JPH07248408A - Excimer laser mirror and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] The present invention is a method for efficiently manufacturing an excimer mirror having excellent excimer laser resistance by arc discharge type ion plating using plasma generated from a pressure gradient type plasma generating means. The purpose is to provide. [Structure] High refractive index material (Al with low absorption in the ultraviolet wavelength range)
Method for manufacturing a mirror for excimer laser having a multilayer structure in which a first layer made of ₂ O ₃ ) and a second layer made of a low-refractive index substance (SiO ₂ ) having a small absorption in the ultraviolet wavelength region are alternately laminated In the step of forming each of the first and second layers, the step of generating plasma by arc discharge in the first vacuum space set to a predetermined pressure, the vaporized materials (Al, Si) corresponding to the film to be formed. ) In a second vacuum space set at a pressure lower than that of the first vacuum space (8 × 10 ⁻⁴ Torr or less), the vaporized material installed in the second vacuum space. And irradiating the plasma with the plasma, and forming the first layer or the second layer while introducing a reaction gas (O ₂ ) in the _second vacuum space.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excimer laser mirror by arc discharge type ion plating, which uses plasma generated from a pressure gradient type plasma generating means, and a manufacturing (film forming) method thereof.

[0002]

2. Description of the Related Art Currently, photolithography is mainly used for processing VLSI devices. Super LS in recent years
As the degree of integration of I-devices increases year by year, development of a short wavelength ultraviolet exposure apparatus capable of processing finer patterns is being actively pursued. Some of these devices include excimer laser reflection mirrors that reflect the excimer laser efficiently (hereinafter referred to as excimer mirrors).
Alternatively, an excimer laser half mirror (hereinafter referred to as an excimer half mirror) having an arbitrary reflectance with respect to an excimer laser is used.

As a conventional excimer mirror, an aluminum (Al) film is generally used. Also,
There is also proposed an excimer mirror in which a protective film such as magnesium fluoride (MgF ₂ ) or lithium fluoride (LiF) is laminated on an Al film to improve durability. Further, an application for an excimer mirror which defines a material of a highly reflective dielectric multilayer film used as an Al protective film (Japanese Patent Laid-Open No. 63-2).
08801). Unlike these, there is also an excimer mirror in which the reflection wavelength region is specified to improve the reflectance. As an example thereof, a multilayer film is known in which dielectrics made of a high refractive index substance and dielectrics made of a low refractive index substance are alternately laminated. These are characterized in that an arbitrary reflection wavelength range and reflectance can be selected by changing the structure of the dielectric multilayer film.

Japanese Patent Laid-Open No. 55-45061 discloses a high-refractive-index dielectric layer (refractive index 1.9) having absorption in the ultraviolet wavelength region.
Above) and an ultraviolet multi-layer film in which an intermediate-refractive-index dielectric layer and a low-refractive-index dielectric layer (refractive index of 1.5 or less) that do not absorb in the ultraviolet wavelength range are laminated. Further, in recent years, the use of excimer half mirrors having an arbitrary reflectance is rapidly increasing. These mirrors are required to have characteristics such as little change in reflectance, change over time, environmental stability, and excimer laser resistance.

Various film forming methods are used for manufacturing these excimer mirrors, for example, a vacuum vapor deposition method and an ion beam sputtering method.

[0006]

An excimer mirror having a dielectric multilayer film has a reflection wavelength range depending on the number of layers of the multilayer film and the structure thereof.
You should be able to set the reflectivity, but in reality the absorption of the film,
It is difficult to obtain the desired reflection wavelength range and reflectance due to scattering and stress. In these excimer mirrors, reflectance at a specific wavelength is important, but wavelength shift and reflectance change have been a problem.

