JPH05164899A - Multilayer film mirror - Google Patents

Abstract

(57) [Abstract] [Purpose] To widen the wavelength range of light that can be reflected. Further, the incident light is reflected over a wide range of incident angles. [Structure] In the multilayer-film reflective mirror 4, the multilayer film 1 has different cycle lengths within its reflection surface 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to multilayer film reflecting mirrors used for light having a wavelength in the soft X-ray region, that is, X-ray lasers, X-ray telescopes, X-ray lithography, X-ray microscopes and the like. The present invention relates to a high reflectance multilayer film reflecting mirror used as an element.

[0002]

2. Description of the Related Art The refractive index (so-called complex refractive index) of a substance with respect to light having a wavelength in the X-ray region (hereinafter referred to as X-ray) is n = (1-δ) -iβ (δ and β are positive real numbers. , I are expressed as imaginary units), and δ and β are both much smaller than 1. Therefore, the refractive index is close to 1, and X-rays are hardly refracted. Therefore, a lens that uses refraction such as light having a wavelength in the visible light region cannot be used.

Therefore, an optical system utilizing reflection is used. However, since the refractive index is also close to 1, the reflectance is very small, and most X-rays are transmitted or absorbed. In order to solve this problem, by laminating multiple layers of a plurality of substances having a refractive index difference as large as possible in the wavelength range of X-rays to be used, a large number of reflecting surfaces that are the interfaces between them are provided.
Based on the theory of optical interference, a multi-layered film reflector was developed in which the thickness of each layer was adjusted so that the phases of the reflected waves from each interface would match.

Such a multilayer-film reflective mirror can reflect X-rays of various wavelengths by selecting the combination of the materials constituting it. Furthermore, the thickness of the layer has the advantage that X-rays can be reflected at a relatively free angle. A typical example of a multilayer film is Cr (chrome) / C
(Carbon), W (tungsten) / C (carbon),
A combination of Mo (molybdenum) / Si (silicon) or the like is known, and it is formed by a thin film forming technique such as sputtering, vacuum deposition, or CVD.

[0005]

By the way, the conditions under which such a multilayer film reflecting mirror reflects X-rays are that the period length of the multilayer film is d, the wavelength of X-rays is λ, and the oblique incident angle of X-rays is. When θ and the diffraction order (integer) are n, it means that the following Bragg equation is satisfied. nλ = 2d sin θ Therefore, in a multilayer-film reflective mirror having a certain period length, when the incident angle of X-ray (determined by the oblique incident angle) is determined, the wavelength of the reflected X-ray is uniquely determined, and If the wavelength is fixed, the reflection angle is uniquely determined.

Further, in the actual reflection by the multilayer film, the reflection angle or wavelength of the X-ray obtained based on the above-mentioned condition has a certain spread, but this spread forms the multilayer film as in the following equation. It becomes smaller as the number of layers increases. Δλ / λ to 1 / N Here, Δλ / λ is the ratio between the range of the wavelength of the reflected X-ray and the peak wavelength at which the highest reflectance is obtained, and N is the number of cycles of the multilayer film. Can be represented. This tendency also applies to the reflection angle.

However, in the multilayer-film reflective mirror, the greater the number of periods, the greater the reflection intensity. Therefore, it was necessary to increase the number of periods to obtain the desired reflection intensity. As a result, the conventional reflecting mirror has a very narrow wavelength region of reflected X-rays and a reflection angle region, and its application is limited to "an optical system that reflects X-rays of a specific wavelength at a specific angle". Was there.

Further, when a multilayer-film reflective mirror is used in an optical system in which the incident angle changes so that the beam is scanned at a certain angle, not only the problem that the reflection angle region is small as described above, but also the small angle region is small. However, there is a drawback that the reflection intensity changes significantly even in the inside. for that reason,
Conventionally, a total reflection mirror has been used for such an optical system. However, there is a drawback that the total reflection mirror can be used only in the oblique incidence optical system, whereas the multilayer film reflection mirror can be combined with an optical system relatively free.

