<azonenberg>
nibbles idly on the <100> face of a sucrose crystal
<pepsi`>
(_)o(_)
<azonenberg>
pepsi`: you didnt know about this channel?
<pepsi`>
no
<pepsi`>
what kind of dastardly chemicals do i need?
<azonenberg>
Not that bad actually
<azonenberg>
for the metal patterning test i did, you need copper, high vacuum and high voltage, photoresist, drain cleaner, pool acid, and drugstore-grade hydrogen peroxide
<azonenberg>
We're still working toward a full IC process, its coming along but slowly
<pepsi`>
can i do this in a spare bedroom?
<pepsi`>
where am i going to get high voltage?
<pepsi`>
and a high vacuum?
<pepsi`>
that sounds noisy
<azonenberg>
pepsi`: high meaning 120 thorugh a variac
<azonenberg>
and the metal evaporation i did in a lab on campus, i am getting a vacuum rig of my own but its not here yet
<swkhan>
i wonder if the glue from copper tape messed with my cvd growth
<swkhan>
how would you get rid of the adhesive? i used isopropanol and acetone
<swkhan>
just standard tedpella copper tape
<azonenberg>
Hmm
<azonenberg>
Single or double sided?
<azonenberg>
And what sort of defects did you observe?
<azonenberg>
Looking at the MSDS and documentation the tape is using an acrylic adhesive
<azonenberg>
acetone dissolves acrylic nicely
<swkhan>
azonenberg: single sided
<swkhan>
well i expect a thin film
<swkhan>
i'm getting clusters
<azonenberg>
What are you depositing
<azonenberg>
and is the tape the source or the substrate?
<swkhan>
zinc oxide onto the copper tape
<azonenberg>
By CVD
<swkhan>
yes
<azonenberg>
ok
<azonenberg>
Have you deposited ZnO on Cu before?
<swkhan>
nope
<azonenberg>
Ok, so no baseline to compare to... hmm
<swkhan>
i mean, i tried it twice on copper tape cleaned with acetone
<azonenberg>
And the same result?
<swkhan>
yes
<swkhan>
ditto with ZnO on aluminum foil
<azonenberg>
Ok, you can rule out a random fluke then
<swkhan>
definitely
<azonenberg>
You got the same result on foil?
<swkhan>
it's different in a way that the clusters aren't as big
<azonenberg>
But not a film
<azonenberg>
so probably not the adhesive's fault
<swkhan>
i repeatedly get weak adhesion of zinc oxide to whatever my substrate is
<azonenberg>
I suspect that you're crystallizing
<swkhan>
on silicon as well
<swkhan>
crystallizing?
<azonenberg>
or something along those lines
<swkhan>
i'm trying to read every book in this field =\
<azonenberg>
and that the deposition preferentially takes place where the material is already there
<azonenberg>
you randomly start depositing faster in one spot (uneven reactant concentrations etc)
<azonenberg>
then that acts as a seed crystal
<swkhan>
i've grown very uniform thin films of aluminum oxide before
<azonenberg>
Just a guess
<swkhan>
using this same reactor
<swkhan>
that's possible
<azonenberg>
but i'd say your chemistry isnt suitable for a thin film
<swkhan>
that's the problem with this whole field. you have to guess unless you're lucky enough to have insitu rheed or something
<azonenberg>
something about your reactants
<azonenberg>
it just isnt stable
<swkhan>
i'm using fairly standard chemicals for zinc oxide: diethyl zinc and water
<azonenberg>
idk, CVD is one of the few deposition techniques i have not used on at least one occasion lol
<azonenberg>
they do not have such a solution for ZnO though
<azonenberg>
at least, not from that vendor
<azonenberg>
Anyway so back to your problem - you trying to do ALD of ZnO
<azonenberg>
And you're doing this by alternating DEZn with H2O?
