<wpwrak>
in the end, you'll have a joystick with which you direct the death ray that picks off those last molecules that resisted everything else you threw at them ;-)
<wpwrak>
azonenberg: you guys lost me at KOH vs. HF. i live in HCl+H2O2 stone age. what do these critters do ? i suppose at least one of them is an etchant, but does this make the other ?
<azonenberg>
wpwrak: HF is hydrofluoric acid, which eats
<azonenberg>
SiO2 (glass) and related materials
<azonenberg>
But not silicon or polymer materials
<wpwrak>
sound like nasty stuff :)
<azonenberg>
HF is quite nasty, thats why i work with 2% solution and am still paranoid with double gloves, a face shield, etc :P
<azonenberg>
Overkill considering the stuff in this concentration is household rust remover
<wpwrak>
i usually consider glass and ceramics as my final barrier ;-)
<azonenberg>
But i've seen what the strong stuff can do
<azonenberg>
My photoresist is a polymer that dissolves in a weak solution NaOH (household lye) when it's been exposed to light
<azonenberg>
UV in particular
<azonenberg>
So you shine UV through your mask onto the resist, then develop
<azonenberg>
Then you can use HF to eat away the glassy layer under it
<azonenberg>
but only where light hit the mask
<wpwrak>
(rust remover) hmm, interesting.
<azonenberg>
It's rare, most rust remover is phosphoric acid
<azonenberg>
But Whink brand is HF based
<azonenberg>
KOH is potassium hydroxide (caustic potash) which will eat silicon
<azonenberg>
It also attacks photoresist so i need the Ta2O5 glass layer as a mask
<azonenberg>
i.e. pattern hardmask with photoresist, then pattern silicon with hardmask
<azonenberg>
using two etch steps
<azonenberg>
The nice thing about KOH is that it's sensitive to the bond structure in the silicon crystal
<azonenberg>
It eats nearly 100x faster along one axis than the other one
<azonenberg>
So by choosing the angle that you cut the wafer vs the bond planes you can get almost no etching (surface on the <111> vector), 57 degree sloped sidewalls (surface on the <100> vector), or vertical sidewalls (surface on the <110> vector)
<wpwrak>
brr. messy. i kinda liked whatshername's transistor-making process you once mentioned. obviously, the process control roles are reversed there, but it seems that isn't nothing too horrible to do
<azonenberg>
Jeri used HF
<azonenberg>
Same concentration as I am - 2% from Whink rust remover
<azonenberg>
The main difference is she was doing patterning by hand with electrical-tape masks etc
<wpwrak>
yeah ;-)
<azonenberg>
I'm doing real lithography at several-micron scales
<azonenberg>
And i'm not to the point i can do transistors at this scale by far
<azonenberg>
The first step is MEMS
<azonenberg>
Build a comb drive
<azonenberg>
And before that, basic 2D engraving in Si
<azonenberg>
Shallow etching, 10 microns or so
<azonenberg>
just characterizing the process
<wpwrak>
i don't know much about mems or their use. i have some ideas what a transistor can be good for, though :) one problem i'd envision is just connectivity. that's some more layers.
<azonenberg>
Connectivity, well
<azonenberg>
Etching metal is a solved problem, so is alignment
<azonenberg>
The unsolved problem is how to get the metal there in the first place
<wpwrak>
yup
<azonenberg>
there are several deposition processes (sputtering and evaporation are the two big ones) but both need high vacuum
<wpwrak>
which requires some alchimist's lab in paris
<azonenberg>
Lol, or something i build here in new york
<wpwrak>
and people are worred about cern's black holes eating geneva ;-)
<azonenberg>
Lol
<azonenberg>
Black is informational only (not on the actual mask)
<azonenberg>
The outer disk around each pattern is the field of view of my exposure system (about 500 microns)
<azonenberg>
Blue areas are masked off, white is to be etched
<azonenberg>
Everything outside the disk is not etched
<wpwrak>
damn small. i still kinda like the idea of a dual BR direct exposure system.
<azonenberg>
I'm still thinking of direct write but not for exposure on the wafer
<azonenberg>
it'll be used for making metal-on-glass masks
<azonenberg>
that are then used in my projection system
<wpwrak>
if you have it, why not use it for everything ?
<azonenberg>
Because it can pattern but has little alignment capability
<azonenberg>
unless you build it in a far more advanced way
<azonenberg>
The idea was, stick mask blank into the system
<azonenberg>
zero it *somewhere* on the blank
<azonenberg>
expose, develop, etch
<wpwrak>
hmm. i'd try to align with perhipheral features. edges, holes made for that purpose, whatever.
