[labnetwork] Metallization on rough ceramic substrates

Sat Jan 5 23:31:17 EST 2019

You did not say what problem you were having, is the photoresist not coming off? Probably getting too hot during metal dep- need to slow down dep rate.

Is the deposited metal coming off as well? Need to plasma etch the “open” area with a short O2 clean before deposition.

Good luck....

Charles Ellis, retired
Formally Auburn University Microlab Manager
________________________________
From: labnetwork-bounces at mtl.mit.edu <labnetwork-bounces at mtl.mit.edu> on behalf of Kamal Yadav <kamal.yadav at gmail.com>
Sent: Friday, January 4, 2019 7:37:01 PM
To: Mark K Mondol
Cc: labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Metallization on rough ceramic substrates

Dear Aditi,

Are you observing undercut in your resist profile before you put metal. Without sufficient undercut [~ 1um] lift off would be challenging regardless of other issues.

The total resist stack should be > 3X the metal you intend to deposit. If you are using LOR, the LOR thx should be > 1.4 times the metal thickness. Bilayer lithography [LOR + Imaging], is little better option for lift off, [however you can still do with single layer provided you have undercut]. The imaging resist to LOR thickness ratio is usually 3:1 or 4:1. I observed it to be a little more challenging in process with ratio of 1:1 or 1:2 as advertised in the LOR datasheets.

Thanks,
Kamal

On Fri, Jan 4, 2019 at 7:52 PM Mark K Mondol <mondol at mit.edu<mailto:mondol at mit.edu>> wrote:

I agree with Noah Clay, he identifies the issues correctly, in my view.

I would add that a general rule of thumb for liftoff is to spin resist about 3X thicker than the metal layer you want to liftoff.

Regards,

Mark K Mondol

On 1/4/2019 2:16 PM, Noah Clay wrote:
Hello Adithi,

As you know, ceramics can be quite porous and metal adhesion can be diminished by surface/internally adsorbed water, organics, etc. Therefore, you may consider deep solvent cleaning, other surface treatments as appropriate (e.g., plasma) for your material and a lengthy dehydration bake prior to resist application.  If pre-resist cleaning proves ineffective, then after resist development, you may consider O2 plasma or, if available, in-situ ion bombardment.  Lastly, given the rough topography of your substrate, there may be undeveloped or underexposed pockets of resist on the substrate, which necessitate optimizing bake, exposure and develop conditions.

As for HMDS (mainly used for Si), without knowing the type of ceramic you’re using, I can’t say that it will be effective as an adhesion promoter.  I very humbly/respectfully disagree with previous comments that HMDS is used mostly for etching, but agree that to facilitate liftoff, a relatively thick LOR layer should be spun and baked before application of imaging resist.

Best,
Noah Clay

Singh Center for Nanotechnology
University of Pennsylvania
Philadelphia, PA

Sent from my iPhone

On Jan 4, 2019, at 08:51, Hitesh Kamble <hit.kamble at gmail.com<mailto:hit.kamble at gmail.com>> wrote:

Hello Adithi,
 In case of HMDS ,it will improve adhesion but resists will not remove easily from surafce.HMDS is mostly use in etching. Since you're having rough surface, Instead of HMDS use LOR 3B or say liftOFF resists which helps to improve liftoff process.
Also for 250nm metallization you need more than 2um thick resists.

We did not do this on ceramic samples exactly but successfully did liftoff on etched/textured glass and etched samples(roughness more than~400nm).
Following are my suggestions:
-Time  Interval between litho and deposition should be lowest as possible
- Dehydration at higher temp and for longer time.
-LOR 3B coating at lower rpm and gradually increase rpm.
-Keep sample in Remover PG and heat at 80C for 5min or more if metal not lifted,(Sonication not recquired in most cases)

Thanks,
Hitesh Kamble
IITBNF-IIT Bombay

On Fri 4 Jan, 2019, 6:08 PM ADITHI U <uadithi at iisc.ac.in<mailto:uadithi at iisc.ac.in> wrote:

Dear All,

      We are having difficulties in doing metal(Ti/Pt) lift off on ceramic substrates. Does any of you have experience on fabricating metal patterns on the rough Ceramic Substrates. Below are the details of the process done.

   The roughness of the ceramic substrates were approximately 400nm. We had used HMDS as adhesion promoter for lithography, the thickness of the Photoresist was ~ 1.5um.The thickness of the Ti/Pt layer was ~ 250nm.  Immediately after lithography the deposition was done  followed by 48 hours of lift off(Acetone) process. Ultrasonication(5-10mins) in Acetone was done after 48hours.

Best Regards

Adithi.U
Senior Facility Technologist,
National Nano Fabrication Centre,
CeNSE, Indian Institute of Science
Bangalore

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Thanks,
Kamal

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