| --- Mon Jul 18 2011 | 00:00 | |
| Laurenceb | hi | 14:16 |
|---|---|---|
| Laurenceb | didnt know there was a channel for this :P | 14:16 |
| Laurenceb | i was thinking about how it might be possible to make a small chip fab for rapid prototyping | 14:16 |
| Laurenceb | has anyone looked at colloidal microjets? | 14:17 |
| azonenberg | Laurenceb: Not that I know of | 14:20 |
| azonenberg | My current focus is MEMS | 14:20 |
| Laurenceb | yeah | 14:20 |
| azonenberg | I have a 20 micron photolithography process working decently well and am in the process of working out some yield issues in a tantalum oxide hardmask | 14:20 |
| azonenberg | to be used for KOH wet etch | 14:20 |
| Laurenceb | wow | 14:20 |
| Laurenceb | i was interested in the possiblility of avoiding masks | 14:20 |
| azonenberg | Hoping to have the body of a comb drive (i.e. minus metal layers) by end of summer | 14:20 |
| Laurenceb | and directly printing | 14:21 |
| azonenberg | Direct write is interesting but wont get you good resolution | 14:21 |
| Laurenceb | colloidal microjets can get very small | 14:21 |
| azonenberg | On say a 600dpi laser printer your lambda (smallest addressible pixel size) is around 42 microns | 14:21 |
| azonenberg | and your design rule is normally 4-5 pixels | 14:21 |
| azonenberg | I do 10x or 40x optical reduction on that to get either a 20 or 5 micron design rule | 14:22 |
| Laurenceb | yeah, i was thinking build from scratch | 14:22 |
| Laurenceb | thats impressive stuff | 14:22 |
| azonenberg | Photolithography is the de facto standard method for a reason :P | 14:22 |
| azonenberg | If you want to avoid masks you're better off using maskless lithography of some sort | 14:23 |
| azonenberg | meaning e-beam or (more affordable) laser direct write | 14:23 |
| Laurenceb | http://en.wikipedia.org/wiki/Colloid_thruster | 14:23 |
| Laurenceb | hmm yeah | 14:23 |
| Laurenceb | ion implantation looks promising | 14:23 |
| azonenberg | I actually was going to use diffusion | 14:24 |
| azonenberg | Emulsitone sells spin coatable solutions of dopants | 14:24 |
| azonenberg | I would deposit those over a photoresist film and pattern by liftoff (or deposit under followed by an HF wet etch) | 14:24 |
| azonenberg | then diffuse in a furnace | 14:24 |
| Laurenceb | wow http://www.mtixtl.com is cheap | 14:27 |
| Laurenceb | didnt realise bare wafers were affordable | 14:27 |
| azonenberg | Yes, MTI is my main supplier for a lot of stuff | 14:27 |
| azonenberg | Not sure if this is where you found it or not, but i'm building a list of vendors on the googlecode site | 14:28 |
| Laurenceb | yeah i saw | 14:28 |
| azonenberg | I also have my lab notes in the repository | 14:28 |
| azonenberg | http://code.google.com/p/homecmos/source/browse/trunk/lithography-tests/labnotes/azonenberg_labnotes.txt?spec=svn101&r=101 is the current version | 14:28 |
| azonenberg | http://colossus.cs.rpi.edu/~azonenberg/images/homecmos/ is where i upload photos from lab sessions | 14:29 |
| azonenberg | Most 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 problem | 14:29 |
| Laurenceb | looks a bit messy | 14:34 |
| Laurenceb | http://colossus.cs.rpi.edu/~azonenberg/images/homecmos/2011-07-05/die_f6/die_f6_002.jpg | 14:34 |
| Laurenceb | http://colossus.cs.rpi.edu/~azonenberg/images/homecmos/2011-07-05/die_f6/die_f6_004.jpg | 14:35 |
| Laurenceb | ^whats that showing? | 14:35 |
| kristianpaul | hi Laurenceb | 14:36 |
| Laurenceb | hi | 14:36 |
| azonenberg | Let's see, die F6... | 14:38 |
| azonenberg | Dark gray background is silicon | 14:38 |
| azonenberg | Lighter 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 |
| azonenberg | The white particles on the background are also under the tantalum layer, causing serious cracking which was destroying my yields for a while | 14:40 |
| azonenberg | The SEM imaging session was intended to diagnose the source of the cracks | 14:40 |
| azonenberg | I eventually traced it to silicon dust left over from cleaving the wafer into indididual dies | 14:40 |
