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 of correcting a critical dimension (CD) variation in extreme ultraviolet (EUV) photolithography, the method comprising:
mapping the CD variation of a wafer exposure field formed by a photolithography system that includes an EUV photolithography photomask;
determining one or a plurality of 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, the change in reflectance being calculated to correct the mapped CD variation;
directing a treatment beam to the region of the reflective multilayer; and
treating the region of the reflective multilayer with the beam in accordance with the determined one or a plurality of parameters.
2. The method of claim 1 , wherein the treatment beam comprises a femtosecond pulsed laser.
3. The method of claim 1 , wherein a parameter of said one or a plurality of parameters is selected from a group of parameters consisting of pulse energy, pulse duration, pulse rate, exposure time, scan rate, focal length, location, distance, and pitch of a scanning pattern.
4. The method of claim 1 , wherein determining said one or a plurality of parameters comprises utilizing a result of a calibration that includes treating a plurality of regions of a reflective multilayer surface in accordance with different values of said one or a plurality of parameters.
5. The method of claim 1 , wherein the treatment beam is directed to the region via a substrate of the photomask.
6. The method of claim 1 , wherein the produced change in reflectance at the working wavelength comprises changing a peak value of a reflectance spectrum of the region or wavelength shifting of a peak of a reflectance spectrum of the region.
7. The method of claim 1 , wherein directing the beam to the region comprises translating a source of the beam or the photomask, or operating beam optics.
8. The method of claim 1 , wherein treating the region with the beam comprises scanning the beam across the region with a raster pattern that includes a sequence of overlapping laser spots.
9. The method of claim 8 , wherein a ratio of a diameter of a laser spot of the sequence of overlapping laser spots to a pitch of the raster pattern is in the range of 1 to 100.
10. The method of claim 1 , wherein an energy density of the treatment is less than 200 mJ/cm 2 .
11. The method of claim 1 , wherein mapping the CD variation comprises examination of a wafer that is printed using the photomask, examination of the photomask, or sensing a pattern of radiation in the photolithography system.
12. The method of claim 1 , wherein the treatment beam heats the region.