<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
<azonenberg>
Ok
<azonenberg>
At what resolution
<swkhan>
i have silicon wafers. i have copper tape. i have copper wire.
<azonenberg>
How thick copper?
<swkhan>
i have phosphoric acid and sodium hydroxide
<azonenberg>
do you want
<swkhan>
i am not sure. rivaling something i could sputter
<azonenberg>
First off, be advised that copper doesnt stick well to Si by itself
<azonenberg>
You normally need a thin Cr adhesion layer
<swkhan>
why not?
<swkhan>
awww
<azonenberg>
And the only process i've gotten good results with is vacuum evaporation
<swkhan>
so electrochemical deposition wouldn't work?
<azonenberg>
Not in a cleanroom, using the one my school's mat sci department uses for SEM sample coating
<swkhan>
what happens if you don't have an adhesion layer?
<azonenberg>
evaporate 5nm Cr + 1000nm Cu without breaking vacuum
<azonenberg>
and it tends to peel off
<azonenberg>
you get more overetch
<azonenberg>
i've had 200nm films with tens of microns of overetch without the adhesion layer
<swkhan>
i don't have access to chromium. i am doing this because a sputtering machine we had broke
<azonenberg>
Do you have access to an evaporator?
<azonenberg>
Electroplating of Cr followed by Cu might work if your wafer is heavily doped
<swkhan>
i don't have access to an evaporator
<swkhan>
i think the wafers are heavily p doped. we also have heavily n doped wafers
<swkhan>
so i'd gotten part of a process ready in my head
<swkhan>
i just finished up reading a textbook that gives me the equivalent knowledge of 1 year's worth of chemistry
<swkhan>
and i feel like i don't know anything when it comes to applying it =\
<azonenberg>
lol
<azonenberg>
I havent taken any chem either
<azonenberg>
And if they're heavily doped in general, you may have luck with electroplatnig
<azonenberg>
If you do, i'd be very interested in details so i can try duplicating the process
<swkhan>
but how does electroplating work with a semiconductor?
<swkhan>
sure, i was trying to come up with my own process
<azonenberg>
You have to have it doped heavily enough that you can make ohmic contacts
<swkhan>
everyone seems to use fancy electrolytic solutions
<swkhan>
may be for a reason...
<azonenberg>
Lol, yes
<azonenberg>
I focused on evaporation as i was depositing metal over a nonconductive surface
<swkhan>
i see
<azonenberg>
I want to build my own evaporator at some point but for now i'm using the one on campus
<swkhan>
cool!
<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)
<azonenberg>
so i just ordered some new filaments and 99.999% copper evaporation pellets from ted pella myself
<swkhan>
oooh
<azonenberg>
they were short on filaments last time i checked
<azonenberg>
In any case, i can definitely provide process development for etching
<azonenberg>
thats a reasonably well studied problem
<azonenberg>
What's your lithography setup look like?
<swkhan>
very crappy. i'm ms. super low budget =)
<swkhan>
i am masking with aluminum foil
<swkhan>
i'm not sure if it'll work
<azonenberg>
Where are you located?
<swkhan>
nasa ames (i work with ucsc)
<azonenberg>
And what kind of feature sizes are you trying to achieve
<swkhan>
to be PhD EE starting this fall =)
<azonenberg>
i mean, are you looking to hit 22nm or 25 microns :P
<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
<azonenberg>
I made one out of a 2x4, an electric drill, and a sanding wheel
<azonenberg>
that has given me good photoresist film quality down to 5 micron features (the smallest i've tried hitting with my exposure system)
<lekernel>
azonenberg, btw, could this spinning technique be used for PCBs as well?
<lekernel>
when you buy microwave-friendly PCB materials like duroid or alumina, they never come with photoresist
<lekernel>
this is quite annoying
<azonenberg>
lekernel: Yes
<azonenberg>
Dip coating is doable as well but requires a big tank
<azonenberg>
Spin coating of copper clad PCB is on the todo list
<azonenberg>
i have blank board but havent tried because i have so much precoated PCB :P
<azonenberg>
But the resist i have was sold for that purpose
<azonenberg>
... oops you left?
<azonenberg>
(16:55:24) azonenberg: Dip coating is doable as well but requires a big tank
<azonenberg>
(16:55:32) azonenberg: Spin coating of copper clad PCB is on the todo list
<azonenberg>
(16:55:45) azonenberg: i have blank board but havent tried because i have so much precoated PCB :P
<azonenberg>
(16:55:52) azonenberg:Â Â But the resist i have was sold for that purpose
<nathan7>
HI AZONENBERG
<azonenberg>
hi nathan7
<azonenberg>
Do you have a GDS viewer program on hand?
