JPH08201593A - Non-spherical surface reflection optical element - Google Patents

Abstract

PURPOSE: To obtain a non-spherical surface reflection optical element fulfilling both of strict shape accuracy and surface accuracy by contacting a reflection part having a parallel surface on the curved surface of a base plate having a curved surface approximated by a non-spherical surface shape with an anodic junction method. CONSTITUTION: A slab shape part 2a (for example, silicon monocrystal) with parallel planes having a front surface with good surface accuracy (for example, maximum surface roughness of 0.001μm or less) and a base plate 1 having a curved surface 3 of a non-spherical shape with good shape accuracy are prepared. Then, on the curved surface 3 of the base plate 1, the slab shape part 2a (reflection part) is contacted with anodic junction method and a non- spherical reflection optical element having a reflection surface 4 with a non- spherical surface shape is completed. To avoid formation of air space at the junction, a hole 5 for venting air is desirably provided in the base plate 1 or the part 2a or in both. This non-spherical reflection optical element can be used in an optical system required of high optical performance as the reflection surface can fulfill both strict shape accuracy and surface accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical reflective optical element.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of semiconductor integrated circuit devices, in order to improve the resolution of an optical system which is limited by the diffraction limit of light, conventional X-rays are replaced with X-rays having a shorter wavelength. The projection lithography technique used has been developed. The X-ray reduction projection exposure apparatus used in this technique mainly includes an X-ray generator 11 and an X-ray illumination optical system 1.
2, the mask 13, the X-ray imaging optical system 14, the stage of the wafer 15, etc. (see FIG. 5).

As the X-ray generator 11, a radiation light source, a laser plasma X-ray source, or the like is used. X-ray illumination optical system 12
Is a mask formed by an oblique incidence mirror that reflects X-rays obliquely incident on the reflecting surface, a multilayer mirror whose reflecting surface is formed of a multilayer film, and a filter that reflects or transmits only X-rays of a predetermined wavelength. Illuminate 13 with X-rays of desired wavelength.

The mask 13 includes a transmission type mask and a reflection type mask. The transmissive mask has a pattern formed by providing a substance that absorbs X-rays in a predetermined shape on a thin membrane made of a substance that transmits X-rays well. On the other hand, the reflective mask is, for example, a pattern formed by providing a portion having a low reflectance in a predetermined shape on a multilayer film that reflects X-rays.

The pattern formed on such a mask is a wafer 15 coated with a photoresist by an X-ray imaging optical system 14 composed of a plurality of multilayer film mirrors and the like.
It is transferred to the resist by forming an image on it. Note that X
Since the line is absorbed by the atmosphere and attenuated, its optical path is arranged in the vacuum container 19 maintained at a predetermined vacuum degree by the exhaust device 20.

The reflection surface of the reflection optical element is almost flat,
It is a spherical surface or a parabolic surface. The reason is that it is practically difficult to form a reflection surface shape that is more complicated than the above shape with high accuracy (surface accuracy and shape accuracy) that is optically required. However, when the reflecting surface is limited to the above shape, the optical performance of the optical system using such a reflecting optical element is also limited.

On the other hand, in an optical system which is required to have high optical performance, a reflective optical element having an aspherical reflective surface in which a reflective surface is difficult to form is required. X-ray optical systems are also required to have an X-ray reflection optical element having an aspherical reflection surface. However, an X-ray reflection optical element that reflects X-rays of a short wavelength has a particularly high (strict) shape. Since precision and surface precision are required, it is particularly difficult to form a reflecting surface having an aspherical shape.

However, if such an aspherical reflecting surface can satisfy the required accuracy of both shape accuracy and surface accuracy, the lens optical system cannot be applied as in the X-ray projection exposure apparatus described above. Since it can be used for a linear optical system and other optical systems, its application range is widened to various devices. For example, in the fields of medicine and biotechnology, which are rapidly advancing in recent years, normal visible light (λ = about 400 n
The resolution is higher than that of a microscope using
Moreover, as a high-resolution microscope capable of clearly observing a living sample (hereinafter referred to as a biological sample, for example, cells, bacteria, sperms, chromosomes, mitochondria, flagella), wavelength λ = 2 to 2 instead of visible light. X-ray microscopes using 5 nm soft X-rays have been studied and are being developed.

