Method and apparatus for performing highly accurate thin film measurements

A method for providing data convergence for a reflectometer measurement, comprising:

• providing a sample having at least one unknown property;
• measuring a reflectance spectrum of the sample, the measurement including a wavelength region in which a sharp spectral feature of the sample is exhibited;
• and
• advantageously utilizing data resulting from the sharp spectral feature exhibited by the sample to determine an actual value of the at least one unknown property.

A method of measuring an unknown value of a property of a sample with a reflectometer, comprising:

• measuring a reflectance spectrum of the sample, at least a portion of the reflectance spectrum including wavelengths below the deep ultraviolet (DUV) region;
• providing an expected reflectance spectrum of the sample utilizing at least one initial assumption regarding the unknown value of the property of the sample;
• and
• calculating a ratio between the expected reflectance spectrum and the measured reflectance spectrum;
• utilizing a derivative of the ratio between the expected reflectance spectrum and the measured reflectance spectrum;
• iteratively adjusting the at least one initial assumption and the expected reflectance spectrum to recalculate the ratio between the expected reflectance spectrum and the measured reflectance spectrum to provide an actual value of the first property.

A reflection measurement apparatus which operates below deep ultra-violet (DUV) wavelengths, the apparatus comprising:

• at least one light source, the at least one light source providing a source beam including at least wavelengths below DUV wavelengths;
• a spectrometer that receives light, including at least wavelengths below DUV wavelengths, reflected from a sample;
• and
• a data fitting routine coupled to the apparatus in hardware or software, the data fitting routine comprising:
• measuring a reflectance spectrum of the sample, the sample having at least one unknown actual value of an unknown property;
• providing an expected reflectance spectrum of the sample utilizing at least one initial assumption regarding the at least one unknown actual value of the unknown property;
• and
• utilizing a ratio between the expected reflectance spectrum and the measured reflectance spectrum to provide an actual value of the first property.