CN115437223A - Calibration method and article manufacturing method - Google Patents

Calibration method and article manufacturing method Download PDF

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Publication number
CN115437223A
CN115437223A CN202210595578.0A CN202210595578A CN115437223A CN 115437223 A CN115437223 A CN 115437223A CN 202210595578 A CN202210595578 A CN 202210595578A CN 115437223 A CN115437223 A CN 115437223A
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China
Prior art keywords
optical system
projection optical
intensity distribution
light intensity
illumination
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CN202210595578.0A
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Chinese (zh)
Inventor
茂泉纯
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Canon Inc
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Canon Inc
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Publication of CN115437223A publication Critical patent/CN115437223A/en
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • 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
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70216—Mask projection systems
    • G03F7/70308—Optical correction elements, filters or phase plates for manipulating imaging light, e.g. intensity, wavelength, polarisation, phase or image shift
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • 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
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/7085—Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • 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
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70591—Testing optical components
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • 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
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70605—Workpiece metrology
    • G03F7/70616—Monitoring the printed patterns
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • 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
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/70858—Environment aspects, e.g. pressure of beam-path gas, temperature
    • G03F7/70883—Environment aspects, e.g. pressure of beam-path gas, temperature of optical system
    • G03F7/70891—Temperature
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
    • H01L21/0271—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers
    • H01L21/0273—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers characterised by the treatment of photoresist layers
    • H01L21/0274—Photolithographic processes

Abstract

The invention relates to a calibration method and an article manufacturing method. Provided is a correction method for correcting optical characteristics of a projection optical system in an exposure apparatus which illuminates a mask with an illumination optical system and projects a pattern of the mask onto a substrate with the projection optical system. The correction method comprises the following steps: a measurement step of measuring optical characteristics of the projection optical system by forming a light intensity distribution A on a pupil plane of the illumination optical system; and a correction step of forming a light intensity distribution B different from the light intensity distribution A on a pupil plane of the illumination optical system, and heating the projection optical system to correct the optical characteristics of the projection optical system, wherein in the correction step, the irradiation condition of the light intensity distribution B when the projection optical system is heated by the light intensity distribution B is determined based on the measurement result in the measurement step, and the projection optical system is heated under the determined irradiation condition of the light intensity distribution B to correct the optical characteristics of the projection optical system.

Description

Calibration method and article manufacturing method
Technical Field
The invention relates to a calibration method and an article manufacturing method.
Background
In a NAND process in a semiconductor process in recent years, a thick film process in which a resist having a thickness of several μm is exposed to form a step of a Word Line Pad (WLP) is mainly used. In the thick film process, the exposure amount at the time of exposure tends to increase because the resist is thick. In the case of a scanner, due to the rectangular slit, a non-rotationally symmetric heat distribution is generated in the projection optical system by exposure, and a non-rotationally symmetric exposure aberration (hereinafter referred to as "exposure astigmatism") is generated. A conventional exposure apparatus irradiates a pupil plane of a projection optical system with infrared light to form a thermal distribution that cancels exposure astigmatism, thereby correcting the exposure astigmatism (patent document 1). Further, electrodes are formed on the lens on the pupil plane of the projection optical system, so that the lens can have an arbitrary thermal distribution, and exposure astigmatism is corrected by controlling the electrodes (patent document 2). These are expensive due to the need to construct special hardware in the projection optical system. As an inexpensive alternative means for correcting exposure astigmatism, a method has also been proposed in which a diffractive optical element is formed on an object surface of a projection optical system, and the diffractive optical element is illuminated to correct exposure astigmatism of the projection optical system (patent document 3).
In this way, dummy (dummy) irradiation (dummy exposure) is performed to correct variation in optical characteristics of the projection optical system. In addition, dummy irradiation may be performed for the purpose of stabilizing the transmittance of the projection optical system.
Documents of the prior art
Patent literature
Patent document 1: japanese patent laid-open No. 2007-317847
Patent document 2: japanese patent laid-open No. 2008-118135
Patent document 3: japanese patent laid-open No. 2001-250761
Disclosure of Invention
Conventionally, as described in patent document 3, a dedicated reticle (reticle) is used for the dummy irradiation. However, the provision of a dedicated reticle leads to an increase in cost, and the time and effort required to replace the reticle when performing the dummy irradiation also increases. On the other hand, correction of optical characteristics of a projection optical system by virtual irradiation without using a dedicated reticle is required to be further highly accurate.
