JP2001241929A - Method and apparatus for measuring aspherical shape, projection optical system and exposing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure an aspheric surface at a high accuracy. SOLUTION: In the aspheric shape measuring method detecting an interference fringe formed by a light reflected from a surface having an aspheric design shape (aspheric surface) under detection and a light reflected from a Fizeau surface by a detector, detecting an interference fringe formed by a light reflected from a known shaped reference surface disposed, instead of the surface under detection and the light reflected from the Fizeau surface, and obtaining the shape of the surface under detection, based on the detected both interference fringes and the shape of the reference surface, the Fizeau surface is an aspheric one in this measuring method, and the shape of at least the aspheric Fizeau surface or the reference surface is set so that the fringe spacings of the interference fringes obtained for the design shape of the surface under detection and obtained for the reference surface are greater than that of an interference fringe obtained for the surface under detection with use of a spherical Fizeau surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical shape measuring method and an aspherical shape measuring device for measuring an aspherical surface shape used for an optical element such as a lens or a mirror with high accuracy. Further, the present invention relates to a projection optical system and an exposure method using an optical element having an aspherical surface.

[0002]

2. Description of the Related Art In processing an optical element such as a lens or a mirror, it is essential to measure a surface shape for measuring a manufacturing error of the surface. Of these optical elements, a spherical Fizeau interferometer is generally used for measuring the surface shape of a surface whose design shape is a spherical surface (hereinafter, referred to as a “test spherical surface”).

[0003] Here, the spherical Fizeau interferometer, like other interferometers, causes light from the surface to be detected to interfere with reference light, which is light reflected from the Fizeau surface, and causes interference fringes generated by this to occur.
It is detected by a detector such as a CD image sensor.
In the spherical Fizeau interferometer, a spherical Fizeau surface is used, and when the shape of the surface to be measured is displaced from the spherical surface, interference fringes of a pattern corresponding to the displacement are detected.
Therefore, the shape of the test spherical surface can be measured as a deviation from the spherical surface (hereinafter, referred to as “aspherical amount”).

On the other hand, in many cases, the spherical Fizeau interferometer is applied as it is to the measurement of the surface shape of a surface of an optical element having a designed aspherical surface (hereinafter, referred to as “test aspherical surface”). In this case, the shape of the test aspherical surface can be measured as an aspherical amount based on the approximate spherical surface.

[0005] In the spherical Fizeau interferometer, when the aspherical amount of the surface to be measured exceeds an allowable range, the measurement accuracy deteriorates. This is because the fringe density of the interference fringes increases as the amount of aspherical surface of the test surface increases, and if the fringe interval is narrower than the resolution of the detector, accurate detection cannot be performed. However, since the design shape of the above-mentioned spherical surface to be measured is a spherical surface, the amount of aspherical surface is within an allowable range and the measurement is performed with sufficient accuracy unless the fabrication error is extremely large.

[0006]

However, the design aspherical surface of the aspherical surface to be examined is
Even if the fabrication error is small, the aspherical amount of the design shape (the shape fabricated without any difference) (hereinafter “design aspherical amount”)
) Exceeds the allowable range, it is inevitable that the measurement accuracy deteriorates, and measurement becomes practically impossible.

[0007] Incidentally, the actual aspheric surface to be measured is a curved surface having a different radius of curvature depending on the radial position, and the fringe density of the interference fringes generated in that case differs depending on the position. Is a surface shape corresponding to a particularly dense position in the interference fringes. The present invention provides an aspherical shape that enables measurement of an aspherical surface (large aspherical surface) whose design aspherical amount exceeds the allowable range of a spherical Fizeau interferometer by increasing the accuracy of the measurement of the aspherical surface. An object of the present invention is to provide a measuring method and an aspherical shape measuring device.
It is another object of the present invention to improve the accuracy of a projection optical system and an exposure method using an optical element having an aspheric surface.

[0008]

According to a first aspect of the present invention, there is provided a method for measuring an aspheric surface shape, comprising the steps of: detecting, by a detector, a surface to be inspected having an aspherical design (an aspheric surface to be inspected); ) And the reflected light from the Fizeau surface are detected by a detector, and the reflected light from a reference surface of a known shape arranged in place of the test surface and the reflected light from the Fizeau surface are detected. The interference fringes formed by the reflected light are detected, and the shape of the test surface is obtained based on the two detected interference fringes and the shape of the reference surface.

In the method for measuring an aspherical surface shape, the Fizeau surface is an aspherical Fizeau surface. Further, the fringe interval of interference fringes obtained with respect to the design shape of the test surface and the fringe interval of interference fringes obtained with respect to the reference surface are all different from each other when the spherical Fizeau surface is used. At least the shape of the aspherical Fizeau surface or the reference surface is set so as to be larger than the fringe interval of the interference fringes obtained.

In the method of measuring an aspheric surface shape according to any one of claims 2 to 6, the amount of the aspheric surface of the Fizeau surface is set between the design shape of the surface to be measured and its approximate spherical surface. Is set to the amount of aspheric surface. At this time, the interference fringes obtained on the test surface have a density corresponding to the difference in the amount of aspherical surface between the test surface and the Fizeau surface. This density is coarser than the density of interference fringes obtained by the spherical Fizeau interferometer on the same test surface, that is, the density corresponding to the difference in the amount of aspherical surface between the test surface and the spherical surface. Therefore, the fringe interval of the interference fringes obtained with respect to the test surface can be reliably increased.

In the method of measuring an aspheric surface shape according to any one of claims 3 to 6, the aspheric amount of the reference surface is set to be smaller than the designed aspheric amount of the test surface. . In the aspherical surface shape measuring method according to claim 4 or 6, the aspherical amount of the reference surface is an aspherical surface between the aspherical Fizeau surface and the approximate spherical surface of the design shape of the test surface. Set to quantity. Further, in the aspherical surface shape measuring method according to claim 5 or 6, the shape of the reference surface is set to a spherical surface.

