ALAN BRIGHTMAN, DAWN STEPHENSON and DECLAN SCANLAN, Edwards Vacuum
Evolving manufacturing processes pose ever changing challenges for the systems tasked with providing stable vacuum in the process chamber and removing excess process gases and by-products. These challenges have expanded beyond the primary concern, mitigating corrosion and deposition to extend pump lifetimes [1], to now include factors that had been regarded as secondary. Examples include pump size and connection configurations to accommodate new cluster tool architectures, performance tunability to facilitate tool-to-tool matching, and a push for commonality over a wide range of applications.
New application challenges
Gone are the days when development efforts focused almost exclusively on shrinking device geometries. Manufacturers now face a rapidly changing mix of new device architectures, fabrication process, and process materials. New process requirements have exceeded the capabilities of existing vacuum systems, requiring the development of new enhanced solutions. Among the most challenging applications are new etch processes. Handling etch process effluent has always included concerns about corrosion and condensation/deposition in the vacuum system (FIGURE 1). Many new processes generate condensable byproducts, such as carbon fluoride (CFn) compounds from through silicon via (TSV) etch and ammonium fluorosilicates ((NH4)2SiF6) from chemical oxide removal (COR). Other processes likely to require enhanced vacuum solutions include polysilicon, metal, aluminum, and tungsten etch, and metal oxide and high-k dielectric atomic layer deposition (ALD). Atomic layer processes use repeating cycles of deposition/deposition or deposition/etch in the same chamber to add or remove material one atomic layer at a time. They may generate both corrosive and condensable byproducts. Some of the most corrosive byproducts do not come from the etch processes themselves, but from chamber cleaning processes like in-situ chamber clean (ISCC) and waferless auto clean (WAC). Looking forward, new feature and device geometries, such as gate-all-around transistors, eDRAM capacitors, buried power rails, and the very high aspect ratio holes and trenches in 3D NAND memory will require continuing refinement of etch solutions.
Fab process management solutions
Perhaps more than any other industry, semiconductor manufacturers strive to achieve uniform, repeatable processes that create identical products time after time. Fab process management programs used to ensure repeatability and uniformity have steadily expanded to include measurement, monitoring, and control of every conceivable input to and output from the process, conditions within process chambers, and every aspect of performance of process tools and supporting systems. Manufacturers are also putting increasing emphasis on handling equipment malfunctions proactively with enhanced fault detection and classification (FDC) and enterprise management systems (EMS). Preventive maintenance strategies are evolving toward predictive maintenance based on real time measurements of relevant operational parameters. All these developments share a need to acquire, store, and analyze massive amounts of data. “Big data” analytical techniques constantly comb through troves of data to reveal correlations that would otherwise go unseen. New, high-speed data communication interfaces like EtherCAT are commonplace. Most equipment incorporates extensive internal diagnostic capabilities. This same investment in communications and connectivity extends from chamber-connected equipment through to equipment in the sub-fab.
This same drive for repeatability and control has led manufacturers to embrace tool-to-tool matching strategies. The concept is simple: make sure each process tool operates the same way as every other tool executing the same process. In practice, this requires that tools be tunable so that their performance can be adjusted to match a common standard. The requirement for tunability also extends to supporting equipment in the sub-fab. For example, vacuum systems might implement active control of pressure in the foreline to ensure uniform, stable vacuum in the chamber.