JPH05232299A - Manufacture of x-ray multilayer film reflector - Google Patents

Abstract

PURPOSE:To prevent mutual diffusion and also to improve heat resistance by forming a multilayer film repeatedly in a plurality of times in a prescribed sequence by using three kinds of substances different in refractive index as targets. CONSTITUTION:A target holder 4 rotates as shown by an arrow P and moves targets 3a to 3c of substances desired to be formed in a film, to a position opposed to an ion source 5. An ion beam 7 being applied from the source 5, vapor produced by sputtering target materials thereby is made to stick on a substrate 1 and thereby a thin film is formed. By this apparatus, Mo, Si and SiO2, for instance, are put as the targets 3a to 3c on the holder 4, an Mo layer (layer A) of a film thickness 25Angstrom , an SiO2 layer (layer C) of a film thickness 5Angstrom and an Si layer (layer B) of a film thickness 40Angstrom are formed fifty times in the sequence of A/C/B/C on the substrate 1 of an Si wafer and thereby a multilayer film of which a periodical length is 75Angstrom and the number of laminates fifty sets is formed. Since a compound of substances being stable thermodynamically is used as a diffusion-preventing layer in this way, mutual diffusion is prevented, heat resistance is also improved and lowering of reflectance is avoided.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an X-ray reduction projection exposure apparatus, an X-ray telescope, an X-ray microscope, an X-ray laser and various X-rays.
The present invention relates to a method for manufacturing a multilayer-film reflective mirror used in a reflective optical system in the X-ray wavelength range in a line analyzer or the like.

[0002]

2. Description of the Related Art For light in the X-ray wavelength range, the refractive index of a material is expressed as n = 1-δ-iβ (δ, β: positive real number), and both δ and β are compared to 1. Very small (refractive index imaginary part β represents absorption of X-rays). Therefore, the refractive index is close to 1 and X-rays are hardly refracted.
Absorb the rays. Therefore, a lens that uses refraction such as light in the visible light region cannot be used for light in the X-ray wavelength region.

Therefore, an optical system utilizing reflection is used. However, since the refractive index is also close to 1, the reflectance is very low and most X-rays are transmitted or absorbed. In order to solve this problem, a material having a large difference between the refractive index in the wavelength range of X-rays used and a vacuum refractive index (= 1) and a material having a small difference are alternately laminated in many layers. Then, a multi-layered film mirror was developed in which a large number of reflecting surfaces, which are the interfaces between them, were provided, and the thickness of each layer was adjusted based on the optical interference theory so that the phases of the reflected waves from the respective interfaces coincided with each other. A typical example of such a multilayer-film reflective mirror is W
(Tungsten) / C (carbon), Mo (molybdenum) /
A combination of Si (silicon) or the like is known. And
These multilayer films have been produced by thin film forming techniques such as sputtering, vacuum deposition, and CVD.

[0004]

The above-mentioned multilayer film artificially constitutes a periodic structure and is inherently unstable. In particular, when using such a multilayer-film reflective mirror for high-intensity X-rays, a part of the X-rays is absorbed by the multilayer film and its substrate, and the energy raises the temperature of the multilayer film. Therefore, reactions such as mutual diffusion and compound formation are promoted in the multilayer film, so that the multilayer film structure is destroyed in a short time and the function as a reflecting mirror is lost.

Recently, as the practical use of the X-ray multilayer mirror is advanced, the heat resistance of the multilayer film has been evaluated, and the heat resistance of some combinations of materials is being clarified. For example, the multi-layer film of the Mo / Si combination has a high reflectance on the long wavelength side of the absorption edge of silicon of 123Å, and thus is excellent as a multi-layer film reflection mirror used in the reflection optical system of the X-ray reduction projection exposure apparatus. ing. However, this multi-layer film has low heat resistance, and the multi-layer film structure is destroyed when heated to about 400 ° C. in vacuum. It is known that this destruction phenomenon is due to the diffusion of silicon into the molybdenum layer and the formation of molybdenum silicide. (See, for example, DGSterns et.al., J.Appl.Phys.67 (1990) 2415.) Therefore, in order to prevent diffusion and improve heat resistance, different refractive indexes are formed in the multilayer film. A multilayer-film reflective mirror has been proposed in which a diffusion prevention layer C layer is provided between a layer A and a layer B made of a substance. However, in all cases, the improvement in heat resistance of the multilayer films was insufficient.

For example, Japanese Patent Laid-Open No. 60-7400 proposes a multi-layer film in which a diffusion preventive layer for silicon (Si) is provided between a metal layer and a boron carbide (B ₄ C) layer. It does not function as a diffusion prevention layer because it easily reacts with the metal to form silicide. Further, Japanese Patent Application Laid-Open No. 2-242201 proposes a multilayer film in which a heat resistance is improved by providing a silicon oxide (SiO ₂ ) layer formed by reactive sputtering at the interface of the multilayer film made of molybdenum and silicon. However, in the film formation by reactive sputtering, the surface of the thin film already formed on the substrate is also exposed to the ions and radicals of the reactive gas at the same time. The freshly formed thin film surface is so active that it readily reacts with such ions and radicals. Therefore, a compounding reaction also occurs on the surface of the thin film on the substrate, and the surface roughness of the thin film remarkably increases. As a result, the interface roughness of the formed multilayer film becomes large and the loss due to scattering is large, so that a high reflectance cannot be obtained. So in this case,
Since the surface of the molybdenum layer is exposed to oxygen plasma to increase the surface roughness, there arises a problem that the X-ray reflectance itself is lowered even though the heat resistance is improved.