By the way, when a multilayer film reflecting mirror is used for a practical optical element such as a Schwarzschild mirror or a spheroidal mirror, these optical elements are generally incorporated into an optical system for use. Therefore, it is often the case that the wavelength of the X-ray to be used and its reflection angle are determined in advance, and the cycle length of the multilayer film is determined accordingly. However, as described above, since the reflection angle region where the multilayer film reflecting mirror shows a high reflectance is very narrow, it is necessary to form the multilayer film with a high precision of 1 Å or less. However, it is difficult to realize this precision with good reproducibility by the current film forming technology.
Therefore, the reflectance of the manufactured optical element becomes significantly smaller than the designed value due to a slight shift of the cycle length, which has been a major problem in practical application of the multilayer-film reflective mirror.

An object of the present invention is to solve such a problem.

[0011]

To achieve the above object, in the present invention, a substance having a small difference between the refractive index of light having a wavelength in the soft X-ray region and a refractive index of vacuum (= 1) and a substance having a large difference are used. In a multilayer film reflecting mirror in which and are alternately laminated, the multilayer films have different cycle lengths in the reflecting surface of the multilayer film reflecting mirror.

[0012]

In the present invention, one multilayer film reflecting mirror is formed so as to have different cycle lengths within its reflecting surface. Therefore, when X-rays of a certain wavelength are incident on the reflecting surface of the multilayer-film reflective mirror at an angle, the X-rays are transmitted only in a portion of the reflecting surface having a periodic length that satisfies the Bragg equation.
The line reflects. Then, if the incident angle of the X-ray is changed a little from this state, the X-ray is reflected only at the portion that satisfies the Bragg equation at this incident angle.

That is, in the multilayer film of the present invention, the value of the period length d in the Bragg equation nλ = 2d sin θ shown below has a certain range. Therefore, when an X-ray having a constant wavelength λ is incident on the multilayer-film reflective mirror of the present invention, its incident angle (the oblique incident angle θ is determined if the incident angle is determined) corresponds to the range of the cycle length d. Within the range of angles (hereinafter referred to as the effective angle region) satisfying the determined Bragg's equation, X-rays are reflected by any part of the reflective surface of the multilayer film.

If the change pitch of the periodic length distribution of the multilayer film with respect to the surface direction of the reflecting surface is made sufficiently smaller than the size of the reflecting surface, the multilayer film reflecting mirror can be made at any angle within the effective angle range. X-rays can be reflected over the entire reflecting surface. The intensity distribution of the X-rays reflected according to the incident angle of the X-rays depends on the ratio of the area occupied by the portions having different cycle lengths (hereinafter referred to as the cycle length distribution) in the reflecting surface of the multilayer film. Therefore, if the cycle length distribution of the multilayer film is made uniform, the intensity distribution of the X-rays reflected by this multilayer film can be made substantially uniform (a trapezoidal intensity distribution can be obtained).

On the contrary, when it is desired to change the intensity distribution of the X-ray according to the reflection angle of the X-ray, the period length distribution should be provided accordingly. Such an effect is peculiar to the present invention. If the number of periods is reduced and the effective angle region is widened in the conventional multilayer film, the intensity distribution of the reflected X-ray has a shape similar to a Gaussian distribution. I can't get it. The case where the wavelength of the X-ray is fixed to a constant value and the incident angle of the X-ray is changed has been described above.
The same applies to the case where the incident angle of X-ray is fixed and the wavelength is changed.

Therefore, when white light is incident on the multilayer-film reflective mirror of the present invention, X-rays having a wavelength corresponding to the periodic length distribution are reflected. Further, if it is desired to always obtain a constant reflectance regardless of the wavelength of the incident X-ray, or to change the reflectance depending on the wavelength of the X-ray, set the period length distribution accordingly. Good. Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto.

[0017]

Embodiment 1 FIG. 1 is a schematic sectional view of a multilayer-film reflective mirror according to a first embodiment of the present invention. The multilayer film reflecting mirror 4 has one side
It is composed of a Si substrate 3 formed in a 25 mm square and a multi-layer film 1 of 100 pairs of cycles (a part of which is omitted in the figure) of chromium and carbon formed on the substrate 3. .. The multilayer film 1 has different periodic lengths in the plane of its reflecting surface 2 as shown in the figure. That is, the cycle length of the "mountain" portion A of the layer is the largest, and conversely, the cycle length of the "valley" portion B is the smallest. And A and B
The portion between has a value between the two cycle lengths A and B, and the value changes almost gently. In addition,
In the figure, since the vertical direction is extremely enlarged with respect to the horizontal direction, the multilayer film 1 seems to have a large undulation, but in reality, it is a substantially flat film.

