Apparatus and method for inspection of a film on a substrate
Methods of and apparatus for inspecting composite layers of a first material formed on a second material are provided including providing an illumination source, illuminating at least a portion of the composite at the layer, receiving light reflected from the sample, determining a spectral response from the received light, and comparing the received spectral response to an expected spectral response.
1. A method of inspecting an oxide layer comprising:
determining a reference spectrum of light reflected from a surface of a first sample of a first material having an oxide film thereon over a wavelength range encompassed by the reflected light, wherein the first sample does not include a predetermined defect;
selecting an illumination source that outputs light encompassing at least part of the wavelength range;
illuminating at least a portion of a second sample of a second material having an oxide layer with the light from the selected illumination source, wherein the light reflected from the first material and light from the selected illumination source reflected from the second material have respective spectral responses over the wavelength range that have a predetermined relationship;
receiving the light output from the illumination source that has reflected from the second sample, including the oxide layer of the second sample;
acquiring a measurement spectrum from the light received at the receiving step over at least part of the wavelength range that is encompassed by the light output from the illumination source;
comparing at least one characteristic of the measurement spectrum to the same at least one characteristic of the reference spectrum, wherein the at least one characteristic varies in a predetermined manner depending upon whether a material and oxide film from which received light reflects contains the predetermined defect; and
determining whether the material and oxide film of the second sample contain the predetermined defect based upon the comparison of the at least one characteristic of the measurement spectrum to the same at least one characteristic of the reference spectrum.
2. The method of claim 1 , wherein the step of determining the reference spectrum comprises acquiring at least one sample spectrum of light reflected from a calibration sample of the material having an oxide layer, where the calibration sample does not have the predetermined defect.
3. The method of claim 1 , wherein the step of determining the reference spectrum comprises acquiring a plurality of sample spectra of light reflected from a calibration sample of the material having an oxide layer, where the calibration sample does not have the predetermined defect, and averaging the plurality of sample spectra to define the reference spectrum.
4. The method of claim 1 , wherein the step of determining the reference spectrum comprises calculating the reference spectrum from a model based on knowledge of the first material and an expected thickness of its oxide film when no defect is present.
5. The method of claim 1 , wherein the illumination source is broadband.
6. The method of claim 1 , wherein the step of receiving the light comprises filtering at least one of the received light and data corresponding to the received light, by wavelength.
7. The method of claim 1 , wherein the at least one characteristic comprises intensity minimum peak wavelength.
8. The method of claim 1 , wherein the at least one characteristic comprises spectral intensity.