| azonenberg | I had done an RCA clean on some of the dies, which didnt seem to make a difference, so i had ruled out chemical contamination | 14:40 |
| azonenberg | But large (micron or more) particulates wont be removed by an RCA clean | 14:41 |
| azonenberg | And i knew there were too many to be room dust | 14:41 |
| azonenberg | I finally identified the contaminant when EDS on a contaminated area showed nothing but silicon | 14:41 |
| azonenberg | I had initially thought it wasnt sensitive enough to pick up the contaminant | 14:41 |
| azonenberg | then i realized the contaminant might actually BE silicon | 14:41 |
| Laurenceb | ESD? | 14:42 |
| Laurenceb | i mean eds | 14:42 |
| azonenberg | Energy dispersive X-ray spectroscopy | 14:42 |
| Laurenceb | ah | 14:42 |
| azonenberg | You hit the sample with an electron beam like in imaging, but you read x-rays coming off the sample | 14:42 |
| Laurenceb | so those cracks are due to the dust? | 14:42 |
| azonenberg | The electrons in the atoms are excited and then drop down to a lower energy level, fluorescing in the process | 14:42 |
| azonenberg | by measuring the x-ray energy level you can identify elements (but not compounds) | 14:42 |
| azonenberg | And correct | 14:43 |
| azonenberg | The coating is made by depositing tantalum chloride dissolved in ethanol by spin coating | 14:43 |
| azonenberg | As it dries, it cracks alogn the edges of the particle | 14:43 |
| Laurenceb | i see | 14:43 |
| azonenberg | Re 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.htm | 14:44 |
| Laurenceb | what are the probes for? | 14:45 |
| azonenberg | The 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 |
| azonenberg | And 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 |
| azonenberg | The probes are for doing testing of finished devices | 14:45 |
| azonenberg | i dont have a wire bonder | 14:45 |
| azonenberg | I do, however, have a wentworth labs probing station and a couple of micropositioners | 14:46 |
| azonenberg | This 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.JPG | 14:46 |
| Laurenceb | are there spin coater photos? | 14:49 |
| azonenberg | Not sure if i have any of the current one uploaded | 14:49 |
| azonenberg | It's a sanding wheel mounted on top of an electric drill | 14:50 |
| azonenberg | Kinda bulky but works | 14:50 |
| azonenberg | I plan to shrink it significantly and make one built on a CPU fan | 14:50 |
| azonenberg | intended for single dies rather than whole wafers | 14:50 |
| azonenberg | I'm also planning to build a small fume hood for doing coating, etching, and similar stuff in | 14:51 |
| azonenberg | basically a 1x2x2 foot plastic box with an opening in the front and a fan on top | 14:52 |
| azonenberg | Either venting outside or through an activated charcoal filter, details TBD | 14:52 |
| azonenberg | Plans will be uploaded as soon as i actually have some time to work on the design | 14:52 |
| azonenberg | Re spin coater, http://i.imgur.com/15JiV.jpg is a shot of my current one (slightly older) | 14:53 |
| azonenberg | The wafer on top isnt mine, its a random 4-inch a friend got off ebay to use as a mechanical dummy | 14:53 |
| azonenberg | But as you can see the coater is capable of handling a full 4-inch wafer | 14:54 |
| azonenberg | Its mounted by double sided tape | 14:54 |
| azonenberg | At 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 base | 14:54 |
| azonenberg | Since then i've switched to a cardboard lip stapled around the sides of the base | 14:54 |
| azonenberg | it lets me easily reach onto the chuck to drip more solution onto a spinning wafer without risking a change of shirt color :P | 14:55 |
| Laurenceb | interesting | 15:05 |
| azonenberg | Heading out to work (a bit late as is), if you have any further questions leave them here and i'll respond this afternoon | 15:06 |
| Laurenceb | i dont understand spin coating | 15:06 |
| Laurenceb | ok | 15:06 |
| azonenberg_work | So I've arranged access to a vacuum evaporator on campus | 17:25 |
| azonenberg_work | I'll be evaporating around 100nm of copper onto some microscope slides as a test | 17:26 |
