#homecmos IRC log for Monday, 2011-07-18

--- Mon Jul 18 201100:00
Laurencebhi14:16
Laurencebdidnt know there was a channel for this :P14:16
Laurencebi was thinking about how it might be possible to make a small chip fab for rapid prototyping14:16
Laurencebhas anyone looked at colloidal microjets?14:17
azonenbergLaurenceb: Not that I know of14:20
azonenbergMy current focus is MEMS14:20
Laurencebyeah14:20
azonenbergI have a 20 micron photolithography process working decently well and am in the process of working out some yield issues in a tantalum oxide hardmask14:20
azonenbergto be used for KOH wet etch14:20
Laurencebwow14:20
Laurencebi was interested in the possiblility of avoiding masks14:20
azonenbergHoping to have the body of a comb drive (i.e. minus metal layers) by end of summer14:20
Laurenceband directly printing14:21
azonenbergDirect write is interesting but wont get you good resolution14:21
Laurencebcolloidal microjets can get very small14:21
azonenbergOn say a 600dpi laser printer your lambda (smallest addressible pixel size) is around 42 microns14:21
azonenbergand your design rule is normally 4-5 pixels14:21
azonenbergI do 10x or 40x optical reduction on that to get either a 20 or 5 micron design rule14:22
Laurencebyeah, i was thinking build from scratch14:22
Laurencebthats impressive stuff14:22
azonenbergPhotolithography is the de facto standard method for a reason :P14:22
azonenbergIf you want to avoid masks you're better off using maskless lithography of some sort14:23
azonenbergmeaning e-beam or (more affordable) laser direct write14:23
Laurencebhttp://en.wikipedia.org/wiki/Colloid_thruster14:23
Laurencebhmm yeah14:23
Laurencebion implantation looks promising14:23
azonenbergI actually was going to use diffusion14:24
azonenbergEmulsitone sells spin coatable solutions of dopants14:24
azonenbergI would deposit those over a photoresist film and pattern by liftoff (or deposit under followed by an HF wet etch)14:24
azonenbergthen diffuse in a furnace14:24
Laurencebwow http://www.mtixtl.com is cheap14:27
Laurencebdidnt realise bare wafers were affordable14:27
azonenbergYes, MTI is my main supplier for a lot of stuff14:27
azonenbergNot sure if this is where you found it or not, but i'm building a list of vendors on the googlecode site14:28
Laurencebyeah i saw14:28
azonenbergI also have my lab notes in the repository14:28
azonenberghttp://code.google.com/p/homecmos/source/browse/trunk/lithography-tests/labnotes/azonenberg_labnotes.txt?spec=svn101&r=101 is the current version14:28
azonenberghttp://colossus.cs.rpi.edu/~azonenberg/images/homecmos/ is where i upload photos from lab sessions14:29
azonenbergMost of these are unmagnified or through one of my light microscopes but i did get two sessions on a SEM on campus to help debug a yield problem14:29
Laurenceblooks a bit messy14:34
Laurencebhttp://colossus.cs.rpi.edu/~azonenberg/images/homecmos/2011-07-05/die_f6/die_f6_002.jpg14:34
Laurencebhttp://colossus.cs.rpi.edu/~azonenberg/images/homecmos/2011-07-05/die_f6/die_f6_004.jpg14:35
Laurenceb^whats that showing?14:35
kristianpaulhi Laurenceb14:36
Laurencebhi14:36
azonenbergLet's see, die F6...14:38
azonenbergDark gray background is silicon14:38
azonenbergLighter gray is tantalum chloride (Emulsitone Tantalumfilm, which would, later in processing, be baked to oxidize it into tantalum oxide to be used as a hardmask)14:39
azonenbergThe white particles on the background are also under the tantalum layer, causing serious cracking which was destroying my yields for a while14:40
azonenbergThe SEM imaging session was intended to diagnose the source of the cracks14:40
azonenbergI eventually traced it to silicon dust left over from cleaving the wafer into indididual dies14:40
azonenbergI had done an RCA clean on some of the dies, which didnt seem to make a difference, so i had ruled out chemical contamination14:40
azonenbergBut large (micron or more) particulates wont be removed by an RCA clean14:41
azonenbergAnd i knew there were too many to be room dust14:41
azonenbergI finally identified the contaminant when EDS on a contaminated area showed nothing but silicon14:41