<azonenberg>
now you have your mask, 100nm of (say) nickel plated on glass
<azonenberg>
With 50 micron (for example) features
<azonenberg>
Feed that into my current exposure system
<azonenberg>
Reduce 10x
<azonenberg>
You now have 5um features and a 2mm FOV, which is enough for a pretty good sized die
<azonenberg>
It'd be enough to build a 4004 i think
<wpwrak>
2 mm is plenty, yes
<azonenberg>
500um is FOV with 40x objective
<azonenberg>
2mm is FOV with 10x
<azonenberg>
But that also means my feature size grows 4x so the only way to prevent that is to make the mask 4x smaller
<azonenberg>
i.e. 50um half-pitch vs 200um (the limit of my printer)
<azonenberg>
I could even hit 5mm if i used the 4x obj but that'd be pushing it
<wpwrak>
or just use direct writing ;)
<azonenberg>
Because i'd need 20um features on the mask
<azonenberg>
And those would be so small i wouldn't be able to see them at 40x magnification easily and get good alignment
<azonenberg>
100x is about the minimum to get micron-level alignment
<azonenberg>
And like i said, i'd love direct write onto the wafer
<azonenberg>
I just think it's beyond trhe scope of a rev 1 process
<wpwrak>
whatever rev 1 may be :) for me, your inverted scope is an excellent hack. not only for the idea itself, but also because it breaks down one of those imaginary barriers.
<azonenberg>
Exactly
<azonenberg>
That was the single biggest unsolved problem for me, my group at RPI was puzzling over lithography and mask alignment for months
<azonenberg>
thinknig about building an optical column from scratch
<azonenberg>
Then i realized we already had one, problem solved
<wpwrak>
but for a more dependable process, it seems to me that BR drives are an excellent opportunity. they have the resolution and, thanks to mass-market volumes, they're relatively cheap.
<azonenberg>
Yeah, I fully agree with you there
<azonenberg>
It's just something that should be saved until the rest of the process is somewhat more mature
<azonenberg>
If you want, i can set you up with access to the project http://code.google.com/p/homecmos/ so you can hack on the wiki and start throwing thoughts in there
<wpwrak>
(building an optical column) looks like one of those problems that seem ridiculously simple - once you've solved them ;-)
<azonenberg>
Exactly, once you have all the numbers and plans anybody can go build it
<azonenberg>
It's the engineering that's hard
<azonenberg>
And, once you've built it, the calibration
<azonenberg>
getting everything precisely in focus
<wpwrak>
i have a strong belief in the law of large numbers ;-)
<azonenberg>
Lol
<azonenberg>
And this is a solved problem with the microscope - which is a pretty nice piece of glass for the price
<azonenberg>
The only big problem is chromatic aberration at higher powers
<azonenberg>
But when using monochromatic light from an LED? Non-issue
<wpwrak>
the microscope looks more like a mid-way point. it solves the problem at hand, showing that it can be solved, but it suffers many limitations as well (FOV, for one)
<azonenberg>
Correcty
<azonenberg>
Hence why it's a rev 1 process
<wpwrak>
besides, it's not really "cheap". while BR is, by and large.
<azonenberg>
The big problem, like i said, with BR is alignment
<azonenberg>
It's going to have to be done like they do with steppers
<azonenberg>
you have purpose-built alignment marks around the edge of the die
<azonenberg>
that it calibrates off
<wpwrak>
i stil think you can just use opportunistic alignment. find any features, and align to them.
<azonenberg>
Maybe for rev 3? But it'd be tricky
<azonenberg>
This would be quite the hack if we pulled it off though
<azonenberg>
Direct write laser lithography system with 5um or better features
<wpwrak>
you only care about repeating what you did before. but there's no absolute origin or orientation.
<wpwrak>
indeed. Intel@Home ;-)
<azonenberg>
Good point, only alignment matters
<azonenberg>
But what about if you have a nearly blank mask?
<azonenberg>
Also, when you say "align to them"
<azonenberg>
The detector is easy
<azonenberg>
But how do you see it?
<azonenberg>
Illuminate with the laser? Bear in mind every laser pulse punches a hole in the photoresist
<wpwrak>
i'd align with the chip/fragment. or if that doesn't work, make a hole and align with that.
<wpwrak>
(not sure about the cleaning, though)
<azonenberg>
Hole meaning drilled?