The present invention provides a technique advantageous for improving the accuracy of correction of optical characteristics of a projection optical system by virtual illumination.
According to the 1 st aspect of the present invention, there is provided a correction method for correcting an optical characteristic of a projection optical system in an exposure apparatus which illuminates a mask with an illumination optical system and projects a pattern of the mask onto a substrate with the projection optical system, the correction method comprising: a measuring step of measuring an optical characteristic of the projection optical system by forming a light intensity distribution a on a pupil plane of the illumination optical system; and a correction step of forming a light intensity distribution B different from the light intensity distribution a on a pupil plane of the illumination optical system and heating the projection optical system to correct the optical characteristics of the projection optical system, wherein in the correction step, an irradiation condition of the light intensity distribution B when the projection optical system is heated by the light intensity distribution B is determined based on a measurement result in the measurement step, and the projection optical system is heated under the determined irradiation condition of the light intensity distribution B to correct the optical characteristics of the projection optical system.
According to the 2 nd aspect of the present invention, there is provided an article manufacturing method comprising: a step of correcting the optical characteristics of the projection optical system by using the correction method according to the above-mentioned aspect 1; a step of illuminating a mask by an illumination optical system, and projecting a pattern of the mask onto a substrate by the corrected projection optical system to expose the substrate; and developing the exposed substrate, wherein an article is manufactured from the developed substrate.
According to the present invention, it is possible to provide a technique advantageous for reducing the time and effort required for replacement of a reticle or the like when performing dummy irradiation, or for reducing the cost involved in the dummy irradiation.
Drawings
Fig. 1 is a diagram showing the structure of an exposure apparatus.
Fig. 2 is a diagram showing a relationship between a focal point and a light amount at the time of aerial image measurement.
Fig. 3 is a diagram showing the wavefront aberration of the Z12 term of the Zernike polynomial (Zernike).
Fig. 4 is a diagram showing a non-rotationally symmetric effective light source distribution used in virtual illumination.
Fig. 5 is a diagram showing the amount of astigmatism fluctuation of the projection optical system based on virtual illumination for each measurement illumination NA.
Fig. 6 is a graph showing a result of fitting the astigmatism fluctuation amount of the projection optical system based on the virtual irradiation for each measurement illumination NA.
Fig. 7 is a flowchart illustrating an exposure method.
(symbol description)
1: an exposure device; 101: a light source; 102: an illumination optical system; 103: a diffractive optical element; 104: a reticle; 106: a reticle stage; 107: a projection optical system; 110: a wafer; 111: wafer mounting table
Detailed Description
Hereinafter, the embodiments will be described in detail with reference to the drawings. The invention according to the claims is not limited to the following embodiments. In the embodiments, a plurality of features are described, but these plurality of features are not necessarily all essential to the invention, and a plurality of features may be arbitrarily combined. In the drawings, the same or similar components are denoted by the same reference numerals, and redundant description thereof is omitted.
< embodiment 1 >
Fig. 1 is a diagram illustrating a structure of an exposure apparatus 1 in the embodiment. In the present specification and the drawings, directions are indicated in an XYZ coordinate system in which a horizontal plane is an XY plane. Generally, a wafer 110 as a substrate to be exposed is placed on a wafer stage 111 such that the surface thereof is parallel to a horizontal plane (XY plane). Therefore, directions orthogonal to each other in a plane along the surface of the wafer 110 are hereinafter referred to as X-axis and Y-axis, and a direction perpendicular to the X-axis and Y-axis is hereinafter referred to as Z-axis. Hereinafter, directions parallel to the X, Y, and Z axes in the XYZ coordinate system are referred to as the X, Y, and Z directions, and a rotation direction around the X axis, a rotation direction around the Y axis, and a rotation direction around the Z axis are referred to as the θ X, θ Y, and θ Z directions, respectively.