| azonenberg_work | Half of them will have PR already on them (lift-off process) | 17:26 |
| azonenberg_work | and the other half will be uncoated (to be patterned by etching) | 17:26 |
| azonenberg_work | Then i'll etch them in SC2 and lift the other ones off in acetone | 17:27 |
| azonenberg_work | See what kind of resolutions i can hit | 17:27 |
| azonenberg_work | On the menu for tonight... sample prep for my evaporation session plus another experiment using thinner photoresist layers | 17:57 |
| Laurenceb_ | hi | 18:26 |
| 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_work | Laurenceb_: Do you mean for transistor contacts? | 18:45 |
| azonenberg_work | Or for wiring at higher levels | 18:46 |
| azonenberg_work | There's normally a silicon dioxide dielectric layer between the silicon and any wiring | 18:46 |
| Laurenceb_ | the transistor contacts | 18:46 |
| azonenberg_work | The only time you break it is for vias between wiring layers | 18:46 |
| azonenberg_work | Or for transistor contacts | 18:46 |
| Laurenceb_ | surely for VCC/VSS you need contacts | 18:46 |
| azonenberg_work | The gate doesnt actually touch anything, its just floating right above the channel | 18:46 |
| Laurenceb_ | yeah sure | 18:46 |
| azonenberg_work | But yes, for the source/drain you do | 18:46 |
| Laurenceb_ | how does that work? | 18:46 |
| azonenberg_work | I actually havent looked into that yet, I do know that you need to contact the silicon somehow | 18:47 |
| azonenberg_work | I also know that if you do it wrong you can form schottky diodes | 18:47 |
| azonenberg_work | But i'm actually not sure what the right way is | 18:47 |
| Laurenceb_ | presumably you need to take off the oxide | 18:47 |
| azonenberg_work | Like i said my current work is on basic 2D patterning and MEMS | 18:47 |
| azonenberg_work | And native oxide is trivial to strip | 18:47 |
| azonenberg_work | 15 sec in dilute HF | 18:47 |
| Laurenceb_ | interesting | 18:48 |
| Laurenceb_ | http://iroi.seu.edu.cn/books/asics/Book2/CH02/CH02.2.htm | 18:48 |
| Laurenceb_ | apparently commercially they use polysilicon deppsition? | 18:48 |
| Laurenceb_ | maybe you could directly PVD onto the silicon with aluminium | 18:48 |
| Laurenceb_ | in a vacuum after stripping | 18:48 |
| azonenberg_work | So they use platinum as the barrier layer before connecting | 18:49 |
| azonenberg_work | And poly is used for the gates | 18:49 |
| Laurenceb_ | ah i see | 18:49 |
| azonenberg_work | I would be doing vacuum evaporation, which is a form of PVD | 18:49 |
| azonenberg_work | for both metals and poly | 18:49 |
| Laurenceb_ | yeah | 18:49 |
| azonenberg_work | i actually have some Si crystals for evaporation now | 18:49 |
| Laurenceb_ | ive seem a machine for that | 18:49 |
| Laurenceb_ | its quite simple really | 18:49 |
| azonenberg_work | But i havent built the evaporator itself | 18:49 |
| azonenberg_work | I get to play with one on campus on thursday | 18:49 |
| Laurenceb_ | ive modified one for degassing resin | 18:50 |
| azonenberg_work | to metalize some microscope slides (sample substrate) for testing my metal process | 18:50 |
| azonenberg_work | The next step would be to buy myself a diffusion pump | 18:50 |
| Laurenceb_ | is the polysilicon really required? | 18:51 |
| azonenberg_work | I could potentially use metal gates as well | 18:51 |
| azonenberg_work | But i'd still need an evaporator | 18:51 |
| Laurenceb_ | there are chemical alu coating techniques | 18:52 |
| azonenberg_work | I want to do patterning by liftoff though | 18:52 |
| Laurenceb_ | i was working with pressure sensors recently | 18:53 |
| azonenberg_work | Interesting | 18:53 |
| Laurenceb_ | they seem quite simple - thin etched layer on a wafer | 18:53 |
| azonenberg_work | Yeah | 18:53 |
| azonenberg_work | I want to build a comb drive, which is nearly as simple | 18:53 |
| Laurenceb_ | might be worth a try at making one | 18:53 |
| azonenberg_work | one KOH etch into <110> Si and one metal etch | 18:53 |
| azonenberg_work | KOH etching is proving painful due to the hardmask not playing nicely | 18:54 |
