More info about sputtering: process parameters, chamber construction----make money online

hey guys in previous videos I've talked

about sputtering and my vacuum chamber

in general but in this video I wanted to

spend a little more time talking about

the actual sputtered parameters and a

few more details in case you wanted to

set up a similar system of your own for

this demonstration I'll sputter some

indium tin oxide and as it turned out I

repaired my cracked disk just by gluing

it down to a thin piece of brass so I

put the whole thing down onto the

sputter head and then clamp it down and

then attach the sputter shield on top of

that so the shield is connected to the

same electrical potential as the base of

the chamber all that aluminum and the

center of the sputter head is isolated

from it however when I checked with an

ohm meter I found a couple mega ohms

resistance and I think this is actually

from the cooling water that's

circulating through the sputter head I

put the bell jar on top and as you can

see there's quite a bit of sputter or

overshoot kind of on the inside of the

bell jar there this is how the system is

plumbed so we have the bell jar here the

diffusion pump here with a butterfly

valve here a valve between the diffusion

pump and the mechanical pump and then

another valve between the chamber and

the mechanical pump so right now the

system is idling with basically all the

valves closed and what I want to do is

pump down the chamber so I'm going to

open this valve here and what that's

going to do is allow the all the air

inside the bell jar to be pumped out by

the mechanical pump directly so I'm

looking at the pressure in the chamber

with a thermocouple gauge and we can see

it's coming down slowly the pump down

with with this size chamber and pump

takes about five or ten minutes

eventually the thing will level off at

about 50 Milot or when the mechanical

pump has done all it can do we want to

switch over to the diffusion pump and we

do that by closing this valve and then

opening this valve and opening this

valve and what that will do is allow a

path to go straight from the chamber

through the diffusion pump to the

mechanical pump and eventually venting

out to the atmosphere

the reason we need all these different

valves is because we can't ever let the

diffusion pump come up to atmosphere so

we can't just pull ruff-ruff pump the

chamber down through the diffusion pump

because this all the oil in here would

be exposed to air atmospheric pressure

air which would be a bad news situation

the diffusion pump produces much higher

vacuums than the mechanical pump can and

after a few minutes of being pumped with

both of these pumps in serial the

chamber pressure is down to about 3 or 4

times 10 to the -5 millibar and we're

using a penning gage here to show the

chamber pressure now as you can see the

thermocouple gage that originally showed

the rough vacuum state of the chamber is

no longer useful because it's reading

off scale if we wanted to thermally

evaporate something we would basically

be ready now where the chamber is at a

good vacuum and we could heat something

up and evaporate it as I showed in

another video

however for sputtering we actually need

to reintroduce gas molecules to the

chamber so we can use those gas

molecules to perform the sputtering in

this case we're going to be using argon

I wanted to have a better handle on

exactly what was going on with the gas

flows in this system and also wanted the

ability to do a process called reactive

sputtering later so I bought a couple of

flow meters and I'm going to show you

how to calculate the chamber pressure

based on the flow rate in and a known

pumping speed so we measured that the

chamber pressure is about 3 times 10 to

the minus 5 millibar when there's

nothing apparently going into the

chamber and what we're going to do is

open one of these flow meters a bit so

that there is three FCC m in this case

of oxygen going into the chamber so an

SCCM is a standard cubic centimeter per

minute after setting the flow meter to 3

SCCM

we've noticed that the chamber pressure

has risen up to about 5 times 10 to the

minus 4 millibar so here's a simple

equation that will come in quite handy

if you're working with a vacuum chamber

it's pressure equals the gas load

by the pumping speed and in this case we

know what the gas load is because we're

introducing it through that flow meter

and we know what the pressure is because

we just measured it but it would be nice

to know what the pumping speed is so

that we can use that in future equations

and to figure out things in the future

so we have to do some conversions here

the gas load is three SCCM minus zero

zero because it was we weren't

intentionally adding anything to the

chamber and then we have to convert

standard cubic centimeters per minute to

millibar liters per second and I'll talk

about those units in a sec so that's

what this is for

and then there's a correction factor for

the flow meter so you'll notice that the

flow meter looks sort of backwards from

the how they're often set up with the

valve on the top this time and the trick

is that when you're using a flow meter

for vacuum applications you want that

that needle valve to be on the output so

that the valve body itself that the flow

meter tube itself is actually

pressurized it doesn't work to do it the

other way because in a high vacuum

situation the gas is in molecular flow

it's not in viscous flow and there's

really nothing to push that flow meter

ball up in a normal pattern and so it

just Bob's around it's practically

unusable so anyway this correction

factor takes into account that the flow

meter body is not at ambient pressure

it's actually at about five psi and five

psi is what's coming out of my welding

cylinders and going into the flow meter

so the fact that there's pressure in

there means that the gas is a little

more dense that it normally would be at

standard conditions and the correction

factor conveniently is just the square

root of the absolute pressure ratio so

we've got basically 14.7 PSI is ambient

and it's 20 absolute going in which is

five psi gauge the pressure is just the

difference of the two readings that we

took with the pen engage and when we do

all the math this comes out to 125

liters per second which if we check the

diffusion pump manual for online it's

actually very close to the real value

surprise

clothes in fact so about this pumping

speed the unit leader per second is

sometimes a little misleading I think

the best way to think about this is just

imagine that you had in your hands a

container that's one liter big and 125

liters per second means that you just

put that container into the vacuum

chamber and then close it and remove it

from the vacuum chamber and empty it out

and then do that again 125 times per

second you'd have 125 liters per second

pumping speed so if the chamber were

completely empty and had no molecules in

there whatsoever then you wouldn't

