EP0352975A2
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EP
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Resolution doubling lithography technique
Assignee: AT&T Inc
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Filing: 1989-07-20
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Granted: —
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Expires: 2009-07-20
Abstract
Abstract A lithography system is disclosed which is capable of doubling the spatial frequency resolution associated with conventional systems. A spatial filter (e.g., 20), positioned to intercept the Fraunhofer diffraction pattern of the mask (e.g., 18) being exposed, is configured to prevent certain orders of the diffraction pattern (in most cases the 0-order and ±2nd, 3rd, ... orders) from reaching the wafer's surface. The remaining orders reaching the wafer surface (in most cases the ± first-order beams) will produce a cos-type interference pattern with a period half of that if the mask grating were imaged without spatial filtering. Therefore, for a system with a given magnification factor m, a mask grating with a period p will be exposed on the wafer surface as a grating with a period of p′=pm/2. Advantageously, the spatial filtering technique of the present invention allows for a variety of different structures (conventional gratings, chirped and phase-shifted gratings, grids, Fresnel zones plates, etc.), as well as structures of different sizes and orientations, to be included on one mask and transferred to the wafer with a single exposure cycle.
Inventors
- 👤 Tatiana Emelianovna Jewell
- 👤 Donald Lawrence White
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 21:14
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/16; G03F7/18; G03F7/70; G03F7/70058; G03F7/70091; G03F7/70216; G03F7/70308; G03F7/70325
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
129 words
A lithography system (e.g., 10) for exposing patterns consisting of regular lines and spaces on a wafer surface, the system comprising an illumination source (e.g., 12); a mask (e.g., 18) containing at least one pattern with a predetermined period p which is illuminated by said illumination source, a Fraunhofer diffraction pattern, including a 0-order, ± first order and a plurality of higher-order beams, created by the illumination passing through the at least one pattern; and an imaging system (e.g., 14, 15, 16) with a predetermined magnification factor m disposed between the mask and the wafer for directing the illumination towards the wafer surface, CHARACTERIZED IN THAT the imaging system includes a spatial filter (e.g., 22) positioned to intercept the Fraunhofer diffraction pattern, said spatial filter including a central obscuration.
Claim 2
Dependent Claim
129 words
A lithography system (e.g., 10) for exposing patterns consisting of regular lines and spaces on a wafer surface, the system comprising an illumination source (e.g., 12); a mask (e.g., 18) containing at least one pattern with a predetermined period p which is illuminated by said illumination source, a Fraunhofer diffraction pattern, including a 0-order, ± first order and a plurality of higher-order beams, created by the illumination passing through the at least one pattern; and an imaging system (e.g., 14, 15, 16) with a predetermined magnification factor m disposed between the mask and the wafer for directing the illumination towards the wafer surface, CHARACTERIZED IN THAT the imaging system includes a spatial filter (e.g., 22) positioned to intercept the Fraunhofer diffraction pattern, said spatial filter including a central obscuration.
Claim 3
Dependent Claim
60 words
A lithography system as defined in claim 1 wherein the illumination source is chosen from the group consisting of coherent illumination and partially coherent illumination, such that the central obscuration of the spatial filter completely intercepts the 0-order beam of the Fraunhofer diffraction pattern, wherein the at least one pattern exposed on the wafer surface comprises a period p′= pm/2.
Claim 4
Dependent Claim
13 words
A lithography system as defined in claim 2 wherein the illumination is coherent.
Claim 5
Dependent Claim
33 words
A lithography system as defined in claim 3 wherein the illumination source is chosen from the group consisting of excimer laser sources, x-ray sources, visible sources, UV sources, near-UV sources, and deep-UV sources.
Claim 6
Dependent Claim
15 words
A lithography system as defined in claim 2 wherein the illumination source is partially coherent.
Claim 7
Dependent Claim
36 words
A lithography system as defined in claim 2 where the at least one pattern contained in the mask is chosen from the group consisting of grating patterns, grid patterns, Fresnel zone plates, and concentric circular patterns.
Claim 8
Dependent Claim
25 words
A lithography system as defined in claim 6 wherein the grating patterns include a plurality of gratings of different periods, phase-shifted gratings, and chirped gratings.
Claim 9
Dependent Claim
33 words
A lithography system defined in claim 6 wherein the mask is transparent and the pattern on the mask consists of regions that produce different phase delay in the light passing through the regions.
