Compliance Metrics for a Reliable Assessment of Parametric Yield

Few would disagree that high parametric yields are indispensable for insuring product yield entitlement. It is, however, not as well recognized by non-practitioners that Cp, Cpk, Cpm, Cpmk, and Z-Score, arguably the most widely used metrics for assessment of process capability, are not very reliable indicators of the health of a manufacturing process. There have been numerous extensions to these capability indices to accommodate non-normal distributions and asymmetric tolerances, but none has yet proven to be robust enough to be reliable for the assessment of any arbitrary distribution. To address this issue, we introduce Composite Parametric Yield, a deceivingly simple metric that provides the most authentic assessment, to date, of parametric compliance. Its three elements-YAT, YWL and Coverage-have been critical pillars of the process technology certification process at Freescale Semiconductor for over seven years now.