#homecmos IRC log for Tuesday, 2011-12-13

horizontallyi'll just paste here. probably most relevant here anyway21:48
horizontally13:33:57 < horizontally> i've had this on hold while i took care of finals and stuff. but back to the photoresist exposure enclosure setup21:48
horizontally13:34:07 < horizontally> i want to spincoat SU-8 (http://memscyclopedia.org/su8.html) to ~20nm - ~200nm thickness21:48
horizontally13:34:31 < horizontally> i noticed that they list a "polymer shrinkage" of 7.5%, which is alarmingly high to me21:48
horizontally13:34:42 < horizontally> in addition, they list the viscosity of the photoresist21:48
horizontally13:34:51 < 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?21:48
azonenberghorizontally: Well, first off22:00
azonenbergI hope you have good funding :p22:00
azonenbergSU-8 is NOT cheap22:01
azonenbergalso, su8 is usually used much thicker22:01
azonenberglike, micron to tens of microns thickness22:01
azonenbergBut yes, given viscosity and spin speed you can compute thickness22:01
azonenbergthis is for psin coating in general, not just su822:01
horizontallyazonenberg: a professor bought too much of it by accident a while ago22:04
horizontallyif 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?22:05
horizontallywell hmm, spin fast and long i guess22:05
horizontallythe duration determines uniformity i presume22:05
horizontallyand the spin rate determines how quickly mass is inertially forced away from the center22:06
azonenberghorizontally: lol, lucky you having extra SU822:24
azonenbergMy guess is, you will not be able to get much submicron22:24
azonenbergthe stuff is very viscous22:24
azonenbergYou might want to look and see if they have a solvent you can dilute it with to go thinner22:24
azonenbergThats what i do with my resist actually22:25
azonenbergits extremely thick and meant for printed circuit boards22:25
azonenbergso i dilute it to 50% v/v with acetone22:25
azonenbergand spincoat that22:25
azonenbergI'm thinking of ordering a photomask from laserlab that's 12.5um design rule22:42
azonenbergdo contact and projection litho off it22:42
azonenbergsee just how far i can push my process22:43
horizontallyand how would you verify the thickness of something?22:56
horizontallywhen you dilute it, does that result in patchier coating?22:58
smedingwith a hammer22:58
horizontallyor rather the thickness + uniformity of thickness22:58
horizontallyi don't want any patchiness compromising the process22:58
azonenberghorizontally: I have not seen nonuniformity from dilution as long as it was mixed thoroughly23:01
azonenbergits a solution, not a suspension23:01
azonenbergand in terms of verifying thickness, i'm used to working with films that are transparent and relatively thin23:02
azonenbergso you can use diffraction23:02
azonenbergsorry, interference23:02
azonenberggiven the known refractive index and color you can compute thickness23:02
bart416xray > colour chart :P23:03
azonenbergWell ok, a full spectrum is better23:04
horizontallyxrays don't destroy the polymer?23:07
azonenberghorizontally: Depends on the energy level23:07
azonenbergbut i think unexposed su8 might be affected23:07
horizontallybut it's all past UV, why does it depend on the energy level at that point?23:07
bart416horizontally, nothing you have access to under normal conditions will be powerful enough for that23:07
azonenbergonce its developed it should be fine23:08
bart416It might count as exposure though23:08
bart416Behaviour is rather unpredictable in that aspect I fear23:08
bart416But considering SU8's properties in general it's probably resistant to radiation damage as well :P23:09
horizontallyoh good23:14
azonenbergMy guess is, it would be exposed by it23:15
bart416horizontally, xray diffraction generally doesn't cause much radiation damage23:20
bart416Only under very specific conditions you end up with intense radiation23:20
bart416+ those setups are in heavily restricted laboratories anyway23:22
bart416So who cares :)23:22
azonenbergbart416: oh, xray diffraction23:23
azonenbergi thought you meant high intensity radiation from like a medical xray system23:24
azonenbergWhich might be powerful enough23:24
azonenbergBecause i've heard of SU8 being exposed by synchotron x-ray emisions23:24
smedingEUV exposing systems are hilariously complicated23:25
azonenbergThat wasnt EUV23:25
azonenbergit was hard x-ray23:25
smedingi know, it's a bit further23:25
smedingstill, i was reminded of it23:25
azonenbergwouldnt surprise me if the setup was maskless lol23:26
azonenbergjust reflect the beam off a moving mirror onto the sample :p23:26
smedinghave you heard of the ASMI rigs for EUV exposure23:26
azonenbergi've heard of ASML23:26
azonenbergand i'm sure they do EUV23:26
azonenbergbut no, i havent heard of any specific apparatus23:27
smedingthe 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 EUV23:27
smedingthe optics are all reflective because you can't really do lenses for EUV23:27
azonenbergsounds... difficult23:27
smedingit's all very silly23:27
azonenbergi remember having heard the molten-tin part23:27
azonenbergwhy are people even pursuing euv?23:28
azonenbergvs stuff like e-beam23:28
azonenbergwhich already exists and has the resolution23:28
azonenbergyou just need to make it faster23:28
azonenbergsay, multiple electron guns23:28
smedingEUV exists too, now23:28
smedingthey're running tests with it at Imec i think23:28
azonenbergit exists23:29
azonenbergbut is not nearly as established23:29
azonenbergthey use e-beam direct write for mask fab now23:29
azonenbergnobody uses euv in production afaik23:29
smedingi haven't heard of much use for e-beam either though23:30
smedingi know a company in Delft is using our uni cleanroom for developing devices for it23:30
azonenbergebeam is not used much in wafer fab23:30
azonenbergbut they make masks with it all the time23:30
smedingbut so far they just seem to have cost a lot of money23:30
smedingand fired their board of directors iirc23:30
azonenbergit's pretty much the de facto standard for producing photomasks i think23:30
azonenbergsputter chrome over glass blank, spin on PR, ebeam expose, develop, etch chrome, strip resist23:30
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