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[Music]
[Applause]
it's ambitious goal
to make your own wafer well you might be
in the right talk now
the following lecture i couldn't resist
our presenter noodle
will explain how to perform electron
beam lithography
but do it yourself way let me switch
over to new who is really down to the
atomic level
of kids so hello hi there hi
our talk is about how to make your own
crappy pmma based resist for ebl
so it's not that it already works
perfectly but
you know it's kind of a start
our primary interest is in kind of
on-ship photonics
if you will so by that we mean
integrating photonic components like
waveguides or gratings on a ship scale
level
and we're also interested in making our
own mems devices
so yeah i guess that sums up what we're
trying to do
of course you could also use ebl and
masks generated by it for semiconductor
stuff
but that's kind of off our scope to be
honest
but also very fast fascinating stuff
actually
so we want to make ebl at home
besides an sem which is actually
relatively cheap
between 400 and 1500 euros if you look
long enough on ebay
so besides an sem you need the chemistry
and the thing is the chemistry the pros
are using for lithography in general
is price-wise pretty hefty
if you go to those go-to vendors it
easily adds up to much more than the
price for a used
shitty old sem itself
so what to do right
cook your own soup and maybe it's good
enough for your and our purposes
so what is ebl ebl stands for electron
beam lithography
in the end it's simply using the rig we
all know for scanning electron beam
microscopy
for lithography the scanning beam
changes the chemical properties like the
solubility of a resist
and that's the way you can draw figures
into the resist
with a beam
what sucks it's super slow compared with
other lithography principles
the electrons are charging the resist
and maybe interfere with the substrate
or whatever you want to ebl
in a bad or maybe destructive way
to prevent this you could try to coat
your stuff
with a thin hopefully not disturbing
conductive layer
but sometimes that's not possible
because it could undermine
what you're actually trying to
accomplish
it's also necessary that your workpiece
is somehow
vacuum compatible if not
maybe it's not the right process for it
on the pro side you have the fact that
it needs no mass
of course there are other maskless
processes like using dlp
dmd based projectors or laser writing
awesome stuff to be honest the other
thing is that in principle
you can achieve pretty high resolutions
with ebl
because you're using electrons you can
neglect the broly wavelength
above 100 nanometer-ish resolutions
completely
there is a wide variety of resists you
can use for ebl
they have different fields of
application
we have tried nitrocellulose nc
but it didn't work so we switch to one
of the most common ebl resists
pmma
pmma comes in chains of different
lengths or molecular weight
you can cut or cross-link them
as far as we know pmma is the best
documented resist for ebl
it's easily available and cheap
you can use many different solvents some
of them
aren't really toxic if you let modern
resists like
ztp aside pmma can achieve the highest
resolutions and aspect ratios
we use pmma as a positive resist
that means that the electrons induce a
chain incision process
which cuts the pmma chains into smaller
parts
which makes them easier soluble soluble
in the developers
the positive process itself is
relatively easy
you apply the resist via spin coating
then you have to pre-bake it to remove
the remaining solvent from the resist
layer
after that you put it in your ebl system
and expose it then you remove the
exposed resist
parts with the developer we are using
mibk for that
after that you can do the next process
step like
physical vapor deposition or
electroplating
to get the final structures you want
the developers composition we are using
is ipa
with mibk three to one
yeah there are many applications of
structured
resists you can use it as a mask as
already explained
but you can also use it as a structural
component for chemistry on ship
applications or in mems
or as a structural dielectric for high
frequency and optical
components
as the ebl system we are using an old
sem
we kind of retrofitted it using a red
pattern as the signal generator
to design your masks or geometry in
general
you can use every cad tool chain you
want
if you use hardware like the red tire
you have access to a wide variety of
tools and scripts
doing the boring stuff like file parsing
for you
we should also mention the most common
mask file formats
first there's gds2
and the more modern oasis
and then there is an idea we had during
the last days that it could be worth it
to try to define
yet another file format for that task
simply because those two that we
mentioned are both lacking many modern
features
which you know from modern cad formats
there are multiple strategies to scan or
expose only the parts of the resist you
want to be
exposed the most common ones are line
style scanning with a fast beam on the
dark parts
and a slow beam on the bright parts
and scanning fast between the polygons
and
slow inside the polygons you want to
expose
we are using red pittaya because they're
readily available and do the job
using simple jupiter notebooks makes it
easy
to script your experiments
electron optics is pretty similar to
