US5440426A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Optical spatial filtering for attenuating the zero diffractive orders of mutually incoherent light beams
Assignee: Individual
•
Filing: 1994-07-13
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Granted: 1995-08-08
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Expires: 2014-07-13
Abstract
Abstract Method and apparatus for forming an image of an object by optical projection with a focusing system comprising the steps of collimating a set of at least two mutually incoherent light beams from the light source to fall on the object from directions that makes the non-diffracted components intersect the aperture stop at a set of points that are distributed over the surface of the stop, attenuating in a spatial filter the zero diffraction order of each beam relative to diffraction orders diffracted in directions towards the centre of the aperture stop, and adding the images formed by the light beams.
Inventors
- 👤 Erland T. Sandstrom
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 18:27
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/70591; G02; G02B; G02B21/00; G03F7/70058; G03F7/70091; G03F7/70108; G03F7/70216; G03F7/70308
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
130 words
A method for increasing the resolution of an optical projection system comprising the steps of: illuminating an object with light from an illumination source; providing a back focal plane of the projection system and an image plane; providing at the back focal plane a non-symmetrical spatial filter having an optical axis; recording an image which comprises the sum of a plurality of partial images at the image plane produced by at least four sequential partial exposures in which the object is illuminated from at least four different oblique directions symmetrically arranged in relation to the optical axis; and rotating the geometry of the spatial filter around the optical axis such that a constant geometrical relation between the oblique illumination beam and the optical axis of the spatial filter is maintained.
Claim 2
Independent Claim
130 words
A method for increasing the resolution of an optical projection system comprising the steps of: illuminating an object with light from an illumination source; providing a back focal plane of the projection system and an image plane; providing at the back focal plane a non-symmetrical spatial filter having an optical axis; recording an image which comprises the sum of a plurality of partial images at the image plane produced by at least four sequential partial exposures in which the object is illuminated from at least four different oblique directions symmetrically arranged in relation to the optical axis; and rotating the geometry of the spatial filter around the optical axis such that a constant geometrical relation between the oblique illumination beam and the optical axis of the spatial filter is maintained.
Claim 3
Dependent Claim
44 words
A method as set forth in claim 11, wherein the light from said illumination source creates a non-diffracted light beam in the partial exposures which is attenuated by an attenuating area of the spatial filter with a transmission in the range 15 to 75%.
Claim 4
Dependent Claim
59 words
A method as set forth in claim 2, wherein the light from said illumination source is linearly polarized with a polarization vector, said rotation step including the substep of rotating the spatial filter between partial exposures such that a constant geometrical relation between the oblique illumination beam, the spatial filter, and the polarization vector is maintained for each exposure.
Claim 5
Dependent Claim
22 words
A method as set forth in claim 2, wherein the object is a photomask and the image is recorded in a photoresist.
Claim 6
Dependent Claim
15 words
A method as set forth in claim 2, wherein the illumination source is a laser.
Claim 7
Dependent Claim
33 words
A method as set forth in claim 2, wherein the spatial filter has a substantially clear area bounded by a bounding contour having an apex with an angle in the range 45-120 degrees.
Claim 8
Dependent Claim
43 words
A method as set forth in claim 6, wherein the light from said illumination source creates a non-diffracted light beam in each partial exposure which is attenuated by an attenuating area located at the apex of the bounding contour of the spatial filter.
Claim 9
Dependent Claim
33 words
A method as set forth in claim 1, wherein the spatial filter has a substantially clear area bounded by a bounding contour having an apex with an angle in the range 45-120 degrees.
Claim 10
Dependent Claim
43 words
A method as set forth in claim 8, wherein the light from said illumination source creates a non-diffracted light beam in each partial exposure which is attenuated by an attenuating area located at the apex of the bounding contour of the spatial filter.
Claim 11
Dependent Claim
59 words
A method as set forth in claim 1, wherein the light from said illumination source is linearly polarized with a polarization vector, said rotation step including the substep of rotating the spatial filter between partial exposures such that a constant geometrical relation between the oblique illumination beam, the spatial filter, and the polarization vector is maintained for each exposure.
Claim 12
Dependent Claim
22 words
A method as set forth in claim 1, wherein the object is a photomask and the image is recorded in a photoresist.
Claim 13
Dependent Claim
15 words
A method as set forth in claim 1, wherein the illumination source is a laser.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1998-08-07 | 1999-02-06 | 1999-08-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-08-07 | 2003-02-06 | 2003-08-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-08-07 | 2007-02-06 | 2007-08-08 | $7700.00 | Window Closed / Lapsed |