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Wafer throughput and particle counts are key metrics for any semiconductor manufacturer's yield enhancement
programs. Recent advancements in diffuser technology have helped manufacturers enhance these metrics while
improving the attributes for most vacuum processes. These processes include dry etch, chemical vapor deposition (CVD),
physical vapor deposition (PVD), rapid thermal processing (RTP) and Epitaxial deposition (Epi).
Execution of membrane diffuser technology dramatically decreases required vent time and has become a highly effective
tool upgrade option. An early implementation of this technology was used on 200mm batch-style loadlocks that had an
inherently large internal volume. The loadlock was prone to long vent cycles to prevent particle contamination.
As the industry transitioned to a 300mm wafer platform, factories increased their development of single-wafer loadlocks
(SWLL) in an effort to boost tool throughput. Gas diffusers with ultra fine filtration membranes solved these issues.
Compared to the 200mm batch-style loadlocks, the SWLLs had extremely low internal volumes and were designed to
cycle vacuum to atmosphere very quickly. With the low volumes inherent in the SWLL, the velocity of the incoming
vent gas became critical, since any particles on the bottom of the loadlock chamber would easily sweep onto the wafer
should they be hit with a high velocity gas. Particles are typically present in the loadlock due to mechanical wafer
handling devices and environmental exposure. Gas diffusers allowed a large, uniform volumetric flowrate of gas into the
loadlock chamber at low downstream gas velocities.
While now standard on most 300mm loadlocks, the majority of 200mm tools in the field do not utilize membrane
diffusers. Typically a screen, frit and/or soft vent procedure is used to control the flow into the loadlock. However, these
tools can now be retrofitted with membrane diffuser technology. The result is a large reduction in particle count while
maintaining throughput levels at a low cost with minimal downtime.
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