normal optics
from the user perspective so you also
have
distortions and such effects
but you can transform your exposure scan
to compensate
compensate for that
for finding the so-called camera
intrinsics
and also for fiducial detection if you
are in need of multiple exposure passes
we recommend opencv
most algorithms you need are readily
available
another annoying effect comes from the
fact that the beam itself is
not infinitely sharp and from the
scattering of the electrons in the
resist and
back scattering from the substrate
that's really the resolution killer if
you go for high resolutions
there are different ways to counteract
that one is to increase the electrons
energy
to make the entry region tighter
an additional way is to correct the
effect via deconvolution
to generate the necessary deconvolutions
kernels
you can measure the effect or simulate
it
pecebl is one open source tool for doing
that
and that's one form of pmma we used you
can easily buy it on amazon
normally it's used to fix fingernails i
guess
dcm is one very popular solvent
but it's also not very healthy
xylo also works and it's not that bad
tolual is pretty good but also
relatively toxic
any soul could be the solvent of choice
it's not toxic relative to the other
stuff
and it works good with pmma but you have
to heat it up to 70 to 90 degrees
celsius
that's our improvised spin coater
it's a dreamer with an sem stub holding
the substrate piece
after spin coating you have to pre-bake
it
at approximately 100 degrees celsius
for a couple of minutes to remove the
solvent
okay that's the test pattern
and our first result not that good
the reference square is 100 micrometers
another try the distance between the
scale lines is 10 micrometers
one example of accidental crosslinking
most of the resist was removed but some
parts with high dosage
are of decreased solubility
that's a better example
another example of accidental cross
linkage
we made last night both squares are
10 micrometers
and thanks to sleepy old joyce for
providing us with the wafers
so thank you yeah
thank you any questions
thanks for the talk so let's have a look
do we have questions no
we don't have any questions here at the
moment um
guys if you wanna ask something if you
wanna ask noodle
go ahead use our communication channels
twitter methadone and irc
otherwise let me quickly
ask you so what about the resolution
range you can
you can get with this technique with
this do it yourself
technique
so your question is how far we got yeah
right yeah
so um yeah in the sub
micrometer scale okay
but it's uh still work in progress so
yeah if we figure out how to
achieve 100 nanometers
i hope
so somebody's interested if the slides
of this talk
are going to be published yeah
i can publish them okay
how can they be found
i put put them on github okay and
link it on our twitter account that
sounds good the twitter
account yeah it's visible so we got it
thanks
so far no more questions
yep let's see if something drops in
is there anything you want to add to
this talk here at this moment
no not much okay yeah
so yeah um there's one thing you
mentioned
one substance which was not as healthy
as it
uh well should be or could be
so what's the toxicity of this one
component you mentioned uh which one
tolu
or dcm both
give you cancer if you're not
yeah so glove and everything
okay well yeah and i would recommend a
fume hood
then yeah yeah yeah
well in the kitchen's possible but you
don't want to mess around with those
chemicals in your kitchen i'd say
yeah that's true yeah okay
more questions that guy that's good so
we have some questions that are coming
up what's
what structures actually do you want to
achieve
by the end of this project is there
anything you have in mind
uh something dedicated dedicated goal
you want to go for
and say okay we got it now with this
type of process
optical gratings for a 400 nanometer
laser light certain application
waveguides
and ratings
okay that's cool to to implement
uh kind of external small
external cavities for diode lasers
yeah okay okay are
those lasers also do it yourself type of
lasers or do you buy them or do you have
a lab accessible for that type of work
uh i buy the diet lasers so
this is normal laser diodes okay
yeah fabry peru the laser diodes
i want to modify them
um yeah sure what's the output power of
those laser diodes
um in the mode i want
to use them um
yes 10 milliwatts but
not not not a very high power well i
think you can already destroy your eye
with that
can you maybe
i shouldn't look well we don't want to
experiment that we don't want to
recommend anything
like that well folks you out there you
know it anyway
uh next questions um what does
the wafer cost irl and
how much is an electron beamer
so our electron beam device is
a very old electron microscope a
scanning electron microscope
and those are around
500 to five hundred euros on ebay
on ebay really okay there are used ones
pretty old ones
sure and well
yeah you only have to attach a signal
generator
like a red pitaya or something like that
and you have um
a crappy evil rig
so how much power does it suck so what's
what's the
uh including the pumps it's uh
two kilowatts one kilowatt so
wow that doesn't i haven't measured so
yeah i'm not sure but nothing special
needed so you can actually
yeah exactly more or less
wow cool well
um have you actually tried optical uv
before using ebl no
