Intro to plasma cleaning----make money online

hey guys I wanted to show you an

interesting method to clean things with

electricity so I've got four very clean

microscope slides here but this is what

they looked like before the cleaning

process the top slide has a thin layer

of photoresist on it the next slide down

has a thin layer of oil that I applied

just by smearing it on the next slide

down has a sharpie mark on it a

permanent marker and I also left a big

fingerprint on it and I also prepared a

slide with a really small amount of

paper super glued to it the paper is

just a kimwipe one of the tests that's

often used to check if a surface is

really clean is called the water break

test and surfaces that have very very

little or no contamination on them will

be very hydrophilic so if you put water

on it it will spread out and not beat up

surfaces that are contaminated with oils

or wax or something like that will have

a tendency to make the water beat up so

in this case on the even on the part

that's supposedly clean if I put a water

drop on it it doesn't spread out quite

so easily whereas on the clean slide I

can spread this water out and it has no

tendency to beat up I can actually make

a really thin sheet of water which is

pretty cool like that I started the

cleaning process by loading the dirty

slides into a vacuum chamber and using

just a mechanical pump lowered the

pressure to about a hundred millet or

the bell jar is wrapped with a about

four turns of copper tubing and the

tubing is connected to an RF transmitter

and matching Network so basically this

is just a radio transmitter that's

broadcasting all the time at about

thirteen point five six megahertz and

the tuner just allows all that RF energy

to go into the coil as opposed to being

reflected back into the transmitter it's

pretty easy to ignite the plasma with

the RF energy so even at just five watts

of RF power it's possible to get the air

plasma ignited

the rapidly changing magnetic field

created by the coil induces currents in

the plasma through you know induction

and so essentially what we have here is

a transformer where the primary winding

is the big copper coil on the outside

and the secondary is the plasma itself

we can also change the effective

cleaning power of the plasma by using a

gas other than air so one very effective

gas is just pure oxygen and creating a

plasma out of pure oxygen creates all

sorts of different ways that the

cleaning can happen the plasma itself is

a mixture of all kinds of different

things

it contains ions it contains photons of

both very short ultraviolet and also

visible a spectrum it contains free

radicals it contains energetic atoms it

contains ozone all kinds of different

things and all these different particles

help clean the surface so for example

very shortwave ultraviolet light that

normally couldn't even pass through air

will pass through the rarefied

environment in the vacuum chamber and so

that really shortwave ultraviolet will

break hydrocarbon bonds the plasma can

also oxidize things just by reacting the

oxygen with it so it's almost like

burning something without a flame

because we're introducing energy into

the system to cause hydrocarbons to

become oxidized in addition to all the

chemical processes that happen the

cleaning is also somewhat physical so

the oxygen molecules and if we were

using air nitrogen molecules could also

just help blast the dirt off of the

surface it works sort of like a little

tiny sand blaster and the high-energy

molecules strike the surface and just

blow the dirt physically off of it

this process is especially effective

against organic compounds because the

things that are containing carbon can be

combined with the reactive oxygen

species in there and the result will be

carbon dioxide or carbon monoxide and

those are gases that can be pumped away

by the vacuum pump so essentially what

we're doing here is converting all the

solid and liquid contaminants on the

surface to gases and then those gases

can be

easily pumped away as you can see the

process is quite effective there's a

small amount of photoresist left on this

slide and if you can see that or not

it's a tiny amount but it's it's

noticeable the way I had these slides

leaned up against a metallic structure

inside the vacuum pump

I think caused the plasma to have some

weak points or something and so most of

this slide is clean but there's a little

bit of residue left here the paper has

been transformed in an interesting way

it's still more or less intact although

you can see that it's been reduced in

mass and it's not really useful as I am

as a paper towel anymore the process is

known as ashing where all the

combustible things have been removed

from this and all that's left are the

inorganic compounds this piece of paper

isn't fully ashed either I think the

whole process would take you know

overnight or a day or something like

that this cleaning process is used

extensively in the semiconductor

industry because it's so effective

generally you would start by cleaning

your things with a mechanical method

like applying a solvent like acetone and

either rubbing the surface or putting it

in an ultrasonic cleaner but the problem

is what if your acetone has half a

percent of impurities in it when you

take the slide out of that bath and the

acetone evaporates it might leave that

half a percent of of contaminants on the

surface so after removing the bulk of

the dirt with with the solvent the

surface of the wafer the slide or

whatever can be loaded into the plasma

chamber and then it gets pretty much

atomically clean I mean that the plasma

chamber has the ability to remove pretty

much everything and if the power levels

are high enough it can actually remove

the substrate itself so I mentioned it

works sort of like a mini sand blaster a

few energy levels are high enough it can

actually cause damage to the surface of

the thing that we're cleaning okay see

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