JPH02145999A - Multi-layered reflecting mirror for x-ray - Google Patents

Abstract

PURPOSE:To obtain a higher reflectivity by laminating multifoldedly thin films of a material of which refraction index differs greatly from that of vacuum, with an intermediary of inserting spacers of a predetermined thickness. CONSTITUTION:On a base plate 10, thin films 2 of a material of which refraction index differs greatly from that of vacuum, are multifoldedly laminated with inserting spacers of a predetermined thickness, while another layers 1 which correspond to a material of which refraction index differs scarecely from that of vacuum, is constituted with a vacuum or an air layer according to a situation where the device is used. With this reason, almost no X-ray is absorbed in the empty layers 1, a loss resulted from the absorption diminishes substantially and thus a high reflectivity can be obtained. Moreover, any problem caused by a difference of thermal expansion indices does not fundamentally occur, any deterioration of an optical characteristic caused by a mutual dispersion of the materials at an interface and therefore even in a case of an X-ray irradiation under a high temperature environment or a highly intensity X-ray irradiation, the device can be employed in a fairly good condition.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to reflective optical systems in the X-ray region in X-ray lithography, X-ray telescopes, X-ray microscopes, X-ray lasers, various X-ray analyzers, etc. This invention relates to a multilayer reflective mirror used.

[Prior art] xa! The refractive index of the substance in the region is expressed as n, = 1-δ-iβ (δ, β: real numbers) (1), where both δ and β are very small compared to 1, that is, the refractive index is is close to 1, and X-rays are hardly refracted, so lenses that utilize refraction of light such as those in the visible light region cannot be used. Therefore, in the X-ray region, optical systems that utilize reflection are used, but X-rays are incident on an ultra-smooth mirror surface coated with platinum or the like at an angle smaller than the critical angle for total reflection (about 6 degrees for a wavelength of 25 people). A total reflection mirror has the problem that almost no reflection occurs at an incident angle closer to perpendicular than the critical angle.

In recent years, in order to solve these problems, a large number of reflective surfaces (for example, several hundred layers) are created by laminating many layers of materials with large differences in refractive index, and each reflected wave is A multilayer reflector has been developed in which the thickness of each layer is adjusted based on optical interference theory so that the phases match.

To explain more specifically, a multilayer film reflecting mirror is obtained by alternately laminating 2 fi 1 m or more of materials that have a large refractive index difference with vacuum and materials that have a small refractive index difference at the X-ray wavelength used. , as a typical combination,
W (tungsten)/C (carbon), Mo (molybdenum)
/Si (silicon) and the like are known, and are formed by thin film forming techniques such as sputtering, vacuum evaporation, and CVD.

In order to obtain a high reflectance with such a multilayer reflector, the refractive index (n = 1-δ-1β) of the Z fffl type (two or more types of materials may be laminated) to be laminated must be set in the wavelength range to be used. It is known that it is sufficient to satisfy the following two conditions.

(Showa 62 Autumn Japan Society of Applied Physics Lecture No. t9p-zn
-z) 1. In order to increase the amplitude reflectance of the interface, the difference in the two substances δ must be large.

2. The β of the two substances must be small in order to reduce loss due to absorption.

Currently, in order to develop multilayer mirrors with higher reflectance, active searches are being made for combinations of materials that satisfy the above conditions.

[Problems to be Solved by the Invention] However, in the conventional technology as described above, substances always absorb X-rays (that is, the refractive index n=1−δ−i
(β of β has a finite size), even if the number of layers is increased by selecting various materials to be laminated, the reflectance saturates at a certain point and it is impossible to obtain a high reflectance. was there. For example, for X-rays with a wavelength of 25 people, even if we optimized the combination of laminated materials and the structure of the multilayer film, we could only obtain a maximum reflectance of about 40 at an incident angle of 25 degrees. (The incident angle is the angle from the film surface. The same applies hereinafter.) In addition, in conventional multilayer film reflectors, different materials are alternately laminated, so due to the difference in thermal expansion coefficient of the materials, X-rays There are problems in that warpage occurs or the film becomes separated by ff1J due to temperature increase due to absorption or the surrounding environment.

