horizontally | homecmos people... do any of you all use spray on photoresist? | 03:22 |
---|---|---|
azonenberg | horizontally: I use spin coating | 03:31 |
azonenberg | spray on is likely to produce an uneven film | 03:31 |
azonenberg | its fine for PCB level feature sizes | 03:31 |
azonenberg | but for anything below 100um its going to be a bumpy surface | 03:32 |
azonenberg | like if you've ever looked at spray paint under a microscope | 03:32 |
azonenberg | looks kind of like sputtered metal but a few million times larger :p | 03:32 |
horizontally | mm | 03:32 |
horizontally | damn because that looks easier to get right | 03:32 |
azonenberg | where are you located - USA? | 03:32 |
horizontally | yeah | 03:32 |
azonenberg | injectorall.com | 03:32 |
horizontally | i want to do what you did with transparencies | 03:33 |
azonenberg | they sell liquid photoresist suitable for spin coating | 03:33 |
azonenberg | i'd buy the 2 ounce bottle, my 8 is still well over half full and is near the expiration date | 03:33 |
horizontally | you use a jeri ellsworth cpu cooling fan method? | 03:33 |
azonenberg | No | 03:33 |
azonenberg | i use a drill and a sanding wheel | 03:33 |
azonenberg | lol | 03:33 |
horizontally | oh okay | 03:33 |
azonenberg | But very similar | 03:33 |
azonenberg | I intend to shrink it, though | 03:33 |
horizontally | i have cpu fans and nonworking drills... | 03:34 |
azonenberg | using either a cpu fan or, more likely, a model aircraft brushless motor and a custom chuck | 03:34 |
azonenberg | but a fan should definitely work | 03:34 |
azonenberg | you just wont be able to handle as large of a sample | 03:34 |
horizontally | but like how do you know when you're done? | 03:34 |
azonenberg | my drill based coater is pretty beefy | 03:34 |
horizontally | and how fast do you spin it | 03:34 |
azonenberg | like, i can easily spin a full 4" wafer | 03:34 |
horizontally | whoa | 03:34 |
azonenberg | Though the largest i realistically work on is a 2" | 03:34 |
azonenberg | 4s are pricey | 03:34 |
azonenberg | and usually i do single chips | 03:34 |
azonenberg | the point is, though, it does have the horsepower for big samples which is nice | 03:34 |
horizontally | you are loaded | 03:35 |
azonenberg | Financially? Far from it | 03:35 |
azonenberg | i'm a grad student | 03:35 |
azonenberg | i make less than $20k a year | 03:35 |
horizontally | oh wow | 03:35 |
azonenberg | Before taxes | 03:36 |
azonenberg | i'm just good at scrounging stuff | 03:36 |
azonenberg | dumpster diving ftw | 03:36 |
horizontally | i'm hungry. gonna go get ramen from the dumpster | 03:36 |
azonenberg | my spin coater was made from a drill a friend didn't need | 03:36 |
azonenberg | a 2x4 | 03:36 |
azonenberg | a sanding wheel from the home depot | 03:36 |
azonenberg | a cardboard box | 03:36 |
azonenberg | a staple gun | 03:36 |
azonenberg | and one or two random bits of hardware | 03:36 |
azonenberg | re speed, i kind of go by ear | 03:37 |
azonenberg | i know what it sounds like at a speed that gives good reuslts :p | 03:37 |
horizontally | qdamn | 03:37 |
azonenberg | The injectorall resist is a little too viscous for my scales of work, it forms a too-thick layer | 03:37 |
azonenberg | so i dilute it 50% with acetone | 03:37 |
azonenberg | by volume | 03:37 |
horizontally | and like what do you do when you're done with it? like it's stopped spinning | 03:37 |
horizontally | doesn't it just settle weirdly? | 03:37 |
azonenberg | no | 03:37 |
azonenberg | Tape the sample down from the back (double sided), form a pool of resist on top | 03:38 |
azonenberg | spin slowly to let it spread, then fast to thin it | 03:38 |
azonenberg | keep on spinning, you'll see diffraction rings appear as the film gets thinner | 03:38 |
azonenberg | when the color stops changing the film thickness has stabilized | 03:38 |
azonenberg | keep on spinning another 10sec or so, then slow down gradually | 03:38 |
azonenberg | then i pick up the sample by the edge with tweezers | 03:38 |
azonenberg | stick on a hot plate for 90sec or so to drive off excess solvent and solidify the film | 03:39 |
azonenberg | and then do litho | 03:39 |
azonenberg | One o fthe problems with my current coater is that its a little large | 03:40 |
azonenberg | so it wont fit into the fume hood i am building easily | 03:40 |
horizontally | you're building a fume hood? | 03:40 |
