JP2003086501A - Wave aberration measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wave aberration measuring machine using a diffraction grating shearing interferometer for a mirror (reflection) type optical system, which can prevent the analysis of zero-order light or high-order overlapped diffracted light from becoming difficult caused by double diffraction interference. SOLUTION: The device includes a pin hole member for generating spherical wave light, a device for holding an optical system to be inspected at a predetermined position, a diffraction grating, a mask member 16 for receiving light from the diffraction grating, a CCD for projecting diffracted light from the mask member 16, a diffracted light selecting means for causing the mask member 16 to selectively transmit only a predetermined order of diffracted light therethrough, and a diffracted light analyzing means for selectively analyzing only the predetermined order of diffracted light component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to precise measurement of wavefront aberration in a mirror (reflection) type optical system.

[0002]

2. Description of the Related Art For example, in a lithography apparatus (exposure apparatus) which is conventionally used for manufacturing a device such as a semiconductor circuit element by a lithography process, light having a wavelength of 193 nm or more has been used as exposure light. However, in recent years, there has been a demand for further subdivision of patterns on a semiconductor circuit, so that an exposure apparatus using a shorter wavelength than ever has been required, and a soft X having a wavelength of 13 nm is required.
Line (Light in this wavelength range is EUV (Extreme Ultra Viole
The development of a projection exposure apparatus using (also referred to as t) is proposed.

However, a light ray in the soft X-ray region has a large absorption effect, and is not suitable for optical control such as focusing and divergence using an optical lens (refractive optical element). Therefore, the control optical system in the soft X-ray region must be a mirror (reflection) type optical system having a reflecting surface.

The projection exposure apparatus using the wavelength range of the soft X-ray projects and exposes a finer pattern than ever, and the wavefront aberration of the exposure is required to be very high in accuracy. For example, it is required to suppress the wavefront aberration within ± 1 nm RMS. Therefore, a wavefront aberration measuring instrument that examines and evaluates the projection exposure optical system (test optical system) that uses the wavelength range of soft X-rays also requires very high resolution, and whether the wavefront aberration is suppressed within ± 1 nm RMS. Examining
For evaluation, a resolution of about 0.5 nm is required. To obtain this resolution without using an optical lens, it is possible to use a diffraction grating shearing interferometer. A wavefront measuring device using a diffraction grating shearing interferometer is a device for causing interference between test wavefronts obtained by laterally shifting an optical wavefront emitted from a test optical system using a diffraction grating.
The phase difference of the interference pattern is shifted using a means for moving the diffraction grating, and the fringe scan method is used to analyze the distortion of the wavefront due to the passage of the optical system under test from the interference pattern.

[0005]

However, when analysis is performed using the diffraction grating shearing interferometer having such a configuration, in order to perform interference of two bundles of the 1st-order diffracted light and the -1st-order diffracted light, high-order light and high-order diffracted light are used. There is a problem that the next diffraction interference light overlaps and the analysis becomes difficult.

The present invention has been made in view of such a problem, and a wavefront aberration measuring instrument using a diffraction grating shearing interferometer for a mirror (reflection) type optical system is provided.
It is an object of the present invention to provide a wavefront aberration measuring instrument that can obtain a required resolution without requiring a complicated analysis due to the influence of secondary light and higher-order diffracted light.

[0007]

In order to solve the above-mentioned problems, a wavefront aberration measuring device of the present invention has a pinhole for generating light of spherical wave by passing light from a light source which supplies light of a predetermined wavelength. A pinhole member having the optical system to be inspected, which holds the optical system to be inspected at a predetermined position, irradiates the optical system with spherical wave light, and emits light from the optical system to be inspected, A diffraction grating arranged at a position for receiving the light emitted from the optical system, a mask member arranged at a position for receiving the light emitted from the diffraction grating by receiving the light emitted from the optical system under test, and a mask member The detection optical system for measuring the interference pattern of the diffracted light and the mask member have a diffracted light selection means for selectively transmitting only diffracted light of a predetermined order.

With the wavefront aberration measuring device having such a structure,
A shearing interferometer can be constructed by using a diffraction grating for a mirror (reflection) type optical system and displacing the wavefront of emitted light, and a mask member can be used to remove the influence of higher-order interference light. Therefore, the analysis is facilitated and the object of the present invention can be achieved.

Incidentally, in the wavefront aberration measuring device having the above structure,
The light receiving member of the detection optical system may be a charge coupled device (CCD).

In the wavefront aberration measuring device having the above-described structure, the mask member may be arranged so as to be disposed at a substantially image forming position of the spherical wave focused by the optical system under test.

In the wavefront aberration measuring device having the above-mentioned structure, the diffracted light selecting means may be structured such that a predetermined number of openings are provided in the mask member.

Further, the diffracted light transmitted through the opening provided in the mask member may be + 1st order and -1st order diffracted light.

In the wavefront aberration measuring device having the above-described structure, when the optical system to be measured is an exposure projection system for transferring the circuit pattern drawn on the reticle surface onto the wafer surface, the optical system to be measured is held by the optical system holding device. The pinhole member may be arranged at a position where the reticle surface is arranged and the mask member may be arranged at a position where the wafer surface is arranged while the system is held at a predetermined position.

In the wavefront aberration measuring device having the above-mentioned structure, the light source may be one of a synchrotron radiation light source, a laser plasma light source, and a discharge plasma light source.

Further, in the wavefront aberration measuring device having the above-mentioned structure, a structure may be used in which a means for converting a spherical wave into a plane wave is provided between the diffracted light selecting means and the light receiving member.

