Silanol concentration depth profiling during plasma deposition of SiO₂ using multiple internal reflection infrared spectroscopy

The SiOH concentration profiles as a function of depth within SiO₂ films deposited from SiH₄, O₂, and Ar containing plasmas were measured using real-time attenuated total reflection Fourier transform infrared spectroscopy. The effective thickness approximation in conjunction with mathematical deconvolution of the temporal evolution of the spatially averaged SiOH concentration during deposition allowed the conversion of integrated SiOH absorbance to local SiOH concentration as a function of distance normal to the substrate surface. Thus, depth profiling of SiOH species in growing SiO₂ films was realized. As an example, SiOH concentration profiles in SiO₂ deposited on Si substrates cleaned with H₂ plasma was studied as a function of SiH₄-to-O₂ gas flow rate ratio. For the depositions performed after H₂ plasma cleaning, the local concentration profiles revealed strong evidence of high SiOH density at the SiO₂-Si interface. This method can be applied to measuring concentration depth profiles of Si-H, Si-F, or any other infrared active species in plasma-deposited films in real time.