Hello folks,

I am looking for a way to make fairly thick microlenses on a patterned
silicon wafer.  The end result I'm hoping to achieve is an array of
hemispherical lenses with a diameter on the order of 20um (though it would
be nice to go even thicker as well if needed).  The lens needs to be
transparent in the visible spectrum (~ 400-800 nm).  Ideally, I'd like to
use glass/PMMA/PDMS, but am open to suggestions.

I've read of groups using photoresist reflow / grayscale lithography to
create the lens shape.  The profile is then transferred to an underlying
layer by RIE.  However, I don't know of any suitable material I could
deposit with the desired thickness (for example, I am limited to ~7um of
SiO2).  Is there anything suitable that I could put down and etch
anisotropically?  I have an ECR etcher (plumbed with SF6 and O2) and an RIE
(CHF3/O2) at my disposal.

Would it be easier to follow the molding approach that people seem to be
using.  (Creating a master and replicating in PDMS).  In this case, I was
hoping my mask aligner could be used for aligning/shaping the lens material.
Once in contact, I could give it a UV flood exposure.  Does this sound
feasible or do I need to apply heat at the same time for any decent molds?

Anyone have any experience making something similar?

Thanks,
Alasdair