For example, FIG. 6 shows a simple structure and optical system of such an X-ray microscope. In FIG.
The X-ray emitted from the X-ray generator 11 is the X-ray illumination optical system 1
It is condensed by 2 and is irradiated on the sample in the sample capsule 16. Then, the X-rays transmitted through the sample form an image of the sample on the X-ray imaging device 18 by the X-ray magnifying optical system 17. The optical path length from the X-ray generator 11 to the X-ray imaging device 18 is, for example, about 2 m.

Reference numeral 19 is a vacuum container, and 20 is an exhaust device for evacuating the interior of the container. If the aspherical reflective optical element can be used for the X-ray illumination optical system 12 and the X-ray magnifying optical system 17, a high-performance X-ray reflective optical system can be configured.

[0011]

Conventionally, the reflecting surface of a reflecting optical element, whether it is axially symmetric or a free-form surface, has been mainly machined and manufactured by an NC machine tool. However, with such a conventional processing method, it is not possible to produce the aspherical reflective optical element having an aspherical reflective surface that requires both strict shape accuracy and surface accuracy, and therefore the aspherical reflective optical element There is a problem that the element cannot be provided.

The present invention has been made in view of the above problems, and an object thereof is to provide an aspherical reflective optical element satisfying both strict shape accuracy and surface accuracy.

[0013]

Therefore, in the first aspect of the present invention, "a reflective member having a parallel surface is bonded to the curved surface of a substrate having an aspherical curved surface to form an aspherical reflective surface. An aspherical reflective optical element (claim 1) ". In addition, the present invention secondly provides an “aspherical reflective optical element (claim 2), wherein the substrate and the reflection member are bonded by an anodic bonding method”.

In the third aspect of the present invention, "the aspherical reflective optical element according to claim 1 or 2, characterized in that a multilayer film for X-ray reflection is provided on the aspherical reflecting surface. "I will provide a.

[0015]

The optical element for aspherical reflection satisfying both strict shape accuracy and surface accuracy is obtained by bonding the reflecting member 2 having parallel surfaces to the curved surface 3 of the substrate 1 having the aspherical curved surface 3.
It can be realized by an aspherical reflective optical element (claim 1) formed by forming an aspherical reflective surface 4 (see FIG. 1).

An example of a method for manufacturing the aspherical reflective optical element of the present invention will be described. First, a surface with good surface accuracy (for example,
A substrate 1 having a parallel flat plate-like member (for example, a silicon single crystal) 2a having a maximum surface roughness of 0.001 μm or less) and an aspherical curved surface 3 having good shape accuracy is prepared (see FIG. 1A). Next, on the curved surface 3 of the substrate 1, the flat plate-shaped member 2a is formed.
Are joined by an anodic bonding method (see FIG. 1B), and the reflecting member 2 having a parallel surface is joined to the curved surface 3 of the substrate 1 having the aspherical curved surface 3 to form an aspherical reflecting surface. The resulting aspherical reflective optical element is completed (see FIG. 1C). The anodic bonding method will be described in detail later.

When the curved surface 3 of the substrate 1 and the member 2a are bonded, particularly when the curved surface 3 of the substrate 1 which is the bonding surface is a concave surface, the bonding surface 3'part of the member 2a closest to the concave surface is joined. Since the joining is performed from the above, it is easy for air to accumulate in the joining portion. Therefore, it is preferable to provide a hole for venting air in the substrate 1 or the member 2a, or both in order to prevent air accumulation (see FIG. 1, an example in which the air vent hole 5 is provided in the substrate 1).

When the air vent hole 5 is provided in the substrate 1, the hole 5 affects the deformation of the reflecting surface portion of the reflecting member 2 located thereabove, so that the hole 5 is provided below the reflecting surface portion where optical characteristics are not particularly required. It is preferable to provide the substrate portion located at the minimum required size. Further, when the air vent hole is provided in the reflection member 2, it is preferable to provide the hole in the reflection surface portion where optical characteristics are not particularly required.

Therefore, it is preferable that the air vent hole is provided in the center of the substrate 1 or the reflecting member 2 with a minimum size. The example of the method for manufacturing the aspherical reflective optical element of the present invention has been described above. By joining the curved surface 3 of the substrate 1 and the member 2a according to the aspherical reflective optical element of the present invention, the aspherical shape of the curved surface 3 of the substrate is transferred to the reflecting member 2 after joining. That is, the joining surface 3 ′ of the member 2 a having good surface accuracy is deformed following the curved surface 3 of the substrate after bonding, so that the aspherical shape of the curved surface 3 of the substrate having good shape accuracy is the same as that of the reflecting member 2 after bonding. It is transferred onto the reflecting surface 4 (good surface accuracy) (see FIG. 1C).
That is, the shape of the reflecting surface 4 is an aspherical reflecting shape having good surface accuracy and shape accuracy.

