Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70058—Mask illumination systems
  • G03F7/70091—Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA]
  • G03F7/70108—Off-axis setting using a light-guiding element, e.g. diffractive optical elements [DOEs] or light guides
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70225—Optical aspects of catadioptric systems, i.e. comprising reflective and refractive elements
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70233—Optical aspects of catoptric systems, i.e. comprising only reflective elements, e.g. extreme ultraviolet [EUV] projection systems

Definitions

• the present invention relates in general to optical projection systems for forming a reduced image of a photomask on a substrate in ultraviolet (UV) optical lithography operations.
• the invention relates in particular to such projection systems that use a Schwarzschild objective for projecting the reduced image.
• a commonly used projection optic for projecting the mask image is a Schwarzschild objective.
• a Schwarzschild objective is one, well-known, embodiment of an on-axis (the optical axis of the projection system) reflective telescope, used in reverse, in which light from the illuminated photomask passes through a primary mirror having a concave reflective surface via a central aperture in the primary mirror, and is reflected from an on- axis convex secondary mirror onto the concave reflective surface of the primary mirror.
• primary mirror and “secondary mirror”, used here and in the description of the invention presented herein below are the terms that are normally used in designating mirrors of a reflective telescope and do not reflect the order in which radiation strikes the mirrors when a reflective telescope is used in reverse as a reducing objective.
• An all-reflective objective such as the Schwarzschild objective has an advantage that reflective optical elements can provide less loss of (UV) light through absorption of the light than refractive elements.
• the Schwarzschild and similar all reflective objectives have a partially offsetting disadvantage that light entering the objective close to the axis or at low inclination to the axis is reflected from the secondary mirror, back through the aperture in the primary mirror, creating, in effect, a "dark zone” or zone of obscuration on the secondary mirror close to the axis.
• apparatus for illuminating a mask with a beam of radiation and projecting an image of the mask on a substrate.
• Such apparatus typically has a mask location at which the mask to be imaged is placed, and an image location at which the substrate is placed to receive the projected image.
• apparatus in accordance with the present invention comprises an objective including a convex first mirror and concave second mirror, spaced apart and facing toward each other.
• the second mirror is larger than the first mirror and has an aperture therein providing optical access to said first mirror.
• a prism is located in the path of the beam of radiation to the mask location.
• the prism has a plurality of facets.
• the facets are configured and arranged such that the beam is divided thereby into a plurality of beam-portions, the beam portions being mutually convergent on leaving the prism.
• the mutually convergent beam-portions intersect in the object location, then mutually diverge through the aperture in the second mirror such that essentially all of the radiation in the beam portions is incident in an annular zone on the first mirror.
• the beam portions incident in the annular zone are reflected onto the second mirror and reflected by the second mirror to a focus in the substrate location.
• the objective is a Schwarzschild objective and the dividing face of the prism has four facets dividing the beam into four portions.
• the prism may have less than four or more than four facets, but the facets preferably meet a common point on the optic axis of the apparatus.
• the inventive optical system is directed primarily to imaging using light from an excimer laser, but is not limited to imaging with such a laser.
• FIG. IA is a plan view schematically illustrating an optical element in accordance with the present invention having one plane face and four surfaces or facets opposite the plane face for dividing a beam of radiation incident thereon into four beam-portions propagating at an angle to each other.
• FIG. IB is a side-elevation view schematically illustrating detail of a first and third of the facets of the optical element of FIG. IA.
• FIG. 1C is a front-elevation view schematically illustrating detail of a first and second of the facets of the optical element of FIG. IA.
• FIG. 2 is an unshaded cross-section view schematically illustrating an optical arrangement in accordance with the present invention wherein a collimated beam is divided into four collimated beam-portions by an example of the four-faceted optical element of FIGS. IA-C, and the four collimated beam-portions are focused by a Schwarzschild objective.