In this way, the preparation of the reference surface having a small amount of aspherical surface and the measurement of the surface shape are performed by preparing a reference surface having the same aspherical amount as the design shape of the test surface and measuring the surface shape. This is easier than the case where the amount of aspherical surface is small. That is, in these aspheric surface shape measuring methods, a reference prototype which is measured with high accuracy can be prepared as a reference surface. In particular, when the shape of the reference surface is a spherical surface, an existing interferometer, such as a spherical Fizeau interferometer or a Point-
The shape of the reference surface can be measured with extremely high precision by a spherical measurement interferometer such as a Diffraction-Interferometer. Therefore, finally, the surface shape of the surface to be detected can be obtained with high accuracy.

In the aspherical surface shape measuring method according to claim 6, the aspherical surface shape of the Fizeau surface and the shape of the reference surface are determined based on a fringe interval of interference fringes obtained with respect to the test surface and the reference surface. Each of the fringe intervals of the interference fringes obtained with respect to the surface is set to be equal to or more than two pixels on the detector. As described above, if the minimum fringe interval d of the interference fringes is larger than twice the pixel pitch P of the detector (2P <d), each pixel of the detector can reliably detect the presence or absence of the fringes. Detection accuracy is improved.

According to a seventh aspect of the present invention, there is provided a method for measuring an aspherical surface according to any one of claims 7 to 9, wherein the reflected light from the surface to be inspected (the aspherical surface to be inspected) whose design shape is an aspherical surface and the known shape. The interference fringes formed by the light reflected from the Fizeau surface are detected by a detector, and the shape of the surface to be detected is obtained based on the detected interference fringes and the shape of the Fizeau surface. In this aspheric surface shape measuring method, the Fizeau surface is an aspherical Fizeau surface. Further, the fringe interval of the interference fringes obtained for the design shape of the test surface is larger than the fringe interval of the interference fringes obtained for the test surface when a spherical Fizeau surface is used. The aspheric Fizeau surface is set.

In the aspherical surface shape measuring method according to claim 8 or 9, the amount of aspherical surface of the Fizeau surface is equal to the amount of aspherical surface between the design shape of the surface to be measured and its approximate spherical surface. Is set. At this time, the interference fringes obtained on the test surface have a density corresponding to the difference in the amount of aspherical surface between the test surface and the Fizeau surface. This density is coarser than the density of interference fringes obtained by the spherical Fizeau interferometer on the same test surface, that is, the density corresponding to the difference in the amount of aspherical surface between the test surface and the spherical surface. Therefore, the interval between the interference fringes obtained with respect to the test surface can be reliably increased.

According to a ninth aspect of the present invention, in the method of measuring an aspherical surface shape, the shape of the Fizeau surface is such that a fringe interval of interference fringes obtained with respect to the test surface is equal to or more than two pixels on the detector. It is set as follows. Thus, the minimum fringe interval d of the interference fringes is larger than twice the pixel pitch P of the detector (2
If P <d), each pixel of the detector can detect the presence or absence of a fringe, so that the detection accuracy of interference fringes is improved.

According to a tenth aspect of the present invention, there is provided an aspherical surface shape measuring apparatus, wherein a Fizeau surface and a light beam emitted from a light source are converted into a predetermined wavefront, and both the Fizeau surface and a test surface having an aspherical design are designed. 10. An aspherical shape measuring device comprising a wavefront converting means for guiding and a detector for detecting an interference fringe formed by light reflected on both surfaces, wherein the Fizeau surface is any one of claims 1 to 9. This is the shape set in the aspherical shape measurement method described in the section. According to this aspherical surface shape measuring device, each of the aspherical surface shape measuring methods described above can be reliably performed.

When an aspherical surface is used as a reference surface, the above-described invention itself can be applied to measurement of the shape of the reference surface to improve the shape of the reference surface. The projection optical system according to claim 11, wherein a surface of an optical member used in the projection optical system is a projection optical system that exposes a pattern drawn on an original plate onto a substrate. A test surface measured by the aspherical shape measurement method according to any one of the above, based on the measured result,
The surface of the optical member is polished to a predetermined accuracy.

Since an optical member polished with high precision is used in this projection optical system, the pattern of the original plate is accurately exposed on the substrate. According to a twelfth aspect of the present invention, in the exposure method of exposing a pattern drawn on an original plate onto a substrate via a projection optical system, a surface of an optical member used in the projection optical system may have a first surface. A surface to be measured measured by the method for measuring an aspheric surface shape according to claim 9, wherein the optical member is polished within a predetermined accuracy based on the measured result.

In this exposure method, a projection optical system using an optical member polished with high precision is used, so that the pattern of the original plate is accurately exposed on the substrate.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] First, a first embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3. FIG. In the present embodiment, when measuring the surface shape of the test aspheric surface 17 ′ of the test object 17, an aspheric surface shape measuring device 10 and a reference prototype 18 having a reference surface 18 ′ of a known shape are prepared. You.

<Configuration of Aspherical Shape Measuring Apparatus> As shown in FIG. 1, an aspherical shape measuring apparatus 1 used in the present embodiment is used.
0 denotes a laser light source 11, a beam expander 12, a deflection beam splitter (PBS) 13, a quarter-wave plate 14,
Wavefront converting means 15, aspherical Fizeau surface 15 ', member (not shown) for supporting test object 17 and reference prototype 18 at test position (dotted line in FIG. 1), beam diameter conversion optical system 19, CC
A two-dimensional image detector 110 such as a D imaging device,
It is connected to a computing device 111 such as a computer and a display device 112 such as a monitor. Incidentally, the conventional spherical Fizeau interferometer is equivalent to one of these optical systems having a spherical Fizeau surface instead of the aspherical Fizeau surface.

