JPH02238400A - Multilayer film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multilayer film suitable for reflecting light in the soft X-ray region6 [Prior Art] The multilayer film is suitable for reflecting light in the visible light region It has been widely used as an anti-reflection coating for light. In recent years, the soft X-ray region (10~10
With the progress of light source development and research, multilayer films are attracting attention as optical elements that can be used in the soft X-ray region.

FIG. 4 shows the structure of a multilayer film for soft X-rays in which heavy elements and light elements are alternately laminated. In the figure, 1 is a layer of a heavy element with a high X-ray reflectance and is called A/l, and 2 is a layer of a light element with a low X-ray reflectance and is called the B layer. 3 is a substrate. In order to efficiently reflect soft X-rays with the multilayer film having the above structure, it is necessary that the difference between the X-ray reflectance of the AJI and the X-ray reflectance of the B layer be large. For this purpose, a heavy element with a high X-ray reflectance is used in the A layer, and a light element with a low X-ray reflectance is used in the B layer. Conventionally used multilayer films include W/C, Mo/SL, Aft/C, for example, if a multilayer film made of W and C is expressed as W/C.
Cu, Au/C. Ta/C. Cu/C, Re/C. W/
Be et al.

[Problem to be solved by the invention]

W/C. Au/C, Ta/C, Cu/C. Re/C,W
/ Be, etc., in a multilayer film such as Be. The B layer is formed from a single element such as C. Since the mutual bond between JM molecules is weak and the light elements that make up the B column have a small atomic radius,
It has a tendency to leave the B layer and easily diffuse into the A layer. For example, the currently used C film is a graphite-like film, and the carbon in the graphite is more easily decomposed and diffused into the A layer than in diamond. Additionally, diamond-like thin films with strong bonds that are difficult to decompose and diffuse are being created, but because they grow in island-like shapes, it is currently difficult to create ultra-thin films with flat surfaces. on the other hand. Be used in W/Be also has a weak bond between Be and tends to grow in an island shape, leaving Bl and diffusing into the A layer. Furthermore, in a multilayer film of metals such as Cu/An, the metal and Cu tend to diffuse into each other due to the nature of the metal. Due to such mutual diffusion, the X-ray reflectance of A/l decreases and at the same time the X-ray reflectance of Bl increases, resulting in a problem in that the reflectance of the multilayer film decreases. Furthermore, since the mutual diffusion between the B layer and the A layer is promoted by time and temperature increase due to light irradiation on the multilayer film, there is a problem that the reflectance of the multilayer film decreases over time.

Substances A and B used in conventional multilayer films are often a combination that forms a compound, and the formed compound is also stable, often forming a compound over several to tens of layers at the interface. . For example, the most commonly used W
In the /C multilayer film, W and C combine at the interface to form WC, and WC is chemically stable and easy to form.6 Furthermore, if Si is used in the B layer, in most cases it will combine with atoms of the A calendar. They combine to form silicide. The formation of several to several tens of layers of compounds at the interface reduces the difference in reflectance between the 5AM and B layers, resulting in a problem in that the reflectance of the multilayer film is significantly reduced.

Be. If layer B is formed with C, etc., it is difficult to form a single-crystal thin film with strong bonds between elements, so it tends to grow in granular form, and the interface with layer A is uneven, causing irregular scattering of X-rays, resulting in a multilayer film. There was a problem in that the reflectance of the film was significantly reduced.

Also, Ba. Using extremely thin Be. In the case of a C thin film, it is currently difficult to form a flat thin film that is chemically stable and has good adhesion to the substrate and heavy element layer while keeping the substrate at a low temperature. Therefore, there was a problem in that the multilayer film peeled off from the substrate over time. Furthermore, S is added to multilayer films using such light elements.
When irradiated with strong light such as R light, heat is instantaneously applied to the multilayer film, causing the temperature to rise locally, causing the thin light element layer of the multilayer film to become chemically unstable and adhesive. As a result, there was a problem in that the multilayer film peeled off from the substrate. Further, when a substrate is heated when forming conventional C, Be, Cu, or Si, there is a problem that a compound is formed with a heavy element at the interface or that the heavy element rapidly diffuses into the element.

