JP2005309288A - Optical element, illuminating optical apparatus and optical apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To illuminate a prescribed range by the prescribed number of apertures even when the size of a light emitting part of a light source is small and to improve the uniformity of illuminance distribution on an illuminated object and the directional characteristic of luminance. <P>SOLUTION: An optical element has a plurality of faces 12a, 12b which are parallel with each other and respectively have prescribed transmission factors and reflection factors. When it is defined that the number of effective faces having prescribed reflection factors and transmission factors is k, provided that k is an integer of ≥2, the transmission factors and reflection factors of respective faces 12a, 12b are set so that the intensities of light beams when the total number of times of transmission or reflection received by the faces 12a, 12b having the prescribed reflection factors and transmission factors is up to 2k-1, however the total intensities of light beams passed through different routes in the same value 2k-1, become almost the same. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an illumination optical apparatus such as a projection apparatus, an exposure apparatus, and a microscope, an optical element suitable for use in the illumination optical apparatus, and an optical apparatus using the illumination optical apparatus.

  In an illumination optical system of an optical device such as a projection device, an exposure device, and a microscope, it is required to be bright over a predetermined range of the object, to have high uniformity of brightness, and to illuminate the object with a predetermined numerical aperture (NA). ing. In particular, Koehler illumination is generally used in terms of brightness uniformity. Various light sources may be used depending on the purpose. However, in an optical device requiring particularly bright illumination such as a semiconductor manufacturing exposure device or a large projection device, a light source with a large amount of light emission is required. A discharge lamp such as a xenon lamp or a laser is used. In addition, these light sources are often used as excitation light sources for fluorescence observation even in a microscope.

  On the other hand, in general, in the lens system where the sine condition is satisfied, the product of the size of the object (diameter viewed perpendicular to the optical axis), and in the illumination optical system, the product of the size of the light source emitting part and the incident-side numerical aperture of this lens system is It has the property of being stored on the injection side. However, since the effective size of the light emitting part of a light source such as a discharge lamp or laser is extremely small, the illumination range or numerical aperture (NA) of the illuminated object is greatly limited. Further, the emission intensity of the discharge lamp is highly dependent on the angle with respect to the direction connecting the electrodes. In the optical device, Koehler illumination is generally used. However, Koehler illumination does not have an averaging effect with respect to the angular direction characteristics of the intensity of the light source, and thus uneven brightness tends to occur even when Koehler illumination is used.

  Therefore, various methods are used to solve the above problems. For example, in an exposure apparatus and a projection apparatus for semiconductor manufacturing, as described in Non-Patent Document 1, by providing a fly-eye lens (fly eye lens) in an illumination system, a light beam from a light source is divided into wavefronts. Thus, a large number of secondary light sources are formed, and the size of the light emitting portion is increased.

As described in Non-Patent Document 2, a light pipe may be used instead of the fly-eye lens, but the operation is the same.
Further, Patent Document 1 discloses a method in which a fly eye lens and a light pipe are used in combination.

Patent Document 2 discloses a method for making the intensity distribution in the beam cross section uniform by combining hologram elements.
Patent Document 3 discloses that a light beam from a light source reflects a polarized light component in a predetermined direction on the first reflecting surface and transmits a polarized light component orthogonal thereto, and is arranged substantially parallel to the first reflecting surface. A method of reflecting light transmitted through the first reflecting surface with the second reflecting surface thus formed is disclosed. According to this method, the light beam from the light source is polarized and split to form two light sources, and an effect equivalent to an increase in the size of the light source can be obtained.
Japanese Patent No. 2712342 JP 2002-202414 A JP 2000-122000 A “Optical Technology Handbook”, Asakura Shoten, 2002, p. 736 “Optical Technology Handbook”, Asakura Shoten, 2002, p. 797

By the way, according to the method using the fly-eye lens described in Non-Patent Document 1, a large number of light source images are formed corresponding to each lens element of the fly-eye lens, and this becomes a secondary light source. As a result, the apparent light source can be enlarged, but on the secondary light source surface at this time, a large number of light source images are discretely arranged two-dimensionally. When Koehler illumination is performed using this secondary light source, the illuminance distribution on the object to be illuminated is made uniform, but the luminance direction characteristics are rather deteriorated, affecting the imaging characteristics of the projection optical system that follows this illumination system. May appear. In addition, the fly-eye lens is generally expensive and contributes to the high cost of the device.
In addition, the method using the light pipe described in Non-Patent Document 2 has basically the same effect as the method using the fly-eye lens described in Non-Patent Document 1, and has the same problems. . Moreover, since it is long as an element, it has become a factor which enlarges an optical system.

Further, according to the method described in Patent Document 1, the effect of uniformizing the illuminance distribution is higher than that of the method described above, and the problem of luminance direction characteristics is somewhat mitigated. There was a problem of becoming.
The method described in Patent Document 2 is effective when a laser is used as the light source. In many cases, the beam cross-sectional intensity distribution of a laser is a Gaussian distribution, but according to this method, a flat intensity distribution can be obtained. However, in general, a hologram element has a strong wavelength dependency of optical characteristics and cannot be used in an optical system having a certain wavelength band.

  Further, according to the method described in Patent Document 3, two apparent light sources can be formed with a simple optical system configuration, and there is some effect in making the brightness uniform. However, since the number of apparent light sources is only two, the uniformizing effect is weak, and further, it is effective only in either the X direction or the Y direction of the illuminated object. In addition, two apparent light sources can be generated by polarization splitting. When Koehler illumination is performed using these light sources, if the object to be illuminated has polarization dependence, the imaging characteristics of the projection optical system that follows this illumination system can be reduced. May have an impact.

