Hi,
        All positive photoresists are 'developed' ( rather dissolved at a
very slow rate in Alkali solution. Infact most company manafactured
Positive Photoresist ( which have PMMA as the main polymer constituent)
Developers ( SHIPLEY Microposit Developer & Olin Hunt Positive
Developer) use NaOH/KOH dilute solutions as prime constituents. So it is
very normal that PMMA degrades in KOH solution.
        We at IIT Bombay use Negative Photo Resists ( Merk Selectilux OR
Waycoat SC 180 ) that use DIAZO polymers + Novolak Resin which withstand
almost all alkaline/acid solution, infact stripping before the next
process requires more than 2hrs of boiling in Conc. H2SO4 + H2O2 solution.
        For a good review read " Semiconductor Photolithography" by
R.B.Moreau, this will give you a range of suitable recipes which do
survive various etching/polishing solutions.
        Another option you have is to coat your surface with Silicon
Nitride or Silicon Dioxide using CVD and then pattern this layer using
PMMA as photoresist and Buffered HF as etchant. ( PMMA survive BHF), and
then using this layer as a mask ( since preferential etch rate of Si in
KOH is much more ( almost 8 times for SiO2 and 20 times for Si3N4) you can
get your desired pattern etched anisotropically in Si.

Contact me if you have any problem or queries regarding the above
protocol.

Regards
Amit Shiwalkar



On Fri, 5 Feb 1999, 9ZC"9N wrote:

> Hello, MEMS.
> I use PMMA as photoresist.
> And I want to use anisotropic etching in Silicon(110).
> But the PMMA is striped in KOH etchant.
> I use KOH, IPA, DI in etchant.
> Someone help me.
> Is the PMMA is striped in KOH etchant in general or I misuse it?
> Please let me know.
> Thank you for reading my mail.
> Sincerely yours.
>
>
> ==================================================
> Fr;} >24B 9+7a E-mail AV http://www.hanmail.net
>
>

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Amit Shiwalkar                         Dept. Of Bio-Medical Engineering.
3,Vasant,                              IIT Bombay.
Carter Road,                           Powai, Bombay-400076
Khar,
Bombay(Mumbai)-400052
INDIA.


                     Email: amits@cc.iitb.ernet.in

" Reality Is a Figment of IMAGINATION "
                                ----------- Amit Shiwalkar

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