Radiant energy – With charged particle beam deflection or focussing – With detector
Reexamination Certificate
2002-01-18
2003-10-28
Hirshfeld, Andrew H. (Department: 2858)
Radiant energy
With charged particle beam deflection or focussing
With detector
C250S3960ML, C250S398000, C250S492230
Reexamination Certificate
active
06639221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to particle imaging systems and more particularly to methods and apparatus for alignment of charged particle beam projection lithography systems.
2. Description of Related Art
A problem with using charged particle projection optics has been the adverse effects of space charge upon beam projection optics. To ameliorate such effects by enhancing charged particle projection optics, hollow beam annular illumination technology is being developed because hollow beam annular illumination technology can suppress space charge effects dramatically. Hollow beam annular illumination with its reduced space charge problems, permits high throughput charged particle lithography equipment to be produced, because with a hollow beam even a projection system which employs a high beam current can produce well focussed images.
U.S. Pat. No. 5,821,542 of Golladay for “Particle Beam Imaging System Having Hollow Beam Illumination” states that “throughput is significantly lower for e-beam exposure systems than for photoexposure systems, thus making e-beam tools too costly for general production.” The Golladay patent states further “Higher throughput in e-beam lithography systems can presently be achieved by increasing the e-beam current, but only with an unacceptable degradation in resolution. The degradation in resolution can be attributed to interactions between electrons within the electron beam. The natural repulsion between electrons, due to having charges of the same polarity, causes a number of deleterious effects which limit resolution at the workpiece . . . ” To overcome the above stated problem the Golladay patent describes a charged particle beam imaging system in which an annular aperture comprises a central circular area which is substantially non-transmissive to a beam of charged particles and a first ring shaped area which is substantially transmissive to the beam of charged particles surrounded by a second ring-shaped area which is substantially non-transmissive to the beam.
U.S. Pat. No. 5,834,783 of Muraki et al. for “Electron Beam Exposure Apparatus and Method and Device Manufacturing Method” and U.S. Pat. No. 5,973,332 of Muraki et al. for “Electron Beam Exposure Method, and Device Manufacturing Method Using Same” describe an E-beam exposure apparatus including a “hollow beam forming stop whose central portion is shielded . . . ” Muraki et al. states “Since the space charge effect of hollow electron beam (hollow cylindrical beam) is smaller than that of a nonhollow electron beam (e.g. a Gaussian beam), the electron beam can be brought to focus on the wafer to form a source image free from any blur on the wafer . . . the electron density at the peripheral portion becomes higher than that at the central portion.”
As is discussed below in more detail, even with the above described advantages of hollow beam systems, there are problems with alignment of the charged particle beam with the apertures which define the configuration of the hollow beam.
SUMMARY OF THE INVENTION
A method and apparatus for aligning a charged particle beam with an aperture includes providing a hollow beam aperture means adapted for shaping a charged particle beam into a hollow charged particle beam. Then direct the charged particle beam through the aperture. Provide deflection coils for deflecting the charged particle beam relative to the aperture. Vary the current to the alignment deflection coils while measuring the aperture electrical current generated by charged particles reaching the hollow beam aperture as a function of the current to the alignment deflection coils. Then adjust the current in the alignment deflection coils based on the aperture electrical current measured to center the charged particle beam on the hollow beam aperture. Preferably, separate hollow beam and peripheral beam apertures with associated sensing and current are used to center the beam on respective ones of the apertures.
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Pfeiffer et al. “Projection reduction exposure with variable axis immersion lenses: Next generation lithography”, J. Vac. Sci. Technol., B 17(6), pp. 1-7 (Nov./Dec. 1999).
Hamdan Wasseem
Hirshfeld Andrew H.
Jones II Graham S.
Nikon Corporation
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