<swkhan>
yes
<azonenberg>
My first guess is that the DEZn prefers to stick to ZnO than your substrate
<azonenberg>
for whatever reason
<azonenberg>
so when the H2O comes in the ZnO grows by a lot and the film elsewhere by only a little
<azonenberg>
I could be wrong
<swkhan>
i don't understand all the modes of growth
<swkhan>
there's 3 epitaxial growth modes i am aware of
<azonenberg>
But its now almost 2 AM and i have class tomorrow morning
<swkhan>
ah, understandable
<swkhan>
thanks for your help =)
<azonenberg>
Keep talking and i'll read it it when i get back
<swkhan>
oh, okay
<swkhan>
there's 3 epitaxial growth modes i am aware of: island formation, film formation, island + film formation
<swkhan>
what's confusing is that film formation mode has been repeatedly demonstrated by many other people for zinc oxide
<swkhan>
so trying to figure out why i get islands and not film formation is my goal
<azonenberg>
You know, this channel is starting to turn into #microfab lol
<azonenberg>
swkhan: considering we now have folks like you who are operating out of "real" labs coming here for advice
<azonenberg>
And I'm not really sure as to why you'd get islands
<azonenberg>
Contamination would be my first guess but if you got good Al2O3 films on the same substrate that's less likely
<azonenberg>
Do you have any photos of the failed depositions?
<azonenberg>
It'd be interesting to see both the experimental setup and what the offending wafers look like
<B0101>
azonenberg:
<B0101>
i have to tell you something
<azonenberg>
?
<B0101>
Latech has increased its price
<azonenberg>
:(
<B0101>
wafers now cost: $18.95 USD
<azonenberg>
Still not too bad
<azonenberg>
mti is 2x that
<B0101>
and you can order 1 wafer for 29+ USD but only for the first order
<B0101>
but 2 wafers are allowed
<azonenberg>
i see
<azonenberg>
Update the iki then i gues
<azonenberg>
gtg
<B0101>
i will, cya
<CIA-67>
homecmos r125 | wiki/Vendors.wiki | Edited wiki page Vendors through web user interface.
<swkhan>
azonenberg: aww i missed you! it may be a real lab, but it's very much in its infancy since no one including the professors or grad students know how to help
<swkhan>
azonenberg: i can show you a picture i took with an optical microscope
<swkhan>
i'll check again later today, but i'm pretty sure that's right. the holes you see are the underlying highly doped silicon (i HF etched the silicon dioxide)
<azonenberg_work>
Scale is in what?
<azonenberg_work>
microns?
<azonenberg_work>
tens of um?
<azonenberg_work>
~1mm FOV, +/- 500, would make sense for 50x
<azonenberg_work>
or 100um, +/- 50, for 500x
<azonenberg_work>
Its usually nice to know what i'm looking at :p
<swkhan>
i have SEM pictures as well. let me dig one up from zinc oxide on aluminum foil
<azonenberg_work>
The JSM-840 in the mat sci lab here has it
<azonenberg_work>
its what i've been using for most of my work as it's much cheaper to use than the zeiss supra 55 in the cleanroom
<swkhan>
ah, i think this is a Hitachi S4800
<swkhan>
so they charge you too?
<azonenberg_work>
The cleanroom costs a ton
<azonenberg_work>
The mat sci lab, well, i have a little arrangement with the lab manager ;)
<swkhan>
i don't think we even have a clean room =\
<swkhan>
i see
<azonenberg_work>
He lets me in off the book as long as i coordinate with him for a time nobody else needs the scope
<azonenberg_work>
and dont use too much time
<swkhan>
cool
<azonenberg_work>
But he supports my work and recognizes i have no budget
<azonenberg_work>
which i'm thankful for
<swkhan>
i have built a similar relationship with the lab manager for the sputterer. i guess i have to garner some sympathy and/or make some food for him if i want that kind of deal =)
<azonenberg_work>
lol
<azonenberg_work>
i've used rpi's cleanroom briefly
<azonenberg_work>
mostly for SEM work when i was doing consulting as an undergrad, failure analysis of some chips
<azonenberg_work>
one or two contact aligners, a stepper
<swkhan>
wow
<azonenberg_work>
PECVD/DRIE
<azonenberg_work>
not sure if we have XeF2 capability
<swkhan>
what's xenon difluoride used for?
<azonenberg_work>
Dry etching of silicon
<swkhan>
cleaning something? etching
<swkhan>
yeah okay
<azonenberg_work>
You sublime it into a vacuum chamber from crystals
<swkhan>
whoa
<azonenberg_work>
vapor pressure is a few mtorr i think? i forget the exact number
<azonenberg_work>
expose your wafer to it, then purge with argon when you're done and repeat
<azonenberg_work>
its isotropic i think
<azonenberg_work>
used for backside etching and stuff when you dont want to risk trace metal contamination
<azonenberg_work>
me, i just use KOH :P
<azonenberg_work>
screw PN junctions, my wafer is a mechanical substrate
<swkhan>
isn't KOH anisotropic?