Furthermore, since mutual diffusion of substances occurs at the interface between different substances, there is also the disadvantage that the characteristics easily deteriorate in high-temperature environments or when the temperature rises due to absorption of high-intensity X-rays. Ta.

The present invention was made in view of these conventional problems, and it is possible to obtain a high reflectance that was theoretically impossible to obtain with conventional multilayer film reflectors, and also has heat resistance. The purpose is to provide an excellent new concept multilayer II@X-ray reflector.

[Means for Solving the Problems] In the present invention, the above-mentioned problems can be achieved by laminating a plurality of fiI films made of a material having a large refractive index difference with vacuum in a predetermined X-ray wavelength range via a spacer of a predetermined thickness. have achieved their goals.

[Function] FIG. 1 is a sectional view showing the basic configuration of the present invention. In the multilayer film reflector according to the present invention, a thin film 2 of a substance having a large refractive index difference with vacuum is laminated on a substrate 10 with a spacer 3 having a predetermined thickness interposed therebetween. The layer corresponding to one substance 'M' (a material with a small refractive index difference from vacuum) is formed of vacuum or air depending on the environment in which it is used. Therefore, the absorption of X-rays in this void layer 1 is almost constant (the absorption of air is not strictly zero, but it is sufficiently small compared to the absorption of solids), and the loss due to absorption is significantly reduced. This makes it possible to obtain a high reflectance that was previously impossible in principle. Also,
Since the interface between the multiple layers is the interface with vacuum (or air), problems caused by differences in thermal expansion coefficients and mutual diffusion of substances do not occur.

In the present invention, the material 11 (thin film 2) laminated via the spacer 3 is not particularly limited, but when its refractive index is n=1-δ-iβ, the material 11 (thin film 2) laminated via the spacer 3 is It is particularly effective to use a material that has a large δ to increase the amplitude reflectance of the interface and a small β to reduce loss due to absorption.

Furthermore, the method for manufacturing the multilayer reflective mirror according to the present invention is not particularly limited. are alternately laminated (spacers are placed in the carbon layer in advance), and then heat treated in an oxygen-containing atmosphere to form 2C+O, -2CO or C+O,
It can be produced by removing carbon as carbon dioxide gas through a -CO2 reaction.

[Example] First, a film forming apparatus commonly used in Examples of the present invention will be described. The device is an f-magnetron sputtering device as shown in Figure 2, with two targets 1
4a and 14b are provided, each of which is provided with a mechanism that moves directly below the substrate 5 and is connected to the high frequency power source 12, so that a multilayer film can be formed by alternately sputtering with two targets. It has become.

A changeover switch is connected to the substrate holder 4 so that it can be set to a ground potential or a negative DC bias can be applied (power supply 13). Further, a shutter 6 that can be rotated and driven in the vertical direction (Z direction) is provided on the front surface of the substrate 5. As shown in FIG. 3, this shutter 6 is provided with an opening 7 and a mesh-like mask 8 to prevent a film from adhering to the substrate 5 during press sputtering and to keep the mask 8 in close contact with the substrate. It is also possible to perform film deposition.

Further, the substrate holder 4 can be moved to the position indicated by the dotted line in the figure, and at that position it is fixed on a stage 9 that can move precisely in the X-Y directions. Then, the light from the YAG laser 15 provided outside the vacuum chamber 16 is introduced through the optical window, focused by the lens 11''C provided in the vacuum chamber, and irradiated onto the substrate 5, and the stage 9 is moved. A predetermined portion of the formed thin film can be removed.

Embodiment 1 FIGS. 4a' to 4e are cross-sectional views showing the manufacturing process of a multilayer mirror according to the first embodiment of the present invention. (Note that the numbers of manufacturing equipment are the same as those in FIG. 2 described above. The same applies hereinafter.