FIG. 4 is a diagram showing the manufacturing process of the multilayer-film reflective mirror of this embodiment. The multilayer film 1 was formed by alternately stacking 100 layers of chromium and carbon by the ion beam sputtering method. At the time of this film formation, the diameter before the surface of the substrate 3
Tungsten wires 5 of about 0.2 mm are arranged at intervals of 0.5 mm. As a result, the sputtered particles 8 sputtered by the ion beam are blocked by the wire 5, and thus it is difficult for the sputtered particle 8 to reach the shadowed portion of the wire 5 on the surface of the substrate 3. As a result, the thickness of the layer formed on the shadowed portion of the wire 5 is reduced. Therefore, if this operation is performed at the time of forming each layer (however, the arrangement position of the wire 5 is not changed), the cycle length of the multilayer film in the shadow of the wire 5 becomes small, as shown in FIG. A multilayer-film reflective mirror 4 having the multilayer film 1 having a period length distribution is manufactured.

The multilayer film 1 has a cycle length of 38 to 42Å
Was formed in the range of. This cycle length adjustment is
It was performed by adjusting the distance between the wire 5 and the substrate 3.
Next, the reflecting mirror 4 is irradiated with CKα rays (wavelength 44.8Å), which are characteristic X-rays generated when an electron beam accelerated by carbon (C) is irradiated, and the incident angle at that time and the reflected X-rays. The relationship with the intensity (hereinafter referred to as incident angle dependency) was investigated.
The result is shown in FIG. 7. As shown in the figure, the reflecting mirror 4 was able to reflect X-rays over a wide incident angle. The intensity of the reflected X-rays was almost constant in the incident angle range of 33 to 36.5 °.

Further, as shown in FIG. 5, when the above-mentioned CKα ray 6 was incident on the reflecting mirror 4 and this reflecting mirror 4 was vibrated, the optical path of the X-ray was bent by about 70 ° and reflected. ± 3 at the same time
The reflected X-ray 7 could be scanned in the range of °.
At this time, the intensity of the reflected X-ray was almost constant even if the scan angle was changed. Further, by increasing the frequency of vibration of the reflecting mirror 4, the reflected X-ray beam could be expanded according to the range of the scan.

As a comparative example, a multi-layered film reflecting mirror in which a multi-layered film of a combination of chromium and carbon, which is formed on the same substrate as that of the present example so as to have a constant cycle length of 40 Å, is laminated with a period number of 100 pairs. It was manufactured, and the incident angle dependence was examined in the same manner as in the example.
The result at this time is shown in FIG. As shown in the figure, the multilayer-film reflective mirror with a uniform cycle length shows a high reflectance only near a specific incident angle, and when the incident angle is changed from this state, the intensity of the X-ray reflected by that angle becomes large. It has fallen.

[0022]

[Embodiment 2] FIG. 2 is a schematic sectional view of a multilayer-film reflective mirror according to a second embodiment of the present invention. The multilayer-film reflective mirror 24 includes a substrate 23 made of Si and formed into a square having a side of 25 mm.
The multi-layered film 21 made of a combination of chromium and carbon having a period number of 100 pairs (a part of which is omitted in the drawing) is formed on the substrate 23.

Wedge-shaped irregularities 11 are provided on the surface of the substrate 23 on which the multilayer film is formed. The period of the unevenness 11 is 0.5 mm
And the depth was 40 nm. On the substrate 23, the first embodiment
Similarly to the above, a multilayer film 21 of a combination of chromium and carbon was formed by the ion beam sputtering method. At this time, the tungsten wires 5 were arranged right above the convex portion D of the unevenness 11 at intervals of 0.5 mm so as to be parallel to this portion D in the plane direction. The multilayer film 21 was formed so that its cycle length was in the range of 38 to 42Å.