<azonenberg_work>
Yes
<swkhan>
to silicon any way
<azonenberg_work>
Very
<swkhan>
i've never seen it in person
<swkhan>
i know we have potassium hydroxide around
<azonenberg_work>
something like 500x faster etch of <100> and <110> than <111> planes
<swkhan>
and i have wafers...
<swkhan>
wow
<azonenberg_work>
i use 30% in water
<swkhan>
i don't understand why. i'll look that up later
<azonenberg_work>
put in a plastic centrifuge tube
<azonenberg_work>
with the die
<swkhan>
i'm reading this book btw: nanostructures and nanomaterials synthesis properties. it seems pretty readible so far. but it doesn't seem to give me any direct insights into what could be going on with the reactor
<azonenberg_work>
and heat that in a water bath a little below boilin
<azonenberg_work>
interesting
<azonenberg_work>
Do you have any low-angle SEM shots at higher resolution?
<azonenberg_work>
I'm interested in what the edge profile of your clumps look like
<azonenberg_work>
I take most of my microscope pics at max resolution because disk space is cheap
<azonenberg_work>
this is SiO2 coated Al wiring on top of an IC with some packaging particles between them
<azonenberg_work>
note the resolution though
<azonenberg_work>
And i dont know how it grows either
<azonenberg_work>
Thats the point
<azonenberg_work>
You want to *watch* it grow
<azonenberg_work>
get a sequence of five or ten pics of the same clump over time
<azonenberg_work>
In ALD you are alternating the two precursors
<swkhan>
yes
<azonenberg_work>
So pull it out after 10, 100, or however many iterations you think is reasonable
<azonenberg_work>
image
<azonenberg_work>
put it back in, hit it a few more times
<azonenberg_work>
image
<azonenberg_work>
And use some kind of a feature on the die to make sure you are looking at the same region
<swkhan>
but then i introduce another variable don't i? if i break vacuum and image, then i don't know if the problem is due to contamination with the outside world or due to a failure of the ALD
<swkhan>
a postdoc in my lab says he used to use a scribe to etch out a letter or some kind of mark on the shiny side up and then grow
<azonenberg_work>
Yes, you do - but the goal here is not necessarily to completely replicate the existing setup
<azonenberg_work>
it's to understand it
<azonenberg_work>
So as long as you keep that in mind you're ine
<azonenberg_work>
fine*
<azonenberg_work>
For example, you may adsorb some water onto the surface
<azonenberg_work>
You may get some particulates
<azonenberg_work>
re water, thats used in your process anyway so you should be ok
<azonenberg_work>
particulates, just try to keep them to a minimum
<azonenberg_work>
when you remove from the reactor, put in a cassette immediately and then image
<azonenberg_work>
Also, image the wafer before you start deposition
<azonenberg_work>
to get a baseline
<azonenberg_work>
For example, if you are scribing marks into the surface you'll get silicon chips kicked up by that
<azonenberg_work>
you need to make sure they're removed
<azonenberg_work>
i'd suggest sonicating in ethanol
<azonenberg_work>
before you do the deposition
<swkhan>
would methanol work? or isopropanol? i don't have ethanol in the lab =(
<azonenberg_work>
you see what i'm saying here? You want to understand potential failure modes and test for them
<azonenberg_work>
and methanol should work fine
<swkhan>
i see
<azonenberg_work>
the ethanol i use actually is denatured with ~5% methanol and some other stuff
<azonenberg_work>
the "other stuff" has caused problems in some processes lol
<azonenberg_work>
i wouldn't mind 95/5 ethanol/methanol
<azonenberg_work>
still undrinkable and untaxed, but all volatiles of similar characteristics
<azonenberg_work>
they add all kinds of other stuff to hardware store denatured alcohol though
<azonenberg_work>
has caused problems when i used it as a solvent for sol-gel deposition
<azonenberg_work>
Actually, on that note
<swkhan>
i think my current problem is the "understanding the potential failure modes" part. let's say i find even patchier growth initially
<azonenberg_work>
Your substrate is silicon?
<azonenberg_work>
or alumina
<swkhan>
the SEM image was on aluminum foil (so i guess alumina)
<swkhan>
and the optical picture was on highly doped silicon with the native oxide removed
<azonenberg_work>
Ok
<azonenberg_work>
Did you do a full RCA clean on the silicon?