In the wavefront aberration measuring device having the above-mentioned structure, a structure having a mask member having a diffracted light selecting means, a switchable pinhole and an opening may be used.

In order to solve the above-mentioned problems, the wavefront aberration measuring instrument of the present invention may be a wavefront aberration measuring instrument having the following constitution in addition to the above-mentioned constitution in which the mask member is provided. The second wavefront aberration measuring device of the present invention includes a light source that supplies light of a predetermined wavelength, a pinhole member that has a pinhole that allows light from the light source to pass therethrough, and generates spherical wave light, and a test object. A test optical system holding device that holds the optical system in a predetermined position, irradiates the test optical system with spherical wave light, and emits light from the test optical system, and a position that receives light emitted from the test optical system. In the wavefront aberration measuring instrument using the diffraction grating shearing interference, which consists of the diffraction grating arranged in and the detection optical system for measuring the interference pattern of the diffracted light from the diffraction grating, only the diffracted light component of the predetermined order is selectively And a diffracted light analysis means for analysis.

Even with the wavefront aberration measuring device having such a configuration, a shearing interferometer can be constructed similarly to the one using the above-mentioned mask member, and the component of the diffracted light which is not used in the analysis can be removed. The analysis becomes easier and the object of the present invention can be achieved.

The diffracted light analyzing means may have fringe scanning means for moving the diffraction grating to perform fringe scanning.

Further, the diffracted light analysis means may compensate the zeroth-order diffracted light component to calculate the wavefront aberration of the optical system under test.

Further, the diffracted light analyzing means has ± 0
The wavefront aberration of the optical system to be tested may be calculated by compensating for the diffracted light components of the second or higher order.

At the time of the calculation, the correction of the 0th order light may be obtained by the calculation formula in the following formula (1). (Where a _{+ 1} , a
₀ and a ₋₁ are the amplitude components of the waves of the + _1st order light, the 0th order light, and the −1st order light, k is the wave number, and w ₊₁ and w ₋₁ are the + 1st order light and the −1st order light, respectively. Is the wavefront aberration, and g _i is 0
Next, it is the interference light intensity value of the diffracted light of the 3rd component of the ± 1st order or the 2nd component of the ± 1st order.
When divided into l (l is a positive number of 3 or more), i = 1, 2,
3, ..., L + 1. )

[0023]

[Equation 1]

When the actual wavefront aberration is calculated by dividing one pitch of the diffraction grating into eight, the wavefront aberration of the optical system to be tested may be calculated by the following equation (2). (Here, k is the wave number, w ₊₁ and w ₋₁ are the wavefront aberrations of the + 1st order light and the −1st order light, respectively, and g ₁ , g ₂ , g ₃ , ..., G ₉ are of the diffraction grating. (This is an interference light intensity value of diffracted light of three components of 0th order, ± 1st order, or two components of ± 1st order when one pitch is divided into eight.)

[0025]

[Equation 2]

Similarly, when one pitch of the diffraction grating is divided into six, the wavefront aberration of the optical system to be tested may be calculated by the following equation. (Here, k is the wave number, w ₊₁ and w ₋₁ are the wavefront aberrations of the + 1st order light and the −1st order light, respectively, g ₁ , g ₂ ,
g _3, ..., g is 0-order, interference light intensity values of the diffracted light of ± 1-order three components or ± 1-order of the two components in the case of 6 dividing one pitch of the diffraction grating. )

[0027]

[Equation 3]

In the wavefront aberration measuring instrument of this structure, the light receiving member of the detection optical system may be a charge coupled device (CCD).

In the wavefront aberration measuring instrument having this structure, the optical system to be inspected is an exposure projection system for transferring the circuit pattern drawn on the reticle surface onto the wafer surface, and the optical system to be inspected by the optical system holding device to be inspected. The pinhole member may be arranged at a position where the reticle surface is arranged, and the light receiving member may be arranged at a position where the wafer surface is arranged while being held at a predetermined position.

In the wavefront aberration measuring device of this structure, the light source may be one of a synchrotron radiation light source, a laser plasma light source, or a discharge plasma light source.

In the wavefront aberration measuring device having this structure, a structure may be used in which a means for converting a spherical wave into a plane wave is provided between the diffraction grating and the light receiving member.

As described above, in the wavefront aberration measuring instrument according to the present invention, there are one having a mask member and one having a diffracted light analyzing means in order to compensate high-order light of 0th order or ± 2nd order or higher. is there. Further, the present invention has a wavefront aberration measuring machine as a third wavefront aberration measuring machine, which has both configurations of these two kinds of wavefront aberration measuring machines, that is, a light source for supplying light of a predetermined wavelength and a light from the light source for passing therethrough. A pinhole member having a pinhole for generating spherical wave light and an optical system under test are held at predetermined positions, and the optical system under test is irradiated with spherical wave light and emitted from the optical system under test. The optical system holding device to be inspected, the diffraction grating arranged at a position to receive the light emitted from the optical system to be inspected, and the position to receive the light emitted from the diffraction grating by receiving the light emitted from the optical system to be inspected. As a wavefront aberration measuring instrument using diffraction grating shearing interference consisting of a mask member arranged and a detection optical system that measures the interference pattern of diffracted light from the mask member, the mask member selectively selects only diffracted light of a predetermined order. Times to penetrate And the light selection means,
A diffracted light analyzing means for selectively analyzing only diffracted light components of a predetermined order may be provided.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a wavefront aberration measuring machine according to the present invention will be described below with reference to FIGS. As a preferred embodiment, consider a case where the measurement target of the wavefront aberration measuring device is an optical system to be inspected of an exposure projection device of semiconductor lithography for EUV light. Therefore, the exposure projection apparatus will be briefly described first.

