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.

April 1996By Comments

Speed counts for everything in the roaring semiconductor business, and Motorola’s chip fabrication plant known as MOS 11 operates around the clock. Work only ceases on Christmas Day or during an emergency. Otherwise, in the plant’s ultrasterile “clean room,” where miniature electronic circuits are built layer by layer on top of silicon wafers, the lights are never turned off and the rows of giant machines are always running. MOS 11 was designed to build the most complex types of microchips, including the PowerPC microprocessor, which serves as the “brain” of the latest generation of Apple computers, and keeping the factory going at top velocity is a logistical juggling act. Before I spent time inside the factory, I had assumed it would run as smoothly as a Swiss watch. In fact, the elaborate machinery used to build the chips’ delicate circuitry needs constant adjusting, and the factory functions more like an orchestra cursed with unusually temperamental instruments, so that the musicians perpetually have to stop and tune while the orchestra is performing.

Built in 1991 at a cost of $1.5 billion, MOS 11 was the first factory in the world to build chips on wafers that are eight inches in diameter—before then, the largest wafers were only six inches across—and it was the first factory to operate a class-one clean room for commercial production, which is three thousand times cleaner than the average hospital operating room. Several other chip factories run by rival companies are scattered throughout the Austin area, which has become known as Silicon Hills; MOS 11 is southwest of the city, behind an office complex that Motorola built off U.S. 290. It takes several years to get a chip factory to run at full capacity, and while MOS 11 has already achieved a production pace that puts it among the world’s top factories, its managers struggle daily to get more good chips from each batch of wafers. (Each wafer yields from several hundred to several thousand chips, depending on the size of the chips being built.) A bewildering number of things can go wrong; as chips have shrunk, they have become more powerful and more efficient, and now a single chip has millions of transistors, diodes, and capacitors crowded into a space the size of a fingernail. The smallest components that MOS 11 builds are about half a micron wide; a strand of human hair, by comparison, is about seventy microns wide. Thus, a dust particle falls on the fragile components with the force of a giant boulder.

Throughout MOS 11, red digital clocks display the hour and minute of the day in military time—a reminder that even if the work never ceases, time is always passing, and the factory is never making enough chips to satisfy the insatiable demand. Over the past decade, the semiconductor industry has expanded fivefold, invigorating the country’s atrophying manufacturing sector and lifting the stock market to new heights. Chips are now found in washing machines, coffee makers, smoke alarms, and answering machines, where they perform invisible miracles of automation. Even though they govern so much of modern life, most people are barely aware of how chips are made; our imaginations are steeped in images of Detroit’s assembly lines or Pittsburgh’s steelmaking furnaces, but the interior of a chip factory is unfamiliar. The new factories are not like the old ones; they are incredibly clean, automated, very efficient, and non-union. The new factories are run by managers who preach teamwork to get employees to devote themselves to the well-being of the factory. There is something eerie about the commitment that an institution such as Motorola requires of its workers—it is like a cult or the military. But the company is also a powerful force in the lives of its employees. It lifts them out of the circumstances they were in, often giving them more responsibility and more money than they ever expected to have. Many of the one thousand people who work in MOS 11 feel that the factory has given them a future. For two weeks in January, I sat in on daily meetings held by MOS 11’s managers to see how they run the factory, and spent time on the factory floor with former equipment operators to see how chips are made and what it is like to work on the modern assembly line.

Bunny Suits

AT 7:30 A.M., MOS 11 EMPLOYEES ON THE FIRST SHIFT STREAM through the front doors of the brown brick building. (“MOS” stands for “metal oxide semiconductor.”) At the same time, weary, dazed-looking people who have finished working the graveyard shift begin to leave. At 8:30 a.m., the factory’s managers gather in a conference room on the second floor to review the previous shifts and try to make sure the place runs smoothly during the next 24 hours. One morning, Steve Brown, the supervisor of the factory’s first shift, sketched what had happened the day before. “Yesterday the WIP was 31,559,” Brown told the other managers, referring to the “work in process,” or the number of wafers going through the factory. “And we did 63,130 turns.” In other words, every wafer had moved through an average of two steps in the assembly process—the industry’s equivalent of breakneck speed. Brown described problems that were likely to impede the flow of wafers through the factory that day: Two fifths of the factory’s low-temperature furnaces weren’t working; one of the machines that check the dimensions of circuits was down; four fifths of the machines that perform a crucial process in an area called etch were out of commission; and an unwieldy bulge of wafers was converging in an area known as diffusion. “A lot of inventory has slammed into there recently,” warned Brown. But MOS 11’s managers cultivate a macho, matter-of-fact presumption that problems will be solved, so nobody seemed alarmed. “No real major issues are expected,” Brown concluded. “We should have a pretty good day.”