Claim 10
Dependent Claim
33 words
A lithography system as defined in claim 2 wherein the spatial filter is essentially opaque, with a pair of apertures which are capable of passing only the ±first-orders of the Fraunhofer diffraction pattern.
Claim 11
Dependent Claim
35 words
A lithography system as defined in claim 2 wherein the spatial filter is essentially transparent, with a vertical opaque stripe of a predetermined width sufficient to intercept the 0-order beam of the Fraunhofer diffraction pattern.
Claim 12
Dependent Claim
72 words
A lithography system as defined in claim 1 wherein the illumination source is chosen from the group consisting of coherent illumination and partially coherent illumination, the illumination source positioned at an oblique angle relative to the optical axis of the lithography system, and the mask containing gratings oriented with the oblique illumination source, the patterns comprising a spatial frequency greater than the coherent cutoff frequency (ξ cc ) of the lithography system.
Claim 13
Dependent Claim
21 words
A lithography system as defined by claim 10 wherein the mask contains both relatively large features (several microns) and grating patterns.
Claim 14
Dependent Claim
119 words
In a projection lithography system, a method of increasing the system resolution, the method comprising the steps of: a) providing a mask containing a series of lines and spaces, defined as a pattern, to be formed on a wafer surface; and b) illuminating the mask provided in step a), the illumination forming a Fraunhofer diffraction pattern in Fourier transform plane of said mask, the Fraunhofer diffraction pattern consisting of a 0-order, ±first-order and a plurality of higher-order beams; CHARACTERIZED IN THAT the method further comprises the step of: c) filtering the Fraunhofer diffraction pattern in the Fourier transform plane so as to remove a central portion of the Fraunhofer diffraction pattern prior to said pattern reaching the wafer surface.
Claim 15
Dependent Claim
119 words
In a projection lithography system, a method of increasing the system resolution, the method comprising the steps of: a) providing a mask containing a series of lines and spaces, defined as a pattern, to be formed on a wafer surface; and b) illuminating the mask provided in step a), the illumination forming a Fraunhofer diffraction pattern in Fourier transform plane of said mask, the Fraunhofer diffraction pattern consisting of a 0-order, ±first-order and a plurality of higher-order beams; CHARACTERIZED IN THAT the method further comprises the step of: c) filtering the Fraunhofer diffraction pattern in the Fourier transform plane so as to remove a central portion of the Fraunhofer diffraction pattern prior to said pattern reaching the wafer surface.
Claim 16
Dependent Claim
21 words
The method of claim 12 wherein in performing step b), the filtering removes the 0-order beam of the Fraunhofer diffraction pattern.
Claim 17
Dependent Claim
25 words
The method of claim 12 wherein performing step b), the filtering removes the 0-order and the plurality of higher-order beams of the Fraunhofer diffraction pattern.
Claim 18
Dependent Claim
36 words
The method of claim 12 wherein in performing step a), the mask contains a plurality of different patterns chosen from the group consisting of grating structures, grid structures, concentric circle structures, and Fresnel zone plate structures.
Claim 19
Dependent Claim
21 words
The method of claim 15 wherein the group of grating structures comprises gratings of different periods, phase-shifted gratings, and chirped gratings.
Claim 20
Dependent Claim
25 words
The method of claim 12 wherein in performing step b), the illumination is chosen from the group consisting of coherent illumination and partially coherent illumination.
Claim 21
Dependent Claim
22 words
The method of claim 17 wherein the coherent illumination is chosen from the group consisting of x-ray, visible, UV, near-UV and deep-UV.
Claim 22
Dependent Claim
54 words
The method of claim 17 wherein the performing step b), the illumination source is located along the optical axis of the lithography system and in performing step c), the filtering removes the 0-order beam of Fraunhofer diffraction pattern, wherein the removal of the 0-order beam results in doubling the resolution of the lithography system.
Claim 23
Dependent Claim
85 words
The method of claim 17 wherein in performing step b), the illumination source is positioned at an oblique angle relative to the optical axis of the lithography system, in performing step a), the mask contains a pattern with a spatial frequency greater than the coherent cutoff frequency of the lithography system, the patterns oriented to be aligned with the oblique illumination source, and in performing step c), the filtering allows the 0-order and a first-order beam to pass through and interfere at the wafer surface.
References Cited (Backward Citations)
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