In the aspherical shape measuring device 10, the beam diameter of the linearly polarized light beam L emitted from the laser light source 11 is expanded by the beam expander 12, and is incident on the PBS 13. The beam L is selected such that its polarization plane is reflected by the PBS 13, and after being reflected by the PBS 13,
The light enters the wavefront converting means 15 and the aspherical Fizeau surface 15 'through the four-wavelength plate 14.

The wavefront converting means 15 converts the wavefront of the incident light beam into the aspherical Fizeau surface 15 'and the aspherical surface 17' of the test object 17 located at the test position (or at the test position). It is designed so as to be converted into a wavefront which is incident on the reference plane 18 ') of the reference prototype 18 substantially perpendicularly and in phase. A part of the light beam incident on the wavefront converting means 15 is reflected on the Fizeau surface 15 'to become a reference light beam LR, and the other part is transmitted through the aspherical Fizeau surface 15' and becomes a predetermined aspherical wave. It becomes a certain measurement light beam LM.

The measuring light beam LM is incident on the aspherical surface 17 'of the test object 17 placed at the test position (or the reference surface 18' of the reference standard 18 placed at the test position). The measurement light beam LM reflected by these surfaces is applied to the aspherical Fizeau surface 1
5 ′, PB through the wavefront converting means 15 and the 波長 wavelength plate 14
It is incident on S13. The measuring light beam LM passes through the quarter-wave plate twice in a reciprocating manner, and the polarization plane is rotated by 90 degrees.
The light passes through S13. Measurement light flux L transmitted through PBS13
The beam diameter of M is converted by the beam diameter conversion optical system 19,
The light enters the two-dimensional image detector 110.

On the other hand, the reference light beam LR reflected by the aspherical Fizeau surface 15 ′ is transmitted to the wavefront converting means 15 and the 波長 wavelength plate 1.
4, the light passes through the PBS 13 and passes through the beam diameter conversion optical system 1
9 and enters the two-dimensional image detector 110. The reference light beam LR interferes with the measurement light beam LM, and forms an interference fringe on the two-dimensional image detector 110. The output of the two-dimensional image detector 110 is taken into the arithmetic unit 111 and analyzed. The arithmetic unit 111 calculates the phase distribution (here, the distribution of the phase difference between the measurement light beam LM and the reference light beam LR is referred to as “phase distribution”) and the surface shape.

In the above configuration, since the position to be inspected and the aspherical Fizeau surface 15 'are arranged close to each other, the influence of vibration or temperature change on the wavefront shape is measured by the measurement light beam LM and the reference light beam LR. Can be made almost the same for both, so that the error generated in the measurement result is small. The above-mentioned aspherical shape measuring apparatus 10 may be provided with a means for slightly moving the wavefront converting means 15 and the Fizeau surface 15 'in the optical axis direction by using a piezo element or the like. By this movement and the calculation (known) such as the phase shift interferometry in the calculation device 111, the calculation accuracy of the phase distribution is further improved. Further, the beam diameter conversion optical system 19 also serves to form an image of the test aspheric surface 17 ′ and the reference plane 18 ′ on the two-dimensional image detector 110, and accurately shapes the test aspheric surface 17 ′. In order to know, the design is reduced distortion. By correcting the abscissa of the interference fringes using the design value or the actually measured value of the distortion, the coordinates on the test aspheric surface 17 ′ and the coordinates on the two-dimensional image detector 110 can be accurately related. .

If the wavefront converting means 15 is designed to convert the wavefront of the incident light beam into a wavefront which is incident on the aspherical Fizeau surface 15 'almost vertically and in the same phase, for example, a spherical surface is used. And those made up of planar lenses, those made up of mirrors, those that include spherical and planar mirrors, those that include aspherical lenses, those that include aspherical mirrors, those that include transmissive diffractive optical elements,
Any of those including a reflection type diffractive optical element may be used.

The reference standard 18 and the test object 17 do not need to be arranged at the same test position, and may be different from each other if the difference between the two positions is known. However,
In that case, the difference between the two positions is measured in advance or is measured as appropriate. <Surface shape measurement procedure> The surface shape measurement procedure of the present embodiment will be described below.

First, the reference prototype 18 is arranged at the position to be inspected by the aspherical shape measuring device 10 to obtain the phase distribution W0 of the reference surface 18 '. Next, the reference prototype 18 is removed from the optical path, and the test object 17 is disposed at the test position.
7 'is obtained.

Next, the phase distribution W1 of the test aspheric surface 17 '
From the phase distribution W0 of the reference plane 18 ′, the reference plane 1
The shape difference Δw1 of the test aspheric surface 17 ′ based on 8 ′ is determined. Further, the shape w0 (known) of the reference surface 18 'is added to the shape difference Δw1 of the test aspheric surface 17' to obtain the test aspheric surface 1 '.
The shape w1 of 7 ′ is calculated. Note that in this surface shape measurement procedure, the order of acquiring the phase distribution W0 of the reference prototype 18 and acquiring the phase distribution W1 of the test aspheric surface 17 'may be interchanged. Further, based on the phase distribution W0 of the reference surface 18 'and the shape w0 (known) of the reference surface 18', the surface shape W4 of the aspherical Fizeau surface 15 'is calculated, and the surface shape W4 and the aspheric surface 17 to be measured are calculated. The shape w1 of the test aspherical surface 17 'may be calculated based on the phase distribution W1 of'.

In the case where the aspherical shape measuring apparatus 10 has a configuration in which the test object 17 and the reference prototype 18 are arranged at different positions, the above-described procedure includes the test object 17 and the reference prototype. Procedure for calculating in advance the difference between the aspheric surface 17 ′ to be measured and the shape of the wavefront incident on the reference surface 18 ′ due to the difference in the arrangement position with respect to the detector 18, and appropriately correcting the above measurement results such as the phase distribution Is added.

