SPI-Module™ Sputter/Carbon Coater System
IV. Comments about "magnetic assisted" sputtering
Magnetically assisted sputtering came into being for SEM sample
preparation some several years ago. Contrary to the previously mentioned
"gimmicks", the innovative use of magnets in the "head" can in fact have
a major impact on the sputtering kinetics and can, therefore, offer
significant advantages. For example, with the right designs, one can
increase the sputter rate by a factor of five to ten times. And for heat
sensitive samples, this translates into to far cooler sputtering, since
the cathode assembly does not really have time to get hot and also, the
exposure to the radiant glow of the discharge doest not linger long
enough to hurt even a sensitive sample as well.
Competitive units, even those that claim to have what are called true
"Magnetron" geometries, do not have the unique magnetron enhanced sputtering
system present in the SPI-MODULE Sputter Coater. Hence, these units, in
general, take longer to deposit 200å of gold.
The first "Magnetron" sputtering systems available for SEM sample
preparation were double to triple the cost of a conventional
(non magnetically-assisted) unit. The big breakthrough at SPI is that we
can offer a magnetically assisted sputtering system for only a nominal
premium over the cost of a non-magnetic and conventional unit. The total
cost of a SPI-MODULE Sputter Coater System is significantly lower in
price than other commercially-available instruments being promoted as
"Magnetron" systems.
With the SPI magnetic enhanced cathode, 20 nm of gold can be
deposited in 15 seconds.
The sputtering time is so fast, the cathode temperature
never really rises delectably above room temperature. This seems to
explain why
the use of an inert gas (Ar, for example) does nothing of real
significance in a SPI-Module Sputter Coater. In this system, the benefit
of reducing the sputtering time from 10 seconds to 8.5 seconds is
insignificant. In a less advanced non-magnetically enhanced system,
however, a reduction from 5 to 4.2 minutes could be quite significant.
One note about working with samples that have been critical point dried:
Because the SPI-MODULE Sputter Coater System does not use a "hot"
cathode, anyone working with critical point dried samples should prepump
the sample using the vacuum system to drive off the surface moisture. So
long as moisture is outgassing from the sample surface, metal deposition
rate in any sputter coater will be unacceptably slow. However, one can
use the "test mode" of the sputter coater (or carbon coater) to "burn
off" adsorbed moisture so that deposition is occurring at all times onto a
sample that is absent a high amount of adsorbed moisture.
SPI-Module™ Sputter/Carbon Coater System
More information on sputtering of metals
The 20 nm in 10 seconds applies for gold cathodes only. Other metals will
sputter at slightly to moderately slower rates depending on work
function. The higher the work function, the more difficult it is to
sputter that particular metal and therefore the slower the sputtering
rate. The precious metals, as a group have the lowest work functions,
and therefore all can be sputter relatively quickly, gold being the
fastest (it has the lowest work function).
Our 10 second tests were made on an ideally flat, planar, nonoff gassing
inert sample. On double-sided tape or sheets or on samples with more
complex geometries, it will take more time to make a suitable coating.
Samples undergoing off-gassing will also take longer because, so long as
the off-gassing continues, the actual deposition rate will be
far less.
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Sunday March 21, 2010
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