| azonenberg | http://www.lithoguru.com/scientist/litho_lite/ausschnitt/rapture.html | 00:09 |
|---|---|---|
| swkhan | hi =) | 20:20 |
| swkhan | i 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 copper | 20:20 |
| azonenberg | Ok | 20:20 |
| azonenberg | At what resolution | 20:20 |
| swkhan | i have silicon wafers. i have copper tape. i have copper wire. | 20:20 |
| azonenberg | How thick copper? | 20:20 |
| swkhan | i have phosphoric acid and sodium hydroxide | 20:20 |
| azonenberg | do you want | 20:21 |
| swkhan | i am not sure. rivaling something i could sputter | 20:21 |
| azonenberg | First off, be advised that copper doesnt stick well to Si by itself | 20:21 |
| azonenberg | You normally need a thin Cr adhesion layer | 20:21 |
| swkhan | why not? | 20:21 |
| swkhan | awww | 20:21 |
| azonenberg | And the only process i've gotten good results with is vacuum evaporation | 20:21 |
| swkhan | so electrochemical deposition wouldn't work? | 20:21 |
| azonenberg | Not in a cleanroom, using the one my school's mat sci department uses for SEM sample coating | 20:21 |
| swkhan | what happens if you don't have an adhesion layer? | 20:21 |
| azonenberg | evaporate 5nm Cr + 1000nm Cu without breaking vacuum | 20:21 |
| azonenberg | and it tends to peel off | 20:21 |
| azonenberg | you get more overetch | 20:21 |
| azonenberg | i've had 200nm films with tens of microns of overetch without the adhesion layer | 20:22 |
| swkhan | i don't have access to chromium. i am doing this because a sputtering machine we had broke | 20:22 |
| azonenberg | Do you have access to an evaporator? | 20:22 |
| azonenberg | Electroplating of Cr followed by Cu might work if your wafer is heavily doped | 20:22 |
| swkhan | i don't have access to an evaporator | 20:22 |
| swkhan | i think the wafers are heavily p doped. we also have heavily n doped wafers | 20:23 |
| swkhan | so i'd gotten part of a process ready in my head | 20:23 |
| swkhan | i just finished up reading a textbook that gives me the equivalent knowledge of 1 year's worth of chemistry | 20:24 |
| swkhan | and i feel like i don't know anything when it comes to applying it =\ | 20:24 |
| azonenberg | lol | 20:24 |
| azonenberg | I havent taken any chem either | 20:24 |
| azonenberg | And if they're heavily doped in general, you may have luck with electroplatnig | 20:24 |
| azonenberg | If you do, i'd be very interested in details so i can try duplicating the process | 20:24 |
| swkhan | but how does electroplating work with a semiconductor? | 20:24 |
| swkhan | sure, i was trying to come up with my own process | 20:24 |
| azonenberg | You have to have it doped heavily enough that you can make ohmic contacts | 20:24 |
| swkhan | everyone seems to use fancy electrolytic solutions | 20:25 |
| swkhan | may be for a reason... | 20:25 |
| azonenberg | Lol, yes | 20:25 |
| azonenberg | I focused on evaporation as i was depositing metal over a nonconductive surface | 20:25 |
| swkhan | i see | 20:26 |
| azonenberg | I want to build my own evaporator at some point but for now i'm using the one on campus | 20:26 |
| swkhan | cool! | 20:26 |
| azonenberg | Not 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 |
| azonenberg | so i just ordered some new filaments and 99.999% copper evaporation pellets from ted pella myself | 20:27 |
| swkhan | oooh | 20:27 |
| azonenberg | they were short on filaments last time i checked | 20:27 |
| azonenberg | In any case, i can definitely provide process development for etching | 20:30 |
| azonenberg | thats a reasonably well studied problem | 20:30 |
| azonenberg | What's your lithography setup look like? | 20:30 |
