JPH0933699A - Method for manufacturing multilayer-film reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a multilayer-film reflector which reduces or eliminates the deformation of a substrate due to the internal stress of a multilayer film which causes the degradation of optical characteristics of the multilayer-film reflector. SOLUTION: Layers 2 are made of a substance which has a little difference between the refractivity to light in a soft X-ray range and the vacuum refractivity, and layers 3 are made of a substance which has a large difference between them. In a method for manufacturing a multilayer-film reflector by laminating the layers 2 and the layers 3 alternately twice or more times on a substrate 1 to form an alternate multilayer film with compressive stress, the deformation of the substrate in a manufactured multilayer-film reflector is eliminated or reduced by cooling the multilayer film to create a condition when it is used after using a substrate made of a material which has a lower thermal expansibility than the multilayer film as the substrate 1 and forming the multilayer film while heating the substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a multi-layered film reflecting mirror used in an X-ray telescope, an X-ray laser, an X-ray lithography and other various X-ray analyzers.

[0002]

2. Description of the Related Art The complex refractive index of a substance with respect to light in the X-ray region is represented by n = 1-δ-ik (δ, k: real number, k indicates X-ray absorption), and both δ and k are 1 Very small compared to. Therefore, in the X-ray region, a lens utilizing refraction like the visible light region cannot be used. Therefore, an optical system using reflection is used.

However, the total reflection critical angle θc (wavelength 10 nm
Since the reflectance is very small at an incident angle closer to vertical than about 20 °), the number of reflecting surfaces (for example, several A multilayer film reflecting mirror in which the thickness of each layer is adjusted based on the optical interference theory so that the phases of the reflected waves match each other is used.

More specifically, the multilayer-film reflective mirror has a material layer (first layer) having a small difference between the refractive index at the X-ray wavelength used and the vacuum refractive index (= 1). It is obtained by alternately laminating a large material layer (second layer) many times. As a typical example, W (tungsten)
/ C (carbon), Mo (molybdenum) / Si (silicon)
Combinations such as the following have been known, and sputtering, vacuum deposition, CVD (Chemical Vapo)
It is formed by a thin film forming technique such as r Deposition).

Since the multilayer-film reflective mirror can also reflect X-rays vertically, it is possible to construct an optical system having a smaller aberration than an oblique-incidence optical system utilizing total reflection. In addition, the multilayer film reflecting mirror has a Bragg formula: 2 dsin θ = mλ
Since the X-ray is strongly reflected only when (d: periodic length of multilayer film, θ: oblique incidence angle, λ: wavelength of X-ray, m: positive integer) is satisfied, it has wavelength selectivity. Here, d corresponds to the layer thickness (film thickness) of a laminate in which the material layer having a small difference in refractive index and the material layer having a large refractive index are laminated one by one.

[0006]

Many thin films have internal stress, and multilayer films used for reflecting mirrors are no exception.
That is, when a multilayer film is formed on the substrate, the substrate is deformed due to the internal stress of the multilayer film, which causes a problem that the optical characteristics of the multilayer film reflecting mirror are deteriorated. When forming a thin film on a disk-shaped substrate, the internal stress sigma is expressed as ^{_{σ = E · t s 2 ·}} δ / {3 (1-ν) t f · (D / 2) 2}. Here, E is the Young's modulus of the substrate, ν is the Poisson's ratio of the substrate, t _s is the thickness of the substrate, t _f is the thickness of the thin film, and D is
Is the diameter of the substrate, and δ is the amount of change in the warp of the substrate before and after thin film formation.

For example, when quartz is used as the substrate, E / (1-ν) = 93.7 GPa, and S as the substrate.
When i (100) is used, E / (1-ν) = 180
It becomes GPa. Here, it is assumed that the substrate has a thickness of 15 mm and a diameter of 80 mm, and a multilayer film having a thickness of 300 nm is formed on the substrate. When the internal stress of the multilayer film is 500 MPa,
The amount of change in the warp of the substrate such as a protrusion or a dent in the central part of the substrate is about 35 nm in the case of a quartz substrate, and Si (10
In the case of 0) substrate, it is about 20 nm.

