Hi Martyn, is it possible that you would require a descum step before the
wet etch?  I fabricate gratings of a similiar period and my process requires
and O2 plasma or O3 descum before wet etching to insure the resist is really
clear in the troughs.  I  am assuming you have a 50% duty cycle  of the
gratings and it is sometimes difficult to clear out the troughs when you
have a sinusiodal profile.  Lastly, are you using an anti-reflection
coating?  Patterning on metal can be challenging.

Good luck,

Scott
----- Original Message -----
From: "Martyn Gadsdon" 
To: 
Sent: Tuesday, September 19, 2006 5:00 AM
Subject: [mems-talk] Minimum feature size using wet etching - 3micro-m?


> Dear All,
>
> I am trying to make a nanowire grating using a simple process. I am
> spinning a layer of photoresist on top of a ~50nm layer of silver or
> aluminium. The photoresist is then exposed and developed to have a
> sinusiodal profile, of  between 200 and 300nm pitch, where the troughs of
> the profile expose the metal underneath. I then aim to etch the exposed
> areas of metal using typical chemistries such as H3PO4:HAc:HNO3:H2O to
> leave an array of parallel metallic wires of the same pitch. However, I
> seem to be having problems and never seem to be able to etch the exposed
> areas.
>
> I have looked into this on the web and came across a short presentation.
>
> The link is:
>
> ccms.ntu.edu.tw/~chihiwu/ch09%20rev3.ppt
>
> and on the slide discussing the disadvantages of wet etching they state:
>
> "Can’t pattern sub-3micro-m feature"
>
> I have worked out they are at the National Taiwan University, but I can
> not find the actual author's name or email address to enquire directly to
> them, so I thought I'd try to see if anyone else can confirm their
> statement.
>
> Can anyone tell me if this is correct and may be the reason why I cannot
> wet etch my 200-300nm profiles, and if so perhaps provide a reference I
> can look up and quote.