| swkhan | very crappy. i'm ms. super low budget =) | 20:31 |
| swkhan | i am masking with aluminum foil | 20:31 |
| swkhan | i'm not sure if it'll work | 20:31 |
| azonenberg | Where are you located? | 20:31 |
| swkhan | nasa ames (i work with ucsc) | 20:31 |
| azonenberg | And what kind of feature sizes are you trying to achieve | 20:31 |
| swkhan | to be PhD EE starting this fall =) | 20:31 |
| azonenberg | i mean, are you looking to hit 22nm or 25 microns :P | 20:32 |
| azonenberg | And do you have a spin coater? If not, as long as you dont need deep submicron resolution they're decently easy to hack together | 20:34 |
| azonenberg | I made one out of a 2x4, an electric drill, and a sanding wheel | 20:36 |
| azonenberg | that has given me good photoresist film quality down to 5 micron features (the smallest i've tried hitting with my exposure system) | 20:36 |
| lekernel | azonenberg, btw, could this spinning technique be used for PCBs as well? | 20:47 |
| lekernel | when you buy microwave-friendly PCB materials like duroid or alumina, they never come with photoresist | 20:48 |
| lekernel | this is quite annoying | 20:48 |
| azonenberg | lekernel: Yes | 20:55 |
| azonenberg | Dip coating is doable as well but requires a big tank | 20:55 |
| azonenberg | Spin coating of copper clad PCB is on the todo list | 20:55 |
| azonenberg | i have blank board but havent tried because i have so much precoated PCB :P | 20:55 |
| azonenberg | But the resist i have was sold for that purpose | 20:55 |
| azonenberg | ... oops you left? | 20:55 |
| azonenberg | (16:55:24) azonenberg: Dip coating is doable as well but requires a big tank | 21:10 |
| azonenberg | (16:55:32) azonenberg: Spin coating of copper clad PCB is on the todo list | 21:10 |
| azonenberg | (16:55:45) azonenberg: i have blank board but havent tried because i have so much precoated PCB :P | 21:10 |
| azonenberg | (16:55:52) azonenberg: But the resist i have was sold for that purpose | 21:10 |
| nathan7 | HI AZONENBERG | 21:51 |
| azonenberg | hi nathan7 | 21:52 |
| azonenberg | Do you have a GDS viewer program on hand? | 21:52 |
| nathan7 | GDS? | 21:52 |
| azonenberg | IC layout database | 21:52 |
| azonenberg | guess not :p | 21:52 |
| nathan7 | mhm | 21:53 |
| nathan7 | How so? | 21:53 |
| CIA-67 | homecmos r115 | trunk/lithography-tests/default_600dpi/ (7 files in 7 dirs) | Committing previous changes to existing test masks | 21:54 |
| azonenberg | I guess i'll just send you a screenshot then h/o | 21:54 |
| nathan7 | :o | 21:55 |
| nathan7 | isitisitA GRATING? | 21:55 |
| azonenberg | Going to be, i havent actually made it yet | 21:55 |
| nathan7 | :D | 21:55 |
| Action: nathan7 kisses azonenberg's feet | 21:55 | |
| Action: azonenberg disinfects feet with IPA | 21:56 | |
| nathan7 | hey | 21:56 |
| nathan7 | that's nazi | 21:56 |
| azonenberg | no, it's just the absence of a foot fetish :p | 21:57 |
| nathan7 | it is a sign of respect | 21:57 |
| azonenberg | In what culture? | 21:59 |
| nathan7 | dunno | 22:00 |
| azonenberg | Here are two different mask patterns I'm considering | 22:14 |
| azonenberg | The left is what i expect it will actually look like | 22:14 |
| azonenberg | the right is what i'll be exposing (compensating for overetch etc) | 22:14 |
| azonenberg | http://i.imgur.com/z76a7.png | 22:14 |
| azonenberg | 1.058 microns per pixel is the nominal scale | 22:15 |
| azonenberg | will be printed at 600DPI and then reduced 40x optically | 22:15 |
| nathan7 | mhm | 22:15 |
| nathan7 | aewesome | 22:15 |
| nathan7 | exciting | 22:16 |
| nathan7 | :D | 22:16 |
