Bill Moffat wrote:
>       This could be difficult.  A possible but expensive answer
> may be a 3D Holographic projection aligner.  Karl Suss used to
> manufacture one this gives you the ability to use a variable
> focus and expose with the same intensity at different focal
> lengths from the mask plane.  If you need more information I
> can probably locate engineers who have used this sort of system
> for exposure down the side of a steeply sloping line with the
> same C.D. at the top, down the slope, and at the bottom of the
> slope.  Bill Moffat

We have done multiple step exposure with different focus heights
(and multiple masks) to pattern lines on anisotropically etched
slopes (up to 350um depth, but the method can theoretically be
used on any depth) with very good CD results. We used a modified
UTS stepper and have a patent on this.
Please contact me for more details and publications if needed.

Greetings,
        Frank Berauer
        Senior R&D Engineer
        Hewlett-Packard Singapore