown to be a very sensitive probe capable of measuring surface coverages lower than 0.1 monolayers of N (6.5×1013 N atoms/cm2). Film composition was monitored as a function of growth to demonstrate the stoichiometry reversal from primarily N-terminated surfaces in thin films to nearly pure SiO2 in films thicker than ∼20 Å. A sample with a 60 Å oxynitride film was depth profiled by etching in HF and was shown, via N 1s absorption spectroscopy, to have N segregation within 10 Å above the Si/SiO2 interface. Core-level PES and MEIS were used to study the growth mechanisms of oxynitrides on Si(100) and these data were used to create a schematic phase diagram showing three distinct regions of oxide formation. A critical N2O pressure was discovered at which oxide growth proceeds at over 1000 times its normal rate.