As mentioned above, in the conventional multilayer film, at the interface between layer A and layer B, the atoms forming layer A and the atoms forming layer B may diffuse into each other or form a compound. Alternatively, the soft X-ray reflectance of the heavy element layer A decreases due to unevenness at the interface, and at the same time the reflectance of the light element/WB increases, making it difficult to maintain the reflectance difference. However, there was a problem in that the reflectance of the multilayer film could not be obtained as per the designed value, and furthermore, there was a problem in that the multilayer film peeled off because the adhesion of the B layer to the substrate or the A layer was poor.

The present invention uses a thin film made of a single light element with weak inter-element bonds in a multilayer film, and prevents the light element from diffusing into the A layer, or because it is difficult to make a flat thin film with good adhesion. The object of the present invention is to obtain a multilayer film that solves the problems of a decrease in X-ray reflectance and peeling of the multilayer film.

[Means to solve the problem]

The above purpose is to create a compound B consisting of boron (B) and carbon (C) that has a complex refractive index comparable to that of a single element in the light element layer.
This is achieved by forming a multilayer film using 4C.

[Operation] The complex refractive index of a substance is expressed as n=1−δ−iβ. δ and β each take a value specific to the substance. FIG. 5 shows δ in the soft X-ray region of C and B elements alone as well as the B4C compound. C. FIG. 6 shows β in the soft X-ray region of B element alone and B4C compound. δ is C, B for 0 to 100 people. Both B and C show almost the same magnitude, and in particular, C and B temporarily decrease at the absorption edge (44 and 31 people, respectively), and B4C has almost the same slope, except for a slight decrease at the absorption edge of B and C. have size. Also, from Fig. 6, β shows that the wavelength λ is O and λ (for 20 people, it is almost the same as C.B.B4C, and for 20 people <λ<<44 people, its size is B<B4
C<C. 44 people〈λ＜70 people, C×B4C×B
So, for 70 people <λ, B<B4C<C.

Therefore, the δ and β of the B4C film are comparable to those of a film made of a single element C, which is commonly used as a multilayer film material, or depending on the wavelength, it has a small complex refractive index that is superior to that of a multilayer film material. has.

In addition to exhibiting optical values comparable to or better than conventional single elements as mentioned above, B4C compounds have a very high melting point of 2350°C and are chemically stable. There is. Therefore, it has the advantage that it is more stable against local heating than conventional films made of single elements, does not decompose or diffuse, and does not change over time.

Furthermore, as can be seen from its high melting point, the bond between B and C is strong, and while simple B and C easily form compounds with heavy elements, B4G does not form compounds with heavy elements.
It does not mix with the heavy element layer at the interface, and there is very little risk of it decomposing and diffusing into the heavy element layer.

In addition, in order to form a film that strongly adheres to the substrate, it is effective to heat the thin film during formation, but heating has not been possible in the past because light elements diffuse or form compounds when heated. However, since B4C is thermally stable compared to single-element thin films, there is little risk of it decomposing and diffusing even when heated to several hundred degrees during fabrication, and by heating the substrate, it can improve adhesion. The CVD method has the advantage of being easy to create a flat thin film.Furthermore, since the substrate can be heated, the CVD method generally has stronger bonds than the sputtering method and can produce a flat thin film. It has the advantage of being able to Also. B4G
Since B has two components, the stress within the thin film, which causes grain growth, can be easily controlled by slightly changing the composition of B and C.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a structural diagram showing an embodiment of a multilayer film according to the present invention.
FIG. 2 is a diagram showing the configuration of the X-ray reflectance measuring system for the multilayer film described above, and FIG. 3 is a diagram showing the X-ray reflectance of the multilayer film in the above example using experimental values and theoretical values. Using B4C for the B layer,
Using W in the A layer, soft X-rays with a wavelength of 39.8 and an incident angle of 7
A multilayer film with the strongest reflection at 0° was designed, and a B4C film 10 and a W film 1 were placed on a substrate 3 using SL as shown in FIG.
A multilayer film was formed by alternately stacking 20 layers of 1 and 1 by sputtering. B4C film is B1, B2
. . B20, W films are indicated as A1, A2 . . . A20, and the thickness of each layer is shown in Table 1.

