bossung curve

**Bossung Curves** are **plots of measured CD (critical dimension) versus focus at various exposure doses** — named after John Bossung, these curves characterize how feature dimensions change with focus and dose, revealing the patterning process window. **Bossung Curve Characteristics** - **Shape**: Parabolic — CD varies quadratically with focus around the best focus. - **Best Focus**: The focus setting at the CD minimum (or maximum, depending on feature type) of the parabola. - **Dose Dependence**: Different dose curves are vertically separated — higher dose produces different CD. - **Isofocal Point**: The focus where CD is independent of dose — the most robust operating point. **Why It Matters** - **Process Window**: The flat top of the Bossung curve defines the usable focus range — wider = larger process window. - **Sensitivity**: Steep Bossung curves indicate high focus sensitivity — tight process control required. - **Monitoring**: Deviations from expected Bossung shape indicate lens aberrations or resist issues. **Bossung Curves** are **the lithographer's roadmap** — showing how feature dimensions respond to focus changes for process window optimization.