Hello,

One way to achieve this is to use a thick resist - something like AZ4620
(I thinks Shipley also makes a thick resist?).
This type of photoresist can be spun on with different thicknesses (up to
100um thick) by varying the rpm spin speed and time.  Therefore, you can
use the masks you already have and do not need to etch away the
substrate(unless you need deeper channels).  Another solution could be to
use SU-8(the patternable one) which also has controllable thickness.

Also, why do you say that the process is slow for prototyping?  It seems
that the mold can be made in less than a day(even with etching), and the
PDMS can be "molded" within a few hours.  Is this what you think is slow?
Or is your etching taking a long time?  Le me know if you would like to
discuss this more.

-Angela Rasmussen
The George Washington University
The Institute of MEMS and VLSI Technologies


 On Wed, 12 May 1999, Marc A. Unger wrote:

>
> Hi There -
>
> We're doing some "soft" lithography - i.e. PDMS casts of Si molds.  Up
> until now, we've been patterning resist and doing bulk etching of Si to
> make our molds.  This works fine, but it's kind of slow for prototyping.
> Does anyone know a way to "print" a pattern 10-15 microns high directly
> on a smooth substrate?  ("Smooth" is relative; things as rough as a
> overhead transparency will probably still work.)  It would be a bonus if
> the process allows adjusting the height of the lines.
>
> By the way, laser printers and thermal transfer printers seem to make lines
> about 5 microns high.  So if anyone knows a way to make a laser printer
> or thermal transfer printer print twice or three times on the same area,
> that might be worth a try, too.
>
> I will summarize replies back to the list.
>
> Thanks in advance,
>
> Marc Unger
> Caltech Applied Physics
> [email protected]
>
>