As shown in FIG. 1, the exposure apparatus 1 uses the EUV so that the illuminance distribution on the projection plane necessary for the uppermost part is uniform.
A light source 2 for emitting light is arranged, a reticle support member 5 is arranged below the light source 2 so as to face the light source 2, and a circuit pattern of an integrated circuit is enlarged on the reticle support member 5 and a reticle is drawn precisely. 4 are arranged. Below the reticle support member 5, a projection optical system 6 composed of a mirror (reflection) type optical system having a light condensing function is arranged, and below it is placed on a stage 8 and coated with a photoresist (semiconductor) wafer. 7 (for example, a silicon wafer) is arranged, and the wafer 7 is configured to be moved and controlled in a horizontal plane with respect to the focal position of the projection optical system 6 by a driving device 9 connected to the stage 8.

In the exposure apparatus 1 having such a structure, the circuit pattern of the reticle 4 is reduced by the projection optical system 6 at a predetermined reduction ratio and projected and exposed on the wafer 7, and the circuit pattern is formed on the wafer 7. Transcribed. At this time, the circuit pattern is transferred to different positions on the wafer 7 by moving the stage 8 every time one projection exposure is completed. Such a stage drive and exposure method is called a step-and-repeat method. In addition to the stage drive / exposure method, there is a scan method in which a drive mechanism is also provided on the reticle support member 5 and the stage 8 and the reticle 4 are relatively moved to perform exposure.

The circuit pattern transferred onto the wafer 7 during this exposure has recently been required to be finer and finer. However, there is a limit to reducing the pattern size, and the minimum pattern size (resolution) R is calculated by the following equation () by the wavelength λ of the light source 2 used for projection by the exposure apparatus 1 and the numerical aperture NA of the projection optical system 6. 4).

[0037]

[Equation 4] R = K · λ / NA (4)

As is clear from the above equation (4), in order to reduce the minimum pattern size R, the constant K is decreased, the numerical aperture NA is increased, or the wavelength λ of the light source 2 to be projected. It can be seen that there are three ways to reduce.

Here, the constant K is a constant determined by the projection optical system and the process, and usually takes a value of about 0.5 to 0.8. The method of reducing the constant K is called super-resolution in a broad sense. Up to now, improvement of projection optical system, deformation projection, phase shift mask method, etc. have been proposed and studied. However, there are drawbacks such as restrictions on the applicable patterns. On the other hand, the numerical aperture NA can be made smaller as the numerical value NA becomes larger from the equation (4), but this causes a problem that the depth of focus becomes shallow. For this reason, there is a limit to increasing the NA value, and it is usually considered to be suitable from about 0.5 to 0.6 because of the balance between the two.

Therefore, the simplest and most effective method for reducing the size R of the minimum pattern is to reduce the wavelength λ of light used for exposure. Therefore, the light beam used for the exposure apparatus 1 that has been put into practical use is g of visible light.
Line (λ = 436 nm) to ultraviolet i-line (λ = 365n)
m), and further to KrF (krypton fluoride) excimer laser (λ = 248 nm) and ArF (argon fluoride) excimer laser (λ = 193 nm), to shorter wavelength light. F2 (fluorine) laser (λ = 157 nm) and soft X-ray (EUV) (λ = 13.4 nm) are considered as candidates for the light source 2 for the next-generation exposure apparatus.

In order to control such a short-wavelength light beam and project a circuit pattern on the wafer 7 surface, a projection optical system 6 having an optical precision corresponding to the wavelength is required. Therefore, by determining whether or not the wavefront aberration of the light emitted from the projection optical system 6 is a wavefront aberration that is practically allowed, the exposure apparatus 1 using the projection optical system 6 can be used as an optical exposure apparatus required as an exposure apparatus. Examining whether it meets the accuracy
A device for evaluation is a wavefront aberration measuring device 1 according to the present invention.
It is 0. Hereinafter, the configuration of the wavefront aberration measuring device 10 according to the preferred embodiment of the present invention will be described with reference to FIG.

The wavefront aberration measuring device 10 is for measuring the wavefront aberration of the projection optical system 6 constituting the exposure apparatus 1, and is a light beam 11 from a light source for supplying EUV light.
Condensing member 12 for reflecting and condensing light, pinhole member 13 having a pinhole for transmitting light from the condensing member 12 and generating spherical wave light, and a projection to be examined / evaluated An optical system holding device (not shown) that holds the optical system 6 at a predetermined position, irradiates the projection optical system 6 with spherical wave light, and emits reflected light from the projection optical system 6, and light emitted from the projection optical system 6. The moving member 18 is arranged at a position for receiving
The diffraction grating 14 that can be moved in the pitch direction of the grating by
The mask member 16 arranged at a position for receiving the light emitted from the diffraction grating 14, a detection optical system (CCD 17) for measuring an interference pattern of the diffracted light from the mask member 16, and the mask member 16 diffracted light of a predetermined order. And a diffracted light selection unit that selectively transmits only the light.

