<azonenberg>
I don't currently have any HNO3 in my lab, I usually let my friend john (the other guy behind siliconpr0n) do the wet lab work
<azonenberg>
He also has a computer-controlled microscope which is able to do automated mass imaging of a large die while i have to take all my pictures by hand
<azonenberg>
i'm catching up, ordered the first batch of parts to CNC my microscope today
<azonenberg>
and i now have a homebrewed fume hood so i'm less concerned about fumes from decapping
<azonenberg>
Why do you ask?
<hideo>
azonenberg: are you walter white?
<azonenberg>
hideo: lol no
<hideo>
:P
<azonenberg>
I do have blue crystals in a cabinet
<azonenberg>
But they're blue raspberry rock candy
<azonenberg>
One of my roommates was watching the show and i freaked him out tossing the packet at him :P
<azonenberg>
you should have seen the look on his face
<hideo>
hahaha
<hideo>
you don't watch bb?
<azonenberg>
Not regularly
<azonenberg>
i've seen a bit here and there
<hideo>
it's really good
<azonenberg>
Most of what I "watch" these days is man pages
<azonenberg>
and journal articles
<hideo>
it's the only tv i watch
<azonenberg>
I probably have another month or so of work to do on general lab tooling
<azonenberg>
then build the spin coater and mask aligner
<azonenberg>
at which point i can start pushing hard
<azonenberg>
see if i can get good patterning in, say, spin-on glass across a full 2" wafer
<azonenberg>
I also need to get a good anisotropic silicon etchant and photoresist developer that are metal-free
<azonenberg>
I've been using NaOH and KOH in the past since MEMS aren't ion sensitive
<azonenberg>
but if i want to do CMOS that'll have to stop
<azonenberg>
TMAH is a bit nasty but i have an interesting idea
<azonenberg>
Since in, i think, both cases it's the OH- that does the dirty work
<azonenberg>
what's a nice nonmetallic organic base that's easy to find? Ammonium hydroxide
<azonenberg>
Somewhat more volatile than TMAH but much easier to get hold of
<hideo>
try it and see
<azonenberg>
For developer, you dont need very aggressive
<hideo>
yeah
<azonenberg>
And for etch, well
<azonenberg>
i dont expect to do through-wafer etches with it
<azonenberg>
for MEMS i can use KOH
<hideo>
tmah is usually diluted as developer
<azonenberg>
Yeah
<azonenberg>
What i mean is, i want to put alignment marks in the silicon
<azonenberg>
to line implants up against
<azonenberg>
That will also function as a test etch for finding orientation if i'm doing KOH etc later on
<azonenberg>
So i only need to go down maybe half a micron, enough to leave a visible edge
<azonenberg>
Thats a more difficult problem i can deal with later
<azonenberg>
but if straight ammonia, perhaps diluted, is usable as developer i'm fine
<azonenberg>
Just have to get something with the same OH- concentration as ~1% TMAH
<azonenberg>
iirc thats whats usually used
<azonenberg>
but for aggressive Si etching you'd use 30% KOH and probably TMAH at a similar concentration
<hideo>
do you have DI water?
<azonenberg>
As of now, just distilled
<azonenberg>
I've focused on lithography and it's pure enough for that
<azonenberg>
i haven't attempted to make transistors
<azonenberg>
it's sat in the plastic jugs for enough months it probably isnt DI grade
<azonenberg>
They're HDPE though so it probably hasnt picked up many metal ions
<azonenberg>
CMOS is a whole other ball game in terms of the necessary purity etc
<azonenberg>
thats why i'm trying to do a comb drive as a first step
<azonenberg>
it demonstrates patterning at the necessary scales but is much more tolerant of ionic contamination
<azonenberg>
And i think i can pull it off in <110> Si with KOH if i angle things right
<hideo>
gah unfortunately i can't say much
<azonenberg>
My plan is to start out by taking a wafer with a single metal layer over oxide, pattern that single metal layer
<azonenberg>
then put overglass over it
<azonenberg>
do flip-chip BGA bonding
<azonenberg>
Just metal, no active components
<azonenberg>
That will let me test metal patterning as well as packaging
<azonenberg>
The next step will be two or three metal layers with CMP in between
<azonenberg>
I'm tentatively thinking copper damascene in spin-on glass
<hideo>
cmp? chem-mechanical polishing?
<azonenberg>
yes
<azonenberg>
if i use thick SOG as the ILD, i might get enough planarity from that
<azonenberg>
Anyway, once i demonstrate a full BEOL process including packaging and flip-chip bonding
<azonenberg>
then i'm going to try doing a MEMS FEOL process for doing the comb drive
<azonenberg>
At the end of that i should be able to make a comb drive in FCBGA
<azonenberg>
four balls, two on each electrode (for stability)
<azonenberg>
500um wafer thickness on the rim for stability, then back-thinned to ~50um in the active area
<azonenberg>
then through wafer etch with the finger pattern
<azonenberg>
it wont be nearly as nice as if i had DRIE but i dont know of any homemade MEMS ever
<azonenberg>
The next step will be to duplicate Jeri Ellsworth's CMOS FEOL process and shrink to the 12.5μm node using my litho process
<azonenberg>
and stick my BEOL on top
<azonenberg>
At which point i should be able to make a 2" wafer full of CD4000 chips and hopefully at least a few of them will work
<azonenberg>
complete with overglass around the bond pads and solder bumps
<azonenberg>
That will be the biggest milestone
<azonenberg>
from then on it's just improving yields until i can make something as big as a microprocessor
<azonenberg>
Debating between making an i4004 (from the original released mask art)
<azonenberg>
and trying to make a custom CPU
<azonenberg>
Do you know if anyone's ever made a BGA-packaged i4004? ;)
<hideo>
nope
<azonenberg>
The other possibility, like i said, is a custom CPU
<azonenberg>
Depends in part on where my yields are at that point and what process node i'm at
<azonenberg>
i can get cheap plastic film masks down to 12.5μm design rules (3.125μm pixels, 4 pixel min-feature design rules)
<azonenberg>
if i want to go finer i'm probably going to have to either kick out major $$$ for chrome on glass
<azonenberg>
Or ditch contact lithography
<azonenberg>
move to projection and build myself a stepper
<azonenberg>
with 4x reduction or so
<azonenberg>
Right now i'm using projection but there's no stepping/scanning
<azonenberg>
so i'm limited to one objective FOV, which is tiny
<azonenberg>
i'm moving to full-wafer contact in the short term but i want to make a stepper/scanner in the long term
<azonenberg>
It also depends on where i am in my education/career at that point
<azonenberg>
once i get out of school and save up for a few years i'm planning to build myself a house (if you can call it that) with a class 1000 cleanroom and a few other nice lab facilities
<azonenberg>
i could quite plausibly be able to do submicron features reliably, though likely not with great yields
<azonenberg>
RIE isn't even out of the question in the long term
<azonenberg>
if i could get the proper plumbing installed and find some cheap stuff used from an old 500nm fab someone is shutting down etc
<azonenberg>
SF6 only would probably be a good initial setup
<azonenberg>
Since if i could do nice vertical trenches in oxide, i could do copper damascene
<azonenberg>
The first step would be sputtering or evaporation, i NEED in-house metal deposition capability more than really sharp etches
<azonenberg>
i'm pretty sure i can do at least 12μm features reliably with wet etching
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<Sync>
azonenberg: for that feature density you don't really need a cleanroom
<Sync>
we do most stuff on laminar flow benches and yields are good
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