Light emitted from the light source 101 enters the illumination optical system 102, forms a desired effective light source distribution by the diffractive optical element 103, and is irradiated onto the reticle 104 (mask, original plate). Thereby, the pattern drawn on the reticle 104 is reduced and projected onto the wafer 110 by the projection optical system 107, and is exposed. The reticle 104 is held by a reticle stage 106, and the reticle stage 106 can be scan-driven in the Y direction. The wafer stage 111 holding the wafer 110 can be scan-driven in the direction opposite to the direction in which the reticle stage 106 is scan-driven at the time of exposure. After the exposure is completed, the wafer stage 111 is driven in steps for exposure for the next imaging. The control unit 100 controls each unit of the exposure apparatus as a whole. The control section 100 may be constituted by a computer device including a processor and a memory.
In the present embodiment, the diffractive optical element 103 is disposed on a surface conjugate to the reticle 104 as an illuminated surface (image surface) or a surface in a fourier transform relationship with the pupil surface of the illumination optical system 102. The diffractive optical element 103 converts the light intensity distribution of the light beam from the light source 101 by diffraction action on a predetermined surface such as a pupil surface of the illumination optical system 102, which is a surface conjugate to the pupil surface of the projection optical system 107, or a surface conjugate thereto, to form a desired light intensity distribution. In the diffractive optical element 103, a Computer Generated Hologram (CGH) designed by a Computer so as to obtain a desired diffraction pattern on the diffraction pattern surface may be used. The light source shape formed on the pupil plane of the projection optical system 107 is referred to as an "effective light source shape". In the present specification, the term "effective light source" refers to a light intensity distribution or an angular distribution of light on an illuminated surface and a conjugate surface thereof. In one example, the diffractive optical element 103 may be a diffractive optical element selected from a plurality of diffractive optical elements that convert light beams from the light source 101 into different light intensity distributions, respectively. Each of the plurality of diffractive optical elements is mounted in, for example, a plurality of slots of a turret (not shown). The plurality of diffractive optical elements can form different effective light source shapes, respectively. The plurality of diffractive optical elements may include diffractive optical elements for anamorphic illumination during exposure. Depending on the effective source shape of the anamorphic illumination, the illumination mode names small σ illumination, large σ illumination, girdle illumination, dipole illumination, quadrupole illumination, and the like. In the present embodiment, the diffractive optical element 103 further includes a diffractive optical element that forms an effective light source shape for adjusting optical characteristics of the projection optical system 107, which is used in a virtual irradiation step described later.
A reticle reference flat plate 105 different from the reticle 104 is formed on the reticle stage 106, and a reticle-side mark 113 for aerial image measurement is arranged on the reticle reference flat plate 105. The reticle-side mark 113 may be a pattern of lines and spaces (lines and spaces) that are periodically arranged. Further, a wafer reference plate 112 is formed on the wafer stage 111, and a wafer side mark 114 for measuring an aerial image is arranged on the wafer reference plate 112. The wafer-side mark 114 may be a pattern of lines and spaces that is the same as the pitch (pitch) of the pattern of lines and spaces of the reticle-side mark 113. Further, a photodetector 115 is formed below the wafer reference flat plate 112.
The lines of reticle side marks 113, wafer side marks 114 and the lines of the pattern of gaps may be chrome and the gaps may be made of glass. The reticle stage 103 is driven and stopped in the Y direction so as to scan, and light emitted from the light source 101 is irradiated to the reticle-side mark 113 on the reticle reference flat plate 105 via the illumination optical system 102. The light that has passed through the reticle-side mark 113 of the reticle reference plate 105 reaches the wafer-side mark 114 on the wafer reference plate 112 via the projection optical system 107. The light that arrives passes through the wafer side mark 114 on the wafer reference flat 112, and reaches the photodetector 115.
(aerial image measurement)
Next, a measurement method of measuring astigmatism, which is an optical characteristic of the projection optical system 107, is explained. As the measurement method, aerial image measurement may be employed. The reticle reference plate is irradiated with light emitted from the light source 101 via the illumination optical system 102, and the reticle side mark 113 is reduced and projected onto the wafer side mark 114 via the projection optical system 107. The wafer stage 111 is driven to scan in the Z direction which is the same as the optical axis direction in a reduced projection state. At the best focus position of the projection optical system 107 in the scan drive, the reduced projected image of the reticle-side mark 113 overlaps the wafer-side mark 114, so the amount of light received by the photodetector 115 becomes maximum. When the focus is out of the optimum focus, the contrast of the image of the reticle-side mark 113 after the reduction projection is lowered and blurred on the wafer-side mark 114 on the wafer reference plate 112, and therefore the amount of light received by the photodetector 115 gradually decreases.
