High resolution imagery systems and methods

• US 5,386,319 A
• Filed: 06/11/1992
• Issued: 01/31/1995
• Est. Priority Date: 10/25/1987
• Status: Expired due to Term

• Current Assignee: High Resolution Optics Corporation (Acacia Research Corporation)
• Original Assignee: Theodore R. Whitney
• Inventors: Whitney, Theodore R.
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): Robbins, Thomas
• Application Number:
  US07/897,248
• Time in Patent Office: 964 Days
• Field of Search: 359/741, 359/742, 359/743, 359/565, 359/566, 359/569, 359/573, 359/575
• US Class Current: 359/575
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4216 correcting geometrical aberrations
• CPC Class Codes: G02B 27/4222 in projection exposure systems, e.g. photolithographic systems
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/188 Plurality of such optical elements formed in or on a supporting substrate
• CPC Class Codes: G03F 7/70066 Size and form of the illuminated area in the mask plane, e.g. reticle masking blades or blinds
• CPC Class Codes: G03F 7/70583 Speckle reduction, e.g. coherence control or amplitude/wavefront splitting
• CPC Class Codes: G03F 9/7049 Technique, e.g. interferometric

Abstract

The current limits of resolution of multi-element optical systems are exceeded by reducing the number of elements while introducing at the critical aperture a blazed transmission grating having grating rings of low bending power defined by multiple plateaus. By illuminating the optical train with monochromatic light that constitutes a multiplicity of distributed sources having a substantial temporal coherence but spatial incoherence and by varying the slopes and widths of the grating rings, local phase delays are introduced that adjust aberrations in the optical system, providing an aligned composite wavefront. The system and method may be used for presenting an image, as for a wafer stepper, or for viewing an image, as in a microscope.

Claims

1. A plate for use in an optical system, for selectively phase delaying different areal components of a substantially monochromatic illuminating beam throughout a cross sectional area, comprising:

a substantially flat, light transmissive, substrate having a plurality of light bending rings thereon defining a base spherical bending characteristic, each of the rings being degined by a succession of plateaus relative to a nominal surface of the substrate, the plateaus varying in height by increments related to a wavelength of optical delay of monochromatic light incident thereon, the maximum height being less than one wavelength or an integral multiple thereof, and the rings varying nonlinearly in width relative to a central axis of the rings, and wherein the rings have a minimum radial width of the order of 10 microns.

2. The invention as set forth in claim 1 above, wherein the rings are defined by light transmissive silica layers deposited on the substrate.

3. The invention as set forth in claim 1 above, wherein the plateaus are defined by layers of varying depths removed from the nominal surface of the substrate.

4. The invention as set forth in claim 1 above, wherein the base spherical characteristic of the plate is selected to compensate for chromatic dispersion of an associated refractive optics system at the frequency of the substantially monochromatic illuminating beam.

5. The invention as set forth in claim 1 above, wherein the rings are disposed in sets defining a pupil function having more than one zone, the combination effectively increasing the depth of focus of the system.

6. The invention as set forth in claim 5 above, wherein the progression of plateaus within successive ring sets is varied to establish a predetermined relationship between the phases of wavefronts passing through adjacent ring sets, such that the pupil function is provided.

7. The invention as set forth in claim 6 above, wherein the progressions are interrupted in π

phase manner.

8. The invention as set forth in claim 1 above, wherein the substrate includes a first annular reference pattern outside the transmissive ring pattern and a second annular reference pattern inside the transmissive ring pattern.

9. The invention as set forth in claim 8 above, wherein the annular reference patterns comprise a plurality of chrome rings on the substrate.

10. A plate for use in an optical system, for selectively phase delaying different areal components of a substantially monochromatic illuminating beam throughout a cross sectional area, comprising:

a substantially flat, light transmissive, substrate having a plurality of light bending rings thereon defining a base spherical bending characteristic, each of the rings being defined by a succession of plateaus relative to a nominal surface of the substrate, the plateaus varying in height by increments related to a wavelength of optical delay of monochromatic light incident thereon, the maximum height being less than one wavelength or an integral multiple thereof, and the rings varying nonlinearly in width relative to a central axis of the rings, and wherein the rings have a minimum radial width of the order of 10 microns, and the ring patterns are separated by selectively placed ring areas which are at least partially opaque.

