The effects of oxygen plasma treatment
on molecular structures
at low-k organosilicate (SiCOH) film surfaces and
buried interfaces were investigated using sum frequency generation
(SFG) vibrational spectroscopy and Raman spectroscopy. SFG and Raman
spectra were acquired from pristine and plasma-treated low-k SiCOH films to characterize the interfacial and bulk molecular
structures of the films before and after plasma treatment. Two SiCOH
films with similar molecular structures but different porosities were
investigated to correlate the effects of plasma treatment to the porosity
of low-k films. SFG spectra indicated that the surface
molecular structure of dense SiCOH films was more resistant to plasma
damage than the surface molecular structure of porous SiCOH films.
Furthermore, the ratio of SFG peak intensities before and after plasma
treatment enabled quantification of methyl depletion at the surface
of SiCOH films after plasma treatment. The molecular structure at
buried Si/SiCOH interfaces was characterized by simulating SFG spectra
from pristine and plasma-treated SiCOH films. SFG spectra from plasma-treated
low-k films were simulated by adjusting the methyl
orientation and number density parameters at the low-k/air interface to match experimental results. Simulated SFG spectra
indicated that methyl groups at the buried interface of both dense
and porous SiCOH films were oriented with a high tilt angle before
and after plasma treatment. The developed methodology is general and
can be extended to characterize the effects of many different plasma
treatments, wet chemical treatments, and surface repair treatments
on the interfacial molecular structures of many polymer or organic
films.