Analysis of intensities of positive and negative ion species from silicon dioxide films using time-of-flight secondary ion mass spectrometry and electronegativity of fragments

Abstract

Intensities of positive and negative ion species emitted from thermally oxidized and plasma-enhanced chemical vapor deposited (PECVD) SiO 2 films were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and the Saha–Boltzmann equation. Intensities of positive and negative secondary ion species were normalized to those of 28Si + and 28Si − ions, respectively, and an effective temperature of approximately (7.2 ± 0.1) × 10 3 K of the sputtered region bombarded with pulsed 22 kV Au 3 + primary ions was determined. Intensity spectra showed polarity dependence on both n and m values of Si n O m fragments, and a slight shift to negative polarity for PECVD SiO 2 compared to thermally oxidized SiO 2 films. By dividing the intensity ratios of negative-to-positive ions for PECVD SiO 2 by those for thermally oxidized SiO 2 films to cancel statistical factors, the difference in absolute electronegativity (half the sum of ionization potential and electron affinity of fragments) between both films was obtained. An increase in electronegativity for SiO m ( m = 1, 2) and Si 2O m ( m = 1–4) fragments for PECVD SiO 2 films compared to thermally oxidized films was obtained to be 0.1–0.2 Pauling units, indicating a more covalent nature of Si–O bonds for PECVD SiO 2 films compared to the thermally oxidized SiO 2 films.