The present invention aims to solve such a problem.

[0008]

To achieve the above object, in the present invention, A / C / B is formed by a sputtering method using three kinds of substances A, B and C having different refractive indexes as targets.
X-ray multilayer mirrors were manufactured by laminating thin films made of the above substances in the order of / C and repeating this multiple times to form a multilayer film. (Claim 1) Then, each of these layers is formed by a sputtering method using an inert gas such as argon. (Claim 2)

[0009]

The X-ray multilayer mirror according to the present invention is
As shown in FIG. 1, A composed of materials having different refractive indexes
The C layer is formed as a diffusion preventing layer between the layer and the B layer. In such a construction, thermodynamically stable C
The layers effectively prevent interdiffusion between the A and B layers, thus significantly improving heat resistance. The C layer, which is the diffusion prevention layer, includes
Thermodynamically stable materials such as oxides, nitrides, and carbides may be used, but it is preferable to select a material that can obtain high reflectance in consideration of optical characteristics.

In the present invention, since three types of individual targets are used, there is no selection limitation on the material of each layer. The outermost surface (incident surface) layer of the multilayer film may be used as the C layer to function as a protective layer of the multilayer film, or the A layer or the B layer may be used as the outermost surface layer. Further, in the present invention, an inert gas such as argon is used when forming each layer by the sputtering method.

Generally, an oxide produced by a sputtering method,
When forming a compound such as a nitride or a carbide, a single substance such as a metal was used as a target. Then, a method has been adopted in which a reactive gas such as oxygen, nitrogen, ammonia, or a hydrocarbon such as methane is mixed into an inert gas such as argon when performing sputtering to synthesize a compound at the time of film formation. However, in this method, since the surface of the thin film already formed on the substrate is also exposed to the ions and radicals of the reactive gas as described above, the surface roughness of the diffusion preventing layer increases. Therefore, the interface roughness of the multilayer film increases.

On the other hand, in the present invention, since only the inert gas such as argon is used also when forming the diffusion preventing layer made of a compound, the roughness of the interface does not occur. Therefore, a multilayer film having high reflectance can be formed. Since the thickness of the diffusion prevention layer may be set to the minimum necessary thickness to obtain the necessary heat resistance, the decrease in reflectance due to the provision of the diffusion prevention layer can be suppressed.

Hereinafter, the present invention will be described in more detail with reference to examples.

[0014]

Example 1 FIG. 2 is a schematic configuration diagram of an ion beam sputtering apparatus used in this example. In the vacuum chamber 10 of this apparatus, there are provided a substrate holder 2 to which the substrate 1 is attached, an ion source 5 and a target holder 4 to which targets 3a, 3b and 3c of three kinds of substances are attached respectively. Target holder 4
Can be rotated as shown by an arrow P in the figure by a rotating means (not shown), and the target of the substance to be film-formed can be moved to a position facing the ion source 5. During film formation, the ion source 5 to the argon ion beam 7
Is irradiated to collide with a target made of a desired substance. Then, vapor generated by sputtering the target material is attached onto the substrate 1 to form a thin film.

In this embodiment, three types of targets of molybdenum, silicon and silicon oxide (SiO ₂ ) were attached to the target holder 4. Then, using a silicon wafer as a substrate, a molybdenum layer (A
Layer), a silicon oxide layer (C layer) having a film thickness of 5Å, a silicon layer (B layer) having a film thickness of 40Å, and a silicon oxide layer (C layer) having a film thickness of 5Å.
Film formation was performed 50 times to form a multilayer film having a cycle length of 75Å and a stack number of 50 as shown in FIG. In this embodiment, a silicon layer is formed as the uppermost layer.

The multilayer film produced as described above was heated in vacuum to examine the heat resistance. As a result, the reflectance did not change up to 450 ° C, and the multilayer structure was destroyed at 550 ° C and the reflectance decreased. As a comparative example, a multilayer film was prepared by alternately laminating 50 layers each of a molybdenum layer having a film thickness of 25 Å and a silicon layer having a film thickness of 50 Å by the same ion beam sputtering apparatus as in the present example. And the heat resistance was investigated similarly. As a result, it no longer reflects at 400 ° C.

