hey everyone I was
finally successful in
depositing a clear conductive layer onto
a microscope slide so this will be the
basis for a lot of my future experiments
in ol Ed's and other display
technologies so let me show you how I
did it the device that's actually doing
the depositing is called a sputter gun
and I machined mine from basic pieces of
metal and I'm going to unscrew it here
like this and eventually the whole thing
just comes off like so and down in the
hole here is a spark plug and it's
facing up towards us so on the underside
there's the rest of the spark plug of
course and then right next to it there's
a needle valve with a hose coming off
and the hose runs to my argon cylinder
so I can control how much argon is
getting into the chamber through the
needle valve and I can get high voltage
into the chamber through the spark plug
and the underside of the sputter gun has
a rod in here that contacts the top of
the spark plug so I have sort of a
shielded entry into the chamber the
sputter gun itself is relatively simple
in construction so let me just take it
apart and show it's inside and then
describe how the whole process works so
the very outside is called a ground
shield and it slides off like this and
the purpose of this is just to keep the
things that you don't want to sputter
inside this so when the shield is on the
only thing that's exposed to the chamber
is the surface of this disc here which
is the thing that we want to sputter to
send off onto the microscope slide so if
we take that off the rest of it is built
like this and between these two layers
is an insulator so we'll take this apart
and currently there's some changes that
I'm going to make to this these are
nylon screws and nuts holding it all
together and nylon is not really a great
vacuum chamber material so eventually
I'm going to upgrade this I'm not quite
sure what I'm going to use instead
and so this part is at the vacuum
chamber case potential let's just call
that ground and then the inner part here
this is where it touches the spark plug
this is all at a negative high voltage
let's say a thousand volts negative so
inside here we've got a very high
potential between this outer shell and
the inner shell but there's a few other
tricks here that allow us to sputter
just the target material and not sputter
the rest of it so I'll open this up and
as you can see I'm missing quite a few
screws because I haven't got the right
ones in yet and I just wanted to test
this quickly inside here is a magnet a
ring magnet neodymium ring magnet and in
a steel pole piece that I turned on the
lathe and so the idea here is that when
the magnet is inserted into here like
this there's a nice magnetic field on
the top here and you can even see one
that I cracked my disk unfortunately so
I'm not going to undo the top layer just
yet but also that there's a ring pattern
where the disk has been eroded by the
sputtering I've also got some holes in
here for a cooling system which
unfortunately I didn't have running yet
that's hence the cracked disc and the
idea with that would be this is a sort
of a Teflon hose it's actually called a
plastic called PFA with a with an o-ring
on like this the hose can be sealed up
to this and then with an o-ring in the
right spot here this whole thing closes
up and I can actually pump water through
the copper block so a lot of sputtering
systems say they require water cooling
and I always you know thought that only
applied to like systems that ran for you
know eight hours a day I figured that
the thermal mass that this block would
be enough to keep me safe for a you know
five minute run but as it turns out not
quite I'm not sure if this was due to my
clamping or you know too much power or
something but I think water cooling is
kind
a necessary thing if you want to sputter
stuff at any reasonable rate okay so let
me tell you how this thing actually
works so if you want to make a nice
uniform coating on something say like a
microscope slide you have a few
different options and two of the most
common ones are evaporation and
sputtering so in a previous video I
described the evaporation process and
this entails heating up the material
that you want to coat
sorry heating up the material with which
you want to make the coating and
typically that's done in a metal boat
like this so what we do is pass a really
high current through here this thing
becomes very very hot white hot even
yellow hot and the material here
evaporates and then condenses on the
thing that you want to coat so this is
you know roughly analogous to boiling
water in the kitchen and then noticing
water droplets condense on a cold window
the downside with this is that you have
to heat up the material to that yellow
hot temperature so if your material
can't take it for whatever reason or if
it changes into another material at that
temperature then this isn't going to
work and when we're talking about making
conductive ITL coatings this is
definitely the case where if you heat IT
o up in a vacuum as far as I know it
reduces itself back down to base metals
and it doesn't work so an alternative
process is called sputtering and this
works by accelerating gas molecules and
slamming the gas molecules at very high
speed into the surface of the material
with which we want to make the coating
