Patent US6329112B1 successfully refreshed from Google Patents.
US6329112B1
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Method for measuring aberration of projection lens, method for forming patterns, mask, and method for correcting a projection lens
Assignee: Hitachi Ltd
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Filing: 1999-11-12
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Granted: 2001-12-11
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Expires: 2019-11-12
Abstract
Abstract Optical systems of projection exposure apparatuses may have aberrations, and this fact may hamper the achievement of predetermined accuracy of dimensions and position of a circuit pattern which is necessary to attain desired device performance. Further, because of the difficulty in measuring the above-described aberrations, it was not possible to correct the optical system so as to realize a substantially aberration-free characteristic.The aberrations of a projection lens can be found accurately by steps of: measuring the light intensities of a projected image of a particular pattern on a mask at n different points in the projected image; and solving n simultaneous equations with m (m<n) unknown weighting coefficients for m known wavefront aberration functions. Based on the aberrations thus found, one can adjust aberration characteristic of the projection lens or correct dimensions and positions of patterns on a mask instead.By means of this method, the performance of semiconductor integrated circuit equipment can be improved. Further, the yield of semiconductor integrated circuits in the manufacturing process with this equipment can be improved.
Inventors
- 👤 Hiroshi Fukuda
- 👤 Seiichiro Shirai
- 👤 Tsuneo Terasawa
- 👤 Katsuya Hayano
- 👤 Norio Hasegawa
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 01:46
CPC Classifications
G; G01; G01M; G01M11/00; G01M11/02; G01M11/0242; G01M11/0257; G01M11/0264; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/70591; G03F7/706
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
118 words
A method for determining aberrations of a projection lens which is used to project a pattern formed on a mask onto a body, comprising the steps of: measuring light intensities of a projected image of a test pattern at different points in said projected image, said test pattern being located within an isoplanatic area of said projection lens on said mask; and finding m aberration coefficients by solving n simultaneous equations (m being an integer not larger than n) having said m aberration coefficients, wherein y(y=m) weighting coefficients in said simultaneous equations are treated as unknown for z(z=m) known wavefront aberration functions in said simultaneous equations, and said simultaneous equations include the result of said measuring light intensities.
Claim 2
Independent Claim
118 words
A method for determining aberrations of a projection lens which is used to project a pattern formed on a mask onto a body, comprising the steps of: measuring light intensities of a projected image of a test pattern at different points in said projected image, said test pattern being located within an isoplanatic area of said projection lens on said mask; and finding m aberration coefficients by solving n simultaneous equations (m being an integer not larger than n) having said m aberration coefficients, wherein y(y=m) weighting coefficients in said simultaneous equations are treated as unknown for z(z=m) known wavefront aberration functions in said simultaneous equations, and said simultaneous equations include the result of said measuring light intensities.
Claim 3
Dependent Claim
50 words
A method for determining aberrations of a projection lens according to claim 1 , wherein said mask used for determining said aberrations is an attenuating phase-shifting mask, and said light intensities are light intensities of sidelobes that emerge in a portion of said projected image of said attenuating phase-shifting mask.
Claim 4
Dependent Claim
30 words
A method for determining aberrations of a projection lens according to claim 1 , wherein said solving n simultaneous equations determines third- and fifth-order coma aberrations of said projection lens.
Claim 5
Dependent Claim
31 words
A method for determining aberrations of a projection lens according to claim 1 , wherein said different points are placed at symmetric points of the projected image of the test pattern.
Claim 6
Dependent Claim
163 words
A method for determining aberrations of a projection lens according to claim 1 , wherein said mask used for determining said aberrations is an attenuating phase-shifting mask, said test pattern is a pattern containing x-pairs of edges which are parallel and symmetric to each other, the step of measuring said light intensities of said projected image includes processes of: transferring the pattern containing said x-pairs of edges on said mask onto a resist film formed on said body with different amounts of exposure through said projection lens; and measuring said amounts of exposure at which a sidelobe emerges at the vicinity of said each pair of edges of said projected image of said test pattern, on respective sides of an attenuating phase-shifting light shielding portion of said projected image, and said m aberration coefficients are found by solving n simultaneous equations using ratios, each of which is calculated from said amounts of exposure which were obtained for each of said x-pairs of edges.