After the meeting was over, I went up to the factory floor with Gregg Willis, a genial 25-year-old who works as a training coordinator. Willis grew up in Austin, loves to hunt, drives a pickup, and sometimes wears a T-shirt that declares he is P.C., or “Proud to be Conservative.” After graduating from high school, he served in the Army and then got a job loading trucks for Coca-Cola, which he found depressing. He started working at Motorola four years ago, and he loves his job. Though most chip factories do their manufacturing on the first floor to reduce the amount of vibration from machines, MOS 11 builds its chips on the third floor, far from the building entrances. Everybody headed for the fabrication area, or “fab” for short, follows a strict protocol to minimize the likelihood of contamination. Before going upstairs, Willis and I slipped blue paper booties over our shoes and put white hairnets on our heads (the cause of “fab hair”). Then we cleaned our hands by sticking them inside special machines that washed them and under air blowers that dried them. Glass display cases nearby contained daily performance reports: One listed recent cases of “scrap,” or faulty wafers that had had to be thrown away, and another showed how many wafers had been shipped to customers so far that month. It was mid-January and the factory was about two days ahead of schedule.

On the third floor, we walked through an air shower—a short hallway full of nozzles that blasted us with purified air to get rid of dust, dirt, and lint—and into the factory’s gowning area. In the gowning area and in the factory proper, the walls were made of aluminum coated with white enamel paint (ordinary paint peels and flakes) and the floor was a series of chrome grates. I looked down through the grates and saw maintenance crews tinkering with the pumps and gas lines downstairs. Everything was bright and shiny and lit by fluorescent lights, and there was a loud hum, which was the noise of purified air being pushed through the factory by 64 giant fans. “The clean room is a regenerative environment,” Juan Morin, a member of the factory’s microcontamination team, had told me earlier. “It’s constantly being contaminated and constantly being cleaned.”

Some people in the gowning area had already suited up in the snow-white Gore-Tex jumpers, called gowns or bunny suits, that are the standard uniform inside the factory. The suits block flakes of dead skin or lint from escaping and fouling up the chips’ circuitry. The workers in bunny suits looked like Star Trek characters. The hood, which resembles a malleable version of a knight’s headgear, goes on first. “That’s inside out,” someone said to me as I pulled mine on. “My first day here, I put my hood on like that.” Then I tried to step into my Gore-Tex jumper without letting any part of it touch the floor, which was nearly impossible to do without falling over. Finally, I pulled on knee-high Gore-Tex boots and put on latex gloves and a face mask. When I was finished, just the skin around my eyes remained uncovered. Willis put on safety glasses, but I didn’t, because I wear glasses anyway. Employees said that putting everything on and then taking it all off every time they leave the third floor is one of the most tiresome things about working in the factory. At the same time, some people like the feeling of anonymity or authority that the suit gives them. “I was in the military, so I look at it as getting dressed for duty,” said Willis. Unless supervisors happen to be carrying a two-way radio, which is a status symbol, it is hard to pick them out of a crowd. But social interactions are not entirely muffled by the suits—operators learn to recognize acquaintances by their build or walk and to gauge a range of feelings by their co-workers’ eyes. They know when someone is smiling from the crinkles behind the safety glasses.

