Jin
Yong Kim1,2, Nhan V. Nguyen1, Hae-Jeong Lee3,
and Debra L. Kaiser2
Yoon-Hae
Kim and Hyeong Joon Kim
In
a few years, semiconductor industry will have no choice but to replace
SiO2-based gate dielectrics and aluminum-based interconnects
with novel alternative materials,according
to the ITRS. In pursuit of low-k interlayer dielectrics (ILD) and Cu interconnect
technology, only porous low-k films (both inorganic and organic or hybrid)
enables a decrease in permittivity to below 2. Film porosity and pore size
distribution define electrical, mechanical, thermal and chemical properties
of the film and itsfeasibility to be adoptedin
fabrication process. Considerable efforts have already been made to evaluate
those properties by using different measurement techniques such as positronium
annihilation lifetime spectroscopy, ellipsometric porosimetry, x-ray reflectivity
(XR), small angle neutron scattering (SANS). Spectroscopic ellipsometry
(SE) is a fast, non-destructive technique used for the routine product
monitoring of single layered and multi-layered thin film structure. Especially,
vacuum ultraviolet (VUV) SE with extended spectral energy up to 9 eV is
a promising tool for structural and optical studies of the films having
high energy absorption tails such as SiOC, spin-on hybrid organic-siloxane,
silicon carbide.
In
this study, SiOC thin films were prepared on p-type (100) Si substrates
by plasma enhanced chemical vapor deposition using a bis-trimethylsilymethane
liquid precursor. Using a commercial rotating analyzer ellipsometer with
a computer-controlled retarder, we measured the ellipsometric angle Y
and D
from 1 eV to 9 eV (138 nm to 1240 nm) at various angles of incidence (65o
to 75o). The VUV-SE results show the SiOC film is transparent
in the region of the energies lower than 5 eV. Fitting the measured spectra
in the transparent region gave us the accurate thickness and porosity of
the SiOC films. After getting those parameters, we could obtain complex
pseudo-dielectric functions of the SiOC films by using the fixed parameters. The
Tauc-Lorentz (TL) or Generalized Tauc-Lorentz (GTL) dispersion functions
were adopted to characterize the dielectric function of the SiOC films. The
inversions of the film dielectric functions were obtained by fitting the
experimental ellipsometric D
and Y
data at each photon energy by using the layer thickness and film porosities
as known values. It was found that a simple model based on the GTL dispersion
gave good fit to the ellipsometric data in low photon energy region. The
VUV-SE study in conjunction with XR and SANS facilitated the precise characterization
of both pore structures and dielectric functions of porous low-k
SiOC thin films.