<nathan7>
GDS?
<azonenberg>
IC layout database
<azonenberg>
guess not :p
<nathan7>
mhm
<nathan7>
How so?
<CIA-67>
homecmos r115 | trunk/lithography-tests/default_600dpi/ (7 files in 7 dirs) | Committing previous changes to existing test masks
<azonenberg>
I guess i'll just send you a screenshot then h/o
<nathan7>
:o
<nathan7>
isitisitA GRATING?
<azonenberg>
Going to be, i havent actually made it yet
<nathan7>
:D
<nathan7>
kisses azonenberg's feet
<azonenberg>
disinfects feet with IPA
<nathan7>
hey
<nathan7>
that's nazi
<azonenberg>
no, it's just the absence of a foot fetish :p
<nathan7>
it is a sign of respect
<azonenberg>
In what culture?
<nathan7>
dunno
<azonenberg>
Here are two different mask patterns I'm considering
<azonenberg>
The left is what i expect it will actually look like
<azonenberg>
the right is what i'll be exposing (compensating for overetch etc)
<azonenberg>
in any case goldfilm is around $500 per 4-ounce bottle last i checked
<azonenberg>
prices vary based on raw material costs
<azonenberg>
it should last you a long time if my experience with tantalumfilm (which actually deposits Ta2O5, not Ta) is any hint
<swkhan>
i still want to deposit some sort of metal onto my nano scale device
<azonenberg>
Sputtering or evaporation is really the best bet
<swkhan>
=(
<azonenberg>
electroplating, among other things
<swkhan>
i'm trying to be creative and use any other methods i've got
<azonenberg>
means that you cannot deposit over an insulator
<bart416>
You can get metalic paint that's slightly conductive
<azonenberg>
bart416: that's a resin with silver flakes etc in it
<azonenberg>
i could not recommend it for anything small
<azonenberg>
"small" meaning <20 um
<bart416>
ah
<bart416>
if it's less than 100 µm plating is your only option
<azonenberg>
swkhan: you still havent told us the feature size and layer thicknesses you'e trying for
<azonenberg>
that makes a huge difference
<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
<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
<swkhan>
at least less than 0.5 mm
<bart416>
yeah, plating for sure
<azonenberg>
swkhan: 500 um? Oh, thats nothing
<azonenberg>
swkhan: I have hit 20um features using a living-room lithography rig
<swkhan>
let's say 20 um with shadow mask?
<azonenberg>
and am pushign to 5
<swkhan>
wow
<bart416>
Reminds me, I need to go and steal some CNC position encoder tomorrow
<azonenberg>
as in, my first and only attempt at 5um litho was last lab session
<azonenberg>
i overdeveloped :(
<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
<berndj>
speaking of vacuum tech, i must practice welding some more
<swkhan>
azonenberg: awww. no way around it?
<azonenberg>
nathan7: MEMS micromirror is a possibility for that
<nathan7>
azonenberg: mhm
<azonenberg>
swkhan: There are some theoretically possible ways
<azonenberg>
You could spin coat with goldfilm or something similar to make a thin conductive surface over the dielectric
<swkhan>
what about silver conducting pens
<azonenberg>
and then electroplate up
<berndj>
azonenberg, do you have any plans for metal contacts yet?
<bart416>
swkhan, silver is easy enough to deposit normally
<azonenberg>
silver pens? Depends on your feature size
<azonenberg>
they're silver flakes in a resin
<azonenberg>
as your feature size approaches flake size you'll get problems
<swkhan>
i am afraid that my deposited insulator might break off or something
<bart416>
Gold is where it gets tricky generally
<azonenberg>
i also am not sure about patterning it
<swkhan>
that was one thing i was considering... patterning
<azonenberg>
swkhan: You are worried about adhesion between the CVD SiO2 and the metal?
<azonenberg>
Or the SiO2 and the underlying Si where you dont have metal
<swkhan>
well i want a top and bottom contact
<swkhan>
so initially yes on sio2
<azonenberg>
Let me get this straight
<swkhan>
and then on some insulator's top side
<azonenberg>
your device consists of silicon, a metal layer, a dielectric layer, and another metal layer
<swkhan>
yes
<azonenberg>
Ok
<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
<swkhan>
ideally i'd like to use the same process for both the top contact and the bottom contact
<swkhan>
how do you know that the adhesion of metal onto silicon isn't bad?