Fig. 2 shows a focus curve when the wafer stage 111 is driven to scan in the Z direction with the best focus therebetween in a state where the reticle-side mark 113 is reduced and projected onto the wafer-side mark 114. When the horizontal axis represents the focal point and the vertical axis represents the light amount of the photodetector 115, the curve is convex upward, and the peak position of the curve is set as the optimum focal point (BF). The method of obtaining the best focus position is an example, and the best focus position may be obtained by other methods.
In order to measure astigmatism, lines and spaces in the X direction and lines and spaces in the Y direction are formed in the reticle-side mark 113 and the wafer-side mark 114. The controller 100 projects the reticle-side mark 113 on the wafer-side mark 114 with the line and the gap in the X direction and the Y direction reduced. In this state, the control unit 100 scans and drives the wafer stage 111 in the Z direction within a range including the optimal focal point for both the line and the gap in the X direction and the Y direction. Then, the control unit 100 obtains the focal curves of the lines and the gaps in the X direction and the Y direction by the scanning driving. The control unit 100 can calculate the optimum focus from the peak positions of the obtained focus curves of the line and the gap in the X direction and the Y direction, respectively, obtain the difference between the calculated optimum focus of the line and the gap in the X direction and the Y direction, and obtain the astigmatism.
Next, when astigmatism of a high order is present in the projection optical system 107, when the astigmatism is measured by the aerial image measurement described above, the measured value of the astigmatism differs depending on the condition of illumination (hereinafter referred to as "measurement illumination") for irradiating the reticle-side mark 113. Due to the light irradiating reticle-side mark 113, 0-order and ± 1-order diffracted lights scatter in accordance with the pitch of the line and the space of reticle-side mark 113. The size and position of the diffracted light on the pupil plane vary depending on the pitch between the lines and spaces of the reticle-side marks 113 and the NA and σ of the measurement illumination. As an example, a case where the projection optical system 107 has a wavefront aberration of the Z12 term of the Zernike polynomial (Zernike) as shown in fig. 3 is considered. The size and position of the light diffracted at the line and space of the reticle-side mark 113 vary on the pupil plane of the projection optical system 107 according to NA and σ of the measurement illumination, and the influence of the wavefront aberration possessed by the projection optical system 107 differs. As a result, astigmatism measured in the aerial image differs depending on NA and σ of the measurement illumination.
(virtual irradiation step)
Next, the virtual irradiation step in the present embodiment will be described. The virtual irradiation step is an adjustment step of irradiating the projection optical system 107 with light so as to adjust the optical characteristics of the projection optical system 107. In the present embodiment, after the adjustment process, an exposure process of exposing the wafer 110 by projecting the pattern of the reticle 104 onto the wafer 110 via the projection optical system 107 may be performed.
In the virtual irradiation step, the 1 st light intensity distribution for adjustment is formed on the pupil plane of the illumination optical system 102 by the diffractive optical element 103. Thereby, a 2 nd light intensity distribution in accordance with the 1 st light intensity distribution is formed on the pupil surface of the projection optical system 107. In the virtual irradiation step of the present embodiment, the 2 nd light intensity distribution is formed on the pupil surface of the projection optical system 107 without using an optical element (such as a reticle dedicated for virtual irradiation) arranged on the object surface of the projection optical system 107. In one example, the reticle reference plate 105 has a mark region where a mark for aerial image measurement is formed and a pixel glass region where no pattern is placed. In this case, in order to form the 2 nd light intensity distribution in the virtual irradiation step, the reticle 104 used in the exposure step is not disposed on the object surface of the projection optical system 107, but a mother glass region of the reticle reference plate 105 is disposed, and the transmission of the measurement light through the mother glass region is measured. In another example, nothing may be disposed on the object surface of the projection optical system 107 in order to form the 2 nd light intensity distribution in the virtual irradiation step. In this case, the light applied to the projection optical system 107 passes through the opening of the object surface of the projection optical system 107. This can be achieved by forming the mark region and an opening for allowing light to pass through on the reticle reference plate 105, and disposing the opening on the object plane of the projection optical system 107 in the virtual irradiation step. Specific examples are described below.