| Laurenceb_ | thats the crystal plane direction? | 18:54 |
| azonenberg_work | Correct | 18:54 |
| azonenberg_work | KOH eats <100> super fast and <110> almost as fast, but <111> almost not at all | 18:54 |
| azonenberg_work | very anisotropic | 18:54 |
| Laurenceb_ | does that mean you can do deep etching ? | 18:55 |
| azonenberg_work | In <110> surfaces, the <111> planes are near vertical | 18:55 |
| azonenberg_work | So yes | 18:55 |
| azonenberg_work | You can get 10:1 aspect ratios or better | 18:55 |
| azonenberg_work | With a *wet etch* | 18:55 |
| azonenberg_work | Doing that with deep RIE or something is trivial, but thats way beyond my capabilities at home | 18:55 |
| azonenberg_work | A wet etch, OTOH, is very feasible | 18:55 |
| Laurenceb_ | i was looking at micro anemometers for uavs | 18:56 |
| azonenberg_work | I've tried several times but in all cases the hardmask was cracked or for whatever reason didnt go where it was supposed to | 18:56 |
| azonenberg_work | And very interesting | 18:56 |
| Laurenceb_ | using hot elements | 18:56 |
| azonenberg_work | Measuring airflow by the delta T between one shielded from air and one that isnt? | 18:57 |
| Laurenceb_ | yes | 18:57 |
| Laurenceb_ | ive tried it with grain of rice lamps | 18:57 |
| azonenberg_work | That sounds like a fairly simple MEMS project | 18:57 |
| azonenberg_work | Within reach of a process like this in a year or so | 18:57 |
| Laurenceb_ | with glass removed | 18:57 |
| azonenberg_work | This is exactly the kind of stuff that i want to be able to do | 18:57 |
| azonenberg_work | Very simple ICs or MEMS, as one-off prototypes etc | 18:58 |
| bart416 | azonenberg, I intend to surpass your madness! | 18:58 |
| azonenberg_work | bart416: If you get a 350nm fab in your garage send me pics :OP | 18:58 |
| azonenberg_work | :P * | 18:58 |
| azonenberg_work | Because thats my ultimate goal for 10-20 years out | 18:58 |
| azonenberg_work | At least submicron for sure | 18:58 |
| bart416 | I'm writing up purposal for my master thesis | 18:58 |
| bart416 | Atomic scale circuits | 18:59 |
| bart416 | Built using a computer controlled stm | 18:59 |
| azonenberg_work | Right now the smallest geometry i've fabbed in anything was 5um (photoresist, not etched into anything) | 18:59 |
| azonenberg_work | And 20um is the smallest feature i've done in Si | 18:59 |
| bart416 | does that surpass your madness, | 18:59 |
| azonenberg_work | It's a tie, at least | 18:59 |
| azonenberg_work | Let me know how it goes | 18:59 |
| bart416 | I wonder if such an idea would be approved | 19:00 |
| azonenberg_work | How would you test said devices? | 19:00 |
| azonenberg_work | Use STM tips as microprobes? | 19:00 |
| bart416 | Yes | 19:00 |
| bart416 | An STM shines at this sort of thing | 19:00 |
| azonenberg_work | You'd need nanometer scale positioning accuracy for multiple probes | 19:00 |
| Laurenceb_ | i still like the idea of maskless | 19:00 |
| azonenberg_work | Laurenceb_: That's possible but much more difficult | 19:00 |
| bart416 | yeah, my idea has some flaws in that aspect | 19:00 |
| azonenberg_work | bart416: You'd need to probe it under a SEM | 19:01 |
| azonenberg_work | Use the SEM to align the probes, then probably turn off the beam to avoid interference from it | 19:01 |
| azonenberg_work | Laurenceb_: The best maskless technique i could think of was e-beam direct write | 19:01 |
| azonenberg_work | Homebrew a SEM that has maybe micron or slight submicron resolution | 19:01 |
| Laurenceb_ | still needs resist | 19:02 |
| azonenberg_work | Use low accelerating voltage to image the sample and line up the pattern on the wafer to your target | 19:02 |
| azonenberg_work | Then turn up to 30 kV and expose | 19:02 |
| azonenberg_work | And yes it does | 19:02 |
| Laurenceb_ | if you could make a nano rpinter... | 19:02 |
| azonenberg_work | The only 100% maskless method i looked at is FIB | 19:02 |
| bart416 | We don't have a SEM at college | 19:02 |
| Laurenceb_ | colloidal microjects look interesting | 19:02 |
