<R0b0t1>
azonenberg: How do you draw onto the miscoscope slide to backwards-project it?
<R0b0t1>
(if that made any sense...
<R0b0t1>
)
<azonenberg>
R0b0t1: I laser-print on transparency film
<R0b0t1>
I assume you can get more resolution that way than you could reasonably etch at this point?
<R0b0t1>
I think you said your feature limit was something like 250µm, could the projection be finer than this with printing?
<azonenberg>
R0b0t1: My printing has a 200 um design rule
<R0b0t1>
Is that the printer or your ability to etch it?
<azonenberg>
The printer
<azonenberg>
600 DPI times about four or five pixels minimum
<azonenberg>
Then I reduce that optically
<azonenberg>
At 40x reduction, that gives me 5um line width
<azonenberg>
And i've fabricated 5um patterns in photoresist before
<azonenberg>
However, my illumination is uneven in the 5um process so i cannot get 5um across the entire FOV
<azonenberg>
Also, none of my fab processes are able to (yet) transfer a PR pattern that small onto something else
<azonenberg>
My liftoff is close to debugged but i havent tried anything smaller than 20um with it
<R0b0t1>
1) What causes the illumination to be uneven, and how would you fix it? 2) What are the typical trace widths in modern ICs?
<azonenberg>
And i need to get thin low-stress films to prevent cracking during the KOH etch
<azonenberg>
The illumination is uneven because i'm using a pocket flashlight as my exposure source :P
<R0b0t1>
.... XD
<azonenberg>
I plan to fix it by buying a fiber-optic microscope illuminator and using that instead
<azonenberg>
when i have $200ish to spare, thats a solved problem
<azonenberg>
Typical trace widths in modern ICs are very roughly double the technology generation size
<azonenberg>
double to triple*
<azonenberg>
So for a 350nm chip a 1um trace size is typical on top metal
<R0b0t1>
When you say "350nm chip" what exactly does that mean?
<azonenberg>
Technically its the half-pitch of a SRAM cell made on that technology generation
<azonenberg>
Which means very little
<R0b0t1>
Oh is it some weird industrial standard?
<azonenberg>
Pretty much
<R0b0t1>
Do traces not go below that or...?
<azonenberg>
Traces are usually several times that
<azonenberg>
The width of a single transistor gate can be less
<R0b0t1>
Oh, I heard something about light... and one micron...
<azonenberg>
for example in microchip's 350nm process i've measured traces on top metal to be around a micron wide
<azonenberg>
I prefer to use more concrete numbers, namely the minimum size design rules for line features, point features, and so on
<azonenberg>
Which accurately describes what i can actually fabricate
<R0b0t1>
yeah
<azonenberg>
So I would describe a process as being a 5um design rule with a 1.058um lambda
<azonenberg>
meaning that all dimensions are multiples of 1.058 um (1/600 inch, the printer dot size, divided by a 40x objective)
<azonenberg>
And that no single structure can be smaller than 5um
<R0b0t1>
Ok, thanks for the answers
<R0b0t1>
I heard some laser engravers can etch glass, so I wondered if they'd be able to etch channels in microscope slides
<R0b0t1>
and then you use capillary action to fill them with ink
<R0b0t1>
but w/e
<azonenberg>
If anything, i'd plate the slide in metal
<azonenberg>
and use the engraver on that
<R0b0t1>
Yeah
<R0b0t1>
lol
<R0b0t1>
I realized it would be easier to just coat it
<R0b0t1>
then remove it
<R0b0t1>
Which kinda could be done with most things, I guess
<R0b0t1>
Or well idk
<azonenberg>
Yeah
<azonenberg>
Metal would work better since its more opaque
<azonenberg>
In any case mask making is not the current bottleneck
<R0b0t1>
Yeah that's what I realized
<R0b0t1>
so everything I was thinking of was a bit too preemptive :p
<azonenberg>
The problem is little details of trying to get the hardmask to work properly
<azonenberg>
Which i hope to solve fairly soon
<R0b0t1>
"work properly"?
<azonenberg>
HF wet etching through PR doesnt work when your photoresist is permeable to F- ions
<azonenberg>
And liftoff is a little tricky if your photoresist is slightly soluble in the hardmask's solvent
<azonenberg>
I'm experimenting and hope to have a workable process soon
<azonenberg>
I think if i hardbake the PR a little longer it will work well with liftoff
<azonenberg>
i just need to densify it to the point that it's just a little less soluble
<berndj>
azonenberg, is the hardmask solution [close to] saturated?
<azonenberg>
berndj: I'm actually not sure
<azonenberg>
it's 16%
<azonenberg>
i havent looked up solubiltiy figures
<azonenberg>
berndj: I am actually thinking of diluting it though
<azonenberg>
Because my current coating method gives poor repeatability due to lack of precise spin speed control
<berndj>
my lone of thinking was, maybe you could concentrate the solution further, hoping to reduce how quickly the PR dissolves?
<azonenberg>
No, it will leave way too thick a layer
<azonenberg>
If i spin really fast i get poor repeatability but low dissolution
<berndj>
but that's by no means a guaranteed result.  and repeatability seems like a more important goal
<azonenberg>
So my thinking is to dilute, quickly coat one drop
<azonenberg>
then use color to determine if another drop is needed
<azonenberg>
All i need is a continuous film
<azonenberg>
I'm using liftoff to pattern so i dont care about exact thickness since i'm not etching it
<berndj>
or if you add some other solute that doesn't influence viscocity so much?
