| horizontally | i'll just paste here. probably most relevant here anyway | 21:48 |
|---|---|---|
| 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 | 21:48 |
| horizontally | 13:34:07 < horizontally> i want to spincoat SU-8 (http://memscyclopedia.org/su8.html) to ~20nm - ~200nm thickness | 21:48 |
| horizontally | 13:34:31 < horizontally> i noticed that they list a "polymer shrinkage" of 7.5%, which is alarmingly high to me | 21:48 |
| horizontally | 13:34:42 < horizontally> in addition, they list the viscosity of the photoresist | 21:48 |
| 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? | 21:48 |
| azonenberg | horizontally: Well, first off | 22:00 |
| azonenberg | I hope you have good funding :p | 22:00 |
| azonenberg | SU-8 is NOT cheap | 22:01 |
| azonenberg | also, su8 is usually used much thicker | 22:01 |
| azonenberg | like, micron to tens of microns thickness | 22:01 |
| azonenberg | But yes, given viscosity and spin speed you can compute thickness | 22:01 |
| azonenberg | this is for psin coating in general, not just su8 | 22:01 |
| horizontally | azonenberg: a professor bought too much of it by accident a while ago | 22:04 |
| 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? | 22:05 |
| horizontally | well hmm, spin fast and long i guess | 22:05 |
| horizontally | the duration determines uniformity i presume | 22:05 |
| horizontally | and the spin rate determines how quickly mass is inertially forced away from the center | 22:06 |
| azonenberg | horizontally: lol, lucky you having extra SU8 | 22:24 |
| azonenberg | My guess is, you will not be able to get much submicron | 22:24 |
| azonenberg | the stuff is very viscous | 22:24 |
| azonenberg | You might want to look and see if they have a solvent you can dilute it with to go thinner | 22:24 |
| azonenberg | Thats what i do with my resist actually | 22:25 |
| azonenberg | its extremely thick and meant for printed circuit boards | 22:25 |
| azonenberg | so i dilute it to 50% v/v with acetone | 22:25 |
| azonenberg | and spincoat that | 22:25 |
| azonenberg | Also | 22:42 |
| azonenberg | I'm thinking of ordering a photomask from laserlab that's 12.5um design rule | 22:42 |
| azonenberg | do contact and projection litho off it | 22:42 |
| azonenberg | see just how far i can push my process | 22:43 |
| horizontally | and how would you verify the thickness of something? | 22:56 |
| horizontally | when you dilute it, does that result in patchier coating? | 22:58 |
| smeding | with a hammer | 22:58 |
| horizontally | or rather the thickness + uniformity of thickness | 22:58 |
| horizontally | i don't want any patchiness compromising the process | 22:58 |
| azonenberg | horizontally: I have not seen nonuniformity from dilution as long as it was mixed thoroughly | 23:01 |
| azonenberg | its a solution, not a suspension | 23:01 |
| azonenberg | and in terms of verifying thickness, i'm used to working with films that are transparent and relatively thin | 23:02 |
| azonenberg | so you can use diffraction | 23:02 |
| azonenberg | sorry, interference | 23:02 |
| azonenberg | given the known refractive index and color you can compute thickness | 23:02 |
| bart416 | xray > colour chart :P | 23:03 |
| azonenberg | Well ok, a full spectrum is better | 23:04 |
| horizontally | xrays don't destroy the polymer? | 23:07 |
| azonenberg | horizontally: Depends on the energy level | 23:07 |
| azonenberg | but i think unexposed su8 might be affected | 23:07 |
| horizontally | but it's all past UV, why does it depend on the energy level at that point? | 23:07 |
| bart416 | horizontally, nothing you have access to under normal conditions will be powerful enough for that | 23:07 |
| azonenberg | once its developed it should be fine | 23:08 |
| horizontally | hmm | 23:08 |
| bart416 | It might count as exposure though | 23:08 |
| bart416 | Behaviour is rather unpredictable in that aspect I fear | 23:08 |
| bart416 | But considering SU8's properties in general it's probably resistant to radiation damage as well :P | 23:09 |
| horizontally | oh good | 23:14 |
| azonenberg | My guess is, it would be exposed by it | 23:15 |
| bart416 | horizontally, xray diffraction generally doesn't cause much radiation damage | 23:20 |
| bart416 | Only under very specific conditions you end up with intense radiation | 23:20 |
| bart416 | + those setups are in heavily restricted laboratories anyway | 23:22 |
| bart416 | So who cares :) | 23:22 |
| azonenberg | bart416: oh, xray diffraction | 23:23 |
| azonenberg | i thought you meant high intensity radiation from like a medical xray system | 23:24 |
| azonenberg | Which might be powerful enough | 23:24 |
| azonenberg | Because i've heard of SU8 being exposed by synchotron x-ray emisions | 23:24 |
| smeding | heh | 23:25 |
| smeding | EUV exposing systems are hilariously complicated | 23:25 |
| azonenberg | (intentionally) | 23:25 |
| azonenberg | That wasnt EUV | 23:25 |
| azonenberg | it was hard x-ray | 23:25 |
| smeding | i know, it's a bit further | 23:25 |
| smeding | :p | 23:25 |
| smeding | still, i was reminded of it | 23:25 |
| azonenberg | wouldnt surprise me if the setup was maskless lol | 23:26 |
| azonenberg | just reflect the beam off a moving mirror onto the sample :p | 23:26 |
| smeding | have you heard of the ASMI rigs for EUV exposure | 23:26 |
| azonenberg | i've heard of ASML | 23:26 |
| azonenberg | and i'm sure they do EUV | 23:26 |
| azonenberg | but no, i havent heard of any specific apparatus | 23:27 |
| 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 | 23:27 |
| azonenberg | lol | 23:27 |
| smeding | the optics are all reflective because you can't really do lenses for EUV | 23:27 |
| azonenberg | sounds... difficult | 23:27 |
| smeding | it's all very silly | 23:27 |
| azonenberg | i remember having heard the molten-tin part | 23:27 |
| azonenberg | why are people even pursuing euv? | 23:28 |
| azonenberg | vs stuff like e-beam | 23:28 |
| azonenberg | which already exists and has the resolution | 23:28 |
| azonenberg | you just need to make it faster | 23:28 |
| azonenberg | say, multiple electron guns | 23:28 |
| smeding | EUV exists too, now | 23:28 |
| smeding | they're running tests with it at Imec i think | 23:28 |
| azonenberg | it exists | 23:29 |
| azonenberg | but is not nearly as established | 23:29 |
| azonenberg | they use e-beam direct write for mask fab now | 23:29 |
| azonenberg | nobody uses euv in production afaik | 23:29 |
| smeding | i haven't heard of much use for e-beam either though | 23:30 |
| smeding | i know a company in Delft is using our uni cleanroom for developing devices for it | 23:30 |
| azonenberg | ebeam is not used much in wafer fab | 23:30 |
| azonenberg | but they make masks with it all the time | 23:30 |
| smeding | but so far they just seem to have cost a lot of money | 23:30 |
| smeding | and fired their board of directors iirc | 23:30 |
| azonenberg | it's pretty much the de facto standard for producing photomasks i think | 23:30 |
| azonenberg | sputter chrome over glass blank, spin on PR, ebeam expose, develop, etch chrome, strip resist | 23:30 |
| --- Wed Dec 14 2011 | 00:00 | |
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