<azonenberg>
Waaay too imprecise
<wpwrak>
yes
<azonenberg>
Do you have any idea how small five microns is?
<azonenberg>
Hint, typical human hair is 20um across
<azonenberg>
Let's say you drill a hole 1mm across
<wpwrak>
you only care about finding the same edge several times again
<azonenberg>
You need to be able to localize to within 1/50 of the hole diameter
<azonenberg>
And you'd need >1 hole to get rotation locked down as well as position
<azonenberg>
It'd just be too imprecise
<wpwrak>
sure. make as many holes as you want. the first one is expensive, the rest is free ;-)
<azonenberg>
lol
<azonenberg>
the other thing is, in MEMS, puncturing the die can be problematic
<azonenberg>
You might need a big piece for a heatsink or whatever
<azonenberg>
It just strikes me as a really bad idea
<azonenberg>
Whereas if the first exposure etched alignment marks into th esurface
<azonenberg>
At 5um pitch
<azonenberg>
We could then see those markings and align future stages to them
<wpwrak>
you don't need the exact position relative to the hole center or such. all you need is an edge you can detect accurately (with significantly less than infinite tries ;). once you have that, you can always reuse that edge.
<azonenberg>
The other thing is, silicon fractures along cleavage planes
<azonenberg>
A hole is a potential fracture point
<wpwrak>
(mems) yeah, dunno about mems.
<azonenberg>
And, on top of that, each edge of the hole is going to be (at the microscale) broken along one of the cleaveage planes
<wpwrak>
could you try to cut/mill a straight line ?
<wpwrak>
you'd of course end up with a jagged edge, because you won't match the substrate's orientation
<azonenberg>
Well, the substrate will have at least one edge (or a flat for a wafer) parallel to a cleavage plane
<azonenberg>
you'd align theta to that
<azonenberg>
So you're aligned to the crystal structure
<wpwrak>
one degree of freedom solved :)
<azonenberg>
(for the first level) and then etch your main pattern plus alignment markings
<azonenberg>
crosses, vernier scale, etc
<azonenberg>
Around the edges
<azonenberg>
Then the next level just aligns to them
<wpwrak>
doesn't sound too bad. you still need at least two edges to align to, though for each step.
<azonenberg>
No, you need one edge for the first step since you know which plane it's on a priori
<azonenberg>
From there on, you have a cross at each side of the die
<azonenberg>
Align x/y to the center of them
<azonenberg>
and theta so that the lines are parallel to your axes
<azonenberg>
google "byu contact aligner" for Bringham Young Universtity's doc on their manual mask aligner
<azonenberg>
We just need to design an automated system that can read those marks
<wpwrak>
that's your microscope process. but what about the BR process ? there's not much a priori there. the machine has to discover everything on its own, each time the die is inserted.
<azonenberg>
no, you misunderstand
<azonenberg>
You stick the die into it, it scans the edge
<azonenberg>
Determines the crystal orientation (if the first run)
<wpwrak>
yes
<azonenberg>
i.e. you tell it "this is a <100> wafer, align X axis to a <111> plane
<azonenberg>
Then it'll center your pattern on the fragment approximately
<azonenberg>
Future exposures will scan the edge, determine the approximate center (to within 100um or so, really coarse) and then locate the alignment crosses
<azonenberg>
which it will use for the real fine alignment
<azonenberg>
The problem is that we need to figure out how to see those marks
<azonenberg>
and get data that a machine vision system can use to determine the actual position of the die and adjust the stage accordingly
<wpwrak>
ah, you're trying to identify features on the die
<azonenberg>
Correct
<azonenberg>
Its the only way to get precise alignment
<azonenberg>
below a hundred microns or so
<wpwrak>
i was thinking of just (re-)identifying the die's shape
<azonenberg>
Not good enough
<azonenberg>
Some of my substrates are precise rectangles 1cm square
<wpwrak>
you don't need a simple euclidian shape. i think it should be sufficient to identify the chaotic edges.
<azonenberg>
Take it from someone who's done a good amount of machine vision
<azonenberg>
Simple euclidean shapes are waaaay easier to work with
<azonenberg>
And you can get better precision with them
<wpwrak>
oh, fiducials are great - if you have them ;-)
<azonenberg>
What do you mean?