why just because you're interested in
electron
beamers yeah that's one thing
the other thing is that
i'm not sure how to achieve
the resolution i want to have and i
guess
all in all an evil system is a more
simpler
system okay
micrometer resolutions
i see all right
oh there's another question here
uh it's about frequency or so now
how fast can the ic switch how fast can
you actually clock it
what well yeah somebody somebody's
asking
how fast uh you could actually switch i
mean if you if you're producing ic
with that technique of how fast okay
so we are don't we don't want to produce
semiconductor
devices like processors or something or
transistors
it's more about means
micro mechanical devices and optical
devices
okay that's our focus i see i see yeah
next question of course where can you
buy the chemicals do you need some
special license for that for example um
chemical uh license or so i mean some
some poisonous license
at least in germany uh they are
available
so you can order them and some at some
online shops like uh s
reach chemicals if someone is interested
so normally um if you
are a larger research facility or
something like that you are able to
order them at sigma oil rich but yeah
they don't talk to mortals like me so
i see okay um
murray questions so they're flowing in
now that's pretty nice actually
um do you package the ic somehow
uh not yet so it's not
in i see in the common sense yeah
currently i'm figuring out how to
mix proper resists so
i'm in a very early stage of doing it so
well no i see packaging necessary
currently okay yeah um how long have you
been actually working on the project
when we're talking about timeline now um
yeah a couple of months
so oh yeah
that's pretty short success then
[Music]
um another question here um how do you
bond
uh those parts actually what material do
you use to pack them up and
something like epoxy yeah so
at the current stage there's no bonding
so but you
you you can use epoxy glue to
glue the chip or whatever on
the holder yeah
[Music]
well there is another question more like
a motivational question
if you could probably name some
exemplary
projects that can be tinkered together
which wouldn't be possible without that
uh type of approach you are pursuing
here
um we are compact uh optical devices
so i guess it's the only way to
to make that ah okay it goes back to
your
yeah your answer before yeah that's my
motivation so
i know that there's there are different
other stuff you can do with it but
i'm not into it yeah so you're more into
optics
okay there is another question that got
in um would it be possible
to do those chips with gates and
everything or
do you need other more exotic stuff
there's a media for that which isn't
available if you want to
build semiconductor ships with
transistors
you need a diffusion or iron implanting
and
such stuff that's much more complicated
than
only the lithography
for the masks okay
and well just my my imagination
where did you guys actually set that all
up in your cellar in the garage
somewhere some rented space or hackspace
where are you actually doing that i mean
laboratory is more or less in the
basement
if you want so okay is it somehow
[Music]
or shall i say is it um
can it be influenced by by um
by motion not by motion by
disturbed basically by by vibrances
yeah yes if you go for really high
resolutions
we are far far away from that kind of
super high resolutions you uh
have problems with um
yeah oscillations induced
by some traffic or
something like that oh god perfect
yeah yeah exactly if something outside
shakes a little bit
that would be a problem if uh we want to
crack
some hypothetical
boundary like 10 or
so nanometers i guess if
that's not easily possible in a normal
room
so yeah in a normal house without the
yeah sure the pro isolation
the theoretical limit with this
technique would be achievable 10
nanometers that's pretty small yeah
theoretical it's possible
this evl in in general not with our rig
but yeah with a professional one uh you
can
get down to five nanometers
so or less so yeah
yeah i don't know what what the actual
limit
currently is so
yeah another question popped up
so do you further treat the finished
wafer after etching
so something you you do there
my plan is to electroplate
some structures on it
electro chemical plating and uh
physical vapor deposition that are
the two things i want to do
all right in the first place and maybe a
little bit of
an isotropic and isotropic etching of
the
substrate so but but first
i want to have a reliable and repeatable
resist working yeah
and somebody is interested um if you
could actually use
uh if you could dose the material uh
somehow to get fats
uh okay yeah that's the semiconductor
stuff
so uh with with diffusion or iron
implanting
that would be possible but i don't own
the
the tools for that so i don't know
i'm more uh an optics guy okay yeah back
back again to the optics i
completely understand yeah all right
um let me see if there's anything
popping up
question wise we had a lot already i
think there is there was a
very very much feedback at the moment um
don't see any new questions popping up
um i thank you again i apologize for the
mega delay we had um glitches
yeah but we made it i'm happy about that
um and
thanks again and let me quickly announce
now in a couple of seconds we're gonna
switch over
to the herald news show over there
oh okay yes
you