#homecmos IRC log for Friday, 2011-08-26

swkhanhi =)20:20
swkhani want to deposit copper onto silicon. i want to be able to pattern where the copper goes for electrical addressability of the devices i want to grow on top of this patterned copper20:20
azonenbergAt what resolution20:20
swkhani have silicon wafers. i have copper tape. i have copper wire.20:20
azonenbergHow thick copper?20:20
swkhani have phosphoric acid and sodium hydroxide20:20
azonenbergdo you want20:21
swkhani am not sure. rivaling something i could sputter20:21
azonenbergFirst off, be advised that copper doesnt stick well to Si by itself20:21
azonenbergYou normally need a thin Cr adhesion layer20:21
swkhanwhy not?20:21
azonenbergAnd the only process i've gotten good results with is vacuum evaporation20:21
swkhanso electrochemical deposition wouldn't work?20:21
azonenbergNot in a cleanroom, using the one my school's mat sci department uses for SEM sample coating20:21
swkhanwhat happens if you don't have an adhesion layer?20:21
azonenbergevaporate 5nm Cr + 1000nm Cu without breaking vacuum20:21
azonenbergand it tends to peel off20:21
azonenbergyou get more overetch20:21
azonenbergi've had 200nm films with tens of microns of overetch without the adhesion layer20:22
swkhani don't have access to chromium. i am doing this because a sputtering machine we had broke20:22
azonenbergDo you have access to an evaporator?20:22
azonenbergElectroplating of Cr followed by Cu might work if your wafer is heavily doped20:22
swkhani don't have access to an evaporator20:22
swkhani think the wafers are heavily p doped. we also have heavily n doped wafers20:23
swkhanso i'd gotten part of a process ready in my head20:23
swkhani just finished up reading a textbook that gives me the equivalent knowledge of 1 year's worth of chemistry20:24
swkhanand i feel like i don't know anything when it comes to applying it =\20:24
azonenbergI havent taken any chem either20:24
azonenbergAnd if they're heavily doped in general, you may have luck with electroplatnig20:24
azonenbergIf you do, i'd be very interested in details so i can try duplicating the process20:24
swkhanbut how does electroplating work with a semiconductor?20:24
swkhansure, i was trying to come up with my own process20:24
azonenbergYou have to have it doped heavily enough that you can make ohmic contacts20:24
swkhaneveryone seems to use fancy electrolytic solutions20:25
swkhanmay be for a reason...20:25
azonenbergLol, yes20:25
azonenbergI focused on evaporation as i was depositing metal over a nonconductive surface20:25
swkhani see20:26
azonenbergI want to build my own evaporator at some point but for now i'm using the one on campus20:26
azonenbergNot many people use it (most people use the matsci lab's sputter coater for SEM prep and the cleanroom's sputtering or e-beam evaporation system for semiconductor processing)20:27
azonenbergso i just ordered some new filaments and 99.999% copper evaporation pellets from ted pella myself20:27
azonenbergthey were short on filaments last time i checked20:27
azonenbergIn any case, i can definitely provide process development for etching20:30
azonenbergthats a reasonably well studied problem20:30
azonenbergWhat's your lithography setup look like?20:30
swkhanvery crappy. i'm ms. super low budget =)20:31
swkhani am masking with aluminum foil20:31
swkhani'm not sure if it'll work20:31
azonenbergWhere are you located?20:31
swkhannasa ames (i work with ucsc)20:31
azonenbergAnd what kind of feature sizes are you trying to achieve20:31
swkhanto be PhD EE starting this fall =)20:31
azonenbergi mean, are you looking to hit 22nm or 25 microns :P20:32
azonenbergAnd do you have a spin coater? If not, as long as you dont need deep submicron resolution they're decently easy to hack together20:34
azonenbergI made one out of a 2x4, an electric drill, and a sanding wheel20:36
azonenbergthat has given me good photoresist film quality down to 5 micron features (the smallest i've tried hitting with my exposure system)20:36
lekernelazonenberg, btw, could this spinning technique be used for PCBs as well?20:47
