Patent ID: 6233046
Filing Date: 2001-05-15
Classification: G01B,G01N

Abstract:
A method of measuring the characteristics of a surface of a monocrystalline silicon wafer subjected to plasma etching, the surface having silicon altered as a result of the plasma etching and being covered by a thin layer of silicon dioxide, the method comprising:measuring, with a spectroscopic ellipsometer, the values of two quantities that are dependent on the thickness of the altered silicon and of the thin silicon dioxide layer with variations in the wavelength of the light of the measurement beam of the ellipsometer,obtaining from these measured values respective experimental curves representing the two quantities as functions of the wavelength,calculating the theoretical curves of the two quantities as functions of the wavelength considering the refractive indices and absorption coefficients of silicon dioxide and of the altered silicon as known parameters and the thickness of the altered silicon layer and the thickness of the thin silicon dioxide layer as unknowns,obtaining the refractive index of the altered silicon by considering the altered silicon as a combination of amorphous silicon and polycrystalline silicon, and in which, during the calculation of the theoretical curves, the proportion (f) of amorphous silicon and of polycrystalline silicon is also considered as unknown,comparing the theoretical curves with the respective experimental curves in order to determine for which values of the unknowns the curves under comparison approximate to one another the best, andextracting from the values determined the value that relates to the thickness of the altered silicon.