Niclas,
The short answer is yes. HMDS chemical symbol NH Si2(CH3)6. The CH3 is
the Methyl, 6 makes it hexa methyl, the Si2Nh portion is the disilazane. If you
can react with hydrogen the Nh becomes NH3, ammonia, leaving behind 2(
Si(CH3)3). This is a complex molecule doth organic, the methyl and inorganic
the Si. The methyl sticking up creates a more and more hydrophobic surface. If
you do a vacuum vapor prime you use the vacuum and heat to totally dehydrate the
surface then there are only hydroxyl ions to work with. The hydroxyl ion has a
very strong bond to the surface but the HMDS reacts with the hydrogen producing
ammonia leaving methyl sticking up. The neat thing is you now have control.
Take Silicon dioxide as a surface. You start with a contact angle of 22 degrees
pretty hydrophilic. 1 minute of prime time in a vacuum vapor primer gives 45
degrees, 2 minutes gives 58 degrees, 3 minutes 65, 4 minutes 72, 5 minutes 75
and so on till all the hydroxyl ions have been converted to methyl. Figures
well over 100 can be achieved with the correct process time. Note of caution
metals have fewer hydroxyl ions and take much longer to convert the surface.
Think 4 times the time for aluminum. This leads to the use of more exotic
primers for faster reactions. Hope this helps. One good note once you have
converted the surface using VVP there is no room for moisture to react with the
surface so the conversion lasts for a very long time. The only information I
have is at least 8 weeks sitting on the Irish coast, i.e. very moist conditions.
If you want to test this send me test units and I will prime them. Bill Moffat
-----Original Message-----
From: Niclas Roxhed [mailto:[email protected]]
Sent: Thursday, January 23, 2003 3:06 AM
To: [email protected]
Subject: [mems-talk] RE: Patterning A Hydrophobic Layer
Dear colleagues
Is HMDS really hydrophobic? I've measured the contact angle of a Si-wafer
treated with HMDS as a adhesion promoter and it turned out to be around 80 deg
and that is also about the values you found in litterature (75-80 deg).
The hydrophobicity of HMDS is a topic witch has been discussed in this forum
before if I remember right. I know that the surface chemistry people use HMDSO
(hexamethyldisiloxane) to make stable real hydrophobic surfaces (contact angle >
90 deg) witch is another monomer then HMDS.
best regards
Niclas Roxhed
>Dear Jessica,
>you did not mention if the hydrophobic layer you are looking for needs to
>have a certain thickness and what your substrate material is. In case the
>substrate is a silicon wafer and the layer could be a monolayer, the easiest
>way is to use the adhesion promoter HMDS (hexamethyldisilazane) as the
>hydrophobic chemical and pattern it with a standard alkaline developer (KOH,
>NaOH).
>You may try the following recipe:
>1) prime your wafer with HMDS (e.g. heat up the wafer to 120 degC and let it
>cool down in a HMDS saturated atmosphere)
>3) coat the wafer with any type of a novolak based photoresist (AZ 1512,
>S1813, ....)
>4) pattern it with an appropriate lithography tool
>5) develop it with an alkaline developer
>6) remove the photoresist with acetone, NMP, etc.
>7) you now have a patterned hydrphobic HMDS monolayer on your wafer
>Best Regards,
>Frank.
>--------------------------------------------
>SUSS MicroTec
>Applications Center Europe
>Frank Runkel
>Schleissheimer Str. 90
>85748 Garching
>Germany
>Fon +49 89 32007 - 302
>Fax +49 89 32007 - 390
>email [email protected]
>> ------------------------------
>>
>> Date: Wed, 22 Jan 2003 12:31:45 +0100
>> From: Jessica Melin
>> To: [email protected]
>> Subject: [mems-talk] Patterning A Hydrophobic Layer
>> Message-ID:
>> Content-Type: text/plain; charset="iso-8859-1" ; format="flowed"
>> MIME-Version: 1.0
>> Content-Transfer-Encoding: quoted-printable
>> Precedence: list
>> Reply-To: General MEMS discussion
>> Message: 3
>>
>> Dear Colleagues,
>>
>> Am searching for practical information / experience on patterning
>> hydrophobic layers. For example, depositing a hydrophobic layer (i.e.
>> C4F8) on a silicon substrate, spinning on positive or negative
>> photoresist (achieving good coverage with or without the use of an
>> adhesive intermediate layer), achieving good lithographic results,
>> and etching the hydrophobic layer resulting in a patterned
>> hydrophobic layer while the silicon retains its surface properties.
>> Alternatively, using a successful lift-off process. Any experiences,
>> information, recipes, etc would be greatly appreciated.
>>
>> Best regards,
>>
>> Jessica Melin
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