) Using a mirror-polished Si wafer as the substrate 20, first apply the mesh-like mask of the shutter 6 to the substrate, set the substrate holder 4 to ground potential, and connect the graphite target 14.
A was sputtered to form a 0 layer 21 having a thickness of 28 layers as shown in FIG. 4a.

Next, without applying a negative DC bias to the holder 4, the Ni
The target 14b is sputtered to form a Ni layer 2 with a thickness of 12 layers.
2 was formed as shown in Figure 4. Applying a negative DC bias to the holder 4 promotes the incidence of A ions in the plasma onto the substrate 20 and removes the concave portions (C
This is to flatten the masked portion during layer formation. The Ni film deposited in the recessed portion of the 0 layer 21 becomes a spacer 23 that supports the Ni layer 22 after the 0 layer is removed. The spacers 23 were arranged in a grid pattern so as to have the strength to maintain the layered structure.

By repeating the above steps 200 times, a Ni/C multilayer film consisting of 200 periodic layers as shown in FIG. 4C was formed. (However, the number of layers is omitted in the figure. The same applies hereinafter.) Next, the substrate holder 4 is moved onto the X-Y stage 9, and the substrate is scanned by irradiating the focused YAG laser. A portion of the multilayer film was removed as shown in Figure 4d. This part is the removal hole 24 for removing the 0 layer in the next step.
However, the removal holes 24 were arranged in spots so as not to reduce the strength of the multilayer film.

Subsequently, the multilayer film is heat-treated in an oxygen atmosphere to remove C[21 as carbon dioxide gas, thereby forming a void layer 25).
A multilayer xt3 reflecting mirror in which Ni layers 22 were laminated with spacers 23 in between as shown in FIG. 4e was obtained. When the reflectance of this multilayer film reflector was measured using X-rays with a wavelength of 25, the peak reflectance was 69 zero, an unprecedentedly high value, as shown in FIG.

In this embodiment, the process of forming the removal holes 24 in the multilayer film may be performed by irradiating the YAG laser in the vacuum chamber 16, or this process may be performed after the substrate is taken out to the atmosphere. For example, photolithography and etching techniques may be used instead of using a YAG laser.

Embodiment 2 FIGS. 5a-5c are cross-sectional views showing the manufacturing process of a multilayer reflective mirror according to a second embodiment of the present invention.

Using a mirror-polished Si wafer as the substrate 30, first, the substrate holder 4 is set to the ground potential and the graphite target 14a is
A 0 layer 31 having a thickness of 35 layers was formed by sputtering. After that, move the substrate holder 4 onto the X-Y stage 9,
By scanning the substrate with irradiation with a focused YAG laser, four parts of the 0 layer 31 were removed as shown in FIG. 5a. At this time, the laser intensity was adjusted in advance to such an extent that only the 0 layer 31 was removed.

Next, the substrate holder 4 was returned to the film forming position, the mesh-like mask of the shutter 6 was brought into close contact with the substrate, and the Ni target 14b was sputtered to form a Ni layer 32 with a thickness of 15 layers. At this time, a negative DC bias was applied to the substrate holder 4, and the recess 33 from which the 0 layer 31 was removed was flattened as shown in FIG. This portion becomes the spacer 33 in this embodiment.

In addition, the area masked during the formation of the C layer becomes the carbon removal hole 34, but a mask with a smaller mask area (larger aperture ratio) than the one used in Example 1 was used in order not to reduce the strength of the layer structure. The film was formed using the following method.

The above process is repeated 200 times to form a Ni/C multilayer film consisting of 200 periodic layers, and then the multilayer film is heat treated in an oxygen atmosphere to remove the 0 layer 31 as carbon dioxide gas and form the void layer 35. Then, as shown in FIG. 5C, a multilayer I'li X-ray reflecting mirror was manufactured in which a Ni layer 32 was laminated with a spacer 33 interposed therebetween.