azonenberg | The photoresist i use is dissolved in a somewhat unpleasant organic solvent | 03:40 |
horizontally | why do you do all this? | 03:40 |
azonenberg | in a well ventilated area its fine | 03:40 |
azonenberg | But if you have all the iwndows closed... | 03:41 |
azonenberg | The design calls for a 2 foot cube of 1/4" plastic sheet | 03:41 |
azonenberg | hot air welded | 03:41 |
azonenberg | and venting out a 6 inch duct to the nearest window | 03:41 |
horizontally | do you print with inkjet or laser printer btw? | 03:41 |
azonenberg | Laser | 03:41 |
horizontally | oh good | 03:41 |
horizontally | i was worried that the laser printers might melt the transparencies | 03:42 |
azonenberg | Maybe inkjet ones | 03:42 |
azonenberg | but mine are rated for laser | 03:42 |
horizontally | rated for? aw damn | 03:42 |
horizontally | so in general transparencies won't work with laser printers? | 03:42 |
azonenberg | i went to staples | 03:44 |
azonenberg | they sold laser and inkjet transparency | 03:44 |
azonenberg | i bought laser | 03:44 |
azonenberg | lol | 03:44 |
horizontally | and so more logistics... how to you get the mask on the photoresist? | 03:46 |
horizontally | oh you solidify okay | 03:46 |
horizontally | i was going to say that spin part would be useless otherwise | 03:47 |
horizontally | what's your light source? | 03:47 |
azonenberg | It hardens a bit during the spinning from solvent evaporation | 03:49 |
azonenberg | then you bake | 03:49 |
azonenberg | the bake is to bring it from tacky to solid, its not liquid by the end of the spinning | 03:50 |
azonenberg | and my lgiht source is a halogen microscope illuminator wit ha fiber optic head | 03:50 |
horizontally | hmm that sounds fancy | 03:50 |
horizontally | i was going to just use a little OSRAM halogen bulbs i found and hook it up to a power supply | 03:51 |
horizontally | i don't know if i need an enclosure or anything | 03:51 |
horizontally | do you just need a light source? does it need to emit UV at all? | 03:51 |
horizontally | because i think this halogen does emit a little UV | 03:51 |
azonenberg | That resist is DNQ-novolac based | 03:51 |
horizontally | wow acroynms | 03:52 |
azonenberg | and is most sensitive to the mercury vapor H to I lines | 03:52 |
horizontally | nyms i always mess that up | 03:52 |
azonenberg | whcih is 405 to 365nm | 03:52 |
azonenberg | blue to longwave UV | 03:52 |
azonenberg | Wideband sources like halogen will work but you need longer exposure than a pure UV source of the same intensity | 03:53 |
azonenberg | they also suffer chromatic aberration which may blur your exposure, however right now my limit is line edge roughness on the mask so its not too bad | 03:53 |
horizontally | how thin can you get your lines by the laserjet printer btw? | 03:54 |
horizontally | what is 1 px width actually in terms of real world lengths | 03:55 |
horizontally | like 1 mm? less? | 03:55 |
horizontally | wow some links online say 0.1 mm (100 um) | 03:55 |
azonenberg | yes | 03:56 |
azonenberg | at 600DPI a pixel is around 43 um | 03:56 |
horizontally | oh wow | 03:56 |
azonenberg | i found five pixels to be a good design rule for minimum feature size | 03:56 |
azonenberg | below that you risk blurring lines together or having breaks in them | 03:56 |
azonenberg | ymmv, test out the specific printer and transparency combo | 03:56 |
azonenberg | but this gives me around 200um features on the mask, reduced 10x by optics to get 20um on the wafer | 03:57 |
horizontally | i need to learn more about how current flow is affected by different materials | 03:57 |
horizontally | like i know very little about schottky junctions | 03:57 |
horizontally | and ohmic contacts | 03:57 |
horizontally | and band diagrams | 03:57 |
horizontally | i suck | 03:57 |
azonenberg | i know little about those too | 03:57 |
azonenberg | hence why i've been doing MEMS :p | 03:57 |
horizontally | isn't that super hard? | 03:58 |
azonenberg | i havent made anything yet :p | 03:59 |
azonenberg | gettting closer though | 03:59 |
horizontally | i'm a mechanical engineering major trying to get into mat sci | 03:59 |
horizontally | and it's tough shit | 03:59 |
horizontally | i don't even know how you do this stuff | 03:59 |
horizontally | are you a crazy good multitasker? | 03:59 |
horizontally | do you have a life outside of this stuff? | 03:59 |
azonenberg | Typical desktop for me: http://i.imgur.com/QWQHA.jpg | 03:59 |