<azonenberg>
I've worked with evaporated Cu over Cr adhesion layers
<azonenberg>
you can put scotch tape onto the die and press it on
<swkhan>
why does chromium keep coming up?
<azonenberg>
then pull off and the metal wont peel
<swkhan>
huh cool
<azonenberg>
Because without the Cr the Cu peels off
<azonenberg>
It wont do so spontaneously but under the slightest provocation it will
<swkhan>
what aspect of science tells you about this stuff?
<swkhan>
i want to learn how to get good at analyzing this
<azonenberg>
for example, when you etch the etchant will get in under the Cu and undercut your mask
<swkhan>
chemistry? physics? what specifically should i study
<azonenberg>
mat sci? Not really sure
<swkhan>
i read a whole book on chemistry but i'm not sure i'm prepared for it
<azonenberg>
My undergrad degree was in comp sci
<swkhan>
oh wow
<swkhan>
my undergrad was in EE (more circuits and programming)
<azonenberg>
swkhan: All of my EE background is self taught
<azonenberg>
i'm now a first year phd student also in comp sci lol
<azonenberg>
havent taken any ee classes whatsoever
<azonenberg>
only engineering course i took was machine shop :P
<swkhan>
wow!!!
<azonenberg>
Re etching, check out "Etch rates for micromachining processing, part ii" and the part 1
<azonenberg>
they're considered the bible of etching
<azonenberg>
My preferred metal etch for Cu and Cr is a dilute version of SC2 from the RCA clean
<swkhan>
well i want to keep it cheap, reproducible, and easy as possible
<azonenberg>
1 part conc. HCl, 6 parts 3% H2O2, 50 parts distilled or DI water
<swkhan>
oh that's easy and reproducible and cheap
<azonenberg>
etches at around 350-400nm/min
<azonenberg>
I'm not even using trace metal grad stuff
<swkhan>
so chromium helps stuff adhese for some reason
<swkhan>
metal to silicon at least
<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
<swkhan>
we have some acids
<swkhan>
we have loads of copper tape and copper wire
<swkhan>
we have fume hoods
<swkhan>
we have a power supply
<swkhan>
we have silicon and that's aluminum foil for shadow masking
<azonenberg>
You dont mask the metal
<azonenberg>
Deposit metal everywhere
<azonenberg>
then etch
<azonenberg>
for electroplating you should be able to do a lift-off proces
<azonenberg>
deposit photoresist over the entire wafer, expose, develop
<azonenberg>
then electroplate
<azonenberg>
it'll only stick to the conductive (uncoated) areas
<azonenberg>
so wherever you have resist there's no metal
<azonenberg>
then you dip it in solvent and you're done
<azonenberg>
But like i said, see about getting down some chrome if you can possibly figure that out
<azonenberg>
i can virtually guarantee you will have adhesion problems without it
<azonenberg>
take it from somebody who tried
<azonenberg>
There are solutions out there for doing Cr plating
<azonenberg>
so i suggest you check them out
<azonenberg>
looks like you can use chromium chloride
<azonenberg>
The benefit of liftoff is that you will be able to get by without etching, it eliminates a process step
<azonenberg>
the downside is that you have to do all of your patterning at once
<nathan7>
azonenberg: I'm considering doing the selective plating trick for PCBs
<azonenberg>
nathan7: you mean lay down resist and plate up?
<nathan7>
mhm
<azonenberg>
I'd be curious to see results
<nathan7>
then have Sn as a resist
<azonenberg>
let me know if you get around to it
<nathan7>
etch with persulphate
<nathan7>
need to order some SnCl2, dissolving Sn solder isn't cost-effective
<azonenberg>
lol
<nathan7>
(probably most of that money ends up in the Ag powder that is a byproduct from the 3% Ag)
<azonenberg>
what about just pure Sn strips?
<nathan7>
was fun to make H2O2 fizz with homemade Ag catalyst though
<nathan7>
3% H2O2, fizzed, fine
<azonenberg>
30? :P
<nathan7>
3%. all I can buy here OTC
<azonenberg>
Same here
<azonenberg>
i'm told you can get 5-10% in some places as a hair bleach
<azonenberg>
but 3% is all i need, in fact sometimes i dilute it
<azonenberg>
since i want a slow and controllable etch
<nathan7>
I read US pharmacies have 35%
<azonenberg>
maybe allowed to sell that highi
<azonenberg>
i called every one in town and nobody has it