lekernelwhen you buy microwave-friendly PCB materials like duroid or alumina, they never come with photoresist20:48
lekernelthis is quite annoying20:48
azonenberglekernel: Yes20:55
azonenbergDip coating is doable as well but requires a big tank20:55
azonenbergSpin coating of copper clad PCB is on the todo list20:55
azonenbergi have blank board but havent tried because i have so much precoated PCB :P20:55
azonenberg But the resist i have was sold for that purpose20:55
azonenberg... oops you left?20:55
azonenberg(16:55:24) azonenberg: Dip coating is doable as well but requires a big tank21:10
azonenberg(16:55:32) azonenberg: Spin coating of copper clad PCB is on the todo list21:10
azonenberg(16:55:45) azonenberg: i have blank board but havent tried because i have so much precoated PCB :P21:10
azonenberg(16:55:52) azonenberg:  But the resist i have was sold for that purpose21:10
nathan7HI AZONENBERG21:51
azonenberghi nathan721:52
azonenbergDo you have a GDS viewer program on hand?21:52
azonenbergIC layout database21:52
azonenbergguess not :p21:52
nathan7How so?21:53
CIA-67homecmos r115 | trunk/lithography-tests/default_600dpi/ (7 files in 7 dirs) | Committing previous changes to existing test masks21:54
azonenbergI guess i'll just send you a screenshot then h/o21:54
nathan7isitisitA GRATING?21:55
azonenbergGoing to be, i havent actually made it yet21:55
Action: nathan7 kisses azonenberg's feet21:55
Action: azonenberg disinfects feet with IPA21:56
nathan7that's nazi21:56
azonenbergno, it's just the absence of a foot fetish :p21:57
nathan7it is a sign of respect21:57
azonenbergIn what culture?21:59
azonenbergHere are two different mask patterns I'm considering22:14
azonenbergThe left is what i expect it will actually look like22:14
azonenbergthe right is what i'll be exposing (compensating for overetch etc)22:14
azonenberg1.058 microns per pixel is the nominal scale22:15
azonenbergwill be printed at 600DPI and then reduced 40x optically22:15
azonenbergnathan7: i should have those etched later today22:20
azonenbergi'll also be doing a PCB but the chemistry is similar enough i can use the same batches of developer and etchant22:20
azonenbergso it'll save me time22:20
azonenbergshould be finished around 22:00 - 23:00 EDT22:21
azonenbergAbout time i did a proper line edge roughness test lol22:21
nathan7it's 00:24 here22:22
bart416btw, in case you're interested in it, a low powered pulsed UV laser is enough to expose photoresist it seems22:22
bart416Can't say much about the resolution yet cause I don't have the right optics for it22:22
azonenbergdefine low powered22:23
azonenberg5 mW? 5 kW? :P22:23
bart416low as in I found it in my desk low, lol22:23
azonenbergAnd are you talking about shining it through lenses and a mask or using it focused to a spot in a direct-write setup?22:23
bart416direct write at the moment22:24
azonenbergdirect write laser is a tech i've wanted to explore for a long time22:24
azonenbergbut been too busy22:24
bart416Well I wanted to see if it was even possible22:24
bart416And looks like it works22:24
azonenbergI already ran the math, it's definitely doable22:24
bart416the laser exposed it sufficiently to develop22:24
berndjyou have a UV laser in your drawer??22:24
azonenberga blu-ray diode on a micron square spot was something like 1ms exposure required22:25
bart416but wasn't focused enough obviously22:25
bart416berndj, you don't want to know what I have in my desk drawers...22:25
azonenbergmaybe less22:25
bart416Actually maybe you do22:25
berndjoh wait, does bluray use UV?22:25
azonenbergberndj: 405nm22:25
azonenberglong UV22:25
berndjclose enough22:25
bart416bluray laser could probably do the trick, but depends on the resist22:25
azonenbergits not 197nm DUV22:25
azonenbergbut for most DNQ-novolac resists anything in the 365-405nm range will work well22:26
azonenbergmercury vapor H- to I-line22:26
bart416An electron gun assembly form a crt, a vidicon tube, copper windings from that crt it seems, 10 nixie tubes22:26
berndjat least normal glass-based optics should still work at 405nm22:26
