[labnetwork] Infrared Inspection System of Chips Bonded to Wafers

[Ryan Rivers]

Hi James,

This isn't going to be what you're looking for, but I got the sense you're
also polling the field for what works. We use two systems at UC Berkeley.

One is a cheap, home built full wafer camera we use to look for macroscopic
bubbles. That's just a raspberry pi and a samsung phone camera with the IR
filters removed, mounted in a delrin tube we had machined in our shop.
Wafer mounts on the top and acts as the filter for the lamp mounted behind
the wafer. A true IR source will run you 10-20k for some defined
wavelength, but there's no benefit and all drawback in this application.
What you want is not true IR, it's wideband inspection - which means it
works for wafers transparent in various parts of the IR band. Resolution is
hundreds of microns/pixel - we've never measured it. Cost maybe $5k in 2015
to build. It basically would give similar information to the idonus above,
it's just not as nice of an interface. It is physically smaller which is a
big plus.

For small scale inspection we use an IR rated microscope that we bought as
salvage and rebuilt. Any microscope with IR transparent objectives and
through substrate lighting will work.

In the end the primary difficulty is that IR wafer imaging exists in an
uncanny valley where there's not a good business case for benchtop models.
Engineering time on them is too expensive and there's too much used
equipment in the market that's easily repaired. Since no one can hit volume
production IR systems sit in a space where they can't really support an
engineering income.

You can save several tens of thousands of dollars by splitting the job into
two tools and specializing them - a two-tool setup can run you ~$10k with a
little finesse and tolerance for repairing salvage equipment.

Hope you find a good solution for your needs. I'd be interested to know if
there's a reasonably priced combo tool on the market.

-Ryan

On Wed, Nov 1, 2023 at 5:37 AM James Grant <James.Grant at glasgow.ac.uk>
wrote:

> Hello,
>
>
>
> Was fairly certain this topic has been covered before on labnetwork but
> couldn’t find anything relevant.
>
>
>
> Many of our plasma etch tool users have to bond piece parts samples to
> silicon carrier wafers (150 or 200 mm diameter). To improve thermal
> conduction we use a bonding medium between the piece part samples and the
> silicon carrier wafer. The challenge is ensuring there are no voids in this
> bonding layer but at the minute we have no way of imaging the stack to
> verify.
>
>
>
> My ever so brief search thus far has rendered one IR system:
>
>
>
> https://www.idonus.com/downloads/idonus_brochure_WBI_2021-01-06.pdf
>
>
>
> It looks decent but stated minimum viewable feature size (1 pixel!!) is
> 200 um for a 200 mm diameter field of view.
>
>
>
> Appreciate one could construct a home-made system but my preference is to
> go for the “easy” approach! There are also other techniques such as
> scanning acoustic microscopy and optical interferometry.
>
>
>
> I guess my questions to the community are:
>
>
>
>    1. What system(s) are you using to inspect bonded wafers/chips?
>    2. What sort of resolutions do you have?
>
>
>
> Cheers,
>
> James
>
> Dr. James Paul Grant
>
> Research Engineer in Plasma Processing
>
> *Plasma Processing Group*
>
> james.grant at glasgow.ac.uk
>
>
>
>       www.JWNC.gla.ac.uk <http://www.jwnc.gla.ac.uk/>
>   LinkedIn.com/company/JWNC
>   @UofG_JWNC <https://twitter.com/uofg_jwnc>
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