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.