process capability

**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.