in-line metrology

In-line metrology encompasses all measurements performed during wafer processing to monitor, control, and optimize the manufacturing process in real-time. **Philosophy**: Measure during manufacturing, not just at the end. Catch problems early before they propagate through subsequent process steps. **Key measurements**: CD (by CD-SEM, OCD), film thickness (ellipsometry, reflectometry), overlay (IBO, DBO), defect inspection, sheet resistance, particle counts. **Sampling**: Not every wafer measured at every step. Sampling plans balance process control needs with metrology throughput and cost. **Feed-forward**: Measurements from one step used to adjust subsequent steps. Example: measured CD after litho used to adjust etch recipe. **Feedback**: Measurements after processing used to adjust the same process on next lot. Example: post-etch CD fed back to litho dose. **SPC integration**: All inline measurements feed into SPC system. Control charts detect trends and excursions. **Automation**: Fully automated measurement recipes. Wafers loaded, measured, and returned to process without operator intervention. **Metrology tool matching**: Multiple metrology tools must give consistent results. Tool-to-tool matching regularly verified. **Data volume**: Modern fabs generate enormous metrology data. Big data analytics increasingly used for process optimization. **APC integration**: Inline metrology data drives APC systems for automatic recipe adjustment. **Cost of metrology**: Balance between measurement cost and value of information. Over-measurement wastes throughput, under-measurement risks yield loss.