Chip Challenges

Semiconductor manufacturers grapple with multiple process and material enhancements.

Some very big changes are afoot in an industry that manufactures some of the smallest pieces of hardware known to man. The way semiconductors are made is changing, and chip manufacturers from Taiwan to Silicon Valley to New York state are gearing up to alter their processes to keep pace. Over the years the semiconductor-manufacturing industry often has had to cope with new technology and manufacturing processes. Today, though, chip makers are being hit with a host of changes all at once. The biggest shifts, likely to affect nearly all chip makers and take place more or less at the same time, are the moves to copper interconnect technology, low-capacitance dielectric insulators, 0.13-micron lithography, and 300-mm wafers. "The likelihood is that most companies in the industry will be doing all these things at once," says James G. Ryan, senior technical staff member and manager of interconnect technology at IBM Microelectronics, Hopewell Junction, N.Y. Driving the conversion to copper interconnects and low-capacitance insulators is the market pressure to achieve continued gains in processing power. "To ensure continued improvement in performance, you need to change materials," Ryan says. For example, one practice that limits the industry's pursuit of further gains in chip performance is the use of aluminum as the material for interconnects-the wiring on a chip. "The aluminum interconnect can't keep pace. It's no longer the transistor that is a limit, it's the wiring," explains Ryan. One problem aluminum has is that it doesn't dissipate heat as well as copper-a key issue for makers of laptop computers and cell phones. Still, the shift to copper interconnects is one that not all semiconductor firms have bought into. "Companies are moving to copper, but most of our competitors are two years behind IBM in this area," he adds. "We've been shipping copper chips since 1998." In addition to IBM, Advanced Micro Devices Inc., Fujitsu Ltd., and Hitachi Ltd. are producing devices using copper interconnects. Perhaps the biggest advantage of copper is that it is a better conductor than aluminum. It's also expected to be cheaper to manufacture chips with copper interconnects, and that's important because the interconnects typically represent half the cost of a wafer. Helping semiconductor manufacturers keep pace with some of these changes are the equipment makers, which in turn are adjusting their products to deal with the move to copper. For example, Philips Analytical Inc., which builds analytical tools for the semiconductor industry, is working with Semitool Inc., a maker of chemical processing equipment, to supply an integrated metal-film metrology system. The system is used to inspect the quality of the layers of copper that go onto the wafer, so that semiconductor makers "can more effectively control the process," says Tom Ryan, marketing manager for the Natick, Mass.-based unit of Royal Philips Electronics NV. "Better process control increases product yields and provides more consistent results for our customers," adds Jurek Koziol, vice president of electrochemical technology at Semitool, based in Kalispell, Mont. The other material shift affecting chip performance is the trend toward lower capacitance dielectric insulating material. One of the potential problems with squeezing more and more lines of copper circuits closer together on a chip is that it increases electrical "cross talk" between wires. This interference can hurt performance and waste power. The lower capacitance dielectric insulator is a material that forms a better seal around the chip's wiring, thus enabling electronic signals to move faster. In dealing with these changes IBM Microelectronics is assuming the roles of both leader and follower. The chip-making division of IBM distinguished itself from the pack by being a leader in embracing silicon germanium (SiGe) chip technology for use in communications devices such as cell phones and Internet appliances. Introduced two years ago, the SiGe technology has been used in more than 8 million chips sold by IBM. Now IBM Microelectronics, which last year received more new patents (830) than any other Big Blue unit, is completing specifications for its next generation of SiGe chips that will feature copper interconnects. Some IBM chips already use copper interconnects, including the chips used in the company's flagship server machines, the RS/6000 series. In the low-capacitance dielectric area IBM is well ahead of the curve. IBM is using a proprietary technique for building chips with the so-called "low-k dielectric" material, but the material itself is commercially available from Dow Chemical Co. Big Blue already is producing chips with this new low-k process on a pilot production line and plans to introduce the technology on its high-volume Burlington, Vt., manufacturing lines next year. The material IBM finally decided to use for the low-k dielectric is called an aromatic thermoset, a plastic resin sold commercially by Dow under the brand name SiLK. This insulating material replaces silicon dioxide, a glass that is used by most chip manufacturers today. IBM claims it is the only company that has successfully integrated a low-k dielectric into a high-volume production process using the copper interconnects in its chips. "A complexity most manufacturers are going to face is changing to copper and low-k dielectric at the same time," says IBM's Ryan. "It's very difficult." The new process is particularly significant because IBM claims it will enable the company to build microchips with a 30% gain in computing speed and performance. "This represents a fundamental shift in the way chips are built," says John Kelly, general manager of IBM Microelectronics. "Along with the move from aluminum to copper to improve chip wiring, we believe this will help IBM maintain a one- to two-year lead over the rest of the industry." Oddly, though, IBM has been noticeably quiet about plans to move to the new 300-mm wafer size from the current industry-standard 200 mm. "We will do 300 mm, but we will not be leading the industry in this area," says Ryan. Most chip makers are moving to the larger format for productivity's sake. The 300-mm wafers can carry two and a half times as many chips as the smaller wafer. At the same time, the processing costs to accommodate the larger format are only about 15% more than a 200-mm production line. "You can get more surface area at about the same processing costs," says IBM's Ryan. Intel Corp., for instance, announced its commitment to the 300-mm format in mid-1999. Many companies already are making the switch. One of the leading suppliers of silicon wafers, Shin-Etsu Handotai Co. Ltd., Tokyo, plans to begin 300-mm wafer production in 2001. Of course, the goal of extending the life of Moore's Law has the industry scurrying to find the next major technology breakthrough. Moore's Law, developed by Gordon Moore, cofounder of Intel, posits that chips will double in processing power roughly every year and a half. But without significant technological leaps that improve the way chips are made, semiconductor makers are very close to bumping up against the physical limitations of both materials and processes. The industry's move to 0.13-micron and smaller lithography reflects the continued effort to pack more circuits on a chip. The 0.13 micron indicates the width of the "gate," or how small the features are on the chip. Many companies today are manufacturing chips at 0.25 and 0.18 micron. As these manufacturers begin to gear up to produce chips that are more powerful and contain the smaller standard of 0.13 and under, they will come up against the physical limitations that are causing the shift to copper interconnects and low-k dielectric insulators. One possibility for a major technological breakthrough is something called extreme ultraviolet (EUV) advanced lithography. EUV is expected to allow semiconductor manufacturers to etch circuit lines smaller than one-tenth of a micron, enabling them to cram still more circuits onto a chip. Ultimately, it could mean chips could be manufactured that are 100 times more powerful, with 100 times more memory, than is possible with today's manufacturing processes. Working on EUV is a group of manufacturers, including Intel, Advanced Micro Devices, and Motorola Inc., together with the Virtual National Laboratory, made up of three U.S. Dept. of Energy labs. According to one estimate, the first chips to be made with EUV technology will run at about 10 gigahertz, one order of magnitude faster than today's fastest chips. Manufacturers are expected to begin using EUV in 2005.

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