bart416a roll of electric cable from a vacuum cleaner I disassembled22:26
bart416two floppy drives22:26
bart416CCFL inverters22:26
azonenbergLol - the desk i'm sitting at right now is pure office22:26
bart416an old soldering iron22:26
azonenbergthe workbench in the other room is where all of the fun stuff is22:27
bart416apperantly water based paint for kids22:27
bart416some dremel tools22:27
bart416hot glue gun22:27
bart416parts of what I think used to be a computer psu22:27
bart4161ohm 5W resistors, too much to count22:27
bart416A dev board of something22:27
bart416hd platers22:27
bart416neodynium magnets22:27
bart416antistatic screen cleaner that I use to clean my whiteboards22:27
bart416enough duct tape to fix anything in the universe except my love life22:28
bart416several pens22:28
bart416a green laser pointer from dx that is advertised as 5mW but actually puts out about 100mW22:28
bart416two sets of callipers22:28
bart416dentist mirror22:28
berndj100mW of green, or 100mW of IR?22:28
bart416Good question22:28
bart416We only compared the intensity with a 100mW one22:29
berndjor, how do you know it's 100mW?22:29
bart416Not the spectrum22:29
bart416Should do that again22:29
bart416well, if it manages to trigger the same displacement in a light intensity meter at same distance22:29
bart416Then it tends to be about the same22:29
bart416Needles as well it seems22:30
bart416An old ring I didn't wish I found22:30
bart416My keys that I lost months ago22:30
bart416nail clippers, yay22:30
bart416a roll meter of 2m22:30
berndji imagine 100mW of green would be pretty damn intense - maybe even visible scattering in air22:30
bart416a spoon22:30
bart416You can see the beam in the air22:30
bart416It also damages cheap cmos sensors22:31
bart416enough 7400 series logic to build a small 1960s era mainframe22:31
bart416an old PS/2 mouse22:31
bart416a snickers bar22:31
bart416desoldering braid22:31
bart416some lcd screens22:31
berndjeither way, i imagine it IS just a doubled Nd:YAG filtering out many more hundreds of mW or IR22:31
bart416A tuner for my guitar that I lost months ago as well22:32
bart416rolls of solder22:32
bart416And I'll have to start digging if I want to see more22:32
bart416That's what's immediately vissible in my drawers22:33
bart416As a matter of fact I also know I have coppersulfate crystals in there somewhere in a sealed bottle22:33
bart416And a silver ring22:33
bart416(That I do want to find but can't be bothered to look for)22:34
bart416Due to the risk of getting stabbed by sewing needles that are near the bottom near the ring22:34
bart416Also a breadboard and a sponge apperantly22:34
bart416And some steppers22:34
bart416And elastics from when I used to wear braces22:35
bart416and average office supplies as well I guess22:35
bart416So I told you what's in my desk22:36
bart416Now your turn :P22:36
Action: bart416 pokes berndj22:37
nathan7well damn22:39
nathan7 00:36:54 < bart416> And elastics from when I used to wear braces22:39
Action: nathan7 puts the goddamn things on22:39
berndjmy turn? oh, i, erm, i don't have anything interesting22:40
berndji don't have drawers!22:40
nathan7oh the curses of being a teenager :|22:40
azonenbergLol, in *this* desk? A slide rule, MIPS instruction set reference, some old graphing calculators22:41
azonenbergtons of batteries ranging from AAA to LiPo for my laptop22:41
berndjonly a PM tube, a 1000A fuse, selenium rectifiers, boring stuff in my junkboxes!22:41
azonenberga big stack of targets from rifle club last semester22:41
azonenbergassorted office supplies22:41
azonenbergand thats about it22:41
azonenbergall of the fun stuff is over in the lab22:41
berndjlooks like if i want to do photo pcb process i'll have to suck it up and find dnq22:43
azonenbergberndj: where you located?22:43
berndjthat's the "normal" pcb PR, right?22:43
azonenbergI believe so, yes22:43
berndjsouth africa22:43
azonenbergits what i've been using for all of my fab22:43
azonenbergand cant help you donw there22:43