azonenberg | does that count as crazy multitasking? | 04:00 |
azonenberg | yes, that is four physical monitors and not virtual desktops | 04:00 |
horizontally | what the hell | 04:01 |
azonenberg | and a life out of home chip fab? Sure | 04:01 |
azonenberg | i'm a phd student in comp sci | 04:01 |
azonenberg | i have homework to grade, office hours to go to, classes to take | 04:01 |
azonenberg | research to do | 04:01 |
azonenberg | :p | 04:01 |
horizontally | jesus christ | 04:01 |
horizontally | can you send me hw4.tex btw? | 04:01 |
azonenberg | lol why :p | 04:02 |
horizontally | i think your latex looks good | 04:02 |
horizontally | i want to use it as a template | 04:02 |
azonenberg | its pretty standard | 04:02 |
horizontally | you can strip out the actual homework if you want | 04:02 |
horizontally | it is, but i developed a lot of shitty habits | 04:02 |
horizontally | usepackage listings... hmm | 04:02 |
azonenberg | http://pastebin.com/JgNn7pYB | 04:02 |
azonenberg | and yeah, makes for nicely formatted source code listings | 04:03 |
azonenberg | remember my degree is in CS, not EE or something like that | 04:03 |
horizontally | i guess i'd just never done \paragraph*{} before | 04:04 |
horizontally | it looks really neat | 04:05 |
azonenberg | yeah, thats pretty much my stnadard homework template | 04:05 |
horizontally | amsfonts... never used that | 04:05 |
azonenberg | that pulls in some stuff necessary for heavy math | 04:05 |
azonenberg | same with amsmat hand amssymb | 04:05 |
azonenberg | i forget what i needed it for but its now in my standard header | 04:05 |
horizontally | i use microtype, no idea why | 04:05 |
horizontally | supposedly makes stuff look good | 04:05 |
azonenberg | i just cut and paste to everything | 04:05 |
horizontally | i have little comments reminding me in the template i have | 04:05 |
horizontally | it's not really a template | 04:05 |
azonenberg | i see | 04:06 |
horizontally | it's like... grab the old file and remove all the junk | 04:06 |
azonenberg | Yeah | 04:06 |
horizontally | put in more junk | 04:06 |
azonenberg | same here | 04:06 |
azonenberg | glad to hear you use latex and not something ugly like, say, ms word | 04:07 |
horizontally | well latex is frankly a waste of time | 04:12 |
horizontally | i am using libreoffice more | 04:12 |
horizontally | especially since i don't have so many equations to show as images | 04:12 |
horizontally | and typing \includegraphics like a dork sucks | 04:12 |
horizontally | especially for like no benefit either | 04:12 |
horizontally | how thick do you grow your oxide btw? | 04:13 |
horizontally | or do you get pregrown oxide wafers? | 04:14 |
horizontally | azonenberg: ? | 04:20 |
azonenberg | whoops back | 04:26 |
azonenberg | and i stopped using OO/LO because it was waaay too heavy and slow | 04:26 |
azonenberg | and my homework/papers are usually math heavy | 04:26 |
azonenberg | and i dont have oxidation capability atm | 04:26 |
azonenberg | a furnace is on the stuff-to-buy-soon list | 04:26 |
azonenberg | the only dielectric i've used so far was high-K | 04:26 |
azonenberg | sol gel Ta2O5 | 04:27 |
horizontally | heavy and slow with your 4 monitors? :p | 04:32 |
horizontally | but yeah math heavy, latex makes a lot of sense | 04:32 |
horizontally | it's when figures of any kind are involved it gets kind of iffy | 04:33 |
horizontally | it's not that hard, but it's just unnecessarily complicated at that point | 04:33 |
horizontally | anyway, you're going to buy a furnace?! | 04:33 |
azonenberg | yes | 04:51 |
azonenberg | small one | 04:51 |
azonenberg | 4 inch cube chamber | 04:51 |
horizontally | huh... a cubic furnace? | 04:52 |
horizontally | how much will it cost you? | 04:53 |
azonenberg | around $1100 | 04:53 |
azonenberg | hence why i dont have it yet | 04:53 |
horizontally | wow! | 04:53 |
azonenberg | http://www.mtixtl.com/compactmufflefurnace4x4x410lupto1200cwith30segmentsprogrammableandgasports.aspx | 04:53 |
azonenberg | ooh, price went up by $100 since last time i checked | 04:53 |
azonenberg | actually no, it was always this price | 04:54 |
azonenberg | 1100 is the max *temperature* :P | 04:54 |
azonenberg | the furnace costs $1289 | 04:54 |
horizontally | oh | 04:56 |
horizontally | you know, i've seen people make omega heaters + heavy duty heat tape | 04:56 |
horizontally | then it's all wrapped in aluminum foil | 04:56 |
