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Evolving subfab vacuum challenges demand collaborative solutions

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Semiconductor manufacturing is no longer focused on Dennard scaling as a principal means to improve performance and reduce costs. Coordinated, lock-step efforts have given way to a sometimes-bewildering collection of new materials and technologies, often adding complexity in the form of new and different process tools, techniques and chemistries. This evolving IC production environment means manufacturers and suppliers need to collaborate in developing next-generation solutions that positively impact climate change, reduce costs and improve device performance.

By Matt Halsey, Edwards Vacuum

Semiconducting manufacturing technologies continue to diversify at all levels, from device architecture to multi-chip and chiplet integration schemes, through an expanding variety of advanced packaging technologies. Long gone are the days when device manufacturers advanced lock step down a road map focused almost exclusively on shrinking device sizes. Gone too is the luxury of developing a new process tool to meet a widely acknowledged, well defined set of requirements, with the assumption that there would be time to fine tune the design based on customer feedback after the product introduction.

In an environment with multiplying pathways to technical and commercial success, close collaboration between device manufacturers and equipment suppliers will acquire increasing importance as both seek to hasten development cycles, reduce time-to-market for new products, and target new products more precisely on key applications.

These same pressures apply in the subfab as well, where exist the essential systems that support the process tools above. Most semiconductor manufacturing processes require a vacuum; consequently, loss of that vacuum will take down a production line just as surely as a failure in the tool itself. Integrating new processes and materials into the production line must include careful consideration of the impacts on the vacuum systems tasked with removing excess gases and byproducts from the tools. Failure to do so will inevitably lead to more frequent maintenance, shorter service lifetimes and reduced reliability. In the worst case, it will result in unplanned down time with all its associated costs.

In addition to changes in processes and materials, vacuum challenges in the subfab include shrinking space, increasing energy costs, and growing concern about the sustainability of the manufacturing process. Many of the design choices will require carefully balanced trade-offs among conflicting requirements.

The Process
The ever-increasing capital cost of new manufacturing capacity at advanced process nodes exerts relentless pressure on manufacturers to increase throughput in order to amortize higher fixed costs over a larger product output. For vacuum systems, higher throughput usually means higher flow rates and larger pumps.

Changes in process chemistry include the use of more aggressive reactions with harsher chemicals which require more resilient pumps. Pumps must incorporate materials and coatings that can withstand process gases and their by-products, as well as the corrosive chemicals used to clean process chambers.

Higher (and sometimes lower) temperatures for critical processes like atomic layer deposition and chemical vapor deposition require pumps that can handle the greater temperature range. Tolerances for rapidly spinning rotors are very tight and thermal expansion must be carefully managed. Materials used for seals at more conventional temperatures may not withstand higher temperatures. Often the temperature profile of the pump and associated piping must be carefully managed to avoid deposition of condensable materials.

Subfab space
Demands for higher throughput are leading manufacturers to put more smaller tools in less space in the fab. Following the convention that supporting systems must fit within the footprint of the process tool as projected down to the subfab, pumps and abatement must also fit in less space while handling increased flows. This can be especially challenging for pumps where the physical size of the pump has a direct relationship to its pumping capacity. Fab operators are currently looking for a 20-30% reduction in pump footprint, just to keep up with decreasing tool size. Stacking pumps in the subfab offers one solution, but there are limits related to safety and maintenance concerns.