monitor wafers

**Monitor Wafers** are **non-product wafers processed alongside production wafers to track process health** — dedicated to specific measurements (film thickness, particle count, electrical parameters) that provide continuous monitoring of tool and process performance without consuming product wafers. **Monitor Wafer Types** - **Particle Monitors**: Bare wafers run through tools to count added particles — track tool cleanliness. - **Film Monitors**: Measure deposited film thickness, uniformity, and composition — track deposition tool stability. - **Electrical Monitors**: Short-loop wafers with test structures — measure transistor parameters (Vth, Idsat, leakage). - **Control Charts**: Monitor wafer data feeds SPC (Statistical Process Control) charts — detect process drift. **Why It Matters** - **Early Warning**: Monitors detect process excursions before they affect production wafers — preventive action. - **Cost**: Monitor wafers consume fab capacity (typically 5-15% of total wafer starts) — minimize while maintaining coverage. - **Correlation**: Monitor-to-product correlation must be established — monitors should predict production performance. **Monitor Wafers** are **the factory's health check** — dedicated wafers that continuously track process performance to catch problems before they affect production.