azonenbergI had initially thought it wasnt sensitive enough to pick up the contaminant14:41
azonenbergthen i realized the contaminant might actually BE silicon14:41
LaurencebESD?14:42
Laurencebi mean eds14:42
azonenbergEnergy dispersive X-ray spectroscopy14:42
Laurencebah14:42
azonenbergYou hit the sample with an electron beam like in imaging, but you read x-rays coming off the sample14:42
Laurencebso those cracks are due to the dust?14:42
azonenbergThe electrons in the atoms are excited and then drop down to a lower energy level, fluorescing in the process14:42
azonenbergby measuring the x-ray energy level you can identify elements (but not compounds)14:42
azonenbergAnd correct14:43
azonenbergThe coating is made by depositing tantalum chloride dissolved in ethanol by spin coating14:43
azonenbergAs it dries, it cracks alogn the edges of the particle14:43
Laurencebi see14:43
azonenbergRe EDS here's a sample result from the next day's session http://colossus.cs.rpi.edu/~azonenberg/images/homecmos/2011-07-11/die_f6/eds04.htm14:44
Laurencebwhat are the probes for?14:45
azonenbergThe guy who runs the electron microscopy lab at my school is very supportive of my work and is willing to give me a few hours of scope time here and there for free :)14:45
azonenbergAnd even if i need more, its only $45 an hour which i can afford (as compared to almost $200/hr for the nice Zeiss in the cleanroom, which i clearly cant afford :P )14:45
azonenbergThe probes are for doing testing of finished devices14:45
azonenbergi dont have a wire bonder14:45
azonenbergI do, however, have a wentworth labs probing station and a couple of micropositioners14:46
azonenbergThis is me practicing by hitting a test point on the side of a small surface mount part (the copper or gold pad the right-hand probe is hitting is about 25 microns square) http://colossus.cs.rpi.edu/pictures/2011/July/7-12-2011%20-%20LGA/S7301366.JPG14:46
Laurencebare there spin coater photos?14:49
azonenbergNot sure if i have any of the current one uploaded14:49
azonenbergIt's a sanding wheel mounted on top of an electric drill14:50
azonenbergKinda bulky but works14:50
azonenbergI plan to shrink it significantly and make one built on a CPU fan14:50
azonenbergintended for single dies rather than whole wafers14:50
azonenbergI'm also planning to build a small fume hood for doing coating, etching, and similar stuff in14:51
azonenbergbasically a 1x2x2 foot plastic box with an opening in the front and a fan on top14:52
azonenbergEither venting outside or through an activated charcoal filter, details TBD14:52
azonenbergPlans will be uploaded as soon as i actually have some time to work on the design14:52
azonenbergRe spin coater, http://i.imgur.com/15JiV.jpg is a shot of my current one (slightly older)14:53
azonenbergThe wafer on top isnt mine, its a random 4-inch a friend got off ebay to use as a mechanical dummy14:53
azonenbergBut as you can see the coater is capable of handling a full 4-inch wafer14:54
azonenbergIts mounted by double sided tape14:54
azonenbergAt the time i took this photo i was using a glass bell jar as a spatter shield, note the circular photoresist drip pattern on the base14:54
azonenbergSince then i've switched to a cardboard lip stapled around the sides of the base14:54
azonenbergit lets me easily reach onto the chuck to drip more solution onto a spinning wafer without risking a change of shirt color :P14:55
Laurencebinteresting15:05
azonenbergHeading out to work (a bit late as is), if you have any further questions leave them here and i'll respond this afternoon15:06
Laurencebi dont understand spin coating15:06
Laurencebok15:06
azonenberg_workSo I've arranged access to a vacuum evaporator on campus17:25
azonenberg_workI'll be evaporating around 100nm of copper onto some microscope slides as a test17:26
azonenberg_workHalf of them will have PR already on them (lift-off process)17:26
azonenberg_workand the other half will be uncoated (to be patterned by etching)17:26
azonenberg_workThen i'll etch them in SC2 and lift the other ones off in acetone17:27
azonenberg_workSee what kind of resolutions i can hit17:27
azonenberg_workOn the menu for tonight... sample prep for my evaporation session plus another experiment using thinner photoresist layers17:57