11. The invention as set forth in claim 10 above, wherein the plate has transmissive patterns defining at least two π

phase related pupil functions and wherein at least one of the ring patterns defining the pupils is at least partially opaque.

12. A light transmissive member for phase compensation of the microstructure of a distributed monochromatic beam in an optical system, comprising:

a base of light transmissive material having a plurality of multi-plateau rings of varying widths, the plateaus varying within the rings in progressive sequences to provide fractional amounts of wave retardation at the wavelength of the monochromatic beam.

13. The member as set forth in claim 12 above, wherein the rings are concentric about a central axis and disposed in sets of varying phase relation to define a pupil function having different zones.

14. A light transmissive member for phase compensation of the microstructure of a distributed monochromatic beam in an optical system, comprising:

a base of light transmissive material having a plurality of multi-plateau rings of varying widths, the plateaus varying within the rings in progressive sequences to provide fractional amounts of wave retardation at the wavelength of the monochromatic beam,

the rings being concentric about a central axis and disposed in sets of varying phase relation to define a pupil function having different zones,

wherein the rings provide maximum bending of the impinging beam of no greater than 5°

, wherein the total local area wave retardation introduced by a ring is in integral multiples proportioned to a wavelength, and wherein there are in excess of about 800 rings for a 5 inches diameter pupil.

15. The member as set forth in claim 14 above, wherein the local area wave retardation is a maximum of about one wavelength, and wherein the rings are of a minimum of about 8 microns in width.

16. A light transmissive member comprising:

a light transmissive substrate having an inner sector comprising a first plurality of rings each defined by a succession of plateaus of incrementally varying heights for selectively delaying the phase of local wavefronts of monochromatic wave energy of a first wavelength passing therethrough;

an intermediate sector comprising a second plurality of rings each defined by a succession of plateaus of incrementally varying heights for selectively delaying the phase of local wavefronts of monochromatic wave energy of a second wavelength passing therethrough; and

at least one reference sector having a plurality of rings of alternating transmissive and non-transmissive material defining a grating; and

wherein all of the rings are concentric with a central axis.

17. The invention as set forth in claim 16 above, where the first plurality of rings is dimensioned with thicknesses and widths for selective phase delay of local wavefronts of light in the ultraviolet region and wherein the individual plateaus vary by regular fractions of the wavelength of the ultraviolet light.

18. The invention as set forth in claim 17 above, wherein the thicknesses and widths of the second plurality of rings in the transmissive region are selected to modify the local wavefronts of light in the red region, and where at least one reference sector includes bands of radially separated alignment grating rings having selected light bending powers, an outermost set of fiducial rings, and an innermost set of fiducial rings.

19. The invention as set forth in claim 18 above, wherein the substrate has a base height level and the tracks within the rings define individual plateaus varying by one-eighth increments having a maximum height equal to approximately seven-eighths of the wavelength of the monochromatic light divided by the index of refraction of the substrate, there being eight plateaus per nominal ring, and wherein the plateau sequences are interrupted in phase fashion to provide a pupil function having at least two zones in the ultraviolet light transmissive region.

20. The invention as set forth in claim 19 above, wherein the ultraviolet transmission region has a pupil function using at least three zones and at least some tracks are partially opaque to provide light blockage of the local wavefronts thereat.

21. An optical element for enhancing specific optical properties in an optical system having a beam path comprising:

a light transmissive plate disposed transverse to the beam path and having patterns of varying thickness configured to introduce varying phase retardation in different parts of the beam moving along the beam path, the patterns being arranged in groups having phase shifts between them, to define different pupil functions in the optical system.

22. An optical element as set forth in claim 21 above, wherein the beam in the optical system is distributed through an area at the plate and the plate has a microstructure of patterns through the area for differentially varying the phase retardation of wavelets in the beam.

23. An optical element as set forth in claim 21 above, wherein the plate is disposed transverse to a central axis and the patterns comprise a plurality of varying rings concentric with the axis, and wherein the phase retardation patterns vary in accordance with radius and the phase shifts between the groups also vary radially.

24. An optical element as set forth in claim 21 above, wherein the patterns also comprise transmissivity variations.

25. An optical element as set forth in claim 24 above, wherein the transmissivity variations comprise areas that are opaque to light.

26. An optical element as set forth in claim 21 above, wherein the phase retardation pattern groupings vary by selective reversal of the pattern progressions to introduce π

radians of phase shifts in areas of the beam path.

27. A light transmissive optical element for providing pupil functions in an optical system, comprising:

a transmissive plate having a plurality of patterns of varying thickness and transmissivity, wherein the patterns include groupings which introduce predetermined phase shifts, reversal phase shifts, and opaque areas, such that the combination of patterns introduces one or more pupil functions in the optical system.

28. An optical element as set forth in claim 27 above, wherein the patterns are disposed as rings about a central axis and comprise rings of varying slope and radial width and vary locally in 0 and π

fashion, where 0 represents a predetermined local phase shift and π

represents a locally reversed phase shift.

29. A light transmissive optical element for providing pupil functions in an optical system, comprising:

a transmissive plate having a plurality of patterns of varying thickness and transmissivity, wherein the patterns include groupings which introduce predetermined phase shifts, reversal phase shifts and opaque areas, such that the combination of patterns introduces one or more pupil functions into the optical system,

the patterns being disposed as rings about a central axis and comprising rings of varying slope and radial width, and varying locally in 0 and π

fashion, where 0 represents a predetermined local phase shift and π

represents a locally reversed phase shift,

the plate further including selective radial variations of 0 and π

phase shift together with opaque areas.

30. An optical system including a lens combination having improved depth of field or resolution or both over than achievable with refractive lens combinations alone comprising:

at least one diffractive element in the lens combination, the diffractive element having a plurality of phase shift patterns therein which vary so as to have reversed phase shifts between them so as to provide a predetermined pupil function.

31. An optical system as set forth in claim 30 above, wherein at least one diffractive element further includes light transmissive patterns thereon varying in accordance with the desired pupil function, and wherein the lens combination comprises principally refractive elements.

32. An optical system as set forth in claim 30 above, wherein the system includes at least two of said diffractive elements.

33. An aspheric optical element for correcting the microstructure of an areal beam disposed about a central axis comprising:

a light transmissive plate having a plurality of concentric patterns thereon, the plate being disposed in the beam path and with the patterns concentric with the central axis, wherein the patterns each introduce progressively varying optical path delay in the beam between selected limits, the patterns varying in radial dimension and in radial position relative to the central axis to introduce an aspheric function in the beam.

34. An aspheric optical element as set forth in claim 33 above, wherein the patterns each have progressively varying heights redirecting wavelet components of the beam to redistribute waves in the beam.

35. An aspheric optical element as set forth in claim 33 above, wherein the patterns are defined by tracks of incrementally varying heights.

36. An aspheric optical element as set forth in claim 33 above, wherein one or more aspheric is used with an optical system having aberration as a system and in the elements thereof, and wherein the aspheric function compensates for system aberration and aberrations of the elements themselves.

37. An optical system comprising:

a number of refractive elements arranged as a lens system and having residual aberration, and

at least one phase plate comprising a holographic element operating in a Bragg regime and also functioning as an asphere to compensate for residual aberration in the refractive elements.

38. A system as set forth in claim 37 above, further comprising monochromatic light source means providing a beam through the refractive elements and phase plate.

39. A system as set forth in claim 38 above, wherein the at least one phase plate comprises means defining an areally distributed transmissive element compensating for spherical-type aberration and non-spherical aberrations.

40. A system as set forth in claim 39 above, wherein the non-spherical aberrations comprise chromatic aberration.

41. A system as set forth in claim 40 above, wherein the at least one phase plate comprises groupings of grating segments which define multiple pupils imparting controlled depth of field, increased resolution and reduced sideband intensity in the optical system.

42. An achromatic optical system comprising:

a plurality of refractive lenses having in combination a negative chromatic dispersion, and

at least one correcting phase plate defining a transmission grating having a positive base power curvature opposing but substantially matching the chromatic dispersion of the refractive lenses.

43. An optical system as set forth in claim 42 above, wherein the refractive lenses are spherical lenses disposed along an optical path wherein the correcting phase plate is disposed along the optical path and comprises a plurality of ring patterns introducing varying phase shift, and wherein the system further includes monochromatic illuminating means.

44. An optical system as set forth in claim 43 above, wherein the monochromatic illuminating means comprises an excimer laser having a chromatic spread compensated by the correcting phase plate.

45. An optical system as set forth in claim 42 above, wherein the system comprises at least two phase plates disposed serially along the optical system.