Hi Martyn,
The limitation for this mininum feature size is related with
photoresist and the etchant, which is considered that the etchant can
not penetrate through such small mask hole to perform wet etching due
to surface tension. My researches show that minimum feature size is
around 2 um with s1813, and it can be reduced by increasing pressure
head. Hope this would be of helps.
Good luck,

Fengyuan Zhang

At 06:00 AM 9/19/2006, you wrote:
>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.
>
>Thank you very much for your time.
>
>Martyn Gadsdon