Patent ID: 8233158

Claim:
Method for determining the thickness and the refractive index of a layer ( 4 ) of a transparent material having a layer thickness between 30 nm and 150 nm which is disposed on a scattering substrate, the method comprising: irradiating a first optical radiation onto the sample ( 4 ) which comprises said scattering substrate and said layer of a transparent material thereon, wherein the first radiation is irradiated onto the surface of the sample ( 4 ) under an angle between 0-5° with respect to normal incidence, and determining a first reflection spectrum ( 10 ) resulting from reflection of the first radiation on the sample ( 4 ), irradiating a second optical radiation onto the sample ( 4 ), wherein the second radiation is irradiated onto the surface of the sample ( 4 ) under an oblique angle, and determining a second reflection spectrum ( 12 ) resulting from reflection of the second radiation on the sample ( 4 ), determining a minimum of the first reflection spectrum ( 10 ), determining a minimum of the second reflection spectrum ( 12 ), and determining the thickness and the refractive index of the layer of a transparent material using the minimum of the first reflection spectrum ( 10 ) and the minimum of the second reflection spectrum ( 12 ).