mask cleaning

**Mask Cleaning** is the **process of removing contamination from photomask surfaces** — critical for maintaining mask quality throughout its lifetime, as particles or chemical residues on the mask (or pellicle) can print as defects on wafers, causing yield loss. **Mask Cleaning Methods** - **Wet Clean**: Sulfuric peroxide mixture (SPM/Piranha), SC1 (NH₄OH/H₂O₂), or ozonated DI water — dissolve organic and particle contamination. - **Dry Clean**: UV/ozone cleaning or hydrogen radical cleaning — gentle, non-contact removal of organic contamination. - **Megasonic**: High-frequency acoustic agitation in cleaning solution — dislodge particles without damaging patterns. - **EUV-Specific**: Hydrogen plasma or radical cleaning — no wet chemistry for EUV reflective masks. **Why It Matters** - **Zero Defects**: A single particle on the mask prints on every wafer — cleaning must achieve near-zero contamination. - **Chrome Damage**: Aggressive cleaning can damage chromium patterns — cleaning chemistry and duration must be carefully controlled. - **Clean Count**: Masks have a limited number of clean cycles — each cleaning slightly degrades the mask (chrome thinning, pellicle degradation). **Mask Cleaning** is **keeping the mask pristine** — removing contamination to ensure every wafer exposure is defect-free.