Laurenceb_hi18:26
Laurenceb_i guess i dont understand CMOS very well, does there have to be a intermediate metal layer between the aluminium and the silicon?18:27
azonenberg_workLaurenceb_: Do you mean for transistor contacts?18:45
azonenberg_workOr for wiring at higher levels18:46
azonenberg_workThere's normally a silicon dioxide dielectric layer between the silicon and any wiring18:46
Laurenceb_the transistor contacts18:46
azonenberg_workThe only time you break it is for vias between wiring layers18:46
azonenberg_workOr for transistor contacts18:46
Laurenceb_surely for VCC/VSS you need contacts18:46
azonenberg_workThe gate doesnt actually touch anything, its just floating right above the channel18:46
Laurenceb_yeah sure18:46
azonenberg_workBut yes, for the source/drain you do18:46
Laurenceb_how does that work?18:46
azonenberg_workI actually havent looked into that yet, I do know that you need to contact the silicon somehow18:47
azonenberg_workI also know that if you do it wrong you can form schottky diodes18:47
azonenberg_workBut i'm actually not sure what the right way is18:47
Laurenceb_presumably you need to take off the oxide18:47
azonenberg_workLike i said my current work is on basic 2D patterning and MEMS18:47
azonenberg_workAnd native oxide is trivial to strip18:47
azonenberg_work15 sec in dilute HF18:47
Laurenceb_interesting18:48
Laurenceb_http://iroi.seu.edu.cn/books/asics/Book2/CH02/CH02.2.htm18:48
Laurenceb_apparently commercially they use polysilicon deppsition?18:48
Laurenceb_maybe you could directly PVD onto the silicon with aluminium18:48
Laurenceb_in a vacuum after stripping18:48
azonenberg_workSo they use platinum as the barrier layer before connecting18:49
azonenberg_workAnd poly is used for the gates18:49
Laurenceb_ah i see18:49
azonenberg_workI would be doing vacuum evaporation, which is a form of PVD18:49
azonenberg_workfor both metals and poly18:49
Laurenceb_yeah18:49
azonenberg_worki actually have some Si crystals for evaporation now18:49
Laurenceb_ive seem a machine for that18:49
Laurenceb_its quite simple really18:49
azonenberg_workBut i havent built the evaporator itself18:49
azonenberg_workI get to play with one on campus on thursday18:49
Laurenceb_ive modified one for degassing resin18:50
azonenberg_workto metalize some microscope slides (sample substrate) for testing my metal process18:50
azonenberg_workThe next step would be to buy myself a diffusion pump18:50
Laurenceb_is the polysilicon really required?18:51
azonenberg_workI could potentially use metal gates as well18:51
azonenberg_workBut i'd still need an evaporator18:51
Laurenceb_there are chemical alu coating techniques18:52
azonenberg_workI want to do patterning by liftoff though18:52
Laurenceb_i was working with pressure sensors recently18:53
azonenberg_workInteresting18:53
Laurenceb_they seem quite simple - thin etched layer on a wafer18:53
azonenberg_workYeah18:53
azonenberg_workI want to build a comb drive, which is nearly as simple18:53
Laurenceb_might be worth a try at making one18:53
azonenberg_workone KOH etch into <110> Si and one metal etch18:53
azonenberg_workKOH etching is proving painful due to the hardmask not playing nicely18:54
Laurenceb_thats the crystal plane direction?18:54
azonenberg_workCorrect18:54
azonenberg_workKOH eats <100> super fast and <110> almost as fast, but <111> almost not at all18:54
azonenberg_workvery anisotropic18:54
Laurenceb_does that mean you can do deep etching ?18:55
azonenberg_workIn <110> surfaces, the <111> planes are near vertical18:55
azonenberg_workSo yes18:55
azonenberg_workYou can get 10:1 aspect ratios or better18:55
azonenberg_workWith a *wet etch*18:55
azonenberg_workDoing that with deep RIE or something is trivial, but thats way beyond my capabilities at home18:55
azonenberg_workA wet etch, OTOH, is very feasible18:55
Laurenceb_i was looking at micro anemometers for uavs18:56
azonenberg_workI've tried several times but in all cases the hardmask was cracked or for whatever reason didnt go where it was supposed to18:56
azonenberg_workAnd very interesting18:56
Laurenceb_using hot elements18:56
