<lekernel>
azonenberg, what's the difference between epitaxy and evaporation/LPCVD?
<azonenberg>
lekernel: I'm not too fami.liar with the details of epitaxy but it forms a single-crystal coating
<azonenberg>
The others form a polycrystalline coating from a vapor, the difference is the source of the vapor
<azonenberg>
evporation is purely physical (heated chunk of the material)
<azonenberg>
CVD (and variants like PECVD, LPCVD, MOCVD) pump in reactive gases that combine or decompose in some way
<azonenberg>
And sputtering is also a physical process but there's an inert gas present to do the sputter
<azonenberg>
Reactive sputtering is a hybrid - vapor is formed by normal sputtering processes but before it hits your sample it reacts with another gas
<azonenberg>
for example using an Ar / N mix to sputter Ti
<azonenberg>
the Ar knocks Ti atoms off the target, which then react with N to form a film of TiN
<azonenberg>
Epitaxy, on the other hand, you are depositing either the same material as your substrate or something with a compatible crystal lattice
<azonenberg>
in either case it forms a single-crystal coating where the atoms are locked to the lattice of your substrate
<azonenberg>
Another important difference is the pressure
<azonenberg>
Sputtering has an inert gas present and CVD has source gases, so both happen at relatively low vacuum (few hundred Pa ish)
<azonenberg>
Mean free path is short and you get a pretty even coating since the atoms bump into each other and are moving pretty randomly
<azonenberg>
Evaporation is done at much low pressure (1E-6 torr ish)
<azonenberg>
Mean free path is comparable or greater than the distance from the source to your sample
<azonenberg>
Which means atoms evaporating from your source travel in pretty much a straight line (not hitting any gas molecules etc) before hitting the sample
<azonenberg>
As a result the coating has some of the characteristics of spray painting - bumps in the surface cast shadows, edges perpendicular to the source are coated thinly if at all, etc
<azonenberg>
which is bad for some processes (filling vias for example) but very good for others (lift-off)
<lekernel>
so, epitaxy is a particular case of evaporation?
<azonenberg>
The source of the vapor for epitaxy can vary
<azonenberg>
I'm not familiar with the usual sources
<azonenberg>
this isnt a process i've considered using either for my fab, or needed for anything at work etc
<azonenberg>
The other processes i've actually studied in some detail
<azonenberg>
In any case i'm heading up to campus now, i've got work to do
<azonenberg>
And a 10:00 (local time) appointment with a SEM :)
<azonenberg>
Expect pictures this evening
<azonenberg_work>
lekernel: back
<azonenberg_work>
On the SEM now taking pics
<azonenberg_work>
probe tips are sharper than i thought
<azonenberg_work>
200nm ish dia flat tip
<bart416>
:D
<bart416>
azonenberg, btw did you think about the destructive stm test?
<lekernel>
epitaxy might be interesting as well - think of microwave transistors, diodes, etc. though I don't know the difficulty level to have equivalent performance with the commercial ones that need an interview to get a quote for
<azonenberg_work>
lol
<azonenberg_work>
worth looking int but prob difficult
<bart416>
lekernel, any ideas for scraping a single layer of atoms of a sample?
<lekernel>
er... maybe with those tunnel microscopes?
<bart416>
Yeah, that's the thing
<bart416>
It's too slow to remove the layer from a large surface
<bart416>
I suggested it somewhat unserious yesterday to use a STM to scan a sample layer by layer
<bart416>
But the more I think about it the more it makes sense
<bart416>
An STM could break a crystal latice
<bart416>
It'd take several millenia to do that for a large surface :p
<lekernel>
what do you need atomic precision for?
<lekernel>
especially on a large surface ...
<bart416>
I want to scan layer per layer with a stm :P
<bart416>
Somebody in ##electronics had a nice idea
<bart416>
Using a pulsed laser with a kerr lens
<lekernel>
mh, maybe the stm isn't the best tool for that
<lekernel>
or maybe you could make it faster by increasing the voltage and the distance between the probe and the sample? (just guessing here)
<bart416>
Maybe
<azonenberg_work>
Pics coming later today
<azonenberg_work>
Some interesting stuff but the guy had to leave before he could show me how to use EDS
<azonenberg_work>
So i have to come back tomorrow
<bart416>
EDS as in what sense?
<azonenberg_work>
energy dispersive spectroscopy
<bart416>
ah
<bart416>
That should show interesting results
<azonenberg_work>
using x-rays emitted from the sample to determine what elements are present
<azonenberg_work>
Which will let me tell whether the stuff i'm looking at is hardmask (tantalum based), photoresist (organic), or a mixture (some of each)
<bart416>
If you're willing to do some math you should be able to get a pretty good formula for it
<azonenberg_work>
http://i.imgur.com/R5o3m.jpg is a quick shot of what i did today (low res, original is 2x in both dimensions)
<azonenberg_work>
This is an etched die (F7) seen at 2000x
<azonenberg_work>
The thin layer on top is hardmask residue (not removed completely by liftoff), the silicon can be seen extending outwards below it to the etched surface in the background
<azonenberg_work>
Diagonal surfaces are <111> planes, the background is a <100> plane
<azonenberg_work>
And the microscopy tools have the software to identify most of the peaks in the chart
<azonenberg_work>
I just dont know how to use it or how to install the detector (it's not installed by default)
<bart416>
heh
<bart416>
read the manual!
<azonenberg_work>
iirc you need to physically remove the backscatter detector to install this one
<azonenberg_work>
keeping the everhart-thornley secondary electron detector for aiming
<azonenberg_work>
(and imaging)
<berndj>
if you forego atom-size res, could you push target atoms around faster than normal with an STM?
<berndj>
just thinking of that destructive test procedure you guys were talking about
<berndj>
(ab)using the STM probe tip as a mechanical cutting tool, in effect
<bart416>
berndj, yeah but a good stm top doesn't come cheap :(
<bart416>
*tip
<berndj>
oh - i was assuming DIY STM with broken lightbulb filament probe!
<bart416>
Those won't do well for atom moving I fear
<berndj>
no?
<berndj>
do you need different / better tips for atom moving than for imaging?