Another semiconductor question

[Spehro Pefhany]

I'm getting some quite large custom devices made on standard silicon
wafers-- what kind of variation can I expect from wafer to wafer as
far as *thickness* goes? How about flatness and parallelism?

The specs I have are very loose (tens of microns, IIRC), and I
suspect it's not a very important parameter for most users.



Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

Should be around 600µm +/- 10µm to 20µm. Depends on what you order,
300µm wafers are also possible.

Is the actual (typical) variation that bad from wafer to wafer?
How much will the thickness typically vary across the wafer?

And why do you care about a few µm?

It does happen to matter in my application.

 

[linnix]

Is the actual (typical) variation that bad from wafer to wafer?
How much will the thickness typically vary across the wafer?

It really depends on the wafer manufacturer and how much you are
wiling to pay. I have seen 10µm spec from wafer to wafer. If you pay
extra, I am sure they can screen and select the uniform one.

 

[Spehro Pefhany]

It really depends on the wafer manufacturer and how much you are
wiling to pay. I have seen 10µm spec from wafer to wafer. If you pay
extra, I am sure they can screen and select the uniform one.

Okay, I hoped someone might know what the *typical* numbers are.

Come to think of it, maybe I have a couple of blank 200mm wafers
kicking around somewhere that I can measure.

 

[Eeyore]

Is the actual (typical) variation that bad from wafer to wafer?
How much will the thickness typically vary across the wafer?


It does happen to matter in my application.

Well ... from work I did ages back on an exciting machine called a Spray
Acid Tool, chemical finishing can probably get pretty damn flat. I wasn't
using it btw, just recommisiong one that the UK distributor didn't want to
support. Interesting job that was too !

Graham

 

[Mike]

I'm getting some quite large custom devices made on standard silicon
wafers-- what kind of variation can I expect from wafer to wafer as
far as *thickness* goes? How about flatness and parallelism?

The specs I have are very loose (tens of microns, IIRC), and I
suspect it's not a very important parameter for most users.

Whether they know it or not, it's important - wafers get back-ground to
order depending on the package. Most packaging requirements are looser than
yours, but there are lots of requirements for very thin grinds these days
(like smartcards and such), which require correspondingly tight tolerances.
Here's a datasheet from Corwil, who do this sort of thing:

http://www.corwil.com/services/waferthinning/pdfs/CORWIL-WaferThinandPolish-Datasheet.pdf

They can hold the thickness variation across a wafer to +/-1.5u, and wafer
to wafer variation within a lot to +/-3u.

-- Mike --