actually be moving any atoms at all so

the pumping speed doesn't really

describe how much mass you're actually

removing from the chamber it only

describes the potential to remove mass

from the chamber if we look at a graph

of a diffusion pumps pumping speed

versus pressure we notice that it's

completely constant all the way down to

essentially zero and at first this seems

really great you'd think oh man this

pump will you know get down to deep

space vacuum I mean it's pumping the

speed is constant all the way to zero

but as I described that's only the

volume once the chamber pressure gets

low enough moving that volume out isn't

really all that helpful so what you can

do is just get a bigger and bigger pump

so the bigger and bigger container being

placed into the vacuum chamber and

closed and removed you'll keep removing

more molecules you can just never really

get all the way to zero a lot of

academic papers and white papers

describe sputtering process where they

make a big deal out of the flow rate

going into the chamber and I always

wondered why they seemed to care more

about the flow rate than the pressure I

mean it seems like if you're you know

interested in this sputtering process

and you know what the argon pressure is

it doesn't really matter what the flow

rate should be because really the

physics of this problem only depend on

pressure and that's true but there's a

big catch the trick is that you want to

have a lot of argon as much as possible

basically flowing into your chamber to

wash away all of the byproducts and

outgassing things you know trace

elements and things that you don't want

part of the process so ideally we would

want the chamber completely

empty and then we put argon in so that

the only thing in there is argon and we

can control the process very carefully

in reality there will be a lot of water

vapor and carbon monoxide and decomposed

bits of the substrate and all kinds of

things floating around in the chamber so

what we want is a high pumping speed and

also a high argon flow rate to make sure

that the gas is fresh in the chamber the

problem is that the pressure also needs

to be pretty low to prevent a

contamination and to prevent these trace

gases from being incorporated into the

substrate coating so we kind of want

everything all at once we want you know

a lot of pumping and a lot of fresh gas

and all this stuff and we compromised

and the main point that you know causes

the compromise to be made is the size of

the pump so 125 litres per second is not

very big as far as industry is concerned

most industrial setups would have like a

turbo molecular pump running 2 or 3 or

even 500 liters per second so I'm going

to scale down most of the values that

I'm going to do in my chamber by about a

factor of 3 to 5 to compensate for this

for sputtering this Itoi found that

fairly low pressures of pure argon can

actually produce fairly good coatings

despite what most of the literature says

I found one paper that talked about long

throw sputtering with just pure argon so

to set up I'm going to set the argon

flow meter to 6 to 8 SC cm and no oxygen

at all and there's another compensation

factor to worry about since this flow

meter is passing are gone and it was

calibrated for air we get to multiply it

by 1.2 in addition to the pressure

compensation factor argon is more dense

than air and so it can push that little

ball up more easily so we have to

compensate for that

after getting the flow rate dialed and I

turn on the RF power source

and turn it up to just about 10 or 20

watts at this point there is no plasma

in the chamber because the pressure is

too low and the reflected power is

fairly high because there's no plasma to

take up that energy

to get the plasma started I close the

valve leading to the diffusion pump just

momentarily any pressure will come up

high enough for the plasma to be ignited

as soon as the ignites I open the

diffusion pump valve because once the

plasma is there it can be sustained at a

much lower pressure I turn the power up

to about 40 watts and after just about

30 seconds of stabilization we can see

that the sensor head is picking up

deposited IT oh it's not a particularly

fast process so we're only getting a few

tenths of an angstrom per second which

means that we need to spend about 30 to

60 minutes on this to get a usable i teo

coating it is possible to turn up the

power and just make the process go

faster but then that also changes how

this thing works and so there's a lot of

variables in play that I myself don't

fully understand after reading a bunch

of academic papers it's pretty clear

that there's quite a bit of contention

even in industrial and research settings

just a few of the important factors of

the distance from the sputter target to

the substrate the RF power being put

into it the geometry of the sputter head

the substrate temperature the target

temperature DC bias applied to either

the substrate or the target argon flow

rate oxygen flow rate total pressure of

the system I mean it just goes on and on

and so dialing in all of these variables

is difficult and I think there's also

multiple solutions that will work well

enough for consumer electronic type

devices which is why there's so many

different kinds of process described in

the academic papers this slide has about

200 nanometers of IPO deposited in just

the way that I showed in this video and

I'm pretty happy with this this is

coming in at about a hundred ohms across

the slide like that which is more than

an order of magnitude improvement over

my last batch so I think with just a

little more tweaking I'll get down to

the I guess industry standard of maybe

20 ohms per square if not it's not

really that big of a deal for making

things like LCDs and displays like that

the surface resistivity of the coating

is not terribly important okay well I

hope that was helpful let me know if you

have any questions about building your

own sputtered system you definitely

don't have to take it to the extreme

that I did for non magnetron sputtering

you don't really need half the equipment

here you can really do it with just a

jar vacuum pump and an a high voltage

supply so I was thinking about making a

video just showing it sort of a cut-down

version to do it with minimal stuff let

me know if you'd have interested in

seeing that okay see you next time bye earn money online by clicking, online money income site, money earning sites, online earning sites, best website to earn money, free money earning sites, money earning websites, get money online, online earning tips, online earning without investment, earn money online without investment for students, earn money by clicking ads, earn money online without investment, online earn money website, online jobs to earn money, best online income site, top 10 online money earning sites, easy income online, easy online earning, earn money online from home, make money online legit, earn money online free fast and easy,