Once we had suited up, I got a lint-free notebook, with pages that were laminated with a barely discernible layer of plastic, and a low-sodium pen. (The sodium in the ink of a normal ballpoint pen can paralyze a factory because it can become a charged ion, travel through the air, and alter the electrical properties of the wafers it lands on.) Then Willis and I walked through a second air shower and stepped into the clean room. Ahead of us stretched a wide central corridor that ran down the middle of the factory, which was the size of a football field. People in bunny suits were ducking through the automatic sliding glass doors that led into the different manufacturing areas—diffusion, photolithography, etch, and films. Above us, the automatic wafer transport system carried boats of wafers on tracks suspended from the ceiling—it looked like a model railroad, but it was nearly silent, because the cars were floating just above the tracks on magnets to avoid creating flakes of metal or rubber that might contaminate the fab. People at Motorola’s other factories call MOS 11 “the Country Club” because of such advanced features, although the level of automation also means there are more machines to go haywire. One time, operators in the photo area heard a colossal crash and discovered that the transport system was busily knocking whole batches of wafers onto the floor. They danced around below, trying to catch the wafers before they smashed to bits, until somebody shut the system down. A completed wafer is worth from $1,000 to $10,000, and watching the valuable merchandise being destroyed horrified the onlookers. “Working in this place is like working in a diamond mine,” said an employee who had been at the scene. “The wafers are like huge, extremely breakable diamonds.”

We headed for the diffusion area, where Willis used to work as an operator. This is where bare silicon wafers enter the manufacturing process, and where the first steps in building chips take place. All the chips that MOS 11 makes—there are about fifty different kinds—are built on wafers that consist mostly of pure silicon in a crystallized form. Crystallized silicon does not conduct electricity well because its molecules are hooked together in a lattice, preventing the electrons from moving around. However, most of the wafers have been doped by the companies that supply them to Motorola so that when they arrive, they contain traces of elements like boron or phosphorus, which allows that part of the wafer to conduct electricity very well. Electronic circuits are constructed from millions of tiny devices that function like switches, alternately allowing or obstructing the flow of electricity, and silicon’s nature as a semiconductor—one of the rare elements that can either block or permit the flow of electricity—makes it an ideal foundation on which to build circuits. Building circuits on silicon is like carving a pattern into a woodblock, except that chemicals are used to do the work, instead of mechanical tools. First a layer of material, such as glass or metal, is deposited across the surface of the entire wafer, then a pattern of circuitry is photographed onto the material, and finally either acid or plasma is used to eat away the glass or metal that isn’t necessary. The material that is left behind becomes the microscopic parts of components such as transistors, diodes, and capacitors. The process is repeated over and over again with layers of different types of materials—it takes from forty to eighty days to build a complete chip—until the circuits are finished.

None of the seventeen workers in the diffusion area were touching wafers with their hands, because scratching a wafer ruins it. Before any circuitry was built, the wafers were cleaned in a series of heavy-duty plastic sinks called a hood. A robotic arm dunked the wafers into the sinks, which held corrosive substances such as sulfuric acid, hydrogen peroxide, ammonium hydroxide, and most dangerous of all, hydrofluoric acid. “That’s nasty stuff,” Willis said. “If it gets on you, you don’t feel it until it starts eating your bones away.”

Motorola’s track record in handling toxic chemicals is one of the best in the industry, but spills are inevitable. One day shortly before my visit, alarms sounded throughout the factory, and everybody was ordered out of the building. One hundred thirty employees from the factory’s emergency response teams fanned out to search for the problem. On the factory’s second floor, they discovered several pools of hydrofluoric acid. Because of an unusual series of events, the factory’s drainage system had reversed itself, and the acid had flowed backward into the factory from waste tanks outside. Nobody was injured and the spill was contained, but the accident sent a jolt of anxiety through the factory and caused production to stop for a full eight hours. A week later, supervisors were still encouraging operators to hustle to make up for the lost time.

After the wafers were cleaned, they were baked in furnaces set into the walls of the diffusion area. The furnaces looked like large microwave ovens, but they cooked the wafers at temperatures ranging from 600 to 1,200 degrees Celsius. While the wafers baked, gases were fed into the ovens, causing layers of new material to form on the wafers as the gases reacted with their surfaces. The bare wafers had looked like dark mirrors, but when they came out of the furnaces, they were magenta, turquoise, and yellow. When they start out in the diffusion area, most wafers begin with what is called an oxide layer, as oxygen is piped into the furnaces to form an extremely thin sheet of silicon dioxide—otherwise known as glass. Glass is a good insulator; among other things, it is used to make transistors, one of the primary building blocks of the chip’s circuitry.

