(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2002/0041377 A1
`(43) Pub. Date:
`Apr. 11, 2002
`Hagiwara et al.
`
`US 20020041377A1
`
`(54) AERIAL IMAGE MEASUREMENT METHOD
`AND UNIT, OPTICAL PROPERTIES
`MEASUREMENT METHOD AND UNIT,
`ADJUSTMENT METHOD OF PROJECTION
`OPTICAL SYSTEM, EXPOSURE METHOD
`AND APPARATUS, MAKING METHOD OF
`EXPOSURE APPARATUS, AND DEVICE
`MANUFACTURING METHOD
`
`(75) Inventors: Tsuneyuki Hagiwara, Tokyo (JP);
`Naoto Kondo, Tokyo (JP); Eiji
`Takane, Tokyo (JP); Hiromi Kuwata,
`Fukaya-shi (JP); Kousuke Suzuki,
`Tokyo (JP)
`
`Correspondence Address:
`OBLON SPIVAK MCCLELLAND MAIER &
`NEUSTADT PC
`FOURTH FLOOR
`1755 JEFFERSON DAVIS HIGHWAY
`ARLINGTON, VA 22202 (US)
`
`(73) Assignee: Nikon Corporation, Tokyo J (JP)
`
`(21) Appl. No.:
`
`09/841,044
`
`(22) Filed:
`
`Apr. 25, 2001
`
`(30)
`
`Foreign Application Priority Data
`
`2000-123553
`Apr. 25, 2000 (JP)
`2000-216868
`Jul. 18, 2000 (JP)
`Dec. 27, 2000 (JP) .................................... .. 2000-398444
`
`Publication Classi?cation
`
`(51) Int. Cl? ................................................... .. G01B 11/26
`(52) Us. 01. ............................................................ ..356/399
`
`(57)
`
`ABSTRACT
`
`The exposure apparatus comprises a mark plate on Which a
`plurality of types of measurement marks each used for
`self-measurement are formed, a reticle stage on Which the
`mark plate is mounted, and an aerial image measurement
`unit. On a slit plate of the aerial image measurement unit, a
`slit is formed extending in the non-scanning direction Which
`Width in the measurement direction is equal to and under
`(Wavelength )t/numerical aperture N.A of the projection
`optical system). Therefore, in a state Where a predetermined
`pattern is illuminated With the illumination light to form an
`aerial image of the pattern via the projection optical system,
`and When the slit plate is scanned in the measurement
`direction With respect to the aerial image, the light having
`passed through the slit during the scanning is photo-electri
`cally converted With the photoelectric conversion element.
`And, based on the photoelectric conversion signal, the
`control unit measures the light intensity corresponding to the
`aerial image With a suf?ciently high accuracy in practical
`usage. In addition, various self-measurements become pos
`sible, by moving the reticle stage so as to position the
`plurality of types of measurement marks respectively in the
`vicinity of a focal position on the object side of the projec
`tion optical system.
`
`1%
`
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`Nikon Exhibit 1024 Page 1
`
`

`

`Patent Application Publication Apr. 11, 2002 Sheet 1 0f 38
`
`US 2002/0041377 A1
`
`Fig. 1
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`MAIN
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`Nikon Exhibit 1024 Page 2
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`

`

`Patent Application Publication Apr. 11, 2002 Sheet 2 0f 38
`
`US 2002/0041377 A1
`
`Fig. 2
`
`Nikon Exhibit 1024 Page 3
`
`

`

`Patent Application Publication Apr. 11, 2002 Sheet 3 0f 38
`
`US 2002/0041377 A1
`
`Fig. 3
`
`Nikon Exhibit 1024 Page 4
`
`

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`Patent Application Publication Apr. 11, 2002 Sheet 4 0f 38
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`Patent Application Publication Apr. 11, 2002 Sheet 6 0f 38
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`Patent Application Publication Apr. 11, 2002 Sheet 7 0f 38
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`US 2002/0041377 A1
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`Nikon Exhibit 1024 Page 8
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`Patent Application Publication Apr. 11, 2002 Sheet 8 0f 38
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`Nikon Exhibit 1024 Page 9
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`Patent Application Publication Apr. 11, 2002 Sheet 9 0f 38
`
`US 2002/0041377 A1
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`Fig. 9A
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`Nikon Exhibit 1024 Page 10
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`Patent Application Publication Apr. 11, 2002 Sheet 10 0f 38 US 2002/0041377 A1
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`Fig. 10
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`Nikon Exhibit 1024 Page 11
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`

