Hi Jochen,

Deposition of a unifrom photoresist coating on wafers with anisotropically
etched three-dimensional silicon structures  is severely limited by the
topography of the surface. So far, only three techniques for the coating of
extreme three-dimensional structures are known:
a) EVG (Electronic Visions  Spray coater) based on an ultrasonic spray
nozzle, which generates an aerosol of small droplets
b) The technique of electrodepositable Shipley Photoresist,
(positive-working Resist PEPR 2400, negative-working resist EAGLE 2100 ED)
c)  Standard spin coating equipment in combination with a specially modified
vacuum chuck  ( DIMES, Delft Institute of Microelectronics and
Sunmicrotechnology, A. Bossche, J.R.Mollinger)

But to produce our three-dimensional silicon structures with 3D-structured
microelectrodes and contact pads, which includes the sharp corners of
through-holes, deep cavities (grooves) and pyramids obtained by anisotropic
etching in 100 silicon, it was necessary to develop a our new electro-spray
coating technique.  The electro-spray coating process consists of two
independent steps:
a) Resist deposition by electrospray ionisation (ESI)
b) Smoothing of resist layer in a slvent atmoshere

Principles of the electrospray process:

The essence of the Electrospray ionization sources use drawn capillaries
with a very small spraying orifice to produce very small sized charged
droplets. Three physical features determine the successful formation of an
electrospray for any given fluid:

The fluid surface tension

The diameter of the capillary tip

The distance between the capillary tip and a counter electrode

The glass capillary generates a distribution of droplets, typically around
1 - 2 µm in size, which are directed by the electric field to the substrate
surface.

Electrospray is a method of generating a very fine liquid aerosol through
electrostatic charging in the most general sense. Electrospray, as the name
implies, uses electricity instead of gas to form the droplets.


Please let me know if i can provide further information or assistance.

With best regards
Andreas

****************************************************************************
****************************
Andreas Scheipers
D-48308 Senden
Germany
[email protected]
Tel.: +49 (0) 2597 96 762
Fax: +49 (0) 2597 96 769



----- Original Message -----
From: "Jochen Zöllin" 
To: "'General MEMS discussion'" 
Sent: Monday, August 18, 2003 5:54 PM
Subject: AW: [mems-talk] Electrodes in Microchannel


Hi Andreas,

I am also thinking about using Eagle Resist form my high topography
substrates.
But what do you mean with your electro-spray coating technique? What's
the different to standard spray-coating?

Hope to hear from you soon!

Best regards,
Jochen Zöllin

IMTEK, Materialien
Albert-Ludwigs-Universität
Georges-Koehler-Allee 103
D-79110 Freiburg, Germany
Tel. +49 761 203 7207
Fax: +49 761 203 7192
E-mail: [email protected]


-----Ursprüngliche Nachricht-----
Von: [email protected]
[mailto:[email protected]] Im Auftrag von
Andreas Scheipers
Gesendet: Montag, 18. August 2003 17:00
An: General MEMS discussion
Betreff: Re: [mems-talk] Electrodes in Microchannel

Hi Tom,

The standard spin coating technology produces highly uniform layer on a
planar surface.
However, in the case where wafer through-holes, pyramids, walls, grooves
or
"high-aspect structures" are present, the coating is rich in striations
and
holes are filled with photoresist. On such coating, lithography could
not be
successfully performed. I would tend to recommend a technique with
electrodepositable photoresist (Shipley ED Eagle 2100 or Pepr 2400) or
our
electro-spray coating technique, which allows uniform photoresist
coverage
(resist thickness varies with the deposition time and is typically
adjusted
between 1µm and 2µm, which is similar to conventional spin-on coating)
on
highly textured surfaces and makes subsequent lithography steps
possible.

For more information
please feel free to contact me.

With best regards
Andreas



Andreas Scheipers
D-48308 Senden
Germany
[email protected]
Tel.: +49 (0) 2597 96 762
Fax: +49 (0) 2597 96 769



----- Original Message -----
From: "Tom Fan" 
To: 
Sent: Wednesday, August 13, 2003 2:15 AM
Subject: [mems-talk] Electrodes in Microchannel


>
>
>
> On the same topic, would 4-um high structures (serving as electrodes)
standing
> on otherwise flat substrates be considered "high-aspect-ratio"
structures?
> Would conventional resist spin coating process do the job? And also
can
the
> lithographic tool handle a height difference of 4 um (if exposures on
and
off
> the structures are desired)?
>
>
> Thanks,
> Tom
>
>


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