JPH0589818A - Multi-layer film reflex mirror - Google Patents

Abstract

PURPOSE:To reduce the coarseness of a multi-layer film to work as a reflex mirror due to crystal grain boundaries of metal elements. CONSTITUTION:In a multi-layer reflex mirror of multi-layer structure, in which two sorts of substances having different refractive included are placed one over another, one sort layers are made from an alloy of transition metal elements having a high melting point, wherein the composition proportion of the alloy shall lie near the eutectic point to present an eutectic reaction. One of the alloy components shall be Pt metal element among transfer metal elements. Besides transition metal element, a semi-metal element is included as the eutectic material. The alloy layer is allowed to work as a reflex surface in an total-reflecting reflex mirror utilizing the reflection to the light in a slant incidence below the all-reflecting critical angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflecting mirror for light in the vacuum X-ray to soft X-ray region having a wavelength of 200 nm or less, and particularly for direct incidence where the incident angle is perpendicular to the mirror surface. Also relates to a multilayer-film reflective mirror having a high reflectance.
By using this multilayer film reflecting mirror as an optical element,
It can be widely used as a soft X-ray optical system such as X-ray lithography, an X-ray microscope, and an X-ray spectroscopic element.

[0002]

2. Description of the Related Art From vacuum ultraviolet rays having a wavelength of 200 nm or less to soft X
With respect to the light in the line region, the critical angle for total reflection is very small in the conventional reflecting mirror, and the reflectance at direct incidence is very small regardless of the substance. Therefore, heretofore, there has been no reflecting mirror which has a high reflectance by directly entering the light in this region. In order to obtain a high reflectance, the incident angle of light on the reflecting mirror must be an oblique incidence of a few degrees, which is less than the critical angle for total reflection. In such an oblique-incidence total reflection mirror, since the incident angle is small, the light irradiation area on the reflection mirror surface is very large, and the size of the reflection mirror itself is very large. Therefore, when designing an optical system, the degree of freedom in design is reduced. Furthermore, it is necessary to satisfy high shape accuracy for the irradiation area over a large area,
Processing is difficult with current substrate processing technology. For these reasons, it has been very difficult to apply to optical systems such as X-ray lithography and X-ray microscope that require high resolution.

Therefore, in order to solve this problem, it has been proposed to design an optical system using a multilayer-film reflective mirror having a high reflectance at normal incidence. A multi-layered film reflector is a reflective surface that accumulates reflective surfaces at regular intervals so as to satisfy the Bragg reflection condition at a certain incident angle for a specific wavelength, and uses the interference of reflected light to increase the intensity of the reflected light and achieve high reflection. It is aimed at realizing the rate.

In an actual multilayer film reflecting mirror, a material having a high refractive index and low absorption at the wavelength of light to be reflected is used as the reflecting layer, and the material is accumulated at a constant interval, so that a large difference in refractive index from the reflecting layer can be obtained. A material having low absorption is used as the spacer layer. That is, the multilayer-film reflective mirror has a multi-layer structure in which the reflective layer and the spacer layer are alternately accumulated in a periodic length determined by the incident angle and the wavelength. A heavy element having a large refractive index is used for the reflective layer. As the spacer layer, a light element with low absorption is used.

Regarding the selection of the constituent material, element selection is performed by utilizing the absorption edge of the element so as to minimize the absorption of X-rays used for achieving high reflectance. That is, a combination is made in which the respective absorption edges of light elements such as C, B, and Si are used, and a transition metal element having an absorption edge in the vicinity of the wavelength is selected as a heavy element. Furthermore, since the multilayer film is exposed to a high-intensity light source such as synchrotron radiation in a vacuum due to its application, heat resistance must be taken into consideration when selecting a material. Therefore, a high melting point transition metal such as Mo or W is used as the transition metal element. Currently, as a combination that can obtain a relatively high reflectance, a Mo / Si multilayer film using the absorption edge of Si, which is a light element, and a W / C multilayer film using the absorption edge of C are well known. ..

Various methods such as magnetron sputtering, electron beam evaporation, ion beam sputtering, and chemical vapor deposition (CVD) are used for forming a multilayer film. Compared to other methods, the multilayer film formed by electron beam evaporation is less dense than other methods,
Since the roughness becomes large, there are problems such as low reflectance.
Further, if the film formation rate is slow, the amount of impurities mixed in from the atmospheric gas increases and the reflectance decreases. Therefore, recently, film forming by magnetron sputtering and ion beam sputtering using a large ion source have become mainstream.