Such a change in substrate shape causes a serious problem because it deteriorates the optical characteristics of the multilayer-film reflective mirror. The present invention has been made in view of the above problems, and manufactures a multilayer-film reflective mirror that reduces or eliminates substrate deformation due to internal stress of the multilayer film, which causes deterioration of optical characteristics of the multilayer-film reflective mirror. The purpose is to provide a method.

[0009]

Therefore, the first aspect of the present invention is to provide "on a substrate, a layer of a substance having a small difference between the refractive index of light in the soft X-ray region and a refractive index of vacuum and a layer of a large substance. By alternately laminating a plurality of times to form an alternating multilayer film having a compressive stress, in the method for manufacturing a multilayer film reflecting mirror, the substrate has a thermal expansion coefficient smaller than that of the multilayer film. A substrate made of a material is used, and after the multilayer film is formed while heating the substrate, the substrate is deformed by cooling the multilayer film to a state in which the multilayer film is used. There is provided a method for manufacturing a multilayer-film reflective mirror (claim 1), characterized in that it is solved or reduced.

The second aspect of the present invention is that "a layer of a substance having a small difference between the refractive index for light in the soft X-ray region and a vacuum and a layer of a large substance are alternately laminated on the substrate a plurality of times. do it,
By forming an alternating multilayer film with tensile stress,
In the method of manufacturing a multilayer-film reflective mirror, a substrate made of a material having a coefficient of thermal expansion larger than that of the multilayer film is used as the substrate, and the multilayer film is formed while heating the substrate. After that, this is cooled to be in a state of using the multilayer film, thereby eliminating or reducing the deformation of the substrate of the multilayer film mirror to be manufactured (claim 2). "I will provide a.

The third aspect of the present invention is that "Si or a Si compound is used as the substance having a small difference in refractive index, and Mo is used as the substance having a large difference in refractive index. Manufacturing method (claim 3) ”.

[0012]

When a certain object is heated, the object expands and its volume increases. The amount of increase depends on the amount of temperature change and the value of the coefficient of thermal expansion of the substance forming the body. A plate made of a substance having a relatively small coefficient of thermal expansion (hereinafter, referred to as a first plate) and a plate made of a substance having a relatively large coefficient of thermal expansion (hereinafter, referred to as a second plate) are bonded together to form a plywood, When this is heated, the volume of the second plate changes more than that of the first plate, so that the plywood warps with the second plate outside and the first plate inside.

If the first plate and the second plate are laminated in a heated state to form a plywood, and then the plywood is cooled, the second plate having a relatively large coefficient of thermal expansion is larger than the first plate. Since the amount of shrinkage due to the temperature decrease (cooling) is large, the plywood warps with the second plate inside and the first plate outside. This phenomenon is called the bimetal effect, and the stress generated by this difference in coefficient of thermal expansion is called thermal stress.

The multi-layer film reflecting mirror is one in which two different substances are alternately laminated on a substrate a plurality of times to form an alternate multi-layer film (hereinafter, simply referred to as a multi-layer film). The original shape (before forming the multilayer film) changes due to the stress that it has. When the multilayer film has a compressive stress, the substrate changes to a convex shape compared to the shape before the multilayer film is formed, and when the multilayer film has a tensile stress, the substrate has a shape before the multilayer film is formed. Compared to concave.

Therefore, in the present invention, when the multilayer film has a compressive stress, a substrate made of a material having a coefficient of thermal expansion smaller than that of the multilayer film is used as the substrate, and the substrate is heated. However, after forming the multi-layer film, the multi-layer film reflecting mirror is manufactured by cooling the multi-layer film to be in a state in which the multi-layer film is used (Claim 1). When the multi-layered film reflecting mirror is manufactured in this way, the temperature of the multi-layered film is lower than that of the substrate (heated state →
When the temperature decreases, the shrinkage amount due to the cooling state, the environment in which the multilayer film is used, etc. is large, so that a tensile stress that warps with the substrate side facing outward is generated, and the compressive stress of the multilayer film can be canceled or relaxed. That is, the deformation of the substrate can be eliminated or reduced.

