JPH06167599A - Production method for multilayer film mirror for x-ray - Google Patents

Abstract

PURPOSE:To produce a multilayer film mirror for X-ray which is superior in heat resistance and has a high reflectivity. CONSTITUTION:A multilayer film consisting of molybdenum and silicon oxide is produced with a microwave magnetron spatter method by setting one of the following conditions. The gap between a base plate 4 and a target 1 is 100 to 200mm, argon gas pressure is 1 to 5mTorr, electric power per unit area impressing to the target 1 is 1.7 to 2.8W/cm<2>, the temperature of the base plate 4 is below 100 deg.C and the electric power is impressed to each target continuously. Each target of 1a, 1b is placed in a sputtering space and shutters 3a, 3b are provided, which other one is closed when one layer is formed. The base plate 4 is passed at a constant velocity in the region sputter atoms fly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a multilayer mirror used in the X-ray wavelength range.

[0002]

2. Description of the Related Art A multilayer film mirror for X-rays has an artificial periodic structure in which a substance having a large scattering for X-rays and a substance having a small scattering for X-rays are alternately laminated. Then, the cycle length of the multilayer film is d, X
When the oblique incidence angle of the rays is θ and the wavelength of the X-rays is λ, the X-rays are reflected when the Bragg's conditional expression 2d sin θ = nλ (n: integer) is satisfied.

A multilayer film made of a combination of molybdenum and silicon (Si) (hereinafter abbreviated as “molybdenum / silicon multilayer film”) exhibits a high reflectance on the long wavelength side of the L absorption edge (123 Å) of silicon. , Is important as a multilayer mirror used in an X-ray reduction projection exposure apparatus using a direct incidence optical system. X like this
The multilayer film used as the line mirror is formed by various thin film forming techniques such as vacuum deposition, sputtering and CVD. It is generally known that a multilayer film having a relatively high reflectance is formed by a magnetron sputtering method which is a kind of sputtering.

By the way, when the multi-layered film mirror is irradiated with light having high intensity such as synchrotron radiation, the surface is locally heated. For example, a mirror used in an illumination optical system of an X-ray reduction projection exposure apparatus is irradiated with light emitted from a light source with almost no reduction in its intensity.
In addition, in the reflective mask in which the reflective portion is formed of a multilayer film, the condensed light is irradiated. In such a case, the surface of the multilayer film may reach a high temperature of several hundreds of degrees. Therefore, heat resistance is required in the multilayer film for light with high intensity. Since the molybdenum / silicon multilayer film has low heat resistance, when it is heated, diffusion occurs between substances forming each layer. As a result, the molybdenum layer is silicidized, or a silicide interface layer is formed at the interface between molybdenum and silicon, and the multilayer film does not satisfy the Bragg's conditional expression, and the reflectance is significantly reduced. In order to improve the heat resistance of the multi-layer film, the material forming the multi-layer film is changed to one that is chemically stable even at high temperature, or the combination of two kinds of substances is changed to one that does not cause diffusion. There is. Conventionally, a multilayer film of a combination of molybdenum and silicon carbide (hereinafter abbreviated as “multilayer film of molybdenum / silicon carbide”) has been used as a multilayer film satisfying these conditions. Since silicon carbide has a higher melting point than silicon and is a chemically stable compound, mutual diffusion with molybdenum hardly occurs even when heated.

[0005]

However, molybdenum /
The multilayer film of silicon carbide has a problem of low reflectance. For example, the theoretical value of the reflectance when X-rays having a wavelength of about 130 Å is vertically incident is about 60% for a molybdenum / silicon carbide multilayer film. This value is the molybdenum /
It is smaller than the theoretical value (about 75%) obtained in the same manner for a silicon multilayer film. In a molybdenum / silicon multilayer film that was actually manufactured, the reflectance was less than the theoretical value due to the instability of the interface and the formation of silicide, but about 50% was obtained (for example, J.Vac.Sci.Technol.B7 (6), 1989, p1702). On the other hand, the actually produced multilayer film of molybdenum / silicon carbide can obtain a reflectance of about 30%, which is about half the theoretical value.