<swkhan>
nope
<azonenberg_work>
That will help to eliminate some variables
<azonenberg_work>
Are you familiar with the process?
<swkhan>
i am aware of it. use sulfuric acid, nitric acid, hf, and water... maybe a few more things
<azonenberg_work>
Remove particulates by sonicating in ethanol or similar (especially if you scribed it)
<azonenberg_work>
nope
<azonenberg_work>
optional degrease in acetone if you suspect organic contamination
<azonenberg_work>
then soak in water for a while
<swkhan>
it's organic contaminant removal then chemical oxide growth and chemical oxide removal right?
<azonenberg_work>
Yes
<azonenberg_work>
So SC1 is ammonia and water, heated
<swkhan>
ah
<azonenberg_work>
and H2O2
<azonenberg_work>
i use 1 part household ammonia to six parts drugstore-grade 3% H2O2 at around 70C
<azonenberg_work>
i think
<azonenberg_work>
check my lab notes for exact temp
<azonenberg_work>
then you strip native oxide in HF, i use 3% Whink brand rust remover
<azonenberg_work>
then trace metal removal in SC2
<azonenberg_work>
1 part conc. HCl : 6 parts 3% H2O2 at ~70C
<azonenberg_work>
10 minutes each for SC1 and SC2, the HF is around 30 sec
<swkhan>
will RCA clean really eliminate variables? what variables would i have right now that would mess me up?
<azonenberg_work>
These are not the original RCA proportions, they're modified for the chemicals i have available, but funciton similarly
<azonenberg_work>
Well, you are removing trace metals and any possible organic residues
<azonenberg_work>
trace metal is less critical for you
<azonenberg_work>
but organic residue could provide either a crystal growth site
<azonenberg_work>
or inhibit the deposition by making the precursors not stick
<azonenberg_work>
As a bare minimum i'd suggest a dip in acetone followed by isopropanol, then blow dry
<azonenberg_work>
ALso, you said you were using aluminum foil
<azonenberg_work>
Lab grade? Kitchen grade?
<azonenberg_work>
Some of them have organic release agents on them, they are not just Al + Al2O3
<azonenberg_work>
I didnt see any organics in the EDS but did you actally check the spectrum for them?
<swkhan>
what is the organic residue?
<azonenberg_work>
All kinds of stuff
<swkhan>
azonenberg_work: what showed up was from autoid. i don't think i explicitly checked
<azonenberg_work>
here's a photo of some
<swkhan>
like if you dip in acetone and then bake it off, wouldn't you just have no more (CH3)2CO?
<swkhan>
why would you have any residue left over?
<swkhan>
i have lab grade aluminum foil
<swkhan>
why acetone then isopropanol by the way?
<azonenberg_work>
Acetone dissolves contaminants well
<azonenberg_work>
but is so volatile it tends to redeposit
<azonenberg_work>
so you swish in IPA, which is less volatile, to dissolve the contaminated acetone out
<azonenberg_work>
otherwise you get streaking, i can show you pics of it
<azonenberg_work>
And lab grade foil probably shouldnt
<azonenberg_work>
looks like it's biological origin
<azonenberg_work>
NaCl plus some Ca and Zn, lots of carbon
<azonenberg_work>
then Si seen through it
<azonenberg_work>
probably dead skin cells, aka ordinary room dust
<swkhan>
it's not a clean room setup, but yes, i was wearing gloves
<swkhan>
i cleaned the copper tape with IPA then acetone
<swkhan>
maybe resulted in some problems
<azonenberg_work>
i'm not in a cleanroom either :P
<swkhan>
the lab grade foil was not cleaned at all
<azonenberg_work>
But i understand the implications of it and take reasonable precautions to at least compensate
<azonenberg_work>
for example i wear a lab coat and hair net to reduce dust coming off me
<azonenberg_work>
That may be overkill
<azonenberg_work>
i also try to avoid ever leaning directly over a sample
<azonenberg_work>
etc
<swkhan>
sure sure
<azonenberg_work>
Anyway so contamination is possible but you cant be sure at this point
<azonenberg_work>
Thats why i suggested imaging the wafer before deposition
<azonenberg_work>
or whatever your substrate is
<swkhan>
i'm confused though... why does acetone redeposit if it's volatile
<azonenberg_work>
It does not redeposit
<azonenberg_work>
it evaporates
<azonenberg_work>
whatever is dissolved in it, though...