At every step along the way—when wafers were put into the hood, and again when they were put into the furnace—the operators entered data into computer terminals that stood on tables made of thin metal rods (to keep dust from collecting). That way, if anything went wrong, engineers would be able to retrace a lot’s history, or if a customer needed to know when an order would be finished, managers could track down where it was in the process. The computers functioned as a two-way communication system: Operators could also check charts to see how much scrap was being produced or whether any bottlenecks were forming in the flow of traffic. In most factories only senior managers would have access to such information, but Motorola’s executives thought employees would work harder if they knew how their contribution fit into the scheme of things. Though managers encourage friendly rivalry among the factory’s divisions, over the past year everyone at MOS 11 has been trying to meet the needs of the people in other parts of the factory who receive their wafers, as well as their own supervisors, so that the entire institution can function more smoothly and produce chips as quickly as possible. “The better my numbers are at the end of the shift, the better I look, right?” said Jesse Barrera, a supervisor in the etch area. “Well, yes, but does the whole factory benefit? Probably not. I’m likely to be flooding the next area with a bunch of work that they can’t even use.”

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.

Raining Metal

The third shift starts at 11:30 P.M. and lasts till 8 a.m. During the night, the area outside the fab is deserted except for robots that move along the gleaming linoleum floors carrying finished wafers over to the shipping area. Not surprisingly, given the hour, the strangest things that happen at MOS 11 usually happen on the third shift. Most recently, a romantic fever seems to have swept through the fab: There is a rumor, neither confirmed nor denied by Motorola, that two employees were caught having sex in a conference room and two others were caught having sex in a car. Such exertion aside, everybody who works the third shift typically functions in a state of perpetual jet lag. And yet the third shift shovels wafers along. “On first shift, you’ve got managers running around, maintenance people working on equipment—lots of issues to deal with,” said Andrew Venson, the 27-year-old training coordinator who showed me around for several nights. “On third shift, you don’t have as much of that going on, and you can just do your work.” Venson moved here from California and tends to stay calm despite the frenzied pace inside the fab, which often makes other employees seem like they’ve been drinking too much coffee. On the weekends, he reverses his sleeping schedule to normal so he can be active in a Jehovah’s Witnesses church. He used to work on the first shift, but when his wife, Jessica, started working at MOS 11, she was assigned to the third shift, so Andrew asked to work then too.

Venson used to be an operator in etch, where wafers are sent from photo. In etch, acids or plasma are used to carve away part of the last layer that was grown on the wafer in diffusion’s furnaces—leaving behind minuscule parts of transistors, capacitors, or diodes. “Think of a chisel chipping away at wood,” said Venson. The acid or plasma removes material except where photoresist remains on the wafer. Afterward, the last of the photoresist is removed; by then, the material it protected has taken on the shape of the pattern that was photographed onto the wafer. In this fashion, the rudimentary parts of a circuit are built. Because etches are irreversible, many of the problems that cause chips to fail occur in this area. Incomplete etching of metal layers, for example, causes electrical shorts in the minute circuitry.

There are two basic types of etches. Wet etches are performed by dunking wafers into hoods that hold corrosive liquids such as sulfuric or nitric acid. Dry etches, which take place in a machine called an etcher, are more complicated. Venson and I went into one of the maintenance areas to look at the etchers. The machines resembled large chrome boxes, and the area was full of skinny pipes carrying chemicals up from below; we were standing in an aisle of etchers that were working on metal layers, and those machines were using chlorine—one of the more toxic gases in the factory. Electrodes inside the etchers excited the chlorine into plasma form, which is a powerful, electrically conducting state (lightning and neon are both examples of plasma). An electrical coil inside the machines then aimed the plasma at the wafer, burning away the material that was bare of photoresist. There was a window on the side of one of the etchers we were looking at, and it was emitting a purple light—the glow of plasma eating metal.

From etch, many wafers go back to diffusion to begin another round through the factory’s divisions—they go back to diffusion’s furnaces, back to the lithocells, and back to etch’s hoods. Sometimes, however, instead of going back to diffusion, wafers acquire additional layers in a part of the factory known as films. Amsale Nunu, the training coordinator who formerly worked as an operator there, is a petite 37-year-old woman with a quiet, engaging manner. Nunu grew up in Ethiopia and immigrated to this country at age 22. She got a high school degree by taking an equivalency exam and began working at Motorola in 1987. Nunu explained that late in the assembly process, layers of metal such as aluminum and titanium (which are used to wire together all the transistors, capacitors, diodes, and other devices that have been built) are sputtered onto the wafers by shooting beams of ionized gas at big tablets of metal, causing metal to rain down onto the wafers in a thin sheet.