<wpwrak>
i'd add them just for fun. and check them if anything goes wrong ;-)
<azonenberg>
The first mask level is positioned approximately
<azonenberg>
Adds marks for all subsequent alignment steps
<azonenberg>
All of the others lock onto those marks
<wpwrak>
well, our problem is that it's easy to write with high precision and within a large area, but it's hard to see things with high precision within a large area
<azonenberg>
Unless you're built into a microscope
<wpwrak>
where "see things" means a generalized kind of vision
<azonenberg>
You need a camera of some sort, which means an optical column
<azonenberg>
I still think the best option is direct write with little to no alignment onto a mask blank
<azonenberg>
followed by manual alignment using the microscope
<wpwrak>
now, there are some things you can see easily, e.g., whether an edge obscures a narrow beam or not
<azonenberg>
But there's another problem
<azonenberg>
Drift
<wpwrak>
drift of what ?
<azonenberg>
As you pan from one side of the die to the other
<azonenberg>
Alignment will gradually be lost
<azonenberg>
due to imprecisions in the motors etc
<azonenberg>
I suspect you'll need to realign periodically during a long run
<azonenberg>
Especially if stepping multiple patterns on multiple dies on one wafer
<azonenberg>
IOW, if i move 1000um right and 1000um left
<azonenberg>
I won't be exactly where i started
<wpwrak>
if you lose alignment within the die, you're probably screwed. well, unless you can model the loss accurately :)
<wpwrak>
yeah, big wafers would be an issue. i can see that.
<azonenberg>
Well, i think we can all agree that the first draft of the bluray system will have little to no visio ncapability
<wpwrak>
but perhaps that's a version 2 problem ? :)
<azonenberg>
and just be direct patterning on mask blanks
<azonenberg>
Vision is a v3 problem
<azonenberg>
v2 is where we introduce laser direct write
<azonenberg>
v1 is transparencies on microscope
<wpwrak>
v3 then :)
<wpwrak>
i think you still need simple vision for lowering the requirements for v2. 2 x BR player plus a photo diode is still a lot more accessible than a camera-ready microscope
<kristianpaul>
hacking  a camera you mean?
<wpwrak>
(fiducials) looking at the patterns, i wonder if they didn't exaggerate perhaps just a little (towards the end) ;-)
<kristianpaul>
i wonder what can you do inverting some lenses on a cheap canon camera, if already on a cheap webcam is not that bad for DIY scopes~
<azonenberg>
Exaggerate? What do you mean
<azonenberg>
When you're trying to get alignment down to a few nm it's kinda important
<wpwrak>
kristianpaul: ah, i think we covered the "mass market camera" side already :) the somethat disappointing result is that they don't go far enough (sample size = 1, so take this for whatever it means :)
<azonenberg>
You need to be able to start from any angle and determine the correct position
<wpwrak>
what you really need is an edge. two for 2D alignment. i even get 45 deg crosses, but stepped bars, extra-narrow edges of rectangles with rounded corners ? :)
<azonenberg>
The rounded corners are an artifact of the etch probably, and the long bars are for theta alignment
<azonenberg>
you need a baseline that's good enough to find the other alignnment mark across the wafer
<azonenberg>
then the small stepped bars are probably a vernier scale
<wpwrak>
okay, but that's more process optimizations then
<azonenberg>
for alignment to below the smallest feature scale you can etch
<azonenberg>
i know that the stepper the guys at work are using (not the same model as the one on this page) has a vernier
<wpwrak>
hmm. still looks suspiciously like a process designed for human vision to me.
<wpwrak>
perhaps for some truly advances computer vision as well. but just to find a few edges ?
<azonenberg>
It's advanced vision
<azonenberg>
Those things cost $40M +
<azonenberg>
Lol
<azonenberg>
For my process i envision using a much simpler alignment strategy
<azonenberg>
Probably just a couple of crosses at 0/90/180/270 degrees
<wpwrak>
i guess that's cheap as far as such things are considered ;-)
<wpwrak>
i'd just let the damn machine scan the ragged edge, that's tens of thousands of data points. if you can't mine a decent position from that, what else can you do ? ;-)
<azonenberg>
The thing is that not all of the dies have ragged edges
<wpwrak>
(BR drive) yes. the idea is to make a direct high-resolution writer from the head assembly of two Blu-Ray readers: one that provides laser and movement in the X direction, and other to move the target in the Y direction.
<lekernel>
roh: how are the rc3 cases going?
<kristianpaul>
lekernel: had you made some tests with OpenCV and mm1?
<lekernel>
no
<kristianpaul>
or and idea where to start with, i think i can econrage a univesiry student to take a look..
<kristianpaul>
ok
<kristianpaul>
or you have own plans for "Open Vision" on mm1 may be?