horizontally | that'd cost you about $200 maybe less | 04:56 |
azonenberg | i need a more controlled environment | 04:56 |
azonenberg | i also need to be able to purge it with N2 or Ar for heating w/o oxidation | 04:56 |
horizontally | so another heater + another heat tape would be about 400 | 04:56 |
azonenberg | and i dont think those are going to hit 1200C | 04:57 |
azonenberg | i mean at that point you are glowing yellow, not even red | 04:57 |
horizontally | they hit 1400... i don't remember if it was F or C | 04:57 |
horizontally | F never mind | 04:57 |
azonenberg | Yeah | 04:57 |
azonenberg | aluminum melts at 660C lol | 04:57 |
azonenberg | but to get good oxidation of silicon you need to hit >1000 | 04:58 |
horizontally | hmm, so that's just the cost of the furnace right? | 04:58 |
azonenberg | yes | 04:58 |
azonenberg | i hope for a cheaper option, yo ucould probably get one cheaper used | 04:59 |
horizontally | you know what... photolithography sounds really involved and will likely contaminate any devices i might want to make | 05:40 |
horizontally | i think i'll try shadow mask lithography | 05:40 |
azonenberg | contaminate? | 05:41 |
azonenberg | how | 05:41 |
horizontally | my worry is that the shadow masks will get crap deposited on them and then next time i try to deposit something using the shadow mask, i'll be redepositing previously deposited material | 05:41 |
horizontally | i'm interested in piezo devices | 05:42 |
azonenberg | so what contaminants are you worried about | 05:42 |
horizontally | i worry that the photoresist step is basically a sort of liquid phase epitaxy | 05:42 |
azonenberg | no, its a polymer | 05:42 |
horizontally | i worry that during the baking, etc. i will get diffusion | 05:42 |
azonenberg | not crystalline or even close to it | 05:42 |
azonenberg | and the bake is done at near room temp | 05:42 |
azonenberg | you can even omit the bake and air dry if you want | 05:42 |
azonenberg | The biggest contaminant from litho is K+ and Na+ ions if you use KOH or NaOH developer | 05:43 |
azonenberg | but there are alternative developers that are metal free | 05:43 |
azonenberg | like TMAH | 05:43 |
azonenberg | and i suspect ammonia would work though i havent tested it | 05:43 |
horizontally | i guess i don't know enough about polymer chemistry | 05:48 |
horizontally | i guess your point is that if it air dries... i don't even really know how diffusion works, but i would think there wouldn't be a large driving force for diffusion... | 05:49 |
horizontally | i know diffusion depends on differences in concentration | 05:49 |
horizontally | but i don't know how that is related to temperature | 05:49 |
azonenberg | diffusion in silicon normally requires high temps | 05:49 |
horizontally | temperature would perhaps increase the decrease the mean free path? | 05:49 |
azonenberg | http://www.emulsitone.com/bsif5x1020.html | 05:49 |
horizontally | it's not silicon i'm worried about | 05:49 |
horizontally | it's what i deposit on top of it | 05:49 |
azonenberg | whoops, wrong listing | 05:49 |
azonenberg | http://www.emulsitone.com/auf.html | 05:50 |
azonenberg | look at the diffusion coefficients as a function of temperature | 05:50 |
azonenberg | So it depends on the density of whatever you are depositing | 05:51 |
azonenberg | if your piezo material is a ceramic i'd guess it doesnt diffuse much | 05:51 |
azonenberg | but the main thing is, photoresist is a huge molecule | 05:51 |
azonenberg | compared to an ion like Na+ or F- | 05:51 |
azonenberg | which penetrates much more rapidly | 05:51 |
azonenberg | its this giant organic compound | 05:51 |
azonenberg | if anything you should be worried about contaminants from the developer | 05:52 |
azonenberg | Not the resist | 05:52 |
azonenberg | and if you use a dev like TMAH or ammonium hydroxide there should not be any problems | 05:52 |
bart416 | horizontally, to diffuse a material into a crystal lattice you need considerable amounts of energy | 05:55 |
bart416 | Most normal chemical reactions are not capable to muster the entropy change required to do such things without some assistance from outside | 05:55 |
horizontally | what about my worry about sputtering a shadow mask onto a sample? | 05:56 |
horizontally | is that feasible? | 05:56 |
horizontally | i guess with ion beam sputtering in particular | 05:57 |
