Andy,

If you have access to any simple lapping equipment, you should be able to get a
roughened surface in a minute or less.  The wafer can be mounted onto a
substrate, such as a glass disk, using a wax or other temporary adhesive.  Mix a
slurry out of Al2O3 grit, maybe about 3µm, with a 1:3 to 1:5 ratio ( v/v
grit:water) and put it into a squeeze bottle.  It won't dissolve, but keep it
suspended by shaking it.  Put some grit onto a flat glass plate and lap the
wafer using a figure eight motion for about a minute, you should be fine.

Often, wafers are thinned after processing using a similar process.  I once had
a process where I had to thin my GaAs wafer and then repolish it.  Your task is
simple by comparison!

Brad Cantos
brad.cantos@holage.com
http://holage.com


On Jan 20, 2010, at 1:38 AM, Andy Irvine wrote:

> Hi all.
>
> Apologies for joining in order to ask a question - very bad form.  I promise
to answer at least one myself!  Anyway...
>
> Any good tips for roughening a GaAs surface?
>
> I'm working with a GaAs(-based) wafer with (curses!) a polished back face, and
am trying to avoid the possibility of multiple optical reflections between the
two faces of the wafer.  I therefore need my back surface to be rough (in fact,
just like any old one-side-polished substrate!).  I'd guess that it's going to
involve mechanical abrasion followed by a preferential etch, but if anyone can
be more specific and save me time (and ideally give me a good chemical-only HF-
free method, please Santa), that'd be extremely helpful.
>
> I've blackened many a surface in my time, but it's remarkably hard to do it
when you actually want to... ;-)
>
> Cheers,
>
> Andy