JP2008198799A - Device and method for measuring wavefront aberration, and exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavefront aberration measuring device capable of measuring aberration to be generated in a diffraction grating. <P>SOLUTION: The wavefront aberration measuring device includes: a first mask 10 having a plurality of first optical parts 11 for generating a spherical wave; the diffraction grading 40 for separating light coming by way of an optical system to be inspected 30 via the first mask; and an operational part 51 for generating information concerning the wavefront aberration of the optical system to be inspected, based on interference patterns to be generated by the mutual interference of separation lights from the diffraction grading. The device also includes: a plurality of second optical parts 21 for generating the spherical wave; and a second mask 20 which is arranged between the optical system to be inspected and the diffraction grading and is movable into/out of an optical path. The operational part generates the information concerning the wavefront aberration of the optical system to be inspected, where the aberration to be generated in the diffraction grading is corrected, based on the first interference pattern to be acquired in a state where the second mask is arranged at the inside of the optical path, and the second interference pattern to be acquired in a state where the second mask is arranged at the outside of the optical path. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavefront aberration measuring apparatus, for example, a measuring apparatus for measuring wavefront aberration of a projection optical system (test optical system) that projects a pattern on a reticle (mask) onto a target object.

  2. Description of the Related Art Conventionally, a projection type exposure apparatus that exposes a pattern formed on a reticle onto an object to be exposed (object to be processed) via a projection optical system when manufacturing a semiconductor element or the like by photolithography has been used. In view of the demand for miniaturization of semiconductor elements, the practical application of a projection exposure apparatus using EUV (Extreme Ultraviolet) light having a wavelength of about 5 to 20 nm, which is shorter than ultraviolet light, has been studied.

  In order to accurately transfer the reticle pattern to the object to be exposed at a specific magnification, the projection optical system needs to have high imaging performance with reduced aberration. In particular, due to the demand for miniaturization of semiconductor elements, the transfer performance has become sensitive to the aberration of the projection optical system. For this reason, it is necessary to measure the wavefront aberration of the projection optical system with high accuracy.

  As a method for measuring the wavefront aberration of a projection optical system for EUV with high accuracy, a point diffraction interferometer (hereinafter referred to as PDI) or a lateral shearing interferometer that does not require advanced alignment such as PDI has been proposed. Yes.

  In the shearing interferometer, a spherical wave emitted from one pinhole provided on the object plane of the test optical system is incident on the test optical system. The wavefront of light emitted from the test optical system is deformed by the aberration of the test optical system. A diffraction grating is disposed under the test optical system, and light emitted from the test optical system is separated as diffracted light of each order by the diffraction grating. Patent Document 1 discloses a shearing interferometer that extracts and interferes only with a specific order of diffracted light from these diffracted lights. Non-Patent Document 1 discloses a shearing interferometer that causes all diffracted light to interfere.

  In a shearing interferometer, light that has passed through a test optical system generally includes wavefront aberration of the test optical system. Furthermore, a new wavefront aberration is superimposed on this light when diffracted by the diffraction grating. The wavefront aberration superimposed here is called diffraction grating aberration.

  The causes of the diffraction grating aberration are as follows: (i) the light beam incident on the diffraction grating is not a parallel light beam but a convergent light beam or a divergent light beam, (ii) there is an error in the attitude of the diffraction grating, and (iii) diffraction There is a manufacturing error in the periodicity of the grating.

  Since the diffraction grating aberration becomes a measurement error of the wavefront aberration of the optical system to be measured, a calibration means for removing the diffraction grating aberration is necessary to realize highly accurate wavefront aberration measurement. As such a calibration method, there is a calibration method disclosed in Patent Document 2 suitable for the shearing interferometer disclosed in Patent Document 1. Further, there is a calibration method disclosed in Patent Document 3 suitable for the shearing interferometer disclosed in Non-Patent Document 1.

  However, in the shearing interferometers disclosed in Patent Document 1 and Non-Patent Document 1, in order to obtain diffracted light having a sufficient intensity for measurement from one pinhole provided on the object surface, the pin has high illuminance. It is necessary to illuminate the hall. For this reason, it is necessary to condense the light from a high-intensity light source into this pinhole.

As a light source, an undulator light source inserted into an electron storage ring is generally available at present. However, since this is a huge facility, it should be used in the assembly line of the exposure apparatus and the place where the exposure apparatus is used. Is difficult. For this reason, it is preferable that a small exposure light source can be shared as a light source for wavefront measurement. Patent Documents 4 and 5 disclose a method for realizing this. Specifically, a large number of pinholes are arranged on the object plane according to a specific arrangement, so that the light use efficiency is increased. As a result, the wavefront aberration of the projection optical system can be measured by a shearing interferometer using a low-intensity light source such as a plasma light source used as an exposure light source.
Japanese Patent Laying-Open No. 2005-159213 (paragraphs 0020 to 0030, FIGS. 1 to 5 and the like) JP-A-2005-351833 (paragraphs 0025 to 0033, FIG. 1, etc.) Japanese Patent Laying-Open No. 2005-294404 (paragraphs 0009 to 0014, FIGS. 1 and 2 etc.) Japanese Patent Laying-Open No. 2006-196699 (paragraphs 0023 to 0050, FIGS. 1 and 2, etc.) JP 2006-332586 A (paragraphs 0017 to 0023, FIG. 1, etc.) Patrik P. Naulleau and Kenneth A. Goldberg, J. Vac. Sci. Technol. B 18 (6), (2000)

  However, even in a shearing interferometer that increases the light utilization efficiency by arranging a large number of pinholes on the object surface according to a specific arrangement, diffraction grating aberration occurs in the diffraction grating used, which is the reason for this. This degrades the measurement accuracy of wavefront aberration. Therefore, in order to realize high wavefront aberration measurement accuracy, calibration means for correcting the influence of diffraction grating aberration is necessary.