The light emitted from the light source 101 passes through the diffractive optical element 103 in the illumination optical system 102, and forms an effective light source distribution (1 st light intensity distribution) as shown in fig. 4 a or 4 b on the pupil plane of the illumination optical system 102. As described above, the diffractive optical element 103 includes a plurality of diffractive optical elements each having a different effective light source shape, and each of the diffractive optical elements is mounted in a plurality of slots of a turntable, not shown, for example. In the present embodiment, the plurality of diffractive optical elements may include a diffractive optical element for adjustment for forming an effective light source distribution as shown in fig. 4 (a) and a diffractive optical element for adjustment for forming an effective light source distribution as shown in fig. 4 (b). When performing the dummy irradiation, a diffractive optical element for adjustment is selected from the turntable, and the selected diffractive optical element is inserted into the optical path between the light source 101 and the reticle 104. As a result, an effective light source distribution (1 st light intensity distribution) as shown in fig. 4 (a) or 4 (b) is formed on the pupil plane of the illumination optical system 102. As described above, a diffractive optical element for anamorphic illumination is also mounted on the turntable. In exposure after the virtual irradiation step, the turntable is controlled so that the diffractive optical element for adjustment used in the virtual irradiation step is retracted from the optical path and the diffractive optical element for anamorphic illumination is inserted into the optical path.
The dotted lines shown in fig. 4 (a) and 4 (b) indicate σ =1, and the white region has light intensity. The generated light of the effective light source distribution (1 st light intensity distribution) reaches the reticle stage 103 via the illumination optical system 102, and a 2 nd light intensity distribution in accordance with the 1 st light intensity distribution is formed on the pupil plane of the projection optical system 107.
In the present embodiment, since the diffractive optical element for adjustment as described above is used, it is not necessary to prepare a reticle for virtual irradiation. That is, in the virtual irradiation step (adjustment step), the 2 nd light intensity distribution is formed on the pupil plane of the projection optical system 107 without using an optical element arranged on the object plane of the projection optical system 107. Therefore, according to the present embodiment, the time and effort required for replacement of the reticle or the like when performing the dummy irradiation can be reduced. Alternatively, since it is not necessary to prepare such a dedicated optical element, the cost for the dummy irradiation can be reduced.
Therefore, in the virtual irradiation step of the present embodiment, the light emitted from the illumination optical system 102 is directly incident on the projection optical system 107 without passing through the reticle 104 on the reticle stage 103. At this time, the reticle 104 may be detached from the reticle stage 103, or the reticle stage 103 on which the reticle 104 is mounted may be driven so as to be retracted from the optical path.
The light incident on the projection optical system 107 is irradiated to an NA stop 108 disposed inside the projection optical system 107 so that the light does not reach the wafer 110. That is, the dummy irradiation step of the present embodiment may be performed in a state where light does not reach the substrate. This is because, when dummy exposure is performed in a state where a wafer is placed on the wafer stage 111, the wafer is exposed to light and cannot be used as a product. When light incident on the projection optical system 107 enters a lens group constituting the projection optical system 107, the lens is heated by the material absorption of the lens and the film absorption of the antireflection film, and the refractive index of the lens changes, thereby generating wavefront aberration. For example, when the effective light source distribution as shown in fig. 4 (a) is generated by the diffractive optical element 103 and made incident on the projection optical system 107, the wavefront aberration of the projection optical system 107 caused by the nitre absorption of the lens and the film absorption of the antireflection film becomes a high-order wavefront aberration as shown in fig. 3. This high-order wavefront aberration is referred to as "high-order astigmatism".
(determination of conditions for virtual irradiation in the virtual irradiation step)
When high-order astigmatism occurs in the projection optical system due to virtual irradiation based on the non-rotationally symmetric effective light source distribution, the amount of fluctuation of the astigmatism of the projection optical system to be measured may be different depending on the illumination condition under which the measurement is performed. Therefore, the relationship of the fluctuation amount of the astigmatism of the projection optical system based on the virtual irradiation may be obtained in advance for each illumination condition when the astigmatism of the projection optical system is measured. However, since the number of illumination conditions that can be obtained in measurement is enormous, it takes time to obtain a relationship of the amount of fluctuation of the astigmatism of the projection optical system by the virtual irradiation for all the illumination conditions, which is not practical, and productivity is also reduced.
