What you want to read up on is "grayscale" lithography. There's quite
a bit of literature out there on the subject specifically for SU-8.
You can achieve beautiful sloping microstructures in SU-8 with this.

However, that's a relatively advanced technique, and if you're new to
the field, consider simply doing multiple exposures of SU-8 on top of
each other to achieve "steps" similar to your desired characteristics.
If you don't need to it be smooth, that's much more likely to succeed.
I'd start with 5 or 6 layers of SU-8 on top of each other, exposed and
developed sequentially to achieve such a pattern.

- Kevin

On Sun, Feb 27, 2011 at 8:43 PM, Tsoll Doiiu  wrote:
> Hello MEMS community!
>
> Does anybody have an idea how to prepare a sloped microchannel in PDMS?
>
> Initially I've tried to do like this: spin-coat PR on Si wafer, than hold the
wafer vertically,
> for like a 1h-4h, hoping  that gravity will make gradient in PR thickness,
than make UV.
> Unfortunatelly, I did not achieve the slope. I used SU 25 for this.
>
> Is there some other way to prepare oblique microchannel?
> The desired sizes are: length - approx. 4cm, initial heigth 200um, final
heigth 20um.
>
> I want to make like this:
> http://img193.imageshack.us/img193/5440/46006411.jpg
>
> Also the ways to prepare slopes with angles 30-70 degrees are strongly wanted.
>
> Thanks in advance!