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Speed of Chips Accelerates With Unwitting Discovery

An Intel team seeking to boost microprocessor performance stumbles across the 'strained silicon' technique.

January 03, 2004|Terril Yue Jones | Times Staff Writer

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.

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