[0007]

In order to achieve a high reflectance of the multi-layer film reflecting mirror, it is necessary to study the selection of the above-mentioned multi-layer film constituent materials and the film forming method. But now
The most important problem to be solved is to reduce the roughness of the multilayer film.

In the case of Mo / Si multilayer film, theoretical calculation shows that a reflectivity of about 80% can be expected with a multilayer structure of 30 sets. However, in the current technology, the multilayer film having a reflectance of about 50% has just begun to be reported. The cause of the decrease in reflectance from this theoretical value is, for example, mixing of impurities from the atmosphere gas during film formation and a change from the value assumed in the design of the optical constant due to the decrease in the density of the thin film.
The main one is X-ray scattering due to the roughness of the multilayer film. The causes of the roughness include the roughness of the substrate itself, the one caused by the film forming method, and the one caused by the material. Among them, the roughness of the substrate itself has become considerably smooth due to the progress of the substrate polishing technique.

Among the causes of roughness, the cause of the material is the problem of crystallization of the metal element used as the reflection layer. Generally, when a transition metal element having a high melting point is laminated on a thin film, the metal element is crystallized to form crystal grains and become in a polycrystalline state. The grain boundaries increase the roughness at the interface of the multilayer film and reduce the reflectance of the multilayer film due to scattering of X-rays due to the roughness. Therefore, how to reduce the roughness due to the crystal grain boundaries is the most important problem to be solved in order to realize a high reflectance multilayer film.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to reduce roughness due to crystal grain boundaries of a metal element in a multilayer film serving as a multilayer film reflecting mirror. To provide possible technology.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0012]

In order to achieve the above object, the present invention provides a multilayer film mirror having a multilayer structure in which two kinds of substances having different refractive indexes are alternately accumulated, and each layer of the multilayer structure. One of the layers is composed of an alloy of a transition metal element having a high melting point, and the composition of the alloy is most characterized in that it has a composition near the eutectic point at which a eutectic reaction is obtained.
A white metal element among transition metal elements is contained as a component of the alloy. In addition to the transition metal element, a semi-metal element as a eutectic material is contained as a component of the alloy.

Further, in a total reflection mirror using reflection at an oblique incident angle of not more than the critical angle for total reflection, the alloy layer is used as a reflection surface.

[0014]

According to the above means, the eutectic reaction in the alloy is used to suppress crystallization in order to amorphize the high melting point transition metal element which is easily crystallized by itself. That is, the heavy element layer of the multilayer film is made of an alloy of a transition metal element having a high melting point, and the composition ratio of the transition metals to be alloyed is within the range where the eutectic reaction can be obtained (within the range of the eutectic line), that is, the eutectic crystal. Amorphization is achieved by selecting the composition ratio near the point.
As a material to be alloyed, among the transition metal elements, Mo, Nb, Os, Re, Ta, W, which have a particularly high melting point, and Sc, Ti, V, Cr, Mn, Fe, Co, N are included.
i, Cu, Y, Zr, Tc, Ag, La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
A high melting point transition metal element such as r, Tm, Yb, Lu, Hf, or Au is used.

In addition, in the present invention, in order to easily achieve amorphization, in addition to the selection of the above composition ratio, material selection is performed such that alloying reduces the critical cooling rate and facilitates amorphization. That is, a transition metal element having a high critical cooling rate and a high melting point which is easily crystallized as a simple substance is an alloy containing a noble metal such as gold, silver, a white metal, or a semimetal as an alloy material for reducing the critical cooling rate. This makes it easier to achieve amorphization in sputtering. For example, white metal elements such as Ir, Os,
By using Pd, Pt, Rh, and Ru as a material for alloying, it is easy to achieve amorphization.

Furthermore, in the present invention, in addition to the selection of the above composition ratio, as a method for facilitating the achievement of amorphization,
A combination of alloys of elements with significantly different atomic radii is used. That is, alloying is performed by combining a transition metal element with a semi-metal having a smaller atomic radius. In the present invention, as the eutectic material, B, C, Al and S which are semi-metals are used.
Amorphization is facilitated by adding i, P, Ge, As, etc. to a transition metal element or an alloy of transition metals.

