Dear Vigneshwaran R M ,

what is the challenge here?

The reflective response of your wafer here is a) due to the reflectivity of your wafer itself and b) due to the intensity distribution of your fluorescence tube of the lamp of your lab at its ceiling.

In order to avoid the strong bright stripe going from upper left to lower right you should have a look at the surface of your wafer having one your white walls of your lab as light source (being some kind of diffuser*)).

A polarizer will not help because a) close to normal concidence there will be no polarization dependence of the wafer reflectivity and b) the fluorescence lamp will have no (significant**)) preferred polarization of its light output.

*) a physics teacher of mine (Dr. Fröhlich) at school told me in the late 1960s, that I should use the ceiling or one of the while walls of the school's physics lab in combination with the sun light of a cloudy or preferently foggy day, to use it as a homogenous unpolarized light source (if need); but not any local light source...

**) The reflector behind the tube will establish some polarization contribution...

Best regards

G.M.

Dear Gerhard Martens ,

Thank you for your response!

1) It is a local light source whose inclination I can vary.

2) I tried using a diffuser like a white board, but I couldn't extract meaningful information from those images, the reason being the surface is so smooth and surface roughness will be in the range of 20-40microns, what will be your suggestion for this?

I also need to do a controlled experiment that's why I cannot use sunlight.

Attaching another image below, captured with a ring light where I couldn't see the surface at all.

You could try inserting a sheet of white paper (not too thick) between your wafer and the light source. This should minimize the reflection on your wafer. Otherwise maybe an illumination with a very small incident angle?

You can check with some neutral density filter.

Valentin Straessle I have tried with a diffused light source it sort of reduced the reflection, since the intensity is more uniform through out, I am not able to get good contrast.

Dear Vigneshwaran R M ,

I think your camera is focussing in the automatic mode. In that case the focussing procedure tries to get the best contrast somehow. However the focus distance is likely found at the light source being reflected by the wafer surface.

You should go for the manual mode and focus onto the wafer surface by hand.

When cleaning/polishing the surface of a ceramic hob you can experience similar things:

a) You can see the intensity distribution of the light source when focussing your eyes onto the lamp (being reflected by the ceramic surface).

b) You can see scratches and the remaining dirt on the surface when focussing your eyes onto the polished surface itself.

Additional option (after properly focussing onto the wafer surface):

Structures in your image due to defects in the wafer surface can be barely seen due their tiny signals. But after taking the image you are able to change brightness/intensity scale (LUT) and the contrast of your image and enhance the low intensity and skip the higher ones...

Furthermore you should zoom onto the surface; at the present magnification (whole wafer diameter at the field of view of the image) you will not be able to resolve tiny structures such as scratches at the wafer surface. The zoom/magnification should be done with the camera... (after that you may additionally zoom by software on the pixel basis)

Good luck and

best regards

G.M.

You can try 1) one polarizer on the camera (have to be rotated to optimal angle), 2) 1 while providing Brewster angle condition https://en.wikipedia.org/wiki/Brewster%27s_angle 3) Cross-polarized illumination/camera

Also

e.g. https://www.motherjones.com/kevin-drum/2018/03/582175/