  The present invention provides a wavefront aberration measuring apparatus capable of measuring diffraction grating aberration, an exposure apparatus including the same, and a wavefront aberration measuring method.

  A wavefront aberration measuring apparatus according to one aspect of the present invention divides light that has passed through a test optical system via a first mask having a plurality of first optical units that generate spherical waves, and the first mask. A diffraction grating; and a calculation unit that generates information related to the wavefront aberration of the optical system to be measured based on an interference pattern formed by the interference of the divided light beams from the diffraction grating. The apparatus is provided with a second mask that has a plurality of second optical units that generate spherical waves and is movable in and out of the optical path between the optical system to be tested and the diffraction grating. The computing unit then obtains the first interference pattern obtained in a state where the second mask is disposed in the optical path and the second interference obtained in a state where the second mask is disposed outside the optical path. Based on the pattern, information on the wavefront aberration of the test optical system in which the aberration generated in the diffraction grating is corrected is generated.

  According to another aspect of the present invention, there is provided a wavefront aberration measuring apparatus comprising: a first mask having a plurality of first optical units that generate spherical waves; and light that has passed through a test optical system via the first mask. And a calculation unit that generates information related to the wavefront aberration of the optical system to be measured based on an interference pattern formed by the interference of the divided light beams from the diffraction grating. This apparatus has a plurality of second optical units that generate spherical waves, and has a second mask that can move in and out of the optical path between the optical system to be tested and the diffraction grating. Then, the calculation unit generates information related to an aberration generated in the diffraction grating based on an interference pattern obtained in a state where the second mask is disposed in the optical path.

  An exposure apparatus that exposes a pattern formed on a reticle on a workpiece using light from a light source, and projects the projection optical system that projects the pattern onto the workpiece and light from the light source. An exposure apparatus having the above-described measuring apparatus that generates information relating to the wavefront aberration of the optical system also constitutes another aspect of the present invention.

  Further, a device manufacturing method including a step of exposing a target object using the exposure apparatus and a step of developing the exposed target object also constitutes another aspect of the present invention.

  Furthermore, in the wavefront aberration measuring method according to another aspect of the present invention, a spherical wave is generated by a plurality of first optical units provided in the first mask, and the spherical wave is incident on a test optical system, The light passing through the test optical system is divided by a diffraction grating, and information on the wavefront aberration of the test optical system is generated based on an interference pattern formed by the split lights from the diffraction grating interfering with each other. The method includes a step of measuring a first interference pattern in a state where a second mask having a plurality of second optical units that generate spherical waves is disposed in an optical path between a test optical system and a diffraction grating; And measuring a second interference pattern in a state where the second mask is disposed outside the optical path. The method includes a step of generating information on the wavefront aberration of the optical system under test in which the aberration generated in the diffraction grating is corrected based on the first and second interference patterns.

  Further, in the wavefront aberration measuring method according to another aspect of the present invention, a spherical wave is generated by a plurality of first optical units provided in the first mask, and the spherical wave is incident on a test optical system, The light passing through the test optical system is divided by a diffraction grating, and information on the wavefront aberration of the test optical system is generated based on an interference pattern formed by the split lights from the diffraction grating interfering with each other. The method includes a step of disposing a second mask having a plurality of second optical units that generate spherical waves in an optical path between a test optical system and a diffraction grating, and the second mask is disposed in the optical path. And a step of generating information relating to aberrations generated in the diffraction grating based on the interference pattern obtained in the state of being arranged in the position.

  According to the present invention, it is possible to generate information relating to the wavefront aberration of the optical system to be measured in which the diffraction grating aberration is corrected from the interference pattern obtained in accordance with the insertion / extraction of the second mask into the optical path. In addition, information about diffraction grating aberration can be generated from the interference pattern obtained with the second mask inserted in the optical path. Accordingly, it is possible to measure the wavefront aberration of the optical system to be measured with high accuracy. Furthermore, a highly accurate evaluation of the wavefront aberration of the projection optical system can be realized by using a low-luminance light source such as an exposure light source.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  First, a wavefront aberration measuring method that is an embodiment of the present invention will be described. A wavefront aberration measuring apparatus as a shearing interferometer is disposed on an object plane of a test optical system and has an object-side pinhole mask (first optical section) having a plurality of pinholes (first optical units) that generate spherical waves from measurement light. 1 mask). In addition, it has a diffraction grating that divides the measurement light that has passed through the optical system to be tested through the object side pinhole mask. Then, the wavefront aberration of the optical system to be measured is calculated from interference fringes (interference patterns) formed by causing the divided lights by the diffraction grating to interfere with each other.

  Furthermore, the wavefront aberration measuring apparatus of the present embodiment has a calibration means described below in order to remove measurement errors generated in the diffraction grating.

  The diffraction grating is arranged downstream of the image plane of the test optical system and at a position where the Talbot (also referred to as Talbot) effect appears, thereby generating a large number of clear interference fringes in the interference image. By analyzing the interference fringes obtained here, an error caused by the diffraction grating, that is, a measurement wavefront W1 including diffraction grating aberration is obtained.

  A method of restoring (recovering) the wavefront from the interference fringes of the shearing interferometer is disclosed in Non-Patent Document 1 and the like.

