Questions about cross-polarizing microcircuit dies

Images made through a microscope. All subject types.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

Olympusman
Posts: 5090
Joined: Sun Jan 15, 2012 12:31 pm

Questions about cross-polarizing microcircuit dies

Post by Olympusman »

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.

Image
This is the die in normal unpolarized tungsten light.

Image

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.

Image

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
Michael Reese Much FRMS EMS Bethlehem, Pennsylvania, USA

Lou Jost
Posts: 5944
Joined: Fri Sep 04, 2015 7:03 am
Location: Ecuador
Contact:

Post by Lou Jost »

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.

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

Post by GaryB »

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

Olympusman
Posts: 5090
Joined: Sun Jan 15, 2012 12:31 pm

Cross-polarization

Post by Olympusman »

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
Michael Reese Much FRMS EMS Bethlehem, Pennsylvania, USA

Lou Jost
Posts: 5944
Joined: Fri Sep 04, 2015 7:03 am
Location: Ecuador
Contact:

Post by Lou Jost »

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.

Post Reply Previous topicNext topic