Process capability analysis is the statistical evaluation of whether a manufacturing process can consistently produce output within specification limits — using indices like Cp, Cpk, Pp, and Ppk to quantify process performance, predict defect rates, and drive continuous improvement in semiconductor manufacturing.

Key Indices

• Cp: Potential capability (spread only, ignoring centering).
• Cpk: Actual capability (spread AND centering).
• Pp: Overall performance (using total variation, not within-subgroup).
• Ppk: Overall performance adjusted for centering.

Cp vs Cpk vs Pp vs Ppk

• Cp/Cpk: Use within-subgroup variation (short-term capability).
• Pp/Ppk: Use overall variation (long-term performance).
• Cpk = Ppk: Process is stable with no between-subgroup variation.
• Cpk > Ppk: Significant between-subgroup shifts present.

Sigma Level Conversion

• Cpk = 1.0 → 3σ → 2,700 DPPM.
• Cpk = 1.33 → 4σ → 63 DPPM.
• Cpk = 1.67 → 5σ → 0.6 DPPM.
• Cpk = 2.0 → 6σ → 0.002 DPPM (3.4 DPMO with 1.5σ shift).

Process capability analysis is the quantitative foundation for process qualification — providing the mathematical proof that a manufacturing process is ready for production.