  Before or after the measurement, a calibration mask (second mask) is placed at the image plane position of the test optical system in the optical path between the test optical system and the diffraction grating. The calibration mask is movable in and out of the optical path between the test optical system and the diffraction grating.

  The calibration mask has a plurality of pinholes (second optical units) that generate spherical waves from transmitted light. The pinhole of the calibration mask is a pinhole having such a small diameter that transmitted light can be regarded as an ideal spherical wave. The same wavefront measurement is performed with the calibration mask installed in this way, and the obtained wavefront is defined as W0.

  The wavefront W1 includes the wavefront aberration W and diffraction grating aberration of the test optical system, but the wavefront W0 does not include the wavefront aberration of the test optical system. That is, the wavefront W0 represents diffraction grating aberration. Therefore, the wavefront W of the test optical system in which the diffraction grating aberration is corrected can be obtained as W = W1−W0.

  In the embodiment, it will be described that wavefront aberration and diffraction grating aberration are calculated or measured. However, it is not necessary to calculate the wavefront aberration or the diffraction grating aberration itself, but the information corresponding to or including the wavefront aberration or the diffraction grating aberration, in other words, the information on the wavefront aberration or the aberration generated in the diffraction grating may be calculated. Any information may be used. Also, “calculate” and “measure” are synonymous with “generate”.

  Hereinafter, the configuration of the wavefront aberration measuring apparatus for measuring the wavefront aberration of the optical system under test in a more specific embodiment of the present invention will be described.

  1 and 2 show a basic configuration of a wavefront aberration measuring apparatus that is an embodiment of the present invention. First, FIG. 1 shows a basic configuration when measuring the wavefront aberration of the optical system 30 to be measured. In the configuration of FIG. 1, since the calibration mask 20 is retracted out of the optical path, the measured wavefront W1 includes the wavefront aberration W and the diffraction grating aberration Wg of the optical system 30 to be measured. That is, the relationship of W1 = W + Wg is established.

  On the other hand, FIG. 2 shows a basic configuration when measuring diffraction grating aberration generated in the diffraction grating 40. The wavefront W0 measured in the configuration of FIG. 2 does not include the wavefront aberration W of the test optical system 30 due to the action of the pinhole of the calibration mask 20 disposed in the optical path, and includes only the diffraction grating aberration Wg. That is, the relationship of W0 = Wg is established.

  Accordingly, only the wavefront aberration of the optical system 7 to be measured can be obtained by subtracting the wavefront W0 measured with the configuration of FIG. 2 from the wavefront W1 measured with the configuration of FIG.

  If the diffraction grating aberration Wg is once measured and stored in a storage device such as a memory, it is not necessary to measure it every time the optical system is measured unless the diffraction grating is replaced. In the case of a projection optical system for an EUV exposure apparatus, the test optical system 30 is usually composed of 6 to 8 mirrors, but is abbreviated in the figure.

  Next, the principle of measurement of the wavefront W1 that is a combined wavefront of the wavefront aberration W and the diffraction grating aberration Wg of the optical system 30 to be measured will be described.

  The object-side pinhole mask 10 is arranged on the object plane of the optical system 30 to be tested, and has a plurality of pinholes 11 as an optical unit that is an area that reflects and emits light. FIG. 3 is a view of the object-side pinhole mask 10 as viewed from the illumination light (measurement light) irradiation side.

The pinhole 11 has a diameter such that the wavefront of the diffracted light generated when irradiated with illumination light becomes an aspherical spherical surface. In general, the pinhole diameter D, the numerical aperture (hereinafter referred to as NA), and the wavelength λ of the diffracted light are:
D ≦ λ / (2NA)
If this condition is satisfied, the diffracted light can be regarded as an aspherical spherical surface.

  When the NA on the image plane side of the test optical system 30 is 0.26 and the magnification is 1/4, the NA on the incident side is 0.065. In this case, if the wavelength λ of the illumination light is 13.5 nm, the diameter of the pinhole 11 for covering the diffraction angle in this range with the diffracted light without aberration is 13.5 / (2 × 0.065). = 104 nm or less. In the following description, the wavelength of illumination light is 13.5 nm unless otherwise specified.

  However, if the pinhole diameter is reduced, the intensity of the diffracted light is also reduced. Therefore, the pinhole diameter is preferably about 100 nm.

  The interval Pp between the plurality of pinholes 11 is set to be equal to or greater than the spatial coherence length of the illumination light so that the diffracted light from them does not interfere with each other.

  FIG. 4 shows the relationship between the distance (interval Pp) and the absolute value of the coherence coefficient when the illumination light NA is 0.052. As can be seen from FIG. 4, the diffracted light from two points separated by 0.16 μm or more in the illumination region hardly interferes because the coherence coefficient is small. In this case, 0.16 μm is the coherence length.

  The object-side pinhole mask 10 is a reflection type in FIG. 3, but may be a transmission type. In the case of the reflection type, a reflection film made of a multilayer film of molybdenum and silicon and an absorption layer of chromium or the like formed thereon are provided on a substrate of silicon or glass. And the hole which penetrates to this reflection layer to a reflection layer is provided as a pinhole. In the case of the transmission type, a through hole is provided as a pinhole in a self-supporting film of a metal having a large light absorption rate such as nickel. In the following description, the object side pinhole mask 10 is assumed to be a reflection type.