The details of the role of the above components will be described. E
The UV light source may be either a synchrotron radiation light source, a laser plasma light source, or a discharge plasma light source as long as it supplies light of a specific wavelength (for example, 13.4 nm). As shown in FIG. 2, the condensing member 12 is composed of a concave mirror, and condenses EUV light that is not suitable for condensing in the refractive optical element to increase the intensity (light amount) of the light.
The pinhole member 13 can generate an ideal spherical wave by the light condensed by the condensing member 12 passing through the pinhole. This ideal spherical wave serves as a reference when examining and evaluating the optical system under test. Projection optical system 6
For example, in FIG. 2, a mirror (reflection) type reduction optical system is formed by two convex mirrors 6a and 6c and two concave mirrors 6b and 6d. When the EUV light forming an ideal spherical wave passes through the projection optical system 6, it becomes EUV light containing information in the projection optical system 6 and is emitted. The EUV light emitted as shown in the figure enters the diffraction grating 14, and the information in the projection optical system 6 (more specifically, the optical mirror surfaces 6a, 6b,
6c, 6d and the like) are emitted with the light wavefronts having the distortions reflected sideways. The mask member 16 is arranged at the focal position of the spherical wave condensed by the projection optical system 6 (that is, the position where the wafer 7 in the exposure apparatus 1 is arranged). This can improve the selectivity of the diffracted light selecting means when the mask member 16 selectively separates the diffracted light of a predetermined order.

As shown in FIG. 3, the mask member 16 is made of EU.
It is configured to have windows 16a and 16b that transmit V rays, and an EUV ray blocking section made of a tantalum (Ta) thin film or the like, which is shown by a meshed section in FIG. The windows 16a and 16b may be holes. An interference pattern of + 1st-order light and -1st-order light transmitted through the windows 16a and 16b is generated. (How to determine the opening positions of the window portions 16a and 16b and the size of the window will be described later, and the transmission is made +
How to identify the primary light and the minus first light will be further described later. ) Transmitting only the + 1st-order light and the -1st-order diffracted light blocks the contribution of unnecessary diffracted light such as the 0th-order light and the high-order light of (±) second-order light or more when analyzing and estimating the wavefront aberration. This is because. (The validity of blocking the 0th-order light and the higher-order light above the + 2nd-order light or below the -2nd-order light is appropriate by the inventor of the present invention.
No. 0-146706 (Japanese Patent Application No. 10-31824). ) In order to cover the information on the wavefront aberration in the projection optical system 6, the phase difference between the + 1st order light and the −1st order light is π /
The phase is shifted by 2 (λ / 4). The moving member 18 is
This is for moving the diffraction grating 14 in the pitch direction with the control accuracy required for analysis. Finally, the CCD 17 is used as a detector for projecting an interference pattern in which two + first-order and −1st-order light waves of the diffracted light emitted from the two windows 16a and 16b of the mask member 16 are projected.

FIG. 4 shows an algorithm 50 for determining the dimensions of the constituent members of the wavefront aberration measuring instrument 10 according to the present invention.
It is shown. There are three stages in total, the first stage is a stage 51 for determining the number of interference light beams finally observed from the resolution required for the wavefront aberration measuring device 10 and the resolution of the CCD 17, and the second stage is a previous stage 51. Based on the result of the above, the step 52 of determining the distance between the windows of the mask member, and finally the third step is the step 53 of determining the diameter of the pinhole and the size of the window of the mask member based on the diameter. The contents of each stage will be specifically described below.

In the first stage, in order to see the wavefront distortion by the projection optical system 6 of the EUV exposure apparatus, the resolution of the wavefront aberration measuring instrument 10 must be at least 0.5 nm as described above. On the other hand, CCD 1 used as a detection optical system
In No. 7, the number of pixels is 1024 × 1024, and the actual size of one side of each pixel is about 10 μm. In principle, an interfering manuscript with a width of 4 pixels or less per interfering manuscript cannot be discriminated, but in consideration of the actually required measurement accuracy, C
A maximum of about 80 diffraction interference patterns will be projected on the screen of the CD 17.

In the second step, the window spacing of the mask member 16 is determined. Consider now that the mask member 16 has two windows 16a and 16b as shown in FIG.
The two windows 16a and 16b are for selectively transmitting the + 1st order light and the −1st order light of the diffracted light from the diffraction grating 14. The spacing between the two windows is determined as follows. First, the distance from the window 16a for the + 1st order light to the CCD screen and -1
When the difference from the distance from the window 16b for the next light to the screen of the CCD 17 is defined as the optical path difference OPD (Optical Path Difference), the relationship with the number N of diffraction interference images projected on the screen of the CCD 17 is expressed by the following equation (5). Given.

[0048]

## EQU5 ## OPD = (N / 2) λ (5)

The relationship between the numerical aperture NA of the projection optical system 6, the distance d between the two windows and the OPD is given by the following equation (6).

[0050]

## EQU6 ## OPD / d = NA (6)

If OPD is eliminated from the equations (5) and (6), the following relational equation (7) is obtained.

[0052]

(7) (N / 2) λ = d × NA (7)

The light source is EUV (λ = 13.4 nm) and C
When the number of interference drafts on the CD17 screen is N = 80 and the projection optical system 6 is a 4 × reduction projection optical system with a numerical aperture NA of 0.25, d = 2144 nm is obtained from the equation (7). In this way, the distance between the windows in the mask member can be determined.

In the third step, the diameter Φ of the pinhole opened in the pinhole member 13 is determined. The diameter Φ of the pinhole is given by the following equation (8), and is about 107 nm when the numerical aperture NA is 0.25 in the projection optical system 6.

