JPH07113679B2 - Multilayer film mirror - Google Patents

Description

The present invention relates to an X-ray reflecting mirror having a multilayer film structure.

(Problems to be Solved by Prior Art and Invention) As shown in FIG. 8 a) as a conventional multilayer film reflecting mirror,
A multilayer-film reflective mirror in which a light element thin film 2 and a heavy element thin film 3 are alternately formed on a substrate 1 at a constant pitch is generally known.
In this case, there is a fixed relationship between the reflectance and the wavelength bandwidth of the reflectance spectrum (when the reflectance is increased by increasing the number of layers, the wavelength bandwidth is narrowed conversely).
It is not possible to obtain an arbitrary wavelength bandwidth while maintaining high reflectance. Also, the integrated reflectance is low. Furthermore, when X-rays having a predetermined wavelength are used as incident light, the incident angle at which Bragg reflection occurs is in a very limited range. Therefore, when a conventional multilayer film is formed on a curved substrate, each point on the surface of the reflecting mirror Against X
Since the incident angles of the lines are different from each other, the area of the reflecting surface that contributes to the Bragg reflection of a predetermined wavelength becomes very small.
Therefore, high reflectance cannot be obtained at a desired wavelength. As another example, there is a multilayer film reflecting mirror in which the pitch gradually changes from the substrate upward as shown in FIG. 8B), but the multilayer film is formed accurately while maintaining a constant pitch change. In addition to being difficult to achieve, there is a drawback that a high peak reflectance cannot be obtained. Further, as the constituent material of the above-mentioned conventional multilayer film reflecting mirror, W, Re, P
Al, Si, C as materials for the heavy and spacer layers such as t, Au
However, in this case, the light element thin film has a large absorption coefficient especially in the soft X-ray region, and there is a drawback that the reflectance cannot be increased. Further, the ion beam sputtering method, which is a conventional method for manufacturing a multilayer-film reflective mirror, has a drawback that an extremely thin film cannot be formed because scattered ions damage the deposited film.

(Means for Solving the Problems) The present invention solves the above-mentioned problems of the prior art, has a high reflectance, and the bandwidth of the reflectance spectrum can be arbitrarily and easily set, but has a curved surface structure. An object of the present invention is to provide a multilayer-film reflective mirror that can obtain high reflectance even in the case of doing so.

In order to achieve the above object, the present invention provides a multilayer film reflecting mirror structure in which a plurality of types of unit multilayer films having different pitches are laminated, so that a wavelength bandwidth suitable for X-ray exposure can be freely and easily obtained. In addition to being selectable, a curved surface structure provides high reflectance. Further, absorption of X-rays on the long wavelength side by the constituent elements of the multilayer film is minimized,
In order to obtain a high reflectance over a wide wavelength range, the pitch of each unit multilayer film is sequentially increased from the substrate side to the upper side. Further, the main feature of the present invention is to increase the reflectance of the reflecting mirror by using B or Be as a constituent material of the light element thin film of the multilayer-film reflecting mirror.

Next, examples of the present invention will be described.

Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

FIG. 1 shows an embodiment of the multilayer-film reflective mirror according to the present invention.
A pitch dn composed of a heavy element thin film 4 having a thickness An, which is a reflection layer, and a light element thin film 5 having a thickness Bn, which is a spacer layer, on a substrate 1.
In this example, M pieces of the periodic unit multilayer film 6 in which Nn layers of the above two-layer film are stacked are sequentially laminated from the substrate 1 side. The principle of optical characteristics of the multilayer-film reflective mirror will be described by taking the case of M = 2 as an example. It is known that a multilayer film having a predetermined pitch reflects X-rays having a constant peak wavelength and a constant bandwidth with high reflectance.
Therefore, in the structure as shown in FIG. 1, in the case of M = 2, that is, the multi-layer film reflecting mirror in which two unit multi-layer films having different pitches are laminated has different center wavelengths λ1 and λ2 corresponding to the respective unit multi-layer films. A high reflectance can be realized over a wide wavelength range by combining the spectra 7 and 8 having a peak at (7, solid line in FIG. 2). The characteristics of the multilayer film reflecting mirror having such a structure are that a characteristic having a high reflectance over a wide wavelength range, that is, a spectral characteristic having a high integrated reflectance can be realized,
The desired wavelength band width can be set by changing the values of the pitch dn, the film thickness An of the heavy element thin film, the film thickness Bn of the light element thin film, and the number M of stacks. Has a wide range of incident angles,
Even if it has a curved structure, a high reflectance can be obtained.

