Determination of chemistry and microstructure in SiO_x (0.1<x<0.8) films by x-ray photoelectron spectroscopy

The stoichiometry of a series of low pressure chemical vapor deposition deposited SiO_x films was determined using x-ray photoelectron spectroscopy (XPS) by two different methods. The first, more traditional, method involved applying relative sensitivity factors to the integrated O 1s and Si 2p peaks, taking into consideration differences in photoemission probabilities of oxidized and elemental silicon. In the second method the Si 2p spectra were curve fit into five peaks corresponding to Si⁰+SiH (99.4 eV), Si¹⁺ (100.3 eV), Si²⁺ (101.2 eV), Si³⁺ (102.0 eV), and Si⁴⁺ (103.0 eV). The five valence states of silicon corresponding to tetrahedrally coordinated silicon bonded to 0, 1, 2, 3, and 4 oxygen atoms. The relative areas of the peaks were combined with the known oxygen coordination numbers to yield stoichiometries. Rutherford backscattering and hydrogen forward scattering were done to verify the XPS quantification and to measure the hydrogen concentration of the films, respectively. The fraction of elemental silicon present as a function of oxygen concentration was compared with the fraction predicted by a random bonding model of silicon and oxygen atoms. The experimental fraction of Si⁰+SiH measured by XPS was greater than the fraction predicted by the random bonding model consistent with distinct regions (or possibly crystallites) of elemental silicon in the oxide matrix. Also, it was established that 3 kV argon sputtering does not preferentially sputter oxygen from either SiO₂ or SiO_x films contrary to previous reports.