The present invention has been made in view of the above-described problems. Even if the size of the light source light emitting unit is small, it can be illuminated with a predetermined numerical aperture over a predetermined range, and at the same time on an object to be illuminated. It is an object of the present invention to provide an optical element, an illumination optical device, and an optical device that have good illuminance distribution uniformity and luminance direction characteristics.
Another object of the present invention is to realize these without a high price and an increase in size of the apparatus with a simple optical system configuration.

In order to achieve the above object, the present invention provides the following means.
The present invention is an optical element having a plurality of surfaces substantially parallel to each other, each surface having a predetermined transmittance and reflectance, and the number of effective surfaces having the predetermined reflectance and transmittance is k. Where k is an integer equal to or greater than 2, and the intensity of light transmitted to the surface having the predetermined reflectivity and transmissivity and the total number of times of reflection or reflection is up to 2k-1, where 2k-1 There is provided an optical element characterized in that the transmittance and the reflectance of each surface are set so that the total intensities of light having the same value and following different paths are approximately the same.

According to the present invention, it is not an expensive optical element such as a conventional fly-eye lens, but it has an easy structure in which a predetermined reflectance and transmittance are provided on a plurality of surfaces, thereby reducing manufacturing costs. be able to.
Furthermore, since the diffraction of light is not used like a hologram, the wavelength dependency of optical characteristics can be reduced, and it can be used for a light source having a predetermined wavelength range.

The present invention also provides an illumination optical apparatus having at least one optical element.
According to this invention, since the manufacturing cost is low and a small optical element is used, it is possible to prevent the entire apparatus from becoming large and expensive.

The present invention is an illumination optical device including an optical element having a plurality of surfaces substantially parallel to each other, each surface having a predetermined transmittance and reflectance, and each surface has a predetermined transmittance and reflectance Provided is an illumination optical device characterized by having a small polarization dependency with respect to incident light.
According to the present invention, the imaging characteristics of the projection optical system that follows the illumination are not affected by the polarization. For example, even when a polarization-dependent sample or the like is observed, the appearance does not change depending on the direction, and more accurate observation is possible.

The present invention includes two optical elements having a plurality of surfaces substantially parallel to each other, each surface having a predetermined transmittance and reflectance, and the two optical elements are arranged in a twisted positional relationship with each other. An illumination optical device is provided.
According to this invention. A secondary light source spread two-dimensionally can be formed.

The present invention also provides an optical device having the illumination optical device, wherein the illumination performed by the illumination optical device is Koehler illumination.
According to this invention, it is possible to perform illumination more uniformly in a state in which the illuminance unevenness and the direction dependency of luminance are reduced by Koehler illumination.

According to the present invention, the illuminance distribution is uniform, and the direction dependency of luminance is small. Therefore, the uniformity of illumination is extremely high, and the required numerical aperture of illumination is ensured even when the light source light emitting unit is small. However, it is possible to realize an illumination optical apparatus that can illuminate over a predetermined range.
Moreover, instead of an expensive optical element such as a fly-eye lens, an optical element having an extremely simple structure in which each surface of one or a plurality of planar substrates has predetermined transmittance and reflectance is used. Therefore, it can be realized at a low cost.
Furthermore, since this optical element is small, the size of the apparatus is not increased as in the case where a light pipe is used.
Further, since this optical element does not use light diffraction unlike a hologram, the wavelength dependency of operation is extremely low, and it can be used for a light source having a predetermined wavelength band.
Furthermore, since this optical element does not use polarization dependency in its operation, there is no problem that the imaging characteristic of the projection optical system following the illumination optical apparatus of the present invention is influenced by polarization.

Hereinafter, an optical element, an illumination optical device, and an optical device according to a first embodiment of the present invention will be described with reference to FIGS.
In the present embodiment, as shown in FIG. 1, a case where an optical apparatus is a microscope 1 and an illumination optical apparatus is applied to an illumination optical system 2 of the microscope 1 will be described.
The microscope 1 includes the illumination optical system 2 that illuminates the specimen 3 that is an observation image, and the observation optical system 4 that observes the specimen 3. Note that the specimen 3 is generally placed on a slide glass.

The illumination optical system 2 includes a light source emitting unit 10, a reflecting mirror 11, a first reflecting element (optical element) 12, a second reflecting element (optical element) 13, a collector lens 14, a field stop 15, an aperture stop 16, A condenser lens 17 and an illumination side filter 18 are provided.
The light source light emitting unit 10 is a light emitting unit formed between electrodes of a discharge lamp such as a high pressure mercury lamp or a xenon lamp. The reflecting mirror 11 is a reflecting mirror having a spheroidal surface, and the light source light emitting unit 10 is disposed at the first focal point of the reflecting mirror 11.

The first reflective element 12 uses a light-transmitting member such as glass as a substrate, and has both surfaces disposed substantially parallel to each other, that is, a first surface 12a and a second surface 12b. .
Further, for example, a dielectric multilayer film is formed on the two surfaces 12a and 12b, and each has a predetermined reflectance and transmittance over a predetermined wavelength range. However, it is desirable that the reflectance of the second surface 12b is close to 100%. Further, the reflectance and transmittance of the two surfaces 12a and 12b are set so as not to have a large polarization dependency, that is, to reduce the polarization dependency with respect to the light incident on the surfaces 12a and 12b. Yes.

