Flexible facilities for 450mm wafer fabs

BY JOE CESTARI, Total Facility Solutions, Plano, Texas

When the commercial semiconductor manufacturing industry decides to move to the next wafer size of 450mm, it will be time to re-consider equipment and facilities strategies. Arguably, there is reason to implement new strategies for any new fab to be built regardless of the substrate size. In the case of 450mm, if we merely scale up today’s 300mm layouts and operating modes, the costs of construction would more than double. Our models show that up to 25 percent of the cost of new fab construction could be saved through modular design and point-of-use (POU) facilities, and an additional 5-10 percent could be saved by designing for “lean” manufacturing.

In addition to cost-savings, these approaches will likely be needed to meet the requirements for much greater flexibility in fab process capabilities. New materials will be processed to form new devices, and changes in needed process-flows and OEM tools will have to be accommodated by facilities. In fact, tighter physical and data integration between OEM tools and the fab may result in substantially reduced time to first silicon, ongoing operating costs and overall site footprint.

POU utilities with controls close to the process chambers, rather than in the sub-fab, have been modeled as providing a 25-30 percent savings on instrumentation and control systems throughout the fab. Also, with OEM process chamber specifications for vacuum-control and fluid-purity levels expected to increase, POU utilities provide a flexible way to meet future requirements.

Reduction of fluid purity specifications on central supply systems in harmony with increases in localized purification systems for OEM tools can also help control costs, improve flexibility, and enhance operating reliability. There are two main reasons why our future fabs will need much greater flexibility and intelligence in facilities: high-mix production, and 1-12 wafer lots.

High-mix production

Though microprocessors and memory chips will continue to increase in value and manufacturing volumes, major portions of future demand for ICs will be SoCs for mobile applications. The recently announced “ITRS 2.0”—the next roadmap for the semicon- ductor fab industry after the “2013” edition published early in 2014—will be based on applications solutions and less on simple shrinks of technology. Quoting Gartner Dataquest”s assessment:

System-on-chip (SoC) is the most important trend to hit the semiconductor industry since the invention of microprocessors. SoC is the key technology driving smaller, faster, cheaper electronic systems, and is highly valued by users of semiconductors as they strive to add value to their products.”

1-12 Wafer Lots

The 24-wafer lot may remain the most cost-effective batch size for low-mix fabs, but for high-mix lines 12-wafer lots are now anticipated even for 300mm wafers. For 450mm wafers, the industry needs to re-consider “the wafer is the batch” as a manufacturing strategy. The 2013 ITRS chapter on Factory mentions in Table 5 that by the year 2019 “Single Wafer Lot Manufacturing System as an option” will likely be needed by some fabs. Perhaps a 1-5 wafer carrier and interface would be a way for an Automated Material Handling System (AMHS) to link discrete OEM tools as an evolution of current 300mm FOUP designs.

However, a true single-wafer fab line would be the realization of a revolution started over twenty years ago when the MMST Program was a $100M+ 5-year R&D effort funded by DARPA, the U.S. Air Force, and Texas Instruments, which developed a 0.35μm double-level-metal CMOS fab technology (with a three-day cycle time). In the last decade BlueShift Technologies was started and stopped to provide such revolutionary technology for vacuum-robot-lines to connect single-wafer chambers all with a common physical interface.

Lean manufacturing approaches should work well with high-mix product fabs, in addition to providing more efficient consumption of consumables in general. In specific, when lean manufacturing is combined with small batch sizes—minimally the single wafer—there is tremendous improvement in cycle-time.

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