An EUV photomask is a patterned reflective mask used for EUV photolithography. At Toppan, we pioneered the commercialization of these reticles starting when the first full field EUV Litho tool was introduced in 2005. Through close collaboration with lithography equipment leaders, photoblank suppliers, reticle equipment vendors, international consortia, and many of our customers, Toppan has emerged as the world's largest commercial EUV supplier.
The primary EUV products we offer are imaging reticles for technology development. These can include various levels of shadow bias, flare correction and OPC. Our leading-edge EUV products are processed on the most advanced equipment and are evaluated using state-of-the-art metrology and characterization tools.
We also offer a variety of specialty EUV photomask products and services including:
- Calibration reticles
- OPC characterization reticles
- EUV Reticle Cleaning
- Dual pod cleaning and handling
EUV Photomask Substrates
An EUV photomask substrate is a sophisticated multi-layer film stack. The films are deposited on a special 6" X 6" substrate that has ULE/LTEM characteristics. Nearly all matter absorbs EUV radiation necessitating that EUV lithography occur under vacuum. An engineering consequence of this requirement is that absorption energy can quickly heat the mask. The low thermal expansion quality of the blank is a critical feature to prevent the mask from warping or otherwise distorting the image. The backside of the substrate has a conductive coating, typically comprised of chrome nitride, to allow for electrostatic chucking.
Between 40 and 50 alternating layers of silicon and molybdenum are deposited on the top of the LTEM substrate to act as a Bragg reflector that maximizes the reflection of the 13.5nm wavelength. This multi-layer reflector is then capped to prevent oxidation, typically with a thin layer of ruthenium. A tantalum boron nitride film topped by a thin anti-reflective oxide acts as the EUV absorber. The absorber has been engineered to have nearly zero etch bias enabling very fine feature resolution.
EUV Photomask Defectivity
A defect free photomask has long been the standard in our industry. We have achieved this goal for optical photomasks, and we are aggressively pursuing this target for multi-layer, multi-material EUV reticles. Toppan, together with its suppliers, industry leaders, and international consortia are working to reduce the occurrence of absorber and multi-layer defects and identify ways to mitigate their impact.
Flatness and Image Placement
Product flatness is another critical characteristic for EUV photomasks. Small changes in the reflector plane, either from local topography or macroscopically across the reticle field, result in variation of the reflection angle. This reflection angle variation reduces the overall imaging efficiency.
After years of advancements, our EUV photomask products meet the most stringent flatness criteria. Low stress in the patterned layer combined with dynamic writing techniques have resulted in registration performance that enable accurate wafer-level overlay tolerances.
Shipment and Handling
Dual pods are necessary for both mask transport and loading into ASML's NXE scanner. Within the NXE, the Outer Pod stays at atmosphere while the EUV Inner Pod (EIP), containing the reticle, is loaded into the tool and pumped down to vacuum. The EIP baseplate along with the reticle are then both loaded onto the reticle stage.
Materials selected for this new carrier mechanism have been optimized both for low outgassing and very low added particles after handling tests. Features of the SEMI E152-compliant pod include windows for reticle identification and alignment.
Special Requests and Projects
EUV lithography is still in its infancy. Understanding how to manufacture your products with this new technique requires further studies and special projects. We support our customers' special requests using our exclusive tool kits. Below are just some of the examples of special work we've completed for our customers.
- Absorber height measurements
- LER studies using SEM micrographs
- Reflectivity measurements
- At 13.5nm
- Through spectrum
- Blank flatness measurements
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