The multilayer-film reflective mirror 2 produced in this way
4, the multilayer film 21 has different periodic lengths in the plane of its reflecting surface 22 as shown in the figure. That is, the period length of the “concave” portion C of the unevenness provided on the substrate 23 is the longest, and conversely, the period length of the “convex” portion D is the smallest. And the part between C and D is 2 of this C and D.
It has a value between two cycle lengths, and the value changes almost gently. In the figure, the vertical direction is extremely enlarged with respect to the horizontal direction.

When the reflecting mirror 24 was irradiated with CKα rays having a wavelength of 44.8Å and the incident angle dependency was examined, the same results as in Example 1 were obtained.

[0026]

[Embodiment 3] FIG. 3 is a schematic sectional view of a multilayer-film reflective mirror according to a third embodiment of the present invention. The multilayer-film reflective mirror 34 includes a substrate 33 made of Si and formed into a square of 25 mm on a side,
It is composed of a multilayer film 31 of a combination of tungsten and carbon formed on the substrate 33.

In the multilayer film 31 of this embodiment, small areas having different cycle lengths are randomly arranged in the plane of the reflecting surface 32. In the figure, the vertical direction is extremely enlarged with respect to the horizontal direction. The multilayer film of the combination of tungsten and carbon is
It is known that heat treatment after film formation changes the cycle length (Japanese Patent Laid-Open No. 2-146000). Therefore, by heating a desired portion of the multilayer film 31 at various temperatures,
Portions having various cycle lengths can be formed in the multilayer film 31.

FIG. 11 shows the relationship between the heating temperature of the multilayer film and the change rate of the cycle length. In the heat treatment, first, a multilayer film reflecting mirror 34 was manufactured by forming a multilayer film 31 having a period length of 31 Å and a period number of 100 pairs (a part is omitted in the figure) on the substrate 33 by an ion beam sputtering method. Then, as shown in FIG. 6, this multilayer film reflecting mirror 34 is installed on the XY stage 10, and the beam diameter of the reflecting surface 32 using the YAG laser 9 as a light source is about 0.1 m.
It was irradiated with m laser light.

The multi-layer film is irradiated with laser light so as to have a thickness of 20 to 600.
It was heated to a temperature randomly selected from the range of ° C. At this time, the entire reflecting surface 32 of the multilayer film 31 was heated in a grid pattern at intervals of 0.1 mm. As a result, the cycle length of the multilayer film could be increased by 1 to 6%. As described above, the multilayer-film reflective mirror 34 having the periodic length distribution as shown in FIG. 3 was manufactured. The multilayer film 31 is formed so that its cycle length is in the range of 31 to 33Å.

This reflecting mirror 34 was irradiated with CKα rays having a wavelength of 44.8Å, and the incident angle dependence at that time was examined. The result is shown in FIG. As shown, the reflector 34 was able to reflect X-rays over a wide angle of incidence. The intensity of the reflected X-ray was almost constant in the incident angle range of 43 to 47 °. Further, as in the first embodiment, the CK
When this reflecting mirror was vibrated while injecting α rays, X
The light path of the line was bent about 90 ° and reflected. At the same time, it was possible to scan the reflected X-ray in the range of ± 4 °. At this time, the intensity of the reflected X-ray was almost constant even if the scan angle was changed. Further, by increasing the vibration frequency of the reflecting mirror, the reflected X-ray beam could be expanded according to the range of the scan.

Since the multilayer film reflecting mirror of this embodiment changes the cycle length (film thickness) after forming the multilayer film, it is manufactured by heating the multilayer film reflecting mirror manufactured by the conventional method. It is possible. Therefore, when the conventional reflecting mirror is used for the optical system and the reduction of the intensity of the reflected light due to the error of the cycle length is recognized, the above-mentioned heat treatment may be performed to obtain the desired intensity. ..

[0032]

Example 4 By the same method as in Example 1, a multilayer film reflecting mirror made of a combination of chromium and carbon as shown in FIG. 1 was produced. This multilayer film was formed so that its cycle length was in the range of 38 to 42Å. Next, a white soft X-ray is incident on this reflecting mirror at an oblique incidence angle of 35.
The relationship between the wavelength and the intensity of the reflected X-ray (hereinafter, referred to as wavelength dependence) was examined by irradiating the laser beam at an angle of. The result is shown in FIG. As shown in the figure, this reflecting mirror was able to reflect X-rays having a wavelength of 45 to 49Å. The intensity of the reflected X-ray was almost constant in this wavelength range.