[0055]

Φ = λ / (2 × (NA / 4)) (8)

In the case of this 4 × reduction projection optical system, the size of the spot appearing on the mask is the pinhole member 1
If the diameter of the pinhole formed in 3 is Φ, then Φ / 4. Then, the spot size becomes about 27 nm. This is an ideal case where there is no aberration, and when there is actually aberration, the spot becomes even larger. In consideration of the above, in order to block 0th-order light and high-order light of ± 2nd-order or more and to allow ± 1st-order light to pass through the window more than enough, in the present embodiment, the window size 1 is set to one side. It is about 250 nm.

As described above, from the wavelength λ of the light source, the numerical aperture of the optical system to be tested, and the resolution required for the examination / evaluation of the optical system to be tested, the wavefront aberration measuring instrument 10 of the present invention can display the image on the CCD 17 screen. The number of diffraction interference patterns, the interval and size of the windows of the mask member 16, and the diameter of the pinhole can be determined.

Here, the diffracted light selection means will be described.
In the present embodiment, the diffracted light selection means is the mask member 16
The windows 16a and 16b opened in the
This is to ensure that the second light and the first light are transmitted. For that purpose, a spot image of the 0th-order light of the diffracted light is found, and the spot image is surely opened in the window 16a of the mask member 16 and the window 1.
It is required to irradiate the intermediate portion 16c of 6b. Since the image of the 0th-order light is formed at the focal position of the projection optical system 6 when the diffraction grating 14 is removed, the diffraction grating 14 in the optical path is once removed and the mask member 16 is irradiated with the 0th-order light at the focal position. The optical device may be assembled so that the condensed EUV light is emitted. Next, the diffraction grating 14 is installed, and the mask member 16 is provided with +1 at substantially the center position of the opening windows 16a and 16b.
The diffraction grating 14 is moved and adjusted so that the second-order light and the −1st-order light are incident. If you install optical equipment like this,
An interference draft reflecting the distortion of the projection optical system 6 appears on the screen of the CCD 17, and the wavefront aberration measuring apparatus 10 that is easy to analyze and has a required resolution can be obtained.

In the above description, the diffraction grating 14 was once removed in order to identify the 0th-order light, but it is not always necessary to do so, and the 0th-order light has the highest intensity as compared with other higher-order lights. Other methods, such as specifying the 0th-order light by using the above, may be used.

Whether or not the wavefront aberration w calculated by the above evaluation procedure is the wavefront aberration allowed by the projection optical system 6 of the exposure apparatus 1 can be known, and the projection optical system 6 can be examined and evaluated accurately.

Next, as a second embodiment of the present invention, a wavefront aberration measuring machine having an analyzing means for evaluating the optical system 6 to be tested without using a mask member will be described. (In the second embodiment, the basic configuration of the wavefront aberration measuring device 10 is the same as that described above (hereinafter referred to as the first embodiment), but is characterized in that the mask member 16 is not provided.) In the measurement, the intensities of the diffracted light are approximately (in the same diffraction image, that is, in the same envelope of the diffracted light intensity) zero-order light, ± first-order light,
± 2nd order light, ...
When extracting the primary light, it is more difficult to exclude the 0th light than the ± 2nd light. Therefore, it is attempted to eliminate the 0th-order light component from the observed interference fringe intensity by a calculation method.
It is an analysis means in the second embodiment.

The analyzing means first ignores the diffracted light of ± 2nd order or higher. The wave functions of the remaining −1st order, 0th order, and + 1st order diffracted light are expressed by the following equations (9) and
It can be given in (10) and (11).

[0063]

[Equation 9]

[0064]

[Equation 10]

[0065]

[Equation 11]

Here, a is an amplitude component, k is a wave number [dimension:
1 / L] and w are wavefront aberrations [dimension: L]. At this time, the actually observed interference fringe intensity is given by the following equation (12).

[0067]

[Equation 12]

Since the phase is laterally shifted in the shearing interferometer, the diffraction grating 14 is moved by the moving member 18 in the pitch direction of the grating by the moving member 18 for this purpose. At this time, the amount of phase shift that changes corresponding to this movement amount Δx is referred to as the phase shift amount Δφ. Assuming that the diffraction grating period is p, the phase shift amount Δφ is 2π when moved by one period, so that the relationships of the following expressions (13) and (14) are satisfied. Where m
Is the order of diffracted light.

[0069]

Δφ = 2πw × Δx (13)

[0070]

(14) w × p = m (14)

When the diffraction grating 14 is shifted by p / 8 in the pitch direction of the grating with respect to the movement amount Δx of the diffraction grating (9
This method is referred to as a 9-bucket method in order to return to the original in step), and the 0th and ± 1st order phase shift amounts Δφ are shown in Table 1 below.

[0072]

[Table 1]

The phase shift amount Δφ and the above equation (13),
Interference fringe intensity g _n of the n-th step of taking into account the (14), the wave function expression amount of phase shift [Delta] [phi (9) ~ (1
It suffices to add it to the phase portion of 1), and in general, it can be written as the following expression (15). Here, N is the number of divisions of lattice movement. For example, it is 8 in the 9-bucket method and 6 in the 7-bucket method described later. A new index l is introduced for convenience of later, N = 2l, l = 3, 4, ...
Is.

[0074]

[Equation 15]

Substituting into the phase change amount Δφ equation (15) in the 9-bucket method shown in Table 1, the following equation (16) representing the interference fringe intensity values g ₂ to g ₉ is obtained as in the equation (12). ~ (2
3) is obtained.

