Method and system for repairing defected photomasks
A system and method for repairing a photomask ( 52 ) for use in a photolithography process is disclosed, the photomask ( 52 ), consisting of a substrate layer ( 38 ) and a chrome layer ( 36 ) over the substrate layer ( 38 ), having a defect ( 42 ) in the chrome layer ( 36 ), the method comprising: providing a pulsed laser source ( 1 ) for generating an ultra-short pulsed laser beam; providing optical elements for scanning, directing and focusing the pulsed laser beam at a desired target location; directing the pulsed laser beam through the substrate and focusing it on a target location located inside the substrate adjacent the defect ( 42 ) to write a diffractive optical element ( 34 ), thus changing the scattering properties of the substrate at the target location.
1. A method for changing the optical properties of a photomask for a photolithography wafer production process, wherein the wafer has a photoresist thereon and the photomask has a substrate layer and a coating layer over the substrate layer, the method comprising:
providing a pulsed laser source for generating an ultra-short pulsed laser beam;
providing optical elements for scanning, directing and focusing the pulsed laser beam at a desired target location; and
directing the pulsed laser beam through the substrate and focusing it on a target location located inside the substrate adjacent the coating layer; and
writing a diffractive optical element, said diffractive optical element comprising a shading element to attenuate the ultraviolet light passing through the photomask below the photoresist printing threshold of the wafer.
2. The method as claimed in claim 1 , wherein the diffractive optical element comprises micro cracks in the substrate.
3. The method as claimed in claim 1 , wherein the diffractive optical element is produced by locally changing the refractive index of the substrate at the target location.
4. The method as claimed in claim 1 , wherein the pulsed laser source comprises an ultra-short pulsed laser source.
5. The method as claimed in claim 4 , wherein the ultra-short pulsed laser source comprises a femto-second laser source.
6. The method as claimed in claim 1 , wherein the diffractive optical element is produced in a tapered shape, the narrower end of the tapered shape being nearer to the coating layer.
7. The method as claimed in claim 6 , wherein the diffractive optical element is conically shaped.
8. The method as claimed in claim 6 , wherein the diffractive optical element is pyramid-shaped.
9. The method as claimed in claim 6 , wherein the diffractive optical element comprises layers of pixels, each layer comprising an array of pixels patterned with a predetermined energy and density and geometry.