  The wavefront aberration of the test optical system 30 changes continuously according to the change of the object position. Therefore, it is necessary to limit the region where the plurality of pinholes 11 are formed (the region where the pinholes 11 are distributed) to a region where the aberration of the optical system 30 to be measured can be regarded as the same. In the present embodiment, the size of the region A in which the plurality of pinholes 11 are formed is set to the size of the region in which the aberration of the optical system to be tested 30 can be regarded as the same, typically about 0.1 mm to 1 mm in diameter. ing. Of course, even if the size of the region A where the plurality of pinholes 11 are formed is larger than the region where the aberration of the optical system 30 to be measured can be regarded as the same, the illumination region IA has the same aberration of the optical system 30 to be measured. The same effect can be obtained if it is limited to a region that can be considered.

  In FIG. 1, an illumination optical system (not shown) collectively illuminates a plurality of pinholes 11 of the object-side pinhole mask 10. Thereby, a plurality of spherical waves are generated.

  The non-aberrated spherical wave diffracted by each pinhole 11 passes through the optical system 30 to be tested and includes the wavefront aberration of the optical system 30 to be measured, and reaches the diffraction grating 40 in that state.

  The diffraction grating 40 is a two-dimensional diffraction grating that splits incident light into a plurality of orders of diffraction light two-dimensionally. In FIG. 1, diffracted light other than the zeroth order generated by the diffraction grating 40 is not shown.

  The diffracted lights of the respective orders generated in the diffraction grating 40 travel in slightly different directions and reach the detection unit 50 which is an interference pattern observation unit. On the detection unit 50, these diffracted lights overlap and interfere with each other in a laterally shifted state, and so-called shearing interference fringes are generated.

  The detection unit 50 is a detector or a camera such as a back-illuminated CCD sensor. The distance Lg between the image plane of the test optical system 30 and the diffraction grating 40 satisfies the following expression (1) so that the Talbot effect for obtaining high-contrast interference fringes appears.

  Note that shearing interference fringes occur regardless of whether the diffraction grating 40 is upstream or downstream of the image plane of the optical system 30 to be tested. However, as will be described later, in consideration of measuring the aberration generated in the diffraction grating 40 by inserting a calibration mask into the image plane, it is necessary to dispose the diffraction grating downstream from the image plane.

Lg = m · Pg ² / λ (1)
Here, Pg is the grating period of the diffraction grating 40, and λ is the wavelength of the measurement light (illumination light). m is an integer other than 0. The reason why m is set to other than 0 is to enable wavefront recovery by the Fourier transform method by generating fine interference fringes called carriers in the interference fringes. Unlike the phase shift method, the Fourier transform method can recover the wavefront from one interference image. For this reason, it is not necessary to provide a phase shift mechanism, and the apparatus configuration can be simplified.

  The Fourier transform method for shearing interferometers is described in detail in M. Takeda, S. Kobayashi, Appl. Opt., Vol. 23 (1984), p. 1760-1764 “Lateral aberration measurements with a digital Talbot interferometer”. Yes.

  In the interference fringes obtained in this way, the light intensity at the location on the straight line passing through the center of the opening of the diffraction grating 40 and the condensing point of the 0th-order diffracted light indicated by the dotted line in the figure can be understood by considering symmetry. In addition, it becomes maximum or minimum. In FIG. 1, it is the maximum.

  Since the space | interval of the pinhole 11 is set more than the spatial coherence length of illumination light, the light reflected by each pinhole 11 does not interfere with each other. Therefore, a large number of interference patterns generated by the light from the pinhole 11 on the detection unit 50 can be simply superimposed. For this reason, even if the illumination light density to each pinhole 11 is low, sufficient light intensity can be obtained on the detection unit 50.

  Furthermore, if the light and dark positions of the interference pattern coincide with each other at this time, an interference pattern having sufficient intensity for measurement can be obtained without degrading the contrast of the interference pattern.

  On the straight line passing through the image of each pinhole 11 and the center of the opening of the diffraction grating 40, the positions of the light and darkness of the respective interference patterns coincide. For this reason, if these straight lines intersect at one point on the image plane of the detection unit 50, the contrast of the interference fringes does not deteriorate.

  As can be seen from FIG. 1, in order to satisfy this condition, the relationship between the grating period Pg and the period Pi of the pinhole image should satisfy the following expression (2).

Pi = Pg · Lc / (Lc−Lg) (2)
Here, Lc is the distance from the image plane of the optical system 30 to be detected to the detection unit 50.

  Further, the period Pp of the pinhole 11 satisfies the following formula (3) when the magnification of the optical system 30 to be tested is β.

Pp = Pi / β (3)
For this reason, the period Pp satisfies the following expression (4), so that the light and dark positions of the interference pattern due to the reflected light from any pinhole 11 (transmitted light in the case of the transmission type) are matched on the detection unit 50. be able to. As a result, the contrast does not deteriorate.

Pp = (Pg / β) · Lc / (Lc−Lg) (4)
As an example, the grating period Pg = 0.87 μm, the distance Lc = 30 mm from the image plane to the detector 50, the distance Lg = 112 μm between the image plane and the diffraction grating 40, and the magnification β = 0.25 of the test optical system 30. In some cases, the period Pp of the pinhole 11 is 3.5 μm.

  If the detection unit 50 is sufficiently away from the image plane, the period Pp of the pinhole 11 may be approximated by the following equation (5), assuming that Lc / (Lc−Lg) ≈1.

Pp = Pg / β (5)
If the object-side pinhole mask 60 shown in FIG. 5 is used instead of the object-side pinhole mask 10, the light utilization efficiency is further increased, and the wavefront measurement with a smaller amount of illumination light becomes possible. The object-side pinhole mask 60 has a plurality of pinhole areas 61 each including a plurality of pinholes 62. The pinhole area 61 is arranged with the same period Pp as the pinhole 11. Since the object-side pinhole mask 60 has a much larger number of pinholes than the object-side pinhole mask 10, the light use efficiency is high. If the distance Lp between the pinholes 62 is shortened, the number of pinholes can be increased, so that the light utilization efficiency can be increased.

