What I want to do in this video and the next one is to give you a flavor
of EUV, which stands for Extreme Ultraviolet Lithography.
Many people believe that this one of the
greatest challenges facing the semiconductor industry right now.
it's said to be the Achilles' heel of
scaling where it takes on this other wise nice
strong and plum the Archillies and the biggest.
Weakness right now is this, extreme ultraviolet, are
the difficulty in getting to extreme ultraviolet photography.
What this image is depicting is the scaling
of the wavelength that we use for lithography.
Or rather, the absence of scaling of the wavelength that we use for lithography.
So it shows that back
around in 1997 when we switch to using this deep
ultraviolet lithography, which is ultra wavelength of 248
nanometer. This was enabled using excimer laser
using krypton fluoride source, which I'll talk about more in a few
minutes. And then back around 2001 to 2002,
we took the next evolutionary step and moved to a wavelength of 193
nanometer, which was enabled using argon-floride laser.
And we have been pretty much stagnant since then.
So in the last 10 years, there hasn't been any
change in the wavelength of the light used for lithography.
And the next step is not an evolutionary step, what we need to do next
to scale the wavelength is to take a quantum leap and go from this
deep ultra violet
to extreme ultra violet wavelength range. And go to
wavelength of 13.5 nanometer. And that's
a huge quantum leap from where we are currently that is 193 nm.
So then we asked ourselves at how did we enable scaling
in the meanwhile, you know, we all seen the technology progress
from 65 to 45.
To 32 to 22 to moving to 15 the next next year.
So the last few videos, we saw that we have
been able to do this by essentially using double patterning .
And going forward using quadruple patterning, and you know,
even going forward using quintuple patterning that allows you
to double your pitch or quadruple your pitch,
Or make your pitch eight eight times if needed.
So then we ask here, do we really need to
take this quantum leap, do we really need extreme ultraviolet lithography?
And the answer to that is yes.
And the reason we need that is because Moore's
law has always been a law about economics.
It has been that moving, scaling each technology
generation, you get 50% reduction in your cost.
You can put twice the number of transistors in the
same area and you will, if you made the same
chip you'd reduce a 50% reduction in your cost and
that has been true up till the 90 nanometer technologies.
So going from
130 to 90nm people did actually use to
achieve close to 50% reduction in the cost.
And that was till this, wavelength of scaling was continuing, and from that
point we moved actually to using
double-patterning, or using, quadruple-patterning, and so on.
And what we have seen is since using
this double patterning adds a lot of process steps.
So the last few videos I describe that moving to a, using say a
self
aligned double patterning scheme, you add four additional
process steps each time you do a double patterning.
And more the number of double patterning steps
you add, you increase your cost.
And so, when we move from this traditional wavelength scaling
to double patterning, we see that reduction in costs achieved
actually went down.
So, instead of getting a 50% reduction in cost, going from
90 to 65 nanometer, people only achieved 12% reduction in cost.
And that has also been
marginally
declining.
And actually, what, this source is that going from 32 to 22 nanometer, you
actually increase your cost, because you are
using so many of these double patterning steps.
That there is no reduction in the
cost even if you scale your transistor dimension.
So this, double patterning or quadruple patterning has really put Moore's law
on life support, and to get it out of there, get it back to a healthy state.
What we need is actually going to extreme ultraviolet lithography.
And extreme ultraviolet lithography, it has always been a moving target.
So realize that we haven't
scaled the wavelength in a decade and people started realizing that they really need to
go to EUV back, you know, back in 2000, 2003 time frame, and they said okay.
will be ready in two years time, you know.
EUV will be there in 2005.
All we need to do is fix the source, and we'll be done.
And back in 2005, they said, oh, the source is not really
ready, and we also discovered that there are some additional problems
that we need to fix in in terms of the optics.
And but we will fix, and it will be ready 2007.
And then people came back in 2007 and said, oh you know, the
source in optics are not really ready yet. There has been significant progress made.
but they're not quite ready for volume production.