azonenbergonly supplier i know outside of large chemical companies is a reseller about 50 miles from Albany, NY22:44
berndjyeah.  everything's available, from china, if you want kiloliter quantities22:44
azonenbergThese guys will sell - to USA at least - in 2, 4, 8, 16 fluid ounce volumes22:44
berndjsome shops have a spray, but i'm suspicious of that and balk at the price22:44
azonenbergpresumably bought by the liter (or more) and repackaged22:44
azonenbergi do not suggest a spray22:44
azonenbergspin coating ftw22:44
berndjok.  what's wrong with spray? pinholes?22:45
azonenbergThats a guess22:45
azonenbergalthough i admit i havent tested22:45
azonenbergBut there's a reason semiconductor work uses spinning :p22:45
bart416Actually, just spotted the ring and managed to pull it out with a tweezer22:45
bart416Spray won't give a nice equal distribution22:45
berndjfor now i'll just try toner transfer though22:46
berndji'll take the build-a-receiver route to getting my ham licence22:47
bart416Just study for the exam22:49
berndjyeah, gotta do that also22:49
berndji want the first class licence, not the baby one you get just from passing the exam22:49
swkhandoes anyone know of a spray can that sprays metal?22:52
swkhani want to be able to deposit metal contacts using it22:52
azonenbergswkhan: How thick?22:52
azonenbergYou can spin coat some metallic solutions22:52
azonenbergBut they're gonna be reeeally thin22:52
swkhanreally think is okay22:53
swkhanpurity is more important i think22:53
swkhanmaybe okay22:53
swkhannot sure22:53
azonenbergWhat are you using it for22:53
azonenbergin any case goldfilm is around $500 per 4-ounce bottle last i checked22:54
azonenbergprices vary based on raw material costs22:54
azonenbergit should last you a long time if my experience with tantalumfilm (which actually deposits Ta2O5, not Ta) is any hint22:54
swkhani still want to deposit some sort of metal onto my nano scale device22:54
azonenbergSputtering or evaporation is really the best bet22:54
azonenbergelectroplating, among other things22:54
swkhani'm trying to be creative and use any other methods i've got22:55
azonenbergmeans that you cannot deposit over an insulator22:55
bart416You can get metalic paint that's slightly conductive22:56
azonenbergbart416: that's a resin with silver flakes etc in it22:56
azonenbergi could not recommend it for anything small22:56
azonenberg"small" meaning <20 um22:56
bart416if it's less than 100 ┬Ám plating is your only option22:57
azonenbergswkhan: you still havent told us the feature size and layer thicknesses you'e trying for22:57
azonenbergthat makes a huge difference22:58
swkhani am not sure how thick i need the metal i'll look around. feature size? let's say smaller is better, but reproducible and cheap is even better22:58
bart416If it's for coating a large object, plate if it's already metalic, else first ensure it's metallic by spray painting it, then plate22:58
swkhanat least less than 0.5 mm22:58
bart416yeah, plating for sure22:59
azonenbergswkhan: 500 um? Oh, thats nothing22:59
azonenbergswkhan: I have hit 20um features using a living-room lithography rig22:59
swkhanlet's say 20 um with shadow mask?22:59
azonenbergand am pushign to 522:59
bart416Reminds me, I need to go and steal some CNC position encoder tomorrow23:00
azonenbergas in, my first and only attempt at 5um litho was last lab session23:00
azonenbergi overdeveloped :(23:00
swkhanokay how about this. i have silicon. i deposit some metal contact on top and then something else on top of the metal no more than let's say 100 nm thickness that's essentially an insulator23:00
azonenbergswkhan: 20um per pixel23:00
azonenbergevaporated Cu on Si23:00
bart416could be worse azonenberg23:00
swkhanaww evaporated...23:00
azonenberg~1000nm Cu over ~5nm Cr23:00
azonenbergdone in one step from two sources w/o breaking vacuum23:01
azonenbergand ok, so you want to deposit an insulator23:01
azonenbergDo you have one in mind?23:01
azonenbergOr at least a deposition process?23:01
nathan7when your MEMS works, azonenberg, could you make it switch two beams?23:01
