reticle / photomask

A reticle or photomask is a glass plate with the circuit pattern used to expose photoresist during lithography. **Construction**: Quartz substrate (transparent to DUV) with chrome or phase-shift patterns (opaque/shifting). **Size**: Typically 6 inch x 6 inch x 0.25 inch for leading-edge lithography. Larger than wafer pattern (uses reduction optics). **Pattern scale**: For 4X reduction lithography, mask pattern is 4X larger than on-wafer pattern. **Pellicle**: Thin membrane stretched above mask surface to keep particles out of focal plane. **Defect sensitivity**: Any defect prints onto every exposure. Masks must be perfect. **Mask shop**: Specialized fabrication facilities make masks using e-beam lithography. **Cost**: Advanced masks cost $100K-$500K+ each. Full mask set (dozens) costs millions. **Write time**: Complex patterns take days to weeks to write with e-beam. **Inspection**: Rigorous inspection for defects. Repair of some defects possible. **EUV masks**: Reflective rather than transmissive. Even more complex and expensive.