  However, if the interval Lp is too short, reflected light from adjacent pinholes (transmitted light in the case of a transmission type) interferes with each other and disturbs their wavefront shapes, resulting in measurement errors. Therefore, it is desirable that the distance Lp be set to a distance as short as possible so that the coherence of light from adjacent pinholes is sufficiently small.

  When the illumination light NA is 0.052, it can be seen from FIG. 4 that the interval Lp may be set to 0.16 μm, which is the distance at which the coherence coefficient becomes 0.

  Further, when the diameter Dw of the pinhole area 61 is increased, the total number of pinholes 62 is increased, and wavefront measurement using a smaller amount of illumination light becomes possible. However, on the other hand, the contrast of the interference pattern observed by the detection unit 50 deteriorates. Therefore, it is necessary to appropriately determine the diameter Dw of the pinhole area 61 in consideration of the intensity of the interference pattern and the deterioration of contrast.

  As an example of the diameter Dw, it is assumed that the grating period Pg = 0.87 μm, the magnification β of the optical system 30 to be tested = 0.25, and that the contrast of the interference pattern is allowed to decrease to 60% when the pinhole mask 10 is used. Dw = 2.1 μm. At this time, if the pinholes 62 are arranged at the above-described interval Lp = 0.16 μm, there are about 160 pinholes 62 in one pinhole area 61. Therefore, when the object side pinhole mask 10 is used. As a result, an interference image having a light intensity of about 160 times that of the image is obtained.

  The calculation unit 51 acquires the interference pattern detected by the detection unit 50 and performs wavefront recovery by the Fourier transform method. The wavefront W1 obtained here includes the diffraction grating aberration Wg as an error in the wavefront aberration W of the test optical system 30.

  Next, the measurement principle of the wavefront W0 that is the diffraction grating aberration Wg will be described with reference to FIG. At the time of measuring the diffraction grating aberration, the calibration mask moving mechanism 25 inserts the calibration mask 20 into the image plane position of the optical system 30 to be tested in the optical path from the optical system 30 to the diffraction grating 40.

  FIG. 6 shows an example of the structure of the calibration mask 20. The calibration mask 20 is provided with a plurality of pinholes 21 as an optical part which is an area through which light is transmitted and emitted. The calibration mask 20 is a transmissive type and has a structure in which a through hole is provided in a self-supporting film of a metal having a large light absorption rate such as nickel. The pinhole 21 has a diameter such that the wavefront of transmitted light is an aspherical spherical surface.

  As described above, when the pinhole diameter D and NA and the wavelength λ of the diffracted light satisfy D ≦ λ / (2NA), the diffracted light can be regarded as an aspherical spherical surface. When the NA on the image plane side of the test optical system 30 is 0.26, the diameter of the pinhole 21 for covering the diffraction angle in this range with diffracted light without aberration is 13.5 / (2 × 0 .26) = 26 nm or less.

  However, if the pinhole diameter is reduced, the intensity of diffracted light is also reduced, so about 26 nm is preferable.

  The intervals (cycles) between the plurality of pinholes 21 are set to be equal to or greater than the spatial coherence length of the illumination light so that the diffracted light from them does not interfere with each other.

  FIG. 7 shows the relationship between the distance between the pinholes 21 and the absolute value of the coherence coefficient when the image plane side NA = 0.26. As can be seen from FIG. 7, the diffracted light from two points separated by 0.031 μm or more in the illumination region hardly interferes because the coherence coefficient is small. In this case, the coherence length is 0.031 μm.

  If the pinholes 21 are periodically arranged and the period Pr is set to a value obtained by the right side Pg · Lc / (Lc−Lg) of the above-described formula (2), as in the case of FIG. Each of the light emitted from the holes 21 generates interference fringes whose bright and dark positions coincide on the detection unit 50. Therefore, interference fringes with sufficient intensity can be obtained without degrading contrast.

  Usually, the distance Lg between the image plane of the test optical system 30 and the diffraction grating 40 and the distance Lc from the image plane of the test optical system 30 to the detection unit 50 are in a relationship of Lg << Lc. . For this reason, if approximated as Lc / (Lc−Lg) ≈1, Expression (6) is established. Therefore, the diffraction grating period Pr may be made equal to the grating period Pg.

Pr = Pg (6)
In general, the period Pg of a diffraction grating used in an EUV shearing interferometer is 0. Since it is several μm to several μm, it is sufficiently larger than the coherence length on the calibration mask, and diffracted lights from different pinholes do not interfere with each other.

  Since the light passing through the pinhole 21 has no aberration, the interference fringes appearing on the detection unit 50 are not affected by the aberration of the optical system 30 to be measured and reflect only the aberration generated in the diffraction grating 40. The calculation unit 51 acquires the interference pattern detected by the detection unit 50 and performs wavefront recovery by the Fourier transform method. Since the wavefront W0 obtained here does not include the wavefront aberration W of the optical system 30 to be measured, only the diffraction grating aberration Wg can be measured.

  In FIG. 2, an object side window mask (third mask) 15 is used instead of the object side pinhole mask 10 installed on the object plane in FIG. The window mask 15 is obtained by forming one reflection window 16 as an optical region having the same size or larger than the region A in which the pinhole 11 is formed in the pinhole mask 10.

  Note that although a reflective window mask is described here, the window mask may be a reflective mask in which a transmission window that transmits light is formed. Each of the reflection window and the transmission window can be said to be an optical region in which illumination light is emitted toward the test optical system.

