JP2006162362A - Reflecting member by multilayer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflecting member by a multilayer film, especially an EUV multilayer film mirror, capable of acquiring a high reflectivity, even in the case of a multilayer film formed by ion beam sputtering or magnetron sputtering. <P>SOLUTION: In this reflecting member by the multilayer film, an intermediate layer 4 having an intermediate refractive index between two material layers is interposed between the two material layers one of which has a relatively low refractive index and the other of which has a relatively high refractive index in a used wavelength area of a soft X-ray, and such layers are laminated repeatedly in due order. The intermediate layer is constituted of boron carbide including an alkali metal or a compound of the alkali metal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a reflecting member made of a multilayer film, and more specifically to an optical component made of a multilayer film formed by ion beam sputtering or magnetron sputtering, particularly an EUV multilayer mirror.

Conventionally, as an EUV multilayer mirror that reflects extreme ultraviolet (hereinafter referred to as EUV) light, a light element with a low absorption at 13.4 nm and a Si layer, which is a high refractive index material, and a heavy element, a low refractive index material. An EUV multilayer mirror having a multilayer structure in which a certain Mo layer is alternately and repeatedly formed with a predetermined film thickness is known.
In such a conventional EUV multilayer mirror, mutual diffusion and interaction occur at the interface between the Mo layer and the Si layer, silicide is formed, interface roughness, refractive index change, etc. occur, as expected. In other words, the reflectance and bandwidth cannot be obtained.

In order to solve these problems, for example, a method for preventing a silicide reaction by forming an intermediate layer of a hydrogenation layer at the interface between the Mo layer and the Si layer has been proposed as in Patent Document 1.
Moreover, in patent document 2, it is Rb, RbCl, RbBr, Sr, Y, Zr, Ru, Rh, Tc, Pd, as a 3rd material layer in the interface of Mo layer and Si layer which are 1st and 2nd material layers. A multilayer mirror has been proposed in which an intermediate layer is formed of a material selected from the group including Nb and Be, and alloys and compounds of these materials.
JP-A-5-297194 JP 2001-51106 A

  However, in the above conventional example, in the multilayer film forming method using the first, second, and third material layers, ion beam sputtering or magnetron sputtering is mainly used, but the ion beam sputtering or magnetron sputtering is used. The film has many dangling bonds due to the principle of the film forming method, and even when a third material that prevents mutual diffusion or mutual reaction is inserted in the intermediate layer as in the above-described conventional example, the reaction with dangling bonds occurs. It was difficult to obtain a multilayer mirror with reflectivity.

  In view of the above-described problems, the present invention provides a reflective member, particularly an EUV multilayer mirror, which is made of a multilayer film that can obtain a high reflectance even in a multilayer film formed by ion beam sputtering or magnetron sputtering. It is the purpose.

This invention provides the member by the multilayer film comprised as follows.
That is, the reflecting member using the multilayer film according to the present invention has a relatively low refractive index between the two material layers having a low refractive index and the other having a high refractive index in the wavelength range of soft X-rays. A reflective member made of a multilayer film in which an intermediate layer having a refractive index is interposed, and these are sequentially and repeatedly laminated, characterized in that the intermediate layer is made of boron carbide containing an alkali metal or an alkali metal compound. Yes.
In the present invention, the two material layers can be composed of molybdenum as the low refractive index material layer and silicon as the high refractive index material layer, and the above configuration of the present invention is applied. Thus, an EUV multilayer mirror having a high reflectivity formed by ion beam sputtering or magnetron sputtering can be configured.

  According to the present invention, it is possible to realize a reflective member, in particular, an EUV multilayer mirror, using a multilayer film that can obtain a high reflectance even in a multilayer film formed by ion beam sputtering or magnetron sputtering.

