Photomasks
Masks in Photolithographic Production
A photomask displays the pattern of an integrated circuit and works as a template or stencil in the photolithographic production of the resulting device. Photomasks are used in the fabrication of high-end electronic components, semiconductor devices, displays, and many other applications. Even though transistors are becoming smaller and smaller, photomask-based UV lithography is still the industry-standard technique for micro-fabrication.
A photomask usually consists of a metal covered soda-lime or quartz plate with transparent openings. The metal absorbs the light at different wavelengths: Standard masks use chrome as absorption material for i-, g-, and h-line. The transparent image on the photomask represents the master template, where the pattern is transferred by a mask aligner or stepper into a photosensitive layer via photolithography. For semiconductor or display applications a whole set of photomasks is required to produce a complete device. For semiconductor manufacturing the photomask is protected by a foil (pellicle) to avoid any contamination.
The image on the photomask is patterned by laser lithography or e-beam lithography depending on the resolution requirements. As a master template for photolithographic manufacturing, the photomask must fulfill stringent requirements. These include key specifications such as linewidth uniformity, pattern position accuracy, edge roughness, and minimum feature size. Additionally, to enable a large process window for the final process, the photomask specifications must be considerably tighter than the target application.
Tight CD uniformity and low edge roughness, considerably better than required for the final application
Precise pattern positioning and plate-to-plate accuracy to enable accurate alignment of multilayer structures
Good Mura conditions to avoid disturbances in regular periodic patterns, especially for display applications
High repeatability to ensure stable photomask quality
High resolution
Tight CD Uniformity
Smooth edge roughness
High placement accuracy
Application images
suitable Systems
VPG+ 200 / VPG+ 400
- Volume Pattern Generator
A production tool for standard photomasks and microstructures in i-line resists.
VPG+ 800 / VPG+ 1400
- Volume Pattern Generator
Photomask production on large substrates, perfect for display applications.
ULTRA
- Laser Mask Writer
A tool specifically designed to produce mature semiconductor photomasks.