`

`Patent Application Publication Apr. 11, 2002 Sheet 11 0f 38
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`Fig.1]
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`Patent Application Publication Apr. 11, 2002 Sheet 12 0f 38 US 2002/0041377 A1
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`Fig. 13
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`Nikon Exhibit 1024 Page 13
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`

`Patent Application Publication Apr. 11, 2002 Sheet 13 0f 38 US 2002/0041377 A1
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`Fig. 15
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`Patent Application Publication Apr. 11, 2002 Sheet 14 0f 38
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`US 2002/0041377 A1
`
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`Patent Application Publication Apr. 11, 2002 Sheet 15 0f 38 US 2002/0041377 A1
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`Nikon Exhibit 1024 Page 16
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`Patent Application Publication Apr. 11, 2002 Sheet 16 0f 38 US 2002/0041377 Al
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`Patent Application Publication Apr. 11, 2002 Sheet 17 0f 38 US 2002/0041377 A1
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`Nikon Exhibit 1024 Page 18
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`Patent Application Publication Apr. 11, 2002 Sheet 18 0f 38 US 2002/0041377 A1
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`Patent Application Publication Apr. 11, 2002 Sheet 19 0f 38 US 2002/0041377 Al
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`Patent Application Publication
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`Apr. 11,2002 Sheet 20 0f 38
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`US 2002/0041377 A1
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`Exhibit 1024
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`Page 21
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`Nikon Exhibit 1024 Page 21
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`Patent Application Publication Apr. 11, 2002 Sheet 21 0f 38
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`US 2002/0041377 A1
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`Fig. 27
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`Page 22
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`Nikon Exhibit 1024 Page 22
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`Patent Application Publication Apr. 11, 2002 Sheet 22 0f 38
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`
`Fig. 28
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`Nikon Exhibit 1024 Page 23
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`Patent Application Publication Apr. 11, 2002 Sheet 23 0f 38
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`US 2002/0041377 A1
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`Fig. 30
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`Nikon Exhibit 1024 Page 24
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`Patent Application Publication Apr. 11, 2002 Sheet 24 0f 38
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`US 2002/0041377 A1
`
`Fig.31
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`Nikon
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`Exhibit1024
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`Page 25
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`Nikon Exhibit 1024 Page 25
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`

`

`Patent Application Publication Apr. 11, 2002 Sheet 25 0f 38
`
`US 2002/0041377 A1
`
`Fig.32
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`Exhibit1024
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`Page 26
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`Nikon Exhibit 1024 Page 26
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`Patent Application Publication Apr. 11, 2002 Sheet 26 0f 38
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`Nikon Exhibit 1024 Page 27
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`Patent Application Publication Apr. 11, 2002 Sheet 27 0f 38
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`US 2002/0041377 A1
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`Nikon Exhibit 1024 Page 28
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`Patent Application Publication Apr. 11, 2002 Sheet 28 0f 38
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`Nikon
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`Page 29
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`Nikon Exhibit 1024 Page 29
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`Patent Application Publication Apr. 11, 2002 Sheet 29 0f 38
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`US 2002/0041377 A1
`
`Fig. 36A
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`Nikon Exhibit 1024 Page 30
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`Patent Application Publication Apr. 11, 2002 Sheet 30 0f 38
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`US 2002/0041377 A1
`
`Fig. 37A
`
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`
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`Exhibit 1024
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`Page 31
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`Nikon Exhibit 1024 Page 31
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`
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`

