try looking into reflowed photoresist (to create the desired phase
profile), followed by a dry etch (to transfer that profile into the
Si)

On 5/12/05, Wilson, Thomas  wrote:
> I am interested in acoustic microscopy and would like to know if anyone
> can provide any information about the current state-of-the-art for
> fabricating a a microlens (1-mm diameter and 1-mm radius of curvature
> concave surface) in [100] silicon, using some sort of dry or wet etching
> technique, or perhaps even mechanical grinding followed by Syton (super)
> polishing. Ideally, the surface would also be very smooth (rmn roughness
> ~1-nm) and have accurate sphericity. All comments appreciated!