#homecmos IRC log for Tuesday, 2012-08-21

--- Tue Aug 21 201200:00
nmz787anyone here?03:36
azonenbergIt's been slow lately but i'm still working on it03:43
azonenbergwas machining some microscope tube parts just a few minutes ago03:43
nmz787so i think i mentioned I was interested in making microfluidics03:45
nmz787and was trying to build a laser CNC to cut silicone03:45
nmz787but I'm wondering how far people here have come03:46
nmz787basically trying to do cost-benefit analysis before putting money down03:46
azonenbergNot sure, my focus personally is mostly on lithography03:46
nmz787(for my own project)03:46
azonenbergi started out doing IC reverse engineering with a friend03:46
azonenbergthen started to realize the basics looked simple enough maybe i could do it03:46
nmz787did you build a lithography setup for yourself?03:47
azonenbergi've gotten patterning at 20um design rules by projection using totally homebrewed setups but i'm going to break down and buy professionally printed masks i think03:47
nmz787do you have a reducer for the mask?03:48
azonenbergI've used a microscope objective but my FOV is super limited as a result03:48
azonenbergmy new plan calls for doing contact masks 1:1 scale on 2-inch wafers03:48
azonenberglaserlab.com makes 8000DPI (12.5um design rule, 3.125um lambda) masks for under $100 each03:48
azonenbergon plastic film03:48
nmz787aren;t masks like $500-800 even at academic prices?03:48
azonenbergThats for chrome on glass03:48
nmz787electron beam ethced quartz03:48
azonenbergfilm is a lot cheaper03:49
nmz787whats the tradeoff?03:49
azonenbergLess resolution, less rigidity. less thermal stability03:49
azonenberge-beam masks can be deep submicron features03:49
azonenbergplastic limits you to a few um03:49
nmz787how do you make those?03:49
nmz787the film ones03:49
azonenbergPhotographic film, pretty much03:49
azonenbergdirect write with a UV laser on an x-y table03:49
azonenbergI'd be buying them, $80ish for a 10x16 inch sheet is a great price03:50
nmz787hmm, so you'd need a CNC03:50
azonenbergconsidering you can cut that up and get a full mask set03:50
azonenbergyou can fit 10+ 2-inch wafer masks on that sheet03:50
azonenbergwith enough margin to hold in an aligner03:50
nmz787would you build or buy an XY table?03:51
azonenbergFor mask making, neither - like i said i'm going to just buy professional masks03:51
nmz787from where?03:51
nmz787you wouldn't happen to be in NYC area?03:52
azonenbergUpstate, actually - near albany03:52
nmz787hmm, I was up in Rochester for a while, but been in NYC for ~2months03:53
azonenbergAh, nice03:53
nmz787I have friends in Albany though03:53
azonenbergi see03:53
azonenbergi'm right across the river (RPI)03:53
nmz787so are you effectively buying the film from laserlab.com?03:54
nmz787or credits from them?03:54
nmz787i don't see BYO-film03:54
azonenbergYeah, you buy the film03:54
azonenbergfrom them03:54
azonenbergYou email the GDS and pay, a day or so later the mask shows up at your front door03:55
azonenbergi havent ordered from them for this project but a group i consulted for used them for a low-res MEMS mask03:55
nmz787seems pretty reasonable03:56
nmz787could effectively cut out the laser CNC in my setup, if I can figure out lithography03:57
nmz787i've made some transistors in a lab i audited once03:57
nmz787but that used a stepper03:57
azonenbergYeah, i intend to start with contact litho and then make an H-line stepper in the future03:57
nmz787what's H line?03:58
azonenbergthat will be a much bigger project and most likely wait until i have a full time job03:58
azonenbergmercury vapor H line03:58
azonenbergthe wavelength03:58
nmz787using it for mono light for interferometric positioning?03:58
azonenbergalternatively I-line, 365nm03:58
azonenbergNo, the exposure wavelength03:58
azonenbergEither of those is a pissibility03:59
nmz787where would you get the gear?03:59
nmz787the stepper?03:59
azonenbergMake it from scratch03:59
azonenbergi mean i'd buy leadscrews and piezos etc03:59
azonenbergprobably use encoders for rough positioning and interferometers for fine03:59
