Evolution of chemical bonding configuration in ultrathin SiOxNy layers grown by low-temperature plasma nitridation

Abstract

Ultrathin silicon oxynitride (SiOxNy) less than 25 Å has been grown by low-temperature (at 450 °C) N2O and NH3 plasma immersion on a Si surface. The bonding structures and their distribution in depth, as well as the quantity of nitrogen in SiOxNy layers are studied by x-ray photoelectron spectroscopy. A good coincidence is established in SiOxNy thickness extracted from the attenuated Si 2p3/2 photoelectron signal and high-resolution transmission electron micrograph. The increase of SiOxNy thickness is fast at the initial growth and slows down as the oxynitride thickens. It is found that nitrogen atoms are concentrated at the SiOxNy/Si interface. The binding energy (BE) of N 1s core levels shows that N atoms are mostly bonded to three Si atoms (the N–Si3 state). Long-time growth of oxynitride will shift N and O 1s core levels to a higher BE due to increments of oxygen in the SiOxNy layer. Exploration of (N2O+NH3) plasma nitridation suggests that the nitrogen content increases with increasing NH3/N2O ratio, whereas the deposition rate of oxynitride decreases. With the understanding of plasma nitridation basics, control of chemical binding structure, nitrogen content, as well as thickness of the SiOxNy layer, is therefore realized.