  By using the window mask 15, it is possible to suppress the loss of light amount compared to the case of using the pinhole mask 10, and it becomes unnecessary to precisely align the object side mask and the image side mask.

  In particular, by making the size of the reflection window 16 larger than the region A in which the pinhole 11 is formed in the pinhole mask 10, the alignment of the window mask 15 can be facilitated and the diffraction grating aberration can be measured with high accuracy. It becomes possible.

  In place of the calibration mask 20, a calibration mask 70 shown in FIG. 8 may be used. In this case, the light utilization efficiency is further increased, and the diffraction grating aberration can be measured with a smaller amount of illumination light.

  The calibration mask 70 has a plurality of pinhole areas 71 each including a plurality of pinholes 72. The pinhole area 71 is arranged with the same period (interval) Pr as the pinhole 21 of the calibration mask 20.

  Since the calibration mask 70 has a much larger number of pinholes than the calibration mask 20, the light use efficiency is high. If the distance Lr between the pinholes 72 is shortened, the number of pinholes can be increased, so that the light utilization efficiency can be further increased.

  However, if the distance Lr is too short, transmitted light from adjacent pinholes interfere with each other and disturb their wavefront shapes, resulting in measurement errors. Therefore, it is necessary to sufficiently reduce the coherence of light from adjacent pinholes.

  When the image plane side NA = 0.26, referring to FIG. 7, it can be seen that the interval Lr should be 0.031 μm or more where the coherence coefficient is small. Increasing the diameter Dr of the pinhole area 71 increases the total number of pinholes 72 and enables wavefront measurement with a smaller amount of illumination light, but on the other hand, contrast of the interference pattern observed by the detection unit 50 Deteriorates. Therefore, it is necessary to appropriately determine the diameter Dr of the pinhole area 71 in consideration of the intensity of the interference pattern and the deterioration of contrast.

  As an example of the diameter Dr, it is assumed that the grating period Pg = 0.87 μm, the magnification β of the test optical system 30 is 0.25, and the contrast of the interference pattern is allowed to be reduced to 60% when the calibration mask 20 is used. Dr = 0.53 μm. If the pinholes 72 are arranged at intervals of 0.031 μm, there are about 160 pinholes 72 in one pinhole area 71, so that the light is about 160 times lighter than when the calibration mask 20 is used. An intense interference image is obtained.

  The size of the region B in which the pinhole 21 or the pinhole area 71 is formed in the calibration masks 20 and 70 may be the same as or larger than the image size of the reflection window 16 in order to facilitate alignment.

  A wavefront aberration measuring apparatus that is Embodiment 2 of the present invention will be described. In this embodiment, the object side window mask 17 shown in FIG. 9 is used in place of the object side window mask 15 described in the first embodiment. The object-side window mask 17 includes a plurality of small reflective windows (third optical units) 18 that are larger in size than the pinholes 11 formed in the object-side pinhole mask 10 and arranged with the same period Pp as the pinholes 11. Have. In addition, although the object side window mask 17 of a present Example is a reflection type, it is good also as a transmission type.

  The size of the region (optical region) C in which the plurality of small reflective windows 18 are formed inside is the same as or larger than the region A in which the plurality of pinholes 11 are formed in the object side pinhole mask 10. In particular, by making the size of the region C larger than the region A, it is possible to measure the diffraction grating aberration with high accuracy while facilitating the alignment of the window mask 17.

  Furthermore, the size of each reflective small window 18 is larger than the size of each pinhole 11. For example, when the size of the pinhole 11 is 100 nm, the diameter of the reflective small window 18 may be 1 μm. Thereby, alignment of the window mask 17 can be made easier.

  Here, the object-side window mask 17 has a smaller total area of reflection parts than the object-side window mask 15. For this reason, the amount of light incident on the test optical system 30 is reduced, and stray light generated there can be reduced.

  For example, when the diameter of the reflection small window 18 is 1 μm, if the arrangement period is 3.5 μm, which is the same as that in the first embodiment, the stray light is reduced to 1/16 due to the area ratio of the reflection portion.

  In this embodiment, either the calibration mask 20 or the calibration mask 70 described in the first embodiment can be used. However, naturally, it is necessary to perform alignment so that the imaging position of the reflective small window 18 of the object-side window mask 17 coincides with the pinhole 21 or the pinhole area 71.

  In the case of the present embodiment, since light is irradiated only on the image portion of the reflection small window 18 on the calibration mask, it is not necessary to use a pinhole arrangement as in the calibration mask 70, and the entire surface of the mask is spaced at an interval Lr. It may be a calibration mask (not shown) having pinholes. In this case, alignment between the object-side window mask 17 and the calibration mask is not necessary.

  Hereinafter, an exposure apparatus that is Embodiment 3 of the present invention will be described with reference to FIG. The exposure apparatus 100 uses EUV light as exposure light. However, light other than EUV light may be used as exposure light.

  The exposure apparatus 100 includes an EUV light source unit 110, an illumination optical system 120, a mask stage 142 on which a mask (reticle) 140 is mounted, a projection optical system 150, and a wafer stage on which a wafer 160 that is an object to be processed is mounted. 162 and a wafer side unit 170.

  The exposure apparatus 100 is a projection type exposure apparatus that exposes a circuit pattern formed on a mask using EUV light as illumination light for exposure onto a wafer 160. Since EUV light has a low transmittance to the atmosphere, the illumination optical system 120 and the like are housed in the vacuum container 102.