In the present embodiment, the reflectance or transmittance does not have a large polarization dependency means that the reflectance for polarized light in any one direction, or the reflectance for polarized light in the direction orthogonal to it. Or, it means 50% or more and 200% or less as compared with the transmittance.
Further, the first surface 12 a is disposed at an angle of approximately 45 degrees with respect to the symmetry axis of the spheroid of the reflecting mirror 11. Furthermore, an infrared light removal filter (not shown) for removing unnecessary infrared light may be inserted between the light source light emitting unit 10 and the first reflecting element 12.

  The second reflective element 13 is an optical element similar to the first reflective element 12. That is, the second reflecting element 13 uses a light-transmitting optical material such as glass as a substrate, and has both a first surface 13a and a second surface 13b that are substantially parallel to each other. The two surfaces 13a and 13b include, for example, a dielectric multilayer film, and have a predetermined reflectance and transmittance respectively over a predetermined wavelength range. However, it is desirable that the reflectance of the second surface 13b is close to 100%. Furthermore, the reflectance and transmittance of the two surfaces 13a and 13b are set so as not to have a large polarization dependency.

The first reflecting element 12 and the second reflecting element 13 are arranged so that the normal lines of the two opposing faces 12a and 13a are in a twisted positional relationship. That is, the first surface 12a of the first reflecting element 12 is approximately 45 degrees with respect to the paper surface in FIG. 1, and the positional relationship is such that the axis of symmetry of the spheroid of the reflecting mirror 11 is perpendicular to the paper surface. Is arranged.
In FIG. 1, for convenience of illustration, the surfaces 12 a and 12 b of the first reflective element 12 and the surfaces 13 a and 13 b of the second reflective element 13 are shown to be parallel.

  The field stop 15 is provided at a position conjugate with the sample 3 with respect to the condenser lens 17, and the aperture stop 16 is provided at a position on the front focal plane of the condenser lens 17. As shown in FIG. 2, the aperture stop 16 has an opening 16a through which light passes, and the size of the opening 16a is variable.

The condenser lens 17 is preferably exchangeable depending on the numerical aperture of the objective lens 20.
The illumination-side filter 18 is a filter that is inserted when performing fluorescence observation using the microscope 1, and its installation position is not limited to the position shown in FIG. They can be arranged appropriately in the system 2.
The collector lens 14, the field stop 15, the aperture stop 16, and the condenser lens 17 are disposed along the optical axis A. The optical axis A intersects the second reflecting element 13 at approximately 45 degrees.

The observation optical system 4 includes an objective lens 20, an observation side filter 21, an imaging lens (also referred to as a lens barrel lens) 22, a staring prism 23, an eyepiece lens 24, a relay lens 25, and an imaging means 26.
In FIG. 1, the objective lens 20 is depicted as an infinitely corrected lens in which the specimen 3 is placed on the front focal plane thereof, but it may be a finitely corrected lens. In this case, the imaging lens 22 is not necessary.
The observation-side filter 21 is a filter that is inserted when fluorescence observation is performed using the microscope 1. The staring prism 23 is a prism that divides a part of the light emitted from the imaging lens 22 by amplitude division and guides it to the eyepiece lens 24. Note that a binocular prism (not shown) may be disposed between the staring prism 23 and the eyepiece lens 24 so that the two eyepiece lenses 24 can be used for observation with both eyes.

  The relay lens 25 is a lens having a predetermined magnification, and transmits a magnified image formed by the objective lens 20 and the imaging lens 22 to the imaging means 26 to re-image it. An image sensor such as a CCD (Charge Coupled Device), a photographic film, or the like can be used for the imaging unit 26.

The operation of the thus configured microscope optical system 1 will be described below. However, since the operation of the observation optical system 4 including the objective lens 20 to the imaging means 26 is the same as the operation of the observation optical system in a normal microscope, description thereof is omitted.
Since the light source light emitting unit 10 is localized in the vicinity of the first focal point of the reflecting mirror 11 having a spheroidal surface, the light 30 emitted from the light source emitting unit 10 and reflected by the reflecting mirror 11 is reflected by the reflecting mirror 11. Toward the second focal point. The light 30 becomes convergent light, passes through an infrared light removal filter or the like provided as necessary, and enters the first reflecting element 12 as light having a predetermined wavelength range.

  Since the first surface 12a of the first reflecting element 12 has a predetermined reflectance and transmittance, the light 30 incident thereon is partially reflected according to the reflectance and transmittance. The part is transparent. The light 31 reflected by the first surface 12a goes to the second reflecting element 13 as it is. On the other hand, the light 32 transmitted through the first surface 12a travels toward the second surface 12b, is reflected with a high reflectance by the second surface 12b, and is incident on the first surface 12a again. The light 32 incident again on the first surface 12 a is partially reflected according to the reflectance and transmittance of the first surface 12 a, partially transmitted and travels toward the second reflective element 13 as light 33.

At this time, since the first surface 12a and the second surface 12b are arranged substantially in parallel, the light 31 and the light 33 are substantially parallel, and the first surface 13a of the second reflecting element 13 is provided. Is incident on.
However, since the normal lines of the first reflective element 12 and the second reflective element 13 are arranged in a twisted positional relationship, the light 31 and 33 are incident upon the first surface 13a. 1 is incident in a state shifted in the Y direction (direction perpendicular to the paper surface) shown in FIG.