• FIG. 2A is an end view of the convex mirror of the Schwarzschild objective shown from the left side of Figure 2. -A-
• FIG. 3 schematically illustrates an optical system layout for imaging a mask on a substrate in accordance with the present invention, in which a laser beam is shaped by a beam-shaping telescope, and is divided into four beam-portions by an example of the four-faceted optical element of FIGS. IA-C, and in which a field lens converges the four beam-portions to intersect on the mask to illuminate the mask, and a Schwarzschild objective images the illuminated mask on the substrate.
• FIG. 4 is an unshaded cross-section view schematically illustrating detail of an example of the beam-shaping telescope, the four-faceted optical element, the field lens, and the Schwarzschild objective of FIG. 3.
• FIG. IA, FIG. IB, and FIG. 1C schematically illustrate an optical beam-dividing element or prism 10 of a type which is used in apparatus in accordance with the present invention.
• Prism 10 in this example thereof, has one plane face 12, which preferably is used as an entrance face, and four faces or facets 14A, 14B, 14C, and 14D, which are preferably used as exit faces.
• the facets are rectangular (square) of equal size and meet at a central apex point 16 of the prism.
• the prism is intended for use with apex 16 thereof aligned on, and entrance face 12 thereof perpendicular to, a longitudinal optical axis 18 of an optical system in accordance with the present invention (see FIG.
• FIG 2 is an un-shaded cross-section view, schematically illustrating a basic optical arrangement 20 in accordance with the present invention, in one transverse axis thereof, for forming a reduced image of a mask on a substrate.
• a prism 10 receives a collimated beam of radiation 22 designated, here, by six rays 24. The beam enters the prism via entrance face 12 thereof and is incident on all four facets (14A-D) of the prism.
• Facets 14B and 14D divide beam 22 into two corresponding beam-portions 22B and 22B designated, respectively, by rays 24B and 24D.
• Those skilled in the art will recognize without further illustrate that there will two corresponding beam-portions (created by facets 14A and 14C of prism 10) in a plane perpendicular to the plane of FIG. 2.
• a mask (not shown) to be imaged would be located in a plane 26 in which beams 22B and 22D (and the two corresponding beam-portions not visible) intersect. At the intersection point of the beam, the intensity or radiation will be about four times that in the original beam 22.
• Primary mirror 32 has a concave reflective surface 34.
• a secondary mirror 36 of the Schwarzschild objective has a convex reflective surface 38.
• surfaces 34 and 38 are spherical surfaces. This, however, such not be construed as limiting the present invention.
• the terms “primary” and “secondary” as applied to mirrors 32 and 36 in this description of the invention are the terms that are normally used in designating mirrors of a reflective telescope, and do not reflect the order in which radiation strikes the mirrors when a reflective telescope is used in reverse as a reducing objective as depicted in FIG. 2.
• the facet inclination angle ⁇ see FIG. 2A
• IB is preferably selected in accordance with the refractive index of the material of prism 10, and the axial distance of the prism from secondary mirror 36, such that preferably, essentially all rays in the diverging beams are incident on reflecting surface 38 of secondary mirror in an annular zone 42 thereof (see FIG. 2A) centered on the system axis, outside the above-discussed, circular "dark zone” or obscuration 44 of the mirror, indicated, here, as bounded by dashed line 46. Accordingly, all rays in the beams are reflected from surface 38 of mirror 36 onto concave reflecting surface 34 of mirror 32, and are reflected to from image points in plane 50 thereby imaging mask plane 26 in plane 50.
• the surface of a substrate (not shown) would be located in plane 50 to receive a mask image.
• the image points are the points at which diverging rays from a corresponding point in the object plane intersect in the image plane.
• Dashed line 46 is approximately the locus of hypothetical ray paths originating on axis 18 at plane 26 (such as the path designated by line dotted line 40) that are at the minimum inclination to axis 18 required to be reflected from surface 38 of mirror 36 onto surface 34 of mirror 32, as indicated by dashed line 4OR. Any ray originating on axis at plane 26 having less than this incidence angle will be reflected back into aperture 30 and, accordingly, will not reach the image plane. Dividing beam 22 in to portions that mutually diverge into the aperture can provide that essentially all of the light (radiation) in the original beam is incident on surface 38 of mirror 36 outside of the dark-zone.
• a beam of collimated radiation is received from some source thereof such as a laser delivering a TEMoo-quality beam, or from a laser via well corrected collimating optics.
• a laser delivering a TEMoo-quality beam
• Certain types of laser deliver beams that need to be "shaped", i.e., have the beam cross-section thereof altered in size or shape, before the beam can be used to illuminate a mask.
• Excimer lasers that are used as radiation (light) sources for mask projection typically deliver a beam that has an elongated cross section, for example, having a length of about 35 millimeters (mm) and a width of about 12 mm.
• FIG. 3 schematically illustrates in functional block-diagram form, an excimer- laser optical apparatus 60 in accordance with the present invention for projecting a mask on a substrate using a Schwarzschild objective.
• Apparatus 60 includes an excimer laser 62 delivering a beam 20 that is substantially collimated but has an elongated cross-section as discussed above.
• the beam traverses a variable attenuator 64 for regulating the power in the beam, and traverses beam-shaping optics (telescope) 66, including cylindrical lenses 68 and 70, that are arranged to reduce the long-axis dimension of the beam.
• Beam 20 leaves beam-shaping optics 68, traverses a prism 10 in accordance with the present invention, then traverses an optional beamsplitter 72.
• Beamsplitter 72 may be used, for example, to direct a small portion of the beam to an apparatus for performing beam diagnostics.
• FIG. 4 is an un-shaded cross-section view schematically illustrating details of one example 6OA of beam-shaping shaping optics, beam-dividing prism, field lens and Schwarzschild objective in the apparatus of FIG. 3.
• the optical path is foreshortened and unfolded, with mirror 74 and beamsplitter 72 omitted, for convenience of illustration.
• beam 22 is not collimated on leaving cylindrical lens 70 of beam-shaping optics 66, but is still divided into four beam-portions, with only portions 22B and 22D visible here, as discussed above with reference to FIG. 2.
• Beam-portions 22B and 22D are individually slightly diverging, but mutually converging.
• Field lens 78 causes the beam-portions to become individually converging and also increases the mutual convergence of the beam-portions. The beam-portions intersect in mask plane
• Objective 30 is arranged with respect to lens 78 such that essentially all of the radiation (light) in all of the beam-portions is incident on convex surface 38 of mirror 36 of the objective in the annular region 42 thereof surrounding dark zone 44 (not shown in FIG. 4) as discussed above with reference to FIG. 2A.
• Light in the beam-portions is reflected from the annular region of mirror 36 onto reflective surface 34 of mirror 32 which reflects the beam portions to image points in an image plane 50 in which substrate 84 would be placed to receive the mask image.
• An incidental, but nonetheless advantageous property of prism 10 is that the prism can serve as a beam homogenizer for providing uniformity of light in the mask plane.
• prism 10 is described above as having four exit-facets, it is possible to deploy, in the above described and other arrangements in accordance with the present invention, a prism having more or less facets (although there must be at least two) without departing from the spirit and scope of the present invention. It is also possible to orient prism 10 such that beam 20 enters the prism via the facets and leaves the prism via face 12 thereof. It is even possible to deploy a prism having sloping facets of on each side thereof, with the corresponding facets on opposite sides of the prism being of the same number and shape, and exactly aligned with each other.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Lenses (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)

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• 2006
  • 2006-02-06 US US11/348,185 patent/US7331676B2/en active Active
  • 2006-02-07 JP JP2007554344A patent/JP4820377B2/ja active Active
  • 2006-02-07 WO PCT/US2006/004458 patent/WO2006086486A2/en not_active Ceased

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