<Design of Each Surface> FIG. 2 shows the aspherical surface amount F2 of the reference surface 18 'and the aspherical surface amount F3 of the aspherical Fizeau surface 15' in this embodiment, and the designed aspherical surface of the aspherical surface 17 'to be measured. It is a figure which compares with quantity F1. In FIG. 2, the reference of the aspherical surface amounts F1, F2, and F3 of each surface is unified to the same approximate spherical surface S (approximate spherical surface of the design shape of the test aspherical surface 17 ') for easy comparison. did. In FIG. 2, the aspherical Fizeau 1
F3, expressed as the aspherical amount of 5 ', is, to be precise,
(Equivalent Fizeau surface aspherical amount) (Equivalent Fizeau surface means that each ray that has traveled straight from the respective position of the aspherical Fizeau surface 15 ′ in the normal direction of the Fizeau surface in the same phase with each other at the test position This equivalent Fizeau surface is also formed by connecting the ends of respective line segments extending by an equal distance from each position of the aspherical Fizeau surface 15 'to the position to be inspected in the direction normal to the Fizeau surface. It is also a surface.)

As is apparent from FIG. 2, in this embodiment,
The aspherical surface amount F3 of the aspherical Fizeau surface 15 'is set to a value between the design shape of the test aspherical surface 17' and its approximate spherical surface S (aspherical amount 0). Here, in general, the interference fringes obtained by the interferometer on the test surface have a density corresponding to the difference in the amount of aspherical surface between the test surface and the reference surface. In other words, the interference fringes become denser as the difference in the amount of aspherical surface increases.

Therefore, the interference fringes obtained by the conventional spherical Fizeau interferometer on the aspherical surface 17 'to be measured are as follows.
The density according to the difference in the amount of aspherical surface between 7 ′ and the spherical surface (generally ΔF0), that is, a relatively high density. On the other hand, the interference fringe obtained by the aspherical shape measuring apparatus 10 (FIG. 1) of the present embodiment on the aspherical surface 17 ′ to be measured is a difference in the amount of aspherical surface between the aspherical surface 17 ′ to be measured and the aspherical Fizeau surface 15 ′ ( The density substantially corresponds to ΔF1), that is, a relatively low density.

If the density of interference fringes is reduced in this way,
As shown in FIG. 3, the minimum fringe interval d of the interference fringes is larger than twice the pixel pitch P of the two-dimensional image detector 110 (2
P <d), preferably more than 4 times (4P <d), more preferably more than 8 times (8P <d). As a result, the detection accuracy of interference fringes is improved. Therefore, the phase distribution W1 of the test aspherical surface 17 'can be obtained with higher accuracy as compared with the case where the conventional spherical Fizeau interferometer is used.

Further, as is apparent from FIG. 2, in the present embodiment, the aspherical amount F2 of the reference surface 18 'is determined by the
7 'is set positively smaller than 7'. In this way, preparing the reference surface 18 ′ having a small amount of aspherical surface in advance and measuring the surface shape is better than preparing the same reference surface as the designed shape of the test aspherical surface 17 ′ and measuring the surface shape. , Which is easier because the amount of aspherical surface is small.

Therefore, in this embodiment, the reference prototype 1
As 8, the reference prototype measured with high accuracy can be prepared. Incidentally, in the example shown in FIG. 2, the aspherical surface amount F2 of the reference surface 18 'is replaced by the aspherical surface amount F of the aspherical Fizeau surface 15'.
By designing the reference surface 18 'to be smaller than 3, the reference surface 18' is made more precise.

Further, in the example shown in FIG.
The aspheric amount F2 of 8 ′ is the difference between the aspheric amount between the reference surface 18 ′ and the aspherical Fizeau surface 15 ′ (generally ΔF2), and the aspherical surface of the test aspherical surface 17 ′ and the aspherical Fizeau surface 15 ′. It is selected so as to be substantially equal to the amount difference (approximately ΔF1).
In this case, the interference fringes obtained for the test aspheric surface 17 'and the interference fringes obtained for the reference plane 18' draw patterns of substantially equal brightness, with opposite lightness and darkness.

If the reference plane 18 'is designed in this manner, the density of the interference fringes obtained for the reference plane 18' will be "coarse" as in the case of the interference fringes obtained for the aspheric surface 17 '(FIG. 3).
(2P <d, preferably 4P <d, more preferably 8P <d). Therefore, the phase distribution W0 of the reference surface 18 'is determined by the
As in the case of the phase distribution W1.

That is, in this embodiment, the phase distribution W0 of the reference surface 18 'in the surface shape measurement procedure,
The phase distribution W1 of 7 'is obtained with high accuracy, and the shape w1 of the test aspheric surface 17' is calculated with high accuracy. Also,
In the present embodiment, in particular, when the aspherical amount of the test aspherical surface 17 ′ is relatively small, a spherical prototype (a prototype having a spherical reference surface) is used instead of the reference prototype 18. Is also possible. In this case, the shape of the reference surface can be measured with extremely high precision by an existing interferometer, for example, a spherical measurement interferometer such as a spherical Fizeau interferometer or a Point-Diffraction-Interferometer.

Therefore, the finally obtained surface shape w1 of the test aspheric surface 17 'can be obtained with high accuracy. In summary, according to the present embodiment, it is possible to measure a large aspheric surface by increasing the accuracy of the measurement of the aspheric surface. <Others> In the above embodiment, as shown in FIG. 2, the aspherical surface amount F2 of the reference surface 18 'is designed to be smaller than the aspherical surface amount F3 of the aspherical Fizeau surface 15'.
If the density of the interference fringes is sufficiently coarse (2P <
d, preferably 4P <d, more preferably 8P <d)
If the surface shape is measured with sufficient accuracy in advance, the surface may be designed to be larger than the aspherical amount F3.