Margin Table 1 Below: The X-ray reflectance measurement of the above multilayer film was carried out using the configuration shown in FIG. Incident X-ray 12 has a wavelength of 39.8 Ag (silver)
The A20 surface was irradiated with characteristic X-rays (M-rays) at an incident angle θl3, and reflected X-rays 14 were measured. An example of the measurement is shown in FIG. In FIG. 3, the horizontal axis is the incident angle, and the vertical axis is the X-ray reflectance. In Fig. 3, the solid line 15 indicates the actual measured value, and the dotted line 1
1'i indicates a calculated value, and the solid line 15 and the dotted line 16 almost match well, indicating that B4C is effective as a multilayer film composition. In place of W above, Au. Re,
Bi, Mo. Similar results can be obtained by using Ta, Rh, etc.

As mentioned above, the δ and β of B4C may be on the same level as a film made of the simple element C, which is generally used as a multilayer film material, or depending on the wavelength, the complex refractive index is small, and it has superior advantages as a multilayer film material. Motsu. The B4C compound has a melting point of 2
It has a very high temperature of 350°C and is chemically stable. Therefore, it has the advantage that it is stable even when subjected to local heating, does not decompose or diffuse, and does not change over time.

In addition, since B4C does not form compounds with heavy elements, there is very little risk that it will mix with the heavy element layer at the interface, decompose and diffuse into the heavy element layer, and compared to a single element thin film, B4C
Because it is thermally stable, there is little risk of it decomposing and diffusing even if heat of several hundred degrees is applied during production, and it has the advantage that it is easy to create a flat thin film with good adhesion by heating the substrate. Therefore, a predetermined thin film can be produced using the CVD method, which generally produces a thin film with stronger bonding than the sputtering method. Furthermore, since B4C consists of two components, it reduces the stress within the thin film that causes grain growth.
It can be easily controlled by slightly changing the composition of B and C.

〔Effect of the invention〕

As described above, the multilayer film according to the present invention is a multilayer film formed by alternately laminating a plurality of thin films each having a different refractive index, and one of the plurality of thin films has a composition of boron (B). and carbon (C), it is possible to obtain a multilayer film that is thermally stable and shows little change over time.
It can be used as a mirror for SR light that needs to reflect strong light. Furthermore, it can be used as a mirror of a plasma light source that generates intense light in a pulsed manner.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram showing an embodiment of a multilayer film according to the present invention;
Figure 2 is a diagram showing the configuration of the X-ray reflectance measurement system for the multilayer film, Figure 3 is a diagram showing experimental values and theoretical values of the X-ray reflectance of the multilayer film, and Figure 4 is a diagram showing the X-ray reflectance measurement system for the multilayer film. A diagram showing the basic structure,
Figure 5 shows the B. C.
A diagram showing the value of the optical constant δ of B4G, Figure 6 is for wavelengths from 0 to
B. for X-rays in the 100 person area. C. It is a figure showing the value of the optical constant β of B4G. 1... A layer of heavy elements 2... BMi of light elements
o... B4C layer patent applicant Nippon Telegraph and Telephone Corporation Representative Patent Attorney Junnosuke Nakamura Incidence e(0) Figure 3 Figure 4 Figure 6

Claims (1)

[Claims] 1. In a multilayer film formed by alternately laminating a plurality of thin films each having a different refractive index, one of the plurality of thin films has a composition consisting of boron (B) and carbon (C). A multilayer film characterized by: