Method for aligning photomasks
CA 1296180 C · Owner: American Telephone And Telegraph Company · Inventors: Watkins, Laurence S.; Harvey, George T.
Overview
Its claims, description and drawings are in the Canadian Patents Database.
Open the CIPO recordAbstract From the Canadian patent
Abstract Photomasks are aligned on opposite sides of a wafer by directing light beams through zone plates in one photomask and through aligned transparent slits on the other photomask. Simultaneous detection of the beams by photodetectors indicates alignment. A method for obtaining precise centering by scanning the slits with the beams sampling light, transmitted through the slits and fitting the samples to a parabola by the use of a computer is also described.
Read the whole patent
Listed from its CIPO record in Patent Yard's archive of Canadian patents past their term. Its claims, description and drawings are in the CIPO record and on Google Patents, and the Claude kit works from them.
Why it's free to use
- Granted February 25, 1992. A Canadian patent filed before October 1, 1989 lasted 17 years from grant, so its term ended February 25, 2009.
- We check Canadian rights only. A patent in its family in another country could still be in force: check its family on Google Patents.
Timeline
Timeline From CIPO dates
Sources & verification
Official CIPO records
Everything on this page comes from the CIPO record linked above. Contains information licensed under the Open Government Licence – Canada.