| azonenberg | nathan7: i should have those etched later today | 22:20 |
| azonenberg | i'll also be doing a PCB but the chemistry is similar enough i can use the same batches of developer and etchant | 22:20 |
| azonenberg | so it'll save me time | 22:20 |
| azonenberg | should be finished around 22:00 - 23:00 EDT | 22:21 |
| azonenberg | About time i did a proper line edge roughness test lol | 22:21 |
| nathan7 | mhm | 22:22 |
| nathan7 | it's 00:24 here | 22:22 |
| bart416 | btw, in case you're interested in it, a low powered pulsed UV laser is enough to expose photoresist it seems | 22:22 |
| bart416 | Can't say much about the resolution yet cause I don't have the right optics for it | 22:22 |
| azonenberg | define low powered | 22:23 |
| azonenberg | 5 mW? 5 kW? :P | 22:23 |
| bart416 | low as in I found it in my desk low, lol | 22:23 |
| azonenberg | And 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 |
| bart416 | direct write at the moment | 22:24 |
| azonenberg | direct write laser is a tech i've wanted to explore for a long time | 22:24 |
| nathan7 | that | 22:24 |
| nathan7 | is | 22:24 |
| azonenberg | but been too busy | 22:24 |
| nathan7 | so | 22:24 |
| nathan7 | cool | 22:24 |
| bart416 | Well I wanted to see if it was even possible | 22:24 |
| azonenberg | Oh | 22:24 |
| bart416 | And looks like it works | 22:24 |
| azonenberg | I already ran the math, it's definitely doable | 22:24 |
| bart416 | the laser exposed it sufficiently to develop | 22:24 |
| berndj | you have a UV laser in your drawer?? | 22:24 |
| azonenberg | a blu-ray diode on a micron square spot was something like 1ms exposure required | 22:25 |
| bart416 | but wasn't focused enough obviously | 22:25 |
| bart416 | berndj, you don't want to know what I have in my desk drawers... | 22:25 |
| azonenberg | maybe less | 22:25 |
| bart416 | Actually maybe you do | 22:25 |
| berndj | oh wait, does bluray use UV? | 22:25 |
| azonenberg | berndj: 405nm | 22:25 |
| azonenberg | long UV | 22:25 |
| berndj | close enough | 22:25 |
| bart416 | bluray laser could probably do the trick, but depends on the resist | 22:25 |
| azonenberg | its not 197nm DUV | 22:25 |
| azonenberg | but for most DNQ-novolac resists anything in the 365-405nm range will work well | 22:26 |
| azonenberg | mercury vapor H- to I-line | 22:26 |
| bart416 | An electron gun assembly form a crt, a vidicon tube, copper windings from that crt it seems, 10 nixie tubes | 22:26 |
| berndj | at least normal glass-based optics should still work at 405nm | 22:26 |
| bart416 | a roll of electric cable from a vacuum cleaner I disassembled | 22:26 |
| bart416 | two floppy drives | 22:26 |
| bart416 | CCFL inverters | 22:26 |
| azonenberg | Lol - the desk i'm sitting at right now is pure office | 22:26 |
| bart416 | an old soldering iron | 22:26 |
| azonenberg | the workbench in the other room is where all of the fun stuff is | 22:27 |
| bart416 | apperantly water based paint for kids | 22:27 |
| bart416 | some dremel tools | 22:27 |
| bart416 | hot glue gun | 22:27 |
| bart416 | parts of what I think used to be a computer psu | 22:27 |
| bart416 | 1ohm 5W resistors, too much to count | 22:27 |
| bart416 | A dev board of something | 22:27 |
| bart416 | hd platers | 22:27 |
| bart416 | neodynium magnets | 22:27 |
| bart416 | antistatic screen cleaner that I use to clean my whiteboards | 22:27 |
| bart416 | enough duct tape to fix anything in the universe except my love life | 22:28 |
| bart416 | several pens | 22:28 |
| bart416 | a green laser pointer from dx that is advertised as 5mW but actually puts out about 100mW | 22:28 |
