Physics / mechanism
Mask blanks are the upstream substrate from which photomasks are made. A blank consists of a low-thermal-expansion glass substrate (typically EUVL-grade Corning ULE or Schott Zerodur, with CTE ~0 ppb/K at 20°C) coated with absorber stack. For EUV, blanks carry a 40-bilayer Mo/Si multilayer reflective stack (~67% peak reflectance at 13.5 nm) deposited by ion-beam sputtering, plus a capping layer (Ru typically) and absorber (TaN or emerging low-n/high-k alternatives targeting phase-shift contrast). Flatness spec is <50 nm P-V across 152 mm; defect density targets <0.01 defects/cm² printable size. Only AGC, Hoya, and S&S Tech supply at volume; EUVL blank supply remains structurally constrained.
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Frontier (open questions)
- To be added.