<azonenberg_work>
has to go somewhere
<swkhan>
oh i see
<azonenberg_work>
So you want to dissolve the contaminant in acetone
<azonenberg_work>
then remove the acetone rather than letting it evaporate
<azonenberg_work>
Never let a cleaning solvent evaporate off yoursample
<swkhan>
huh, that makes sense
<azonenberg_work>
Either submerge it in something else and then let the pure solvent evaporate
<azonenberg_work>
Or blow dry
<azonenberg_work>
when i say blow, i dont mean forced evaporation
<azonenberg_work>
i mean use high pressure N2 etc to physically knock the droplets off
<azonenberg_work>
before they evaporate
<swkhan>
i've seen an N2 gun. i know what you mean. i could hook that up
<azonenberg_work>
Ideally, blow dry after submerging in fresh solvent
<swkhan>
i see
<azonenberg_work>
So first you dilute the contaminated stuff, then you remove it before evaporaiton
<azonenberg_work>
The result of letting it dry typically is a white residue consisting of salts etc
<azonenberg_work>
in a ring around the perimeter of the drop
<swkhan>
what if i don't clean the wafer at all?
<swkhan>
just use it as is
<swkhan>
or... hmm i cut it so there's silica dust now
<azonenberg_work>
Exactly
<azonenberg_work>
as a minimum you need to remove the particles
<azonenberg_work>
That dust was killing my yields for several weeks
<azonenberg_work>
before i figured it out
<azonenberg_work>
EDS wouldnt show the contaminant because it was the same material as my substrate
<azonenberg_work>
i was bashing my head on it for a while
<azonenberg_work>
i tried RCA cleanin (which doesnt remove large dust, only trace films etc)
<azonenberg_work>
i tried wearing a surgical mask and hair net
<swkhan>
huh, wow
<azonenberg_work>
then finally i tried imaging a bare die before processing
<azonenberg_work>
and i saw silicon dust all over it
<azonenberg_work>
that wasnt on an uncut wafer
<swkhan>
oh wow
<azonenberg_work>
So this is a very real potential problem
<azonenberg_work>
if you didnt remove particles from your silicon i'd blame that right away
<azonenberg_work>
unless you were doinga full uncut wafer
<azonenberg_work>
like i said, image the sample - however big it is - at low angle
<azonenberg_work>
look for dust
<swkhan>
no i definitely cut the wafer
<azonenberg_work>
in secondary electron images they will show up as bright spots
<swkhan>
so sonicate it off?
<azonenberg_work>
Yes thats one way
<azonenberg_work>
Use somethign with low surface tension
<azonenberg_work>
absolutely not water
<swkhan>
take a little test tube and put some organic solvent in (acetone preferably?)
<swkhan>
low surface tension...
<swkhan>
meaning it tends to evaporate easily?
<swkhan>
or doesn't bead up i guess
<azonenberg_work>
no, as in it forms a film rather than beading up
<azonenberg_work>
Because if it beads up it concentrates particles inside as it does so
<swkhan>
that makes sense
<azonenberg_work>
if it forms a film the dust slips off
<azonenberg_work>
Also, if you have any lint-free swabs, kimwipes, etc
<swkhan>
i don't think they are called test tubes, but what are those things that have a lid on top
<swkhan>
i have kim-wipes
<azonenberg_work>
you can try soaking it in solvent and gently wiping the die with one
<azonenberg_work>
you dont want to use much pressure
<azonenberg_work>
just drag the corner over it
<azonenberg_work>
to avoid scratching
<swkhan>
hmm
<azonenberg_work>
Then optically image at ~400x to verify you are free of dust
<azonenberg_work>
and you mean centrifuge tubes?
<swkhan>
how well does dust stay off?
<swkhan>
yes centrifuge tubes
<swkhan>
that's what i was thinking of
<azonenberg_work>
i <3 those things
<swkhan>
how long would you sonicate for? the postdoc seems to always wait 60 minutes
<azonenberg_work>
bought a case of 2000 ~1ml ones and i use them all the tie
<azonenberg_work>
my glass test tubes havent been touched sin ethe day i opened the box lol
<azonenberg_work>
these things are small, nonbreakable, disposable
<azonenberg_work>
not etched by HF
<swkhan>
lol. there's a guy in ##chemistry who was desperate for some and was willing to buy from me
<swkhan>
glass not etched by HF? o_O
<swkhan>
diluted HF?