Further, in the present invention, when the multilayer film has a tensile stress, a substrate made of a material having a coefficient of thermal expansion higher than that of the multilayer film is used as the substrate,
Further, the multilayer film reflecting mirror is manufactured by forming the multilayer film while heating the substrate, and then cooling the substrate to bring it into a state in which the multilayer film is used (claim 2). When a multilayer mirror is manufactured in this way, the amount of shrinkage of the substrate due to the temperature drop (heating state → temperature drop, cooling state, environment in which the multilayer film is used, etc.) is lower than that of the multilayer film at room temperature and atmospheric conditions. Therefore, a compressive stress that warps with the substrate side inside is generated, and the tensile stress of the multilayer film can be offset. That is, the deformation of the substrate can be eliminated or reduced.

Generally, when a multilayer film is formed by a sputtering method, the stress possessed by the multilayer film is likely to be a compressive stress, and when a multilayer film is formed by a vacuum vapor deposition method, a tensile force is applied. Easy to get stress. Further, as the substrate, a glass substrate such as quartz or a silicon single crystal is generally used. Table 1 shows the thermal expansion coefficients of Mo, Si and Si compounds.

Since Mo has a larger coefficient of thermal expansion than Si and Si compounds, Mo / Si or M
When a multilayer film of an o / Si compound is formed on a Si or Si compound substrate by a sputtering method, tensile stress occurs due to the bimetal effect of the Mo layer, so that the compressive stress of the multilayer film can be relaxed. When a multilayer film is formed by a vacuum vapor deposition method, if crown glass is used for the substrate, the crown glass is Mo or Si.
Alternatively, since the coefficient of thermal expansion is larger than that of the Si compound, compressive stress is generated. Therefore, the tensile stress of the multilayer film can be relaxed by this compressive stress.

As described above, after using a substrate made of a material selected according to the coefficient of thermal expansion of the multilayer film and the type of stress possessed by the multilayer film, and forming the multilayer film while heating the substrate, By subjecting this to room temperature and atmospheric conditions, it is possible to eliminate or reduce substrate deformation of the manufactured multilayer film reflecting mirror. Further, as a result, it is possible to prevent the deterioration of the optical characteristics due to the change of the substrate shape of the manufactured multilayer film reflecting mirror, and to obtain a good optical system.

Si or a Si compound is used as a substance having a small difference in refractive index according to the present invention, and M is used as a substance having a large difference.
It is preferable to use o because high reflectance can be obtained in the soft X-ray region (particularly, in the soft X-ray having a wavelength of 13 nm, which is promising in X-ray reduction projection exposure). As the Si compound, for example, SiC or SiN can be used.

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

[0022]

[Table 1]

[0023]

Example 1 In this example, a Mo / Si multilayer film was formed on a quartz substrate (substrate thickness 15 mm, diameter 80 mm). Using the targets of Mo and Si, the Si layer 2 and the Mo layer 3 are formed on the substrate 1 by the ion beam sputtering method.
Were alternately laminated to form a multilayer film. At this time, the substrate was heated to 55 ° C. before the film formation, and after the temperature was stabilized, the film formation was performed while maintaining the temperature at 55 ° C. After the film formation was completed, the substrate was cooled to room temperature and placed in an air atmosphere.

The period length of the Mo / Si multilayer film is 6.7 nm,
Γ (= Mo layer thickness / period length) is ⅓, and the number of stacked layers is 50
Made a pair. FIG. 1 shows a schematic cross-sectional view of a multilayer film reflecting mirror (in FIG. 1, the number of layers of the multilayer film is smaller than the actual number). The stress of the manufactured multilayer-film reflective mirror was about 3 MPa (compressive stress), and the amount of change in the warp of the substrate was about 0.2 nm. On the other hand, in the case of the multilayer-film reflective mirror manufactured without heating the substrate, the stress was about 385 MPa (compressive stress) and the amount of change in the warp of the substrate was about 29 nm. It was found that the amount of deformation of the substrate was larger than that of the multilayer film reflecting mirror.

