mask blank

**Mask Blank** is the **starting substrate for photomask fabrication** — a high-quality fused silica (quartz) plate coated with an opaque absorber layer (typically chromium or, for EUV, a multilayer reflective coating), ready for pattern writing and processing. **Mask Blank Specifications** - **Substrate**: Ultra-low-expansion fused silica (6" × 6" × 0.25" for DUV; 6" × 6" × 0.25" for EUV). - **Flatness**: <50nm flatness for EUV blanks — flatness directly transfers to patterning focus errors. - **Absorber**: Chromium (DUV), TaBN/TaBO (EUV) — high optical density at operating wavelength. - **Defect-Free**: Zero printable defects required — even a single embedded defect can kill yield. **Why It Matters** - **Starting Quality**: Mask blank quality sets the floor for final mask quality — defects in the blank propagate to the wafer. - **EUV Challenge**: EUV mask blanks are extremely difficult to manufacture — no pellicle protection for embedded defects. - **Cost**: Advanced EUV mask blanks cost $20K-$50K each — blank quality is critical to mask yield. **Mask Blank** is **the canvas for the mask** — the ultra-pure, ultra-flat starting substrate that determines the ultimate quality of the finished photomask.