| bart416 | two sets of callipers | 22:28 |
| bart416 | dentist mirror | 22:28 |
| berndj | 100mW of green, or 100mW of IR? | 22:28 |
| bart416 | Good question | 22:28 |
| bart416 | We only compared the intensity with a 100mW one | 22:29 |
| berndj | or, how do you know it's 100mW? | 22:29 |
| bart416 | Not the spectrum | 22:29 |
| bart416 | Should do that again | 22:29 |
| bart416 | well, if it manages to trigger the same displacement in a light intensity meter at same distance | 22:29 |
| bart416 | Then it tends to be about the same | 22:29 |
| bart416 | Needles as well it seems | 22:30 |
| bart416 | An old ring I didn't wish I found | 22:30 |
| bart416 | My keys that I lost months ago | 22:30 |
| bart416 | nail clippers, yay | 22:30 |
| bart416 | a roll meter of 2m | 22:30 |
| berndj | i imagine 100mW of green would be pretty damn intense - maybe even visible scattering in air | 22:30 |
| bart416 | a spoon | 22:30 |
| bart416 | You can see the beam in the air | 22:30 |
| berndj | wow | 22:31 |
| bart416 | It also damages cheap cmos sensors | 22:31 |
| bart416 | enough 7400 series logic to build a small 1960s era mainframe | 22:31 |
| bart416 | an old PS/2 mouse | 22:31 |
| bart416 | a snickers bar | 22:31 |
| bart416 | desoldering braid | 22:31 |
| bart416 | some lcd screens | 22:31 |
| berndj | either way, i imagine it IS just a doubled Nd:YAG filtering out many more hundreds of mW or IR | 22:31 |
| bart416 | A tuner for my guitar that I lost months ago as well | 22:32 |
| bart416 | pencils | 22:32 |
| bart416 | rolls of solder | 22:32 |
| bart416 | And I'll have to start digging if I want to see more | 22:32 |
| bart416 | That's what's immediately vissible in my drawers | 22:33 |
| bart416 | As a matter of fact I also know I have coppersulfate crystals in there somewhere in a sealed bottle | 22:33 |
| bart416 | And a silver ring | 22:33 |
| bart416 | (That I do want to find but can't be bothered to look for) | 22:34 |
| bart416 | Due to the risk of getting stabbed by sewing needles that are near the bottom near the ring | 22:34 |
| bart416 | Also a breadboard and a sponge apperantly | 22:34 |
| bart416 | And some steppers | 22:34 |
| bart416 | And elastics from when I used to wear braces | 22:35 |
| bart416 | and average office supplies as well I guess | 22:35 |
| bart416 | So I told you what's in my desk | 22:36 |
| bart416 | Now your turn :P | 22:36 |
| Action: bart416 pokes berndj | 22:37 | |
| nathan7 | well damn | 22:39 |
| nathan7 | 00:36:54 < bart416> And elastics from when I used to wear braces | 22:39 |
| Action: nathan7 puts the goddamn things on | 22:39 | |
| azonenberg | lol | 22:40 |
| berndj | my turn? oh, i, erm, i don't have anything interesting | 22:40 |
| berndj | i don't have drawers! | 22:40 |
| nathan7 | oh the curses of being a teenager :| | 22:40 |
| azonenberg | Lol, in *this* desk? A slide rule, MIPS instruction set reference, some old graphing calculators | 22:41 |
| azonenberg | tons of batteries ranging from AAA to LiPo for my laptop | 22:41 |
| nathan7 | o: | 22:41 |
| berndj | only a PM tube, a 1000A fuse, selenium rectifiers, boring stuff in my junkboxes! | 22:41 |
| azonenberg | a big stack of targets from rifle club last semester | 22:41 |
| azonenberg | assorted office supplies | 22:41 |
| azonenberg | and thats about it | 22:41 |
| azonenberg | all of the fun stuff is over in the lab | 22:41 |
| berndj | looks like if i want to do photo pcb process i'll have to suck it up and find dnq | 22:43 |
| azonenberg | berndj: where you located? | 22:43 |
| berndj | that's the "normal" pcb PR, right? | 22:43 |
| azonenberg | I believe so, yes | 22:43 |