Therefore, in the present embodiment, the measurement of the variation amount of the optical characteristic (astigmatism) before and after the virtual irradiation (light irradiation) during the predetermined irradiation time is performed a plurality of times under mutually different measurement illumination conditions (measurement step). The measurement illumination condition may be an illumination condition used in exposure in the exposure process. Next, fitting of a function depending on the parameters of the measurement illumination conditions is performed on the information of the fluctuation amount of the optical characteristics before and after the light irradiation under each measurement illumination condition obtained in the measurement step (fitting step). Then, the conditions for the virtual irradiation in the virtual irradiation step are determined based on the fitted function (determination step).
Next, a process of obtaining the relationship of the astigmatism fluctuation amount of the projection optical system 107 with respect to the virtual irradiation will be described. The state of the projection optical system 107 before the virtual irradiation is performed is preferably a cooling state. The cooling state means that the projection optical system 107 is familiar with the ambient temperature surrounding the projection optical system 107 without exposing and virtually irradiating the lens group in the projection optical system 107. First, astigmatism of the projection optical system 107 before virtual irradiation is measured under an arbitrary measurement illumination condition. The astigmatism measurement value is set to AS0. The measurement illumination forms an effective light source distribution a that can be generated by the diffractive optical element 103 configured within the illumination optical system 102, which is different from the effective light source distribution B used in the virtual illumination. The diffractive optical element 103 in the illumination optical system 102 can be switched between a case of using it for virtual illumination and a case of measuring astigmatism of the projection optical system 107. For example, a diffractive optical element for virtual irradiation and a diffractive optical element for astigmatism measurement may be mounted on the turntable, and the turntable may be controlled so as to switch the diffractive optical elements at the time of virtual irradiation and at the time of measurement.
Next, the virtual irradiation is performed for a time T with the effective light source distribution as shown in fig. 4 (a). The wavefront aberration of the projection optical system 107 after the virtual irradiation becomes astigmatism having a high order as shown in fig. 3. Next, after the virtual irradiation, astigmatism of the projection optical system 107 is measured under the arbitrary measurement illumination condition described above. The astigmatism measurement value is set AS1. AS shown in equation (1), the difference between the astigmatism measurement value AS0 of the projection optical system 107 before virtual irradiation and the astigmatism measurement value AS1 of the projection optical system 107 after virtual irradiation under the above-described arbitrary measurement illumination condition is divided by the virtual irradiation time T. Thereby, the amount of astigmatism variation (Coef) of the projection optical system 107 based on the virtual irradiation is calculated. Here, the astigmatism of the projection optical system 107 is measured immediately after the virtual irradiation to obtain the astigmatism fluctuation amount, but this is merely an example. For example, astigmatism of the projection optical system 107 may be measured every elapsed time after the virtual irradiation, temporal characteristics of the energy of the virtual irradiation and the measured astigmatism of the plurality of projection optical systems 107 may be modeled, and an amount of fluctuation of the astigmatism of the projection optical system 107 based on the virtual irradiation may be obtained.
Coef＝(AS1-AS0)/T (1)
Next, in the present embodiment, the astigmatism fluctuation amount of the projection optical system 107 by the virtual irradiation described above is acquired for 4 measurement illumination conditions with different NA. For example, the 4 different measured illuminations NA are 0.55, 0.65, 0.75, 0.86. In fig. 5, the amount of astigmatism variation of the projection optical system 107 based on the virtual illumination under each measurement illumination condition is shown. In fig. 5, the abscissa axis represents the measurement illumination NA, and the ordinate axis represents the amount of astigmatism variation of the projection optical system 107 by the virtual illumination. Here, astigmatism of the projection optical system 107 before and after the virtual irradiation is performed with the virtual irradiation time T set to 5 seconds is measured, and a variation amount of astigmatism of the projection optical system 107 by the virtual irradiation under each measurement illumination condition is obtained by equation (1). Here, when the amount of fluctuation of astigmatism of the projection optical system 107 by the virtual illumination is negative, it means that the best focus of the X pattern of the reticle-side mark 113 on the reticle reference plate 105 exists in a direction away from the projection optical system 107. In addition, when the amount of astigmatism variation is negative, it means that the best focus of the Y pattern of the reticle-side mark 113 on the reticle reference plate 105 exists in a direction close to the projection optical system 107.
