Since the invention of the integrated circuit in 1958, the number of processing steps required to make one has grown from less than 10 to several hundreds. At the same time, the silicon wafers on which the ICs are produced have gone from being coin-sized to being dinner-plate-sized.
Today, one of these 300-millimeter wafers can yield more than 700 ICs. And that, for a growing number of chip makers, is precisely the problem. With such a large number of ICs coming from a single wafer and with wafers coming off manufacturing lines at rates of tens of thousands a month, companies can quickly find themselves suffering from chip glut, especially in turbulent markets.
For the past five years, since the bursting of the dot-com bubble in 2000 sent semiconductor sales into a tailspin, the industry has been struggling to rid itself of excess inventory. In the second quarter of 2001, the entire supply chain, including chip makers, distributors, contract manufacturers, and consumer-product manufacturers, was stuffed with an excess of chips worth more than US $13 billion, according to some estimates. Companies stopped hiring new employees and laid off existing ones. As a result, semiconductor industry jobs in the United States alone dropped from 268 000 in 1999 to 235 100 in July 2003, according to the U.S. Department of Labor. As recently as the third quarter of last year, chip oversupply was still at a worrisome $1.6 billion, according to a preliminary analysis by iSuppli Corp., a research firm in El Segundo, Calif. [See graph, "]
Clearly, the semiconductor industry is still facing serious problems as it claws its way back toward profitability and sustained employment growth. And for economic and technological reasons, the relentless drive toward faster, cheaper, and smaller chips is a growing problem. The solution, we believe, lies in a fundamental change in the machines that process the wafers: a switch from batch to single-wafer manufacturing.
The single-wafer approach is a completely serial one, in which just one wafer is processed at a time, all the way through the factory from start to finish. There is never a time when the machines work on a large batch of wafers at the same time, as they do today. The single-wafer technique will solve the oversupply problem by shortening the time it takes to make a finished, packaged chip to less than one month, rather than the three months or more that is typical today. Basically, with single-wafer manufacturing, semiconductor companies will be able to produce chips quickly when the orders come in, in the exact quantities specified by those orders. There will be no need to build up huge inventories that may just sit on shelves until they become obsolete.
And it isn't just boutique chips, which are made in small quantities, that would benefit from the single-wafer approach. Even commodities like static random-access memory (SRAM) and microcontroller chips, which suffer from periodic oversupply and the resulting price plunges and reduced profits, would benefit from a more agile response to changing market demands.
So what will it take to shift to single-wafer manufacturing? First, consider today's typical semiconductor plant. It combines single- and batch-processing steps; some of the machines process wafers in groups, while others already process them singly. True single-wafer manufacturing eliminates all the batch processes and uses only machines that process wafers one at a time. Today, only a few semiconductor plants have switched over completely to single-wafer manufacturing.
In 2001, Trecenti Technologies Inc. of Hitachinaka, Japan (now part of Renesas Technology Corp.), adopted 100 percent single-wafer processing for the fabrication of advanced semiconductor ICs on 300-mm wafers. The company's experience with this technique has been remarkable. It has found that it can reduce manufacturing time from 90 to 30 days, and the number of days needed for each chip layer has dropped from 2.25 to 0.25. Even more remarkable is the improvement in the fabrication time for a wafer of SRAM chips made up of 130-nanometer structures. That time has dropped from about 60 days to fewer than six days.
Several other IC manufacturers are also currently considering 100 percent single-wafer processing. Freescale, Philips, and STMicroelectronics have formed the Crolles2 Alliance. Its 300-mm wafer facility, in Crolles, France, uses single-wafer processing for most steps. Tokyo-based Toshiba Corp.'s minifab, in Oita City, Japan, is another example of IC manufacturing dominated by single-wafer processing.