INSITU DIFFERENTIAL REFLECTANCE STUDY OF THE ETCHING OF SIO2-FILMS

A differential reflectance technique has been applied to study the etching of SiO2 films on Si substrates in situ in the liquid (HF/H2O) environment as well as ex situ. Essentially, the technique scans an incident optical beam in the spectral range of 200-800 nm across two adjacent samples at near normal incidence and the reflected beams are detected using lock-in amplification so as to measure only the difference in the reflectance spectra. This study demonstrates the great sensitivity of the technique to follow the etching experiment in situ, and in conjunction with simulated spectra and ex situ results, a new spectral feature is seen which may be evidence for an electric double layer at the Si surface in the etch solution.