azonenberg | horizontally: that implies making a mask that's small enough | 05:57 |
azonenberg | And in that case you should be evaporating, not sputtering | 05:57 |
azonenberg | better shadowing properties | 05:58 |
azonenberg | but that basically degenerates to a lift-off process | 05:58 |
azonenberg | at the max resolution (mask in contact with wafer) | 05:58 |
azonenberg | At which point your mask is probably photoresist | 05:58 |
horizontally | mm, the evaporator is busted. some 3 phase thing issue | 05:59 |
horizontally | i guess i have to use photolithography then | 05:59 |
horizontally | or maybe not i should revisit a few things | 05:59 |
horizontally | 1. quantify the issue of contamination due to photoresist | 06:00 |
azonenberg | It's virtually nil | 06:00 |
azonenberg | the issue is developer | 06:00 |
azonenberg | and a suitable choice of developer can minimize that | 06:00 |
horizontally | 2. quantify the issue of contamination due to a shadow mask with an ion beam sputtering system | 06:00 |
horizontally | knowing that it's argon @ 8 kV and 6 mA | 06:00 |
azonenberg | i dont know enough about the particulars of sputtering to give you any kind of estimates | 06:01 |
azonenberg | but sputtering is generally conformal | 06:01 |
azonenberg | i dont think it'd work well for masking | 06:01 |
azonenberg | and how would you make a mask at that size without photoresist and optical reduction? | 06:01 |
horizontally | well i've managed like 500 um - 1 mm line widths | 06:01 |
horizontally | nothing great | 06:01 |
azonenberg | yeah, when you hit 20um without photolithography come talk to me lol | 06:02 |
horizontally | just using tape, then just using paper, then aluminum foil | 06:02 |
azonenberg | you are going to need a reduction step in there somewhere | 06:02 |
horizontally | maybe, maybe not | 06:02 |
azonenberg | Depends on your desired feature size i guess | 06:03 |
azonenberg | about to hit the sack, class tomorrow and i want to be at least somewhat awake for it :p | 06:03 |
horizontally | all right thanks a lot | 06:03 |
horizontally | i got gobs to think about | 06:03 |
horizontally | bart416: sorry did not mean to ignore you. i read what you said and i'll just have to learn more about diffusion and polymers | 06:03 |
bart416 | A crystal lattice has what we call grid energy | 06:06 |
bart416 | to diffuse particles into the crystal you need at least the grid energy in most cases | 06:06 |
bart416 | the grid energy being the entropy difference between the bound and unbound state of the atoms or molecules in the crystal | 06:07 |
horizontally | going back to the sputtering just out of curiosity, if you knew the energy with which the ion beam struck a target and you knew the shortest distance between the target and the sample, could you figure out whether the sputtered atoms will undesirably etch the shadow mask? | 06:58 |
horizontally | you're just giving me stronger resolve to read through the fundamentals of materials science and engineering | 06:58 |
horizontally | aw man i forgot to ask azonenberg how he aligns the mask | 07:05 |
horizontally | or lock the mask for the matter | 07:05 |
horizontally | tape? | 07:05 |
azonenberg | horizontally: i mostly do projection litho | 14:06 |
azonenberg | using my microscope | 14:06 |
azonenberg | so i turn the lamp down low, align the mask to the wafer using the microscope stage to move the wafer around | 14:07 |
azonenberg | then turn it up high to expose | 14:07 |
horizontally | azonenberg: how do you "hold the mask down" | 21:06 |
azonenberg | horizontally: hold it down? What do you mean | 22:33 |
azonenberg | on the projection plate? | 22:33 |
azonenberg | It's small enough that i just let it sit | 22:34 |
azonenberg | for contact i'd need something like vacuum | 22:34 |
horizontally | like how do you get the mask stay on top of the thing you're covering and not fidget? | 22:34 |
azonenberg | The photomask just sits there | 22:34 |
azonenberg | sometimes i tape the corners to the slide | 22:34 |
horizontally | hmm | 22:34 |
horizontally | okay, that's what i was thinking of doing too | 22:34 |
horizontally | cool | 22:34 |
azonenberg | but i'm projecting so i can handle pretty coarse errors | 22:34 |
azonenberg | as the error gets 10x smaller on the wafr | 22:34 |
horizontally | mm | 22:35 |
horizontally | i was planning on doing it without a microscope | 22:35 |
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