The most complicated and dangerous machines in films are the ion implanters, where phosphorus, boron, and arsenic are fired into the wafers. Maintenance crews that work on them are screened for arsenic poisoning once a year, and the operators who run them wear badges that measure radiation levels. Nunu and I went into a maintenance area to look at an ion implanter. Inside the machine was a large metal wheel that holds the wafers as they are implanted. When the machine is operating, the wheel spins at 1,200 revolutions per minute to make sure the ions are distributed evenly, and it goes so fast that the individual wafers become a shiny blur. To create ions, gaseous forms of elements such as phosphorus, boron, or arsenic are piped into the machine, where electrodes excite them until some of their electrons are knocked off. The remaining molecules—or ions—have a charge, and the direction and speed of their movement can be governed by an electrical field. The ion implanter uses such a field to accelerate the ions to high speeds and slam them into the wafers. Once implanted, the ions alter the electrical properties of the wafer, transforming electrically neutral material into a good conductor of electricity.

The Detectives

In the forty to eighty days that it takes for a wafer to make it all the way through the assembly process, as many as fifty layers of material will be grown and patterned and etched. The finished wafers are sealed in a protective glass coating and carried down to the testing area on the factory’s first floor in a dumbwaiter. There the chips are fired up with electrical current to see if they work. All the components of the chip are wired to metal pads that rim its border, and the testing machines apply current to these pads through minute needles while a computer evaluates the chip’s performance. When I was there, one screen showed a problematic wafer on which only 20 percent of the finished chips were working. “Must be PowerPC,” quipped Russell Reed, a wise-cracking engineering student from New York who was the training coordinator who showed me around the test floor. The PowerPC chip goes through twice as many steps as some of the other devices that MOS 11 makes, and not surprisingly, the factory’s yields on the PowerPC are lower than those for less complicated chips. The finished wafers are sent to assembly sites around the world, where they are cut into individual chips with a diamond saw.

Whenever operators on the test floor discover wafers with chips that fail in a regular pattern—sometimes they have “dead edges,” when all the chips at the border fail, or “dead centers,” when the chips in the middle don’t work—a team of device engineers will try to figure out what went wrong. (One of the greatest sources of contamination is the factory’s equipment, which needs oil and grease to function and can have parts that flake.) Every morning during the 8:30 staff meetings, device engineers report to the factory’s managers about the latest yields of every chip that MOS 11 makes. One morning, device engineer George Campbell told the assembled managers about problems with a certain kind of memory chip. In essence, too many of the chips had poorly defined circuits, and current wasn’t flowing where it should. “We had high leakage fallout,” Campbell told the group. In the days to come, Campbell had to figure out why this was happening.

Campbell and the other device engineers are like detectives. They spend a lot of time poring over data from the testing machines, and they spend a lot of time staring at chips under microscopes. Sometimes they will painstakingly remove one layer at a time from a wafer, which is called deprocessing, in search of the defect that has caused chips to malfunction. Because the causes of failure are almost always as small as the components themselves, it can be maddeningly difficult to discern what went wrong. Once they think they have isolated the cause of a systematic failure, the device engineers will repeatedly run batches of wafers through the step where they suspect it occurred, to determine whether their hunch is correct. If it is, then the assembly process is changed so that the source of failure is removed—hopefully without causing any new problems. The trick is to do all this in a matter of days. “The whole time, either part of the factory has ground to a halt and is waiting for you to finish the work, or else they are running with unacceptably low yields,” said Chris Magnella, the process engineering manager. “We can’t solve a problem in months—it isn’t cost effective.”

As soon as MOS 11’s employees get really good at building chips of a certain scale, Motorola asks them to make devices with even smaller components, to keep up with the semiconductor industry’s perpetual revolution. That allows the factory to jam more transistors and capacitors onto the chips, making them faster and giving them more power. When MOS 11 was first built, the factory warmed up by making chips with features that were 0.8 microns in size. Now MOS 11’s managers are concentrating on producing higher yields of chips whose component parts are 0.65 microns, while they also build chips with features that are only 0.5 microns and push the factory to start building components with parts that are even smaller. “You just keep working on the product,” said Bill Walker, MOS 11’s creator. “You tweak the process and identify what we call the manufacturing window, and then you get the process established to the point where it’s well controlled, so that you know you can repeat it, time after time, for ever and ever.”

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