SPI Silicon Nitride Membrane Windows™
Information about the Si3N4 stoichiometry
We are often times asked about how certain we are about the stoichiometry
being Si3N4.
This is a good question since often times, because of the
uncertainty surrounding the deposition, it is not uncommon to see silicon
nitride described as SixNy.
Actually silicon nitride can be grown in a number of different ways.
The SPI Silicon Nitride Membrane Windows are grown exclusively by Low
Pressure Chemical Vapor Deposition (LPCVD) at about 700° C and at reduced
pressure. It produces very high quality and stoichiometrically pure
Si3N4.
It is highly chemically resistant and doesn't (in our experience) fatigue
or suffer from creep, two very important characteristics to be a
successful support film for TEM studies.
Our process should not be confused with films grown by Plasma Enhanced
CVD. This is a low temperature process but the films have the stoichiometry
SixNyHz
and some people say Oa Cb.
In intense x-ray beams or at high temperature the hydrogen can be driven
off by annealing the film and the stress builds up (undesirable).
The films grown by this method are also prone to the formation of
pin-holes.
With our process, we can also alter deposition parameters to produce
silicon rich Si3N4
which is still LPCVD. It is the technique which we
use to produce films thicker than 200 - 250 nm.
So while in general, many persons growing films of
silicon nitride often times don't know the true stoichiometry,
they just make reference to the film as
Si3N4.
But in our case, we
really do know the stoichiometry and therefore always reference the
thin film as being Si3N4.
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Sunday October 12, 2008
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