azonenberg_workMeasuring airflow by the delta T between one shielded from air and one that isnt?18:57
Laurenceb_yes18:57
Laurenceb_ive tried it with grain of rice lamps18:57
azonenberg_workThat sounds like a fairly simple MEMS project18:57
azonenberg_workWithin reach of a process like this in a year or so18:57
Laurenceb_with glass removed18:57
azonenberg_workThis is exactly the kind of stuff that i want to be able to do18:57
azonenberg_workVery simple ICs or MEMS, as one-off prototypes etc18:58
bart416azonenberg, I intend to surpass your madness!18:58
azonenberg_workbart416: If you get a 350nm fab in your garage send me pics :OP18:58
azonenberg_work:P *18:58
azonenberg_workBecause thats my ultimate goal for 10-20 years out18:58
azonenberg_workAt least submicron for sure18:58
bart416I'm writing up purposal for my master thesis18:58
bart416Atomic scale circuits18:59
bart416Built using a computer controlled stm18:59
azonenberg_workRight now the smallest geometry i've fabbed in anything was 5um (photoresist, not etched into anything)18:59
azonenberg_workAnd 20um is the smallest feature i've done in Si18:59
bart416does that surpass your madness,18:59
azonenberg_workIt's a tie, at least18:59
azonenberg_workLet me know how it goes18:59
bart416I wonder if such an idea would be approved19:00
azonenberg_workHow would you test said devices?19:00
azonenberg_workUse STM tips as microprobes?19:00
bart416Yes19:00
bart416An STM shines at this sort of thing19:00
azonenberg_workYou'd need nanometer scale positioning accuracy for multiple probes19:00
Laurenceb_i still like the idea of maskless19:00
azonenberg_workLaurenceb_: That's possible but much more difficult19:00
bart416yeah, my idea has some flaws in that aspect19:00
azonenberg_workbart416: You'd need to probe it under a SEM19:01
azonenberg_workUse the SEM to align the probes, then probably turn off the beam to avoid interference from it19:01
azonenberg_workLaurenceb_: The best maskless technique i could think of was e-beam direct write19:01
azonenberg_workHomebrew a SEM that has maybe micron or slight submicron resolution19:01
Laurenceb_still needs resist19:02
azonenberg_workUse low accelerating voltage to image the sample and line up the pattern on the wafer to your target19:02
azonenberg_workThen turn up to 30 kV and expose19:02
azonenberg_workAnd yes it does19:02
Laurenceb_if you could make a nano rpinter...19:02
azonenberg_workThe only 100% maskless method i looked at is FIB19:02
bart416We don't have a SEM at college19:02
Laurenceb_colloidal microjects look interesting19:02
azonenberg_workWhich is sloooow and not cheap19:02
bart416I think the university has a few19:02
azonenberg_workbart416: Go to a school with that kind of gear19:02
azonenberg_workif you can possibly find one19:02
bart416Belgian universities/colleges don't have that sort of resources available themselves generally19:03
bart416Usually research spin offs do though19:03
bart416Or they buy time on private ones as needed19:03
azonenberg_worki see19:03
azonenberg_workRPI is a bit better funded, i guess19:03
bart416How much do you pay per year for college/university?19:03
azonenberg_workThe cleanroom has a zeiss supra SEM as well as a FIB19:03
azonenberg_workAnd an AFM19:03
azonenberg_workThe mat sci department has a TEM, a FESEM, another SEM, and i think maybe an STM19:04
azonenberg_workAnd hmm19:04
azonenberg_workBefore scholarships etc i think the cost of attendance (tuition + room and board) is around $50k / yr19:04
bart416If they have a AFM they most likely have an STM as well19:04
bart416STMS are cheaper19:04
azonenberg_workI paid much less than that19:04
bart416By law it's set to about 550 euro / year here ;)19:04
azonenberg_workAnd now that i'm a grad student i get free tuition + stipend... yay teaching assistantships19:05
bart416There are a few private universities but those are for humanities19:05
bart416Not sciences19:05
azonenberg_workI see19:05
azonenberg_workRPI is the oldest engineering school in the USA... they've been around for a while :)19:05
Laurenceb_RPI?19:10
Laurenceb_thats some crazy tuition fees19:11
bart416Laurenceb, exactly19:12