[0076]

[Equation 16]

[0077]

[Equation 17]

[0078]

[Equation 18]

[0079]

[Formula 19]

[0080]

[Equation 20]

[0081]

[Equation 21]

[0082]

[Equation 22]

[0083]

[Equation 23]

From the above, the following two equations (24) and (2
5) is obtained.

[0085]

[Number 24] (g4 + g8) - (g2 + g6) = 8a +1 a -1 sin [k (w +1 -w -1)] ... (24)

[0086]

[Number 25] (g1 + g5) - (g3 + g7) = 8a +1 a -1 cos [k (w +1 -w -1)] ... (25)

From equations (24) and (25), the phase k (w ₊₁ −) obtained by removing the 0th-order light by the 9-bucket method (8 divisions) is used.
The following analytical expression (26) for obtaining w ₋₁ ) is obtained.

[0088]

[Equation 26]

Alternatively, considering that g ₁ = g ₉ , the phase k excluding the influence of the 0th-order light by the following 9-bucket method is used.
The following analytical expression (27) for obtaining (w ₊₁ −w ₋₁ ) is obtained.

[0090]

[Equation 27]

[0091] The difference from the equation (26) or equation (27), + 1-order light of the wavefront aberration w ₊₁ and -1 order light wavefront aberration w _-1 [Delta] w
(= W _{+ 1} -w- ₁ ) is known. The difference Δw is regarded as the differential value of the wavefront aberration, and the wavefront aberration of the optical system 6 to be detected is detected.

There is a 7-bucket method in which the lattice spacing is divided into 6 (returning to the same phase in 7 steps), in addition to the 9-bucket method in which the lattice spacing is divided into 8 parts. Table 2 shows the 0th and ± 1st order phase shift amounts Δφ when the diffraction grating 14 is shifted by p / 6 in the grating pitch direction with respect to the movement amount Δx of the diffraction grating in the 7-bucket method. .

[0093]

[Table 2]

Substituting the parameters in the 7-bucket method shown in Table 2 into the general formula (15) of the interference fringe intensity g _n at the nth step, the following formulas (28) to (34) can be written. . Here, N (= 2l) = 6.

[0095]

[Equation 28]

[0096]

[Equation 29]

[0097]

[Equation 30]

[0098]

[Equation 31]

[0099]

[Equation 32]

[0100]

[Expression 33]

[0101]

[Equation 34]

From the above equations (28) to (34), the following equations (35) to (37) are obtained.

[0103]

[Equation 35]

[0104]

[Equation 36]

[0105]

[Equation 37]

From these equations (35) to (37), the phase k (w _{+ 1-} w) is obtained by removing the influence of the 0th order light by the following 7-bucket method.
_The following analytical expression (38) for obtaining ₋₁ ) is obtained.

[0107]

[Equation 38]

Up to this point, the 9-bucket method and the 7-bucket method have been described.
l: l = 1, 2, 3, ...) In general, 0th-order light can be compensated. When the diffraction grating is moved by one cycle, the phase shift amount Δφ is 2π, so that even division results in a certain interference intensity g _i (i = 1, 2, ..., L + 1).
And the sum of those (g _{i + l} ) that are further shifted by π phase is 0
An equation is obtained in which the contribution of the next-light component (a ₀ or w ₀ ) disappears.
The equation can be directly obtained by directly substituting it into the equation (15), and when specifically written down, it becomes the following equation (39). For more than 7 buckets, some (g _i + g obtained from equation (39)
_{When i + l} ) is combined, an expression for calculating the amplitude components a _-1 , a ₀ , a ₊₁ phase k (w ₊₁ -w _-1 ) is always obtained (proof not shown).

[0109]

[Formula 39]

Further, a finer division (11
Bucket, 13 buckets, ...)
It may be possible to perform equivalent wavefront aberration measurement with a smaller number of divisions (buckets). For example, the 16-partition 17-bucket method includes the 8-partition 9-bucket method as it is, and thus the 9-bucket method is sufficient. The method of multi-division is
This is advantageous in that each interference fringe intensity measurement is statistically averaged, but on the contrary, high precision and fine control are required, which is also disadvantageous in cost. Therefore, the 9-bucket method and the 7-bucket method are practically useful in that they can be analyzed without knowing the original amplitude of the wave function.

From the equations (26), (27) and (38), k (w ₊₁ −w ₋₁ ) is obtained, and the wavefront aberration Δw is obtained from the obtained value.
The test optical system can be examined and evaluated by obtaining (= w _{+ 1} -w- ₁ ).

By the above evaluation procedure, it is possible to know whether or not the wavefront aberration w calculated by the second embodiment is the wavefront aberration allowed as the projection optical system 6 of the exposure apparatus 1, and the examination / evaluation of the projection optical system 6 is accurate. I can do it well.

Up to now, as the first embodiment of the present invention,
A wavefront aberration measuring device configured by providing a mask member that selectively transmits the 1st-order and -1st-order diffracted light will be described.
As an embodiment, a wavefront aberration measuring machine configured to have an analyzing unit that arithmetically corrects a 0th-order light component from interference intensities obtained by mixing a plurality of fringe scan methods from a mixture of 0th-order light and ± 1st-order light has been described. It was

Next, as a third embodiment of the present invention, an ideal spherical wave is produced from the pinhole member 13 and the optical system 6 under test is detected.
The light emitted from the optical system 6 to be measured is irradiated onto the diffraction grating 14
Optical interference (CCD17)
The basic structure common to the first and second embodiments, such as the observation in step 1, is left as it is, and the mask member 16 is arranged between the diffraction grating 14 and the CCD 17 as in the first embodiment. Is disposed at a substantially image forming position of the optical system to be inspected, and +1 through the mask member 16 and -1 and -1.
Consider a wavefront aberration measuring device having a configuration using the analyzing means in the second embodiment using the intensity of the interference fringes formed on the light receiving surface of the CCD 17 by the next diffracted light.

