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From:
Carey Pico <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 19 Oct 1999 23:01:35 -0700
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Chuck
Ask your supplier.  If this is the Plasma Etch in Carson City, NV, they have
as good of handle as any (I think Continental Circuits (AZ?) was their
partner for microvias).  Otherwise, get an experienced plasma guy to explore
your parameters space for a good process.  It's not easy.

For literature, track down a book called "Plasma Etching-An introduction"
edited by Dennis Manos and Daniel Flamm (interlibrary loan).  It's a
semiconductor book, but the chemistry is the same.  For the record, the
plasma chemistry is general at best.

In general, the O2 plasma is etching to form CO/CO2 gas byproducts while the
CF4 component creates some sidewall residue in the form of H2-CF4/CHF3 (the
C and the H comes from the polymer).  The sidewall residue is used to
enhance anisotropy (something present PWB etchers don't do well).  Gas
pressure (10 mT vs. 0.1mT) makes a huge difference on the overall process
(and etch rate, but not as you'd expect intuitively).

Nonuniformity across the sample is caused by many issues: spatial and
temporal variations in plasma/gas species during etch, poor cathode (sample
holder) design in terms of electric fields and gas flow, gas ratio, etc.
Because of the limited plasma etch chamber design, there is not a lot of
finess you can do.  Experiment with gas pressures, gas ratios, and bias.  It
is not an easy thing to do without help.  I would tend to try a low gas
pressure (I don't know your system, but well below 1mT), fix the bias, and
vary the gas ratio.  The low gas pressure bypasses the fluid flow dynamics
you'll face at a few mT, but at a cost of a slow process.  Once you
understand that, increase the pressure (you'll have to limit the current)
and
repeat in the region you feel works best (but exploring outside the comfort
zone).  Then adjust the bias and optimize.


Odds are, you won't have any time to do the above, but that's how you go
about it from scratch.

Good luck.  If you're lucky, someone here will feel sorry for you and give
their recipe away.


Carey

-----Original Message-----
From: Hawkins, Chuck <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, October 19, 1999 1:51 PM
Subject: [TN] Plasma etch desmear


Looking for technical information on plasma etch.  Specifically we are using
a Plasma Etch Inc. chamber.  13.56 MHz RF.  Etching Arlon 45N.
Uniformity of etch is terrible.
CF4/O2 gas

[log in to unmask] <mailto:[log in to unmask]>
972 603-7202

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