euv lithography basics

**EUV Lithography** — Extreme Ultraviolet lithography using 13.5nm wavelength light to pattern the finest features on modern chips (7nm and below). **Why EUV?** - 193nm DUV required quad-patterning for sub-7nm features — complex, expensive, low yield - EUV's 14x shorter wavelength enables single-exposure patterning - Simplifies process from 4 litho steps to 1 per critical layer **Key Challenges** - **Source**: Tin droplets hit by CO2 laser create plasma emitting EUV. Only ~5% of input power becomes usable light - **Optics**: No lens transmits EUV — must use reflective mirrors (multilayer Mo/Si coatings, 70% reflectivity per mirror) - **Vacuum**: EUV is absorbed by air — entire light path must be in vacuum - **Mask**: Reflective instead of transmissive. Defect-free mask blanks are extremely difficult **Current Status** - ASML is the sole supplier of EUV scanners - NXE:3600 (0.33 NA): Used for 7nm-3nm production - EXE:5200 (0.55 NA High-NA): For 2nm and beyond — $350M+ per tool **EUV** was 20+ years in development and represents one of the greatest engineering achievements in manufacturing history.