<azonenberg_work>
no, i mean the centrifuge tubes
<azonenberg_work>
And i actually have little experience with sonication as i dont have an ultrasound rig myself yet
<azonenberg_work>
its on the to-buy-once-this-paycheck-clears list
<azonenberg_work>
along with a few undoped 2-inch <110> wafers
<azonenberg_work>
I can say, unless you are worried about fragile MEMS structures being damaged (certainly not the case with a blank wafer)
<azonenberg_work>
more can never hurt
<swkhan>
well it can in terms of time wasted
<swkhan>
i wish i had a good scientific explanation for all the actions i took in lab
<swkhan>
you seem to complement what i've been reading very well =)
<azonenberg_work>
Some of the cleaning stuff is empirical because you dont know what you are targeting
<azonenberg_work>
contamination is often an unknown
<azonenberg_work>
So you think "what will it take to remove XYZ?"
<azonenberg_work>
try it
<azonenberg_work>
if it works, odds are XYZ is your contaminant
<azonenberg_work>
and you now know how to remove it
<azonenberg_work>
Assuming your problem is contamination
<azonenberg_work>
which i consider likely but far from definite
<swkhan>
so okay let's consider this situation... i go down to the optical microscope + raman and see no dust. take it to the SEM and see no noticeable silica dust, proceed to ALD without any cleaning or maybe a water soak?
<azonenberg_work>
Sounds reasonable if you are worried about dust
<azonenberg_work>
But i'd suggest an acetone + IPA dip to rule out oils etc
<azonenberg_work>
say, you brushed a finger of you glove against it that had touched your bare hand while putting it on
<azonenberg_work>
that might leave fingerprint oilis
<azonenberg_work>
oils*
<azonenberg_work>
Then go on to the ALD and image after say 20% of your normal deposition time
<azonenberg_work>
put back in, run another 20%, image
<azonenberg_work>
observe some things
<swkhan>
i'm fairly certain i didn't do that, but if i just sprayed the acetone onto the silicon sample and then used a kim wipe to wipe away the contaminants, what would you say?
<azonenberg_work>
* How soon does it clump? Are you getting a film that degenerates into clumping?
<swkhan>
sure
<azonenberg_work>
* How do the clumps grow? DO they form early on and just get bigger, or do new ones appear? When they grow, do they grow out or up or both?
<azonenberg_work>
and i'd suggest dipping it in a beaker and then blowing dry
<azonenberg_work>
thats what i usually do
<swkhan>
i'm trying to arm my self with as many tools as possible ahead of time
<azonenberg_work>
radioshack duster spray, i kid you not
<swkhan>
regarding dipping, doesn't that result in more contaminated acetone?
<azonenberg_work>
is my poor man's solution for the lack of an N2 gun
<azonenberg_work>
andif you swish it around
<azonenberg_work>
you dilute the contaminant a lot
<azonenberg_work>
then you blow it off
<swkhan>
so let's say i get clumps that form early on and just get bigger. that's ostwald ripening right?
<azonenberg_work>
i dont know the technical term off the top of my head
<swkhan>
it's where little things form bigger things because it is thermodynamically more stable to be that way
<azonenberg_work>
Yeah
<azonenberg_work>
Thats my guess as to what might be going on if you are not having contamination issues
<swkhan>
so what does that imply? i get frustrated by knowing this theoretical stuff and not knowing how to apply it
<azonenberg_work>
well, brief readin suggests ostwald ripenin is mostly a liquid phase process
<swkhan>
i'm going to sputter zinc on quartz today. maybe using purer copper foil too
<swkhan>
i should get the heck into lab. it's 10 am!
<azonenberg_work>
its 13:00 here lol
<azonenberg_work>
i'm midway between my two classes of the day
<azonenberg_work>
and also, here's a question
<azonenberg_work>
You desire a ZnO thin film on something
<azonenberg_work>
Must it be done by CVD?
