Wafer Madness
Twenty-four hours a day at Motorola’s MOS 11 factory outside Austin, workers race to build the complex computer chips that power our brave new world. For two weeks, I was one of them.
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Teamwork is crucial because as chip factories have gotten more sophisticated, the cost to build them has multiplied. “Time to money, that’s what the key is,” said Bill Walker, who built the $1.5 billion factory and is now in charge of three of Motorola’s chip factories and both of its research laboratories in Austin. (Motorola is now the largest private employer in Austin.) “If you’re going to spend that much, then you’ve got to start paying back very fast, or else you can’t survive in this industry.” Ironically, the greatest threat now facing MOS 11 is that chip manufacturers may be hurt by their own success. In the past year Motorola’s stock has fallen from $82 to $52, and the stocks of rivals such as Intel and Advanced Micro Devices have taken similar plunges. MOS 11’s employees are mystified—they keep surpassing their quotas, and Motorola recently chalked up another quarter of record earnings. But Wall Street analysts fear that as factories like MOS 11 start improving their yields, and as factories that were built even more recently (like Motorola’s latest factory, MOS 13, on the east side of Austin) get up to full speed, they may cause a glut of computer chips. A glut could make the price of chips slump, and that would devastate the competitive, low-profit-margin semiconductor industry. However, given Motorola’s huge investment in MOS 11, even if a surfeit of chips were to occur, the only option the factory’s employees would have would be to make chips even more quickly.
Photo Finish
By the time a wafer has been through diffusion, it has a uniform coating of material across its surface. The next step is to photograph a blueprint of the chip’s circuitry onto the wafer in the photolithography area. A certain mythology has grown up around the photo division, which uses machines that are considered challenging to operate. “They think they are fighter jocks,” said one Motorola employee. Bob Sepulveda, who works in the training department with Willis, used to be an operator in photo, and he showed me around the area. Sepulveda, who is 33, grew up in Austin. After graduating from high school, he worked in several restaurant kitchens before coming to Motorola. “Two different kinds of people work in the fab,” he said. “There are people who are really ambitious and want to move up as soon as possible, and then there are people who just want to do their job and go home. I was somewhere in the middle.” He expected to remain on the factory floor for several years, but because of Motorola’s rapid expansion, the company quickly promotes employees who perform well. Sepulveda is smart, animated, and good with people, and he was asked to move into the training department last November, after only a year and nine months.
Sepulveda was working the second shift, which begins at 3:30 p.m. and ends at midnight. On the second shift, the factory changes: There is more bantering in the hallways, and the atmosphere is looser, largely because almost everyone who works in the evening is under 25. Many are college students putting themselves through school, while others are recent high school graduates. Every shift begins with an informal meeting called a passdown, to brief the arriving operators on how the last shift went and to set performance goals for their shift. We suited up along with the second-shift employees and went into the fab for the photo passdown, where white-suited operators were standing in a circle around their supervisor, Bruce Palmquist. “Our returns yesterday were pretty spectacular,” Palmquist was telling the operators. “You guys came through with flying colors. We had zero scrap.” He had to shout to be heard over the constant hum of the fans and the machinery. “Unfortunately, today won’t be as good a day,” he added. During the first shift, maintenance crews had discovered a leak in one of the pipes that carry wastewater from the factory floor, and the crews had shut down MOS 11’s water supply to fix the problem. (Making chips requires immense amounts of water—MOS 11 consumes 352 million gallons a year, mainly because water is one of the factory’s primary cleaning agents.) When the water stopped flowing, hundreds of wafers were stuck in photo’s lithocell machines—giant cameras that photograph patterns of circuitry onto the wafers—and weren’t bathed in water within the required time. Photo’s processes are unusual in that they can be done over, but at the cost of precious hours. “First shift had to redo three hundred and seventeen wafers,” Palmquist said, prompting groans. The operators were way behind schedule and faced a huge backlog of new inventory. “We need to pull together and make it happen.”
The operators went to their stations. As wafers arrived, workers known as stagers brought the wafers and matching reticle (a piece of glass with a pattern of circuitry outlined in chrome on its surface) over to the lithocell machines. The lithocells looked like aluminum closets with runways leading in and out of them. Operators programmed the machines, then loaded boats of wafers onto the runway, which is called a track. A robotic arm then moved one wafer at a time down the track: First the wafer was heated on a hot plate to get rid of moisture on its surface, and then the wafer was spun on a turntable while photoresist was poured onto it. Photoresist is a light-sensitive liquid that quickly hardens upon contact with air, coating the wafer with a solid shell—as if a special kind of film were glued to the wafer. Finally, the wafer was carried into the closetlike box, called a stepper, where light was shone through the reticle, photographing its pattern repeatedly across the photoresist on the wafer’s surface, once for every chip. Afterward, the wafer was put into a basin where it was rinsed in developing fluid and then in water. The photoresist that had been exposed to light was washed away, baring the material below, while the resist that was not exposed remained behind. Now the surface of the wafer was no longer uniform: Wherever the reticle had cast a shadow, there were raised ridges of photoresist. These ridges would provide a template for the etch division.
Before the patterned wafers left photolithography to be etched, they were inspected at least three times. It is crucial to catch mistakes before the surface of the wafer is permanently carved up. First, wafers are examined under high-powered microscopes by operators looking for anything out of the ordinary, such as patterns of photoresist with fuzzy edges, which might lead to faulty circuitry. The microscopes offer the workers a rare window onto the tiny structures they have been erecting. At 5 times life-size, a chip that has already circled through the factory’s processes several times looks like an orderly village from the window of a plane—the components form neat lines and rectangles like far-off boulevards and buildings. At 150 times life-size, the chip looks more like the work of a mad plumber, as the individual transistors and capacitors are revealed to be an incredibly complicated and colorful maze of parts. Novice operators get motion sickness from whizzing around the surface of the chip in search of flaws. Often they come across one of the fanciful insignia on the wafers: a tiny version of Motorola’s logo—the letter M inside a circle—or the outline of a little man with bulging biceps, which is found on PowerPC chips. After the operators inspect the chips, one computer-operated microscope checks that the pattern of photoresist is precisely aligned with any layers of circuitry already built below, and a second computer-operated microscope checks the topography of the ridges of photoresist to make sure they aren’t too thick or too thin. If the height or width of the miniature troughs and walls were even a fraction off target, then the etching process might not work as it was supposed to.
The night that I attended the photo passdown meeting, maintenance crews got most of the lithocell machines running before the second shift was half over, and the operators pushed through enough inventory to ensure that things were running smoothly again by the time the third shift arrived. There was no way for the division to catch up to where it should have been, but given how the night began, the performance was considered a triumph.
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