  The dielectric properties of noncrystalline hafnium silicon oxynitride
(HfSiON) films with a variety of atomic compositions were investigated. The
films were deposited by reactive sputtering of Hf and Si in an O, N, and Ar
mixture ambient. The bonding states, band-gap energies, atomic compositions,
and crystallinities were confirmed by X-ray photoelectron spectroscopy (XPS),
reflection electron energy loss spectroscopy (REELS), Rutherford backscattering
spectrometry (RBS), and X-ray diffractometry (XRD), respectively. The optical
(high-frequency) dielectric constants were optically determined by the square
of the reflective indexes measured by ellipsometry. The static dielectric
constants were electrically estimated by the capacitance of Au/HfSiON/Si(100)
structures. It was observed that low N incorporation in the films led to the
formation of only Si-N bonds without Hf-N bonds. An abrupt decrease in band-gap
energies was observed at atomic compositions corresponding to the boundary
where Hf-N bonds start to form. By combining the data for the atomic
concentrations and bonding states, we found that HfSiON can be regarded as a
pseudo-quaternary alloy consisting of four insulating components: SiO$_2$,
HfO$_2$, Si$_3$N$_4$, and Hf$_3$N$_4$. The optical and static dielectric
constants for the films showed a nonlinear dependence on the N concentration,
whose behavior can be understood in terms of abrupt Hf-N bond formation.
