Diverging needs for process tools
08/01/2002
Several factors are creating the need for greater diversity in process tools, and those toolmakers that recognize emerging requirements are making changes to their designs that should pay off in the future. The large-volume semiconductor fabs are splitting into two camps, the commodity chip group that makes mainstream memories and microprocessors, and the foundries, which process a growing array of application-specific chips, including CMOS system-on-a-chip ICs. The foundries have closed the technology gap, so they now rival the leading integrated device manufacturers (IDMs) in their ability to make high-performance and high-circuit-density chips. As a result, they are doing a steadily increasing share of global wafer processing, not just for fabless design firms, but also for some of the major IDMs such as Motorola and NEC.
A foundry may be a high-volume factory, but it has quite different requirements than a DRAM or microprocessor fab. Both are mass-production factories that can benefit from fast robotics and cluster tools for single-wafer processing, some built-in metrology, and other tool enhancements. But while commodity fabs may make millions of chips from the same mask set, foundries are finding the average lot for their new 300mm fabs to be in the range of 3-7 wafers! Naturally the foundries want the shortest-wavelength stepper/scanners feasible, because this lowers the requirements for resolution enhancement techniques (RETs), which dramatically boost the complexity and cost of mask sets. Commodity fabs can stretch the lives of their lithography systems by applying strong RET methods, making 150nm devices on 248nm steppers, for example, and the extra mask costs can be amortized over hundreds of thousands of the same chips.
Foundries also need to get devices to market quickly for their customers, so flexible tools with quick set-up times are more critical than in a commodity chip fab where millions of chips may run through without any changes in recipes or set-ups. High throughput is important to both of them.
There is also growing demand for a variety of other specialized chips and discretes, including RF and microwave devices for wireless, satellite, and similar applications, optoelectronics, microelectromechanical systems (MEMS), and data storage devices, such as read/write heads. Smaller fabs, and more specialized manufacturers that make these various products, may want more flexibility with faster set-up times. Lower tool costs may be more important to them than high throughput.
This growing number of niche markets have a need for process tools, but equipment designed for mass-production fabs is unlikely to be the best solution for them. Compound semiconductors generally are made on smaller wafers than CMOS devices, and special devices such as MEMS and read/write heads for disk and tape drives use much thicker resists and have special requirements for sidewalls and other features, such as openings under bridges or cantilevers. Packaging functions are now scaling down toward what used to be on-chip circuit dimensions, especially for bump packaging technology, so some tool and mask companies are coming up with specially designed tools to provide solutions for this fast-growing segment.
Other smaller fabs — for ASICs, programmable logic, special memories, linear chips, discretes, and even specialized devices for optoelectronics — might make use of general purpose tools, although they also have more specialized needs. Price also may be more important to them than high throughput and extensive automation.
The result is a much wider spectrum of process tool options and accessories, and a more varied infrastructure to provide needed resists, specialty chemicals, gases, and other associated products. Japanese companies are working on flexible, lower-cost tools that can perform multiple process steps in the same chamber, and they plan to use them in mini-fabs built for fabrication of critical SOCs, such as Sony's 128-bit microprocessor for its PlayStation.
The new 300mm mass-production fabs use sealed FOUPs and minienvironments so that cleanroom requirements can be relaxed, and workers don't need to practice such extensive gowning. Their role is more one of monitoring the automation and doing maintenance and troubleshooting, rather than moving cassettes around and loading process tools. These tools need to be highly automated with built-in monitoring to flag any problems, and new software is required to tie them into fab-wide data collection systems for yield analysis, fault detection and correction, and e-diagnostics.
These diverse needs are requiring toolmakers to come up with a rich assortment of designs, tuned to diverse segments of the market. As a result, there is room for many small, agile, innovative tool companies as well as the giant firms that mainly serve the mass-production fabs. Those vendors that have successfully struggled through the harshest downturn the industry has ever seen should have many opportunities going forward. As world economies turn and end-markets begin to heat up again, all the hard work of reinventing the industry's process tool set should pay off handsomely.
Robert Haavind
Editor in Chief