#homecmos IRC log for Wednesday, 2011-07-20

azonenberglekernel: https://www.facebook.com/pages/Lift-off/13568613313149100:21
azonenbergOh, the interesting things you can find when facebook crawls all of wikipedia looking for fanpages...00:22
azonenberg_labSo I'm prepping samples for an experiment to be done on thursday03:02
azonenberg_labAny ideas as to how to store microscope coverslips or slides (to be used as substrates for deposition) in a clean environment for a day or two? Preferably padded so i can carry them around03:02
azonenberg_labLooks like i need more gel boxes o_O running out03:11
azonenberg_labbut i have one left03:11
azonenberg_labSo now i have 17 samples which are going to be coated in 100nm ish of Cu on thursday03:59
azonenberg_labFour of <100> Si and the rest of glass03:59
azonenberg_labNext step is to expose some of these guys with simple test patterns so i can do lift-off03:59
azonenberg_labTrying half-strength photoresist (watered down with acetone) now04:51
azonenberg_labI'm expecting better resolution and shorter exposues04:52
azonenberg_labAt the cost of increased permeability04:52
CIA-67homecmos r102 | trunk/lithography-tests/labnotes/azonenberg_labnotes.txt | Today's lab notes05:25
azonenbergThis is getting annoying05:46
azonenbergAll of my processes seem to be working decently well (so far) except the KOH isnt playing well05:46
azonenbergBecause i cant get hardmask to work05:47
azonenbergI'm starting to wonder if maybe i should just try CMOS05:47
Laurencebwhy is hardmask needed?11:13
azonenbergLaurenceb: Because photoresist is attacked by KOH14:15
azonenbergAs well as related etchants like NaOH and TMAH14:15
Laurencebsilicon entchants?14:18
azonenbergLaurenceb: Correct14:19
Laurenceb do silicon dioxode etchants eat photoresist?14:19
azonenbergNot exactly14:19
azonenbergBut F- ions have a tendency to diffuse through photoresist14:20
Laurencebhow is it done commercially?14:20
azonenbergThey dont actually damage it but they appear on the other side14:20
Laurenceb- dioxide etching14:20
azonenbergThey normally use fluoride-proof resists14:20
azonenbergAlso, the usual mask for silicon etching is silicon nitride14:20
azonenbergWhich is deposited by reactive sputtering or LPCVD14:21
Laurencebi see14:21
Laurencebi dont understand how spin coating leaves an eavent coat14:21
azonenbergI dont know all of the physics either, you'd think it'd be thinner in the middle and thicker around the rim14:22
azonenbergI mean, there is frequently a ring around the *very* edge14:22
azonenbergBut that due to edge effects (surface tension etc)14:22
azonenbergthe thickness in the remaining area is normally extremely even14:23
Laurenceboh with my aerosol precipitator, we found you could get even a repoducable coats14:23
Laurencebas the precipitate was nonconductive and blocked the field14:23
Laurenceb- allowed a static buildup that blocked the field14:23
azonenbergAnd I think my problem is that my hardmask is soluble in alcohol14:23
azonenbergBut so is my photoresist14:23
Laurencebunfortunately it ended up quite thick14:24
azonenbergSo the two are interacting somehow14:24
azonenbergThe resist dissolves slowly, it doesnt disintegrate like it would with say acetone14:24
azonenbergBut i think its contaminating the film somehow14:24
Laurencebi saw some papers on using electrostatic dust precipitation to coat nonconductive surfaces uniformly14:24
azonenbergwell i just came up with a very interesting idea14:25
azonenbergGonna have to prepare some samples tonight to test14:25
azonenbergOne is to try using an evaporated metal hardmask to pattern tantalum chloride by a wet etch in alcohol14:30
azonenbergAnother one is to use evaporated metal directly as a hardmask for KOH etch (but only certain metals are compatible)14:30
azonenbergAnd another is to use evaporated metal as a hardmask for etching tantalum oxide14:31
azonenbergAnd still another is to try something i should have done a long time ago14:33
azonenbergNow that i have ammonia i can synthesize ammonium fluoride and, by extension, buffered oxide etch14:33
azonenbergWhich i'm told diffuses through photoresist much less than pure HF14:33
azonenberggaah, going to be fun going to work today while thinking about this :P14:34
azonenbergMy last attempt at buffering HF used NaOH14:44
azonenbergDidnt end well14:44
azonenbergTook the photoresist right off14:44
azonenbergWhat, you didnt know the channel existed? Been working here for like two months lol14:45
azonenberghttp://code.google.com/p/homecmos/source/browse/trunk/lithography-tests/labnotes/azonenberg_labnotes.txt?spec=svn102&r=102 is my current lab notes if you have any suggestions14:45
Laurencebbefore copper was used on commercial fab, was CPM necessary?14:47
Laurencebi dont see that being practical to do cheaply14:50
SolidRavenWhat CPM?14:50
SolidRavenStop the acronyms14:50
SolidRavenThey can mean loads of things14:50
Laurencebsurface polishing14:51
SolidRavenThe thing about polishing is, you could get an old industrial machine fairly cheaply14:53