  The light 31 and 33 incident on the second reflecting element 13 are subjected to the same action as when the light 30 is incident on the first reflecting element 12, and become the light 31a and 31b and the light 33a and 33b. Head to 14. At this time, before entering the collector lens 14, the light 31 a and 31 b and the light 33 a and 33 b are respectively images 40 to 43 of the light source light emitting unit 10 at positions corresponding to the second focal point of the spheroid of the reflecting mirror 11. Tie.

Strictly speaking, the light 31a, 31b and the light 33a, 33b are reflected by the first surfaces 12a, 13a of the first reflecting element 12 and the second reflecting element 13, or transmitted therethrough and the second surface 12b. , 13b, the position of connecting the image of the light source light emitting unit 10 in the direction of the optical axis A is different, but the optical path length from the light source light emitting unit 10 to the second focal point through the reflection surface of the ellipsoidal surface is different. In comparison, the optical path length when passing through the first reflecting element 12 and the second reflecting element 13 is extremely short, so that substantially four images of the light source emitting part 10 are formed in the same plane. You can think.
In FIG. 1, the position corresponding to the second focal point of the spheroid is shown to be between the second reflective element 13 and the collector lens 14, but is not limited to this. The first reflective element 12 and the second reflective element 13 may be positioned.

The light 31a, 31b and the light 33a33b incident on the collector lens 14 pass through the illumination side filter 18 and the field stop 15 which are arranged as necessary, and as shown in FIG. The images 45 to 48 are formed.
FIG. 2 is a view of the aperture stop 16 as viewed in the direction of the optical axis A, and shows a state in which the size of the aperture 16a is maximized. The images 45 to 48 of these light source light emitting units 10 may be considered as images 40 to 43 of the light source light emitting unit 10 formed in the vicinity of the second focal point of the reflecting mirror 11 relayed by the collector lens 14 at a predetermined magnification. it can.

As shown in FIG. 2, the image 45 and the image 46 and the image 47 and the image 48 of the light source light emitting unit 10 are formed symmetrically with respect to the Y axis at a position slightly shifted in the Y direction leaving an overlap. This deviation is due to the action of the first reflecting element 12.
Similarly, the images 45 and 47 and the images 46 and 48 of the light source light emitting unit 10 are formed at positions slightly shifted in the X direction leaving an overlap. This deviation is due to the action of the second reflecting element 13.

  Therefore, the above-described deviation amount can be adjusted by appropriately selecting the thicknesses or refractive indexes of the first reflecting element 12 and the second reflecting element 13. Thus, if the brightness of the images 45 to 48 of the light source light emitting unit 10 is approximately equal, even if the light source light emitting unit 10 has uneven light intensity depending on the location, a plurality of light source images are formed at the position of the aperture stop 16. Since they are shifted and overlapped, a secondary light source with less brightness unevenness depending on the place is formed. At the same time, the apparent size of the light source is increased, so that it is easy to ensure the necessary numerical aperture of illumination.

Here, the setting of the reflectance and transmittance of each surface 12a to 13b of the first reflecting element 12 and the second reflecting element 13 will be described with reference to FIG.
FIG. 3 is a diagram in which only the light source unit (the light source light emitting unit 10 and the reflecting mirror 11) and the first reflecting element 12 shown in FIG. 1 are taken out.

As described above, in order to reduce the brightness unevenness in the opening 16a, the brightness of the images 45 to 48 of the light source light emitting unit 10 needs to be approximately equal. In order to realize this, the intensity of the light 31 that is obtained by reflecting the light 30 that is emitted from the light source unit and is incident on the first reflecting element 12 on the first surface 12a, and the light 30 is the first surface. The reflectance and transmittance of the first surface 12a are set so that the intensity of the light 33 that is transmitted through 12a, reflected by the second surface 12b, and again transmitted through the first surface 12a is approximately equal. .
Specifically, when the absorption of the film formed on the first surface 12a is negligibly small, and the reflectance of the second surface 12b is almost 100%, the reflection of the first surface 12a is reflected. The rate may be about 38%, and thus the transmittance may be about 62%.

However, in practice, as shown in FIG. 3, the light 32 transmitted through the first surface 12a is reflected by the second surface 12b, reflected by the first surface 12a (light 35), and the second surface 12b. And there is light 37 that emerges through a path of reflection and transmission through the first surface 12a. Similarly, in the second reflection element 13, there is light that is reflected twice by the second reflection surface 13b. .
Thereby, in the aperture stop 16, as shown in FIG. 4, an image 49 of the light source light emitting unit 10 is formed, which is different from the images 45 to 48 of the main light source light emitting unit 10, and a part thereof covers the opening 16a. Therefore, the uniformity of the brightness distribution in the opening 16a is somewhat deteriorated.

  However, the intensity at which each of the images 49 of the light source light emitting section 10 passes through the opening 16a is compared with the intensity of the light source light emitting section images 45 to 48 when the reflectance of the first surface 12a is about 38%. About 15% at most. Moreover, since the microscope 1 is usually used in a state where the aperture stop 16 is somewhat narrowed, that is, in a state where the size of the opening 16a is somewhat small, the influence is further reduced and can be substantially ignored.