| berndj | south africa | 22:43 |
| azonenberg | its what i've been using for all of my fab | 22:43 |
| azonenberg | and cant help you donw there | 22:43 |
| azonenberg | only supplier i know outside of large chemical companies is a reseller about 50 miles from Albany, NY | 22:44 |
| berndj | yeah. everything's available, from china, if you want kiloliter quantities | 22:44 |
| azonenberg | These guys will sell - to USA at least - in 2, 4, 8, 16 fluid ounce volumes | 22:44 |
| berndj | some shops have a spray, but i'm suspicious of that and balk at the price | 22:44 |
| azonenberg | presumably bought by the liter (or more) and repackaged | 22:44 |
| azonenberg | i do not suggest a spray | 22:44 |
| azonenberg | spin coating ftw | 22:44 |
| berndj | ok. what's wrong with spray? pinholes? | 22:45 |
| azonenberg | Thats a guess | 22:45 |
| azonenberg | although i admit i havent tested | 22:45 |
| azonenberg | But there's a reason semiconductor work uses spinning :p | 22:45 |
| bart416 | Actually, just spotted the ring and managed to pull it out with a tweezer | 22:45 |
| bart416 | lol | 22:45 |
| bart416 | Spray won't give a nice equal distribution | 22:45 |
| berndj | for now i'll just try toner transfer though | 22:46 |
| berndj | i'll take the build-a-receiver route to getting my ham licence | 22:47 |
| bart416 | Just study for the exam | 22:49 |
| berndj | yeah, gotta do that also | 22:49 |
| berndj | i want the first class licence, not the baby one you get just from passing the exam | 22:49 |
| swkhan | does anyone know of a spray can that sprays metal? | 22:52 |
| swkhan | i want to be able to deposit metal contacts using it | 22:52 |
| azonenberg | swkhan: How thick? | 22:52 |
| azonenberg | You can spin coat some metallic solutions | 22:52 |
| azonenberg | But they're gonna be reeeally thin | 22:52 |
| azonenberg | http://www.emulsitone.com/auf.html | 22:52 |
| swkhan | really think is okay | 22:53 |
| swkhan | purity is more important i think | 22:53 |
| azonenberg | 10nm? | 22:53 |
| azonenberg | :P | 22:53 |
| swkhan | maybe okay | 22:53 |
| swkhan | not sure | 22:53 |
| azonenberg | What are you using it for | 22:53 |
| azonenberg | in any case goldfilm is around $500 per 4-ounce bottle last i checked | 22:54 |
| azonenberg | prices vary based on raw material costs | 22:54 |
| azonenberg | it should last you a long time if my experience with tantalumfilm (which actually deposits Ta2O5, not Ta) is any hint | 22:54 |
| swkhan | i still want to deposit some sort of metal onto my nano scale device | 22:54 |
| azonenberg | Sputtering or evaporation is really the best bet | 22:54 |
| swkhan | =( | 22:54 |
| azonenberg | electroplating, among other things | 22:54 |
| swkhan | i'm trying to be creative and use any other methods i've got | 22:55 |
| azonenberg | means that you cannot deposit over an insulator | 22:55 |
| bart416 | You can get metalic paint that's slightly conductive | 22:56 |
| azonenberg | bart416: that's a resin with silver flakes etc in it | 22:56 |
| azonenberg | i could not recommend it for anything small | 22:56 |
| azonenberg | "small" meaning <20 um | 22:56 |
| bart416 | ah | 22:57 |
| bart416 | if it's less than 100 µm plating is your only option | 22:57 |
| azonenberg | swkhan: you still havent told us the feature size and layer thicknesses you'e trying for | 22:57 |
| azonenberg | that makes a huge difference | 22:58 |
| swkhan | i 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 better | 22:58 |
| bart416 | If it's for coating a large object, plate if it's already metalic, else first ensure it's metallic by spray painting it, then plate | 22:58 |