As a method of joining the member 2a to the curved surface 3 of the substrate 1 having the curved surface 3, an organic adhesive, a metal adhesive used by brazing or soldering, a glass adhesive, or the like is used. Examples thereof include a joining method using an agent, a joining method by welding such as laser welding, seam welding, and ultrasonic welding, and an anodic joining method. The joining method by welding includes a method of joining two members through a joining material and a method of joining two members directly without a joining material.

When the curved surface 3 of the substrate and the member 2a are bonded by a bonding method using an adhesive or a bonding material among such bonding methods, the curved surface of the substrate (bonding surface of the substrate) 3 and the bonding surface 3'of the member 2a. Although an adhesive layer or a bonding material layer is interposed therebetween, if the thickness of this layer is large, it becomes difficult to transfer the shape of the curved surface 3 of the substrate to the reflecting member 2 after bonding. Further, when an adhesive layer or a bonding material layer is interposed between the curved surface of the substrate (bonding surface of the substrate) 3 and the bonding surface 3 ′ of the member 2a, there is a problem that the bonding strength decreases due to a difference in thermal expansion coefficient and plasticity,
The problem of deterioration of the bonding strength due to aging tends to occur.

When the substrate 1 and the member 2a are joined by a welding method without using a joining material, it is necessary to heat the substrate 1 or the member 2a to a temperature equal to or higher than the melting point or the softening point thereof. Difficult to do. Therefore,
As a joining method, it is possible to join at a relatively low temperature, and it is not necessary to use a joining material.
The anodic bonding method capable of accurately transferring the above shape to the reflecting member 2 after bonding is preferable (claim 2).

The anodic bonding method is a bonding method which enables bonding at a temperature lower than the original (when no DC voltage is applied) bonding temperature by applying a DC voltage between two members to be bonded. It can be applied to the joining of dielectrics (for example, glass or ceramics) and metals (unit metals, alloys, semiconductors). When performing anodic bonding, it is preferable to first polish and smooth the respective bonding surfaces of the dielectric and metal to be bonded. This smoothing has the effect of increasing the bonding strength. For example, it is preferable that the maximum surface roughness is 0.05 μm or less.

In anodic bonding, the bonding surfaces of both materials are superposed, heated at a temperature lower than the softening point of the dielectric and the melting point of the metal, and a relatively high direct current voltage is applied between both materials. , The two are joined. The polarity at this time is + on the metal side and − on the dielectric side. The heating temperature is
Depending on the combination of materials and the smoothness of the joint surface,
It is often 0 to 600 ° C. The better the smoothness of the joint surface and the smaller the hardness of the dielectric material, the lower the heating temperature the joint becomes possible.

The applied voltage is a DC voltage, and in the case of an AC voltage, no junction is made. Also, the polarity must be + on the metal side. The magnitude of the applied voltage depends on the combination of materials,
200 to 20 depending on the smoothness of the joint surface and the heating temperature
In many cases, it is 00V, and in general, around 1000V is suitable. The upper limit value is the upper limit value that does not cause destruction by sparks.

Voltage application time (bonding completion time)
Depends on the heating temperature and the applied voltage, but the higher the heating temperature and the higher the applied voltage, the shorter the time, and generally about several minutes. Anodic bonding is generally carried out in air, but it can also be carried out in an atmosphere of oxygen, steam, nitrogen, hydrogen, argon, vacuum or homing gas.

In order to increase the bonding strength by the anodic bonding, it is preferable to select a combination in which the difference in the coefficient of thermal expansion between the dielectric material as the material to be bonded and the metal is small. For example,
A combination in which the difference in coefficient of thermal expansion is 50% or less is preferable. Examples of dielectrics suitable for anodic bonding include soft glass (for example, borosilicate glass), hard glass, optical glass, ceramics (for example, β-alumina ceramics),
There are fused quartz, sapphire, porcelain and the like, and as metals suitable for combination with each of these dielectrics, for example, kovar, chromium alloy, tantalum, silicon, germanium, molybdenum, tungsten, G
aAs and the like.

Even in the case of a combination of the above-mentioned suitable dielectric material and a metal material having a difference in coefficient of thermal expansion from the dielectric material of more than 50%, the bonding strength can be increased by forming the metal material into a thin film. Is. Examples of such metals include copper,
Examples include iron, nickel, iron-nickel alloys, chromium, aluminum, magnesium, titanium and beryllium. Of the combinations of the above materials, the one particularly suitable for anodic bonding is a combination of borosilicate glass and silicon in terms of versatility and processing accuracy. In anodic bonding by this combination, bonding can be performed at a relatively low bonding temperature and in a short time.

