I would only add to this that current density is not always uniform across
all plated areas if you have a photoresist mask and there are some very
small features and some larger features. The current can distribute itself
so that the smaller features have a higher current density than the larger.
Also, I'm not sure reverse pulse plating has any effect on gold - the gold
plates out of solution, but it does not plate back into solution if the
voltage is reversed. (This is certainly true of the solution I use, which
is Enthone BDT-200 - does anyone know if it's true for all solutions?) In
other words, if you used a gold anode while plating, it would not lose any
mass.
David Nemeth
Senior Process Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA
Ph: (703) 961-9573 x206
Fax:(703) 961-9576
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Igor Kadija
Sent: Monday, January 28, 2002 9:51 PM
To: [email protected]
Subject: Re: [mems-talk] Electroplating Gold
Dear Sonia,
if you still have the problem of rough gold plating you may need to
re-evaluate your plating process. The quality of your plating including
roughness, uniformity, purity, density, electrical properties etc, depends
in general on a number of parameters. To mention a few, not necesarily in
order of importance:
1. plating temperature
2. current density (usually expressed in mA/cm2 or A/dm2 or A/ft2 and
refering to the area of MEMS patterns on the wafer to be electroplated)
3. current mode (DC, pulse, reverse pulse etc.)
4. electroplating solution composition, additives and quality of maintenance
5. cell/equipment design (anode geometry, anode position, tank shape etc.)
6. mixing/stirring conditions
7. quality of the seed layer
8. quality of the adhesion layer
9. quality of photoresist material
10. quality of imaging
11. pre-plating steps, cleaning, rinsing etc.
12. MEMS design, geometry, etc.
Your rough finish may be there for a number of reasons. Most probably your
current density was OK, since you wanted to grow (I suppose, advised by the
supplier) 2 microns/20 min, corresponding to 1.5- 2.0 mA/cm2 (most Golds are
in the range of 1-10 mA/cm2). If your mixing was reasonable and you have an
adequate plating cell and, your photoresist is adequately processed and, the
pattern is a simple step-and-repeat pattern with small aspect ratio or there
is no pattern at all and, you have properly cleaned and rinsed your wafer
and, the roughness is uniform across the wafer, you probably have the
problem with either solution maintenance (you should establish solution
quality with the Hull Cell, a simple test to determine solution quality and
performance prior to electroplating of the wafer; suppliers sometimes
provide the service and help re-establish the solution), or the specific
solution you use to perform the plating actually delivers that finish at 2
micron thickness (how rough is rough, RMS?)or, the seed layer and/or
adhesion layer are inadequate. If your contact with solution supplier for
advice as already suggested by others (Stonas, Berg, Desta, e-mails) did not
produce a satisfactory result I suggest that you take care/verify the above
parameters. I hope this helps. Good luck!
Sincerely,
Igor Kadija
[email protected]
www.fibrotools.com
201/670-8397
At 03:23 PM 1/25/02 +0000, you wrote:
>Dear All,
>
>I am trying to electroplate gold on top of silica: for that I sputtered a
>few nm Ti and then few nm of gold on top of the silica and place that in
>the electroplating solution at 50C. I used a current of 50mA that will
>give us around 2 micron thick layer of gold in 20min.
>
>The surface appear with a lot of roughness.... Could somebody give me some
>advice? Am I using the correct parameters for current and temperature to
>get an uniform layer?
>
>Thank you very much for your help!
>
>Sonia.
>
>*****************************************************
>
>Sonia Garcia-Blanco
>
>Department of Electronics and Electrical Engineering
>University of Glasgow
>Oakfield Ave.
>G12 8LT
>Glasgow
>
>Phone:
> Office: (0141) 339 8855 ext 0101
> Lab: (0141) 330 6014
>Email: [email protected]
>
>****************************************************
>_______________________________________________
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