Next, the soft X-ray reflectance of each of the multilayer film produced in this example and the multilayer film produced in the comparative example was measured by s-polarized light using synchrotron radiation. The incident angle of the synchrotron radiation was set to 15 ° with respect to the normal line of the multilayer film so that the peak of reflectance was generated near the wavelength of 135 Å. As a result, the reflectance of the multilayer film of this example was 66% with respect to the reflectance of 72% of the multilayer film of the comparative example, and no significant reduction in reflectance was observed due to the provision of the diffusion prevention layer. ..

[0018]

Second Embodiment FIG. 3 is a schematic configuration diagram of a high frequency magnetron sputtering apparatus used in this embodiment. In a vacuum chamber 10 of this apparatus, a substrate holder 2 for mounting a substrate 1 and a target 3 of three kinds of substances are provided.
a, 3b, and 3c are provided. The high frequency power supplies 6a, 6b and 6c are connected to the respective targets. The substrate holder 2 is configured to be rotatable, and the substrate 1
Are able to pass over each target. Each target has its own shutter,
A shield plate is provided between the targets. (Neither is shown.) During film formation, argon gas is introduced into the vacuum chamber 10 and high frequency power is applied to each target. At this time, the shutters of the targets of the material to be formed are opened, and the shutters of the other targets are closed. Then, the material of the target with the shutter opened is sputtered and the generated vapor is adhered onto the substrate 1 to form a thin film.

In this embodiment, three types of targets, molybdenum, silicon and silicon carbide (SiC) were used.
Then, using a silicon wafer as a substrate, the substrate 1
Molybdenum layer (A layer) with a film thickness of 25Å, silicon carbide layer (C layer) with a film thickness of 10Å, silicon layer (B layer) with a film thickness of 30Å, film thickness
The silicon carbide layer (C layer) of 10 Å was deposited 50 times in this order,
A multilayer film with a cycle length of 75Å and a stack number of 50 was formed.
In this embodiment, a silicon layer is formed as the uppermost layer.

The multilayer film produced as described above was heated in vacuum to examine the heat resistance. As a result, the reflectance did not change up to 600 ° C, and the multilayer structure was destroyed at 800 ° C and no reflection occurred. As a comparative example, a multilayer film was manufactured by alternately laminating 50 layers each of a molybdenum layer having a film thickness of 25 Å and a silicon layer having a film thickness of 50 Å by using the same apparatus as this example. And the heat resistance was investigated similarly. As a result, it no longer reflects at 400 ° C.

Next, the soft X-ray reflectance of each of the multilayer film produced in this example and the multilayer film produced in the comparative example was measured in the same manner as in Example 1. As a result, the reflectance of the multilayer film of this example is 72% as compared with the reflectance of the multilayer film of the comparative example.
It was 68%, and a significant decrease in reflectance due to the provision of the diffusion preventing layer was not recognized. It should be noted that, in each of the embodiments, the heat resistance improvement of the multilayer film reflecting mirror of the combination of molybdenum / silicon, which is of high practical importance, is described.
It goes without saying that the present invention can be applied to a multilayer-film reflective mirror made of a combination of other substances.

By the way, in a conventional multi-layer film reflecting mirror in which two kinds of substances are alternately laminated, the compound such as oxide, nitride or carbide used as the diffusion preventing layer in the present invention is used for one of the substances. Can also improve heat resistance. However, in this case, the reflectance is inevitably lowered. This is because, in general, a material suitable for obtaining a high reflectance does not match a material having a thermodynamically stable diffusion preventing effect.

[0023]

As described above, according to the present invention, compounds such as thermodynamically stable oxides, nitrides and carbides are provided in the multilayer film as the diffusion preventing layer. Diffusion can be effectively prevented. Therefore, the heat resistance of the multilayer film is significantly improved. Further, when forming a film by sputtering, the surface roughness of the thin film does not increase because the sputtering is performed only with an inert gas. Therefore, a multilayer film having a high reflectance can be manufactured.

The present invention is applicable to multilayer optical systems used for high-intensity X-ray sources such as synchrotron radiation in the future, or extremely harsh durability like X-ray laser resonators. The effect can be largely exerted for required applications.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a multilayer film manufactured according to the present invention.

FIG. 2 is a schematic configuration diagram of an ion beam sputtering apparatus used in Example 1.

FIG. 3 is a schematic configuration diagram of a high frequency magnetron sputtering apparatus used in Example 2.

[Explanation of symbols for main parts]

 1 substrate 2 substrate holder 3a target 3b target 3c target 4 target holder 5 ion source 6a high frequency power source 6b high frequency power source 6c high frequency power source 7 ion beam 10 vacuum chamber

Claims (3)

[Claims] 1. Three types of substances A having different refractive indexes,
By the sputtering method targeting B and C, A
/ C / B / C in the order of thin films of the above substances,
A method for manufacturing an X-ray multilayer film reflecting mirror, characterized in that a multilayer film is formed by repeating this a plurality of times. 2. The method for manufacturing an X-ray multilayer mirror according to claim 1, wherein the target is irradiated with ions of an inert gas when the sputtering is performed. 3. The substance C is a compound of an oxide, a nitride, or a carbide.
And a method for manufacturing an X-ray multilayer mirror according to claim 2.