SPI Supplies™ Brand of Plasma Etchers, Cleaners, and Ashers
Chemistry of the plasma and what can be etched
Introduction:
What can be etched at any given time will dependent on the feed gas being used
for the etching (hereafter, when we refer to "etching", one could substitute
"ashing" or even "cleaning") because it is the chemistry of the plasma that
determines just what will be etched. For example, just about anything carbonaceous,
including diamond and most other polymers including PFTE and polyimide can be etched
readily with pure oxygen.
Most metal oxides can be etched with argon. Passivation layers such as SiO2 or
Si3N4 can be removed only with CF4 or 90% CF4/10% O2.
Silicon can be etched with
SiF4. Aluminum can be etched with BCl3.
For some polymers the etching at room temperature can be painfully slow, even
with pure oxygen so if one can keep the sample heated
As indicated above, the SPI Plasma Prep II is also widely used to remove organic
residues and/or contaminants from non-flat surfaces that can become trapped in
difficult-to-reach areas such as on newly manufactured (non-polymeric) prosthetic
devices. A quick treatment with oxygen, for example, will remove such residues or
other layers of carbonaceous composition and there will be an immediate improvement
in wettability and overall adhesion characteristics.
One can speed up greatly the etching rate by keeping the sample at an elevated
temperature. This can be readily done by taking a small piece of ceramic, for
example one that might be a block that is 50 mm x 50 mm x 10 mm thick, first
putting it into an oven at some temperature, for example, 200° C, and then
transferring the hot ceramic block to the plasma etcher and then placing the
sample to be etched onto the heated ceramic block. In the case of polyimide
for example, a plasma etch in a mixture of 30% CF4/70% O2 at 250° C, will
remove 8 µm of hard baked polyimide in about 4 minutes.
In general, the etch rate can be increased, sometimes dramatically if the sample
is heated as described above.
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Friday July 04, 2008
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