by Paul McLellan
At SEMICON last month, Rohit Pal of GlobalFoundries gave a presentation on their methodology for reducing process variation. It was titled Cpk Based Variation Reduction: 14nm FinFET Technology.
Capability indices such as Cpk is a commonly used technique to assess the variation maturity of a technology. It looks at a given parameter’s variability and compares it to 6 sigma. The higher the number the better, 1.33 should have the process yielding close to 100% (for that parameter) and 2 is the full 6 sigma. Using Cpk makes it easy to track metrics to assess variation improvement for a technology. They can also be used as a gating item for technology milestone achievement. However, it is not truly an absolute value, it is a function of the specification limits.