Lithography Answers Blowin’ in our Wind?

As is often the case during the
nighttime panels at SPIE, there was a fair bit of silliness in
Tuesday night’s panel discussion, “Future Projection
Lithography: Optical or EUV?” It’s a serious enough
question, but after a very long day of listening to detailed
technical presentations, attending customer/supplier meetings, and
perusing the exhibit floor, these leaders of the teams trying to
find answers to extremely difficult lithographic challenges were
ready to loosen up a bit.

The tone was set very aptly by
IBM’s Kit Ausschnitt, who entertained the audience with a
reading of his latest musical adaptation — this time, with
apologies to Bob Dylan, with Blowin’ in Our Wind:

How many nodes must a man walk
down

Before you call him a
man?

Yes, ‘n’ how many chips must he
fabricate

Before using all the
sand?

Yes, ‘n’ how many times must the
molten tin fly

Before EUV is banned?

The answer, my friend, is
blowin’ in our wind,

The answer is blowin’ in our
wind.

The topic for the night took a
closer look at just what was likely or necessary to keep walking
down those nodes. There are of course no easy answers, and the
panelists came with often starkly differing views.

One of the more telling moments of
the evening was watching Freescale’s Will Conley laugh
continuously as his friend Kevin Cummings so doggedly presented
ASML’s company line on EUV. As Ausschnitt alludes to in his
lyrics, there has been pretty much talk this week at the Advanced
Lithography conference with regard to the “molten tin”
flying through the EUV systems (some are referring to the exposure
systems as deposition systems because of those sputtering tin
targets).

But one of the key arguments that
evening was not related to the technology and all the challenges
that it faces, but the questionable economic models surrounding it.
Ausschnitt stood up during the Q&A period to ask how ASML could
have a cost-of-ownership (CoO) model showing EUV as the more
cost-effective solution when they have no high-power source, no
defect-free mask and no workable resist on which to base their
model. It is understood that any cost model at this point is going
to have to be based on a certain amount of assumptions. But what
was disconcerting was Cummings’ answer to the question: Since
they have to assume something, they assume the numbers that are
needed to make EUV successful. That wasn’t a very comforting
explanation in itself, but when pressed on that point, Cummings
followed it up with, “We have a program in place that we
believe in, and you’re the judge. Either we convince you or
we don’t.”

How many screens must a man
project

Before he can fill the
sky?

Yes, ‘n’ how many jeers must one
man get

Before he can hear hecklers
cry?

Yes, ‘n’ how many snores will it
take till he knows

That too many brain cells have
died?

The answer, my friend, is
blowin’ in our wind,

The answer is blowin’ in our
wind.

But I don’t mean to just
partake in EUV bashing here. Indeed, a lot of slides were projected
Tuesday evening, and it’s not as if optical lithography faces
a particularly rosy outlook itself. Double patterning, for example,
is widely considered the route for extending the lifetime of
immersion lithography, but it doesn’t present a very friendly
cost model, particularly for chipmakers producing fewer wafers per
mask, which Conley pointed out, being with one such chipmaker. In
separate conversations, Conley has told me how much Freescale is
taking its designs back to the drawing board to make them more
litho-friendly in an effort to increase the process window without
having to resort to double patterning. During the panel discussion,
he said, “You can call it DFM, but it’s just
survival.”

Tony Yen of TSMC labeled double
patterning as a one-generation extension of immersion lithography.
Although that is debatable, the EUV contingent has presented some
compelling information on how they plan to take that technology all
the way down to the 11 nm node.

Looking at high-index immersion
lithography as a means of extending optical lithography also does
not keep the hecklers at bay. Ben Eynon, Sematech’s associate
director of lithography, presented a relatively balanced view of
the challenges presented by both EUV and 193 nm immersion
lithography. One important point he made about the high-index lens
material (LuAG) needed for 1.70 NA imaging is that the lens
material absorption is at about 0.07/cm, and needs to reach
0.01/cm. Those numbers are a little outdated, since Schott is
talking this week about having achieved 0.05/cm, but especially
given that the absorption target is now <0.005/cm, the concerns
are still valid.

How many years can a speaker
present

Before the same SPIE?

Yes, ‘n’ how many molds can he
nanoimprint

Before one is defect
free?

Yes, ‘n’ how many talks can a
man suffer through,

Pretending he just doesn’t
see?

The answer, my friend, is
blowin’ in our wind,

The answer is blowin’ in our
wind.

There were several other excellent
presentations given during the panel by Tim Brunner of IBM,
Tatsuhiko Higashiki of Toshiba, Winfried Kaiser of Carl Zeiss, and
Kurt Ronse of IMEC. And the main recurring theme was certainly that
nothing is going to be easy. Although the panel was focused on
projection lithography, Higashiki did a nice job of pulling in
discussion of more of the options, including maskless lithography
and nanoimprint. But, as he pointed out, they all have significant
development challenges. For a company like Toshiba, competing to
push NAND flash as quickly and as far as they can, they will grab
hold of any technology that can promise a boost in resolution and
continued scaling. But those solutions need to come sooner rather
than later.

As Conley noted among his multiple
quotations of Yogi Berra, “It ain’t over till
it’s over.”

Meanwhile, there’s more to be
said about nanoimprint. Molecular Imprints had a couple
announcements this week — one on the release of the
Imprio 300, with improvements in throughput and more, and
another on Sematech’s
purchase of an Imprio 300 (yes, the journalists around here
were a bit annoyed that we weren’t told about the Sematech
purchase during our briefings with Molecular Imprints and/or
Sematech just one or two days before, but such is the nature of
press release approval processes). Anyway, there’s more to be
said about all of that, and the buzz around here at the show, so
stay tuned…