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Questions about cross-polarizing microcircuit dies

 
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Olympusman



Joined: 15 Jan 2012
Posts: 3268

PostPosted: Mon Mar 20, 2017 2:53 pm    Post subject: Questions about cross-polarizing microcircuit dies Reply with quote

When I set up a microcircuit die on my scope, I always drop inna polarizer to see what if any effect has on cross-polarization of a microchip. Sometimes the effect is negligable and sometimes the effect subtley enhances the colors on the chip. However, at times the cross-polarization effect is far too profound as shown in this test series.


This is the die in normal unpolarized tungsten light.



This is the same die with what I consider normal cross-polarization - not too heavy and not too unfortunate if you don't mind viewing through the popular Grape Soda filter.



This is the strongest cross-polarization. In the CMOS microscope software, this represents almost mass extinction of the image -- the gain had to be jacked up hugely and the image is almost all noise.
The question is - what accounts for these variations from sublety to almost useless image enhancement?
Is it the substrate of the die or is the fact that the acid process used to expose the die from its package destroys the passivation of the die?
Any insight would be appreciated.

Regards

Mike
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Lou Jost



Joined: 04 Sep 2015
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PostPosted: Mon Mar 20, 2017 4:10 pm    Post subject: Reply with quote

With typical linear-polarizing filters, short-wavelength light is polarized less efficiently than long-wavelength light. So when you are near extinction, in highlights the stuff that gets through is going to be grape-juice-purple.

Circular polarizers sometimes have other color casts in highlights. I don't know why.
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GaryB



Joined: 29 Jul 2016
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PostPosted: Mon Mar 20, 2017 8:45 pm    Post subject: Reply with quote

I dunno, the third one looks pretty awesome to me!
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Olympusman



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PostPosted: Tue Mar 21, 2017 9:28 am    Post subject: Cross-polarization Reply with quote

The polarizing filters in my metallurgical microscope setup are definitely linear, since they are cut from a sheet of polarizing film.
The difference between a linear polarizer and a circular polarizer is that the circular filter has a quarter wave filter built-in. This is to prevent problems with metering and autofocusing systems in electronic based cameras.

Mike
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Lou Jost



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PostPosted: Tue Mar 21, 2017 9:42 am    Post subject: Reply with quote

I figured they were linear. Those always make purple in specular highlights, for the reason I gave above.

I would like to understand the physical reason why circular polarizers sometimes give other color casts.
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