Aluminum Nitride

Joey Doll jcdoll at
Sat Sep 20 21:06:44 PDT 2008

Thanks for the feedback re: the phosphoric acid etch, that would have been a
major issue. I just found a paper reporting that 25% TMAH at room
temperature etches aluminum nitride, so I will use that instead of the hot
phosphoric acid. Then I could use aluminum to mask the TMAH etch, unless I'm
lucky and room temperature TMAH doesn't attack photoresist like it does at
higher temperatures. Using oxide as a phosphoric acid etch mask would have
been tricky, because removing it afterwards with HF would have also attacked
my titanium underlayer. Anyways though, problem solved I hope.
I wasn't too concerned about etching metal-containing wafers on stsetch,
because that part of my process is identical to the piezoresistive
cantilever process used in the ME342/E341 class process and research
projects back to Beth Pruitt's graduate work, at least. I will be careful
about that step though. Mainly I wanted to ensure that my use of aluminum
nitride in the lab sounds good.

Thanks again,

On Fri, Sep 19, 2008 at 3:33 PM, Mary Tang <mtang at> wrote:

> Hi Joey --
> Thanks for the detailed process flow, as really helps...  If I read
> correctly, your request is for etching metal-containing wafers on the
> stsetch, with the consideration that no metal is expected to be exposed to
> plasma.  I think we'll need a SpecMat quorum to decide that, so can't answer
> right now.  However, I do think that you will have a problem with resist
> surviving the hot phosphoric acid.  I would suggest that either using
> p5000etch metal chamber to plasma etch AlN (another SpecMat request) or
> depositing an oxide on top of the AlN, patterning that with a plasma or wet
> oxide etch, removing the resist, then using the hard mask for the AlN etch.
> Mary
> Joey Doll wrote:
>> Hi again -
>> I have been working with a vendor in San Jose to have aluminum nitride
>> deposited, and I would like to submit a new specmat request.
>> The vendor is
>> Hionix
>> 2363 Bering Drive, San Jose, CA 95131, USA
>> +1(408) 526-2333
>> <>
>> The aluminum nitride sputtering is performed in a system that is only used
>> to aluminum and titanium sputtering, normally for backend CMOS
>> interconnects. Sputtering is performed with an aluminum target with nitrogen
>> ambient at ~200C. This is in contrast with the system at Berkeley which is
>> also used for platinum.
>> My process flow would be as follows:
>> * start with a new DP SOI
>> * clean wafer @ SNF
>> * have titanium underlayer and aluminum nitride sputtered at Hionix (with
>> an additional RCA clean there)
>> * lithography on top of the aluminum nitride (on ASML)
>> * etch the aluminum nitride with phosphoric acid @ 120C on wbgeneral
>> * strip the photoresist
>> * lithography on top of the titanium
>> * etch the titanium using standard ti wet etch on wbmetal
>> * strip the photoresist
>> * blanket sputter aluminum on gryphon
>> * lithography on top of the aluminum
>> * etch with standard al etch on wbmetal (which doesn't attack the aluminum
>> nitride or titanium)
>> * strip the photoresist
>> * frontside lithography with spr220
>> * frontside STS etch on wafer to release front of cantilevers
>> * strip the photoresist
>> * backside lithography using spr220
>> * backside STS etch to release wafers
>> * oxide release on AMTEtcher
>> * strip the photoresist
>> The aluminum nitride would only be brought into the lab already deposited
>> on wafers, and the phosphoric acid would be drained down the AWN system once
>> returning to room temperature. Also, the aluminum nitride, aluminum and
>> titanium will be protected by photoresist while in STS and AMTEtcher. I have
>> been characterizing the films with XRD for the past month or so and am ready
>> to start fabricating working devices as soon as the material is approved.
>> Thanks for your consideration and please let me know if you have any
>> questions.
>> - Joey
>> On Tue, Jan 22, 2008 at 8:52 AM, Ed Myers <edmyers at <mailto:
>> edmyers at>> wrote:
>>    Joey,
>>    One of our weak areas is RF sputtering.  This is need for reactive
>>    deposition of insulating materials.  As a result, we can not
>>    support your request due to hardware limitations.  If you have any
>>    questions please let me know.
>>    Regards,
>>    Ed
>>    At 10:47 AM 1/19/2008, Joey Doll wrote:
>>        Hi -
>>        I'm considering a process which would use aluminum nitride as a
>>        piezoelectric actuator layer. I wasn't able to find anything
>>        mentioned
>>        about it on the SNF website and was wondering if there is a
>>        recipe /
>>        it would be possible to sputter it on grypon or metallica? It is
>>        sputtered up at Berkeley
>>        ( and I was
>>        hoping to use it instead of other materials like ZnO or PZT in
>>        order
>>        to keep my wafer semi-clean. Please let me know what you think.
>>        Thanks!
>>        Joey
> --
> Mary X. Tang, Ph.D.
> Stanford Nanofabrication Facility
> CIS Room 136, Mail Code 4070
> Stanford, CA  94305
> (650)723-9980
> mtang at
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