`

`Patent Application Publication Apr. 11, 2002 Sheet 31 0f 38
`
`US 2002/0041377 Al
`
`(SIGNAL INTENSITY)
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`Nikon
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`Exhibit 1024
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`Page 32
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`Nikon Exhibit 1024 Page 32
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`Patent Application Publication Apr. 11, 2002 Sheet 32 0f 38
`
`US 2002/0041377 A1
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`Fig. 39
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`Exhibit1024
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`Page 33
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`Nikon Exhibit 1024 Page 33
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`

`

`Patent Application Publication Apr. 11, 2002 Sheet 33 0f 38
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`US 2002/0041377 A1
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`Fig. 40
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`Exhibit1024
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`Page 34
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`Nikon Exhibit 1024 Page 34
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`Patent Application Publication Apr. 11, 2002 Sheet 34 0f 38
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`US 2002/0041377 A1
`
`Fig. 41
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`Nikon Exhibit 1024 Page 35
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`Patent Application Publication Apr. 11, 2002 Sheet 35 0f 38
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`US 2002/0041377 A1
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`Fig. 42A
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`Nikon Exhibit 1024 Page 36
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`Patent Application Publication Apr. 11, 2002 Sheet 36 0f 38
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`US 2002/0041377 A1
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`Fig. 43
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`
`202
`
`204
`
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`Nikon
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`Nikon Exhibit 1024 Page 37
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`Patent Application Publication Apr. 11, 2002 Sheet 37 0f 38
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`US 2002/0041377 A1
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`Fig. 44
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`Nikon
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`Page 38
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`Nikon Exhibit 1024 Page 38
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`Patent Application Publication Apr. 11, 2002 Sheet 38 0f 38
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`US 2002/0041377 A1
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`Fig. 45A
`
`PRIOR ART
`
`
`
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`PRIOR ART
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`(DIFFERENTIALVALUEOFTHESIGNAL
`
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`
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`
`Nikon
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`Page 39
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`Nikon Exhibit 1024 Page 39
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`

