Nova Patents
EP0779528A2

High numerical aperture ring field optical reduction system

Abstract

An optical projection reduction system used in photolithography for the manufacture of semiconductor devices having a first mirror pair (M1, M2; M1', M2'; M1'', M2''), a second field mirror pair (M3, M4; M3', M4'; M3'', M4''), and a third mirror pair (M5, M6; M5', M6'; M5'', M6''). Electromagnetic radiation form a reticle or mask (10) is reflected by a first mirror pair to a second field mirror pair forming an intermediate image (24, 24', 24''). A third mirror pair re-images the intermediate image to an image plane at a wafer (22). All six mirrors are spherical or aspheric and rotationally symmetrical about an optical axis (OA). An annular ring field is obtained, a portion of which may be used in a step and scan photolithography system. In another embodiment, weak refracting elements (R1, R2, R3) are introduced to further reduce residual aberrations allowing a higher numerical aperture. In the catoptric embodiment of the present invention, a numerical aperture of 0.25 is obtained resulting in a working resolution of 0.03 microns with electromagnetic radiation having a wavelength of 13 nanometers. The optical projection reduction systems are intended for use at extreme ultraviolet to the soft X-ray wavelength range. The present invention, provides a relatively high numerical aperture and uses substantially all reflective elements, greatly facilitating the manufacture of semiconductor devices having feature sizes below 0.25 microns.

EP0779528A2, drawing sheet 1
Sheet 1 of 7

Term

Term ended

Projected expiry passed 18 November 2016, 9.8 years ago.

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20 claims: 4 independent, 16 dependent

  1. 1
    An optical reduction system for use in photolithography, from the long conjugate end to the short conjugate end, comprising:a first mirror pair;a field mirror pair positioned to receive electromagnetic radiation reflected from said first mirror pair;and a third mirror pair positioned to receive electromagnetic radiation reflected from said field mirror pair,    whereby an intermediate image is re-imaged to a final image at an image plane.
  2. 11
    An optical reduction system for use in photolithography, from the long conjugate end to the short conjugate end, comprising:a first mirror pair;a field mirror pair, said field mirror pair positioned to receive a chief ray reflected from said first mirror pair diverging away from an optical axis and converting it to a chief ray converging towards the optical;and a third mirror pair, said third mirror pair positioned to receive the chief ray reflected from said field mirror pair,    whereby a reduced image of an object is formed.
  3. 12
    An optical reduction system for use in photolithography, from the long conjugate end to the short conjugate end, comprising:a first concave mirror;a second mirror;a third concave mirror;a fourth concave mirror;a fifth convex mirror;and a sixth concave mirror,    whereby two of said first, second, third, fourth, fifth or sixth mirrors act as a field mirror pair.
  4. 16
    An optical reduction system for use in photolithography, from the long conjugate end to the short conjugate end, comprising:a first concave mirror;a second mirror positioned to receive reflected electromagnetic radiation from said first concave mirror;a third concave mirror positioned to receive reflected electromagnetic radiation from said second mirror;a fourth concave mirror positioned to receive reflected electromagnetic radiation from said third concave mirror;a fifth convex mirror positioned to receive reflected electromagnetic radiation from said fourth concave mirror;and a sixth concave mirror positioned to receive reflected electromagnetic radiation from said fifth convex mirror, said first, second, third, fourth, fifth and sixth mirrors being centered on an optical axis, said third concave mirror receiving a chief ray diverging away from the optical axis, and said fourth concave mirror receiving the chief ray reflected from said third concave mirror and reflecting the chief ray causing it to converge toward the optical axis.
Independent claims4