bart416The tuition fees for 10 students of theirs are probably more than the budget the electronics department at our college gets for research and equipment >_>19:12
azonenberg_workLaurenceb_: The school president is also getting rich off our tuition :(19:14
azonenberg_workShe makes like 1.5M USD a year19:14
Laurenceb_i graduated 2 years ago and owed UKP20K19:14
azonenberg_workWhats that in USD?19:14
bart416I'll graduate in 2 years assuming I stay here and I'll owe nobody anything19:15
azonenberg_workbart416: I dont actually owe much due to scholarships etc19:15
azonenberg_workBut on paper the tuition is still insanely high19:15
bart416Due to me being lazy in highschool it's near impossible to get scholarships :(19:15
azonenberg_worki see19:15
bart416+ my father alone already earns too much for me to be able to apply to a government scholarship as well19:16
bart416And a NCO doesn't earn that much...19:16
azonenberg_workI see19:17
Laurenceb_about 14 or something19:17
azonenberg_workWell in any case, homebrew is always cheaper than buying this kind of stuff commercially19:18
azonenberg_workI'm just using their resources because they're available, and with the intention of it being temporary19:18
azonenberg_worktest on their unit, then build a version of my own19:19
bart416heh19:19
azonenberg_workAnd then document how i did it so people without these opportunities can build straight off my lab notes19:19
Laurenceb_i dont see why FIB is impractical for this sort of stuff19:20
Laurenceb_but you cant FIB conductors19:20
azonenberg_workLaurenceb_: It's possible19:20
azonenberg_workJust very slow19:20
azonenberg_workYou can, actually19:20
azonenberg_workTwo ways19:20
azonenberg_workFirst is subtractive - sputter/evaporate the metal and then use the ion beam to cut traces out of the background19:21
azonenberg_workSecond is additive19:21
azonenberg_workI dont fully understand the process but i recall it being something like targeted sputtering19:21
azonenberg_workthe ion beam hits a chunk of (say) tungsten or platinum19:21
Laurenceb_dont you need really powerful beam for cutting?19:21
Laurenceb_the targeted spluttering sounds sane19:21
bart416Depends on the thickness of the material19:22
azonenberg_workthen sends those atoms flying at high speed into your substrate, where they stick19:22
azonenberg_workI know its done19:22
azonenberg_workAnd our FIB is capable of both additive and subtractive machining19:22
azonenberg_workBut its normally waaaay too slow to be of much use for anything big19:22
azonenberg_workIts main use is thinning of samples for TEM19:22
Laurenceb_it doesnt sound completely impractical to build19:22
azonenberg_workOr for failure analysis19:22
Laurenceb_or for prototyping19:22
azonenberg_workFIB for prototyping would be as slow as ebeam19:23
azonenberg_workif not more19:23
Laurenceb_depends what you are making i guess19:23
azonenberg_workYeah19:23
azonenberg_workI still like mask lithography19:23
azonenberg_workBut i want to use laser direct write for making the masks19:23
bart416All a FIB really is is a particle accelerator19:23
azonenberg_workright now i'm doing printing onto a transparency19:23
azonenberg_workbart416: Not just19:23
bart416the basic form of it is19:24
azonenberg_workA particle accelerator plus the ability to aim the beam precisely :P19:24
Laurenceb_i have a laser galvo off ebay19:24
Laurenceb_but its analogue19:24
bart416I wonde rif you could hijack the electron cannon of a TV for this sort of thing19:24
bart416use an ion source instead of an electron source19:24
azonenberg_workI was actually considering using an electron gun for my homebrew SEM19:24
azonenberg_workBut thats a year or more out19:24
azonenberg_worki want to get most of the fab worked out by then19:24
Laurenceb_i guess you could have a two axis mechanical rig then an electrostatic or magnetic two or single axis ion beam19:25
Laurenceb_for fine detail19:26
azonenberg_workMove the stage for coarse stuff19:26
azonenberg_workthen beam shift for fine19:26
Laurenceb_yes19:26
azonenberg_workThats how SEMs do it too19:26
Laurenceb_my origional idea for maskless was wet process using colloidal microjet19:27
Laurenceb_you can get to crazy small droplet sizes19:27