The metal element which is a heavy element is alloyed and the crystallization of the metal element is suppressed by the eutectic reaction in the alloying.
Further, by setting the composition ratio of the alloy near the eutectic point, it is possible to realize a multilayer film having an amorphous structure with little influence of primary crystals. Therefore, since the multilayer film according to the present invention has an extremely smooth interface without crystal grain boundaries of metal elements, it is possible to suppress the decrease in reflectance due to roughness and realize a multilayer film with high reflectance. Further, this thin film of an alloy having an extremely smooth surface can realize high reflectance even when applied to the reflecting surface of a total reflection mirror for oblique incidence.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Example 1 In Example 1, in a Mo / Si multilayer film using the absorption edge of Si which is a light element, a heavy element is used in order to suppress crystallization of Mo which is a transition metal having a high melting point. A multi-layered film reflection mirror was prepared by using as an alloy of Ru and Mo, which are platinum group metals. By alloying with Ru,
The critical cooling rate is smaller than that of Mo alone, and the effect of amorphization can be expected by rapid cooling in sputtering. Further, when the alloy composition ratio is Mo _1-x Ru _x , the effect of amorphization by the eutectic reaction is expected in the composition of x = 0.3 to 0.5 which is the range of the eutectic line. it can. However, in consideration of the influence of the primary crystal due to the composition shift from the eutectic point, in Example 1, Mo _0.57 Ru which is the eutectic point was used.
A composition of _0.43 was chosen. Regarding the composition of the alloy, Auger electron spectroscopy (AES: Auger Electron Spectrosco
At the same time as the optimization was carried out using a quantitative analysis by py), the uniformity in the depth direction was confirmed. Regarding the homogeneity of the alloy within the plane, the distribution was examined using EPMA to confirm the homogeneity within the plane.

The film is formed by surface roughness 3Å (root mean square roughness: RM).
S: Rot Mean Square) This was performed by magnetron sputtering on a Si substrate polished to the following. The formed multilayer film is for direct incidence at a wavelength of 124Å, and as shown in FIG.
Periodic length 61.7Å, heavy element layer (Mo _0.57 Ru _0.43 ) 23.
30 sets of 4Å and 38.3Å of light element layer (Si) were laminated.
The theoretical reflectance is 80.4% when there is no surface roughness. In addition, a reflectance of 73.3% can be expected even in consideration of a reduction in reflectance due to scattering due to the roughness of the substrate (3Å (RMS)).

The crystal peaks of the formed multilayer film by wide-angle X-ray diffraction (XD: X-ray Diffraction) were examined, and in the conventional Mo / Si multilayer film, Mo (11
While the diffraction peak due to the crystal plane of 0) is observed,
In the multilayer film of Example 1, no diffraction peaks due to Mo and Ru crystals were observed, and it was found that the multilayer film had an amorphous structure. Also, in the cross-sectional observation by TEM, it was confirmed that the conventional Mo / Si multilayer film had no crystal lattice in the Mo layer and had an amorphous structure.

Further, the roughness of the multilayer film of Example 1 was evaluated. As an evaluation method, the atomic force microscope (AFM: Atomic Force Mi) with high spatial resolution can be used to evaluate the roughness due to grain boundaries with extremely short spatial wavelengths.
croscopy). The conventional Mo / Si multilayer film has
In contrast to the surface roughness of 6 Å (RMS), which is greater than that of the substrate, the multilayer film of Example 1 has a roughness reduced to about 3 Å (RMS), which is almost the same as that of the substrate. I found out that In addition, a transmission electron microscope (TEM: Trans)
Cross-section observation and A by mission Electron Microscopy)
Also in the analysis of the ES in the depth direction, it was confirmed that the interface of the multilayer film of Example 1 had higher steepness than that of the conventional Mo / Si multilayer film.

The reflectance of the multilayer film of this Example 1 was evaluated by soft X-ray, and as a result, a reflectance of 71.3% was obtained. The reflectance of the Mo / Si multilayer film formed under the same conditions was 53.6%. It was found that the multilayer film of this example provided a reflectance of 1.3 times or more that of the conventional Mo / Si multilayer film. Furthermore, the reflectance of the Ru / Si multilayer film formed under the same conditions was 59.4%. These results are summarized in Table 1. From the table, in the case of the multilayer film of the present Example 1, the measured reflectance is close to 90% with respect to the theoretical reflectance when there is no roughness, and it is possible to reduce the roughness at the interface due to the amorphization. It can be seen that the reflectance is improved.

[0024]

[Table 1]

Further, when this multilayer film is formed on a curved quartz substrate and applied to an actual optical system, scattering of X-rays due to roughness is reduced, and the resolution of the optical system is a conventional multilayer film reflecting mirror. Improved compared to.