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`US 2002/0041377 A1
`
`Apr. 11, 2002
`
`AERIAL IMAGE MEASUREMENT METHOD AND
`UNIT, OPTICAL PROPERTIES MEASUREMENT
`METHOD AND UNIT, ADJUSTMENT METHOD OF
`PROJECTION OPTICAL SYSTEM, EXPOSURE
`METHOD AND APPARATUS, MAKING METHOD
`OF EXPOSURE APPARATUS, AND DEVICE
`MANUFACTURING METHOD
`
`BACKGROUND OF THE INVENTION
`
`[0001]
`
`1. Field of the Invention
`
`[0002] The present invention relates to an aerial image
`measurement method and unit, an optical properties mea-
`surement method and unit, an adjustment method of a
`projection optical system, an exposure method and appara-
`tus, a making method of the exposure apparatus, and a
`device manufacturing method. More particularly, the present
`invention relates to an aerial image measurement method
`and an aerial image measurement unit that measure an aerial
`image formed on an image plane by a projection optical
`system, an optical properties measurement method and an
`optical properties measurement unit that measure the optical
`properties of the projection optical system utilizing the aerial
`image measurement method, an adjustment method to adjust
`the projection optical system based on the measurement
`results of the optical properties measured by the optical
`properties measurement method, an exposure apparatus that
`comprises the aerial image measurement unit and an expo-
`sure method that uses the projection optical system which
`optical properties is adjusted by the adjustment method, a
`making method of the exposure apparatus that include the
`process of measuring the optical properties of the projection
`optical system by the optical properties measurement
`method, and a device manufacturing method that uses the
`exposure apparatus.
`
`[0003]
`
`2. Description of the Related Art
`
`[0004] When devices such as a semiconductor device or a
`liquid crystal display device are conventionally manufac-
`tured in a photolithographic process, a projection exposure
`apparatus that transfers a pattern of a photomask or a reticle
`(hereinafter generally referred to as a “reticle”) onto a
`substrate such as a wafer on which a photosensitive agent
`such as a photoresist is coated on the surface via a projection
`optical system is used. The reduction projection exposure
`apparatus (generally referred to as a stepper) based on the
`step-and-repeat method, or the scanning projection exposure
`apparatus (generally referred to as a scanning stepper) based
`on the step-and-scan method are examples of such a pro-
`jection exposure apparatus.
`
`In the case of manufacturing devices such as a
`[0005]
`semiconductor, it is necessary to overlay and form many
`layers of different circuit patterns on a substrate. Therefore,
`it is important to precisely overlay the reticle on which the
`circuit pattern is drawn with the pattern already formed on
`each shot area of the substrate. In order to perform such a
`precise overlay, it is a mandatory for the image forming
`characteristics of the projection optical system to be adjusted
`to a desired state.
`
`[0006] As a premise of adjusting the image forming char-
`acteristics of the projection optical system, the image form-
`ing characteristics have to be precisely measured. And as the
`measurement method of the image forming characteristics,
`
`the method is mainly used (hereinafter referred to as the
`“exposing method”) where exposure is performed using a
`reticle for measurement on which marks (mark patterns) for
`a predetermined measurement are formed, and the image
`forming characteristics is calculated based on measurement
`results of measuring a resist image, which is obtained by
`developing the substrate on which the projected image of the
`measurement marks is transferred and formed. Other than
`
`the method to calculate the image forming
`this method,
`characteristics based on measurement results of measuring
`an aerial
`image (projection image) of the measurement
`marks formed by the projection optical system by illumi-
`nating the reticle for measurement with the illumination
`light (hereinafter referred to as the “aerial image measure-
`ment method”) is also used.
`
`[0007] The conventional aerial image measurement was
`generally performed in the following manner. That is, for
`example, as is shown in FIG. 45A, an opening plate 123 on
`which a square opening 122 is formed, is arranged on a
`substrate stage. The opening plate 123 is scanned via the
`substrate stage in the direction indicated by the arrow A,
`with respect to the aerial image MP' of the measurement
`marks of the reticle for measurement formed by the projec-
`tion optical system (not shown in FIGS), and the illumina-
`tion light which has passed through the opening 122 is
`photo-detected and photo-electrically converted by a pho-
`toelectric conversion element. With this photoelectric con-
`version, a photoelectric conversion signal (light intensity
`signal corresponding to the aerial image) as is shown in
`FIG. 45B, can be obtained. Next, by differentiating the
`waveform of the photoelectric conversion signal shown in
`FIG. 45B, a differential waveform as is shown in FIG. 45C
`is obtained. And, based on the differential waveform, as is
`shown in FIG. 45C, a well-known predetermined signal
`processing such as the Fourier Transform Method is per-
`formed, and the optical image (aerial image) of the projected
`measurement marks is obtained.
`
`[0008] Details of such measurement of the aerial image
`and the detection of distortion and the like of the projection
`optical system based on this measurement are disclosed, for
`example, in Japanese Patent Laid Open (Unexamined) No.
