Critical dimension variation correction in extreme ultraviolet lithography
A method of correcting a critical dimension (CD) variation in extreme ultraviolet (EUV) photolithography includes mapping the CD variation of a wafer exposure field formed by a photolithography system that includes an EUV photolithography photomask. Parameters of a treatment to produce a change in reflectance at a working wavelength of EUV radiation in a region of a reflective multilayer of the photomask are determined, the change in reflectance being calculated to correct the mapped CD variation. A treatment beam is directed to the region. The region is treated with the beam in accordance with the determined parameters.
1. A method for reducing reflection by a black border of a photomask for EUV photolithography, the method comprising:
directing a treatment beam from a radiation source to a reflective multilayer of the photomask at the black border; and
treating the reflective multilayer at the black border with the treatment beam so as to reduce reflection of the multilayer to at least a predetermined reflectance value.
2. The method of claim 1 , wherein the treatment beam is directed to the reflective multilayer through a backside coating and a photomask substrate.
3. The method of claim 1 , wherein the predetermined reflectance value is 5%.
4. The method of claim 1 , wherein the treatment beam heats the reflective multilayer.
5. The method of claim 1 , wherein directing the treatment beam comprises directing the treatment beam to the reflective multilayer at a defective region of the black border.