and when that happens at just the right
energy levels
it actually chips off a few molecules of
the surface off the surface of this
material and they go spraying off into
the chamber and eventually they'll land
on the thing that you want to coat so
here's a cross-section view of the
sputter gun the I teo disc is the thing
with which we want to make the coating
and then we've got our magnetic pole
piece here with north and south poles it
doesn't matter which is which I don't
think the idea with the pole piece being
that the magnetic flux goes through the
steel and then back up you know through
here
the magnetic field lines look like this
this whole intersection here is at about
negative a thousand volts and the outer
section is at zero so when we pump down
the chamber to a very low pressure and
put our thousand volt potential
difference on here the remaining gas
molecules in the chamber will ionize
basically just like they do in a neon
sign and the trick with the magnet is
that it concentrates all of the
electrons in this area and it does this
because the electrons are relatively
lightweight and they have charged so the
moving electrons are affected by these
magnetic field lines in fact they
actually spiral around the magnetic
field line so we concentrated all the
electrons in this area however it's not
the electrons that are actually doing
the sputtering for us what happens is
these spiraling fast-moving electrons
end up ionizing more gas molecules and
it's actually the gas molecules that are
attracted to this negative potential and
hit the surface and cause the sputtering
to happen which is why this is negative
and the shield is relatively positive
for at zero this negative voltage
attracts those positive gas molecule
ions and that's what causes the
sputtering the reason that we use argon
is because we don't want an incoming gas
molecule to react chemically with our
material here so for example let's just
say we were sputtering aluminum and we
had oxygen up here what might happen is
a really energetic oxygen molecule might
hit this and create aluminum oxide it
might not actually sputter the material
it might react with it and sometimes
that's desirable depending what kind of
process we're doing but generally want
to control those gases very carefully so
for a lot of sputtering we just use pure
argon the exact pressure at which this
whole process works is very critical to
determining the success of your coating
so if you have no gas molecules up here
obviously the process doesn't work at
all because there's nothing to cause the
sputtering
that's at a really really high vacuum at
really really poor vacuums if you have
tons and tons of gas molecules up here
it's true you'll certainly be able to
slam that into the surface however the
high pressure is such a good conductor
because there's so many ions it's tough
to get the voltage high enough so that
the incoming ions are going too slow to
cause the sputtering to happen you'll
have a nice glow discharge and things
will look like they're working but you
just can't get the voltage high enough
without you know blowing everything up
basically another problem is that if you
have tons of gas molecules up here when
you eventually do sputter off a piece of
the material it's going to interact or
it's going to hit those gas molecules
and that may or may not be a good thing
depending how your setup is configured
so if your surface tech code is kind of
up here you generally want these these
sputtered molecules to have a fairly
clear path toward it if there's so many
gas molecules up here that a lot of the
sputtered material interacts with the
gas and kind of starts flowing that may
be a bad thing because they're going to
escape and coat other things on the
surface of your chamber it seems in the
literature that most people prefer 10 to
100 Millett or for proper sputtering
pressures but it's also very common to
use the diffusion pump anyway and pump
the chamber way down as low as you can
get it basically just to clean
everything to get the water molecules
and everything to evaporate off the
surface and then backfill it with argon
back up to the pressure that you want in
my first few experiments here I've
noticed that controlling the pressure is
actually surprisingly difficult and also
as the literature says has a pretty
profound effect on how the sputter
process is going I've been using an
electrophoresis power supply for my
first attempts here and it turns out to
be a very non-ideal power supply for
this purpose besides all the stupid
safety interlocks that are make it
difficult to use the supply goes into
its current limit condition kind of too
quickly and it's hard to get a
consistent voltage current out of it it
is nice that it has a constant power
function so you can actually
a desired wattage and then play with the
chamber pressure and it will balance the
voltage and current without exceeding
that power limit however I think for
future experiments what I'm going to use
is just a microwave oven transformer
with the standard diode and control it
with a very AK
I've also been working with photoresist
and making patterns with it using some
UV lamps so this will be coming up in a
future video ok see you next time bye
s
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