`10-209031.
`
`[0009] With the conventional aerial image measurement
`method described above, however, since the aerial image
`intensity was measured by scanning a large opening as is
`shown in FIG. 45B, it turned out that a large scale of a
`low-frequency component was mixed with the aerial fre-
`quency component that characterizes the profile of the aerial
`image. On the other hand, the dynamic range of the signal
`processing system arranged on the latter stage of the pho-
`toelectric conversion element is limited, and since the reso-
`lution of the signal processing system to the dynamic range
`is also limited (for example, around 16 bit at the current
`level), the S/N ratio of the signal component which reflects
`the profile of the aerial
`image turned out
`to be small.
`Therefore,
`the conventional aerial
`image measurement
`method was sensitive to noise, and the deterioration of the
`image profile was large when the aerial image was converted
`to the aerial image intensity signal, thus, it was difficult to
`measure the aerial image with a sufficient accuracy.
`
`[0010] Besides this method, conventionally, mainly for the
`purpose of detecting the image forming position of a pattern,
`
`Nikon
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`
`details of a unit having a slit scanned with respect to the
`aerial image of the pattern is disclosed, for example, in
`Japanese Patent Laid Open No. 58-7823, and the like. With
`the unit disclosed in the publication, however, the width of
`the slit was set in correspondence with the shape of the
`reticle pattern (reference pattern). Therefore, it was difficult
`to accurately measure the aerial image of patterns having
`various shapes (including sizes).
`
`In addition, when the optical properties of the
`[0011]
`projection optical system is measured by the aerial image
`measurement, there are cases when the position of the aerial
`image within the plane perpendicular to the optical axis of
`the projection optical system is measured, and the optical
`properties of the projection optical system is calculated
`based on the measurement results. In such a case, however,
`measurement errors caused by the drift of the laser interfer-
`ometer measuring the position of the aerial image measure-
`ment unit and the like sometimes occurred, during the
`measurement.
`
`[0012] With the conventional exposure apparatus, when
`the so-called self-measurement of the optical properties of
`the projection optical system and the like was performed
`using its own aerial image measurement unit or other units,
`a reticle used solely for measurement (hereinafter referred to
`as a “measurement reticle”) on which measurement marks
`are formed was mainly used.
`
`In the case self-measurement was performed using
`[0013]
`the measurement reticle, however, the measurement reticle
`had to be installed each time the measurement was per-
`formed. And particularly with the recent exposure apparatus
`performing various self-measurements, for example, when
`various self-measurements were successively performed,
`the measurement reticle had to be exchanged to a different
`reticle each time a different measurement was performed,
`which made the exchanging operation and the measurement
`reticle management complicated.
`
`In addition, the posture of the measurement reticle
`[0014]
`changed each time the measurement reticle was installed in
`the apparatus, which sometimes caused measurement errors.
`In addition, when measurement reticles were used, since the
`exchanging time of the measurement reticle and the reticle
`used for manufacturing devices under normal operation such
`as during continuous operation led to reducing the through-
`put of the exposure apparatus, it was difficult to frequently
`perform the self-measurement described above.
`
`SUMMARY OF THE INVENTION
`
`[0015] The present invention has been made in consider-
`ation of the circumstances described above, and has as its
`first object to provide an aerial image measurement method
`and an aerial image measurement unit that are capable of
`measuring an aerial image with a sufficient accuracy.
`
`[0016] The second object of the present invention is to
`provide an optical properties measurement method and an
`optical properties measurement unit
`that can accurately
`measure the optical properties of the projection optical
`system.
`
`invention is to
`[0017] The third object of the present
`provide an adjustment method of a projection optical system
`that can adjust the optical properties of the projection optical
`system with high precision.
`
`[0018] The fourth object of the present invention is to
`provide an exposure method and an exposure apparatus that
`contribute to improving the productivity of a device.
`
`invention is to
`[0019] The fifth object of the present
`provide a making method of an exposure apparatus that is
`capable of accurately transferring a pattern onto a substrate.
`
`[0020] And, the sixth object of the present invention is to
`provide a device manufacturing method that can improve the
`productivity of a device.
`
`In general, the resolution (resolving power) R of a
`[0021]
`projection optical system in an exposure apparatus is
`expressed, well known as the Rayleigh criterion, as R=k><
`)L/N.A. ()L is the wavelength of the illumination light, NA.
`is the numerical aperture of the projection optical system,
`and k is a constant determined by the photoresist process
`(the process coefficient) besides the resolution of the resist).
`The inventor (Hagiwara) focused on this point, and from the
`results of performing various experiments and the like,