<azonenberg>
Not sure if i could do that without affecting the generated film
<berndj>
i'm still surprised that spin coating gives a roughly uniform-thickness coat
<azonenberg>
I think the best bet is just to not leave it on the film long
<azonenberg>
on the resist*
<azonenberg>
I'll be testing that tonight
<azonenberg>
then later in the week taking it up to rpi's materials research center
<azonenberg>
a guy there is willing to give me a few hours on a SEM
<berndj>
nice!
<azonenberg>
So i can do low-angle cross sections etc of my dies to date
<azonenberg>
and measure sharpness of my probe tips
<azonenberg>
My work between now and then will focus on getting a wide variety of samples to image
<azonenberg>
for example, resist on silicon that's been developed but not etched or anything
<azonenberg>
so i can study the adhesion at the interface
<berndj>
heh, reminds me of that old joke. stop me if you know it; i'll adapt to your probe tip
<azonenberg>
hardmask that's been coated but not exposed to acetone
<azonenberg>
hardmask that's been exposed to acetone before baking
<azonenberg>
hardmask that's been lifted off both before and after baking
<azonenberg>
Basically i want dies at every stage of processing that might be causing the problem
<berndj>
world's best inventor invents the sharpest needle the world has ever seen, shows it to the world's tech companies. the swiss look and say, 'no need for this'. germans say, 'impressive, ja? but we can't think of anything to do with it.' japanese say, 'hmm, interesting, we don't know what to do with it, but we drilled a hole down the middle for you'
<berndj>
do you nead to cleave the dies to get a cross section, or do you do that with SEM magic?
<azonenberg>
Lol
<azonenberg>
And actually, if i cleave them the film will likely chip off the edge (though a micron or so away it'll be fine
<azonenberg>
My plan is to place them at a steep angle (maybe 70 degrees)
<azonenberg>
and then image from that angle
<azonenberg>
I can also do a true xc with a 90 deg shot
<azonenberg>
But i think high angle is more likely to be suitable than full perpendicular
<azonenberg>
In any case i'll fool around once i hop on the scope
<azonenberg>
I'll need a few minutes to get familiar with it anyway as i havent used this instrument before
<azonenberg>
SEMs have more controls than optical scopes so learning which one does what can be a little tricky the first time you use one you havent used before
<azonenberg>
The cleanroom on campus has a zeiss supra 55 which i've used before, but its expensive to use
<berndj>
why "expensive" - actual running costs or rather opportunity costs?
<azonenberg>
Not sure, all i know is that's what they charge people
<azonenberg>
They charge a definite profit if you arent under an RPI grant
<azonenberg>
if you're a local researcher they charge your grant at a reduced rate
<azonenberg>
This one is much cheaper to use (about $60 vs $190 an hour) than the one in the cleanroom (because it isnt in a cleanroom) and the guy is even willing to let me use it for a couple of hours at no charge
<berndj>
nice
<azonenberg>
Though if more than a couple of hours is required i'll need to shell out some $$
<berndj>
probably under "if we need it we'll kick you off" terms?
<azonenberg>
Most likely i'd be bottom of the priority queue, but thats to be expected
<berndj>
i think i only ever saw one SEM
<R0b0t1>
They charge you to use the equipment...?
<berndj>
hehe, almost like an observatory's director's discretionary time
<azonenberg>
berndj: Pretty much, the guy i'm talking to is the director of the microscopy lab for the mat sci department
<azonenberg>
R0b0t1: Most resources are available at no charge but a few things like the SEMs are expensive to run (spare parts and such)
<azonenberg>
Especially if they're in a high-maintenance lab like a cleanroom
<berndj>
would you have to coat your chip?  or wouldn't there be any PR / hard mask solvent left to screw up the vacuum
<azonenberg>
berndj: Everything will be baked to drive off solvents etc before i bring it up there
<azonenberg>
I'll be coating them but not for that reason
<azonenberg>
It's difficult to image non-conductive materials (like the hardmask) with a SEM because the electron beam builds up on the surface and gives it a negative charge
<azonenberg>
Which repels the inbound electrons and eventually gives you a blank image
<berndj>
when i was little i used to think the bugs etc. in SEM pics were still alive
<azonenberg>
The solution is to sputter it in a few nm of gold or platinum or similar
<azonenberg>
and ground it
<R0b0t1>
You mean they didn't just snap a still? D:
<R0b0t1>
(lols)
<azonenberg>
R0b0t1: Electron microscopes only work in vacuum
<azonenberg>
berndj: Generally if you're doing school-sponsored research they charge your research grant for the lab time
<berndj>
i imagine many insects could survive a vacuum though
<azonenberg>
typically at-cost and sometimes even a bit lower
<berndj>
yeah. well, *somebody* has to pay
<azonenberg>
But if you're an outside user they charge the cost of time plus profit
<azonenberg>
So i'm quite lucky to have found someone willing to give me even a couple of hours on one
<azonenberg>
And at a reasonable rate should i decide i need more time
<berndj>
i suppose in a case like yours, sometimes you can pay in the form of having something really interesting to tell whoever owns the gear
<azonenberg>
berndj: Thats basically why he's letting me on lol
<azonenberg>
but it's not enough to give me 50 hours of free sem time :P
<azonenberg>
Maybe 5
<azonenberg>
berndj: Also, some field emission SEMs can run at decently low vacuum (lower resolution in that mode though)
<azonenberg>
And people have successfully imaged live insects on them
<berndj>
yowzer
<R0b0t1>
:o
<azonenberg>
I dont remember the exact details but it's been done