The structure, constituent materials, and optical characteristics of the multilayer-film reflective mirror in this example will be described in more detail.

Since the long wavelength component of the light source is more easily absorbed by the constituent material of the multilayer film than the short wavelength component, the unit multilayer film having the peak wavelength of the reflectance spectrum on the short wavelength side, that is, the unit multilayer film with the smallest pitch dn By stacking on the substrate so that the pitch dn increases toward, the long wavelength component is mainly reflected by the upper unit multilayer film and the short wavelength component is reflected by the lower unit multilayer film, so that the influence of absorption is reduced. It can be made smaller and a higher reflectance can be realized.

Further, the multilayer mirror in the present invention is characterized in that B or Be is used as the material of the light element thin film. The effect will be described below. When the complex refractive index of the multilayer film constituent material is 1-δ-iβ, the complex amplitude reflectance at the interface of the multilayer film is (Δδ +
It is proportional to iΔβ). However, Δδ and Δβ are the differences in the refractive index and the absorption coefficient between the heavy element thin film and the light element thin film. Further, in order to obtain a higher peak reflectance, it is desirable that the absorption of soft X-rays by the spacer layer material is small. 1 in FIG.
Shows the absorption coefficient μ of various elements in the wavelength range of ~ 1000Å. In the soft X-ray region important for X-ray exposure, the absorption coefficient of B or Be is lower than the absorption coefficient of C which has been widely used as a conventional spacer layer material.
The absorption coefficient of Be is significantly different from that of C. Regarding the refractive index, the refractive index of B or Be is lower than that of C in the soft X-ray region (reference, P. L. Henke et al. “Atomic Data and Nuclear Data Tables”).
(1982), Vol. 27. Therefore, by using B or Be instead of C which is generally used for the conventional spacer layer material, Δδ and Δβ are increased in the soft X-ray region, and the spacer is Since the absorption of soft X-rays by the layer material is reduced, a very high reflectance can be obtained.For example, according to the calculation by the present inventor, the W / Be multilayer mirror has a peak wavelength λp = 11.
Compared with the W / C multilayer mirror in Å, the peak reflectance of nearly double is obtained.

Further, as a feature of the multilayer-film reflective mirror according to the present invention, each of the M type unit multilayer films constituting the multilayer-film reflective mirror has an optimum An / dn ratio such that a maximum peak reflectance can be obtained. Can be mentioned. Therefore, it is possible to obtain the maximum peak reflectance with respect to the soft X-ray having the predetermined wavelength band. When the reflectance spectrum of the W / Be multilayer film reflecting mirror (M = 2) having the structure of FIG. 1 proposed as one embodiment of the present invention is calculated, a spectrum as shown by the solid line 9 in FIG. 4 is obtained. Was given. For comparison, the reflectance spectrum of the conventional W / C multilayer mirror is shown by a broken line 10 (Table 1, design parameters of both multilayer mirrors and peak reflectance RP, wavelength bandwidth Δλ / λ, integral Reflectance IR). The multilayer reflector (M = 2) proposed by the present invention has an integrated reflectance about three times higher than that of the conventional multilayer reflector (M = 1) having a periodic structure.

The above-mentioned examination using a light element such as B or Be having a smaller absorption coefficient than C as the spacer layer material of the multilayer film reflection mirror has been made at a wavelength λ = 124 Å. Literature, T. W. Barbie
Junior X Ray Micro Skopy, "X
-Ray Microscopy, editated by G.Schmahl and D.Rudol
ph, (Springer-Verlag, 1984) "p144-162). However, in the soft X-ray region on the shorter wavelength side, which is particularly important for X-ray exposure, the structure of the multilayer mirror and the An / dn ratio are also No consideration has been given to the included studies, and no proposal has been made to the laminated structure of multilayer films having different pitches as in the present invention.

Although the multilayer-film reflective mirror is a plane mirror in the above description, the curved surface can collect X-rays and increase the intensity of the reflected X-rays.
Since the multilayer mirror having a laminated structure according to the present invention provides a wide reflectance spectral bandwidth, it is meant to provide a high reflectance over a wide Bragg angle α. Therefore,
It is suitable for the structure of a curved-surface multilayer film reflecting mirror having a certain spread in the incident angle and the outgoing angle. This point will be described in detail below.