| azonenberg_work | Which is sloooow and not cheap | 19:02 |
| bart416 | I think the university has a few | 19:02 |
| azonenberg_work | bart416: Go to a school with that kind of gear | 19:02 |
| azonenberg_work | if you can possibly find one | 19:02 |
| bart416 | Belgian universities/colleges don't have that sort of resources available themselves generally | 19:03 |
| bart416 | Usually research spin offs do though | 19:03 |
| bart416 | Or they buy time on private ones as needed | 19:03 |
| azonenberg_work | i see | 19:03 |
| azonenberg_work | RPI is a bit better funded, i guess | 19:03 |
| bart416 | How much do you pay per year for college/university? | 19:03 |
| azonenberg_work | The cleanroom has a zeiss supra SEM as well as a FIB | 19:03 |
| azonenberg_work | And an AFM | 19:03 |
| azonenberg_work | The mat sci department has a TEM, a FESEM, another SEM, and i think maybe an STM | 19:04 |
| azonenberg_work | And hmm | 19:04 |
| azonenberg_work | Before scholarships etc i think the cost of attendance (tuition + room and board) is around $50k / yr | 19:04 |
| bart416 | If they have a AFM they most likely have an STM as well | 19:04 |
| bart416 | STMS are cheaper | 19:04 |
| azonenberg_work | I paid much less than that | 19:04 |
| bart416 | By law it's set to about 550 euro / year here ;) | 19:04 |
| azonenberg_work | And now that i'm a grad student i get free tuition + stipend... yay teaching assistantships | 19:05 |
| bart416 | There are a few private universities but those are for humanities | 19:05 |
| bart416 | Not sciences | 19:05 |
| azonenberg_work | I see | 19:05 |
| azonenberg_work | RPI 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 fees | 19:11 |
| bart416 | Laurenceb, exactly | 19:12 |
| bart416 | The 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_work | Laurenceb_: The school president is also getting rich off our tuition :( | 19:14 |
| azonenberg_work | She makes like 1.5M USD a year | 19:14 |
| Laurenceb_ | i graduated 2 years ago and owed UKP20K | 19:14 |
| azonenberg_work | Whats that in USD? | 19:14 |
| bart416 | I'll graduate in 2 years assuming I stay here and I'll owe nobody anything | 19:15 |
| azonenberg_work | bart416: I dont actually owe much due to scholarships etc | 19:15 |
| azonenberg_work | But on paper the tuition is still insanely high | 19:15 |
| bart416 | Due to me being lazy in highschool it's near impossible to get scholarships :( | 19:15 |
| azonenberg_work | i see | 19:15 |
| bart416 | + my father alone already earns too much for me to be able to apply to a government scholarship as well | 19:16 |
| bart416 | And a NCO doesn't earn that much... | 19:16 |
| azonenberg_work | I see | 19:17 |
| Laurenceb_ | about 14 or something | 19:17 |
| azonenberg_work | Well in any case, homebrew is always cheaper than buying this kind of stuff commercially | 19:18 |
| azonenberg_work | I'm just using their resources because they're available, and with the intention of it being temporary | 19:18 |
| azonenberg_work | test on their unit, then build a version of my own | 19:19 |
| bart416 | heh | 19:19 |
| azonenberg_work | And then document how i did it so people without these opportunities can build straight off my lab notes | 19:19 |
| Laurenceb_ | i dont see why FIB is impractical for this sort of stuff | 19:20 |
| Laurenceb_ | but you cant FIB conductors | 19:20 |
| azonenberg_work | Laurenceb_: It's possible | 19:20 |
| azonenberg_work | Just very slow | 19:20 |
| azonenberg_work | You can, actually | 19:20 |
| azonenberg_work | Two ways | 19:20 |
| azonenberg_work | First is subtractive - sputter/evaporate the metal and then use the ion beam to cut traces out of the background | 19:21 |
| azonenberg_work | Second is additive | 19:21 |
| azonenberg_work | I dont fully understand the process but i recall it being something like targeted sputtering | 19:21 |
| azonenberg_work | the ion beam hits a chunk of (say) tungsten or platinum | 19:21 |
| Laurenceb_ | dont you need really powerful beam for cutting? | 19:21 |
| Laurenceb_ | the targeted spluttering sounds sane | 19:21 |