According to the configuration of the present invention described above, carbonization including an alkali metal or an alkali metal compound between the first material layer and the second material layer having different low refractive indexes within the used wavelength range of soft X-rays. By interposing a boron intermediate layer, it is possible to suppress mutual diffusion and interaction at the interface between the first material layer and the second material layer, and to realize a reflective member with a multilayer film having high reflectivity. can do. These are based on the following knowledge of the present inventors.
In the case of a general (Mo) / (Si) structure without an intermediate layer formed by ion beam sputtering or magnetron sputtering, the Mo film is formed on the Si film, contrary to the case where the Si film is formed on the Mo film. In this case, the thickness of the silicide layer due to mutual diffusion or mutual reaction is different. These are considered to be due to the difference in energy of the sputtered particles, and it is difficult to form a multilayer film with little mutual diffusion and mutual reaction by optimizing the process conditions. At this time, as a method for preventing the formation of silicide, when a measure is taken to simply sandwich the Mo and Si layers with an intermediate layer of boron carbide (B ₄ C), the film formed by sputtering is generally argon (Ar ) Is ionized and the target material is knocked out, so it is very difficult to form a stoichiometric boron carbide film on the substrate, particularly when boron carbide (B ₄ C) as a compound target material is formed. Thus, a boron carbide film having many dangling bonds is formed. These dangling bonds are bonded to active and film-structured Mo and Si, and are stabilized by mutual diffusion and interaction.
In the present invention, the monovalent alkali metal or alkali metal compound is put into the intermediate layer boron carbide (B ₄ C) film in an optimal ratio or a ratio that provides an optimal concentration distribution in the thickness direction. This method is intended to further suppress interdiffusion and interaction by terminating and stabilizing the dangling bonds.
In particular, the alkali metal is preferably lithium (Li) that is less absorbed at the EUV light wavelength, and the alkali metal compound is boron (B) and lithium compounds that are less absorbed at the EUV light wavelength, such as LiB ₂ and LiB _12. Is preferred.

  In other words, lithium has the smallest ionic radius of 0.074 nm among metal elements, can enter the gap between boron and carbon, and has a high probability of terminating dangling bonds and makes it a smooth interface. it can. In other words, by terminating the dangling bonds generated at the time of film formation with Li, which is a monovalent alkali metal, mutual diffusion and interaction can be suppressed, thereby forming a smooth interface. The smooth interface becomes a reflection surface, and further strengthens by interference, and it becomes possible to realize an EUV multilayer mirror with high reflectivity.

Next, the configuration of the EUV multilayer mirror in the present embodiment will be described with reference to the drawings.
FIG. 1 shows a cross-sectional view of an EUV multilayer mirror according to the present embodiment.
As shown in FIG. 1, the EUV multilayer mirror has a mirror substrate 1 having a smooth surface and a material layer 2 having a small absorption index and a large refractive index, and a material layer 3 having a small refractive index. Similarly, the material layer 4 having a small absorption with respect to the used wavelength and having an intermediate refractive index between the material layers 2 and 3 is sandwiched, and the sandwiched structure is sequentially repeated.

Here, for example, the material layer 2 is made of silicon (Si), the material 3 layer is made of molybdenum (Mo), and the material layer 4 is made of boron carbide containing an alkali metal or an alkali metal compound, and these are repeatedly laminated.
The thickness of each layer in this multilayer structure is set to a value in which the EUV light reflected at the interface between the layers is intensified, the material layer 2 made of silicon is about 3 nm, the material layer 3 made of molybdenum is about 4 nm, The material layer 4 made of boron carbide containing an alkali metal or an alkali metal compound is about 0.5 nm.

Examples of the present invention will be described below.
In this example, the present invention was applied to form an EUV multilayer mirror.
FIG. 2 shows a schematic configuration of a sputtering apparatus used for manufacturing the EUV multilayer mirror of the present embodiment.
In FIG. 2, 1 is a mirror substrate, 2 is a silicon (Si) layer, 3 is a molybdenum (Mo) layer, and 4 is an intermediate layer made of boron carbide containing an alkali metal or an alkali metal compound.
5 is a vacuum chamber, 6 is a main valve, 7 is an exhaust system, 8 is a gas supply system, and 9 is a mass flow controller.
10 is a molybdenum (Mo) target, 11 is a silicon (Si) target, 12 is a boron carbide target containing an alkali metal compound (high concentration), and 13 is a boron carbide target containing an alkali metal compound (low concentration).
14 is a sputtering power source, 15 is a shutter, and 16 is a target switching drive system.

Formation of the multilayer film by the Si layer 2 and the Mo layer 3 of the EUV multilayer mirror and the intermediate layer 4 of boron carbide containing an alkali metal compound in the present embodiment is performed in the following procedure.
As shown in FIG. 2, a cryopump, which is a main pump, passes through a main valve 6 in a vacuum chamber 5 while a substrate 1 having a rough surface or a flat surface is set on a substrate holder. Exhaust with an exhaust system 7 such as a turbo molecular pump.
After the ultimate pressure in the vacuum chamber is sufficiently evacuated to 1 × 10 ⁻⁵ Pa or less, the argon gas controlled by the mass flow controller 9 from the gas supply system 8 is converted into a molybdenum (Mo) target 10 and a silicon (Si) target 11. Then, 10 sccm is supplied to each of the targets 12 and 13 having different ratios of alkali metal compound and boron carbide. The argon gas controlled by the mass flow controller is supplied to the molybdenum (Mo) and silicon (Si) cathodes via the rotating gas introduction mechanism, and the pressure inside the vacuum chamber becomes 0.06 Pa.