azonenbergSiO2 for example can be formed by processes ranging from PECVD of SiH4 to sol-gel deposition23:01
azonenbergnathan7: you mean a relay of some sort?23:01
swkhani have the insulator deposition process down. cvd23:01
nathan7azonenberg: yeah23:01
nathan7azonenberg: for light23:01
swkhani was just wondering how i can get a metal contact23:02
swkhandoesn't have to be deposited23:02
azonenbergok, so now i'm starting to get the picture23:02
nathan7azonenberg: so I could alternately spectrometer a reference and a sample23:02
azonenbergyou have access to CVD SiO223:02
swkhansorry it took me so long to explain azonenberg =\23:02
azonenbergyou have blank wafers23:02
swkhani have blank wafers23:02
azonenbergand you want to put metal directly on top of the Si23:02
swkhanyes but not using the cvd23:02
azonenbergDo you have any need to deposit metal over a dielectric layer?23:02
swkhanjust out in the open in a fume hood or something23:02
swkhani do, yes23:03
nathan7azonenberg: http://upload.wikimedia.org/wikipedia/commons/1/17/IR_spectroscopy_apparatus.svg23:03
azonenbergThat rules out electroplating23:03
berndjspeaking of vacuum tech, i must practice welding some more23:03
swkhanazonenberg: awww. no way around it?23:03
azonenbergnathan7: MEMS micromirror is a possibility for that23:03
nathan7azonenberg: mhm23:03
azonenbergswkhan: There are some theoretically possible ways23:03
azonenbergYou could spin coat with goldfilm or something similar to make a thin conductive surface over the dielectric23:03
swkhanwhat about silver conducting pens23:03
azonenbergand then electroplate up23:03
berndjazonenberg, do you have any plans for metal contacts yet?23:03
bart416swkhan, silver is easy enough to deposit normally23:04
azonenbergsilver pens? Depends on your feature size23:04
azonenbergthey're silver flakes in a resin23:04
azonenbergas your feature size approaches flake size you'll get problems23:04
swkhani am afraid that my deposited insulator might break off or something23:04
bart416Gold is where it gets tricky generally23:04
azonenbergi also am not sure about patterning it23:04
swkhanthat was one thing i was considering... patterning23:04
azonenbergswkhan: You are worried about adhesion between the CVD SiO2 and the metal?23:04
azonenbergOr the SiO2 and the underlying Si where you dont have metal23:05
swkhanwell i want a top and bottom contact23:05
swkhanso initially yes on sio223:05
azonenbergLet me get this straight23:05
swkhanand then on some insulator's top side23:05
azonenbergyour device consists of silicon, a metal layer, a dielectric layer, and another metal layer23:05
azonenbergTackling them one at a time, adhesion of metal to silicon isnt that bad if you evaporate but I am not too familiar with adhesion of electroplated films23:06
swkhanideally i'd like to use the same process for both the top contact and the bottom contact23:06
swkhanhow do you know that the adhesion of metal onto silicon isn't bad?23:06
azonenbergI've worked with evaporated Cu over Cr adhesion layers23:06
azonenbergyou can put scotch tape onto the die and press it on23:06
swkhanwhy does chromium keep coming up?23:06
azonenbergthen pull off and the metal wont peel23:06
swkhanhuh cool23:07
azonenbergBecause without the Cr the Cu peels off23:07
azonenbergIt wont do so spontaneously but under the slightest provocation it will23:07
swkhanwhat aspect of science tells you about this stuff?23:07
swkhani want to learn how to get good at analyzing this23:07
azonenbergfor example, when you etch the etchant will get in under the Cu and undercut your mask23:07
swkhanchemistry? physics? what specifically should i study23:07
azonenbergmat sci? Not really sure23:07
swkhani read a whole book on chemistry but i'm not sure i'm prepared for it23:07
azonenbergMy undergrad degree was in comp sci23:07
swkhanoh wow23:07
swkhanmy undergrad was in EE (more circuits and programming)23:07
azonenbergswkhan: All of my EE background is self taught23:09
azonenbergi'm now a first year phd student also in comp sci lol23:09
azonenberghavent taken any ee classes whatsoever23:09
