Three different HF:alcohol solutions are investigated to etch native
SiO2 and passivate Si(100) surfaces with H which can the be
desorbed at low temperature (T < 600°C). The resulting passivated Si(100)
surfaces are compared using as a reference Si(100) passivated by a standard
aqueous HF: solution (1:98 parts of HF: H2O). After a modified
RCA cleaning, Si(100) etched by HF:Methanol, HF:IPA, or HF:Ethanol, is
characterized by Ion Beam Analysis (IBA), Tapping Mode Atomic Force
Microscope (TMAFM), and Fourier Transform Infrared Spectroscopy (FTIR). The
absolute coverage of O and C is measured by nuclear reaction analysis (NRA)
combined with ion channeling at 3.05 MeV for O and 4.265 MeV for C. Hydrogen
is measured via the elastic recoil detection (ERD) of
4He2+ at 2.8 MeV.
Compared to aqueous HF, HF:alcohol passivates Si(100) leaving a lower O
residue by an average factor of 0.62 and a similar C residue. H coverage is
higher by an average factor of 1.43. Surface coverages are found to be
reproducible in average by 1.4 × 1014 atoms/cm2 for C,
and by 1.25 × 1014 atoms/cm2 for O when measured by
IBA on samples identically processed. H coverage is reproducible within 5.5%
when measured by ERD.
Selective area analysis by TMAFM shows that an increasing number of
particulates is responsible for the apparent increase in root-mean -square
(rms) surface roughness when the rms is measured over a whole image. Taking
this effect into account, all passivated surfaces exhibit similar roughness
when compared to the original Si(100) surface with little difference between
alcohols and with the reference aqueous HF solution.
FTIR in the attenuation total reflection (ATR) mode detected SiHx
species mostly as a dihydride. Both IBA and FTIR detected significant levels
of oxygen on surfaces passivated HF in alcohol and aqueous HF. This
indicates that while Si(100) exhibits more H when passivated with HF in
alcohol and can be desorbed at lower temperature than when treated with
aqueous HF, H is not bonded to Si only but likely bonds into a more complex
surface termination, such as SiOH.