Next, the functionalization of the astigmatism variation amount of the projection optical system 107 by the virtual irradiation obtained for each measurement illumination condition and the parameter depending on the measurement illumination condition will be described. The astigmatism fluctuation amounts of the projection optical system 107 based on the virtual illumination of the aforementioned 4 different measurement illuminations NA are set to Coef1, coef2, coef3, and Coef4. In addition, the parameter for measuring the illumination condition is set as the measurement illumination NA. The control unit 100 fits astigmatism fluctuation amounts Coef1, coef2, coef3, and Coef4 of the projection optical system 107 based on the virtual irradiation with a polynomial function (for example, a 2-order function) depending on the measurement illumination NA as a parameter of the measurement illumination condition as shown in equation (2). The function to be fitted as shown in formula (2) is an example, and other functions may be used. In equation (2), coef is the amount of astigmatism variation of the projection optical system 107 based on the virtual illumination, NA is the measurement illumination NA, α is a coefficient proportional to the square of the measurement illumination NA, β is a coefficient proportional to the measurement illumination NA, const is a constant independent of the measurement illumination NA. Here, fitting is performed by a function depending on the measurement illumination NA, but a function using information of the effective light source in addition to the measurement illumination NA may be used.
Coef＝α·NA 2 +β·NA+Const (2)
Fig. 6 shows the results of the fitting. Fig. 6 shows a graph of the amount of astigmatism fluctuation for the measurement illumination NA, as in fig. 5. That is, the abscissa represents the measurement illumination NA, and the ordinate represents the amount of astigmatism variation of the projection optical system 107 by the virtual irradiation. In fig. 6, the dots indicate the astigmatism fluctuation amounts of the projection optical system 107 by the virtual irradiation, which are obtained under the 4 measurement illuminations NA in fig. 5. In fig. 6, the dotted line indicates the result of fitting the polynomial expression (2) to the astigmatism fluctuation amount of the projection optical system 107 by the virtual irradiation acquired under the 4 measurement illuminations NA. The coefficients α, β, and the constant Const obtained here may be stored in, for example, a memory in the control unit 100, and set as parameters of the exposure apparatus 1. The control unit 100 can predict the amount of astigmatism variation of the projection optical system 107 based on the virtual irradiation of an arbitrary measurement illumination NA using these parameters.
(Exposure method)
The exposure method in the present embodiment will be described with reference to the flowchart of fig. 7. Fig. 7 shows an example of performing virtual irradiation between lots. In the exposure method, the "exposure operation" refers to, for example, an operation related to a series of exposures in 1 lot (for example, 25 wafers).
First, before starting the exposure operation, the control unit 100 measures astigmatism of the projection optical system 107 in step S1. Next, in step S2, the control unit 100 determines whether or not the measured astigmatism of the projection optical system 107 is larger than a predetermined threshold value. If the astigmatism is larger than the threshold value, the process proceeds to step S3.
In step S3, the control unit 100 predicts the amount of astigmatism variation of the projection optical system 107 based on the virtual illumination using the measurement illumination NA set in the exposure operation. In this prediction, the measured illumination NA set in the exposure operation, and the coefficient α, the coefficient β, and the constant Const which are obtained in advance by the above-described processing and stored in the memory may be used. That is, the prediction is performed based on the fitted function described above. Then, the control unit 100 sets the conditions for light irradiation in the dummy irradiation step based on the predicted amount of fluctuation in astigmatism and the astigmatism of the projection optical system 107 measured in step S1. The condition of the light irradiation in the virtual irradiation step may be an irradiation time (virtual irradiation time) or an irradiation amount (virtual irradiation amount) of the light irradiation in the virtual irradiation step.
Thereafter, in step S4, the control unit 100 executes the virtual irradiation under the conditions determined in step S3. This can reduce astigmatism of the projection optical system 107.
When it is determined that the astigmatism is equal to or less than the threshold value in step S2 or after the completion of the virtual irradiation step in step S4, the control unit 100 starts the exposure operation (exposure step) in step S5. Thereafter, in step S6, the control unit 100 ends the exposure operation.
As described above, according to the exposure method of the present embodiment, the conditions of the dummy irradiation step are determined using the function fitted in advance, and therefore, the method is advantageous in terms of productivity. After the virtual irradiation in step S4 is performed, a measurement step for checking whether or not astigmatism of the projection optical system 107 is reduced may be performed. When the desired reduction in astigmatism of the projection optical system 107 is not obtained by the virtual irradiation in step S4, the conditions for the virtual irradiation may be changed and the virtual irradiation may be performed again. In the above-described exposure method, the dummy irradiation is performed between the lots, but the dummy irradiation may be performed within the lots.