In the above embodiment, as shown in FIG. 2, the aspherical surface amount F2 of the reference surface 18 'is the difference between the aspherical surface amount of the reference surface 18' and the aspherical Fizeau surface 15 '(generally ΔF2).
Is selected so as to be substantially equal to the aspherical amount difference (approximately ΔF1) between the test aspherical surface 17 ′ and the aspherical Fizeau surface 15 ′, but the density of interference fringes is made sufficiently coarse (FIG. 3). As shown in (2), different values may be selected as long as 2P <d, preferably 8P <d.

The configuration of the aspherical surface measuring device 10 includes a plurality of types of reference prototypes, a plurality of types of aspherical Fizeau surfaces,
A configuration may be provided in which a plurality of types of wavefront converting means are provided, and a means for automatically selecting and setting a combination that satisfies a predetermined relationship (for example, the relationship shown in FIG. 2) from among them. [Second Embodiment] Next, a second embodiment of the present invention is shown in FIG.
This will be described with reference to FIGS.

Here, only the differences from the first embodiment will be described. In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 4, in the surface shape measurement of the aspherical surface 27 ′ of the test object 27 in the present embodiment, the aspherical surface 27 ′ is
Are divided into two regions Da and Db as shown in FIG. 1, and the surface shape is individually measured for each of these regions Da and Db. The reason why the test aspherical surface 27 'is divided and measured in this way is to increase the measurement accuracy by setting each measurement target to a surface having as small an aspherical amount as possible.

In FIG. 5, an area Da is a circular area such that 0 ≦ r ≦ ra2 is satisfied with respect to the radial position r of the aspheric surface 27 ′ to be inspected, and an area Db is an aspheric surface to be inspected. This is a ring-shaped area where rb1 ≦ r ≦ rb2 is satisfied for the radial position r of 27 ′. Each value ra2, rb
Since the relationship between 1 and rb2 is 0 ≦ rb1 ≦ ra2 ≦ rb2, the regions Da and Db have overlapping regions. This is based on the measurement result of the overlapping region. This is to remove the influence of the posture difference of the test object 27 generated in a procedure described later.

<Structure of Aspherical Shape Measuring Apparatus> In this embodiment, as shown in FIG.
Two reference surfaces are prepared: a reference surface 28a '(reference prototype 28a) used for measuring the surface shape of the region Da and a reference surface 28b' (reference prototype 28b) used for measuring the surface shape of the region Db. The aspherical shape measuring device 20 of the present embodiment includes:
Aspherical Fizeau surface 2 used in surface shape measurement of region Da
5a 'and an aspherical Fizeau surface 25b' used for measuring the surface shape of the region Db. In this aspherical surface shape measuring apparatus 20, when the aspherical Fizeau surface 25a 'is used, a wavefront converting means 25a designed to form a wavefront which is substantially perpendicular to the aspherical Fizeau surface 25a' and enters in the same phase is provided. Applied, while the aspheric Fizeau surface 25
When b 'is used, a wavefront converting means 25b designed to form a wavefront which is substantially perpendicular to the aspheric Fizeau surface 25b' and is incident at the same phase is applied.

<Surface shape measurement procedure> First, the aspheric surface 2 to be inspected
In measuring the area Da of 7 ', the aspherical Fizeau surface 25a' and the wavefront converting means 25a are arranged in the aspherical shape measuring device 20, and the test object 27,
The reference prototypes 28a are arranged in order, and the phase distribution W
1a and the phase distribution W0a of the reference plane 28a 'are obtained.
Then, the shape w1a of the region Da is calculated from the phase distributions W1a and W0a and the shape (known) of the reference surface 28a '.

In measuring the area Db of the aspherical surface 27 'to be measured, the aspherical Fizeau surface 25b' and the wavefront converting means 25b are arranged in the aspherical shape measuring device 20, and the measurement is performed at the position to be measured. The test object 27 and the reference prototype 28a are arranged in order, and the phase distribution W1b of the region Db and the reference surface 28b '
And the phase distribution W0b. And the phase distribution W1
The shape w1b of the region Db is calculated from b, W0b, and the shape (known) of the reference surface 28b '.

Further, the shape w1a of the region Da and the region Db
From the shape w1b of FIG.
Based on the phase distribution or surface shape obtained for the region satisfying ≦ r ≦ ra2, the influence of the posture difference of the test object 27 is removed. As a result, the entire shape w1 of the test aspheric surface 27 'is obtained. In the surface shape measurement procedure, the order of acquiring the phase distributions of the regions Da and Db and the reference surfaces 28a and 28b does not have to be the order described above.

<Design of Each Surface> FIG. 6 shows the aspheric amount F2a of the reference surface 28a ', the aspheric amount F2b of the reference surface 28b', and the aspheric amount F3 of the aspheric Fizeau surface 25a 'in this embodiment.
FIG. 6A is a diagram comparing the aspherical surface amount F3b of the aspherical Fizeau surface 25b ′ with the designed aspherical surface amount F1a of the region Da and the designed aspherical surface amount F1b of the region Db.

In FIG. 6, the reference of the aspherical surface amounts F1a, F2a, and F3a is unified to the same approximate spherical surface Sa (the approximate spherical surface of the design shape of the region Da) for easy comparison. Further, the reference of each aspherical surface amount F1b, F2b, F3b is unified to the same approximate spherical surface Sb (approximate spherical surface of the design shape of the region Db). Incidentally, F4 indicates the design aspherical amount of the test aspherical surface 27 'with reference to the approximate aspherical surface S of the entire surface of the test aspherical surface 27'.