X is formed on the reflecting surface of the aspherical reflecting optical element of the present invention.
When the multilayer film for line reflection is provided (claim 3), the device can be used as an X-ray reflection optical device. As the multilayer film for X-ray reflection, for example, Mo / Si, Mo / Si compound, Ru / Si, Ru / Si compound, Rh / Si, Rh
/ Si compound, W / C, W / Si, Ni / C, Cr /
C, Mo / B ₄ C, Mo / SiC, Ru / B ₄ C, Ni
It is possible to use any one of the combinations of / V ₂ O ₅ and Cr / V ₂ O ₅ , which are alternately laminated a plurality of times.

The method for producing an aspherical reflective optical element having a reflection surface provided with a multilayer film for X-ray reflection (claim 3) is roughly divided into a method of performing anodic bonding after forming the multilayer film, and a method of anodic bonding. After that, there is a method of forming a multilayer film. When the curved surface of the joint surface between the substrate and the reflecting member is small, it is easy to form a desired multilayer film (alternate multilayer film in which the ratio of the thicknesses of constituent layers and the thickness of each constituent layer are constant) even after bonding. When the degree of curved surface is large, if a desired multilayer film is formed after joining, the film forming process such as setting of film forming conditions becomes complicated. Therefore, when the curved surface of the bonding surface is large, it is preferable to form the multilayer film before bonding.

In the present invention, by proposing both methods, a method for producing an aspherical reflective optical element having a reflective surface provided with a multilayer film for X-ray reflection (claim 3) is provided regardless of the shape of the bonding surface. it can. The aspherical reflective optical element according to the present invention can be used in an optical system of various devices (for example, an illumination optical system such as a microscope). Furthermore, the optical element having the multilayer film formed thereon can be applied to an optical system of an X-ray microscope or an X-ray lithography apparatus. Further, the method for producing an aspherical reflective optical element of the present invention can be applied not only to optical elements but also to various mechanical system elements.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0033]

Embodiment 1 FIG. 1 is a process drawing showing a method for manufacturing an aspherical reflective optical element of this embodiment, and FIG. 1C is a schematic side view of a completed aspherical reflective optical element. The procedure for producing the aspherical reflective optical element of this example will be described below. First, a parallel flat plate member (for example, a silicon single crystal) having a surface with good surface accuracy (maximum surface roughness 0.001 μm or less) 2
a, a substrate (borosilicate glass) 1 having a curved surface 3 and an air vent hole 5 that are close to an aspherical shape with good shape accuracy
Was prepared (see FIG. 1A).

Member 2a to be joined before anodic joining
And the bonding surfaces 3 and 3'of the substrate 1 are polished and smoothed (0.05
The maximum surface roughness was less than or equal to μm). The anodic bonding is the member 2a.
In the state where the substrate 1 is heated to about 400 ° C., the polarity of the member 2a side electrode 6 is +, and the polarity of the substrate 1 side electrode 6 ′ is −.
Then, a DC voltage of about 700 V was applied (Fig. 1B).
reference).

Bonding is completed in about 10 minutes, and the reflecting member 2 having parallel surfaces is bonded to the curved surface 3 of the substrate 1 having the aspherical curved surface 3 to form the aspherical reflective surface 4. The aspherical reflective optical element is completed (see FIG. 1C). In addition,
When the curved surface 3 of the substrate 1 and the member 2a are bonded, since the curved surface 3 of the substrate 1 which is the bonding surface is a concave surface, the bonding surface 3 ′ of the member 2a closest to the concave surface is bonded.
Air is likely to accumulate at the joint.

Therefore, to prevent air accumulation,
A hole 5 for venting air was provided in the substrate 1. Further, since the air vent hole 5 affects the deformation of the reflecting surface portion of the reflecting member 2 located thereabove, the substrate portion located below the reflecting surface portion where optical characteristics are not particularly required, that is, the substrate 1 It was installed in the center with the minimum size. By bonding the curved surface 3 of the substrate 1 and the member 2a, the shape of the curved surface 3 of the substrate was transferred to the reflecting member 2 after bonding. That is, the joining surface 3 ′ of the flat plate-shaped member 2 a having good surface accuracy is deformed following the curved surface 3 of the substrate after the bonding, so that the aspherical shape of the curved surface 3 of the substrate having good shape accuracy is the reflecting member after the bonding. It was transferred to the reflecting surface 4 of 2 (good surface accuracy) (see FIG. 1C). That is, the shape of the reflecting surface 4 is
The reflecting surface was an aspherical surface having good surface accuracy and shape accuracy.