The mask member 16 sufficiently blocks the diffracted light of ± 2nd order light or more, but the intensity of the 0th order light is the strongest among the diffracted lights.
The 0th-order light component may leak from a or 16b.
However, in the third embodiment, since the component of the 0th-order light can be further corrected by the analyzing means, the wavefront aberration can be calculated sufficiently, and the examination / evaluation of the optical system 6 to be inspected can be performed with high accuracy.

In the first, second and third embodiments as well, if the wavefront aberration measuring machine 10 is constructed as described above and the measurement result is analyzed as described above, the EU
The light source that provides V light (soft X-ray light) does not necessarily have to be a synchrotron radiation light source with high spatial coherence, and even if it is a laser plasma light source or discharge plasma light source with lower spatial coherence, the wavefront aberration w It is possible to calculate and evaluate / evaluate the EUV exposure apparatus using these EUV light sources.

Further, an aspherical wave reflecting mirror for converting a spherical wave into a plane wave may be provided between the mask member 16 and the CCD 17 in the configurations of the first, second and third embodiments.
When laterally offset spherical waves interfere with each other, even if the optical system under test is aberration-free, an interferogram having a measurement principle error will be formed due to coma aberration caused by the arrangement, but the spherical wave is converted into a plane wave. As a result, it is possible to eliminate coma aberration caused by the arrangement, so that it is possible to form a linear interference pattern. A mask member 16 having the opening windows 16a and 16b and a mask member having a switchable pinhole and an opening may be provided. When the mask member 16 is switched to a mask member having a pinhole and an opening, it is possible to switch to a point diffraction interferometric measurement method in which an ideal diffractive spherical wave is generated from the pinhole as reference light and measurement light is generated from the opening. In the case of point diffraction interferometry, it is suitable for highly accurately measuring an optical system to be tested having a relatively small wavefront aberration. On the other hand, in the case of shearing interferometry, even an optical system under test having a large wavefront aberration can be measured.

[0118]

As described above, according to the wavefront aberration measuring instrument of the present invention, a wavefront aberration measuring instrument using diffraction grating shearing interference with respect to a mirror (reflection) type optical system can be constructed, and a mask member and an analyzing means. Since it blocks diffracted light of 0th order or higher than ± 2, it does not require complicated analysis due to the influence of diffracted light of 0th order or higher order, and obtains the resolution required for examination / evaluation by measurement. It is possible to provide a wavefront aberration measuring device capable of performing the above.

[Brief description of drawings]

FIG. 1 is a schematic view of a (semiconductor) exposure apparatus for explaining an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a wavefront aberration measuring device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining a mask member of the wavefront aberration measuring device according to the embodiment of the present invention.

FIG. 4 is a flow chart for explaining a method of determining the configuration of the wavefront aberration measuring machine according to the embodiment of the present invention.

[Explanation of symbols]

1 Exposure device 2 light sources 4 reticle 6 Projection optical system (test optical system, test optical system holding device) 7 wafers 10 Wavefront aberration measuring instrument 13 pinhole material 14 diffraction grating 16 Mask member 16a, 16b windows (openings) 17 CCD (detection optical system)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mikihiko Ishii             Marunouchi 3 2-3 No. 3 shares, Chiyoda-ku, Tokyo             Ceremony Company Nikon (72) Inventor Katsumi Sugisaki             Marunouchi 3 2-3 No. 3 shares, Chiyoda-ku, Tokyo             Ceremony Company Nikon (72) Inventor Katsuhiko Murakami             Marunouchi 3 2-3 No. 3 shares, Chiyoda-ku, Tokyo             Ceremony Company Nikon F term (reference) 2G086 HH06                 2H097 CA15 LA10                 5F046 FA10 GA03 GA14 GB01 GB03                       GB07 GB09

Claims (21)

