Back to results
US 6,664,012 B2Granted
Through-the-lens alignment for photolithography
AssigneeAnvik Corporation
InventorChristopher C. Nunes
Life of this patent
Estimating the term…
Loading patent…
Loading patent…
AssigneeAnvik Corporation
InventorChristopher C. Nunes
Estimating the term…
Photolithographic processes require alignment of substrate to mask prior to exposure. Alignment accuracy becomes critical as feature size diminishes. For alignment tolerances above 1 μm, off-axis camera-based techniques are acceptable, but require frequent calibration. Through the lens (TTL) on-axis alignment is much preferred, not requiring frequent calibrations and having superior alignment accuracies, even though usually more complicated and expensive. This invention provides a simple, easy to incorporate TTL, on-axis alignment technique for alignment accuracies of 1 μm, such as scan-and-repeat patterning systems that employ a unitary mask-substrate stage and a folded projection imaging system. There is a master alignment mark adjacent to the mask, which is imaged onto a phosphor screen with the same radiation as is to be used for patterning. The resulting fluorescent image becomes a virtual master mark, visible to the alignment camera through a lens/compensator assembly after passing through the final fold mirror and not being reflected back towards the mask. The final fold mirror is optimized to pass radiation at the virtual master mark wavelength and reflect the exposure wavelength. Coordinates are developed and used thereafter to align the mask and substrate to one another.
An alignment system for projection imaging of microelectronics, using a mask and substrate mounted for production of a mask image for patterning the substrate, mask and substrate being mounted on a common scanning platform, with the optical path from a light source, through refractive elements, mask, reverser unit, projection lens and by reflection from a reflective element, a fold mirror, to the substrate, the image being of the operating wavelength for treatment of the substrate, said operating wavelength being the wavelength that the projection system refractive elements typically are designed and coated to pass optimally while reflective elements reflect such operating wavelength while passing at least one other wavelength, which may be identified as a secondary wavelength comprising:
The method of aligning a mask and substrate for projection imaging, postulating two alignment marks on both the mask and substrate, a master alignment mark adjacent to said mask, a phosphor screen adjacent to said substrate, using a projection imaging system with an operating wavelength to which said substrate is susceptible, a positioning stage with location feedback to which the substrate is attached, and a single scanning stage to which the mask, master alignment mark, positioning stage and phosphor screen are attached, characterized by the following steps:
The method of developing a virtual mask alignment mark for projection imaging, postulating a mask at a known location and at least one alignment mark on said mask and at least one related alignment mark on a substrate, using a projection imaging system with an operating wavelength and optical elements including at least one transmissive element and at least one reflective element, and mounting said mask and a substrate on a positioning stage with location feedback,
Dependencies are inferred from the claim text.