Quartz crystal thickness monitor for vapor deposition in vacuum----make money online

hey everyone I wanted to say thanks for

all the recent donations in the past few

weeks that received a whole bunch of

really cool interesting pieces of

equipment that will be making

appearances in future videos so let me

know if you want a personal shout out

when I make those and I'll put your name

in the video over the past few weekends

I've made a lot of pieces of glass

coated with indium tin oxide which is

supposed to be a transparent conductor

but unfortunately none of the pieces

that I've made have conducted really

very well at all I mean we're talking

like the mega ohms and there's I think

I've probably found the reason for this

finally I've been trying to make the IT

Oh glass by evaporating pieces of indium

tin oxide and the way that I do this is

by putting a small chip of already

formed I tio in a metal boat and then

heat the boat up and in a vacuum

environment the molecules of indium tin

oxide come off of the surface because

the material is just so hot and then

deposit on the glass surface which is

nearby a problem with this is that in

the vacuum environment I tio may not be

stable I've had a tough time finding

resources for this but at such low

pressures the oxygen wants to leave the

tin and then you end up with just a

metallic tin deposit instead of a tin

oxide deposit so I've tried all kinds of

things to get around this I went as far

as building a digital temperature

controlled kiln with an argon atmosphere

so that I could anneal the pieces

afterwards in argon I also could hook up

oxygen to that to make an oxygen furnace

I also connected tanks of oxygen and

argon to my vacuum chamber and tried

evaporating the I tio in atmospheres of

varying concentrations of oxygen the one

thing I don't have is a mass flow

controller so I couldn't really get an

exact ratio of argon and oxygen but I

certainly tried different pressures of

each gas individually unfortunately none

of this worked I made plenty of pieces

that were certainly thick enough in ITL

coating thick enough to be conductive

and certainly a lot of them were not

trying

parent but I couldn't really get

transparent and also conductive or even

really conductive on the ones that

weren't so transparent so anyway I'm

finally coming down to building a

sputter color which is what I should

have done in the first place but I'll

have another video about that in the

future

today I wanted to talk about monitoring

the thickness of the film that we're

creating inside a vacuum chamber and so

I picked up this bit of kit on eBay and

what this is is a quartz crystal

thickness monitor or sometimes called I

think a micro balanced and the way this

works is you put a quartz crystal in the

vacuum chamber right next to the glass

that we're going to coat with i.t oh and

the crystal is resonating at say six

mega Hertz and as the eye tío evaporates

and forms a film on the glass substrate

it also forms a coating on the quartz

crystal which is exposed and as the

quartz crystal grows in thickness its

frequency will start to drop and this

box here measures the frequency drop and

displays the thickness of the film on

the front so there's an equation that

you can use to figure out how a change

in frequency will result in a or

corresponds to a change in film

thickness the inputs and outputs are

pretty simple it just has a coax BNC

connector on the back which connects

which supplies DC power to the

oscillator and also receives the six

megahertz signal in from the crystal and

it has a relay output and the purpose of

that is so that you can set like a

desired thickness on the front panel and

then press Start and it will use the

relay to start your at your deposition

process and then it will monitor the

thickness and then stop the process when

the film has reached the desired

thickness so very helpfully the

manufacturer of this device still has

the manual for it online or they go scan

and this device came out in 1986 back

when manuals had full schematics and

even a foil layout for the PCB so

figuring out how this thing worked is

actually a lot easier with that in hand

it's basically based around this chip

which for some reason they decided

needed a heatsink

and that is an AM 95 13 which is

basically just a counter so what this

circuit does is just count the incoming

pulses from the six megahertz crystal

and it measures those in a time period

and then figures out how much the

frequency has changed so there doesent

when I opened this up I expect to define

like a really precise temperature a

temperature controlled crystal

oscillator or some sort of a precise

time base but it actually doesn't need

that because all it's measuring our

reference are relative differences so

the only clock element in here is this

plain old four megahertz not temperature

controlled oscillator there and when you

first power it up it just zeroes itself

to whatever signal is coming in the way

it works is that the drift caused by or

the shift in frequency caused by the

process being deposited onto the quartz

crystal inside the vacuum chamber will

be so much bigger than any drift caused

by temperature variations that there's

really no reason to have a much more

accurate time base in the device so the

counter here is controlled by a z80 CPU

and this is a display driver for the

front panel the 7-segment displays and

then there's two eeproms which probably

have all the character data for the

front panel and this is a ram which is

powered by these battery backups here

and the idea for that is just to store

these front parameters are the the front

panel parameters that the user has to

put in so they in the manual it says

it's supposed to keep its memory for 60

days and that's the purpose of those big

batteries there so to test this thing

out and also potentially to use it in

the real vacuum chamber

I needed a six megahertz crystal that

was exposed that I could actually

deposit something onto the surface and

very helpfully suggested by one of my

YouTube viewers I should just get one of

these TTL oscillator cans and cut the

top off which is exactly what I did and

it took a few tries I had to figure out

how deep I could cut in and how much

clearance it was actually inside so that

I didn't more anything up but eventually

I got the program set and cut a bunch

open so now if I press the start button

the shutter open light comes on

if there were a rate happening it would

show that it would integrate that into a

total thickness and this device actually

allows the total thickness to go up or

down which at first doesn't seem to make

any sense how could the material

disappear once it's been deposited but I

think in some processes you actually

have the surface re-emit mass at least

maybe it's changing structure if it's

becoming more porous or something but

the rate here is measured in angstroms

per second and the total thickness is in

thousand angstroms and an angstrom is a

tenth of a nanometer so if I just use

some of this this is a refrigerant just

a very heavy gas and I'm not even really

changing the temperature I'm just

blowing some across the surface of the

crystal we can see that it's measuring a

rate and also accumulating some total

thickness here what's cool is if I went

when the gas dissipates it actually

drops down pretty close to zero again

because the crystal has returned to its

original frequency these quartz crystal

sensors can be used in a lot of

different environments it doesn't just

have to be for sensing a film thickness

in a vacuum chamber for example you can

put the entire crystal into a liquid

environment and coat one side of the

crystal with some sort of a biologically

active surface and when you submerge the

whole thing in liquid you can tell if

there's things bonding to one surface or

not if they prefer to bond to that

biologically active site you can

actually measure the mass of that tiny

amount of you know molecules bonding to

it I think these are also used in gas

sensors where you can coat one surface

of the quartz crystal with the substance

that locks down a certain gas and then

when that gas blows across the crystal a

very very small number of atoms or

molecules latch on to it and change the

mass on one side of the surface so

they're amazingly sensitive devices okay

so hopefully next time I'll have that

inside the vacuum chamber and measuring

real film thickness in real time okay

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