If the reflectance is low, it is necessary to lengthen the irradiation time in order to obtain the desired X-ray intensity, which greatly affects the characteristics of the device using the multilayer mirror. For example, in an exposure apparatus or the like, there arises a problem that the exposure time becomes long and the throughput decreases. Particularly, in the X-ray reduction projection exposure apparatus, many multi-layer film mirrors are required to form the illumination optical system and the imaging optical system of the mask. Considering an optical system composed of n multi-layer film mirrors each having a reflectance of R, the reflectance of the entire optical system is R ⁿ . If the reflectance of one multilayer film mirror can be increased by ΔR,
The reflectance of the entire optical system is (R + ΔR) ^{n to} R ⁿ (1 + nΔ)
R / R). Therefore, if the reflectance of each multilayer mirror can be increased by 2%, the reflectance of the entire optical system composed of five multilayer mirrors is improved by 10%. From this, it can be seen that improving the reflectance of the multilayer mirror even a little affects the efficiency of the entire optical system.

For the above reasons, there has been a demand for a multilayer mirror having a higher heat resistance and a higher reflectance than ever before. The present invention aims to meet such a need.

[0008]

[Means for Solving the Problems] As a result of intensive studies conducted by the present inventors for the above purpose, an X having a multilayer film in which molybdenum layers and silicon carbide layers are alternately laminated.
In the method for manufacturing a multilayer mirror for wires, by forming each of the layers by a high frequency magnetron sputtering method and setting any one of the following conditions (a) to (g) at the time of forming by the high frequency magnetron sputtering method, It has been found that a multilayer mirror having excellent heat resistance and high reflectance can be manufactured. (A) The distance between the substrate on which the multilayer film is formed and the target is set within a range of 100 to 200 mm (claim 1). (B) The argon gas pressure is set within the range of 1 to 5 mTorr (Claim 2). (C) The high frequency power applied to the target is set in the range of 1.7 to 2.8 W / cm ² per unit area of the target (claim 3). (D) The temperature of the substrate on which the multilayer film is formed is room temperature to 1
Maintaining a temperature below 00 ° C (claim 4). (E) The high frequency power is continuously applied to the target made of molybdenum or silicon carbide during the formation of the multilayer film (claim 5). (F) A target made of molybdenum and silicon carbide is placed in a space for sputtering, and a shutter is provided in front of each target. When a layer of one target material is formed, the shutter of the target of the material is opened and the other is opened. Closing the shutter (claim 6). (G) Forming each of the layers by passing the substrate on which the multilayer film is formed at a constant speed in a region where sputtered atoms come in front of the target, facing the target (claim 7). .

Incidentally, these conditions (a) to (g) may be set only one, or may be set in combination.

[0010]

[Function] When forming a multilayer film by the magnetron sputtering method, it is generally known that a multilayer film having a high reflectance can be obtained by lowering the pressure of the argon gas introduced into the space for sputtering (JJAP29 (3), 1990, P56
9). Also, when the cross section of the multilayer film is observed by a transmission electron microscope, it is clearly observed that the flat interface without waviness is formed when the argon gas pressure is lowered.

In film formation by sputtering, argon atoms are always incident on the surface of the substrate. The argon atom physically adsorbs for a certain period of time, stays on the substrate surface, and then desorbs. On the other hand, sputtered atoms (target material) incident on the surface of the substrate move on this surface and settle at a stable position, but if there are argon atoms adsorbed on the surface, this movement is hindered. Therefore, when the argon gas pressure is reduced to reduce the number of argon atoms incident on the surface of the substrate, the surface mobility of sputter atoms increases and a flat thin film (layer) grows.

The effect of lowering the argon gas pressure in the production of a multilayer film by sputtering can be explained as above. However, the pressure of the argon gas cannot be reduced as much as possible, and is limited to the value required to maintain the discharge. Then, in the present invention, the argon pressure is within the range of 1 to 5 mTorr. Note that high-frequency sputtering in which a high-frequency voltage is applied can maintain discharge at a lower pressure than DC sputtering in which a direct-current voltage is applied.
Therefore, it is advantageous to manufacture a multilayer film mirror for X-ray in which the pressure in the sputtering space is preferably low.

