# US 5,700,601 A · Photomask, manufacture of photomask, formation of pattern, manufacture of semiconductor device, and mask pattern design system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,700,601 A - Document ID: US5700601A - Status: Granted - Kind: A - Application number: 08/495,836 - Filed: 1995-06-28 - Granted: 1997-12-23 - Earliest claimed: 1994-06-29 - Assignees: Hitachi, Ltd. - Inventors: Norio Hasegawa; Tsuneo Terasawa; Hiroshi Fukuda; Katsuya Hayano; Akira Imai; Akemi Moniwa; Shinji Okazaki - Web page: https://patentgrep.com/patent/US5700601A ## CPC - G03F 1/32: Attenuating PSM [att-PSM], e.g. halftone PSM or PSM having semi-transparent phase shift portion,; Preparation thereof - G03F 1/26: Phase shift masks [PSM]; PSM blanks; Preparation thereof - G03F 1/36: Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes - G03F 7/70283: {Mask effects on the imaging process} - G03F 7/70433: {Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors} - G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G) ## Abstract A photomask used for printing a mask pattern by projection optics, in which a main pattern formed of a transparent area is provided in a semitransparent area formed of a semitransparent film and a phase shifter, and the phase angles of light beams passing through respective areas are different from each other substantially by 180.degree.. The photomask is intended to prevent a reduction in a production yield due to a resolution failure of the photomask, and to prevent generation of an unnecessary projected image. In this photomask, a transparent auxiliary pattern having the same phase angle of light as that of the transparent area is disposed around a main pattern formed of the transparent area, and a distance D between the center or a desired center line of the main pattern and that of the auxiliary pattern satisfies the relationship of D=b.lambda./NAm , where NAm is a mask-side numerical aperture of a projection lens, .lambda. is a wavelength of exposure light, and <b> is a coefficient in the range of 1.35<b.ltoreq.1.9. ## Claims ### Claim 1 A photomask comprising a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of a light beam passing therethrough as that of a light beam passing through said transparent area is disposed around a main pattern formed of said transparent area, and a distance D between the center or a desired center line of said main pattern and that of said auxiliary pattern satisfies the relationship of D =b.lambda./NAm , where NAm is a mask-side numerical aperture of a projection lens, A is a wavelength of exposure light, and <b> is a coefficient in the range of 1.35 <b.ltoreq.1.9. ### Claim 2 (depends on 1) A photomask according to claim 1, wherein said main pattern is formed in a circular shape, and said auxiliary pattern is formed in an annular shape. ### Claim 3 (depends on 1) A photomask according to claim 1, wherein the width of said auxiliary pattern is expressed by the relationship of b.lambda./NAm, where NAm is a mask-side numerical aperture of a projection lens, .lambda. is a wavelength of exposure light, and <b'> is a coefficient in the range of 0.07.ltoreq.b'.ltoreq.0.25. ### Claim 4 A photomask comprising a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of a light beam passing therethrough as that of a light beam passing through said transparent area is disposed around a main pattern formed of said transparent area, and said auxiliary pattern is provided on an area of said photomask corresponding to an area of the projected main pattern which is located outwardly from an intermediate point between a first sub-peak and a second sub-peak generated around said projected main pattern and inwardly from said second sub-peak. ### Claim 5 (depends on 4) A photomask according to claim 4, wherein said main pattern is formed in a circular shape, and said auxiliary pattern is formed in an annular shape. ### Claim 6 (depends on 4) A photomask according to claim 4, wherein the width of said auxiliary pattern is expressed by the relationship of b'.lambda./NAm, where NAm is a mask-side numerical aperture of a projection lens, .lambda. is a wavelength of exposure light, and <b'> is a coefficient in the range of 0.07.ltoreq.b'.ltoreq.0.25. ### Claim 7 A method of forming a pattern comprising the steps of: (a) preparing a photomask, said photomask including a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of a light beam passing therethrough as that of a light beam passing through said transparent area is disposed around a main pattern formed of said transparent area, and a distance D between the center or a desired center line of said main pattern and that of said auxiliary pattern satisfies the relationship of D =b.lambda./NAm , where NAm is a mask-side numerical aperture of a projection lens, .lambda. is a wavelength of exposure light, and <b> is a coefficient in the range of 1.35 <b.ltoreq.1.9; (b) exposing a thin film made of a photoresist formed on a substrate using said photomask by projection optics; and (c) forming a pattern by development. ### Claim 8 (depends on 7) A method of forming a pattern according to claim 7, wherein said exposure is performed under a condition that a coherence factor .sigma. of said projection optics satisfies the