| bart416 | Depends on the thickness of the material | 19:22 |
| azonenberg_work | then sends those atoms flying at high speed into your substrate, where they stick | 19:22 |
| azonenberg_work | I know its done | 19:22 |
| azonenberg_work | And our FIB is capable of both additive and subtractive machining | 19:22 |
| azonenberg_work | But its normally waaaay too slow to be of much use for anything big | 19:22 |
| azonenberg_work | Its main use is thinning of samples for TEM | 19:22 |
| Laurenceb_ | it doesnt sound completely impractical to build | 19:22 |
| azonenberg_work | Or for failure analysis | 19:22 |
| Laurenceb_ | or for prototyping | 19:22 |
| azonenberg_work | FIB for prototyping would be as slow as ebeam | 19:23 |
| azonenberg_work | if not more | 19:23 |
| Laurenceb_ | depends what you are making i guess | 19:23 |
| azonenberg_work | Yeah | 19:23 |
| azonenberg_work | I still like mask lithography | 19:23 |
| azonenberg_work | But i want to use laser direct write for making the masks | 19:23 |
| bart416 | All a FIB really is is a particle accelerator | 19:23 |
| azonenberg_work | right now i'm doing printing onto a transparency | 19:23 |
| azonenberg_work | bart416: Not just | 19:23 |
| bart416 | the basic form of it is | 19:24 |
| azonenberg_work | A particle accelerator plus the ability to aim the beam precisely :P | 19:24 |
| Laurenceb_ | i have a laser galvo off ebay | 19:24 |
| Laurenceb_ | but its analogue | 19:24 |
| bart416 | I wonde rif you could hijack the electron cannon of a TV for this sort of thing | 19:24 |
| bart416 | use an ion source instead of an electron source | 19:24 |
| azonenberg_work | I was actually considering using an electron gun for my homebrew SEM | 19:24 |
| azonenberg_work | But thats a year or more out | 19:24 |
| azonenberg_work | i want to get most of the fab worked out by then | 19:24 |
| Laurenceb_ | i guess you could have a two axis mechanical rig then an electrostatic or magnetic two or single axis ion beam | 19:25 |
| Laurenceb_ | for fine detail | 19:26 |
| azonenberg_work | Move the stage for coarse stuff | 19:26 |
| azonenberg_work | then beam shift for fine | 19:26 |
| Laurenceb_ | yes | 19:26 |
| azonenberg_work | Thats how SEMs do it too | 19:26 |
| Laurenceb_ | my origional idea for maskless was wet process using colloidal microjet | 19:27 |
| Laurenceb_ | you can get to crazy small droplet sizes | 19:27 |
| bart416 | You could use a pulsed laser maybe? | 19:27 |
| bart416 | With a kerr lens | 19:28 |
| azonenberg_work | bart416: I want to do laser but not for maskless litho | 19:28 |
| azonenberg_work | It would be for generating the mask | 19:28 |
| azonenberg_work | sputter a microscope slide in a few hundred nm of metal | 19:28 |
| Laurenceb_ | but youd still need a way to metal coat | 19:28 |
| azonenberg_work | Laurenceb_: Evaporation | 19:28 |
| Laurenceb_ | - with microjet | 19:28 |
| Laurenceb_ | yeah but then you need vaccuum | 19:28 |
| azonenberg_work | You'd need that for a lot of processes | 19:29 |
| bart416 | yeah, but you can use the laser through the glass of the vaccuum chamber if you make it well | 19:29 |
| azonenberg_work | And the problem with microjet is that you cant do anything that isnt soluble in a compatible liquid | 19:29 |
| azonenberg_work | bart416: You misunderstand | 19:29 |
| azonenberg_work | Coat the sample in metal, then remove from vacuum | 19:29 |
| azonenberg_work | spin coat in photoresist | 19:29 |
| azonenberg_work | and use a UV laser to expose the resist | 19:29 |
| bart416 | You could also do that | 19:30 |
| azonenberg_work | Then develop and etch | 19:30 |
| azonenberg_work | and use the result as a contact mask | 19:30 |
| Laurenceb_ | i saw some ideas about using 'nanoparticles'/dust in a carrier liquid | 19:31 |
| Laurenceb_ | then sintering/diffusing | 19:31 |
| Laurenceb_ | cant see it working well with Al | 19:31 |
| Laurenceb_ | chemical plating with two liquids might work | 19:32 |
| azonenberg_work | Hmm | 19:33 |
| azonenberg_work | Well, Al is being phased out due to higher resistance | 19:33 |
