Tahir Ghani at Intel. Pakistani participates in straining semiconductors

Special thanks to Irfan Zia for the input.

Speed of Chips Accelerates With Unwitting Discovery
An Intel team seeking to boost microprocessor
performance stumbles across the 'strained silicon'
technique.
By Terril Yue Jones
Times Staff Writer

January 3, 2004

At first, it looked like a mistake.

Mark Bohr and his team of computer-chip engineers at
Intel Corp.'s Hillsboro, Ore., campus were trying to
enhance the performance of transistors, the building
blocks of a microprocessor. They were focusing on
reducing the electrical resistance, which in turn
would speed the flow of electrons and allow the chip
to process data faster.

One experiment back in the summer of 2000 produced
results that were far better than expected. In fact,
the performance boost was so off the charts that there
had to be another explanation.

There was.

It turned out that the Intel team had stumbled onto a
technique known as "strained silicon," in which stress
is applied to silicon atoms so that electrons can flow
between them faster. Intel will bring the technology
to market early in 2004 in the generation of chips
that succeeds the popular Pentium 4.

Several industry heavyweights had long been trying to
incorporate strained silicon into their chips to
improve efficiency. IBM Corp. had been publishing
research papers on the topic for more than a decade.
Advanced Micro Devices Inc., Texas Instruments Inc.
and other chip makers were all eagerly researching the
subject as well.

At Intel, strained silicon was not a priority. But the
company, whose chips power more than 80% of the
world's PCs, was the first to figure out how to apply
the technology to massive volumes of chips at low
cost. It just didn't know it at the time.

"We kind of backed into it," said Bohr, 50, who is
director of microprocessor technology for Intel's
Technology and Manufacturing Group.

Semiconductor makers are constantly searching for ways
to shrink transistors and microprocessors to pack more
computing power onto their chips. The state of the art
for chip components currently is 90 nanometers, which
makes them about 1,500 times more narrow than a human
hair. But as they approach the physical limits of how
small such components can be, engineers must look for
other ways to enhance chip performance.

Enter strained silicon. The technique relies on
silicon compounds to stretch silicon atoms in some
directions and compress them in others, like a
molecular version of Silly Putty.

When a chemical compound called silicon germanium is
next to pure silicon, for instance, the bigger silicon
germanium molecules stretch the lattice structure of
neighboring silicon atoms, increasing the distance
between some of them by about 1%. It may not sound
like much, but it's enough to speed the flow of
electricity by up to 30% in certain transistors. That
means data can be processed faster too.

"It's like widening the lanes for traffic," said Rob
Willoner, a manufacturing technology analyst at
Intel's headquarters in Santa Clara, Calif.

Tahir Ghani and Kaizad Mistry, electrical engineers
who work for Bohr, spent a good deal of 1999 and 2000
experimenting with silicon germanium to boost
electricity flow through transistors. Initially, they
expected to see about a 10% improvement.

Instead, they recorded speeds up to 30% faster.

"When we saw the higher performance improvements, we
thought we had something big," recalled Ghani, who
grew up in Pakistan. Added Mistry, whose childhood was
divided between India and the U.S.: "The first
excitement was that that number was as large as it
was, because that's really our job: to make that
number as large as possible."

Bohr responded by adding extra engineers to the
project, and hundreds of sophisticated experiments
were drawn up. In all, roughly 40 people were
dedicated to unraveling the mystery.

The challenge, Mistry said, was conducting a
painstaking analysis of the electrical measurements to
"try to figure out what is going on inside that
microscopic piece of silicon that you can't really
see."

For a full year, the members of Bohr's team carefully
retraced their steps. They wanted to be able to
control the degree of strain on the silicon and
reproduce their results consistently.

Ghani, 43, and Mistry, 42, conducted their
investigation in cubicles, conference rooms and the
sterile "clean room" where chips are manufactured.
They communicated incessantly, frequently messaging
each other and Bohr from their wireless laptop
computers.

At home, Ghani would put his three young children to
bed, then log on to his computer. Mistry would tuck in
his two kids and join Ghani online. Then they would
stay up until midnight poring over reports and
discussing them via e-mail or on the phone.

Ghani would be awakened by phone calls at all hours of
the night from Intel technicians: A result wasn't what
was anticipated. The instructions weren't clear. What
should we do?

By the end of 2000, Bohr and his lieutenants had
determined that the silicon germanium was causing
strain. Then they had to ensure they understood the
process and could repeat it reliably enough to
manufacture chips in large quantities.

Progress was very methodical, the scientists said.
There were no occasions of running breathlessly to a
colleague with a ream of computer printouts or
high-fives in the clean room, as one might imagine if
Hollywood were to turn the story into a film.

"Most learning happened in meetings," Ghani said.

Long stretches of intense lab work were only
occasionally broken up by social activities, such as
an excursion to see "Star Wars: Episode II Attack of
the Clones" in the spring of 2002.

Intel said little about its suspicions as it continued
its top-secret research. Then it astounded the
industry in August 2002 when it said its new
generation of 90-nanometer chips would include
strained silicon.

Intel "stunned analysts and sent competitors into
catch-up mode," the trade publication Electronic
Engineering Times wrote at the time.

"It's a phenomenal step," said Gene Fitzgerald, a
professor of materials science and engineering at MIT
and an expert on strained silicon.

Intel found it could implement strained silicon fairly
inexpensively and improve electricity flow by 25% to
30%. That meant computers that could process data
faster, though Intel won't say how much.

"We're getting good improvement in chip performance
with almost no increase in cost," Willoner said.

Experts knew it wasn't idle talk coming from the
world's largest producer of computer microprocessors.

"Intel clearly was the first one to start talking
about using strained silicon, and when they talk, they
typically are pretty far along with their
implementation, " said Risto Puhakka, vice president
of VLSI Research, a San Jose firm that monitors the
industry.

IBM executives say too much is being been made of
Intel's introduction of the first mass-market chip
with strained silicon. The Armonk, N.Y., company began
shipping some chips that include layers of strained
silicon during the fourth quarter of 2003--the same
time period as Intel.

Intel "is trying to introduce confusion because it's
embarrassing to admit that this has been out there for
a decade," said IBM Chief Technologist Bernie
Meyerson, who is credited with developing ways to grow
large amounts of silicon germanium. However, he
declined to identify which IBM chips contain strained
silicon or which customers were buying them.

No. 2 chip maker AMD, which is researching strained
silicon and other technologies with IBM, isn't
planning to sell microprocessors with a significant
degree of strained silicon until 2005 or 2006, said
Craig Sander, a vice president at the Sunnyvale,
Calif., company.

"AMD is selling chips with a low level of strain, but
not on the order of magnitude of Intel," Sander said.
"Strain is not new; getting high levels of strain is
more new."

Nathan Brookwood, principal analyst with the Saratoga,
Calif.-based market research firm Insight 64,
acknowledged that IBM had been the first to show that
strained silicon would improve chip performance.

"But as far as I know," he said, engineers at Intel
"are the first folks to commercialize the process, so
that gives them some bragging rights."
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