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.