Hello Alasdair.

A few thoughts on microlens fabrication:

Gray-scale lithography will certainly work and you listed some
difficulties that are present, but I will add in that gray-scale
lithography masks are extremely expensive.

Your idea to use your mask aligner for lens molding is a very good one,
and is indeed the way that many manufacturers are creating microlenses
today.  There are several optical-grade UV curable materials on the
market today.  With these materials you create the lens exactly in the
way you mentioned in your email below, namely dispense the material in a
puddle on your substrate, align your master (mold), and flood expose the
material to cure it.  No heat is required in this process.

Feel free to contact me as we have a lot of experience in microlens
fabrication if you would like more information.

Best Regards,

Dustin Warren, PE

EV Group
invent * innovate * implement
Application Engineer - Direct: +1 (480) 305 2447, Main: +1 (480) 305
2400 Fax: +1 (480) 305 2401
Cell: +1 (480) 274 3894
E-Mail: D.Warren@EVGroup.com, Web: www.EVGroup.com



-----Original Message-----
From: Alasdair Rankin [mailto:arankin@groupivsemi.com]
Sent: Wednesday, November 04, 2009 12:51 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Microlens fabrication

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