Since the magnetron sputtering apparatus is characterized by high-speed film formation, it is usually designed by making the space between the target and the substrate on which the multilayer film is formed as small as possible so that the loss due to collision scattering in the sputtering space becomes small. Has been done. Therefore, the distance is generally set to 5 to 10 cm. When the inventors conducted a film forming experiment of a molybdenum / silicon carbide multilayer film using the distance between the target and the substrate as a parameter, the distance between the target and the substrate was 5
At ~ 10 cm, the X-ray reflectance was low because the molybdenum layer and the silicon carbide layer were mixed together. On the other hand, when the distance was increased and set within the range of 10 to 20 cm, the intermixing between the layers became limited only near the interface, and the X-ray reflectance was significantly improved.

Mixing between the layers of such a multilayer film causes a large amount of kinetic energy when sputter atoms, particularly molybdenum atoms, which are heavy elements, enter the substrate, and thus violently collides with the surface of the growing multilayer film. It is thought that this is due to The high X-ray reflectance obtained in the present invention is that the frequency of collision between sputter atoms and argon atoms increases as the distance between the target and the substrate increases, and the movement of the sputter atoms incident on the substrate increases. It is considered that the energy was moderately attenuated.

By the way, even if the gas pressure is increased instead of increasing the distance between the target and the substrate, the effect of increasing the frequency of collision between sputtered atoms and argon atoms can be obtained. However, in that case, as described above, the effect of hindering the surface movement of the sputtered atoms by the argon atoms adsorbed on the substrate surface becomes large, and the flat interface is not formed.

As described above, the present invention can reduce the effect that the argon atoms adsorbed on the substrate surface hinder the surface movement of sputtered atoms by lowering the argon gas pressure. Further, by making the distance between the target and the substrate relatively large and lowering the kinetic energy when the sputtered atoms are incident on the substrate due to the collision with the argon atoms, it is possible to prevent mixing due to the collision. As a result of these, it becomes possible to manufacture a multilayer film having a high reflectance for X-rays.

The high-frequency power applied to the target is 1.7-2. 7 by experiments so that the sputtered atoms have an appropriate kinetic energy and an appropriate deposition rate can be obtained.
A value of 8 W / cm ² was obtained and set within this range. This corresponds to an applied power of 300-500 W for a 6 inch diameter target. Also, if the substrate temperature during film formation is high,
In addition to promoting mutual diffusion between the layers of the multilayer film, the mobility of sputtered atoms on the substrate surface becomes too large, and fine crystal grains larger than the layer thickness grow, impairing the flatness of the interface. In order to prevent this, the substrate temperature at the time of forming each layer was kept from room temperature to 100 ° C. or lower.

The present invention will be described in more detail below with reference to examples.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of a parallel plate type high frequency magnetron sputtering apparatus used in the method for manufacturing an X-ray multilayer mirror of the present invention. This apparatus includes a molybdenum target 1a, a silicon carbide target 1b, high-frequency power supplies 2a and 2b for supplying individually controlled high-frequency power to the respective targets, shutters 3a and 3b individually provided to the targets, And a substrate holder 5 having a mechanism (not shown) for holding and rotating the substrate 4.
Is equipped with. The substrate holder 5 is rotatable at a constant rotation speed. Each target has a diameter of 6 inches, and the distance d between the substrate and each target is 130 mm. It should be noted that the partition plate 6 is provided so that sputtered atoms of molybdenum and silicon carbide do not mix between the two targets.
Is provided.

The molybdenum / silicon carbide multilayer film was manufactured by the following procedure. First, a cleaned (100) silicon wafer was used as a substrate and attached to the substrate holder 5. Then, after exhausting to a pressure of 5 × 10 ⁻⁷ Torr or less, the flow rate was controlled by a mass flow controller to introduce argon gas into the apparatus. (The exhaust system and the gas introduction system are not shown.) At this time, the pressure of the argon gas is 3 mTorr.
And Before forming each layer, the shutters 3a, 3b
While both were closed, high frequency power was applied to each target to perform pre-sputtering for 30 minutes. This pre-sputtering is a process for stabilizing the discharge and removing the dirty portion on the surface of the target. The high frequency power was 300 W applied to any target. The high frequency power was applied to the target continuously without interruption until the formation of the multilayer film was completed. This makes it possible to stabilize the discharge state and prevent fluctuations in the film formation rate during the formation of the multilayer film.