  In the case where the aperture stop 16 is often used in the open state, the uniformity of the brightness distribution in the open state opening 16a is set by setting the reflectance of the first surface 12a to about 40% to 45%. Some improvement can be made. There is also light that is reflected three or more times at the second surface 12b of the first reflective element 12 or the second surface 13b of the second reflective element 13, but the opening 16a is opened even when opened. Since it does not pass, it can be ignored.

Thus, a secondary light source with little brightness unevenness is formed in the aperture 16 a of the aperture stop 16 by shifting and overlapping a plurality of images of the light source light emitting unit 10, and the sample 12 is illuminated via the condenser lens 17. To do. The illumination at this time is Koehler illumination, similar to the illumination in a general microscope. Therefore, the sample 12 not only has less illuminance unevenness but also less luminance direction dependency, so that more uniform illumination is possible.
That is, according to the present invention, the illuminance distribution is uniform and the luminance direction dependency is small. Therefore, the illumination uniformity is very high, and the required light aperture is small even if the size of the light source light emitting unit 10 is small. The illumination optical system 2 capable of illuminating over a predetermined range while ensuring the number can be realized.

  In addition, since the reflection and transmission characteristics of the surfaces 12a to 13b of the first reflection element 12 and the second reflection element 13 do not have a large polarization dependency, the degree of polarization of the images 45 to 48 of the light source light emitting unit 10 is small. Even when the specimen 12 having polarization dependency is observed, there is no problem that the appearance changes depending on the direction of the specimen.

  Further, the first reflecting element 12 and the second reflecting element 13 are not expensive optical elements such as a conventional fly-eye lens, but only the predetermined reflectance and transmittance are given to the respective surfaces 12a to 13b. Therefore, the manufacturing cost can be reduced. Further, unlike the conventional light pipe, it can be made small, so that it can be made compact. Further, since the first reflecting element 12 and the second reflecting element 13 do not use light diffraction unlike a hologram, the wavelength dependence of optical characteristics is extremely low, and a light source having a predetermined wavelength band is used. Can be used.

  Next, an optical element, an illumination optical device, and an optical device according to a second embodiment of the present invention will be described with reference to FIGS. In the description of this embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

In this embodiment, the overall optical system configuration is the same as that of the first embodiment, but is different from the first embodiment in the configuration and operation of the first reflecting element and the second reflecting element. .
FIG. 5 shows a first reflecting element (optical element) 50 in the present embodiment. The second reflective element in the present embodiment also has the same configuration as the first reflective element 50.

  As shown in FIG. 5, the first reflective element 50 is configured by bonding two substrates made of a light-transmitting optical material such as glass, that is, a first substrate 51 and a second substrate 52. And the first surface 53 of the first substrate 51, the surface 54 which is a bonding surface of the second surface of the first substrate 51 and the first surface of the second substrate 52, and the second surface of the second substrate 52. The surfaces 55 are substantially parallel to each other.

  The first substrate 51 and the second substrate 52 may be configured to have different materials and thicknesses, but in the present embodiment, both are described as being the same. For example, a dielectric multilayer film is formed on the three surfaces 53, 54, and 55 (each of the first surface, the second surface, and the third surface of the first reflecting element). 45 and 55 each have a predetermined reflectance and transmittance over a predetermined wavelength range. However, it is desirable that the third surface 55 has a reflectance close to about 100%. Further, the reflectance and transmittance of the three surfaces 53, 54, and 55 are configured not to have a large polarization dependency.

The operation of the illumination optical system 2 having the first reflecting element 50 and the second reflecting element according to this embodiment configured as described above will be described below.
Similar to the first embodiment, the light 60 emitted from the light source light emitting unit 10 becomes convergent light and passes through an infrared light removal filter or the like (not shown) provided as necessary, and then has a predetermined wavelength range. Is incident on the first reflective element 50.

Since the first surface 53 of the first reflective element 50 has a predetermined reflectance and transmittance, the light 60 incident on the first surface 53 is partially reflected and partially transmitted according to the reflectance and transmittance. To do. The light 61 reflected by the first surface 53 goes directly to the second reflecting element.
On the other hand, the light 62 transmitted through the first surface 53 is incident on the second surface 54, and is partially reflected and partially transmitted according to the reflectance and transmittance of the surface 54. The light 63 reflected by the surface 54 is incident again on the first surface 53, and a part of the light 63 is reflected and a part of the light is transmitted according to the reflectance and transmittance of the first surface 53. The light 64 that has passed therethrough is directed to the second reflecting element, and the reflected light 65 is directed to the second surface 54.

  The light 66 transmitted through the surface 54 is reflected by the third surface 55 with a high reflectivity, and is incident on the second surface 54 again. A part of the light 66 is reflected according to the transmittance and the reflectivity. Is transparent. Thus, the light 60 incident on the first reflective element 50 branches according to the reflectance and transmittance of each surface 53, 54, 55, and repeats reflection and transmission a predetermined number of times from the first reflective element 50. Light is emitted as light 61, 64, 67, 68 or the like.