Claim 7
Dependent Claim
295 words
A method for determining aberrations of a projection lens according to claim 5 , wherein said x-pairs of edges which are parallel and symmetric to each other are respective pairs of opposed sides of an octagonal opening located in an attenuating phase-shifting partially light-shielding portion of said mask, and wherein four coma aberration coefficients a1, a2, a3, and a4 of said projection lens are found by steps of: measuring the amount of exposure g at which a sidelobe emerges at one side of each pair of said opposed sides of said projected image of said octagonal opening in a direction normal to said opposed sides (θ=0, P/4, P/2, 3P/4) and the amount of exposure h at which sidelobes emerge at both sides of each pair of said opposed sides of said projected image, for four pairs of said opposed sides of said projected image; calculating the ratio r(θ) of h to g, for the four pairs of said opposed sides of said projected image, to find the maximum value of the wavefront aberrations f(θ) thereby for each direction (θ=0, P/4, P/2, 3P/4), respectively; and then solving the following simultaneous equations, a1w1 ( θ ) + a2w2 ( θ ) + a3w3 ( θ ) + a4w4 ( θ ) = f ( θ ) ( θ = 0 , P / 4 , P / 2 , 3 P / 4 ) wherein w1 ( θ ) = cos ( θ ) , w2 ( θ ) = sin ( θ ) , w3 ( θ ) = cos ( θ ) , w4 ( θ ) = sin ( θ ) .
Claim 8
Dependent Claim
47 words
A method for forming patterns, wherein said patterns are formed by use of said projection lens whose aberration characteristic was adjusted based on the amounts of aberrations which were determined by the method for determining aberrations of a projection lens as set forth in claim 1 .
Claim 9
Dependent Claim
68 words
A method for forming patterns, comprising the steps of: determining aberrations of said projection lens by the method as set forth in claim 1 ; adjusting said projection lens based on said determination of said aberrations, leaving residual aberrations; estimating influence of said residual aberrations; correcting said mask so as to counterbalance said influence, so as to form a corrected mask; and forming patterns using said corrected mask.
Claim 10
Dependent Claim
57 words
A corrected mask produced by a process comprising the steps of: determining aberrations of said projection lens by the method as set forth in claim 1 ; adjusting said projection lens based on said determination of said aberrations, leaving residual aberrations; estimating influence of said residual aberrations; and correcting said mask so as to counterbalance said influence.
Claim 11
Dependent Claim
22 words
A method for determining aberrations of a projection lens according to claim 1 , wherein said test pattern has an octagonal opening.
Claim 12
Independent Claim
125 words
A method for correcting a projection lens which is used to project a pattern formed on a mask onto a body, comprising the steps of: measuring light intensities of a projected image of a test pattern at different points in said projected image, said test pattern being located within an isoplanatic area of said projection lens on said mask; finding m aberration coefficients by solving n simultaneous equations (m being an integer not larger than n) having said m aberration coefficients, wherein y(y=m) weighting coefficients in said simultaneous equations are treated as unknown for z(z=m) known wavefront aberration functions in said simultaneous equations, and said simultaneous equations include the result of said measuring light intensities; and adjusting said projection lens based on said aberration coefficients.
Claim 13
Independent Claim
125 words
A method for correcting a projection lens which is used to project a pattern formed on a mask onto a body, comprising the steps of: measuring light intensities of a projected image of a test pattern at different points in said projected image, said test pattern being located within an isoplanatic area of said projection lens on said mask; finding m aberration coefficients by solving n simultaneous equations (m being an integer not larger than n) having said m aberration coefficients, wherein y(y=m) weighting coefficients in said simultaneous equations are treated as unknown for z(z=m) known wavefront aberration functions in said simultaneous equations, and said simultaneous equations include the result of said measuring light intensities; and adjusting said projection lens based on said aberration coefficients.
Claim 14
Dependent Claim
20 words
A method for correcting a projection lens according to claim 11 , wherein said test pattern has an octagonal opening.
Claim 15
Independent Claim
109 words
A method for determining aberrations of a projection lens which is used to project a pattern formed on a mask onto a body, comprising the steps of: measuring light intensities of a projected image of a test pattern at different points in said projected image, said test pattern having an octagonal opening, said test pattern being located within an isoplanatic area of said projection lens on said mask; and finding m aberration coefficients by solving n simultaneous equations (m being an integer not larger than n) having said m aberration coefficients for m known wavefront aberration functions, and said simultaneous equations include the result of said measuring light intensities.
Claim 16
Independent Claim
109 words
A method for determining aberrations of a projection lens which is used to project a pattern formed on a mask onto a body, comprising the steps of: measuring light intensities of a projected image of a test pattern at different points in said projected image, said test pattern having an octagonal opening, said test pattern being located within an isoplanatic area of said projection lens on said mask; and finding m aberration coefficients by solving n simultaneous equations (m being an integer not larger than n) having said m aberration coefficients for m known wavefront aberration functions, and said simultaneous equations include the result of said measuring light intensities.
References Cited (Backward Citations)
US6130747A
Cited
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