FIG. 5 shows a second embodiment of the multilayer-film reflective mirror according to the present invention, and is a sectional view of a curved multilayer-film reflective mirror in which a multilayer film 12 is formed on a cylindrical surface substrate 11 having a radius of curvature R. Here, the structure of the multilayer film 12 is assumed to be a stack of a plurality of unit multilayer films as shown in the embodiment of FIG. It is assumed that parallel X-rays 13 are incident on the reflecting mirror at a point 14 on the mirror surface at a glancing angle θ and are reflected. At this time, the reflected light has a reflectance spectrum having a peak wavelength of λP1 and a wavelength bandwidth of Δλ / λ, as shown in FIG. However, when the position of the reflection point deviates from 14, the peak wavelength of the reflectance spectrum also changes, and the reflectance at the wavelength λP1 also decreases. When the position of the reflection point is further shifted, the reflectance spectrum has a reflectance of 0 at λP1 as shown in FIG. The reflection point at this position is 15,
Let L be the distance between 14 and 15. That is, the glancing angle in FIG. 5 is θ
From .theta .-. DELTA..theta., The reflectance spectrum of the reflected light changes from FIG. 17 to FIG. However, in FIG.
There is also a point where the reflectance at the wavelength λP1 is 0 at a position opposite to 15 apart from L by. Therefore, the total of the reflected light from the reflection points in the range of 2L centering on 14 is the focus 16
Is the reflection intensity of λP1 at. In this case, the wider Δλ / λ of the reflectance spectrum is, the longer L is, and the intensity of the wavelength λP1 at 16 is increased. The multilayer mirror according to the present invention has a larger Δλ / λ than a conventional mirror having a periodic structure (M = 1) and a high reflectance, so that the intensity of the reflected light of the wavelength λP1 at the focus 16 is large. This is true even for wavelengths other than λP1, so after all, the reflected light with high intensity is focused 16
Can be obtained at. An example of the multilayer-film reflective mirror according to the present invention is (i) W / Be multilayer-film reflective mirror (M = 2) and (ii) conventional structure.
For W / C multilayer mirror (M = 1), length of L (λP1
= 11Å) are compared. (I) and (ii) λP1 = 11 respectively
When the reflectance spectrum in Å has a peak reflectance of about 20%, Δλ / λ is 24% for (i) and 6% for (ii).
It is a degree. However, (i) is d1 = 37Å, d2 = 43Å, (i
In i), d = 39.5Å. In this case, if the difference in the glancing angles at points 14 and 15 is Δθ, L is represented by R · Δθ · π / 180, and (i) has L which is about four times as large as (ii). Therefore,
The intensity of λP1 = 10Å at the focal point 16 is (i) about four times larger than (ii). This tendency is due to other wavelengths λ in the soft X-ray region.
The same is true for P1.

So far, the embodiments of the multilayer-film reflective mirror according to the present invention have been described. Next, an example of a method for manufacturing the multilayer-film reflective mirror will be described. FIG. 7 shows an example of a method for manufacturing a multilayer-film reflective mirror. First, the principle of atomic beam generation will be described with reference to FIG. Ar gas of about 10 ^-2 to 10 ^-3 torr was introduced into the atomic beam source through the gas inlet 19 and the anode electrode 20 was charged with 3 to 3
When a high voltage of about 9 kv is applied, glow discharge is started between the anode electrode 20 and the cathode electrodes 21, 22. The electrons emitted from the surfaces of the cathode electrodes 21 and 22 are the central anode electrode 2
High frequency vibration around 0. In the atomic beam source, a large number of ions are generated by collision of oscillating electrons with Ar atoms. The ions are accelerated towards the cathodes 21,22. Since electrons having a large collision cross-section exist near the cathode, they are easily combined with the ions accelerated at several kv and become atomic beams 23 having the same energy as the ions, which are taken out from the beam emission port 24.

The method for manufacturing a multilayer-film reflective mirror according to the present invention applies an Ar atomic beam 23 obtained by using the atomic beam source to a multilayer-film constituent material 25 as a target, and sputtered sputtered particles 26 are deposited on a substrate 27. Then, the film is formed.
The heavy element thin film and the light element thin film are formed by alternately exchanging the targets.