In addition to Example 1 described above, in the case where Mo is taken as an example of a transition metal having a high melting point, an example of an alloy having a composition near the eutectic point in combination with a platinum group element other than Ru will be given below. I will give you. In the case of an alloy of Ir and Mo, the alloy composition ratio is Mo _0.69 Ir which is the eutectic point.
Select a composition around _0.31 . In the case of an alloy of Os and Mo, as the alloy composition ratio, a composition around Mo _0.79 Os _0.21 which is the eutectic point is selected. In the case of an alloy of Pd and Mo, the composition around the eutectic point Mo _0.46 Pd _0.54 is selected as the alloy composition ratio. In the case of an alloy of Pt and Mo, as the alloy composition ratio, a composition around Mo _0.74 Pt _0.26 , which is the eutectic point, is selected.
In the case of Rh and Mo, as the alloy composition ratio, a composition around Mo _0.60 Rh _0.40 which is the eutectic point is selected. Table 2 shows the theoretical reflectance and the actually measured reflectance in these combinations.
In each case, the effect of reducing roughness due to amorphization was obtained as in the above-described examples, and a higher reflectance was obtained compared to the conventional Mo / Si multilayer film.

[0027]

[Table 2]

In the first embodiment, the case of a binary alloy of a high melting point transition metal Mo and a white metal is taken as an example.
The effect of the present invention can be obtained in a combination of a transition metal and a white metal other than the above, a combination of transition metals, and a multi-component alloy of three or more elements.

Example 2 In Example 2, a multilayer film made of a combination of Mo and C was prepared as an example of a multilayer film made of an alloy of a high melting point transition metal element and a semimetal. As the composition ratio of the alloy, Mo _0.83 C _0.17 which is the eutectic point was selected. In this case as well, similar to Example 1 above, amorphization was achieved and a multilayer film with high reflectance was obtained. In Example 2, a binary alloy of Mo and C was given as an example of a multilayer film made of an alloy of a transition metal element having a high melting point and a semimetal. However, a combination of a transition metal other than Mo and other semimetals are used. The effect of the present invention can be obtained even in combination with a metal and further in a multi-component alloy of three or more elements.

In the above-mentioned embodiments, an example is given of the multilayer film reflecting mirror, but even if the film made amorphous by the alloying of the present invention is used for the reflecting surface of the oblique reflection total reflection mirror, the crystallization is suppressed. The effect of reducing roughness can be expected. To confirm this, the Mo _0.57 Ru _0.43 alloy film of this example was applied as a single-layer film as a reflecting surface of a grazing incidence total reflection mirror. An improvement in reflectance was obtained due to a decrease in roughness.

In the above embodiments, the heavy element layer of the multilayer film reflecting mirror or the reflecting surface of the oblique incidence total reflecting mirror is alloyed according to the present invention to achieve amorphization and to reduce roughness. We have realized a highly reflective mirror with an extremely smooth interface and surface. Therefore, in the above examples, the composition of the eutectic point was selected in consideration of the influence of the primary crystal and the like in order to achieve the amorphization.

Here, the problem to be solved in the present invention is to increase the reflectance by reducing the roughness of the multilayer film reflecting mirror, and when complete amorphization is not achieved due to the influence of primary crystals, that is, , Even when it has an amorphous-like structure containing very fine crystals, the growth of the crystal grain boundaries is hindered by the effect of alloying, and the roughness reduction is achieved, so that the high reflectance targeted by the present invention is achieved. Have a sufficient effect on Therefore, when complete amorphization is not achieved due to the influence of primary crystals, that is,
Even in the case of having an amorphous-like structure containing extremely fine crystals, the effects of the present invention can be expected sufficiently.

Next, the alloying method according to the present invention will be described by taking a binary alloy of a transition metal element and a white metal element having a high melting point as an example. As a method for alloying, if there is not much difference in melting points of the materials to be alloyed, it is possible to use a target obtained by sintering powders mixed in advance in a predetermined composition ratio. However, when the difference in melting point between the materials to be alloyed is large or when the composition ratio is adjusted, the sintering target is inconvenient. Therefore, as shown in FIG. 2, a composite target in which materials to be alloyed are combined in a mosaic shape is used. The shape of the mosaic includes radial, double-sided, and coaxial ring shapes, but considering the erosion distribution of the magnetron, it is possible to adjust the composition ratio by selecting a shape that is proportional to the target area and composition ratio. To do.