relationship of .sigma..ltoreq.0.3. ### Claim 9 A method of forming a pattern comprising the steps of: (a) preparing a photomask, said photomask including a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of a light beam passing therethrough as that of a light beam passing through said transparent area is disposed around a main pattern formed of said transparent area, and said auxiliary pattern is provided on an area of said photomask corresponding to an area of the projected main pattern which is located outwardly from an intermediate point between a first sub-peak and a second sub-peak generated around said projected main pattern and inwardly from said second sub-peak; (b) exposing a thin film made of a photoresist formed on a substrate using said photomask by projection optics; and (c) forming a pattern by development. ### Claim 10 (depends on 9) A method of forming a pattern according to claim 9, wherein said exposure is performed under a condition that a coherence factor .sigma. of said projection optics satisfies the relationship of .sigma..ltoreq.0.3. ### Claim 11 A photomask comprising a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of light as that of said main pattern and having a dimension being a resolution limit of projection optics or less is disposed at an area of said photomask corresponding to a position where interference light beams from different two sides of a main pattern formed of said transparent area overlap each other. ### Claim 12 (depends on 11) A photomask according to claim 11, wherein the center of said auxiliary pattern is located at a position in which a distance D from said two sides of said main pattern satisfies the relationship of D=d.lambda./NAm, where NAm is a mask-side numerical aperture of a projection lens, .lambda. is a wavelength of exposure light, and <d> is a coefficient in the range of 0.4.ltoreq.d.ltoreq.0.7. ### Claim 13 A photomask comprising a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein at least two main patterns each being formed of said transparent area are disposed, and one or a plurality of transparent auxiliary patterns having the same phase angle of light as that of said main pattern and having a dimension being a resolution limit of projection optics or less is disposed at a position in which a distance S from the centers of said two main patterns satisfies the relationship of S=s.lambda./NAm, where NAm is a mask-side numerical aperture of a projection lens, .lambda. is a wavelength of exposure light, and <s> is a coefficient in the range of 0.8.ltoreq.s.ltoreq.1.1. ### Claim 14 A photomask comprising a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein at least two main patterns each being formed of said transparent area are disposed, and one or a plurality of transparent auxiliary patterns having the same phase angle of light as that of said main pattern and having a dimension being a resolution limit of projection optics or less is disposed at a position of said photomask corresponding to a position where first sub-peaks around main peaks of the projected main patterns are overlapped to each other. ### Claim 15 A photomask comprising a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein at least two main patterns each being formed of said transparent area are disposed, and one or a plurality of transparent auxiliary patterns having the same phase angle of light as that of said main pattern and having a dimension being a resolution limit of projection optics or less is disposed at a position of said photomask corresponding to a position where diffraction light beams from said main patterns are overlapped to each other at the same phase angle. ### Claim 16 A method of forming a pattern comprising the steps of: (a) preparing a photomask, said photomask including a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of light as that of a main pattern is disposed at an area where an angle formed by intersections of desired two sides or extension lines thereof of said main pattern formed of said transparent area is less than 180.degree. in said semitransparent area; (b) exposing a photoresist formed on a substrate by projection optics using said photomask; and (c) forming a pattern by development. ### Claim 17 A method of forming a pattern comprising the steps of: (a) preparing a photomask, said photomask including a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of light as that of a main pattern and having a dimension being a resolution limit of projection optics or less is disposed at an area of said photomask corresponding to a position where interference light beams from different two sides of said main pattern formed of said transparent area overlap each other; (b) exposing a photoresist formed on a substrate by projection optics using said photomask; and (c) forming a pattern by development. ### Claim 18 A method of forming a pattern comprising the steps of: (a) preparing a photomask, said photomask including a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein at least two main patterns each being formed of said transparent area are disposed, and a transparent auxiliary pattern having the same phase angle of light as that of said main pattern and having a dimension being a resolution limit of