[labnetwork] PDMS mold process?

[pennell at cnf.cornell.edu]

Hi Russ,

PDMS mold fabrication is pretty straightforward. Mask material depends on
how deep into the silicon wafer they want to etch. You'll want a tool that
can run the Bosch process with C4F8 and SF6. We have two at Cornell
NanoScale Facility. A photoresist mask with 1-2 um of resist should yield
you up to 50 um of etch depth. Beyond that you'd want to use a silicon oxide
mask as it has higher selectivity and can allow you to etch through a wafer.

 

1.	Coat, bake, expose and develop resist pattern
2.	Perform an oxygen descum plasma process to clean resist residue from
open areas.
3.	Deep silicon etch process - number of loops depends on etch rate -
dependent on open silicon area, for PDMS molds the wafer is mostly bare
silicon, so open areas will etch slower. Also depends on the tool. Some of
the work I've done in this area has me yield a 20 um deep feature in about
30 minutes of etch time per wafer.
4.	Wet strip photoresist
5.	Coat with hydrophobic coating like FOTS or the PDMS will permanently
bond to the mold and not release.

 

We do this process regularly at CNF. If you don't have the tools or
resources, we could possibly do it as a remote process for you.

 

Best Regards,

Tom Pennell

Cornell NanoScale Facility

 

From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of
vsoares at inesc-mn.pt
Sent: Thursday, September 4, 2025 9:10 AM
To: 'Russ Renzas' <rrenzas at unr.edu>; 'Lab Network' <labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] PDMS mold process?

 

Hi Russ,

 

We make PDMS molds in our lab but we have banned it from the cleanroom. It
tends to stick everywhere and since it's transparent, you often don't notice
it until it's too late. We have had pieces sticking on the bottom of wafers.

So now the molds are made outside the cleanroom inside a laminar flow hood.

 

Melhores Cumprimentos/ Best Regards

 

Virginia Soares

 

INESC-MN

Rua Alves Redol,9

1000-029 LISBON

PORTUGAL

Tel: +3513100237

https://inesc-mn.pt

 

From: labnetwork <labnetwork-bounces at mtl.mit.edu
<mailto:labnetwork-bounces at mtl.mit.edu> > On Behalf Of Russ Renzas
Sent: 4 de setembro de 2025 01:22
To: Lab Network (labnetwork at mtl.mit.edu <mailto:labnetwork at mtl.mit.edu> )
<labnetwork at mtl.mit.edu <mailto:labnetwork at mtl.mit.edu> >
Subject: [labnetwork] PDMS mold process?

 

Is anyone familiar with PDMS (or other material) mold fabrication? Any
procedures or gotchas to worry about? 

 

Bio faculty member asking if we can make molds in our fab. I only know how
to make semiconductor, photonic, and quantum devices. 

 

Thanks!

 

Russ

 

Russ Renzas

University of Nevada, Reno

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