Roger is probably correct about aligning the etch to the crystal. It turns
out that the flats that are ground on a wafer can be off by as much as a few
degrees. So if you rely on alignment to the flat, that may not work too
well. There are several solutions to this problem. You could buy special
wafers from some of the smaller vendors with a tighter flat orientation
spec. You could do a two step etch, where the first etch finds the crystal
and the second etch is the real deal. Finally, if you need square holes, you
can use round patterns on your mask and allow the etch to find the crystal
for you (this technique can also be helpful for a two step etch).

As far as contamination goes, you'll often get better results if you can get
your hands on clean room grade KOH. Some vendors sell it in liquid form,
which is really handy. If you're willing to dig through the literature,
there are lots of useful papers with D.L. Kendall as one of the authors. He
wrote a lot of papers in the 70s and 80s about etching 110 silicon, though
the information still applies. I think there might also be other effects of
unwanted additives on waviness of etch surfaces.

Bill Eaton
Materials & Analysis Manager
NP Photonics

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Roger Shile
> Sent: Thursday, July 10, 2003 8:57 AM
> To: General MEMS discussion
> Subject: Re: [mems-talk] Re: V-grooves
>
>
> If you're using a crystallographic etch, such as KOH, edges
> of the grooves
> will be stepped of they aren't aligned with the <110> planes
> of the Si.
>
> I have seen residue after KOH etching Si which appears which
> appears as
> submicron globs on a SEM, though I can't see it on an optical
> microscope.
> This particular contamination is easily removed with Piranha.
>  I am curious
> to know what it is.
>
> Roger Shile
>
> ----- Original Message -----
> From: "Romana Maryla Krolikowska" 
> To: 
> Sent: Thursday, July 10, 2003 5:18 AM
> Subject: [mems-talk] Re: V-grooves
>
>
> > I  am trying to etch V-grooves in 100 Silicon wafers. I use
> a silicon
> > nitrate as a protective layer (approx. 50nm). I use a
> perspex beaker and
> > teflon holder. I am  having  a few problems with the process.
> > 1. the side walls of my V-grooves show often waviness
> > 2. the walls are often contaminated with small particles
> (in the form of
> > whitish grains) which are difficult to remove. (I use an
> acid bath to
> > remove it).
> > Could anyone help and suggest some solutions?
> >
> > Thanks in advance
> >
> > Maryla
> >
> > Laser Physics Centre,
> > Ausralian National University
> > Canberra
> >
> >

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