EUV Pellicle is the ultra-thin protective membrane mounted above the EUV photomask surface to prevent particle contamination from landing on the mask pattern during lithography exposure — one of the most challenging material science problems in semiconductor manufacturing because the pellicle must be transparent to 13.5nm EUV light (>90% transmittance), survive intense EUV radiation and hydrogen plasma, maintain structural integrity across a 110mm × 144mm clear aperture at <50nm thickness, while remaining particle-free over months of production use.

Why EUV Pellicles Are Critical

In DUV lithography, every production reticle has a pellicle — a transparent membrane spaced ~6mm above the mask surface. Any particle that lands on the pellicle is too far from the focal plane to print on the wafer. Without pellicles, particles on the mask surface print as defects on every die, every wafer, every lot — potentially destroying millions of dollars of product before detection.

EUV initially launched without pellicles because no material could survive EUV irradiation. Fabs compensated with extreme reticle handling protocols: robotic handling in vacuum, real-time particle monitoring, and frequent reticle inspections. But as EUV moved to high-volume manufacturing (HVM), particle-related yield losses from pellicle-free operation became intolerable.

Pellicle Material Challenges

• Transmittance: EUV photons at 13.5nm are absorbed by virtually all materials. The pellicle must be extremely thin (<50nm) to transmit >90% of EUV light. Even 2% transmittance loss reduces scanner throughput and increases cost per wafer.
• Thermal Survival: At 250W+ EUV source power, the pellicle absorbs 10-25W of EUV energy in a ~150cm² area. With no conduction path (membrane in vacuum, supported only at the edges), the membrane temperature reaches 500-1000°C. It must not deform, crack, or degrade.
• Hydrogen Resistance: The EUV scanner chamber contains hydrogen plasma (H₂) for mirror cleaning. The pellicle must resist hydrogen embrittlement and chemical etching.

Pellicle Materials

• ASML EUV Pellicle (Current): Polycrystalline silicon (p-Si) membrane, ~50nm thick, with capping layers. Transmittance: ~88-90%. Withstands current EUV power levels but approaches thermal limits at >400W. Being deployed in production.
• Carbon Nanotube (CNT) Pellicle: A mesh of aligned or random CNTs is inherently porous (>90% void), providing higher transmittance (>95%) and better thermal radiation at high temperature. Under development by multiple companies.
• Metallic / Ceramic Membranes: Research candidates including Ru, ZrSr, and boron-carbon composites that trade transparency for thermal and mechanical robustness.

Impact on High-NA EUV

ASML's High-NA EUV scanners (0.55 NA) require pellicles with even higher transmittance because the mask is illuminated at larger angles, increasing the effective path length through the membrane. This further constrains material choices and drives the urgency of CNT pellicle development.

EUV Pellicle is the thinnest and most stressed component in the entire semiconductor manufacturing equipment chain — a membrane so thin it's nearly invisible, protecting a $300K mask from particles while surviving an environment that would vaporize most materials, embodying the extreme engineering required for EUV lithography to work in production.