Next, when a sputtering power of 200 W is supplied from the sputtering power source 14 to each cathode, a discharge is formed between each target and the ground. When the surface of each target is cleaned and the target temperature is constant and the film formation speed is stable, the shutter 15 on the front surface of the Si target is opened, and the first layer is formed under the condition that the film thickness of the substrate having unevenness or planar shape is uniform. To do.
After forming a silicon film with a thickness of 3 nm, the Si shutter is closed.

Next, the target is switched by the target switching drive system 16, and boron carbide containing an alkali metal or an alkali metal compound is formed with a thickness of 0.5 nm, Mo is formed with a thickness of 4 nm, and an alkali metal or an alkali metal compound is changed with the same operation as described above. The boron carbide film is deposited to 0.5 nm. These four layers of silicon (Si), molybdenum (Mo), and boron carbide containing an alkali metal or an alkali metal compound are paired, and 40 to 50 pairs are repeatedly stacked. Further, the final layer is formed with a Si film, and the process is completed.
Note that the concentration distribution in the thickness direction of the boron carbide film containing an alkali metal or an alkali metal compound can be achieved by switching between the target 12 having a high ratio and the target 13 having a low ratio. As the concentration distribution in the thickness direction, the alkali metal or alkali metal compound concentration is preferably high in the vicinity of the interface. These can be achieved by film formation that switches to the targets 12, 13, and 12.
Finally, after the supply of sputtering power and the introduction of gas are stopped, the main valve is closed, N ₂ gas is supplied into the vacuum chamber to release it to the atmosphere, the substrate is taken out, and the film forming process is completed.

  According to the present embodiment, the intermediate layer described above can suppress mutual diffusion and interaction at the interface between the Si layer 2 and the Mo layer 3, and thus suppress mutual diffusion and interaction. With such a configuration, a smooth interface is formed, and such a smooth interface of each layer becomes a reflection surface, which is further strengthened by interference, and an EUV multilayer mirror with high reflectivity can be realized.

  In the above embodiments and examples of the present invention, the film configuration in which the silicon layer, the intermediate layer, the molybdenum layer, and the intermediate layer are stacked in this order on the mirror substrate 1 has been described. The present invention is not limited to a multilayer film having a configuration, and can naturally be applied to a multilayer film having a film configuration in which a molybdenum layer, an intermediate layer, a silicon layer, and an intermediate layer are stacked in this order on the mirror substrate 1.

Sectional drawing which shows the structure of the EUV multilayer mirror in embodiment of this invention. The figure which shows schematic structure of the sputtering device used for manufacture of the EUV multilayer mirror in Example 1 of this invention.

Explanation of symbols

1: Mirror substrate 2: Silicon (Si)
3: Molybdenum (Mo)
4: Boron carbide containing alkali metal or alkali metal compound 5: Vacuum chamber 6: Main valve 7: Exhaust system 8: Gas supply system 9: Mass flow controller 10: Molybdenum (Mo) target 11: Silicon (Si) target 12: Alkali Boron carbide target containing metal compound (high concentration)
13: Boron carbide target containing an alkali metal compound (low concentration)
14: Sputtering power supply 15: Shutter 16: Target switching drive system

Claims (6)

An intermediate layer having an intermediate refractive index between the two material layers is interposed between two material layers, one of which has a low refractive index and the other has a high refractive index, within the wavelength range of soft X-rays. It is a reflective member with a multilayer film that is sequentially and repeatedly laminated,
A reflective member made of a multilayer film, wherein the intermediate layer is made of boron carbide containing an alkali metal or an alkali metal compound.   2. The multilayer film reflecting member according to claim 1, wherein the two material layers have a low refractive index material layer made of molybdenum and a high refractive index material layer made of silicon. 3.   The multilayer member according to claim 1 or 2, wherein the intermediate layer has a concentration distribution of the boron carbide and the alkali metal or the alkali metal compound in a thickness direction.   The reflective member by a multilayer film according to any one of claims 1 to 3, wherein the alkali metal is lithium and the compound of the alkali metal is a lithium compound. The reflective member using a multilayer film according to claim 4, wherein the lithium compound is LiB ₂ or LiB ₁₂ .   The multilayer film reflecting member according to any one of claims 1 to 5, wherein the multilayer film is a multilayer film mirror that reflects extreme ultraviolet light formed by ion beam sputtering or magnetron sputtering.

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