<azonenberg_work>
Off the top of my head i'm wondering if reactive sputtering might work
<azonenberg_work>
i know its done for nitrides and i think oxynitrides
<azonenberg_work>
Because that should be quite uniform
<azonenberg_work>
not saying to abandon all your work, but at least consider alternatives if you cant get this process to work
<swkhan>
azonenberg_work: that's something i was planning on trying as well. sputtering zinc oxide as a seed on top of various things... copper, aluminum foil, sputtered zinc even
<swkhan>
azonenberg_work: my professor wants to be sure that the ALD i put together isn't a fluke with aluminum oxide
<swkhan>
zinc oxide is a weird material though
<swkhan>
i guess i'm insecure about it not being single crystal
<azonenberg_work>
I dont know the microstructure
<azonenberg_work>
to me it's sunscreen and diaper rash cream :p
<azonenberg_work>
But as a metal oxide i'd assume its amorphous
<azonenberg_work>
ALD is normally used as an epitaxy technique so i'm a little confused as to how it works with amorphous materials
<swkhan>
but if it's epitaxial growth, and i have silicon (100) underneath, shouldn't i get ZnO (100)?
<swkhan>
but... since zinc oxide does not have a cubic crystal structure, it's a bit weirder
<azonenberg_work>
Exactly, thats why its wierd lol
<azonenberg_work>
Not only is it not the same structure
<swkhan>
hmm i wonder about alumina then
<azonenberg_work>
the lattice spacing is different
<azonenberg_work>
The alumina is obviously not monocrystalline
<azonenberg_work>
My guess is that you are growing at grain boundaries or something like that
<azonenberg_work>
or lattice defects
<azonenberg_work>
where you have a couple of atoms aligned at the right spacing
<swkhan>
oh what the heck it's trigonal Al2O3?
<azonenberg_work>
then you nucleate there and it starts growing epitaxially on top of that little speck of ZnO
<swkhan>
that seems intuitive to me as well
<azonenberg_work>
I'm now starting to suspect that might be your problem
<swkhan>
the problem i'm actually trying to address is why i get poor adhesion
<azonenberg_work>
Adhesion, oh
<azonenberg_work>
Thats a horse of a different color :p
<azonenberg_work>
Fails the scotch-tape test i assume?
<azonenberg_work>
Well, to begin - if you are only growing on lattice defects you are getting strong bonds at a handful of sites
<azonenberg_work>
but otherwise not very strong
<azonenberg_work>
Explore growth on some other materials
<azonenberg_work>
Off the top of my head, a lot of things do not stick that well to Si
<azonenberg_work>
Have you read "Etch rates for micromachining processing, part 2"?
<azonenberg_work>
There's a section in there talking about film adhesion of the materials they tested
<swkhan>
azonenberg_work: it fails the pick-it-up-with-a-pair-of-tweezers-without-scrapping-it test =(
<azonenberg_work>
evaporated Cr is a very popular adhesion layer
<azonenberg_work>
Ti works too
<azonenberg_work>
and do you mean without it falling off completely?
<swkhan>
have you figured out why?
<swkhan>
and no i haven't
<azonenberg_work>
Or you scratch it
<azonenberg_work>
Metal tweezers will scratch all kinds of stuff
<swkhan>
azonenberg_work: i can take a napkin and wipe it off
<azonenberg_work>
...
<azonenberg_work>
ok, thats even worse than my evaporated copper without Cr lol
<swkhan>
lol
<azonenberg_work>
Without Cr, tape takes it rigth off
<azonenberg_work>
and it floats off during etch
<azonenberg_work>
with Cr it sticks well, tape doesnt even touch it
<azonenberg_work>
Just as a totally random idea
<swkhan>
yeah, i still haven't figured out why Cr and Ti are so frequently used as adhesion layers
<azonenberg_work>
Evaporate or sputter Cr onto something
<azonenberg_work>
then try growth on that
<swkhan>
what about platinum? we don't have chromium to my knowledge
<azonenberg_work>
you'll be gettin a nice polycrystalline layer of a single material
<azonenberg_work>
Hmm, i think Pt needs an adhesion layer :p
<azonenberg_work>
Cr, Ti, and some other odd materials
<azonenberg_work>
Read the paper i mentioned
<swkhan>
okay
<azonenberg_work>
they alk about adhesion of a lot of transition metals
<azonenberg_work>
What are you studying again btw?
<azonenberg_work>
ee? chem? phys?