Therefore, the reflecting mirror of this embodiment can be used as a filter for reflecting only X-rays in a specific wavelength range. In this case, the intensity of the X-ray can be made almost constant in the wavelength range of the reflected X-ray. Further, as shown in the drawing, the intensity change from the reflected wavelength to the non-reflected wavelength is rapid, so that the reflected wavelength range is clear. The filter having such characteristics is unique to the present invention.

The combination of multilayer films and the film forming method are not limited to those shown in Examples 1 to 4. For example, a multilayer film of a combination of molybdenum / silicon and chromium / carbon may be used. The multilayer film is formed by vacuum vapor deposition, CV
You may use D etc. The layers may be formed in any order in which the multilayer film is formed. Further, in the multilayer-film reflective mirror of the present invention, since the multilayer films are formed so as to have different cycle lengths, unevenness is formed on the uppermost layer (having a reflecting surface) as shown in FIG. Is formed. However, as shown in FIG. 2, a planar uppermost layer may be provided by forming another film on this uppermost layer.

[0035]

As described above, the multilayer-film reflective mirror according to the present invention, when used as a reflective mirror for light having a wavelength in the soft X-ray region, has a wider range of incident angles than conventional reflective mirrors. This incident light can be reflected. In addition, the wavelength range of X-rays that can be reflected can be widened.

Therefore, an X-ray having a certain wavelength is reflected with a desired intensity distribution within a specific incident angle range, or an X-ray having a desired wavelength range can be obtained from a white X-ray incident from a certain angle. It becomes possible to reflect with an intensity distribution.
Further, a multilayer film reflecting mirror used in an optical system in which the wavelength of X-rays and the reflection angle thereof are determined requires high-precision cycle length controllability during film formation, but the reflecting mirror according to the present invention has a wide range of characteristics. Since it has a period length, the reflectance does not significantly decrease due to an error in the period length when the multilayer film is formed. Therefore, it is possible to always reflect X-rays of high intensity.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a multilayer-film reflective mirror of Example 1.

FIG. 2 is a schematic sectional view showing a multilayer-film reflective mirror of Example 2.

FIG. 3 is a schematic sectional view showing a multilayer-film reflective mirror of Example 3.

FIG. 4 is a schematic view showing a manufacturing process of the multilayer-film reflective mirrors of Example 1 and Example 2.

FIG. 5 shows an application example of the multilayer-film reflective mirror according to the present invention, showing a state in which the reflective mirror is vibrated and the reflected X-rays are scanned.

6A to 6C are schematic diagrams showing a manufacturing process of the multilayer-film reflective mirror of Example 3.

7 is a diagram showing the incident angle dependence of X-rays reflected by the multilayer-film reflective mirror of Example 1. FIG.

FIG. 8 is a diagram showing the incident angle dependence of X-rays reflected by the multilayer-film reflective mirror of Example 3.

FIG. 9 is a diagram showing wavelength dependence of X-rays reflected by the multilayer-film reflective mirror of Example 4.

FIG. 10 is a diagram showing the incident angle dependence of X-rays reflected by a conventional multilayer-film reflective mirror.

FIG. 11 is a diagram showing the rate of change of the cycle length due to heating in a multilayer film of a combination of tungsten and carbon.

[Explanation of symbols for main parts]

 DESCRIPTION OF SYMBOLS 1 Multilayer film 2 Reflective surface 3 Substrate 4 Multilayer film reflective mirror 5 Tungsten wire 6 Incident X-ray 7 Reflective X-ray 8 Sputtered particle 9 YAG laser 10 XY stage 11 Concavities and convexities provided on the substrate 21 Multilayer film 22 Reflective surface 23 Substrate 24 Multilayer Reflector 31 Multilayer 32 Reflective Surface 33 Substrate 34 Multilayer Reflector

Claims (1)

[Claims] 1. A multilayer-film reflective mirror comprising a material having a small difference between a refractive index of light having a wavelength in the soft X-ray region and a vacuum, and a material having a large difference, which are alternately laminated. The multi-layered film reflecting mirror, wherein the multi-layered films have different cycle lengths within the reflecting surface of the.