Further, when the normal incidence soft X-ray reflectance of the multilayer-film reflective mirror of this embodiment was measured by using radiated light, a wavelength of 1
The value was about 68% at 3 nm, which was almost the same value as that of the multilayer-film reflective mirror manufactured without heating the substrate.

[0026]

[Embodiment 2] In this embodiment, a Mo / SiC multilayer film is formed into Si.
(100) substrate (substrate thickness 15 mm, diameter 80 mm)
A film was formed thereon. Using each target of Mo and SiC,
SiC on the substrate 1 by the ion beam sputtering method
Layer 2 and Mo layer 3 were alternately laminated to form a multilayer film. At this time, before the film formation, the substrate was heated to 250 ° C., and after the temperature was stabilized, the film formation was performed while maintaining the temperature at 250 ° C. After the film formation was completed, the substrate was cooled to room temperature and placed in an air atmosphere.

The cycle length of the Mo / SiC multilayer film is 6.7 nm,
Γ (= Mo layer thickness / period length) is ⅓, and the number of stacked layers is 50
Made a pair. FIG. 1 shows a schematic cross-sectional view of the multilayer-film reflective mirror (in FIG. 1, the number of layers of the multilayer film is smaller than the actual number). The stress of the manufactured multilayer-film reflective mirror was about 2 MPa (tensile stress), and the amount of change in the warp of the substrate was about 0.08 nm. On the other hand, in the case of the multilayer-film reflective mirror manufactured without heating the substrate, the stress was about 363 MPa (compressive stress) and the amount of change in the warp of the substrate was about 14 nm. It was found that the amount of deformation of the substrate was larger than that of the multilayer film reflecting mirror.

Further, when the normal incidence soft X-ray reflectance of the multilayer-film reflective mirror of this embodiment was measured by using radiated light, a wavelength of 1 was obtained.
The value was about 51% at 3 nm, which was almost the same value as that of the multilayer-film reflective mirror manufactured without heating the substrate.

[0029]

As described above, according to the present invention, it is possible to manufacture a multilayer-film reflective mirror which reduces or eliminates substrate deformation due to internal stress of the multilayer film, which causes deterioration of optical characteristics of the multilayer-film reflective mirror. You can Further, as a result, it is possible to prevent the deterioration of the optical characteristics due to the change of the substrate shape of the manufactured multilayer film reflecting mirror, and to obtain a good optical system.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a multilayer reflector (one example) according to the present invention.

[Explanation of Signs of Main Parts] 1 ... Substrate 2 ... Si or Si compound layer 3 ... Mo layer
that's all

Claims (3)

[Claims] 1. A layer of a substance having a small difference between the refractive index of light in the soft X-ray region and a vacuum and a layer of a large substance are alternately laminated on a substrate to have a compressive stress. In the method for manufacturing a multilayer-film reflective mirror by forming an alternating multilayer film, a substrate made of a material having a thermal expansion coefficient smaller than that of the multilayer film is used as the substrate, and the substrate is heated. However, after the multilayer film is formed, it is cooled to be in a state of using the multilayer film, thereby eliminating or reducing the substrate deformation of the manufactured multilayer film reflector. Manufacturing method. 2. A substrate having a tensile stress by alternately laminating a plurality of layers of a substance having a small difference between the refractive index of light in the soft X-ray region and a vacuum in a soft X-ray region and a layer of the same having a large difference on the substrate. In the method of manufacturing a multilayer-film reflective mirror by forming an alternating multilayer film, a substrate made of a material having a coefficient of thermal expansion larger than that of the multilayer film is used as the substrate, and the substrate is A multilayer film reflection characterized by eliminating or reducing substrate deformation of a manufactured multilayer film reflection mirror by forming the multilayer film while heating and then cooling the multilayer film to a state before use. Mirror manufacturing method. 3. The material having a small difference in refractive index is Si
Alternatively, a Si compound is used, and Mo is used as a large substance, and the method for manufacturing a multilayer-film reflective mirror according to claim 1 or 2.