<swkhan>
EE
<swkhan>
they just state it makes a good adhesion layer
<azonenberg_work>
Yeah, nobody knows exact details - the very strong Cr-O bond is something to do with it i think
<azonenberg_work>
and i just find it kinda funny that i'm helping *you* with this stuff as someone who hasnt taken any EE classes except one on networking :p
<swkhan>
i know right. i feel so incompetent =(
<swkhan>
i spent the greater part of this year building the ALD
<swkhan>
lots of hardware and software
<swkhan>
no chemistry or physics really
<azonenberg_work>
yeah... lab stuff is something you cant really do in a lecture
<azonenberg_work>
you have to just go do it
<azonenberg_work>
In any case, another idea is just to go and find papers talking about ZnO
<swkhan>
i've been doing that all week
<swkhan>
i forgot to mention earlier
<swkhan>
one paper said that the deposition rate is roughly 2x what i thought it was
<swkhan>
so i may have been depositing 100 nm films rather than 50 nm films
<azonenberg_work>
ok
<swkhan>
so i'm going to make a list of stuff i want to do today
<azonenberg_work>
Have you checked if there is any ZnO thin film in the open areas?
<azonenberg_work>
iow, you are getting clumps
<azonenberg_work>
But is it *all* in the clumps?
<azonenberg_work>
do you have clumps and blank?
<azonenberg_work>
or is it clumps over fil,
<azonenberg_work>
film*
<swkhan>
it could be clumps with a thin film under
<swkhan>
so things to do today: 1. try to get a "time lapse" view of what is going on 2. properly clean stuff (in lieu of RCA, sonicate with acetone + silicon sample in centrifuge tube sealed and placed in warm water) 3. sputter zinc on quartz and deposit ZnO 4. deposit on very high purity copper
<swkhan>
i think i'm going to have to hunt for H2SO4
<swkhan>
but it seems like everyone uses an RCA clean process
<azonenberg_work>
Yeah, its the industry standard for silicon cleaning
<azonenberg_work>
been used since the 1950s
<mrdata>
HNO3?
<azonenberg_work>
mrdata: hno3 is an oxidizing acid
<azonenberg_work>
you run the risk of growing too much sio2
<mrdata>
oh
<mrdata>
finishing companies use HNO3 when cleaning aluminum for plating
<mrdata>
HF also, ithink
<swkhan>
i think i'm also going to change my deposition temperature
<swkhan>
also my # of cycles
<swkhan>
i got a loaded day ahead of me
<swkhan>
it's 11 am... i'm going to be in lab until 8 pm for sure
<azonenberg_work>
lol have fun
<azonenberg_work>
i'm in an incredibly boring class
<mrdata>
oh? what class
<azonenberg_work>
But the time passes faster when i'm working on FPGA stuff during the lecture P
<azonenberg_work>
database systems
<mrdata>
is never bored; there's always something to do while listening to dull lectures
<azonenberg_work>
I said the class was boring
<azonenberg_work>
not that i was bored
<mrdata>
are they teaching about normalization?
<azonenberg_work>
subtle difference
<mrdata>
tuning?
<azonenberg_work>
and theyre just getting into how to choose keys
<azonenberg_work>
its all noob-level stuff
<mrdata>
marvelous
<mrdata>
i could teach that
<mrdata>
do they use any UML?
<azonenberg_work>
Not yet, thank god
<azonenberg_work>
i've been exposed to it in software design & doc already
<azonenberg_work>
and want nothing more to do with it :p
<mrdata>
lol. uml isnt terrible at showing data models
<mrdata>
i make heavy of of those in db design
<mrdata>
s/of/use/
<berndj>
in real life nobody uses UML; everyone just draws boxes and random lines on whiteboards
<azonenberg_work>
berndj: yeah
<swkhan>
well i'm still looking stuff up. seems like temperature is a big deal for the quality of the ZnO crystallinity
<swkhan>
The degree of preferred orientation (I002/I101) for the ZnO thin film frown at 170 °C is much higher than that grown at 130 °C. -> what does I002/I101 mean? that the 002 plane and the 101 plane are equally preferred?
<azonenberg_work>
hmm
<azonenberg_work>
i think that it prefers 002 to 101
<swkhan>
huh
<swkhan>
well this is really insightful
<swkhan>
"It may be said that the crystallinity of the ZnO film grown by ALD with a process time per cycle of 10 s at 170 °C is better than that grown by ALD with a process time per cycle of 4.35 s at the same technique. In general amorphous films are obtained if the film growth rate is high or if the substrate temperature is low in an ALD process. This may be because there is no time enough for reactants to move to equilibrium atomic sites under such conditi
<swkhan>
that last line!
<swkhan>
totally makes sense
<azonenberg_work>
Nice
<azonenberg_work>
So the cycle times are very important