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.