[Claims] 1. A light source for supplying light of a predetermined wavelength, a pinhole member having a pinhole for transmitting light from the light source to generate light of a spherical wave, and a test optical system held at a predetermined position. Then, a test optical system holding device that irradiates the test optical system with the spherical wave light and emits light from the test optical system, and is arranged at a position for receiving light emitted from the test optical system. A diffraction grating, a mask member arranged at a position for receiving light emitted from the diffraction grating by receiving light emitted from the optical system to be measured, and an interference pattern of diffracted light from the mask member is measured. A wavefront aberration measuring instrument using diffraction grating shearing interference composed of a detection optical system, wherein the mask member has a diffracted light selecting means for selectively transmitting only diffracted light of a predetermined order. . 2. The wavefront aberration measuring machine according to claim 1, wherein the light receiving member of the detection optical system is a charge coupled device (CCD). 3. The wavefront aberration measurement according to claim 1 or 2, wherein the mask member is arranged at a substantially image forming position of the spherical wave focused by the optical system to be tested. Machine. 4. The wavefront aberration measurement according to claim 1, wherein the diffracted light selection unit is configured by providing a predetermined number of openings in the mask member. Machine. 5. The wavefront aberration measuring device according to claim 4, wherein the diffracted light transmitted through the opening provided in the mask member is diffracted light of + 1st order and −1st order. 6. The test optical system is an exposure projection system for transferring a circuit pattern drawn on a reticle surface onto a wafer surface, and the test optical system holding device causes the test optical system to move to the predetermined position. 2. The method according to claim 1, wherein the pinhole member is arranged at a position where the reticle surface is arranged, and the mask member is arranged at a position where the wafer surface is arranged while being held by the wafer. Item 6. The wavefront aberration measuring device according to any one of items 5. 7. The light source is a synchrotron radiation source,
7. The wavefront aberration measuring device according to claim 1, wherein the wavefront aberration measuring device is one of a laser plasma light source and a discharge plasma light source. 8. The wavefront according to claim 1, further comprising means for converting a spherical wave into a plane wave between the diffracted light selecting means and the light receiving member. Aberration measuring machine. 9. The wavefront aberration measuring device according to claim 1, further comprising a mask member having the diffracted light selection means, a switchable pinhole, and an opening. . 10. A light source for supplying light of a predetermined wavelength, a pinhole member having a pinhole for transmitting light from the light source to generate light of a spherical wave, and an optical system to be tested held at a predetermined position. Then, a test optical system holding device that irradiates the test optical system with the spherical wave light and emits light from the test optical system, and is arranged at a position for receiving light emitted from the test optical system. In a wavefront aberration measuring instrument using diffraction grating shearing interference, which comprises a diffraction grating and a detection optical system for measuring an interference pattern of the diffracted light from the diffraction grating, only a diffracted light component of a predetermined order is selectively analyzed. A wavefront aberration measuring instrument having diffracted light analyzing means. 11. The wavefront aberration measuring device according to claim 10, wherein the diffracted light analysis unit includes a fringe scanning unit that moves the diffraction grating to perform fringe scanning. 12. The wavefront aberration measuring device according to claim 10, wherein the diffracted light analysis means corrects a 0th-order diffracted light component to calculate a wavefront aberration of the optical system under test. 13. The diffracted light analysis means is 0 order and ± 2.
The wavefront aberration measuring instrument according to claim 10 or 11, wherein the wavefront aberration of the optical system to be tested is calculated by compensating for diffracted light components of the following or higher order. 14. The compensation of the 0th-order light is expressed by the following equation: (Here, a ₊₁ , a ₀ , and a _-1 are the amplitude components of the waves of the + _1st order light, the 0th order light, and the -1st order light, respectively, k is the wave number, and w ₊₁ and w _-1 are These are wavefront aberrations of the + 1st order light and the −1st order light, respectively, and g _i is the interference light intensity value of the diffracted light of the 0th order, ± 1st order three components or ± 1st order 2 components, and the index i is the diffraction grating. 14. When 1 pitch of is divided into 2l (l is a positive number of 3 or more), i = 1, 2, 3, ..., l + 1. Wavefront aberration measuring instrument. 15. The wavefront aberration of the optical system under test (Where k is the wave number and w ₊₁ and w _-1 are +1 respectively
The wavefront aberrations of the second-order light and the first-order light, g ₁ , g ₂ , g ₃ ,
…, G ₉ is 0 when 1 pitch of the diffraction grating is divided into 8
Next, it is the interference light intensity value of the diffracted light of the three components of the ± 1st order or the two components of the ± 1st order. ) The wavefront aberration measuring device according to any one of claims 11 to 13, wherein 16. The wavefront aberration of the optical system to be inspected (Where k is the wave number and w ₊₁ and w _-1 are +1 respectively
The wavefront aberrations of the second-order light and the first-order light, g ₁ , g ₂ , g ₃ ,
…, G ₇ is 0 when 1 pitch of the diffraction grating is divided into 6
Next, it is the interference light intensity value of the diffracted light of the three components of the ± 1st order or the two components of the ± 1st order. ) The wavefront aberration measuring device according to any one of claims 11 to 13, wherein 17. The wavefront aberration measuring device according to claim 10, wherein the light receiving member of the detection optical system is a charge coupled device (CCD). 18. The test optical system is an exposure projection system for transferring a circuit pattern drawn on a reticle surface onto a wafer surface, and the test optical system holding device moves the test optical system to the predetermined position. 11. The device according to claim 10, wherein the pinhole member is arranged at a position where the reticle surface is arranged, and the light receiving member is arranged at a position where the wafer surface is arranged while being held by the pinhole member. Item 18. The wavefront aberration measuring device according to any one of items 17. 19. The wavefront aberration measuring device according to claim 10, wherein the light source is one of a synchrotron radiation light source, a laser plasma light source, and a discharge plasma light source. 20. The wavefront aberration measurement according to claim 10, further comprising means for converting a spherical wave into a plane wave between the diffraction grating and the light receiving member. Machine. 21. A light source for supplying light of a predetermined wavelength, a pinhole member having a pinhole for transmitting light from the light source to generate light of a spherical wave, and a test optical system held at a predetermined position. Then, a test optical system holding device for irradiating the test optical system with the light of the spherical wave and emitting light from the test optical system, and a position arranged to receive the light emitted from the test optical system. A diffraction grating, a mask member arranged at a position for receiving light emitted from the diffraction grating by receiving light emitted from the optical system to be measured, and an interference pattern of diffracted light from the mask member is measured. In a wavefront aberration measuring instrument using diffraction grating shearing interference consisting of a detection optical system, the mask member selects diffracted light selection means for selectively transmitting only diffracted light of a predetermined order, and selects only diffracted light component of a predetermined order. To A diffracted light analyzing unit for analyzing the wavefront aberration measuring device.