In FIG. 6, the aspherical Fizeau 25
F3a, F3b shown as aspherical amounts of a ′ and 25b ′
Is exactly the "aspherical amount of the equivalent Fizeau surface" (the equivalent Fizeau surface is the aspherical Fizeau surface 25a ').
(Or 25b ') are light waves that travel straight from the respective positions in the normal direction of the Fizeau surface in the same phase as each other at the test position. The equivalent Fizeau surface can also be formed by connecting the ends of the respective line segments extending by an equal distance from each position of the aspherical Fizeau surface 25a '(or 25b') to the position to be inspected in the direction normal to the Fizeau surface. It is also a surface. ).

As is apparent from FIG. 6, in the present embodiment,
The aspherical surface amount F3a of the aspherical Fizeau surface 25a '
a is set to a value between the design shape of a and the approximate spherical surface Sa (aspherical amount 0), and the aspherical amount F of the aspherical Fizeau surface 25b 'is set.
3b is set to a value between the design shape of the region Db and its approximate spherical surface Sb (aspherical amount 0). According to this setting, the interference fringes obtained for the regions Da and Db of the test aspheric surface 27 ′ are sufficiently “coarse” (as shown in FIG. 3, 2P <
d, preferably 4P <d, more preferably 8P <d)
It can be. As a result, the detection accuracy of interference fringes is improved.

Therefore, the phase distribution W of the regions Da and Db
1a and W1b can be obtained with higher accuracy as compared with the case where a conventional spherical Fizeau interferometer is used. As is apparent from FIG. 6, in the present embodiment, the aspherical amount F2a of the reference surface 28a 'is set to be actively smaller than the area Da of the test aspherical surface 27'. 28b 'aspherical amount F
2b is set positively smaller than the area Db of the aspheric surface to be measured.

As described above, the reference surface 28 having a small amount of aspherical surface.
a ′ and 28b ′ are prepared in advance and the surface shape is measured by preparing the same reference plane as the design shape of the regions Da and Db,
In addition, as compared with the case of measuring the surface shape, it is easier because the amount of the aspherical surface is smaller.

Therefore, in this embodiment, the reference prototype 2
As 8a and 28b, reference prototypes measured with high accuracy can be prepared. In the example shown in FIG. 6, the aspherical surface amounts F2a and F2b of the reference surfaces 28a 'and 28b' are respectively obtained from the aspherical surface amount F3a of the aspherical Fizeau surface 25a 'and the aspherical surface amount F3b of the aspherical Fizeau surface 25b'. Are designed to be even smaller, so that the reference surfaces 28a 'and 28b' are made more precise.

In the example shown in FIG. 6, the reference surface 28
The aspherical amount F2a of a ′ is selected such that the aspherical amount difference between the reference surface 28a ′ and the aspherical Fizeau surface 25a ′ is substantially equal to the aspherical amount difference between the region Da and the aspherical Fizeau surface 25a ′. On the other hand, the aspherical amount F2b of the reference surface 28b '
Is the difference between the reference surface 28b 'and the aspherical Fizeau surface 25b'.
Are selected so as to be substantially equal to the difference in the amount of aspherical surface.
In this case, the interference fringes obtained for the region Da and the reference plane 2
The interference fringes obtained with respect to 8a 'draw a pattern of substantially equal brightness with opposite light and dark, while the interference fringes obtained with respect to the area Db and the interference fringe obtained with respect to the reference plane 28b' have opposite light and dark. Draw a pattern with approximately equal luminance.

By designing the reference planes 28a 'and 28b' in this manner, the density of the interference fringes obtained for the reference planes 28a 'and 28b' can be changed to "Density" in the same manner as the interference fringes obtained for the areas Da and Db. Coarse ”(as shown in FIG.
P <d, preferably 4P <d, more preferably 8P <
d). Therefore, the reference plane 28
The phase distributions W0a and W0b of a 'and 28b'
As with the phase distributions W1a and W1b of a and Db, they can be obtained with high accuracy.

That is, in the present embodiment, the phase distribution W0 of the reference surfaces 28a ', 28b' in the surface shape measurement procedure.
a, W0b, and phase distributions W1a, W1b of regions Da, Db
Is obtained with high accuracy, and, consequently, the shape w1 of the test aspheric surface 27 'is calculated with high accuracy. Further, in the present embodiment, especially when the aspherical amount of each area Da, Db of the aspherical surface 27 ′ to be inspected is relatively small, the reference prototypes 28a, 28b
, It is also possible to use a spherical prototype. In that case, existing interferometers, such as spherical Fizeau interferometers or Po
An interferometer for measuring a sphere, such as an int-Diffraction-Interferometer, can measure the shape of a reference surface with extremely high accuracy.

Therefore, the finally obtained surface shape w1 of the aspherical surface to be inspected 27 'can be obtained with high accuracy. In summary, according to the present embodiment, the measurement of the aspherical surface can be performed with high accuracy, and the measurement of the large aspherical surface can be performed. <Others> In the above embodiment, two sets of the aspherical Fizeau surface and the reference prototype are prepared according to the number of divisions of the area 2. However, one set of the aspherical Fizeau surface and the reference prototype are used. And may be shared for measurement of two regions. In this case, the positional relationship of the aspheric surface to be measured, the reference prototype, and the wavefront converting means on the optical axis may be changed according to the region to be measured.

In the present embodiment, the number of areas of the aspherical surface to be inspected is set to 2. However, when the amount of aspherical surfaces of the aspherical surface to be inspected is large, the number of areas of the aspherical surface is reduced so that the amount of aspherical surfaces in each area becomes small. May be increased. In addition, as described above, the aspherical shape measuring device 10 and the aspherical shape measuring device 20 described in each embodiment change the shape of the aspherical Fizeau surface (and the corresponding shape) depending on the shape of the test aspherical surface to be measured. (The content of the wavefront conversion means). Therefore, when the aspherical shape measuring device 10 and the aspherical shape measuring device 20 have an aspherical Fizeau surface having a predetermined shape, the shape of the aspherical Fizeau surface allows the measurement of a test object to be measured. The shape of the spherical surface is limited to some extent. In this case, it is preferable to preliminarily indicate on an outer case or the like of these devices so that the user can know how much aspheric surface the device targets.