`discovered that when the width of aperture used in aerial
`image measurement in the scanning direction was set con-
`sidering at least either the illumination light wavelength A or
`the numerical aperture N.A. a favorable result could be
`obtained in aerial image measurement. The aerial image
`measurement method related to the present invention is
`devised based on such new information by the inventor
`(Hagiwara).
`
`[0022] According to the first aspect of this invention, there
`is provided an aerial image measurement method to measure
`an aerial
`image of a predetermined mark formed by a
`projection optical system, the measurement method includ-
`ing: the step of illuminating the mark with an illumination
`light and forming an aerial image of the mark on an image
`plane via the projection optical system; and the step of
`scanning a pattern forming member, which has at least one
`slit-shaped aperture pattern extending in a first direction
`within a two dimensional plane perpendicular to an optical
`axis of the projection optical system which width perpen-
`dicular to the first direction within the two dimensional
`
`plane serving as a second direction is set in consideration of
`at least one of a wavelength A of the illumination light and
`a numerical aperture N.A. of the projection optical system,
`in the second direction within a surface close to the image
`plane parallel to the two dimensional plane, and photo-
`electrically converting the illumination light having passed
`through the aperture pattern and obtaining a photoelectric
`conversion signal which corresponds to an intensity of the
`illumination light having passed through the aperture pat-
`tern.
`
`[0023] With this method, the predetermined mark is illu-
`minated with the illumination light, and the aerial image of
`the mark is formed on the image plane via the projection
`optical system. And, with respect to this aerial image, the
`pattern forming member is scanned in the second direction
`within a surface parallel to the two dimensional plane in the
`vicinity of the image plane. The pattern forming member, in
`this case, has at least one slit-shaped aperture pattern extend-
`ing in the first direction within the two dimensional plane
`perpendicular to the optical axis of the projection optical
`system which width perpendicular to the first direction
`within the two dimensional plane serving as the second
`direction is set in consideration of at least either the wave-
`
`length )» of the illumination light or the numerical aperture
`
`Nikon
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`US 2002/0041377 A1
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`Apr. 11, 2002
`
`N.A. of the projection optical system. Also, the illumination
`light having passed through the aperture pattern is photo-
`electrically converted and the photoconversion signal cor-
`responding to the intensity of the illumination light that has
`passed through the aperture pattern is obtained. And, by
`performing a predetermined process on the photoconversion
`signal, the aerial image (image intensity distribution) can be
`obtained.
`
`[0024] That is, an aerial image of a predetermined pattern
`can be obtained based on the slit-scan method. In this case,
`since the width of the slit-shaped aperture pattern in the
`scanning direction is set with consideration of at least either
`the wavelength of the illumination light or the numerical
`aperture N.A of the projection optical system, it becomes
`possible to measure the aerial image with sufficient accu-
`racy.
`
`In this case, the width of the aperture pattern in the
`[0025]
`second direction may be set only in consideration of either
`the wavelength A of the illumination light or the numerical
`aperture N.A of the projection optical system, or it may be
`set in consideration of both the wavelength A of the illumi-
`nation light and the numerical aperture N.A. of the projec-
`tion optical system. In the latter case, since the width of the
`aperture pattern in the scanning direction is set in consid-
`eration of both the wavelength A and the numerical aperture
`N.A. that are the 2 parameters affecting the resolution, it
`becomes possible to measure the aerial image with more
`accuracy, compared with the former case.
`
`image measurement method
`aerial
`[0026] With the
`according to the present invention, it is preferable for the
`width of the aperture pattern in the second direction to be
`greater than zero, and equal to and under the wavelength of
`the illumination light divided by the numerical aperture N.A.
`of the projection optical system (MNA) The reason for
`setting the width of the aperture pattern in the scanning
`direction equal to and under ()L/N.A.), first of all, is because
`when the inventor (Hagiwara) repeatedly performed simu-
`lations and experiments under the conditions of the width of
`the aperture pattern in the scanning direction (referred to as
`2D) as 2D=f()\./N.A.)=Il’()\./N.A.), favorable results (suffi-
`ciently practical results) were obtained in the case when the
`coefficient was n=1. And, secondly, as will be referred to
`later on, since the photoelectric conversion signal above is
`to become a convolution of the aperture pattern and the
`intensity distribution of the aerial image, from the aspect of
`measurement accuracy, the width of the aperture pattern in
`the scanning direction 2D is better when narrower.
`
`In this case, it is further preferable for the width of
`[0027]
`the aperture pattern in the second direction to be equal to and
`under the ()L/N.A.) multiplied by 0.8. As is mentioned above,