After the pre-sputtering, a multilayer film is formed. At this time, the substrate holder 5 is rotated at a speed of 3.7 rpm. Then, first, the shutter 3a of the molybdenum target 1a was opened while the shutter 3b of the silicon carbide target 1b was closed. Then, the substrate holder 5 was rotated 6 times to form a film during this period, and a molybdenum layer having a thickness of 35 Å was formed. Next, the shutter 3a is closed and the silicon carbide target 1
The shutter 3b of b is opened. Then, the substrate holder 5 is set to 19
During rotation, film formation was performed during this period to form a silicon carbide layer having a thickness of 38Å. By repeating the above operation 50 times, a molybdenum / silicon carbide multilayer film having a period length d = 73Å and a stacking number N = 50 was produced.

When changing the cycle length of the multilayer film and the thickness of each layer, the rotation speed of the substrate holder 5 and the high frequency power applied to each target may be adjusted. In this embodiment, each layer of the multilayer film is formed in a plurality of rotations without being formed in one rotation in order to improve the controllability of the film thickness and prevent the substrate temperature from rising. . In this embodiment, the substrate temperature during film formation is not particularly controlled,
The rise in substrate temperature was less than about 50 ° C. Although the apparatus becomes complicated, the temperature control may be performed by attaching a substrate cooling mechanism. Further, although the parallel plate type high frequency magnetron sputtering apparatus is used in the present embodiment, the same effect can be obtained by using another type of apparatus, for example, a carrousel type high frequency magnetron sputtering apparatus as shown in FIG. It is possible to play.

For the multilayer mirror for X-ray having the multilayer film of molybdenum / silicon carbide manufactured in this way, S
X-ray reflectance measurement using polarized light was performed. FIG. 3 shows the measurement result. The horizontal axis of the graph represents wavelength and the vertical axis represents reflectance. When measured at an angle of incidence of 30 ° from the normal, it showed a high reflectance of over 55% at a wavelength of about 130Å. From these results and calculation simulation, it was found that the molybdenum / silicon carbide multilayer film according to the present invention has an unprecedented high reflectance of about 50% or more in this wavelength range even when X-rays are vertically incident. .

When the X-ray multilayer mirror was heated in a vacuum at 400 ° C. for 1 hour and then the reflectance was measured in the same manner, no decrease in reflectance was observed. Furthermore, no change was observed in the reflection wavelength or the half-value width of the peak, and no change in the structure such as a change in the cycle length was observed. on the other hand,
When a multilayer mirror having a molybdenum / silicon multilayer film is heated in the same manner, its reflectance is about 90 at 200 ° C compared to before heating.
% At 400 ° C. to about 5%.

[0025]

As described above, according to the present invention, it is possible to provide a multilayer film mirror for X-rays, which has a molybdenum / silicon carbide multilayer film which is superior in heat resistance and has a higher reflectance than ever before. Such a multi-layer film mirror for X-ray is heated to a high temperature such as a multi-layer film mirror used for vertical incidence in an X-ray reduction projection exposure device, an illumination optical system in an X-ray reduction projection exposure device, or a reflective mask. It can be used as a multilayer film (mirror) as described above. Further, since the reflectance is higher than that of the conventional mirror, the exposure time can be shortened. Therefore, the throughput of the exposure apparatus and the like can be improved.

The present invention can be carried out without making major changes to the conventional commercially available high-frequency magnetron sputtering apparatus, such as setting the argon gas pressure when forming a multilayer film and setting the distance between the substrate and the target. It has the advantage of being able to. The multilayer mirror for X-ray is X
Not limited to use in line-reduction projection exposure, it can be used for all X
It goes without saying that it can be applied to the use of the multilayer mirror for lines such as an X-ray microscope, an X-ray telescope, and an X-ray laser.

