Try grayscale lithography. Check this paper:

   A. Sure, T. Dillon, J. Murakowski, C. Lin, D. Pustai, and D. Prather,
"Fabrication and characterization of three-dimensional silicon tapers,"
Opt. Express 11, 3555-3561 (2003)

and also the papers by Brian Morgan et al at U of Maryland.

B.B.


> Subject:[mems-talk] Silicon Ramp Needed
> From: "[email protected]" 
> Date: Wed, 19 Apr 2006 21:44:53 -0400
> To: [email protected]
>
> OK Mems people, work with me. This is a real question.  How can I make a
> silicon ramp 5um tall on one end and 1um on the other, 250um long, 5um
> wide?  I'm starting with a 5um layer of Si on a substrate.  The real
> question is how to etch/make a smooth, ramp, type structure.  I feel a few
> lith steps of 1um 4 times to build "stairs" and then figure a way to smooth
> the 1um steps.  Anyone????
>
> Brent
>