`from the aspect of measurement accuracy, the width of the
`aperture pattern in the scanning direction 2D is better when
`narrower, and according to the simulations and experiments
`performed by the inventor (Hagiwara), it has been confirmed
`that the results are further practical when the width of the
`aperture pattern in the scanning direction 2D is equal to and
`under 80% of the (MNA)
`
`[0028] When considering the limitations from the aspect
`of throughput, however, if the width 2D is too narrow, the
`light intensity of the light having passed through the aperture
`pattern becomes too weak, and difficult to measure, there-
`fore, a width of a certain range is necessary.
`
`image measurement method
`aerial
`[0029] With the
`according to the present invention, the width of the aperture
`pattern in the second direction may be half a minimum pitch
`multiplied by an odd number, the minimum pitch being a
`pitch of a line and space pattern in a limit of resolution set
`by illumination conditions including properties of the illu-
`mination light and the type of the pattern.
`
`In the case of a normal pattern without using the
`[0030]
`phase-shifting method, under the conditions of conventional
`illumination, the minimum pitch referred to above is almost
`equal to )L/N.A. Whereas, in the case of a phase-shifting
`pattern, that is, in the case of a phase-shifting mask (phase-
`shifting reticle) pattern employing the phase-shifting
`method, it is confirmed that the minimum pitch becomes
`almost )L/(ZN.A.). As the phase-shifting mask, the half-tone
`type, or the Levenson type, can be listed.
`
`image measurement method
`aerial
`[0031] With the
`according to the present invention, when a wavelength of the
`illumination light is expressed as hand a numerical aperture
`of the projection optical system is expressed as N.A, the
`width of the aperture pattern in the second direction may be
`set as {)L/(ZN.A.)} multiplied by an odd number.
`
`image measurement method
`aerial
`[0032] With the
`according to the present invention, the measurement method
`can further include the steps of: obtaining a spacial fre-
`quency distribution by performing a Fourier Transform on
`the photoelectric conversion signal; converting the spacial
`frequency distribution into a spectrum distribution of its
`original aerial
`image by dividing the spacial frequency
`distribution with a frequency spectrum of the aperture
`pattern that is already known; and recovering the original
`aerial image by performing an inverse Fourier Transform on
`the spectrum distribution.
`
`[0033] According to the second aspect of this invention,
`there is provided a first optical properties measurement
`method to measure optical properties of a projection optical
`system,
`the measurement method including:
`the step of
`illuminating a predetermined mark with an illumination light
`and forming an aerial image of the mark on an image plane
`via the projection optical system;
`the step of scanning a
`pattern forming member, which has at least one slit-shaped
`aperture pattern with a predetermined slit width extending in
`a first direction within a two dimensional plane perpendicu-
`lar to an optical axis of the projection optical system, within
`a surface close to the image plane parallel
`to the two
`dimensional plane in a second direction which is perpen-
`dicular to the first direction, and photo-electrically convert-
`ing the illumination light having passed through the aperture
`pattern and obtaining a photoelectric conversion signal
`which corresponds to an intensity of the illumination light
`having passed through the aperture pattern; and the step of
`obtaining optical properties of the projection optical system
`based on the photoelectric conversion signal.
`
`[0034] With this method, the predetermined mark is illu-
`minated with the illumination light, and the aerial image of
`the mark is formed on the image plane via the projection
`optical system. In this state, the pattern forming member is
`scanned within a surface close to the image plane parallel to
`the two dimensional plane in the second direction which is
`perpendicular to the first direction, and the illumination light
`having passed through the aperture pattern is photo-electri-
`cally converted and the photoelectric conversion signal
`
`Nikon
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`Exhibit1024
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`Page 42
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`Nikon Exhibit 1024 Page 42
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`US 2002/0041377 A1
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`Apr. 11, 2002
`
`Which corresponds to the intensity of the illumination light
`having passed through the aperture pattern is obtained. In
`this case,
`the pattern forming member has at
`least one
`slit-shaped aperture pattern With a predetermined slit Width
`extending in a first direction Within a two dimensional plane
`perpendicular to an optical aXis of the projection optical
`system. And, based on the photodetection signal, the optical
`properties of the projection optical system are obtained.
`
`[0035] That is, by the slit-scan method, the aerial image of
`the predetermined mark can be obtained, and since the
`optical properties of the projection optical system are
`obtained based on the obtained photodetection signal,
`it
`becomes possible to measure the optical properties of the
`projection optical system With high precision.
`
`In this case, the mark can consist of a line and space
`[0036]
`mark that has a periodicity in a direction corresponding to
`the second direction, detection of the photoe