More specifically, the transmission on the first surface 53 is T ₁ , the reflection is R ₁ , the transmission on the second surface 54 is T ₂ , the reflection is R ₂ , and the transmission on the third surface 55 is T ₃ , when the reflection is expressed as R ₃ , the light 61 is R ₁ , the light 64 is light that follows the path of T ₁ R ₂ T ₁ , the light 67 is T ₁ T ₂ R ₃ T ₂ T ₁ , and T _As a superposition of light that has followed two paths ₁ R ₂ R ₁ R ₂ T ₁ , the light 68 is T ₁ R ₂ R ₁ R ₂ R ₁ R ₂ T ₁ , T ₁ R ₂ R ₁ T ₂ R ₃ T ₂ T ₁ , T ₁ T ₂ R ₃ R ₂ R ₃ T ₂ T ₁ , and T ₁ T ₂ R ₃ T ₂ R ₁ R ₂ T ₁ To do.
Further, although light having a large number of reflections and transmissions is also emitted, the intensity is weak, and since it is almost blocked when reaching the aperture stop 16 and does not contribute to illumination, it is ignored in the following description.

Next, these lights 61, 64, 67 and 68 are incident on the second reflecting element and are subjected to the same action as the light 60 incident on the first reflecting element 50. The light emitted from the second reflecting element forms a plurality of images of the light source light emitting unit 10 at the position of the aperture stop 16 via the collector lens 14 as in the first embodiment.
This is shown in FIG. FIG. 6 is a view of the aperture stop 16 as viewed in the direction of the optical axis A. As illustrated in FIG. 6, the plurality of images 70 of the light source light emitting unit 10 are arranged in the X direction and the Y direction in a state of being shifted while leaving an overlap. At this time, nine images 70 of the main light source emitting unit 10 can be formed, compared with four in the first embodiment. The images 70 of these nine main light source light emitting units 10 are light having a total number of reflections and transmissions of 5 or less in each of the first reflection element 50 and the second reflection element (in the first reflection element 50, It is an image formed by light 61, 64, 67).

  An image 71 shown in FIG. 6 is a light source formed by light having a total number of reflections and transmissions of seven times (light 68 in the first reflection element 50) in the first reflection element 50 or the second reflection element. 2 is an image of the light emitting unit 10. In FIG. 6, the image 70 of the light source light emitting unit 10 is illustrated as being partially overlapped only between adjacent images. However, depending on the size and interval of each image, only between the adjacent images. Instead, two or more adjacent images may partially overlap.

  Here, the reflectance of the first surface 53 of the first reflecting element 50 is about 24%, and accordingly the transmittance is about 76%, the reflectance of the second surface 54 is about 41%, and thus the transmittance is If the reflectivity of the third surface 55 is set to approximately 59% and approximately 59%, the light 61, 64, 67 (that is, the total number of transmissions or reflections is 5 or less (calculated from the equation 2k-1 where k = The intensity of the light 3) is substantially the same, and the intensity of the light 68 is about half that of the lights 61, 64, and 67.

The lights 64 and 67 are lights emitted in a state where the lights following different paths are superimposed, and the intensities of the lights 64 and 67 are the total intensity.
If the same setting is made for the second reflecting element, the nine main images 70 of the light source light emitting unit 10 have substantially the same intensity, and they are arranged evenly while leaving an overlap between the images. A secondary light source with uniform brightness is formed at 16a. In addition, since the number of the main images 70 of the light source emitting part 10 formed is as many as nine as compared with the first embodiment, a secondary light source with higher brightness averaging effect and higher uniformity can be realized. .

As in the case of the first embodiment, as shown in FIG. 6, a part of the image 71 of the light source emitting unit 10 may be applied to the opening 16a. At this time, the uniformity of the brightness distribution of the opening 16a is increased. Somewhat worse. However, in this case as well, the influence is almost eliminated by slightly reducing the aperture stop 16. Further, when the aperture stop 16 is often used in the open state, the light use efficiency is slightly deteriorated. However, as shown in FIG. 7, the interval between the images 70 and 71 of the light source emitting part 10 is somewhat widened. Thus, the image 71 of the light source light emitting unit 10 can be prevented from covering the opening 16a. The interval between the images 70 and 71 of the light source emitting unit 10 can be increased by appropriately increasing the surface interval between the first reflecting element 50 and the second reflecting element.
As described above, according to the present embodiment, it is possible to realize the illumination optical system 2 with higher uniformity while having the same effects as the first embodiment.

  Next, an optical element, an illumination optical device, and an optical device according to a third embodiment of the present invention will be described with reference to FIGS. In the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

In this embodiment, the overall optical system configuration is the same as that of the first embodiment, but the configuration and operation of the first reflective element and the second reflective element are different from those of the first embodiment. Yes.
FIG. 8 shows a first reflecting element (optical element) 80 in the present embodiment. Note that the second reflective element in this embodiment has the same configuration as the first reflective element 80.

As shown in FIG. 8, the first reflecting element 80 includes two substrates made of a light-transmitting optical material such as glass, that is, a first substrate 81 and a second substrate 82, having a predetermined interval. The structure is arranged with a gap. The first substrate 81 and the second substrate 82 are integrally held by a frame (not shown). The first substrate 81 and the second substrate 82 each have two substantially parallel surfaces, that is, the second surface 84, which is the same as the first surface 83 of the first reflecting element 80, and the third surface. The second surface 84 and the third surface 85 are arranged so as to be substantially parallel to each other. The first substrate 81 and the second substrate 82 may be configured to have different materials and thicknesses, but in the present embodiment, both are described as being the same.
For example, a dielectric multilayer film is formed on the four surfaces 83, 84, 85, and 86, and each has a predetermined reflectance and transmittance over a predetermined wavelength range. However, it is desirable that the fourth surface 86 has a reflectance close to about 100%. Further, the reflectance and transmittance of the four surfaces 83, 84, 85, 86 are configured not to have a large polarization dependency.