| azonenberg_work | Modern ICs are moving toward Cu, which has its own set of problems | 19:34 |
| azonenberg_work | the most obvious being that Cu diffuses into Si and disrupts PN junctions | 19:34 |
| azonenberg_work | so you need a barrier metal | 19:34 |
| azonenberg_work | usually its not even a metal, i've heard TiN (a ceramic) is commonly used | 19:34 |
| azonenberg_work | just a few nm to prevent diffusion | 19:34 |
| Laurenceb_ | eww | 19:35 |
| Laurenceb_ | i dont think its worth trying to emulate the state of the art | 19:35 |
| azonenberg_work | I'm not recommending it, just saying Al isnt the only option | 19:35 |
| bart416 | Can't you use SiO2 as barrier? | 19:37 |
| azonenberg_work | bart416: No | 19:38 |
| azonenberg_work | a) you need metal-to-Si contacts, the barrier between them has to be conductive | 19:38 |
| bart416 | ah | 19:38 |
| azonenberg_work | b) metal ions diffuse through SiO2 | 19:38 |
| bart416 | You meant contacts themselves | 19:38 |
| azonenberg_work | And the barrier has to completely surround the wire | 19:38 |
| azonenberg_work | Normally you do a dual damascene process | 19:38 |
| azonenberg_work | Etch trace outlines into SiO2 | 19:38 |
| azonenberg_work | Sputter with barrier | 19:38 |
| azonenberg_work | Then fill with copper | 19:39 |
| Laurenceb_ | http://iroi.seu.edu.cn/books/asics/Book2/CH02/CH02.2.htm | 19:39 |
| Laurenceb_ | ^thats good | 19:39 |
| azonenberg_work | CMP down until you've removed all of the Cu/barrier from the raised areas | 19:39 |
| azonenberg_work | and are down to the SiO2 with stuff inside | 19:39 |
| azonenberg_work | Then you do a second barrier sputter, one last CMP | 19:39 |
| bart416 | Copper diffuses through glass? | 19:39 |
| azonenberg_work | and then deposit dielectric for the next layer | 19:39 |
| bart416 | mhhh | 19:39 |
| azonenberg_work | bart416: Apparently | 19:39 |
| bart416 | you wouldn't guess that | 19:40 |
| azonenberg_work | Nope | 19:41 |
| azonenberg_work | My guess is it was discovered by experiment :P | 19:41 |
| azonenberg_work | chips werent working | 19:42 |
| azonenberg_work | then they analyzed them and found Cu in the silicon | 19:42 |
| azonenberg_work | only way it could have gotten there is through the glass | 19:42 |
| bart416 | must depend on the thickness of the glass I guess | 19:42 |
| Laurenceb_ | polishing sounds tricky | 19:42 |
| bart416 | how so? | 19:42 |
| bart416 | That sounds like the easy part | 19:43 |
| Laurenceb_ | to uniform thickness over a large area? | 19:43 |
| azonenberg_work | Laurenceb_: CMP isnt that bad if you have an optical flat to work with | 19:43 |
| bart416 | semiconductor large? | 19:43 |
| bart416 | Not really that hard | 19:43 |
| azonenberg_work | bart416: 12-inch wafer large | 19:43 |
| bart416 | mhhh, that's more problematic | 19:44 |
| azonenberg_work | to uniform thickness within a few nm | 19:44 |
| azonenberg_work | Yeah, it gets tricky :P | 19:44 |
| bart416 | if it's only a small area just use a fast object | 19:44 |
| bart416 | *fast spinning | 19:44 |
| bart416 | anything would do | 19:44 |
| azonenberg_work | bart416: They usually use random orbitals on a polishing pad mounted over an optical flat | 19:44 |
| bart416 | I'd try a laser again | 19:44 |
| bart416 | Just cause I can | 19:45 |
| bart416 | lol | 19:45 |
| bart416 | a high power CO2 laser | 19:45 |
| bart416 | Have the beam graze the wafer | 19:45 |
| Laurenceb_ | that would never work | 19:46 |
| bart416 | Actually it should | 19:47 |
| bart416 | If you spin the wafer | 19:47 |
| azonenberg_work | lol i dont think it would | 19:49 |
| azonenberg_work | You're polishing to deep sub-wavelength levels | 19:50 |
| azonenberg_work | The wafers i have are flat to 5 angstroms | 19:50 |
| Laurenceb_ | co2 is what? 10um | 19:50 |
| bart416 | you're assuming a perfect beam :P | 19:50 |
| bart416 | Industrial cutting lasers are far from that :( | 19:50 |
| azonenberg_work | Lol | 19:50 |
| Laurenceb_ | whats usually used as the insulation between metal layers? | 19:50 |
| azonenberg_work | Laurenceb_: SiO2 | 19:51 |
