Why Fabs Worry About Tool Parts
How a single O ring can affect yield, and what to do about it.
Achieving high yields with acceptable costs is becoming much more difficult as chipmakers migrate to next-generation 3D NAND and finFET devices—but not just because of rising complexity or lithography issues.
To fabricate an advanced logic chip, for example, a wafer moves from one piece of equipment to another in what amounts to 1,000 process steps or more in a fab. Any glitch with the equipment or a process step can cause defects, thereby impacting yield. The culprit may be a malfunction in seemingly insignificant parts or sub-systems in the equipment itself.
Simply put, defects introduced by process-critical components in fab equipment can impact wafer yields, according to members from SEMI’s Semiconductor Components, Instruments, and Subsystems (SCIS) Special Interest Group, an organization that represents suppliers of components and sub-systems. The issues have been known for some time, but they are expected to become more problematic as chipmakers move to 10nm/7nm and beyond, according to SCIS. The group’s members include GlobalFoundries, IM Flash, Intel, Micron, TI and Samsung as well as major fab tool and component suppliers.
The components and sub-systems in fab equipment are taken for granted, but they play a critical role in the semiconductor supply chain. For example, the more sophisticated fab tools incorporate more than 50,000 parts from dozens of suppliers. Chambers, pumps, RF generators, seals and valves are among the key components in a tool.
Generally, the components are robust and don’t cause problems, but at times they can contribute to issues in the fab. For instance, based on real events from chipmakers, here’s just a small sample of what can go wrong in the fab:
• The wrong O-rings were installed in a portion of the sub-fab, which could cause
contamination in the flow. An O-ring is a part that serves as a seal in a system. • A pressure regulator malfunctions in the ultra-pure water system, causing
contamination in the process. • A liner material breach occurs in a bulk chemical distribution system, causing
corrosion in the unit.
“Sub-components have a major impact in facility systems, which in turn affects fab equipment performance,” said Norm Armour, managing director of worldwide facilities and corporate EHS at Micron Technology. “Our su