  Here, the distance S between the first substrate 81 and the second substrate 82 is set based on the following equation, where d is the thickness of the first substrate 81 and n is the refractive index.

The interval S may be set so as to be shifted within a range of about ± 50% from the value obtained by this equation. However, in this embodiment, the interval S is set to a value obtained by this equation.
As yet another configuration, a gap is not formed between the second surface 84 and the third surface 85, and three substrates similar to the first substrate 81 or the second substrate 82 are bonded together, and the bonding surface thereof. Thus, the second surface 84 and the third surface 85 may be used.

The operation of the illumination optical system 2 having the first reflecting element 80 and the second reflecting element configured as described above will be described below.
As in the first embodiment, the light 90 emitted from the light source light emitting unit 10 becomes convergent light, passes through an infrared light removal filter or the like (not shown) provided as necessary, and then has a predetermined wavelength range. Is incident on the first reflective element 80. Thereafter, similarly to the second embodiment, reflection or transmission is repeated a predetermined number of times on each surface 83, 84, 85, 86 and emitted from the first reflection element 80 as light 91, 92, 93, 94, 95, etc. To do.

More specifically, the transmission on the first surface 83 is T ₁ , the reflection is R ₁ , the transmission on the second surface 84 is T ₂ , the reflection is R ₂ , and the transmission on the third surface 85 is T _3. When reflection is expressed as R ₃ , and reflection at the fourth surface 86 is expressed as R ₄ , the light 91 is R ₁ , the light 92 is light following the path of T ₁ R ₂ T ₁ , and the light 93 is T _1. As a superposition of the light following the two paths of T ₂ R ₃ T ₂ T ₁ and T ₁ T ₂ R ₁ R ₂ T ₁ , the light 94 is converted into T ₁ R ₂ R ₁ R ₂ R ₁ R ₂ T ₁ , T ₁ R ₂ R ₁ T ₂ R ₃ T ₂ T ₁ , T ₁ T ₂ R ₃ R ₂ R ₃ T ₂ T ₁ , T ₁ T ₂ R ₃ T ₂ R ₁ R ₂ T ₁ , and T ₁ T ₂ T ₃ R ₄ T ₃ as T ₂ T superposition of light following the paths of five kinds of _1, the light 95 is _{T 1 R 2 R 1 R 2} R 1 R 2 R 1 R 2 _{1, T} 1 of _{R 2 R 1 T 2 R 3} T 2 R 1 R 2 T 1, T 1 R 2 R 1 T 2 T 3 R 4 T 3 T 2 T 1 light traced the path of the 13 kinds, such as Inject as a stack.
Further, although light having a large number of reflections and transmissions is also emitted, the intensity is weak, and since it is almost blocked when reaching the aperture stop 16 and does not contribute to illumination, it is ignored in the following description.

Next, the lights 91, 92, 93, 94, and 95 are incident on the second reflecting element and are subjected to the same action as the light 90 that is incident on the first reflecting element 80. The light emitted from the second reflecting element forms a plurality of images of the light source light emitting unit 10 at the position of the aperture stop 16 via the collector lens 14 as in the first embodiment.
This is shown in FIG. FIG. 9 is a view of the aperture stop 16 as viewed in the direction of the optical axis A. As shown in FIG. 9, the plurality of images 100 of the light source light emitting unit 10 are arranged in the X direction and the Y direction in a state of being shifted while leaving an overlap between adjacent images. At this time, 16 main images 100 of the light source light emitting unit 10 are formed, compared with 9 in the second embodiment. The main image 100 of these 16 light source light emitting units 10 is light having a number of reflections and transmissions of 7 or less in each of the first reflection element 80 and the second reflection element (in the first reflection element 80, the light 91, 92, 93, 94).

  An image 101 shown in FIG. 9 is a light source formed by light having a total number of reflections and transmissions of 9 times (light 95 in the first reflection element 80) in the first reflection element 80 or the second reflection element. 2 is an image of the light emitting unit 10. In FIG. 9, the image 100 of the light source emitting unit 10 is illustrated so as to partially overlap only between adjacent images. However, depending on the size and interval of each image, not only between adjacent images. Two or more adjacent images may partially overlap.

  Here, the reflectance of the first surface 83 of the first reflecting element 80 is about 17%, and therefore the transmittance is about 83%, the reflectance of the second surface 84 is about 25%, and thus the transmittance is If the reflectivity of about 75%, the third surface 85 is about 42%, and therefore the transmittance is about 58% and the reflectivity of the fourth surface 86 is about 100%, the light 91, 92, 93, 94 That is, the intensity of light (that is, light having a total number of transmissions or reflections of 7 or less (calculated from Equation 2k-1 where k = 4)) is substantially the same, and the intensity of the light 95 is the light 91, 92, 93, 94. It becomes about half of the strength.

The lights 92, 93, and 94 are lights that are emitted in a state where the lights that follow different paths are superimposed, and the intensity of each of the lights 92, 93, and 94 is the total intensity thereof.
For the second reflecting element, if the same setting is made, the intensity of the main image 100 of the 16 light source light emitting units 10 will be substantially the same, and these will remain even in an offset state while leaving an overlap between adjacent images. Therefore, a secondary light source with uniform brightness is formed in the opening 16a. Moreover, compared to the second embodiment, the number of main images 100 of the light source light emitting section 10 formed is as large as 16, so that the brightness averaging effect is high and a more uniform secondary light source is realized. it can.