Further, as shown in FIG. 3, high frequency (RF)
By making the electrode of the coaxial ring shape and arranging the material to be alloyed in the coaxial ring shape and sputtering at the same time,
There is a method of alloying during sputtering. In FIG.
6 is a vacuum container, 7 is a rotary substrate holder, 8 is a substrate for forming a multilayer film, 9 is a shutter that can be opened and closed at high speed, 1
Reference numeral 0 is a deposition preventive plate for preventing contamination of the vacuum container due to sputtered particles, 11 and 12 are high melting point transition metal element targets and platinum group element targets arranged in a coaxial ring shape, and 13 is a light element target. The multilayer film is sputtered and formed by opening and closing a high-speed shutter for an arbitrary time while the substrate mounted on the rotary substrate holder revolves around the target. In this method, the shutter opens and closes by regarding the coaxial ring target as one target. In addition, the composition ratio can be adjusted by applying high frequency (R
F) It is performed by controlling the power. Therefore, it has a feature that adjustment can be performed more easily than when a mosaic target is used.

Further, as shown in FIG. 4, a target of each material to be alloyed is sputtered respectively, and the substrate is rotated on these targets to form a very thin (one atomic layer or less) laminated film. By doing so, there is a method of alloying during film formation. In the case of this method, during the heavy element sputtering, the shutter (9) of the light element target (13) is used.
C) is closed and the metal element target (1
The shutters (9A, 9B) of 1, 12) are opened, the substrate (8) is revolved, and the ultrathin film of the metal element is laminated by rotating the substrate.

Although the present invention has been specifically described based on the embodiments above, it is needless to say that the present invention is not limited to the embodiments and can be variously modified without departing from the scope of the invention. Absent.

[0037]

As described above, according to the present invention, since the multilayer film reflecting mirror has an amorphous structure by alloying, there is no crystal grain boundary at the multilayer film interface and an extremely smooth interface is formed. Since it has, it can have a high reflectance close to the theoretical value. Therefore, when used as a reflecting mirror of an optical system for light in the vacuum UV to soft X-ray region having a wavelength of 200 nm or less, the optical system can be designed at an angle close to direct incidence, and X-ray lithography and X-ray can be used. It is very useful for high resolution X-ray optical systems such as microscopes and X-ray telescopes. Furthermore, since it has a high reflectance, it is possible to prevent a significant decrease in reflectance due to an increase in the number of mirrors, which has been a problem in conventional optical design. Have an effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of Example 1 of a multilayer-film reflective mirror of the present invention,

FIG. 2 is a configuration diagram of a mosaic target for explaining the alloying manufacturing method according to the present invention,

FIG. 3 is a conceptual diagram of a sputtering apparatus using a coaxial ring target for explaining an alloying manufacturing method according to the present invention,

FIG. 4 is a conceptual diagram of a sputtering apparatus for alloying with a multilayer structure for explaining the alloying manufacturing method according to the present invention.

[Explanation of symbols]

1 ... Heavy element layer (Mo _0.67 Ru _0.43 ), 2 ... Light element layer (S
i) 3 ... Substrate, 4 ... Platinum group element, 5 ... High melting point transition metal element, 6 ... Vacuum container, 7 ... Rotating substrate holder, 8 ...
Substrate, 9A, 9B, 9C ... High-speed shutter, 10 ... Adhesive plate, 11 ... Platinum group element target, 12 ... High melting point transition metal element target, 13 ... Light element target.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Torii 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Tsutomu Mizoda 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. A multi-layered film mirror having a multi-layered structure in which two kinds of substances having different refractive indexes are alternately accumulated, wherein one layer of each layer of the multi-layered structure is made of an alloy of a transition metal element having a high melting point, A multilayer film mirror, wherein the composition ratio of the alloy is a composition near the eutectic point at which a eutectic reaction is obtained. 2. The multilayer-film reflective mirror according to claim 1, wherein a white metal element among transition metal elements is contained as a component of the alloy. 3. The multilayer-film reflective mirror according to claim 1, wherein, in addition to a transition metal element, a semi-metal element is included as a eutectic material as a component of the alloy. 4. A total reflection mirror, which utilizes reflection at oblique incidence below a critical angle for total reflection, according to any one of claims 1 to 3.
A total reflection mirror, wherein the alloy layer described in 1) is used as a reflection surface.