| swkhan | at least less than 0.5 mm | 22:58 |
| bart416 | yeah, plating for sure | 22:59 |
| azonenberg | swkhan: 500 um? Oh, thats nothing | 22:59 |
| azonenberg | swkhan: I have hit 20um features using a living-room lithography rig | 22:59 |
| swkhan | let's say 20 um with shadow mask? | 22:59 |
| azonenberg | and am pushign to 5 | 22:59 |
| swkhan | wow | 22:59 |
| bart416 | Reminds me, I need to go and steal some CNC position encoder tomorrow | 23:00 |
| azonenberg | as in, my first and only attempt at 5um litho was last lab session | 23:00 |
| azonenberg | i overdeveloped :( | 23:00 |
| swkhan | okay 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 insulator | 23:00 |
| azonenberg | http://colossus.cs.rpi.edu/~azonenberg/images/homecmos/2011-08-06/S7301603.JPG | 23:00 |
| azonenberg | swkhan: 20um per pixel | 23:00 |
| azonenberg | evaporated Cu on Si | 23:00 |
| bart416 | could be worse azonenberg | 23:00 |
| swkhan | aww evaporated... | 23:00 |
| azonenberg | ~1000nm Cu over ~5nm Cr | 23:00 |
| azonenberg | done in one step from two sources w/o breaking vacuum | 23:01 |
| nathan7 | :> | 23:01 |
| azonenberg | and ok, so you want to deposit an insulator | 23:01 |
| azonenberg | Do you have one in mind? | 23:01 |
| azonenberg | Or at least a deposition process? | 23:01 |
| nathan7 | ooh | 23:01 |
| nathan7 | when your MEMS works, azonenberg, could you make it switch two beams? | 23:01 |
| azonenberg | SiO2 for example can be formed by processes ranging from PECVD of SiH4 to sol-gel deposition | 23:01 |
| azonenberg | nathan7: you mean a relay of some sort? | 23:01 |
| swkhan | i have the insulator deposition process down. cvd | 23:01 |
| nathan7 | azonenberg: yeah | 23:01 |
| nathan7 | azonenberg: for light | 23:01 |
| swkhan | i was just wondering how i can get a metal contact | 23:02 |
| swkhan | doesn't have to be deposited | 23:02 |
| azonenberg | ok, so now i'm starting to get the picture | 23:02 |
| nathan7 | azonenberg: so I could alternately spectrometer a reference and a sample | 23:02 |
| azonenberg | you have access to CVD SiO2 | 23:02 |
| swkhan | sorry it took me so long to explain azonenberg =\ | 23:02 |
| azonenberg | you have blank wafers | 23:02 |
| swkhan | i have blank wafers | 23:02 |
| azonenberg | and you want to put metal directly on top of the Si | 23:02 |
| swkhan | yes but not using the cvd | 23:02 |
| azonenberg | Do you have any need to deposit metal over a dielectric layer? | 23:02 |
| swkhan | just out in the open in a fume hood or something | 23:02 |
| swkhan | i do, yes | 23:03 |
| nathan7 | azonenberg: http://upload.wikimedia.org/wikipedia/commons/1/17/IR_spectroscopy_apparatus.svg | 23:03 |
| azonenberg | That rules out electroplating | 23:03 |
| berndj | speaking of vacuum tech, i must practice welding some more | 23:03 |
| swkhan | azonenberg: awww. no way around it? | 23:03 |
| azonenberg | nathan7: MEMS micromirror is a possibility for that | 23:03 |
| nathan7 | azonenberg: mhm | 23:03 |
| azonenberg | swkhan: There are some theoretically possible ways | 23:03 |
| azonenberg | You could spin coat with goldfilm or something similar to make a thin conductive surface over the dielectric | 23:03 |
| swkhan | what about silver conducting pens | 23:03 |
| azonenberg | and then electroplate up | 23:03 |
| berndj | azonenberg, do you have any plans for metal contacts yet? | 23:03 |
| bart416 | swkhan, silver is easy enough to deposit normally | 23:04 |
| azonenberg | silver pens? Depends on your feature size | 23:04 |
| azonenberg | they're silver flakes in a resin | 23:04 |