azonenbergonly engineering course i took was machine shop :P23:09
azonenbergRe etching, check out "Etch rates for micromachining processing, part ii" and the part 123:09
azonenbergthey're considered the bible of etching23:10
azonenbergMy preferred metal etch for Cu and Cr is a dilute version of SC2 from the RCA clean23:10
swkhanwell i want to keep it cheap, reproducible, and easy as possible23:10
azonenberg1 part conc. HCl, 6 parts 3% H2O2, 50 parts distilled or DI water23:10
swkhanoh that's easy and reproducible and cheap23:10
azonenbergetches at around 350-400nm/min23:11
azonenbergI'm not even using trace metal grad stuff23:11
swkhanso chromium helps stuff adhese for some reason23:11
swkhanmetal to silicon at least23:11
swkhani think i'd like to electroplate as that seems like the method that has the most chance for success given our lab setup23:11
swkhanwe have some acids23:12
swkhanwe have loads of copper tape and copper wire23:12
swkhanwe have fume hoods23:12
swkhanwe have a power supply23:12
swkhanwe have silicon and that's aluminum foil for shadow masking23:12
azonenbergYou dont mask the metal23:25
azonenbergDeposit metal everywhere23:25
azonenbergthen etch23:25
azonenbergfor electroplating you should be able to do a lift-off proces23:25
azonenbergdeposit photoresist over the entire wafer, expose, develop23:25
azonenbergthen electroplate23:25
azonenbergit'll only stick to the conductive (uncoated) areas23:26
azonenbergso wherever you have resist there's no metal23:26
azonenbergthen you dip it in solvent and you're done23:26
azonenbergBut like i said, see about getting down some chrome if you can possibly figure that out23:26
azonenbergi can virtually guarantee you will have adhesion problems without it23:26
azonenbergtake it from somebody who tried23:26
azonenbergThere are solutions out there for doing Cr plating23:27
azonenbergso i suggest you check them out23:27
azonenberglooks like you can use chromium chloride23:28
azonenbergThe benefit of liftoff is that you will be able to get by without etching, it eliminates a process step23:30
azonenbergthe downside is that you have to do all of your patterning at once23:30
nathan7azonenberg: I'm considering doing the selective plating trick for PCBs23:32
azonenbergnathan7: you mean lay down resist and plate up?23:32
azonenbergI'd be curious to see results23:32
nathan7then have Sn as a resist23:32
azonenberglet me know if you get around to it23:32
nathan7etch with persulphate23:33
nathan7need to order some SnCl2, dissolving Sn solder isn't cost-effective23:33
nathan7(probably most of that money ends up in the Ag powder that is a byproduct from the 3% Ag)23:33
azonenbergwhat about just pure Sn strips?23:34
nathan7was fun to make H2O2 fizz with homemade Ag catalyst though23:34
nathan73% H2O2, fizzed, fine23:34
azonenberg30? :P23:34
nathan73%. all I can buy here OTC23:35
azonenbergSame here23:35
azonenbergi'm told you can get 5-10% in some places as a hair bleach23:35
azonenbergbut 3% is all i need, in fact sometimes i dilute it23:35
azonenbergsince i want a slow and controllable etch23:35
nathan7I read US pharmacies have 35%23:36
azonenbergmaybe allowed to sell that highi23:36
azonenbergi called every one in town and nobody has it23:36
azonenbergalso, http://unitednuclear.com/index.php?main_page=product_info&cPath=16_17_69&products_id=20423:36
berndji can get 12% OTC here, just a random pharmacy23:36
azonenbergyou want something like that presumably23:36
berndjsome of the homebrew pcb guys were talking about 30% H2O2 at pool shops23:37
azonenbergberndj: i know people who have gotten up to 30% somewhere23:37
azonenbergbut i dont know where23:37
berndjbut i suspect they mistook "30 volume" for "30 percent"23:37
azonenbergthe strongest i've seen in supermarkets or drugstores is 3%23:37
azonenbergand i've seen enough of what it does on contact with things to know that this guy's 30% really was what the label said :P23:37
berndjrocket fuel23:38
azonenbergPretty much23:39
--- Sat Aug 27 201100:00

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