In each of the above embodiments,
Reference prototype, aspherical Fizeau surface, wavefront conversion means corresponding to the aspherical Fizeau surface, prepare a plurality of combinations consisting of, further, according to the shape of the test aspherical surface to be measured, A device (for example, a computer) that automatically determines a combination that satisfies the relationship (for example, the relationship shown in FIG. 6) may be used.

When an aspherical surface is used as a reference surface in each of the above embodiments, any one of the above embodiments may be applied to shape measurement of the reference surface. This makes it possible to measure the shape of an aspherical surface having a larger aspherical amount as a result. [Application Example] Next, an application example of the present invention will be described.

According to the first and second embodiments described above, a test object such as an aspherical mirror or an aspherical lens can be measured with high accuracy. If such measurement reveals that the shape accuracy of the test object is not sufficient, the test object may be polished so that the shape error is compressed, and driven within the predetermined accuracy. it can.
The aspherical mirror and aspherical lens manufactured with high precision in this way can be applied to various devices.

For example, various devices that require mirrors and lenses manufactured with high precision include soft X-rays (wavelength
-15 nm: Extreme Ultra Violet) There is a projection optical system for an exposure apparatus and a projection optical system for an X-ray exposure apparatus. Here, the projection optical system 70 for a soft X-ray exposure apparatus disclosed in WO99 / 26728 (PCT published specification) and the like will be described in detail with reference to FIG. As shown in FIG. 7, the light beam EL from the light source is reflected by the mirror M and is irradiated on the reticle R on the reticle stage RST. The light beam reflected by reticle R is irradiated onto wafer W on wafer stage WST via projection optical system 70. In order to form a semiconductor circuit (chip) by exposing the semiconductor circuit pattern drawn on the reticle R onto the wafer W, the reticle R and the wafer W are scanned synchronously in the direction indicated by the arrow in the figure. .

The projection optical system 70 includes a first mirror M1, a second mirror M2, a third mirror M3, and a fourth mirror M4 for sequentially reflecting the EUV light EL reflected by the reticle R. Element) and these mirrors M1 to M
4 holding the lens barrel PP. The first
The reflecting surfaces of the mirror M1 and the fourth mirror M4 have an aspheric shape, the reflecting surface of the second mirror M2 is a flat surface,
The reflection surface of the mirror M3 has a spherical shape. Each reflecting surface achieves a processing accuracy of about 1/50 to 1/60 or less of the exposure wavelength with respect to the design value, and has an error of 0.2 to 0.3 nm or less in RMS value (standard deviation). In this application example, these first mirrors M1 having an aspheric design shape are used.
The first embodiment and the second embodiment described above are applied to check whether the fourth mirror M4 is processed within the error.

The material of each mirror is low expansion glass or metal, and on its surface, a reflective layer for EUV light is formed by a multilayer film in which two kinds of substances similar to the reticle R are alternately stacked. In this case, as shown in FIG. 7, a hole is provided in the fourth mirror M4 so that the light reflected by the first mirror M1 can reach the second mirror M2. Similarly, the light reflected by the fourth mirror M4
The first mirror M1 is provided with a hole so that it can reach. Of course, instead of making a hole, the outer shape of the mirror may be formed to have a notch through which a light beam can pass.

Further, since the environment in which the projection optical system 70 is placed is a vacuum, there is no place for heat to escape due to the irradiation of exposure illumination light. Therefore, the mirrors M1 to M4 and the mirror M
A heat pipe HP connects between the lens barrels PP holding 1 to M4, and a cooling device for cooling the lens barrel PP is provided. That is, the lens barrel PP is connected to the inner mirror holding portion 71.
And a cooling jacket 72 as a cooling device mounted on an outer peripheral portion thereof. A spiral structure for flowing a cooling liquid from the inflow tube 74 to the outflow tube 76 is provided inside the cooling jacket 72. A pipe 78 is provided. The cooling water flowing out of the cooling jacket 72 via the outflow tube 76 exchanges heat with the refrigerant in a refrigerating device (not shown), is cooled to a predetermined temperature, and then cooled through the inflow tube 74. The cooling water is circulated in this manner.

In the projection optical system 70, the mirrors M1, M2, M2 are irradiated by the exposure illumination light (EUV light) EL.
3. Even if heat energy is given to M4, heat pipe H
Heat exchange is performed between the lens barrel PP whose temperature has been adjusted to a constant temperature by P, and the mirrors M1, M2, M3, and M4 are cooled to a constant temperature. In this case, as shown in FIG. 7, mirrors M1, M2, M4, etc. are not only on the back side but also on the front side (reflection side).
The heat pipe H is also used for the portion where the illumination light for exposure is not irradiated.
Since P is attached, the cooling of each mirror is performed more effectively than when only the back surface is cooled. It is preferable to control the temperature so as to match the cooling temperature.

Needless to say, as described above, the first mirror M1 and the fourth mirror M4, which require extremely high accuracy,
In the measurement of the surface shape of the mirror M4, the minimum fringe interval d of the interference fringes is determined.
(See FIG. 3) is the pixel pitch P of the two-dimensional image detector 110.
Aspherical Fizeau surface to be sufficiently larger than 8 times
The shape of the reference prototype is selected.

[0073]

As described above, according to the present invention, the measurement of an aspherical surface can be performed with high accuracy, and the measurement of a large aspherical surface can be performed.
As a result, accurate exposure transfer can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment.

FIG. 2 is a diagram comparing an aspheric amount F2 of a reference surface 18 ′ and an aspheric amount F3 of an aspheric Fizeau surface 15 ′ with a designed aspheric amount F1 of a test aspheric surface 17 ′.