bart416You could use a pulsed laser maybe?19:27
bart416With a kerr lens19:28
azonenberg_workbart416: I want to do laser but not for maskless litho19:28
azonenberg_workIt would be for generating the mask19:28
azonenberg_worksputter a microscope slide in a few hundred nm of metal19:28
Laurenceb_but youd still need a way to metal coat19:28
azonenberg_workLaurenceb_: Evaporation19:28
Laurenceb_- with microjet19:28
Laurenceb_yeah but then you need vaccuum19:28
azonenberg_workYou'd need that for a lot of processes19:29
bart416yeah, but you can use the laser through the glass of the vaccuum chamber if you make it well19:29
azonenberg_workAnd the problem with microjet is that you cant do anything that isnt soluble in a compatible liquid19:29
azonenberg_workbart416: You misunderstand19:29
azonenberg_workCoat the sample in metal, then remove from vacuum19:29
azonenberg_workspin coat in photoresist19:29
azonenberg_workand use a UV laser to expose the resist19:29
bart416You could also do that19:30
azonenberg_workThen develop and etch19:30
azonenberg_workand use the result as a contact mask19:30
Laurenceb_i saw some ideas about using 'nanoparticles'/dust in a carrier liquid19:31
Laurenceb_then sintering/diffusing19:31
Laurenceb_cant see it working well with Al19:31
Laurenceb_chemical plating with two liquids might work19:32
azonenberg_workHmm19:33
azonenberg_workWell, Al is being phased out due to higher resistance19:33
azonenberg_workModern ICs are moving toward Cu, which has its own set of problems19:34
azonenberg_workthe most obvious being that Cu diffuses into Si and disrupts PN junctions19:34
azonenberg_workso you need a barrier metal19:34
azonenberg_workusually its not even a metal, i've heard TiN (a ceramic) is commonly used19:34
azonenberg_workjust a few nm to prevent diffusion19:34
Laurenceb_eww19:35
Laurenceb_i dont think its worth trying to emulate the state of the art19:35
azonenberg_workI'm not recommending it, just saying Al isnt the only option19:35
bart416Can't you use SiO2 as barrier?19:37
azonenberg_workbart416: No19:38
azonenberg_worka) you need metal-to-Si contacts, the barrier between them has to be conductive19:38
bart416ah19:38
azonenberg_workb) metal ions diffuse through SiO219:38
bart416You meant contacts themselves19:38
azonenberg_workAnd the barrier has to completely surround the wire19:38
azonenberg_workNormally you do a dual damascene process19:38
azonenberg_workEtch trace outlines into SiO219:38
azonenberg_workSputter with barrier19:38
azonenberg_workThen fill with copper19:39
Laurenceb_http://iroi.seu.edu.cn/books/asics/Book2/CH02/CH02.2.htm19:39
Laurenceb_^thats good19:39
azonenberg_workCMP down until you've removed all of the Cu/barrier from the raised areas19:39
azonenberg_workand are down to the SiO2 with stuff inside19:39
azonenberg_workThen you do a second barrier sputter, one last CMP19:39
bart416Copper diffuses through glass?19:39
azonenberg_workand then deposit dielectric for the next layer19:39
bart416mhhh19:39
azonenberg_workbart416: Apparently19:39
bart416you wouldn't guess that19:40
azonenberg_workNope19:41
azonenberg_workMy guess is it was discovered by experiment :P19:41
azonenberg_workchips werent working19:42
azonenberg_workthen they analyzed them and found Cu in the silicon19:42
azonenberg_workonly way it could have gotten there is through the glass19:42
bart416must depend on the thickness of the glass I guess19:42
Laurenceb_polishing sounds tricky19:42
bart416how so?19:42
bart416That sounds like the easy part19:43
Laurenceb_to uniform thickness over a large area?19:43
azonenberg_workLaurenceb_: CMP isnt that bad if you have an optical flat to work with19:43
bart416semiconductor large?19:43
bart416Not really that hard19:43
azonenberg_workbart416: 12-inch wafer large19:43
bart416mhhh, that's more problematic19:44
azonenberg_workto uniform thickness within a few nm19:44
azonenberg_workYeah, it gets tricky :P19:44
bart416if it's only a small area just use a fast object19:44
bart416*fast spinning19:44
bart416anything would do19:44
azonenberg_workbart416: They usually use random orbitals on a polishing pad mounted over an optical flat19:44
bart416I'd try a laser again19:44
bart416Just cause I can19:45