| azonenberg_work | It can be deposited by several methods | 19:51 |
| azonenberg_work | Sputtering (rare but not unheard of) | 19:51 |
| bart416 | Sputtering glass seems rather problematic | 19:51 |
| azonenberg_work | PECVD, usually of SiH4 (most common but requires complex equipment and toxic gases) | 19:51 |
| azonenberg_work | And sol-gel | 19:51 |
| azonenberg_work | spin coating liquid precursors | 19:52 |
| azonenberg_work | Which is what i plan to do | 19:52 |
| azonenberg_work | http://www.emulsitone.com/sif.html | 19:52 |
| Laurenceb_ | wonder if you could use polymers | 19:55 |
| bart416 | polymers might be hard to etch with conventional methods | 19:56 |
| azonenberg_work | bart416: The problem with polymers is that they're often removable by two methods | 19:58 |
| azonenberg_work | a) organic solvents | 19:58 |
| azonenberg_work | b) strong oxidizing acids | 19:58 |
| azonenberg_work | Unfortunately, both will also remove photoresist | 19:58 |
| bart416 | hence, problematic with conventional methods :P | 19:58 |
| azonenberg_work | Yep | 19:58 |
| Laurenceb_ | FIB only kind of fails if you want insulating layers on the top | 19:59 |
| bart416 | You could try using heat to kill the polymer | 20:00 |
| bart416 | instead of chemical reactions | 20:00 |
| bart416 | expose it to short bursts of IR that are blocked by the photoresist of choice | 20:01 |
| Laurenceb_ | microjet sol-gel printing :P | 20:02 |
| Laurenceb_ | interesting idea.. sort of selective laser ablation | 20:02 |
| bart416 | stop thinking conventional, it's more fun to try something new for this sort of projects | 20:02 |
| Laurenceb_ | thats exactly what im doing | 20:03 |
| Laurenceb_ | id like to make it maskless and avoid spin coating etc etc | 20:04 |
| Laurenceb_ | i guess vaccuum pumps are a pita too | 20:06 |
| Laurenceb_ | if you could have maybe a two axis stage that prints onto the wafer, and no vacuum itd be amazing | 20:06 |
| Laurenceb_ | is it possible to do diffusion out of a vacuum? | 20:08 |
| Laurenceb_ | actually jero ellsworth did it in nitrogen | 20:09 |
| Laurenceb_ | i wonder how bad splattering would be with a microjet | 20:11 |
| Laurenceb_ | you can get droplets up to tens of Km/s with those things O_o | 20:12 |
| bart416 | you can do sputtering outside a vacuum, diffusion might be a bit tricky | 20:12 |
| bart416 | Maybe with some noble gas | 20:12 |
| Laurenceb_ | not if you deposit onto the surface | 20:12 |
| Laurenceb_ | you just heat to a few hundered C | 20:12 |
| bart416 | you want an even coating right? | 20:13 |
| Laurenceb_ | http://vimeo.com/2423528 | 20:14 |
| Laurenceb_ | eyes on the screen guys, eyes on the screen | 20:28 |
| bart416 | Too busy with complicated theoretical physics and shapes that I can't physically represent :( | 20:30 |
| Laurenceb_ | i cant believe it works with conductive epoxy | 20:33 |
| azonenberg | Laurenceb_: Photoresist for ablation doesnt seem necessary | 21:44 |
| azonenberg | Just do laser hits | 21:44 |
| azonenberg | Also, sputtering is normally done at low pressure but its not hard vacuum | 21:44 |
| azonenberg | pump down to 20 mtorr then sputter at 50-100 | 21:45 |
| Action: Laurenceb_ zzz | 22:10 | |
| SolidRaven | azonenberg, you don't even need to go that low | 23:02 |
| azonenberg | SolidRaven: Agreed | 23:02 |
| azonenberg | This is just how i've usually seen it done | 23:02 |
| azonenberg | and i meant 30, not 20 | 23:02 |
| SolidRaven | Doesn't matter that much :P | 23:02 |
| SolidRaven | The thing is, you could theoretically sputter coat at atmospheric pressure | 23:03 |
| azonenberg | Its just less efficient iirc | 23:03 |
| azonenberg | But i'd still need inert gas | 23:03 |
| azonenberg | And it'd take forever | 23:04 |
| SolidRaven | Maybe you should use an oversized tesla coil to create the electric field? | 23:04 |
| SolidRaven | Its dangerous, it looks cool | 23:05 |
| SolidRaven | And it's insane enough that it might just work! | 23:05 |
| azonenberg | Lol | 23:14 |
| --- Tue Jul 19 2011 | 00:00 | |
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