FIG. 3 is a diagram showing a relationship between a pixel pitch P of a two-dimensional image detector 110 and a minimum fringe interval d of interference fringes.

FIG. 4 is a diagram illustrating a second embodiment.

FIG. 5 is a diagram illustrating a method of dividing a test aspheric surface 27 according to a second embodiment.

FIG. 6 is an aspherical surface amount F2a of the reference surface 28a ′, and the reference surface 28;
b ′, the aspheric amount F3a of the aspheric Fizeau surface 25a ′, and the aspheric amount F of the aspheric Fizeau surface 25b ′
FIG. 3B is a diagram comparing 3b with a design aspherical amount F1a in a region Da and a design aspherical amount F1b in a region Db.

FIG. 7 is a diagram showing a projection optical system 70 to which the present invention is applied.

[Explanation of symbols]

 Reference Signs List 10, 20 Aspherical shape measuring device 11 Laser light source 12 Beam expander 13 Polarizing beam splitter 14 1/4 wavelength plate 15 Wavefront converting means 15 'Aspherical Fizeau surface 15, 25a, 25b Wavefront converting means 17, 27 Test object 17 ', 27' Aspherical surface to be inspected 18, 28a, 28b Reference prototype 18 ', 28a', 28b 'Reference surface 19 Beam diameter conversion optical system 110 Two-dimensional image detector 111 Arithmetic unit 112 Display unit 70 Projection optical system M1, M2, M3, M4 mirror

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/30 515D F-term (Reference) 2F064 AA09 BB04 BB05 CC04 DD02 DD05 EE05 FF01 GG23 GG38 GG47 GG51 GG70 HH03 HH08 JJ01 2F065 AA53 BB22 BB25 CC21 DD03 FF51 GG04 GG12 HH03 JJ03 JJ26 LL09 LL36 LL37 NN05 QQ21 QQ29 QQ32 SS13 2G086 FF01 5F046 BA03 CB03 CB12

Claims (12)

[Claims] 1. A detector detects interference fringes formed by reflected light from a test surface having an aspheric design shape and reflected light from a Fizeau surface, and is arranged in place of the test surface. The interference fringes formed by the reflected light from the reference surface having a known shape and the reflected light from the Fizeau surface are detected, and based on the two detected interference fringes and the shape of the reference surface, the shape of the surface to be measured is determined. In the method for measuring an aspherical surface shape to be determined, the Fizeau surface is an aspherical Fizeau surface, and the fringe interval of interference fringes obtained with respect to the design shape of the test surface and the fringe interval of interference fringes obtained with respect to the reference surface The shape of at least the aspherical Fizeau surface or the reference surface is set so that both are larger than the fringe interval of interference fringes obtained with respect to the test surface when using a spherical Fizeau surface. Aspherical shape measurement Method. 2. The aspherical shape measurement according to claim 1, wherein the aspherical amount of the Fizeau surface is set to an aspherical amount between a design shape of the test surface and an approximate spherical surface thereof. Method. 3. The aspherical shape measuring method according to claim 2, wherein the aspherical amount of the reference surface is set smaller than the aspherical amount of the design shape of the test surface. 4. The amount of aspherical surface of the reference surface is set to an amount of aspherical surface between the aspherical Fizeau surface and an approximate spherical surface having a design shape of the surface to be measured. Aspheric shape measurement method. 5. The method according to claim 3, wherein the shape of the reference surface is set to a spherical surface. 6. The aspherical shape of the Fizeau surface and the shape of the reference surface are such that a fringe interval of interference fringes obtained on the test surface and a fringe interval of interference fringes obtained on the reference surface are different. The aspherical shape measuring method according to any one of claims 1 to 5, wherein both are set to be equal to or more than two pixels on the detector. 7. An interference fringe formed by a reflected light from a test surface having an aspherical design shape and a reflected light from a Fizeau surface having a known shape is detected by a detector, and the detected interference fringe and the Fizeau surface are detected. In the aspherical shape measuring method for obtaining the shape of the test surface based on the shape of the, the Fizeau surface is an aspherical Fizeau surface, fringe spacing of interference fringes obtained with respect to the design shape of the test surface However, when using a spherical Fizeau surface, the aspherical Fizeau surface is set so as to be larger than the fringe interval of interference fringes obtained with respect to the test surface, wherein the aspherical shape measurement method . 8. The aspherical shape measurement according to claim 7, wherein the amount of aspherical surface of the Fizeau surface is set to an amount of aspherical surface between a design shape of the surface to be measured and an approximate spherical surface thereof. Method. 9. The shape of the Fizeau surface is set such that a fringe interval of interference fringes obtained with respect to the test surface is equal to or more than two pixels on the detector. The method for measuring an aspheric surface shape according to claim 7 or 8. 10. A Fizeau surface, wavefront converting means for converting a light beam emitted from a light source into a predetermined wavefront and guiding the light beam to both the Fizeau surface and a test surface having an aspheric design shape, and reflections on both surfaces. An aspherical shape measuring device comprising a detector for detecting interference fringes formed by light, wherein the Fizeau surface is set in the aspherical shape measuring method according to any one of claims 1 to 9. An aspherical shape measuring device, characterized in that the shape is a shape to be formed. 11. A projection optical system for exposing a pattern drawn on an original plate onto a substrate, wherein a surface of an optical member used in the projection optical system is according to any one of claims 1 to 9. A projection optical system, characterized in that the surface of the optical member is polished to a predetermined accuracy based on a result of the measurement by the aspherical shape measurement method. 12. An exposure method for exposing a pattern drawn on an original plate onto a substrate via a projection optical system, wherein a surface of an optical member used in the projection optical system is provided.
A surface to be measured measured by the aspherical surface shape measuring method according to any one of claims 9 to 9, wherein the optical member is polished to a predetermined accuracy based on the measured result. Exposure method.