Analysis of structural distribution of nitrogen-incorporated species at the interface of silicon oxide films on silicon using time-of-flight secondary ion mass spectrometry and poisson approximation.

Structural distributions of nitrogen-incorporated species at the interface between silicon and SiO2 films for plasma-enhanced chemical vapor deposited (PECVD) SiO2 films have been analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and the Poisson approximation. Depth profiles of the intensity of Si3(+) cluster ions were used to determine the depth-resolution function of the analytical system that causes beam-induced broadening effects in the depth profiles. The full width at half-maximum (fwhm) of the resolution function was approximately 1.6 nm for 22 kV Au3(+) primary ions and sputter etching by Ar(+) at 1 kV. The intensity profile of Si3O2N(+) secondary ion species at the interface was analyzed by assuming a Poisson distribution with a series of delta-layers. Convolution of the postulated signals with the depth resolution function was carried out to simulate depth profiles of Si3O2N(+) ion species, which exhibit slow leading and sharp trailing edges. The analysis showed that the thickness of the delta-layer associated with the most probable existence of nitrogen-incorporated species is approximately 0.8 nm, and the fragmented species decreased from the interface to the SiO2 bulk film with a decay length of approximately 1.5 nm.