A feature of such a multilayer-film reflective mirror manufacturing method is that a smooth multilayer film with few irregularities at the interface can be formed. As a result of the evaluation of the multilayer film interface using the X-ray diffraction (Cu-Kα ray) by the present inventors, the unevenness was about 1Å. Therefore, it was found that an extremely smooth multilayer film was formed. further,
A feature of this method is that an extremely thin continuous film can be formed. From the observation result of the multilayer film and the single layer film by the transmission electron microscope, it was found that the manufacturing method formed a thin film of about 10 Å for each of W and Be. Taking W as an example, the minimum thickness of a continuous thin film formed conventionally is 30Å,
It is understood that an extremely thin thin film can be formed by this manufacturing method. Further, since the sputtering rate is very stable (the fluctuation of 1 hour or less per hour in the measurement by the inventors), it can be said that the method has a very good film thickness controllability. Further, when Be is used as the material for forming the spacer layer of the multilayer film, the sputter rate is high (the Sputter rate of Be was 1.74Å / min, and the sputter rate of C was 0.38Å / min according to the measurement by the present inventors). Therefore, a multilayer film reflecting mirror can be produced in a short time. From the above, according to the method for producing a multilayer film mirror, a multilayer film mirror having an extremely smooth multilayer film interface, that is, scattering of X-rays at the multilayer film interface is extremely small,
It is possible to manufacture a multilayer-film reflective mirror having a reflectance close to the theoretical value. Further, it is possible to manufacture a multilayer-film reflective mirror having a fine pitch with good manufacturing accuracy.

(Effects of the Invention) The multilayer-film reflective mirror according to the present invention is useful as various spectroscopic elements and band filters because it has a multiplicity of reflectance and a controllable spectral bandwidth. Further, in the soft X-ray region which is particularly important for X-ray lithography, the W / Be according to the present invention is
Since the multi-layered film reflecting mirror can obtain a large reflectance over a wide viewing angle, when the soft X-ray is focused, it is possible to obtain a reflected light intensity several times higher than that of the conventional multi-layered film reflecting mirror.
Therefore, when applied to X-ray lithography, the exposure time can be greatly shortened, and the resolution in forming a fine pattern is improved, which is useful as a condenser reflecting mirror. Furthermore, the wavelength bandwidth of the multilayer film can be freely changed relatively easily.

[Brief description of drawings]

FIG. 1 is a three-dimensional view showing the structure of one embodiment of the multilayer-film reflective mirror according to the present invention, FIG. 2 is a diagram for explaining the principle of optical characteristics of the multilayer-film reflective mirror according to the present invention, and FIG. FIG. 4 is a diagram showing the wavelength dependence of the absorption coefficient, FIG. 4 is a diagram showing the reflectance spectrum of the multilayer-film reflective mirror according to the present invention, and FIG. 5 is another example of the multilayer-film reflective mirror according to the present invention. A diagram showing a cylindrical multilayer reflecting mirror and a state of condensing X-rays by the reflecting mirror,
FIG. 6 is a diagram for explaining the reflectance spectrum characteristics of a cylindrical multilayer mirror, FIG. 7 is an example of a method for manufacturing a multilayer mirror according to the present invention, and FIG. 8 is a structure of a conventional multilayer mirror. Show. 1 ... Substrate 2 ... Spacer layer 3 ... Reflective layer 4 ... Reflective layer 5 ... Spacer layer 6 ... Unit multilayer film 7 ... Reflectance spectrum 8 ... Reflectance spectrum 9 ... W / Be multilayer film Reflectance spectrum of reflecting mirror (M = 2) 10 …… W / C Reflecting spectrum of multilayer film reflecting mirror (M = 1) 11 …… Cylindrical surface substrate 12 …… Multilayer film reflecting mirror 13 …… Injection according to the present invention X-ray 14 …… Reflecting point 15 …… Reflecting point 16 …… Focus 17 …… Reflectance spectrum 18 …… Reflectance spectrum 19 …… Gas inlet 20 …… Anode electrode 21 …… Cathode electrode 22 …… Cathode electrode 23 ...... Atomic beam 24 …… Beam emission port 25 …… Multilayer film material 26 …… Sputtered particles 27 …… Substrate

Continuation of the front page (56) Reference JP-A-60-7400 (JP, A) JP-A-61-42815 (JP, A) Proceeding of the Society of Photo-Optical Instrumentation on Engineers, Vol. 563 (1985) (US) "Paper name; Layered Synthetic Microstructures for Solar EU UV Telescopes" (presenter: Ritva AM Keski-Kuha et al.

Claims (3)

[Claims] 1. A multi-layered film mirror obtained by alternately stacking a heavy element thin film and a light element thin film on a substrate, wherein a multi-layered film having a predetermined pitch and a predetermined number of layers is used as a unit multi-layered film. A multilayer film reflecting mirror, characterized in that a plurality of unit multilayer films having different pitches and the number of layers are laminated on a substrate in such a manner that a plurality of unit multilayer films having smaller pitches are sequentially increased upward. 2. The multilayer-film reflective mirror according to claim 1, wherein the substrate has a curved surface. 3. The material of the light element thin film is B or Be.
The multilayer film reflecting mirror according to claim 1 or 2, characterized in that