Methods and apparatus for spectral luminescence measurement
One embodiment relates to a computer-implemented method of processing spectral luminescence mapping data obtained from a substrate, the substrate having an epitaxial layer stack that includes a multiple quantum well. A spectral luminescence and an epi thickness at a location on the substrate are obtained. A spectral modulation for the location may be computed given the epi thickness and material indices of refraction. The underlying luminescence spectrum may then be generated by dividing the measured spectral luminescence by the spectral modulation. Subsequently, a peak wavelength and other parameters may be obtained from the underlying luminescence spectrum. In another embodiment, the underlying luminescence spectrum may be determined, without the epi thickness measurement, using a self-consistent technique. Another embodiment relates to an apparatus for spectral luminescence mapping and epitaxial thickness measurement. Other embodiments, aspects and features are also disclosed.
1. A computer-implemented method of processing a spectral luminescence map for a target substrate which has an epitaxial layer stack that includes a multiple quantum well, the method comprising:
performing a measurement to obtain a measured spectral luminescence for a location on the target substrate;
constraining a line shape for an underlying local luminescence spectrum;
generating a computed spectral luminescence for the location using a seed epi layer thickness value; and
determining a local thickness parameter and parameters of the underlying local luminescence spectrum so as to minimize a difference between the computed spectral luminescence and the measured spectral luminescence for the location.
2. The method of claim 1 , wherein the computed spectral luminescence is a multiplication of the underlying local luminescence spectrum and a local spectral modulation, further wherein the local spectral modulation is generated by a Fabry-Perot cavity type computation based on the local thickness parameter.
3. The method of claim 2 , wherein the parameters of the underlying local luminescence spectrum include a peak wavelength for the location.
4. The method of claim 3 wherein the parameters of the underlying local luminescence spectrum further include a peak intensity and a full-width at half-maximum (FWHM) for the location.
5. The method of claim 1 , wherein the luminescence mapping data comprises photoluminescence mapping data.
6. The method of claim 1 , wherein the luminescence mapping data comprises electroluminescence mapping data.
7. The method of claim 1 , wherein the seed epi layer thickness value comes from prior knowledge or a prior measurement.
8. An apparatus for performing spectral luminescence measurements on a target substrate and processing spectral luminescence mapping data obtained from the target substrate, the target substrate having an epitaxial layer stack that includes a multiple quantum well, the apparatus comprising:
a processor for executing computer-readable instruction code so as to process data;
data storage for storing non-transitory computer-readable instruction code and the data; and
non-transitory computer-readable instruction code stored in the data storage for
performing a measurement to obtain a measured spectral luminescence for a location on the target substrate, constraining a line shape for an underlying local luminescence spectrum,
generating a computed spectral luminescence for the location using a seed epi layer thickness value, and
determining a local thickness parameter and parameters of the underlying local luminescence spectrum so as to minimize a difference between the computed spectral luminescence and the measured spectral luminescence for the location.
9. The apparatus of claim 8 , wherein the computed spectral luminescence is a multiplication of the underlying local luminescence spectrum and a local spectral modulation, further wherein the local spectral modulation is generated by a Fabry-Perot cavity type computation based on the local thickness parameter.
10. The apparatus of claim 9 , wherein the parameters of the underlying local luminescence spectrum include a peak wavelength for the location.
11. The apparatus of claim 10 , wherein the parameters of the underlying local luminescence spectrum further include a peak intensity and a full-width at half-maximum (FWHM) for the location.
12. The apparatus of claim 8 , wherein the luminescence mapping data comprises photoluminescence mapping data.
13. The apparatus of claim 8 , wherein the luminescence mapping data comprises electroluminescence mapping data.
14. The apparatus of claim 8 , wherein the seed epi layer thickness value comes from prior knowledge or a prior measurement.