  The EUV light source 110 is a light source that oscillates EUV light, and is a discharge excitation plasma type EUV light source that generates EUV light by converting Xe gas, Sn vapor or the like into plasma by discharge. Further, as the EUV light source 110, a laser excitation type plasma EUV light source for generating plasma by condensing and irradiating Xe or Sn with a high-power pulse laser may be used.

  The illumination optical system 120 is an optical system that propagates EUV light and illuminates the mask 140. In this embodiment, the illumination optical system 120 includes a parallel conversion optical system, an integrator 123, an aperture stop 124, an arc optical system, a plane mirror 127, a plane mirror 130, and a switching mechanism 132.

  The parallel conversion optical system has a function of receiving EUV light from the EUV light source 110 and converting it into a parallel light beam, and includes a concave mirror 121, a convex mirror 122, and a plane mirror. The integrator 123 has a plurality of cylindrical reflection surfaces, fly-eye or fish phosphorus-like fly-eye reflection surfaces, and the like, and uniformly illuminates the mask 140 with a predetermined NA. The integrator 123 is configured to be switchable with the plane mirror 130 by the switching mechanism 132, and is disposed on the optical path during exposure.

  On the reflecting surface of the integrator 123, an aperture stop 124 having an opening surface disposed substantially perpendicular to the reflecting surface is disposed. The aperture stop 124 defines the distribution shape of the effective light source, and defines the angular distribution of light that illuminates each point on the mask 40 that is the illuminated surface.

  The arc optical system has a function of condensing the luminous flux from the integrator 123 in an arc shape, and includes a convex mirror 125 and a concave mirror 126.

  The flat mirror 127 reflects the image-side light beam of the arc optical system so as to splash it up to the mask 140 and makes it incident at a predetermined angle. The plane mirror 130 is switched to the integrator 123 by the switching mechanism 132 when measuring the wavefront of the projection optical system 150 and is arranged on the optical path. The light reflected by the plane mirror 130 is reflected by the arc optical system and condensed on the object plane of the projection optical system 130.

  The mask 140 is a reflective mask, on which a circuit pattern (or image) to be transferred is formed, and is supported and driven by a mask stage 142. Diffracted light emitted from the mask 140 is reflected by the projection optical system 150 and projected onto the wafer 160. The mask 140 and the wafer 160 are arranged in an optically conjugate relationship.

  At the time of wavefront measurement of the projection optical system 150, the object side pinhole mask 10 or the object side window masks 15 and 17 of the measurement apparatus described in the first and second embodiments are arranged instead of the mask 140. The object-side pinhole mask 10 or the object-side window masks 15 and 17 are disposed on a dedicated stage or mask stage 142 for measuring wavefront aberration. Instead of the object side pinhole mask 10, an object side pinhole mask 60 may be used.

  The projection optical system 150 has a function of projecting the mask pattern onto the wafer 160, and is a test optical system for the wavefront aberration measuring apparatus. The projection optical system 150 applied to EUV light is extremely sensitive to positional accuracy and thermal deformation, and it is necessary to measure wavefront aberration between exposures and adjust the mirror position based on the measurement results to provide feedback. There is. Further, impurities adhere to the multilayer mirror of the projection optical system 150 and cause a chemical change, so that a phase change due to a so-called contaminant also occurs. For this reason, it is necessary to measure the wavefront aberration of the projection optical system 150 due to the exposure wavelength on the exposure apparatus main body, but the exposure apparatus 100 is equipped with the wavefront aberration measuring apparatus described in the first and second embodiments, and this requirement. Is satisfied.

  The wafer stage 162 supports and drives the wafer 160. Further, a wafer side unit 170 constituted by the diffraction grating 40, the calibration mask 20 or the calibration mask 70 and the calibration mask moving mechanism 25 is also mounted on the wafer stage 162. The wafer side unit 170 can move in a direction perpendicular to the optical axis. When the wafer 160 is exposed, the wafer side unit 170 is retracted from the optical path.

  When measuring the wavefront aberration of the projection optical system 150, the switching mechanism 132 switches the integrator 123 to the plane mirror 130. As a result, the light that has been expanded in an arc shape can be collected on the object plane of the projection optical system 150, and the light efficiency at the time of measurement can be improved. The mask 140 is replaced with the object side pinhole mask 10 or the object side window mask 15. Further, a wafer side unit 170 is positioned on the optical path instead of the wafer 160. In this state, an interference image that is affected by the aberration of the diffraction grating 40 and an interference image that does not receive the interference image are collected by the procedure described in the first embodiment. Based on these images, the wavefront aberration of the projection optical system 150 is acquired by the calculation unit 51 (not shown in FIG. 8).

  Next, an embodiment of a device manufacturing method using the above-described exposure apparatus 100 will be described with reference to FIGS. Here, FIG. 11 is a flowchart for explaining the manufacture of a semiconductor device (a semiconductor chip such as an IC or LSI, or a liquid crystal panel or a CCD sensor).

  In step 1 (circuit design), a semiconductor device circuit is designed.

  In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced.

  On the other hand, in step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon.

  Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer.

  The next step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer produced in step 4, and is a process such as an assembly process (dicing, bonding), a packaging process (chip encapsulation), or the like. including.

  In step 6 (inspection), the semiconductor device manufactured in step 5 undergoes inspections such as an operation confirmation test and a durability test. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 12 is a detailed flowchart of the wafer process in Step 4 shown in FIG.

  In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the wafer surface.

  In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like.

  In step 14 (ion implantation), ions are implanted into the wafer.

  In step 15 (resist process), a photosensitive material is applied to the wafer.

  Step 16 (exposure) uses the exposure apparatus 100 to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed.