By the way we also realized that you know, there are
a lot of problems in the resist and that requires a lot of
development
if you need to go to EUV as well. And, and then
you know, we will, we will fix we will fix it by 2009.
And you know, then people come back in 2009 and said, oh,
you know, it's the source and optics and resist are not ready yet.
But we discovered that, you know, that additional problems that you
get in the roughness of the resist, if you do to extreme
ultra violet lithography as well
But they said you know, this we will, we will take care
of it, don't worry about it, by 2013 it will be ready.
So there are, what we see is
first of all it
has always been a moving target since the last 10 years and
people have come to live with the fact that it has been a moving target.
Now atleast we now know that these are the main issues that we need to
address, and hopefully, thankfully no new issues will pop up, but you never know.
So, what I want to give you is, give you a
flavor of why ? ofcourse it has been a moving target, but,
that's not because.
It's not like the U.S. Congress where they just like to kick the can down
every 2 years,
there's some real challenges involved in the physics.
So, what are some of the issues involved in the physics of going to EUV or
going to extreme ultraviolet light. So what I am showing here is the
different spectra of light
involved.
So anything above, above 400 nanometer is called
ultraviolet it goes into the visible or the ultraviolet spectrum.
Anything below 10 nanometer is called X-ray radiation.
even between 400 and 10 nanometer, it's a wide range.
So between 400 to 100 nanometer, this is what we call
a deep UV light, or DUV. And below If you go below
100 nanometer up to 10 nanometer, that's what you call extreme ultraviolet light.
And DUV, it can say, you know, it has more resemblance to UV light.
EUV has more resemblance to X-rays. And all this
is governed by the energy of the photon involved at that particular wavelength,
which is described by this nice equation that Mr. de Broglie himself described.
And what it says is that energy related to
this wavelength by e equal to h c by lambda.
And if you translate into some numbers
for the light we are trying to study here,
it translates into that it's related by this particular equation.
So according to this equation, if you have a lambda of a micron, or 1000
nanometer, that corresponds to energy of a photon of 1.2 eV.
So what does that mean for the wavelengths that we
are trying to study, or the wavelengths involved in lithography.
So, what it means for the wavelengths involved in lithography is, I described to
you that so far. We have used this 248 nanometer
or 193 nanometer light, and we have used
this excimer laser based on krypton fluoride or argon fluoride.
And if you plug those numbers into this into this.
If you plug this wavelength into this equation,
what you get is, for for 248
nanometer what we have is a wavelength
corresponds to energy of photon of 5 electron volt.
Similarly, if you have 193 nanometer, corresponds to
a photon energy of 6.4 electron volt.
And these are not
these are not very high energy, and they are not very harmful either.
So, if, if any of you have undergone LASIK
treatment, where they use laser to fix your eye prescription.
They say to you that this excimer laser at this particular wavelength.
So we know you can't cause too much harm with them.
But what
extreme ultraviolet requires, is that it requires
a wavelength target that is 13.5 nanometer.
And if, if you plug that into this equation,
what you get essentially is an energy of 92 ev.
So, 92 ev is a lot of energy for one photon.
My advice to you is if you see a photon with 92 electron volt of
energy, try to get out of its way, because it can cause you a lot
of harm.
But besides that another problem with having this much high energy
is now if you have a photon of energy of 92 electron volt.
It will get absorbed by pretty much everything that you put in it's way.
So, suppose you had if you want to focus light which has a high energy and you
put a lens most of the photon will actually not come out of this lens because
most of them will get absorbed within this lens
If you reflect that photon using a mirror you will, again, lose half of
the light at this reflection, because this mirror will absorb half of these photons.
Similarly, if you generate these photons using a plasma
source that plasma itself will absorb half of these photons.
So each, first of all it's very difficult to
generate these photons.
And once you generate them it's, it's, they will get absorbed by whatever
you, that you put in their way to reflect them or to focus them.