In my experience, no more than 5 minutes of ultrasonic agitation are
required to liftoff most films, and in general no damage occurs even
to very high resolution patterns. Also, I would start with the lowest
power of the ultrasonic that your bath will allow - its usually
unnecessary to go to high power for liftoff.
Also, generally I'm more concerned with thick films (rather than thin)
being damaged by ultrasonic agitation. This is because you need to be
concerned with the ratio of forces required to tear the film and the
force to peel the film. The force to peel the film in always the same,
but tearing the film requires more force when it is thick and hence
you're more likely to peel it off completely during liftoff.
Another trick regarding lift-off which might be useful - this is
especially useful when you're using SU-8: if after 15 minutes in the
ultrasonics bath no liftoff occurs, you can put the sample into an
oxygen plasma asher (not an RIE system, but an isotropic asher) for
some long time and repeat the liftoff. Usually plasma will etch resist
through any small holes that were formed in the material covering it
and after that liftoff will proceed very quickly.
On Tue, Mar 16, 2010 at 7:10 AM, Harsh Sundani wrote:
> Hi Li,
>
> I have successfully lifted-off metal films of similar thickness by a 20-30 min
ultrasonic dip. I don't think it will damage the film.
>
> Regards,
>
> Harsh Sundani
> Graduate Research Assistant, University of Toledo, Toledo, Ohio.
>
>
>> Date: Mon, 15 Mar 2010 23:20:29 -0400
>> From: anli5210@gmail.com
>> To: mems-talk@memsnet.org
>> Subject: [mems-talk] Does ultrasonic damage metal film during lift-off?
>>
>> Hi all,
>>
>> I'm doing lift-off using ultrasonic bath after soak my samples in NMP
>> overnight. However, some parts are difficult to be lifted off.
>> Thus, I increased the ultrasonic cleaning duration. But I'm afraid a long
>> ultrasonic cleaning (20-30min) might damage the metal film which is 150nm
>> sputtered Al.
>>
>> Would that be a problem?
>>
>> Thanks,
>>
>> Li. Zhang