Methods and systems for identifying features

1. A method of identifying a feature, comprising:

transmitting a first light such that the first light is incident on a multi-layer stack, wherein the multi-layer stack includes the feature and a region without the feature;

transmitting a second light such that it is incident on the multi-layer stack;

detecting a first narrow-band light reflected from the feature and the region without the feature, wherein the feature has a first reflectance in a first wavelength of the narrow-band light and the region without the feature has a second reflectance in the first wavelength of the first narrow-band light;

detecting a second narrow-band light reflected from the feature and the region without the feature, wherein the feature has a third reflectance in a second wavelength of the second narrow-band light and the region without the feature has a fourth reflectance in the second wavelength of the second narrow-band light, wherein the second narrow-band light has the second wavelength different from the wavelength;

generating, based on the narrow-band light, a first image indicative of where the first reflectance and the second reflectance occur on the multi-layer stack;

generating, based on the second narrow-band light, a second image indicative of where the third reflectance and the fourth reflectance occur on the multi-layer stack; and

subtracting or dividing the first image by the second image or the second image by the first image to generate a processed image.

2. The method of claim 1 , further comprises identifying the feature based on where the first reflectance is indicated to occur on the multi-layer stack by the image.

3. The method of claim 1 , wherein a first illumination angle of the first light is higher than a second illumination angle of the second light.

4. The method of claim 1 , further comprises identifying the feature based on a contrast in pixel intensity in the processed image between the feature and the region without the feature.

5. The method of claim 1 , further comprises:

transmitting a third light such that it is incident on the multi-layer stack;

detecting a photo-luminescent light from the feature and the region without the feature, wherein the feature has a first photo-luminescent characteristic in response to the third light and the region has a second photo-luminescent characteristic in response to the third light; and

generating, based on the photo-luminescent light, a photo-luminescent image indicative of where the first photo-luminescent characteristic and the second photo-luminescent characteristic occur on the multi-layer stack.

6. The method of claim 5 , further comprises identifying the feature based on the photo-luminescent image.

7. The method of claim 1 , wherein the first light is a narrow-band light.

8. The method of claim 1 , wherein the first wavelength of the first light is lower in energy than a bandgap of at least a layer of layers in the multi-layer stack.

9. The method of claim 1 , wherein:

the first light is a broadband light; and

a broadband response light is generated in response to the broadband light impinging on the feature and the region without the feature;

further comprising filtering the broadband response light to generate the first narrow-band light and the second narrow-band light.

10. A feature identification system, comprising:

one or more light sources configured to:

transmit a first light such that it is incident on a multi-layer stack, wherein the multi-layer stack includes the feature and a region without the feature; and

transmit a second light such that it is incident on the multi-layer stack;

one or more detectors configured to:

detect a first narrow-band light reflected from the feature and the region without the feature, wherein the feature has a first reflectance in response to a first wavelength of the first narrow-band light and the region without the feature has a second reflectance in response to the first wavelength of the first narrow-band light; and

detect a second narrow-band light reflected from the feature and the region without the feature, wherein the feature has a third reflectance in response to a second wavelength of the second narrow-band light and the region without the feature has a fourth reflectance in response to the second wavelength of the second narrow-band light, wherein the second narrow-band light has the second wavelength different from the wavelength; and

an imaging system configured to:

generate, based on the first narrow-band light, a first image indicative of where the first reflectance and the second reflectance occur on the multi-layer stack;

generate, based on the second narrow-band light, a second image indicative of where the third reflectance and the fourth reflectance occur on the multi-layer stack; and

subtract or divide the first image by the second image or the second image by the first image to generate a processed image.

11. The feature identification system of claim 10 , wherein the imaging system is further configured to identify the feature based on where the first reflectance is indicated to occur on the multi-layer stack by the image.

12. The feature identification system of claim 10 , wherein a first illumination angle of the light is higher than a second illumination angle of the second light.

13. The feature identification system of claim 10 , wherein the imaging system is further configured to identify the feature based on a contrast in pixel intensity in the processed image between the feature and the region without the feature.

14. The feature identification system of claim 10 , wherein:

the one or more light sources is further configured to transmit a third light such that it is incident on the multi-layer stack;

the detector is further configured to detect a photo-luminescent light from the feature and the region without the feature, wherein the feature has a first photo-luminescent characteristic in response to the third light and the region has a second photo-luminescent characteristic in response to the third light; and

the imaging system is further configured to generate, based on the photo-luminescent light, a photo-luminescent image indicative of where the first photo-luminescent characteristic and the second photo-luminescent characteristic occur on the multi-layer stack.

15. The feature identification system of claim 14 , wherein the imaging system is further configured to identify the feature based on the photo-luminescent image.

16. The feature identification system of claim 10 , wherein the first light is a narrow-band light.

17. The feature identification system of claim 10 , wherein the first wavelength of the first light is lower in energy than a bandgap of at least a layer of layers in the multi-layer stack.

18. The feature identification system of claim 10 , wherein:

the first light is a broadband light; and

a broadband reflected light is generated in response to the broadband light impinging on the feature and the region without the feature;

further comprising a plurality of optical filters configured to filter the broadband reflected light to generate the first narrow-band light and the second narrow-band light.

19. The feature identification system of claim 18 , further comprises two or more high-pass filters, low-pass filters, or band-pass filters configured to filter the broadband reflected light to generate the first narrow-band light and the second narrow-band light.