| azonenberg | as your feature size approaches flake size you'll get problems | 23:04 |
| swkhan | i am afraid that my deposited insulator might break off or something | 23:04 |
| bart416 | Gold is where it gets tricky generally | 23:04 |
| azonenberg | i also am not sure about patterning it | 23:04 |
| swkhan | that was one thing i was considering... patterning | 23:04 |
| azonenberg | swkhan: You are worried about adhesion between the CVD SiO2 and the metal? | 23:04 |
| azonenberg | Or the SiO2 and the underlying Si where you dont have metal | 23:05 |
| swkhan | well i want a top and bottom contact | 23:05 |
| swkhan | so initially yes on sio2 | 23:05 |
| azonenberg | Let me get this straight | 23:05 |
| swkhan | and then on some insulator's top side | 23:05 |
| azonenberg | your device consists of silicon, a metal layer, a dielectric layer, and another metal layer | 23:05 |
| swkhan | yes | 23:05 |
| azonenberg | Ok | 23:05 |
| azonenberg | Tackling 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 films | 23:06 |
| swkhan | ideally i'd like to use the same process for both the top contact and the bottom contact | 23:06 |
| swkhan | how do you know that the adhesion of metal onto silicon isn't bad? | 23:06 |
| azonenberg | I've worked with evaporated Cu over Cr adhesion layers | 23:06 |
| azonenberg | you can put scotch tape onto the die and press it on | 23:06 |
| swkhan | why does chromium keep coming up? | 23:06 |
| azonenberg | then pull off and the metal wont peel | 23:06 |
| swkhan | huh cool | 23:07 |
| azonenberg | Because without the Cr the Cu peels off | 23:07 |
| azonenberg | It wont do so spontaneously but under the slightest provocation it will | 23:07 |
| swkhan | what aspect of science tells you about this stuff? | 23:07 |
| swkhan | i want to learn how to get good at analyzing this | 23:07 |
| azonenberg | for example, when you etch the etchant will get in under the Cu and undercut your mask | 23:07 |
| swkhan | chemistry? physics? what specifically should i study | 23:07 |
| azonenberg | mat sci? Not really sure | 23:07 |
| swkhan | i read a whole book on chemistry but i'm not sure i'm prepared for it | 23:07 |
| azonenberg | My undergrad degree was in comp sci | 23:07 |
| swkhan | oh wow | 23:07 |
| swkhan | my undergrad was in EE (more circuits and programming) | 23:07 |
| azonenberg | swkhan: All of my EE background is self taught | 23:09 |
| azonenberg | i'm now a first year phd student also in comp sci lol | 23:09 |
| azonenberg | havent taken any ee classes whatsoever | 23:09 |
| azonenberg | only engineering course i took was machine shop :P | 23:09 |
| swkhan | wow!!! | 23:09 |
| azonenberg | Re etching, check out "Etch rates for micromachining processing, part ii" and the part 1 | 23:09 |
| azonenberg | they're considered the bible of etching | 23:10 |
| azonenberg | My preferred metal etch for Cu and Cr is a dilute version of SC2 from the RCA clean | 23:10 |
| swkhan | well i want to keep it cheap, reproducible, and easy as possible | 23:10 |
| azonenberg | 1 part conc. HCl, 6 parts 3% H2O2, 50 parts distilled or DI water | 23:10 |
| swkhan | oh that's easy and reproducible and cheap | 23:10 |
| azonenberg | etches at around 350-400nm/min | 23:11 |
| azonenberg | I'm not even using trace metal grad stuff | 23:11 |
| swkhan | so chromium helps stuff adhese for some reason | 23:11 |
| swkhan | metal to silicon at least | 23:11 |
| swkhan | i think i'd like to electroplate as that seems like the method that has the most chance for success given our lab setup | 23:11 |
| swkhan | we have some acids | 23:12 |
| swkhan | we have loads of copper tape and copper wire | 23:12 |