Further, in the present invention, one of the reasons why the mixing of the interfaces between the layers of the multilayer film can be reduced is that the kinetic energy of sputter atoms, especially molybdenum atoms, can be adjusted to an appropriate value. Therefore, the present invention can be applied not only to a multilayer film of a combination of molybdenum and silicon carbide, but also to a multilayer film of a combination of molybdenum and another light element (eg, silicon oxide, silicon nitride, boron carbide). Is.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a parallel plate type high frequency magnetron sputtering apparatus used in an example of a method for producing a multilayer film according to the present invention.

FIG. 2 is a schematic configuration diagram of a carousel type high frequency magnetron sputtering apparatus which is another embodiment of the method for producing a multilayer film according to the present invention.

FIG. 3 is a measurement result of X-ray reflectance by synchrotron radiation of a molybdenum / silicon carbide multilayer film manufactured by the manufacturing method of the present invention.

[Explanation of symbols for main parts]

 1a Molybdenum target 1b Silicon carbide target 2a High frequency power supply 2b High frequency power supply 3a Shutter 3b Shutter 4 Substrate 5 Substrate holder 6 Partition plate

Claims (7)

[Claims] 1. A method for manufacturing a multilayer film mirror for X-rays, which has a multilayer film in which layers made of molybdenum and layers made of silicon carbide are alternately laminated, wherein each of the layers is formed by a high frequency magnetron sputtering method and at the time of forming the layers. X is characterized in that the distance between the substrate on which the multilayer film is formed and the target is set in the range of 100 to 200 mm.
Method for manufacturing multilayer mirror for wire. 2. A method for manufacturing a multilayer film mirror for X-rays, which has a multilayer film in which layers made of molybdenum and layers made of silicon carbide are alternately laminated, wherein each layer is formed by a high frequency magnetron sputtering method, and A method for manufacturing a multilayer film mirror for X-rays, wherein the argon gas pressure is set within a range of 1 to 5 mTorr. 3. A method of manufacturing a multilayer film mirror for X-rays, which has a multilayer film in which layers made of molybdenum and layers made of silicon carbide are alternately laminated, wherein each layer is formed by a high frequency magnetron sputtering method, and A method of manufacturing a multilayer film mirror for X-rays, wherein the high frequency power applied to the target is set in the range of 1.7 to 2.8 W / cm ² per unit area of the target. 4. A method for manufacturing a multilayer film mirror for X-rays, which has a multilayer film in which layers made of molybdenum and layers made of silicon carbide are alternately laminated, wherein each layer is formed by a high frequency magnetron sputtering method, and The temperature of the substrate on which the multilayer film is formed is room temperature or
A method for producing a multilayer mirror for X-rays, characterized by maintaining the temperature below 100 ° C. 5. A method for manufacturing a multilayer film mirror for X-rays, which has a multilayer film in which layers made of molybdenum and layers made of silicon carbide are alternately laminated, wherein each layer is formed by a high frequency magnetron sputtering method and at the time of formation. A method for producing a multilayer film mirror for X-rays, wherein high frequency power is continuously applied to the target made of molybdenum or silicon carbide during the formation of the multilayer film. 6. A method of manufacturing a multilayer mirror for X-rays, which has a multilayer film in which a layer made of molybdenum and a layer made of silicon carbide are alternately laminated, wherein each layer is formed by a high frequency magnetron sputtering method, and sputtering is performed. A target made of molybdenum and silicon carbide is installed in the space to be operated, and a shutter is provided in front of each target. When forming a layer of one target material, open the shutter of the target of that material and close the other shutter. A method for manufacturing an X-ray multilayer mirror, comprising: 7. A method of manufacturing a multilayer film mirror for X-rays, which has a multilayer film in which layers made of molybdenum and layers made of silicon carbide are alternately laminated, wherein each of the layers is formed by a high frequency magnetron sputtering method. A multilayer film mirror for X-rays, characterized in that each layer is formed by passing a substrate on which a film is to be formed, in front of a target, in a region where sputtered atoms fly, facing the target at a constant speed. Manufacturing method.