EP0267721A2
Expired / Lapsed
EP
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Determination of best focus for step and repeat projection aligners
Assignee: HP Inc
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Filing: 1987-11-02
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Granted: —
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Expires: 2007-11-02
Abstract
Abstract A reticle design is provided for step and repeat projection aligners which, when patterned on a wafer (10), allows quick macroscopic evaluation of best focus for used in fabricating integrated circuits. The reticle pattern consists of opaque lines and spaces of widths slightly above the resolution limit of the resist/aligner system. The macroscopic determination of best focus, being macroscopically visible, eliminates the need for microscopic determination, thereby providing a quick and easy method. The best focus determination is made by forming an array (22) of resist fields (14ʹ) on the wafer, subjecting each field to a different focus and exposure. Upon development, those fields away from the best focus and at the larger exposure doses will be removed, leaving a parabola (24) of fields whose apex (26) is at high exposure. Best focus is the focus setting used to print the row of fields (B) containing the apex. The procedure may be used at different lens locations and reticle orientations to quantify lens aberrations and field tilt. The method of the invention is also suitably used to qualitatively and quantitatively diagnose and characterize the lens, by printing full fields (34) with varying focus. In this manner, lens astigmatism and curvature and field tilt can be mapped, measured, and understood.
Inventors
- 👤 Catherine G. Kroko
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 23:45
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/7055; G03F7/70558; G03F7/70591; G03F7/706; G03F7/70605; G03F7/70616; G03F7/70641; G03F9/00; G03F9/70; G03F9/7003; G03F9/7023; G03F9/7026
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
86 words
A method for determining best focus of a projection aligner from a focus/exposure matrix, comprising (1) exposing a two-dimensional matrix of resist fields on a polished side of a flat surface of a wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and spaces of widths slightly above the resolution limit of the resist/aligner system and (2) determining the focus value of the apex of the resulting parabola, which is said best focus.
Claim 2
Independent Claim
86 words
A method for determining best focus of a projection aligner from a focus/exposure matrix, comprising (1) exposing a two-dimensional matrix of resist fields on a polished side of a flat surface of a wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and spaces of widths slightly above the resolution limit of the resist/aligner system and (2) determining the focus value of the apex of the resulting parabola, which is said best focus.
Claim 3
Dependent Claim
16 words
The method of Claim 1 wherein said parabola is made obvious by developing the resist pattern.
Claim 4
Dependent Claim
21 words
The method of Claim 1 wherein said apex is on a row of constant focus and best focus is that value.
Claim 5
Dependent Claim
26 words
The method of Claim 1 wherein said apex is between two rows of constant focus, and best focus is obtained by interpolating between said two rows.
Claim 6
Dependent Claim
51 words
A reticle design for use in step and repeat projection aligners which, when patterned in a resist layer on a wafer, allows quick macroscopic evaluation of best focus, said reticle design comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system.
Claim 7
Dependent Claim
51 words
A reticle design for use in step and repeat projection aligners which, when patterned in a resist layer on a wafer, allows quick macroscopic evaluation of best focus, said reticle design comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system.
Claim 8
Dependent Claim
19 words
The reticle design of Claim 5 wherein said widths range from about 1 to 25% above said resolution limit.
Claim 9
Dependent Claim
11 words
The reticle design of Claim 5 wherein said lines comprise chrome.
Claim 10
Dependent Claim
43 words
The reticle design of Claim 5 wherein said lines are of a width to provide line widths on said wafer from about 1.2 µm and less and spacing of said lines on said wafer from about 1.0 µm and less at nominal exposure.
Claim 11
Independent Claim
153 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify aberrations and tilt thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating the measurement at other locations on the lens, by masking the reticle to a field size smaller than the full field and desired lens locations, on additional wafers, whereby any difference in best focus across the field indicates the presence of at least one of aberrations and tilt.
Claim 12
Independent Claim
153 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify aberrations and tilt thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating the measurement at other locations on the lens, by masking the reticle to a field size smaller than the full field and desired lens locations, on additional wafers, whereby any difference in best focus across the field indicates the presence of at least one of aberrations and tilt.
Claim 13
Independent Claim
152 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify lens tilt thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating these steps at at least five locations on the field by masking the reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of lens tilt may be extracted by looking for linear variations in the best focus values across the lens.
Claim 14
Independent Claim
152 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify lens tilt thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating these steps at at least five locations on the field by masking the reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of lens tilt may be extracted by looking for linear variations in the best focus values across the lens.
Claim 15
Independent Claim
158 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify field curvature thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating these steps at at least five locations on the field by masking the reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of field curvature may be extracted by looking for second order variations, after removing the linear components, in the best focus values across the lens.
Claim 16
Independent Claim
158 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify field curvature thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating these steps at at least five locations on the field by masking the reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of field curvature may be extracted by looking for second order variations, after removing the linear components, in the best focus values across the lens.
Claim 17
Independent Claim
172 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify astigmatism thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating the foregoing steps with the reticle aligned in different orientations to supply information about sagittal and tangential components, (5) repeating the foregoing steps at different locations on the lens by masking the reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of astigmatism at any lens location is determined by the difference between best focus in two orthogonal directions, sagittal and tangential.
Claim 18
Independent Claim
172 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner to quantify astigmatism thereof comprising: (1) forming a two-dimensional matrix of resist fields on a polished side of a flat wafer by varying exposure in one dimension and varying focus in the other, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist to obtain a parabolic pattern, the apex of which is at high exposure, (3) determining the focus value of the apex, which is the best focus, (4) repeating the foregoing steps with the reticle aligned in different orientations to supply information about sagittal and tangential components, (5) repeating the foregoing steps at different locations on the lens by masking the reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of astigmatism at any lens location is determined by the difference between best focus in two orthogonal directions, sagittal and tangential.
Claim 19
Independent Claim
195 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner by viewing the whole field simultaneously to quantify aberrations and tilt thereof comprising: (1) forming a matrix of maximum-sized resist fields on a polished side of a flat wafer by varying exposure and keeping focus constant, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist, (3) determining the best focus for any location as the center of the fields having resist present at that location, (4) repeating the determination at all desired locations, (5) exposing additional wafers for all reticle orientations desired and repeating the best focus determination, (6) comparing the various best focus values obtained, whereby astigmatism is determined by the difference in best focus at any location between best focus for sagittal and tangential lines resulting from reticle orientations and whereby tilt is determined as the linear component of the variation in average of sagittal and tangential best focus across the lens and whereby field curvature is determined by any second order variation remaining after removal of the linear component.
Claim 20
Independent Claim
195 words
A method of diagnosing and characterizing a lens in a step and repeat projection aligner by viewing the whole field simultaneously to quantify aberrations and tilt thereof comprising: (1) forming a matrix of maximum-sized resist fields on a polished side of a flat wafer by varying exposure and keeping focus constant, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above the resolution limit of the resist/aligner system, (2) developing the resist, (3) determining the best focus for any location as the center of the fields having resist present at that location, (4) repeating the determination at all desired locations, (5) exposing additional wafers for all reticle orientations desired and repeating the best focus determination, (6) comparing the various best focus values obtained, whereby astigmatism is determined by the difference in best focus at any location between best focus for sagittal and tangential lines resulting from reticle orientations and whereby tilt is determined as the linear component of the variation in average of sagittal and tangential best focus across the lens and whereby field curvature is determined by any second order variation remaining after removal of the linear component.
References Cited (Backward Citations)
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