| swkhan | we have fume hoods | 23:12 |
| swkhan | we have a power supply | 23:12 |
| swkhan | we have silicon and that's aluminum foil for shadow masking | 23:12 |
| azonenberg | You dont mask the metal | 23:25 |
| azonenberg | Deposit metal everywhere | 23:25 |
| azonenberg | then etch | 23:25 |
| azonenberg | for electroplating you should be able to do a lift-off proces | 23:25 |
| azonenberg | deposit photoresist over the entire wafer, expose, develop | 23:25 |
| azonenberg | then electroplate | 23:25 |
| azonenberg | it'll only stick to the conductive (uncoated) areas | 23:26 |
| azonenberg | so wherever you have resist there's no metal | 23:26 |
| azonenberg | then you dip it in solvent and you're done | 23:26 |
| azonenberg | But like i said, see about getting down some chrome if you can possibly figure that out | 23:26 |
| azonenberg | i can virtually guarantee you will have adhesion problems without it | 23:26 |
| azonenberg | take it from somebody who tried | 23:26 |
| azonenberg | There are solutions out there for doing Cr plating | 23:27 |
| azonenberg | so i suggest you check them out | 23:27 |
| azonenberg | looks like you can use chromium chloride | 23:28 |
| azonenberg | The benefit of liftoff is that you will be able to get by without etching, it eliminates a process step | 23:30 |
| azonenberg | the downside is that you have to do all of your patterning at once | 23:30 |
| nathan7 | azonenberg: I'm considering doing the selective plating trick for PCBs | 23:32 |
| azonenberg | nathan7: you mean lay down resist and plate up? | 23:32 |
| nathan7 | mhm | 23:32 |
| azonenberg | I'd be curious to see results | 23:32 |
| nathan7 | then have Sn as a resist | 23:32 |
| azonenberg | let me know if you get around to it | 23:32 |
| nathan7 | etch with persulphate | 23:33 |
| nathan7 | need to order some SnCl2, dissolving Sn solder isn't cost-effective | 23:33 |
| azonenberg | lol | 23:33 |
| nathan7 | (probably most of that money ends up in the Ag powder that is a byproduct from the 3% Ag) | 23:33 |
| azonenberg | what about just pure Sn strips? | 23:34 |
| nathan7 | was fun to make H2O2 fizz with homemade Ag catalyst though | 23:34 |
| nathan7 | 3% H2O2, fizzed, fine | 23:34 |
| azonenberg | 30? :P | 23:34 |
| nathan7 | 3%. all I can buy here OTC | 23:35 |
| azonenberg | Same here | 23:35 |
| azonenberg | i'm told you can get 5-10% in some places as a hair bleach | 23:35 |
| azonenberg | but 3% is all i need, in fact sometimes i dilute it | 23:35 |
| azonenberg | since i want a slow and controllable etch | 23:35 |
| nathan7 | I read US pharmacies have 35% | 23:36 |
| azonenberg | maybe allowed to sell that highi | 23:36 |
| azonenberg | i called every one in town and nobody has it | 23:36 |
| azonenberg | also, http://unitednuclear.com/index.php?main_page=product_info&cPath=16_17_69&products_id=204 | 23:36 |
| berndj | i can get 12% OTC here, just a random pharmacy | 23:36 |
| azonenberg | you want something like that presumably | 23:36 |
| berndj | some of the homebrew pcb guys were talking about 30% H2O2 at pool shops | 23:37 |
| azonenberg | berndj: i know people who have gotten up to 30% somewhere | 23:37 |
| azonenberg | but i dont know where | 23:37 |
| berndj | but i suspect they mistook "30 volume" for "30 percent" | 23:37 |
| azonenberg | the strongest i've seen in supermarkets or drugstores is 3% | 23:37 |
| azonenberg | and 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 :P | 23:37 |
| berndj | rocket fuel | 23:38 |
| azonenberg | Pretty much | 23:39 |
| --- Sat Aug 27 2011 | 00:00 | |
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