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(12) United States Patent (10) Patent N0.: US 6,672,739 B1 Argyle Et Al US006672739B1 (12) United States Patent (10) Patent N0.: US 6,672,739 B1 Argyle et al. (45) Date of Patent: Jan. 6, 2004 (54) LASER BEAM HOMOGENIZER IBM Technical Disclosure Bulletin vol. 37 (12), 469—471 (1994). (75) Inventors: Bernell Edwin Argyle, Hopewell H. J. Gerritsen, W. J. Hannon, and E. G. Ramberg; Elimi Junction, NY (US); Je?'ery Gregory nation of speckle noise in holograms With redundancy McCord, San Jose, CA (US) Applied Optics vol 7 (11), 2301—2311, (1968). Gordon W. Ellis; Fiber—optic phase randomiZer fro micro (73) Assignee: International Business Machines scope illumination by laser J. Cell. Biology vol 83, p303 , Corp., Armonk, NY (US) (1979). ( * ) Notice: Subject to any disclaimer, the term of this Robert Hard, Robert Zeh, and Robert D. Allen; Phase patent is extended or adjusted under 35 randomized laser illumination for microscopy , J. Cell Sci. U.S.C. 154(b) by 0 days. 23, 335—343 (1977). S. K. Dey, M. J. BoWman, and A. D. Booth; AneW technique (21) Appl. No.: 09/386,017 for improving domain pictures in Kerr—effect microscopy using a laser source; J. Scienti?c Instr. (J. Physics E) vol 2, (22) Filed: Aug. 30, 1999 162—164 (1969). Malcolm J. BoWman; TWo neW methods f improving optical (51) Int. Cl.7 .............................................. .. F21K 27/06 image quality; Appl. Optics vol. 7 2280—2284 (1968). * cited by examiner (52) US. Cl. ......................... .. 362/259; 362/553; 372/9; 385/28; 385/901 Primary Examiner—Sandra O’Shea Assistant Examiner—John Anthony Ward (58) Field of Search ............................ .. 385/15, 27, 28, (74) Attorney, Agent, or Firm—Rodney T. Hodgson 385/29, 31, 32, 39, 133, 901, 147; 362/553, (57) ABSTRACT 259; 372/9, 12—15 An apparatus, system, and method for illuminating a litho (56) References Cited graphic mask or an object in a microscope is presented, Whereby the output of a laser beam homogeniZer is imaged U.S. PATENT DOCUMENTS on to a ?eld such as the object plane for lithographic 4,744,615 A * 5/1988 Fan et a1. .. 219/121.61 application or on to the rear focal plane of an epi illuminat 5,634,920 A * 6/1997 Hohla . .. 606/12 ing objective lens as a source for Wide ?eld illumination at 5,889,278 A * 3/1999 Richard ................ .. 250/214 R an object plane in a microscope (for application to magni?ed OTHER PUBLICATIONS imaging of Weak phase objects)., and the image of the output is dithered With respect to the ?eld B. E. Argyle, D. A. Herman, and B. Petek; Reduction of coherence—related noise in laser based imaging systems 40 Claims, 7 Drawing Sheets 12 U.S. Patent Jan. 6, 2004 Sheet 1 0f 7 US 6,672,739 B1 F.i9‘ 1 10 j Prlor Art 101 Fig. 2 Prior Art 10] Fig. 3 19 Prior Art 30 Fig. 4 Prior Art U.S. Patent Jan. 6, 2004 Sheet 2 0f 7 US 6,672,739 B1 62 Fig. 14 U.S. Patent Jan. 6, 2004 Sheet 3 0f 7 US 6,672,739 B1 U.S. Patent Jan. 6, 2004 Sheet 4 0f 7 US 6,672,739 B1 U.S. Patent Jan. 6, 2004 Sheet 5 0f 7 US 6,672,739 B1 U S Patent Jan. 6, 2004 Sheet 6 0f 7 US 6,672,739 B1 U S Patent Jan. 6, 2004 Sheet 7 0f 7 US 6,672,739 B1 US 6,672,739 B1 1 2 LASER BEAM HOMOGENIZER SUMMARY OF THE INVENTION The present invention is a system, apparatus and method FIELD OF THE INVENTION for uniformly illuminating a ?eld, (such as an object in an object plane or the rear focal plane of an epi illuminating The ?eld of the invention is the ?eld of apparatus for objective lens) by imaging the output aperture of a laser or homogenizing laser light for illumination of objects in other light beam homogeniZer on the ?eld using an appa microscopes and in photolithographic applications. ratus Which dithers the image of the output of the beam BACKGROUND OF THE INVENTION homogeniZer With respect to the ?eld perpendicularly to the optical axis or dithers the output of the beam homogeniZer 10 Lasers may be used as illumination sources for micro so that the image of the beam homogeniZer dithers With scopes and for photolithographic systems. Laser beams are respect to the object or the rear focal plane. The dither typically single mode beams or multimode beams, and the means, in a preferred embodiment, is synchroniZed With beam homogeneity and coherence properties of such beams dynamic effects in the object or With a video recording may not be sufficient for the application. For single mode device to provide enhanced resolution. laser beams, the light distribution is Gaussian in a line taken 15 perpendicular to the beam. For uniform illumination, the