[0037]

Embodiment 2 FIG. 2 is a schematic side view of an aspherical reflective optical element of this embodiment. The optical element has a dielectric layer (borosilicate glass layer, thickness 0.4 μm) 9 on the curved surface 3 of a substrate (stainless steel) 1 having an aspherical curved surface 3 with good shape accuracy.
Is provided, and the substrate 1 is anodically bonded through the dielectric layer 9 to the reflecting member 2 (single crystal silicon) having a surface with a good surface accuracy (maximum surface roughness of 0.001 μm or less) and a parallel surface. Is an aspherical reflective optical element formed by forming an aspherical reflective surface 4.

[0038]

Third Embodiment FIG. 3 is a schematic side view of an aspherical reflective optical element of this embodiment. The optical element has a flat plate member (borosilicate glass) 2b on a parallel plane before bonding and a silicon layer (thickness:
0.4 μm) 10 is provided, the reflecting member 2 having a surface with a good surface accuracy (maximum surface roughness of 0.001 μm or less) and a parallel surface through the silicon layer 10, and an aspherical curved surface 3 having a good shape accuracy. It is an aspherical reflective optical element formed by anodic bonding with the substrate 1 having the above.

[0039]

Fourth Embodiment FIG. 4 is a schematic side view of an aspherical reflective optical element of this embodiment. The optical element has a surface (maximum surface roughness 0.001 μm) with good surface accuracy on the curved surface 3 of a substrate (borosilicate glass) 1 having an aspherical curved surface 3 with good shape accuracy.
m or less) and a reflecting member 2 (single crystal silicon) having parallel surfaces are anodically bonded to each other to form an aspherical reflecting surface 4 on the surface 4 of the aspherical reflective optical element (on the surface of the member 2),
X-ray reflective multilayer film (Mo / Si alternating multilayer film, 50-100)
Pair) 7 is a film formed on the aspherical reflective optical element. A film forming apparatus such as an ion beam sputtering apparatus or a magnetron sputtering apparatus was used for forming the X-ray reflective multilayer film.

The optical element of this example could be used as an X-ray reflection optical element.

[0041]

As described above, since the reflecting surface of the aspherical reflective optical element of the present invention can satisfy both strict shape accuracy and surface accuracy, an optical system which requires high optical performance. Can be used for

[Brief description of drawings]

FIG. 1 is a process drawing showing a method for manufacturing an aspherical reflective optical element of Example 1.

FIG. 2 is a schematic side view of an aspherical reflective optical element of Example 2.

FIG. 3 is a schematic side view of an aspherical reflective optical element of Example 3.

FIG. 4 is a schematic side view of an aspherical reflective optical element of Example 4.

FIG. 5 is a configuration diagram of an X-ray reduction projection exposure apparatus.

FIG. 6 is a configuration diagram of an X-ray microscope.

[Explanation of symbols for main parts]

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Reflective member (after being joined to substrate 1) 2a ... Flat plate member having parallel planes (before being joined to substrate 1) 3 ... Curved surface of substrate (Aspherical shape) 3 '... Joining surface of flat plate member 2a 4 ... Aspherical reflecting surface 5 ... Air vent hole 6 ... Flat plate member 2a side electrode 6' ... Substrate 1 side electrode 7 ... Multilayer film for X-ray reflection 8 ... DC power supply 9 ... Dielectric (borosilicate glass) layer 10 ... Silicon layer 11 ... X-ray generator 12 ... X-ray illumination optics System 13 ... Mask 14 ... X-ray imaging optical system 15 ... Wafer 16 ... Sample capsule 17 ... X-ray magnifying optical system 18 ... X-ray imaging device 19 ... Vacuum container 20 ... Exhaust device or above

Claims (3)

[Claims] 1. An aspherical reflective optical element comprising a substrate having an aspherical curved surface and a reflective member having a parallel surface bonded to the curved surface to form an aspherical reflective surface. 2. The aspherical reflective optical element according to claim 1, wherein the substrate and the reflecting member are bonded by an anodic bonding method. 3. The aspherical reflective optical element according to claim 1, wherein a multilayer film for X-ray reflection is provided on the aspherical reflecting surface.