However, as shown in FIG. 9, a part of the image 101 of the light source light emitting unit 10 may be applied to the opening 16a, which causes a slight deterioration in the uniformity of the brightness distribution of the opening 16a. However, in this case as well, as in the second embodiment, the influence is almost eliminated by slightly reducing the aperture stop 16. In addition, when the aperture stop 16 is often used in an open state, the light utilization efficiency is slightly deteriorated, but the interval between the images 100 and 101 of the light source emitting unit 10 is somewhat increased as in the second embodiment. As a result, the image 101 of the light source light emitting unit 10 can be prevented from covering the opening 16a. The interval between the images 100 and 101 of the light source emitting unit 10 can be increased by appropriately increasing the surface interval between the first reflecting element 80 and the second reflecting element.
As described above, according to the present embodiment, it is possible to realize the illumination optical system 2 with higher uniformity than the second embodiment while having the same operational effects as the first and second embodiments.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in each of the above embodiments, a substrate or the like may be added to the first reflective element and the second reflective element to increase the number of reflective and transmissive surfaces. At this time, k (k is an integer equal to or greater than 2) is the number of effective surfaces (the number of bonding surfaces is one) that the first reflective element or the second reflective element has predetermined reflectance and transmittance. ), The total number of transmissions or reflections received at these surfaces is the sum of the light intensity up to 2k-1 (for light that has the same 2k-1 value and follows a different path). The transmittance and reflectance of each surface may be set so that the (intensity) is substantially the same. In this way, more images of the light source light emitting portions are formed on the aperture stop, and the averaging effect can be enhanced.

Further, if the first reflecting element and the second reflecting element are configured to have different transmission / reflection surfaces, secondary light sources having different sizes in the X direction and the Y direction can be formed. This includes a case where there is no one of the first reflective element and the second reflective element as a special case.
Further, in each of the embodiments described above, the optical apparatus has been described as a microscope, but the present invention is not limited to application to a microscope, and can be used in various optical apparatuses such as an exposure apparatus and a projection apparatus.

It is a figure which shows 1st Embodiment of the microscope which concerns on this invention, Comprising: It is a figure which shows a whole optical system. It is a figure which shows the state which looked at the aperture stop of the microscope shown in FIG. 1 in the direction of an optical axis, Comprising: It is a figure which shows the state in which the image of the main light source light emission part was formed in the opening. It is a figure which shows the 1st reflective element and light source light emission part of the microscope shown in FIG. 1, Comprising: The state which the light which injected into the 1st reflective element repeats permeation | transmission and reflection, is branched into several light, and is inject | emitted. FIG. It is a figure which shows the state in which the image of the main light source light emission part and the image of the light source light emission part different from this image were formed in the aperture stop shown in FIG. It is a figure which shows the 1st reflective element and light source light emission part in 2nd Embodiment of the microscope based on this invention, Comprising: The light which injected into the 1st reflective element repeats permeation | transmission and reflection, and branches into several light FIG. It is a figure which shows the state which looked at the aperture stop of the microscope in 2nd Embodiment of the microscope based on this invention in the direction of the optical axis, Comprising: The image of the main light source light emission part, and the light source light emission part different from this image It is a figure which shows the state in which the image was formed. FIG. 6 is a diagram illustrating a state in which the main light source light emitting unit image and the image of another light source light emitting unit different from the image are expanded from the state illustrated in FIG. 6 so that the image of the other light source light emitting unit does not cover the opening. It is. It is a figure which shows the 1st reflective element and light source light emission part in 3rd Embodiment of the microscope based on this invention, Comprising: The light which injected into the 1st reflective element repeats permeation | transmission and reflection, and branches into several light FIG. It is a figure which shows the state which looked at the aperture stop of the microscope in 3rd Embodiment of the microscope which concerns on this invention in the direction of the optical axis, Comprising: The image of the main light source light emission part, and the light source light emission part different from this image It is a figure which shows the state in which the image was formed.

Explanation of symbols

1 Microscope (optical device)
2 Illumination optical system (illumination optical device)
12, 50, 80 First reflective element (optical element)
12a, 13a, 51, 83 First surface 12b, 13b, 52, 84 Second surface 13 Second reflecting element (optical element)
53, 85 Third surface 86 Fourth surface

Claims (5)

  An optical element having a plurality of surfaces substantially parallel to each other, each surface having predetermined transmittance and reflectance, wherein k is the number of effective surfaces having the predetermined reflectance and transmittance, where k is If it is an integer greater than or equal to 2, the intensity of the total number of transmissions or reflections received by the surface having the predetermined reflectance and transmittance up to 2k-1, but the value of 2k-1 is the same. The optical element is characterized in that the transmittance and the reflectance of each surface are set so that the total intensity of the light following different paths is substantially the same.   An illumination optical apparatus comprising at least one optical element according to claim 1.   An illumination optical device having an optical element having a plurality of surfaces substantially parallel to each other, each surface having predetermined transmittance and reflectance, wherein the predetermined transmittance and reflectance of each surface is incident light An illumination optical device characterized by having a small polarization dependence.   A plurality of optical elements each having a plurality of surfaces substantially parallel to each other, each of which has a predetermined transmittance and reflectance, and the two optical elements are arranged in a twisted positional relationship with each other. Illumination optical device.   An optical device comprising the illumination optical device according to any one of claims 2 to 4, wherein the illumination performed by the illumination optical device is Koehler illumination.

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