Note that in this embodiment, the spacer 33. The carbon removal holes 34 were arranged in a grid pattern, but they were arranged narrowly and roughly so as not to reduce strength.

When the reflectance of this reflector was measured using X-rays with a wavelength of 25, a peak reflectance of 73% was obtained as shown in FIG.

Embodiment 3 FIGS. 6a"-'c are sectional views showing the manufacturing process of a multilayer reflective mirror according to a third embodiment of the present invention.

A mirror-polished Si wafer is used as the substrate 40, and the graphite target 14a is first set with the substrate holder 4 at ground potential.
A zero layer 41 having a thickness of 42 layers was formed by sputtering. Thereafter, the substrate holder 4 was moved onto the X-Y stage 9, and a part of the 0 layer 41 was removed as shown in FIG. 6a by scanning the substrate with irradiation with a focused YAG laser. At this time, the laser intensity was adjusted in advance to such an extent that only the 0 layer 21 was removed. A spacer 43 will be formed in the removed portion later.

Next, the substrate holder 4 is returned to the film-forming position, and without applying a negative DC bias, the Ni target 14b is sputtered to flatten the Ni layer 42 with a thickness of 18 to the concave portion where the layer 41 has been removed. was formed. Thereafter, the substrate holder 4 was moved onto the XY stage 9 again, and a portion of the Ni layer 42 was removed as shown in FIG. 6 by irradiating the substrate with a focused YAG laser and scanning the substrate. The laser intensity at this time was adjusted in advance to such an extent that only the Ni layer 42 was removed. The removed portion will later become a removal hole 44 of layer 0.

The above steps are repeated 200 times to form a Ni/C multilayer film consisting of 200 periodic layers, and this is heat treated in an oxygen atmosphere to remove the 0 layer 41 as carbon dioxide gas to form a void layer 45. As shown in FIG. 6C, a multilayer X-ray reflector was prepared in which a Ni layer 42 was laminated with a spacer 43 interposed therebetween.

In this embodiment, the spacers 43 are arranged in a lattice shape so as to have the strength to maintain the layered structure, and the carbon removal holes 44 are arranged in spots so as not to reduce the strength.

When the reflectance of such a multilayer one-distance reflector was measured using X-rays of 25 wavelengths, a peak reflectance of 75% was obtained as shown in FIG.

Embodiment 4 FIGS. 7a' to 7e are cross-sectional views showing the manufacturing process of a multilayer reflective mirror according to a fourth embodiment of the present invention.

A mirror-polished Si wafer is used as the substrate 50, the substrate holder 4 is set to the ground potential, and a graphite target 14a and a Ni target 14b are sputtered alternately to form a layer 51 with a thickness of 50 and a thickness of 50, as shown in FIG. 7a. A multilayer film was formed by alternately stacking 200 Ni layers 52 each.

Next, a photoresist 56 was applied thereon, and by exposure, the resist 56 was removed only at the portions where the spacers 53 and the carbon removal holes 54 were to be provided. This was dry-etched using a gas mainly composed of A' and 0. I did it.

After that, the resist 56 is once removed, and the resist 57 is removed again.
The resist 57 was coated, exposed and developed, and only the portions that would become the spacers 53 were removed. As shown in FIG. 7C, Ni11! is applied by sputtering or vacuum evaporation to the same thickness as the multilayer film. After forming the resist 58, the resist 57 was peeled off (so-called lift-off), and as shown in FIG. 7d, unnecessary portions of the Ni film were removed and spacers 53 were formed.

Next, by heat-treating this in an oxygen atmosphere, the 0 layer 5
1 is removed as carbon dioxide gas from the removal hole 54 to form a void layer 55.
A multilayer X-ray reflecting mirror in which a Ni layer 52 was laminated with a spacer 53 interposed therebetween as shown in FIG. 7e was fabricated.

In this embodiment, the spacers 53 are arranged in a grid pattern so as to have the strength to maintain the layered structure, and the carbon removal holes 54 are arranged in spots so as not to reduce the strength.