SolidRavenYou know, for watch making and so on14:53
SolidRavenThose are usually rather precise14:53
SolidRavenSo with minor modifications you should be able to get them to the level required to polish a wafer14:53
Laurencebi was interested in tabletop fab14:54
SolidRavenYou somehow see this as a huge machine14:55
SolidRavenIt generally isn't14:55
SolidRavenI'm talking about watch making equipment :P14:55
SolidRavenGoes in the same category as those small lathes14:56
SolidRavenThat's actually another thing you could use to polish them14:56
SolidRavenAssuming you find a good enough tool14:57
SolidRavenYou know Laurenceb a good average lathe will let you go down to 10┬Ám or even smaller14:59
SolidRavenAnd some of the better CNC lathes can go sub micrometer...15:00
SolidRavenSo really, look into it15:00
SolidRavenBut don't use the automatic feed of a small lathe if you want precision, too much shocks :(15:01
SolidRavenActually, now that I think of it15:03
SolidRavencooling, you'll need that if you use a lathe15:03
SolidRavenBlast it with a jet of nitrogen15:03
SolidRavenSo go and get your jewelry lathe that's precise enough15:04
SolidRavenThe reason lathes are generally not used at such precision is the lack of measurement instruments and the lack of need to do so15:15
SolidRavenIt's cheaper to work at a precision of 0.1mm than at 0.01 or 0.001mm15:15
SolidRavenBut mechanically they're capable of going down to that precision15:16
azonenberg_workLaurenceb: I think you meant CMP15:20
azonenberg_workNot CPM15:20
azonenberg_workAnd it was still used before copper damascene processing to some extent15:20
azonenberg_workMost submicron aluminum processes use it15:21
azonenberg_workThe reason is that the depth of field of your litho process is less than the thickness of a metal layer15:21
azonenberg_workSo you need to have a flat surface for exposing the mask onto15:21
azonenberg_workI was actually expecting to planarize during some of my processing so i bought a quart of 50nm colloidal silica slurry from ted pella15:23
azonenberg_workHavent had a chance to actually try any real processing with it15:23
Laurencebthats small15:26
azonenberg_workThats the particle size, it can actually polish to below that15:27
azonenberg_workProbably 10-25nm surface roughness as a guess15:27
azonenberg_workIn any case its far better than i need for depositiong 50-100nm (or thicker) films with 5-20um horizontal feature sizes15:28
azonenberg_workLol so just for the heck of it i was reading up on metal etchants and found a section on platinum16:32
azonenberg_workThe two etches they suggest are aqua regia and molten sulfur :P16:32
SolidRavenNot really a shocker16:46
SolidRavenYou just listed two of the few things capable of harming platinum16:46
azonenberg_workI'm surprised they didnt just say "effectively indestructible"16:46
azonenberg_workas i dont think either of those etches is very selective :P16:47
azonenberg_workThey'll eat almost anything you can try to mask it with16:47
SolidRavenwell, aqua regia doesn't harm polymers all that much16:47
Action: azonenberg_work gets terrible idea16:48
SolidRaven+ you could use titanium oxides to protect the wafer...16:48
azonenberg_workDoes aqua regia eat silicon?16:48
SolidRavenThose are resistant to aqua regia16:48
SolidRavenNot sure16:48
SolidRavenBut I doubt it'll be healthy for the other wafer16:48
azonenberg_workI was going to suggest using a platinum or gold hardmask (which i can sputter or even deposit by sol-gel)16:49
azonenberg_workthen use aqua regia to etch it through photoresist16:49
azonenberg_workHalf jokingly, i dont want to have the stuff around right now (no fume hood)16:49
SolidRavenThat'd probably work16:49
SolidRavenI wonder if it harms silicium16:49
azonenberg_workIn the meantime what i want to try is making some BOE16:49
SolidRavenGet a silicium crystal and dump it in some aqua regia16:49
SolidRavenThe chemistry department should have some spare aqua regia anyway16:50
SolidRavenIt's ideal for cleaning things16:50
azonenberg_workIf i can get my photoresist to survive a BOE etch then i'm in good shape16:50
azonenberg_workspin coat tantalum oxide and pattern by straightforward wet etch16:50
SolidRavenazonenberg, seriously if you use titanium you could use aqua regia to etch!16:58
azonenberg_workI have no way to deposit titanium17:00
azonenberg_workAt least not yet17:00
azonenberg_workI'd need to sputter or evaporate and i dont have the equipment for either atm17:00
SolidRavenYou could also use the aqua regia to deposit gold on a surface now that I think about it17:02
SolidRavenBut that'd require a (large) current :(17:02
azonenberg_workElectroplating gold from aqua regia? Yeah17:03
azonenberg_workI could synthesize copper chloride easily enough and electroplate it potentially17:03
azonenberg_workI just dont know if it would give good results17:03
azonenberg_workI also dont think copper would work well as a hardmask17:04
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