bart416lol19:45
bart416a high power CO2 laser19:45
bart416Have the beam graze the wafer19:45
Laurenceb_that would never work19:46
bart416Actually it should19:47
bart416If you spin the wafer19:47
azonenberg_worklol i dont think it would19:49
azonenberg_workYou're polishing to deep sub-wavelength levels19:50
azonenberg_workThe wafers i have are flat to 5 angstroms19:50
Laurenceb_co2 is what? 10um19:50
bart416you're assuming a perfect beam :P19:50
bart416Industrial cutting lasers are far from that :(19:50
azonenberg_workLol19:50
Laurenceb_whats usually used as the insulation between metal layers?19:50
azonenberg_workLaurenceb_: SiO219:51
azonenberg_workIt can be deposited by several methods19:51
azonenberg_workSputtering (rare but not unheard of)19:51
bart416Sputtering glass seems rather problematic19:51
azonenberg_workPECVD, usually of SiH4 (most common but requires complex equipment and toxic gases)19:51
azonenberg_workAnd sol-gel19:51
azonenberg_workspin coating liquid precursors19:52
azonenberg_workWhich is what i plan to do19:52
azonenberg_workhttp://www.emulsitone.com/sif.html19:52
Laurenceb_wonder if you could use polymers19:55
bart416polymers might be hard to etch with conventional methods19:56
azonenberg_workbart416: The problem with polymers is that they're often removable by two methods19:58
azonenberg_worka) organic solvents19:58
azonenberg_workb) strong oxidizing acids19:58
azonenberg_workUnfortunately, both will also remove photoresist19:58
bart416hence, problematic with conventional methods :P19:58
azonenberg_workYep19:58
Laurenceb_FIB only kind of fails if you want insulating layers on the top19:59
bart416You could try using heat to kill the polymer20:00
bart416instead of chemical reactions20:00
bart416expose it to short bursts of IR that are blocked by the photoresist of choice20:01
Laurenceb_microjet sol-gel printing :P20:02
Laurenceb_interesting idea.. sort of selective laser ablation20:02
bart416stop thinking conventional, it's more fun to try something new for this sort of projects20:02
Laurenceb_thats exactly what im doing20:03
Laurenceb_id like to make it maskless and avoid spin coating etc etc20:04
Laurenceb_i guess vaccuum pumps are a pita too20:06
Laurenceb_if you could have maybe a two axis stage that prints onto the wafer, and no vacuum itd be amazing20:06
Laurenceb_is it possible to do diffusion out of a vacuum?20:08
Laurenceb_actually jero ellsworth did it in nitrogen20:09
Laurenceb_i wonder how bad splattering would be with a microjet20:11
Laurenceb_you can get droplets up to tens of Km/s with those things O_o20:12
bart416you can do sputtering outside a vacuum, diffusion might be a bit tricky20:12
bart416Maybe with some noble gas20:12
Laurenceb_not if you deposit onto the surface20:12
Laurenceb_you just heat to a few hundered C20:12
bart416you want an even coating right?20:13
Laurenceb_http://vimeo.com/242352820:14
Laurenceb_eyes on the screen guys, eyes on the screen20:28
bart416Too busy with complicated theoretical physics and shapes that I can't physically represent :(20:30
Laurenceb_i cant believe it works with conductive epoxy20:33
azonenbergLaurenceb_: Photoresist for ablation doesnt seem necessary21:44
azonenbergJust do laser hits21:44
azonenbergAlso, sputtering is normally done at low pressure but its not hard vacuum21:44
azonenbergpump down to 20 mtorr then sputter at 50-10021:45
Action: Laurenceb_ zzz22:10
SolidRavenazonenberg, you don't even need to go that low23:02
azonenbergSolidRaven: Agreed23:02
azonenbergThis is just how i've usually seen it done23:02
azonenbergand i meant 30, not 2023:02
SolidRavenDoesn't matter that much :P23:02
SolidRavenThe thing is, you could theoretically sputter coat at atmospheric pressure23:03
azonenbergIts just less efficient iirc23:03
azonenbergBut i'd still need inert gas23:03
azonenbergAnd it'd take forever23:04
SolidRavenMaybe you should use an oversized tesla coil to create the electric field?23:04
SolidRavenIts dangerous, it looks cool23:05
SolidRavenAnd it's insane enough that it might just work!23:05
azonenbergLol23:14
--- Tue Jul 19 201100:00

Generated by irclog2html.py 2.9.2 by Marius Gedminas - find it at mg.pov.lt!