[labnetwork] Question: adhesion of metal to BPDA/PPD polyimide

[Dan P. Woodie]

A solid cure of the polyimide is critical, as the imidization reaction releases water as a by-product, which will cause bubbling and delamination issues for any films over it. The challenge is that you never reach 100% curing as it is an asymptotic approach. So, you need to ensure that the cure is done at a sufficiently long enough time and high enough temperature that no further cross-linking will occur during any subsequent steps. You may want to also consider using Cyclotene from Dow instead of polyimide. It has many properties like polyimide but does not have any volatile byproducts from the cross linking, so issues like this mostly go away. I used it for my thesis electroplating copper into some thick structures and is an improvement on polyimide in many aspects.

Dan

Daniel Woodie
Interim Asst. Director of Facilities / Safety Manager / Facilities Engineer - (formerly an engineer at the Cornell NanoScale Facility)
College of Engineering

From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Massey, Travis
Sent: Monday, February 6, 2023 1:59 PM
To: Beaudoin, Mario <beaudoin at physics.ubc.ca>; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Question: adhesion of metal to BPDA/PPD polyimide

Hi Mario,

We use PI-2600 (2610 and 2611) extensively with Ti-Pt and Ti-Au metallization (sputtered).  Films are 2 um and 5 um, respectively.

Recipes and procedures are often tailored to specific toolsets and projects, so let’s start higher level with some general thoughts:


  1.  I suggest a vacuum dehydration bake before each film deposition – so, before the polyimide and again before the metal.  We use our polyimide oven for this.  The dehydration bake before metal dep has had a marked impact on our metal adhesion.
  2.  Are you imizing your polyimide at >350 C under an inert (N2) atmosphere?  We do 375C because nothing in our stack is that temperature sensitive.  Occasionally our oven crashes before reaching 375C and I’ve seen bubbles beneath the metal and other issues down the line.  I’ve heard of some people curing the polyimide at lower temperatures, and while you can drive off all the solvent and get a mechanically stable film, the imidization may be incomplete.
  3.  Our process deviates from the datasheet on the softbake.  We softbake for 10 minutes at 95C (so, lower temp for longer time).  This is unusually cool for NMP drive-off, but the process has worked for our team since long before I arrived.  If your films are thicker, you may need to increase one parameter or the other.
  4.  Does your polyimide curing oven get used for organics other than polyimide?
  5.  I avoid adhesion promoters between Si and PI unless it’s strictly necessary (and it’s generally not, for my processes).  I view it as another variable and possible contaminant down the line – this contamination possibility is why I bring it up here.  That said, others in my facility have used adhesion promoters for polyimide on glass without issue… but it’s good to reduce variables where you can.


I’m happy to discuss further if you have additional questions/issues or want a detailed procedure.

Best,
Travis Massey
Lawrence Livermore National Laboratory
7000 East Avenue, Livermore, CA 94550
925-422-9509 (desk)
925-495-7103 (work cell)
massey21 at llnl.gov<mailto:massey21 at llnl.gov>


From: labnetwork <labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu>> On Behalf Of Beaudoin, Mario
Sent: Wednesday, February 1, 2023 11:08 AM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] Question: adhesion of metal to BPDA/PPD polyimide


Dear Networkers,

I'm new to polyimide processing.  We have a student project that requires deposition of metal on polyimide (BPDA/PPD PI-2600 series from HD microsystems).  We tried liftoff with depositon of Ti/Pt by Ebeam.  Despite a 1min O2 plasma, albeit at low power, the metal was peeling off.  Moreover, the photoresist was also peeling off from the polyimide.  Does anyone have a good working recipe for metalization of polyimide?

Thanks,

Mario
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