  By repeatedly performing these steps, multiple circuit patterns are formed on the wafer. Since the manufacturing method of the present embodiment uses a projection optical system adjusted based on the aberration measured with high accuracy, it is possible to manufacture a highly accurate semiconductor device that has been difficult to manufacture.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the present invention can be applied to a step-and-repeat type exposure apparatus.

It is an optical path figure at the time of measuring the wavefront aberration of the test optical system in the wavefront aberration measuring apparatus which is Example 1 of this invention. It is an optical path figure at the time of measuring the diffraction grating aberration in the said measuring apparatus. 2 is a plan view showing an object-side pinhole mask used in Example 1. FIG. In Example 1, it is a graph which shows the relationship between the distance between two points on the object side pinhole mask when NA = 0.052, and the absolute value of the coherence coefficient. It is a top view which shows the object side pinhole mask which has a group structure pinhole used in Example 1. FIG. 2 is a plan view showing a calibration mask used in Example 1. FIG. 6 is a graph showing a relationship between a distance between two points on an object-side pinhole mask having a group structure pinhole and an absolute value of a coherence coefficient when NA = 0.26 in Example 1. FIG. 6 is a plan view showing a calibration mask having a group structure pinhole used in Example 1. FIG. It is a top view which shows the object side window mask used in the wavefront aberration measuring apparatus which is Example 2 of this invention. It is a block diagram which shows the structure of the exposure apparatus which is Example 3 of this invention. It is a flowchart for demonstrating the device manufacturing method using the said exposure apparatus. 12 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Object side pinhole mask 11 Pinhole 15 Object side window mask 16 Reflection window 20 Calibration mask 21 Pinhole 25 Calibration mask moving means 30 Test optical system 40 Diffraction grating 50 Detection part 51 Calculation part 60 Object side pinhole mask 61 Pin Hole area 62 Pinhole 70 Calibration mask 71 Pinhole area 72 Pinhole

Claims (9)

A first mask having a plurality of first optical units that generate spherical waves, a diffraction grating that divides the light that has passed through the optical system to be tested through the first mask, and the divided light from the diffraction grating mutually A wavefront aberration measuring device having a calculation unit that generates information on the wavefront aberration of the optical system under test based on an interference pattern formed by interfering with
A plurality of second optical units that generate spherical waves, and a second mask that is movable in and out of an optical path between the optical system to be tested and the diffraction grating,
The computing unit includes a first interference pattern obtained in a state where the second mask is disposed in the optical path, and a second interference pattern obtained in a state where the second mask is disposed outside the optical path. Based on the above, the wavefront aberration measuring apparatus is characterized in that it generates information on the wavefront aberration of the optical system under test in which the aberration generated in the diffraction grating is corrected. A first mask having a plurality of first optical units that generate spherical waves, a diffraction grating that divides the light that has passed through the optical system to be tested through the first mask, and the divided light from the diffraction grating mutually A wavefront aberration measuring device having a calculation unit that generates information on the wavefront aberration of the optical system under test based on an interference pattern formed by interfering with
A plurality of second optical units that generate spherical waves, and a second mask that is movable in and out of an optical path between the optical system to be tested and the diffraction grating,
The wavefront aberration measuring apparatus, wherein the calculation unit generates information on aberrations generated in the diffraction grating based on an interference pattern obtained in a state where the second mask is disposed in the optical path. When obtaining the first interference pattern, a third mask is used instead of the first mask,
In the third mask, the size of the optical region for emitting light toward the test optical system is larger than the size of the region in which the plurality of first optical portions of the first mask are formed. The wavefront aberration measuring apparatus according to claim 1, wherein: The third mask has a plurality of third optical units that emit light toward the test optical system inside the optical region,
4. The wavefront aberration measuring device according to claim 3, wherein the size of each of the third optical units is larger than the size of each of the first optical units.   5. The wavefront aberration measuring apparatus according to claim 1, wherein the plurality of second optical units are arranged with the same period as a grating period of the diffraction grating. An exposure apparatus that exposes an object to be processed with a pattern formed on a mask using light from a light source,
A projection optical system that projects the pattern onto the object;
An exposure apparatus comprising: the measurement apparatus according to claim 1, wherein information on wavefront aberration of the projection optical system is generated using light from the light source. Exposing the object to be processed using the exposure apparatus according to claim 6;
And a step of developing the exposed object to be processed. A spherical wave is generated by a plurality of first optical units provided in the first mask, the spherical wave is incident on a test optical system, and light passing through the test optical system is divided by a diffraction grating, A wavefront aberration measuring method for generating information on the wavefront aberration of the optical system under test based on an interference pattern formed by interference between split lights from a diffraction grating,
Obtaining a first interference pattern in a state where a second mask having a plurality of second optical parts for generating spherical waves is disposed in the optical path between the optical system to be tested and the diffraction grating;
Obtaining a second interference pattern with the second mask disposed outside the optical path;
Generating a wavefront aberration information of the optical system under test in which the aberration generated in the diffraction grating is corrected based on the first and second interference patterns. . A spherical wave is generated by a plurality of first optical units provided in the first mask, the spherical wave is incident on a test optical system, and light passing through the test optical system is divided by a diffraction grating, A wavefront aberration measuring method for generating information on the wavefront aberration of the optical system under test based on an interference pattern formed by interference between split lights from a diffraction grating,
Disposing a second mask having a plurality of second optical parts for generating spherical waves in an optical path between the optical system to be tested and the diffraction grating;
And a step of generating information relating to an aberration generated in the diffraction grating based on an interference pattern obtained in a state where the second mask is disposed in the optical path.