< embodiment of method for producing article >
The method for manufacturing an article according to the embodiment of the present invention is suitable for manufacturing articles such as micro devices such as semiconductor devices and devices having a microstructure, for example. The method for manufacturing an article according to the present embodiment includes a step of forming a latent image pattern in a photosensitive agent applied to a substrate (a step of exposing the substrate) using the exposure apparatus, and a step of developing the substrate after the latent image pattern is formed in the step. The above-described manufacturing method includes other known steps (oxidation, film formation, vapor deposition, doping, planarization, etching, resist stripping, dicing, adhesion, packaging, and the like). The method for manufacturing an article according to the present embodiment is more advantageous than conventional methods in at least 1 of the performance, quality, productivity, and production cost of the article.
The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the claims are appended for purposes of disclosing the invention.

Claims (15)

1. A correction method for correcting an optical characteristic of a projection optical system in an exposure apparatus that illuminates a mask with an illumination optical system and projects a pattern of the mask onto a substrate with the projection optical system, comprising:
a measuring step of measuring an optical characteristic of the projection optical system by forming a light intensity distribution a on a pupil plane of the illumination optical system; and
a correction step of forming a light intensity distribution B different from the light intensity distribution A on a pupil plane of the illumination optical system, and heating the projection optical system to correct the optical characteristics of the projection optical system,
in the above-mentioned correction process, the correction process,
determining, based on the measurement result in the measurement step, an irradiation condition of the light intensity distribution B when the projection optical system is heated by the light intensity distribution B, and heating the projection optical system under the determined irradiation condition of the light intensity distribution B to correct an optical characteristic of the projection optical system.
2. The correction method according to claim 1,
the irradiation conditions of the light intensity distribution B are determined using the values of the parameters of the light intensity distribution a.
3. The correction method according to claim 1,
the amount of fluctuation of the optical characteristics of the projection optical system, which is caused by heating the projection optical system with the light intensity distribution B, is calculated using the value of the parameter of the light intensity distribution a, and the irradiation conditions of the light intensity distribution B are determined based on the calculated amount of fluctuation.
4. The correction method according to claim 3,
the amount of fluctuation of the optical characteristics of the projection optical system, which is caused by heating the projection optical system with the light intensity distribution B, is calculated from a correlation between the amount of fluctuation and a value of a parameter of the light intensity distribution at the pupil plane of the illumination optical system.
5. The correction method according to claim 4,
the correlation is obtained by using a measurement result obtained by measuring a plurality of times a variation amount of optical characteristics of the projection optical system caused by heating the projection optical system by the light intensity distribution B by setting parameters of the light intensity distribution formed at a pupil plane of the illumination optical system to mutually different values.
6. The correction method according to claim 1,
the light intensity distribution B heats the projection optical system by the projection optical system without passing through an optical element disposed on an object surface of the projection optical system.
7. The correction method according to claim 6,
the optical element has an unpatterned area,
the light irradiated to the projection optical system in the correction process transmits the region.
8. The correction method according to claim 1,
in the correcting step, the light irradiated to the projection optical system passes through an opening of an object surface of the projection optical system.
9. The correction method according to claim 1,
the correction process is performed in a state where light does not reach the substrate.
10. The correction method according to claim 9,
the substrate is set in a state where light does not reach the substrate by using a diaphragm disposed inside the projection optical system.
11. The correction method according to claim 2,
the parameter is at least 1 of NA and information about an effective light source.
12. The correction method according to claim 1,
the light intensity distribution a is an illumination condition used in exposure of the substrate.
13. The correction method according to claim 1,
the irradiation condition is an irradiation time or an irradiation amount.
14. The correction method according to claim 1,
the optical characteristic includes astigmatism.
15. A method of manufacturing an article, comprising:
a step of correcting the optical characteristics of the projection optical system by using the correction method according to claim 1;
a step of illuminating a mask by an illumination optical system, and projecting a pattern of the mask onto a substrate by the corrected projection optical system to expose the substrate; and
a step of developing the substrate after exposure,
wherein an article is manufactured from the developed substrate.
CN202210595578.0A 2021-06-03 2022-05-30 Calibration method and article manufacturing method Pending CN115437223A (en)

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