BRIEF DESCRIPTION OF THE DRAWINGS “top” of the beam may be used, but much of the light intensity is then throWn aWay. Multimode beams may have FIG. 1 shoWs a prior art system of a laser beam homog a “top hat” distribution, but unless all modes have nearly eniZer. equal population, the intensity may vary over the “top hat”. FIG. 2 shoWs a prior art system for homogeniZing a laser In applications Where intense laser light exposes highly beam. non-linear photoresists, for example, to produce highest FIG. 3 shoWs a prior art system. resolution exposure in photoresist, a feW percent variation in FIG. 4 shoWs a prior art system. light intensity may be suf?cient to degrade the system capability. For microscopic investigations of Weak phase 25 FIG. 5 shoWs a sketch of the system of the invention. objects, such variation may also lead to masking of the small FIGS. 6(a—a) shoW images of the ?ber face recorded for difference in re?ected light from neighboring objects, and to various different dithering means producing motions up to introduction of artifacts related to the coherence of light several mode spacings. re?ected from different parts of the objects in the ?eld of FIGS. 7(a—a) shoW object images corresponding to the vieW. various modal ?ber patterns and dithering means recorded in An excellent overvieW of microscope illuminators is FIG. 6. included in S. Inoue, Video Microscopy, Plenum Press, NeW FIG. 8(a) shoWs an image of the ?ber face recorded as a York, NY, 1986. doughnut-shaped time average of circularly dithered motions larger than a face. Prior art systems have used systems of diffusers in the 35 laser beam path to homogeniZe the beam. Prior art systems FIG. 8(b) shoWs an object image When a dithering-means such as outlined in an abstract by G. W. Ellis, “A Fiber-Optic axis of rotation is Misaligned With the optic axis by 30 Phase-RandomiZer for Microscope Illumination by Laser”. degrees. J. Cell Biol. 83, 303a (1979), have used optical ?bers as FIG. 9 shoWs an object image When a dithering-means beam homogeniZers to convert near single mode laser beams axis of rotation is aligned Parallel to the optic axis. to multimode beams for illumination systems in micro FIGS. 10(a—b) shoW object images comparing hg-arc and scopes. Prior art systems have used light tunnels, as in US. dithered laser Illumination. Pat. No. 4,744,615, and systems of lenses, as in US. Pat. No. FIGS. 11(a—b) shoW an image of the dithered ?ber face 4,475,027, and holographs, as in US. Pat. No. 5,610,733, to and the associated object image, respectively. homogeniZe laser beams. The output of such beam homog 45 eniZers is often insufficient for exacting lithographic and FIG. 12 shoWs an an image of the difference betWeen tWo microscopic Work, especially on a small scale. Prior art object images taken sequentially in time. systems R. D. Allen, “Phase-Randomized Laser Illumination FIG. 13 shoWs an object image presenting magneto-optic for Microscopy”, J. Cell Sci. 23, 335 (1977), have used polar Kerr contrast. rotating Wedges in combination With a diffuser in a laser FIG. 14 is a sketch of a holloW pieZoelectric tube holding beam to move the laser beam around on the object being an optical ?ber. illuminated. Such rotating Wedges average out small scale inhomegenuities in the laser beam, but leave large scale DETAILED DESCRIPTION OF THE inhomogenuities in place. INVENTION OBJECTS OF THE INVENTION 55 FIG. 1 shoWs a prior art system such as described in detail in US. Pat. No. 4,744,615, Whereby a laser 10 produces a It is an object of the invention to produce an apparatus, laser beam 12 Which passes through an optical system 13 system, and method for illuminating an object or mask (here denoted as a simple lens) into the entrance aperture 14 uniformly over a certain area. of a laser beam homogeniZer 15. The laser beam homog It is an object of the invention to produce an apparatus, eniZer may be constructed from four re?ecting plates (only system, and method for illuminating Weak phase object in a tWo shoWn in the elevation vieW of FIG. 1) arranged in the microscope With high ef?ciency. form of a square or rectangular tube. Anumber of light rays It is an object of the invention to produce an apparatus, 16 are shoWn as a guide to the eye. The exit aperture 17 of system, and method for illuminating an object or mask the beam homogeniZer 15 is imaged by an optical system 18 uniformly over a certain area With high efficiency, and to 65 (here denoted by a symbol for a lens)on to an object 19.
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