exposure latitude

**Exposure Latitude (EL)** is the **range of exposure doses within which the patterned CD stays within specification** — expressed as a percentage of the nominal dose, EL measures how tolerant the patterning process is to dose variations. **Exposure Latitude Details** - **Definition**: $EL = frac{E_{max} - E_{min}}{E_{nom}} imes 100\%$ where $E_{max}$ and $E_{min}$ are the doses at the CD spec limits. - **Typical Values**: Dense lines/spaces: 5-15% EL; isolated features: 10-20% EL; contact holes: 3-10% EL. - **Mask MEEF**: Mask Error Enhancement Factor amplifies mask CD errors — effectively reducing EL. - **Stochastic Effects**: At EUV, stochastic (shot noise) effects reduce effective EL — especially for small features. **Why It Matters** - **Dose Uniformity**: Scanner dose uniformity must be within the EL — typically ±0.5-1% uniformity required. - **Throughput**: Higher resist sensitivity allows lower dose → higher throughput, but may reduce EL. - **Contacts**: Contact holes have the smallest EL — the most dose-sensitive features. **Exposure Latitude** is **the dose tolerance** — how much exposure dose can vary while still producing features within CD specification.