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<horizontally>
i'll just paste here. probably most relevant here anyway
<horizontally>
13:33:57 < horizontally> i've had this on hold while i took care of finals and stuff. but back to the photoresist exposure enclosure setup
<horizontally>
13:34:31 < horizontally> i noticed that they list a "polymer shrinkage" of 7.5%, which is alarmingly high to me
<horizontally>
13:34:42 < horizontally> in addition, they list the viscosity of the photoresist
<horizontally>
13:34:51 < horizontally> if i know the viscosity and i know the desired thickness of my photoresist film while acknowledging that the photoresist does shrink when baked before exposure to UV, can i figure out how fast and how i have to spin it?
<azonenberg>
horizontally: Well, first off
<azonenberg>
I hope you have good funding :p
<azonenberg>
SU-8 is NOT cheap
<azonenberg>
also, su8 is usually used much thicker
<azonenberg>
like, micron to tens of microns thickness
<azonenberg>
But yes, given viscosity and spin speed you can compute thickness
<azonenberg>
this is for psin coating in general, not just su8
<horizontally>
azonenberg: a professor bought too much of it by accident a while ago
<horizontally>
if i spin it really fast i should be able to get it to the right thickness right? or rather, if i spin for long enough?
<horizontally>
well hmm, spin fast and long i guess
<horizontally>
the duration determines uniformity i presume
<horizontally>
and the spin rate determines how quickly mass is inertially forced away from the center
<azonenberg>
horizontally: lol, lucky you having extra SU8
<azonenberg>
My guess is, you will not be able to get much submicron
<azonenberg>
the stuff is very viscous
<azonenberg>
You might want to look and see if they have a solvent you can dilute it with to go thinner
<azonenberg>
Thats what i do with my resist actually
<azonenberg>
its extremely thick and meant for printed circuit boards
<azonenberg>
so i dilute it to 50% v/v with acetone
<azonenberg>
and spincoat that
<azonenberg>
Also
<azonenberg>
I'm thinking of ordering a photomask from laserlab that's 12.5um design rule
<azonenberg>
do contact and projection litho off it
<azonenberg>
see just how far i can push my process
<horizontally>
and how would you verify the thickness of something?
<horizontally>
when you dilute it, does that result in patchier coating?
<smeding>
with a hammer
<horizontally>
or rather the thickness + uniformity of thickness
<horizontally>
i don't want any patchiness compromising the process
<azonenberg>
horizontally: I have not seen nonuniformity from dilution as long as it was mixed thoroughly
<azonenberg>
its a solution, not a suspension
<azonenberg>
and in terms of verifying thickness, i'm used to working with films that are transparent and relatively thin
<azonenberg>
so you can use diffraction
<azonenberg>
sorry, interference
<azonenberg>
given the known refractive index and color you can compute thickness
<bart416>
xray > colour chart :P
<azonenberg>
Well ok, a full spectrum is better
<horizontally>
xrays don't destroy the polymer?
<azonenberg>
horizontally: Depends on the energy level
<azonenberg>
but i think unexposed su8 might be affected
<horizontally>
but it's all past UV, why does it depend on the energy level at that point?
<bart416>
horizontally, nothing you have access to under normal conditions will be powerful enough for that
<azonenberg>
once its developed it should be fine
<horizontally>
hmm
<bart416>
It might count as exposure though
<bart416>
Behaviour is rather unpredictable in that aspect I fear
<bart416>
But considering SU8's properties in general it's probably resistant to radiation damage as well :P
<horizontally>
oh good
<azonenberg>
My guess is, it would be exposed by it
<bart416>
horizontally, xray diffraction generally doesn't cause much radiation damage
<bart416>
Only under very specific conditions you end up with intense radiation
<bart416>
+ those setups are in heavily restricted laboratories anyway
<bart416>
So who cares :)
<azonenberg>
bart416: oh, xray diffraction
<azonenberg>
i thought you meant high intensity radiation from like a medical xray system
<azonenberg>
Which might be powerful enough
<azonenberg>
Because i've heard of SU8 being exposed by synchotron x-ray emisions
<smeding>
heh
<smeding>
EUV exposing systems are hilariously complicated
<azonenberg>
(intentionally)
<azonenberg>
That wasnt EUV
<azonenberg>
it was hard x-ray
<smeding>
i know, it's a bit further
<smeding>
:p
<smeding>
still, i was reminded of it
<azonenberg>
wouldnt surprise me if the setup was maskless lol
<azonenberg>
just reflect the beam off a moving mirror onto the sample :p
<smeding>
have you heard of the ASMI rigs for EUV exposure
<azonenberg>
i've heard of ASML
<azonenberg>
and i'm sure they do EUV
<azonenberg>
but no, i havent heard of any specific apparatus
<smeding>
the EUV lasers use a stream of droplets of molten tin, track them with 3 cameras, then fire an IR laser at them to produce the EUV
<azonenberg>
lol
<smeding>
the optics are all reflective because you can't really do lenses for EUV
<azonenberg>
sounds... difficult
<smeding>
it's all very silly
<azonenberg>
i remember having heard the molten-tin part
<azonenberg>
why are people even pursuing euv?
<azonenberg>
vs stuff like e-beam
<azonenberg>
which already exists and has the resolution
<azonenberg>
you just need to make it faster
<azonenberg>
say, multiple electron guns
<smeding>
EUV exists too, now
<smeding>
they're running tests with it at Imec i think
<azonenberg>
it exists
<azonenberg>
but is not nearly as established
<azonenberg>
they use e-beam direct write for mask fab now
<azonenberg>
nobody uses euv in production afaik
<smeding>
i haven't heard of much use for e-beam either though
<smeding>
i know a company in Delft is using our uni cleanroom for developing devices for it
<azonenberg>
ebeam is not used much in wafer fab
<azonenberg>
but they make masks with it all the time
<smeding>
but so far they just seem to have cost a lot of money
<smeding>
and fired their board of directors iirc
<azonenberg>
it's pretty much the de facto standard for producing photomasks i think
<azonenberg>
sputter chrome over glass blank, spin on PR, ebeam expose, develop, etch chrome, strip resist