Hi Anirban,

Is there any special reason that you dont use image reversal lithography?

If you have a step gives to same pattern with image reversal lithography, I
recommend you use this step.

Beacuse you will have a clear under cut with image reversal then you will be
able to lift-off your patterns.

With your current process, you have thick resist but the profile of resist is
positive due to direct lithography.

This gives you continuous metal deposition profile which prevents to good lift-
off.

Best Regards.

> Date: Tue, 14 Jul 2009 15:08:58 -0500
> From: for.anirban@gmail.com
> To: mems-talk@memsnet.org
> Subject: Re: [mems-talk] Correct way of doing Lift-off process
>
> Hey Mikas,
>
> I am a follower of this MEMS forum and I would be interested to know about a
> little bit more in regards to to S18XX processing and S1818 processing which
> you have mentioned in your post.
>
> Recently I am doing lift off with S1813 and my processing is failing
> everytime over the past few weeks.
>
> Here is my process conditions with S1813.
>
> Substrate: silicon nitride on Si
> Spin coating: HMDS for proper adhesion
> for S1813 500 rpm for 10 secs, 1000 rpm for 1000 secs,
> 1800 rpm for 15 secs
> the thickness in the alpha step shows around 1.3 microns
> Pre baking time: 110'c for 3 mins
> Exposure: Intensity is 10mW/cm2 Time; 15 secs for a total dose of
> 150mJ/cm2**
> development: MF 319 for 30 secs
> Smallest feature size: 10 ums
>
> Physical vapor deposition: Sputtering
> Ti about 60nm
> Cu about 200nm
>
> The sample is then placed under Acetone ultrasonics for 1 hr for lift off.
> ** the contact of the mask with the sample is extremely good since S1813
> hardly gives you any edge bead and the exposure is done in contact.
>
> But unfortunately the process is failing since either most of the patterns
> are peeled away after lift off or are poorly lifted off which chunks of
> metal still remaining in the sample.
>
> I will be interested to know about any suggestions for the above processing.
> Further, it will be nice if you can let us know about the routine procedure
> of S1818 that you follow for lift off.
>
> Thanks a lot
> Anirban