nmz787hmm, and still order the masks?03:59
nmz787oh, is that how they'd do it03:59
azonenbergThat's a long-term project04:00
azonenbergfirst step is to do contact litho04:00
nmz787see i got confused after the interferometer and thinking of how much vibration the whole system would have04:00
nmz787and then needing an optical vibe dampened table04:00
azonenbergi would definitely use a vibration dampening table if i went that far04:00
azonenbergat 1um features its not that bad04:00
nmz787but I'm only aiming for <10 micron sized features now04:01
azonenbergEven that is a bit tricky04:01
azonenbergsmallest i've done reliably with my homebrew setup was 20, i hit 5 experimentally04:01
nmz787so maybe I can try this laserlab.com and contact lith04:01
azonenbergbut most of that was my cheap objective i was using04:01
nmz787that was you making your own masks though, right?04:01
azonenbergi was using inkjet or laser pinted 200um masks04:01
azonenbergthen reducing with a horribly hacked setup04:01
azonenbergcontact litho with professional masks should give good results04:02
nmz787sure, so contact should be fine with the professional film masks04:02
azonenbergthats the plan04:02
nmz787so is it actually in contact, or separated slightly?04:02
nmz787i imagine the photoresin is liquid or tacky04:02
azonenbergyou bake off the solvent first04:03
azonenbergits quite solid04:03
azonenbergNormally you bring the wafer into contact, back off a micron or so, then align04:03
azonenbergthen bring into full contact for exposure04:03
nmz787are there any chemistries that are suited to home/home-business?04:05
azonenbergfor photoresist?04:05
nmz787i'd just be doing soft-lithography04:05
azonenbergi dont know as much about fluidic stuff04:05
azonenbergDNQ-novolac can be obtained for PCBs from injectorall.com04:05
azonenbergthe solvent is a little nasty so you probably want exhaust in the area you're actually coating04:06
nmz787where you expose the resist, develop and clean off, then pour silicon on top, cure, peel off04:06
azonenbergonce dried its pretty harmless04:06
azonenbergthe developer is dilute NaOH / KOH / TMAH or, hypothetically but not tested, dilute ammonia04:06
azonenbergand i dont know anything about microfluidic patterning of silicone or polymers in general04:07
azonenbergi've always coated it over a metal layer, then etched04:07
nmz787hmm, well thanks for the site links04:08
nmz787this page says 'emulsion side'04:11
nmz787does that mean it may have a 3D surface patterned on it?04:11
azonenbergThe film is a solid plastic base with a photosensitive later on top04:12
azonenbergyou typically want that layer against your wafer to avoid diffraction around it04:12
azonenbergrather than having the plastic in between04:12
azonenbergIn most cases you want a PD mask04:13
azonenbergVPD is the ordering code at 8000 DPI04:13
nmz787i'm wondering if I can just pour silicone on top of that04:14
azonenbergon top of the resist?04:15
azonenbergi dont know anything about patterning silicone but you could potentially do a lift-off type process04:15
azonenbergcoat a glass substrate with photoresist04:15
azonenbergexpose all of the areas you do not want channels04:15
azonenbergdevelop, now your channels are high spots where there's resist and background is low spots04:16
azonenbergthen coat silicone over the glass04:16
azonenbergafter it cures, peel off the glass plate04:16
azonenbergand remove the resist with a solvent04:16
nmz787but i was saying pouring it on the film from laserlab04:25
nmz787if its already 3D04:25
azonenbergno, odds are its not04:25
azonenbergits just reacting internally04:25
azonenbergalso, you dont want to screw up your mask in the event of a process defect :P04:25
nmz787what if the resist peels off the glass when you start peeling off the silicone?04:26
azonenbergDoesnt matter04:28
azonenbergyou just wash it off with a solvent04:28
azonenbergi dont think acetone eats PDMS04:28
nmz787i'm not sure04:29
--- Wed Aug 22 201200:00

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