When the reflectance of this reflector was measured using X-rays of 25 wavelengths, a peak reflectance of 76% was obtained as shown in FIG.

In this example, when forming the spacer 53, taper etching was performed, a Ni film was formed thereon, and unnecessary portions were removed by lift-off. As shown, the 0 layer 52 is over-etched compared to the 5 Ni layers, and the surface is covered with 5 in 2 layers.
Thin lI! 159 may be formed, and the spacer 60 made of W may be formed as shown in FIG. 8 by filling the WWA selective growth technique by plasma CVD using WF6 gas. In this case, the spacer 60 made of W may be formed. W is dotted in a grid pattern in the layer 51, but there is no particular disadvantage in terms of reflectance.Furthermore, the 5 inch 2 layer 59 formed on the surface may be left as is, or it may be removed later. Also good.

Although four embodiments of the present invention have been described above, it goes without saying that the multilayer film reflecting mirror according to the present invention is not limited to those manufactured by the above method.

In Examples 1 to 3, the Ni layer was formed by applying a negative DC bias to the substrate in order to planarize it, but if the 0 layer is not too thick, the film may be formed without applying a bias.

In addition, in the above embodiment, the substrate and the multilayer film were made of different materials, but if the difference in thermal expansion coefficient between the multilayer film and the substrate becomes a problem depending on the usage conditions, the substrate may also be made of the same material as the multilayer film. Just do it.

[Effects of the Invention] As described above, the present invention has advantages that cannot be obtained with conventional multilayer film reflecting mirrors by laminating thin films of materials with a large refractive index difference with vacuum through spacers of a predetermined thickness. It has an extremely excellent effect of being able to obtain a very high reflectance.

The multilayer reflective mirror according to the present invention has significantly less X-ray absorption than conventional ones, so it is in the soft X-ray region (50 to 100 degrees
eV), and those used in the long wavelength range are easier to manufacture because the layer thickness may be thicker.

In addition, since the interface in the multilayer reflector of the present invention is the interface with vacuum or the atmosphere, there is basically no problem caused by differences in the coefficient of thermal expansion of substances, and there is no problem due to mutual diffusion of substances at the interface. Since no deterioration of properties occurs, it can be suitably used even in environments with high product temperatures or when irradiating high-intensity X-rays.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the basic configuration of the present invention, Figure 2 is a configuration diagram of the RF magnetron sputtering apparatus used in the embodiment of the present invention, and Figure 3 is an explanatory diagram of the shutter used in the apparatus shown in Figure 2. , Fig. 4 a'-e. Figure 5 a'-c and Figure 6 a Nc are the first embodiment of the present invention. Second. FIGS. 7a-'e are sectional views illustrating the manufacturing process of the third embodiment, and FIGS. 10, 11, and 12 are graphs showing the reflectance measurement results of multilayer mirrors according to the first, second, third, and fourth embodiments of the present invention. [Explanation of symbols of main parts] ] 1・・・・・・・・・・・・・・・Void layer 2...
・・・・・・・・・・・・・・・Thin films 14a, 14b
・・・・・・・・・・・・Target 4・・・・・・・
・・・・・・・・・・・・Substrate holder 5・・・・・・・
・・・・・・・・・・・・Substrate 6・・・・・・・・・・・・
・・・・・・Shutter 9・・・・・・・・・・・・
・・・・・・X-Y stage lO・・・・・・・・・・
・・・・・・YAG laser 20.30, 40.50
. . . Si substrate 21.31, 41.51 . . . 0 layer 22.32, 42.52 . . . Ni layer 23, : 13, 43, 53. fiO...Spacer 2
4.34, 44.54...Removal hole 25.35, 45.55...Void layer

Claims (1)

[Claims] A multilayer X-ray reflecting mirror is made by laminating a plurality of thin films of a material that has a large refractive index difference with vacuum in a predetermined X-ray wavelength range via spacers of a predetermined thickness.