projection optics or less is disposed at a position in which a distance S from the centers of said two main patterns satisfies the relationship of S=s.lambda./NAm, where NAm is a mask-side numerical aperture of a projection lens, .lambda. is a wavelength of exposure light, and <s> is a coefficient in the range of 0.8.ltoreq.s.ltoreq.1.1; (b) exposing a photoresist formed on a substrate by projection optics using said photomask; and (c) forming a pattern by development. ### Claim 19 A method of forming a pattern comprising the steps of: (a) preparing a photomask, said photomask including a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein at least two main patterns each being formed of said transparent area are disposed, and a transparent auxiliary pattern having the same phase angle of light as that of said main pattern and having a dimension being a resolution limit of projection optics or less is disposed at a position of said photomask corresponding to a position where first sub-peaks around main peaks of the projected main patterns are overlapped to each other; (b) exposing a photoresist formed on a substrate by projection optics using said photomask; and (c) forming a pattern by development. ### Claim 20 A method of forming a pattern comprising the steps of: (a) preparing a photomask, said photomask including a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein at least two main patterns each being formed of said transparent area are disposed, and a transparent auxiliary pattern having the same phase angle of light as that of said main pattern and having a dimension being a resolution limit of projection optics or less is disposed at a position of said photomask corresponding to a position where diffraction light beams from said main patterns are overlapped to each other at the same phase angle; (b) exposing a photoresist formed on a substrate by projection optics using said photomask; and (c) forming a pattern by development. ### Claim 21 A method of forming a pattern of a photomask comprising a semitransparent area and a transparent area for at least exposure light, in which a phase angle of a light beam passing through said semitransparent area is different from a phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having a same phase angle of a light beam passing therethrough as that of a light beam passing through said transparent area is disposed around a main pattern formed of said transparent area, comprising the steps of: (a) determining said auxiliary pattern of the photomask used for pattern printing by projection optics using a mask pattern design system, said process of determining said auxiliary pattern comprising the steps of: (1) calculating, on the basis of data of at least two of the main patterns formed in said photomask and parameters representing an optical condition of said projection optics, a light intensity distribution of a projected image of said main pattern obtained by said projection optics, (2) determining an area where a light intensity is more than a specified value, excluding an area corresponding to said main pattern, on the basis of said light intensity distribution of the projected image and said main patterns, and (3) determining one or a plurality of auxiliary patterns on an area of said photomask corresponding to said area where the light intensity is more than said specified value when said area is determined, and (b) forming said main pattern and said determined auxiliary patterns on said photomask; and (c) projecting and exposing a pattern by projection optics using said photomask formed with said main pattern and said determined auxiliary patterns. ### Claim 22 A method of forming a pattern of a photomask comprising a semitransparent area and a transparent area for at least exposure light, in which the phase angle of a light beam passing through said semitransparent area is different from the phase angle of a light beam passing through said transparent area substantially by 180.degree., wherein a transparent auxiliary pattern having the same phase angle of a light beam passing therethrough as that of a light beam passing through said transparent area is disposed around a main pattern formed of said transparent area, comprising the steps of: (a) determining said auxiliary pattern of the photomask used for pattern printing by projection optics using a mask pattern design system, said process of determining said auxiliary pattern comprising the steps of: (1) moving, on the basis of data of at least two of the main pattern forming said photomask, an contour line of each of said main patterns outwardly by a specified distance L, thereby determining the enlarged contour line of each of said main patterns, (2) detecting a position where said enlarged contour lines are close to each other at a specified distance M or less, and (3) determining one or a plurality of auxiliary patterns of a specified shape on said position where said enlarged contour lines are close to each other when said position is determined; and (b) forming said main pattern and said determined auxiliary pattern on said photomask; and (c) projecting and exposing a pattern by projection optics using said photomask formed with said main pattern and said determined auxiliary patterns.