In this paper the analysis of a family of rough silicon single crystal surf
aces covered with native oxide layers is performed using a combined optical
method based on a multisample treatment of the experimental data obtained
using variable angle of spectroscopic ellipsometry and near normal spectros
copic reflectometry. Within this analysis the values of the thicknesses of
the native oxide layers are determined together with the values of statisti
cal parameters of roughness, i.e, with the rms values of the heights and th
e values of the autocorrelation lengths, fur all the samples studied. For i
nterpreting experimental data the perturbation Rayleigh - Rice theory and s
calar diffraction theory are employed. By means of the results of the analy
sis achieved using both the theories limitations of the validity of these t
heories is discussed. The correctness of the values Of the statistical para
meters determined using the optical method is verified using AFM measuremen
ts.