Impurities are likely to be mixed into the interface of the dielectric multilayer film during the film forming process. This impurity causes a problem that excimer laser durability (hereinafter referred to as excimer laser resistance) deteriorates. For example, in the vacuum vapor deposition method, since the evaporated material is deposited on the substrate without being ionized, the density of the formed film tends to be low, and it is difficult to obtain desired reflectance and excimer laser resistance. In addition, it is necessary to reduce the water content in the film in order to enhance the excimer laser resistance.
Must be heated to about ℃. Therefore, there is a problem that the thermal deformation of the substrate (lens or the like) on which the film is formed must be taken into consideration.

Since the ion beam sputtering method can form a high-density thin film, a thin film excellent in excimer laser resistance is easily formed. However, there is a problem that the film cannot be formed efficiently because the target is not used efficiently and the film forming speed is low. Further, in the conventional ion plating method, since the substrate is cleaned by plasma during film formation, a thin film having excellent adhesion can be easily formed without heating the substrate. However, it was still necessary to heat the substrate in order to achieve the desired environment resistance. Also, in this method low vacuum (relatively high pressure)
Since the film formation proceeds below, the formed thin film was liable to contain water, impurities, etc., so that the purity of the film was easily lowered. Therefore, there is also a problem that the formed thin film is inferior in excimer laser resistance.

As described above, it has been difficult to manufacture an excimer mirror having a desired wavelength range and reflectance by the conventional film forming method. The present invention has been made in view of such problems, and an object thereof is to efficiently manufacture (form a film) an excimer mirror having excellent excimer laser resistance.

[0010]

To achieve the above object, the present invention comprises a first layer made of a high-refractive-index substance having a small absorption in the ultraviolet wavelength region and a low-refractive-index substance having a small absorption in the ultraviolet wavelength region. In a method of manufacturing a multi-layer structure excimer laser mirror in which second layers are alternately laminated, in the forming process of each of the first and second layers, (a) a first pressure set to a predetermined pressure. The step of generating plasma by arc discharge in a vacuum space, (b) the vaporized material corresponding to the film to be formed,
Installing in a second vacuum space set to a pressure lower than the first vacuum space, and (c) irradiating the plasma to the vaporized material installed in the second vacuum space, A method for manufacturing an excimer laser mirror, comprising the step of forming the first layer or the second layer while introducing a reaction gas in the second vacuum space.
(Claim 1) In the manufacturing method according to claim 1, the first and second
When forming the layer of the
A method for manufacturing a mirror for an excimer laser, which is characterized in that it is set to 10 ^-4 Torr or less. (Claim 2) The evaporation material for forming the thin film of the high refractive index material is aluminum (Al), and the evaporation material for forming the thin film of the low refractive index material is silicon (Si), and the reaction gas Is oxygen (O ₂ ), The method for manufacturing an excimer laser mirror according to claim 1 or 2, (claim 3).

The high refractive index material is aluminum oxide,
An excimer laser mirror manufactured by the method for manufacturing an excimer laser mirror according to claim 3, wherein the low refractive index material is silicon oxide.

[0012]

[Function] The present inventors have found that "aluminum oxide (Al ₂ O ₃ )"
A layer having a multi-layer structure in which layers made of silicon oxide and layers made of silicon oxide (SiO ₂ ) are alternately laminated "to generate plasma by arc discharge in a first vacuum space set to a predetermined pressure. When the plasma is produced (deposited) by the arc discharge type ion plating method using the pressure gradient type plasma generating means for introducing the plasma into the second vacuum space set to a pressure lower than that of the first vacuum space, the excimer resistance is increased. The inventors have found that a mirror excellent in laser characteristics can be efficiently formed, and have completed the present invention.

The cause of this is that the density of the plasma generated in the second vacuum space by the pressure gradient type plasma generating means is high, and the position where the thin film is formed in the second vacuum space (the substrate is installed). It is conceivable that the ionization degree in the vicinity of the position () is high. In particular, by setting the pressure during film formation in the second vacuum space to 8 × 10 ⁻⁴ Torr or less, mixing of particles (particles other than the thin film constituents) into the film formed is suppressed. Therefore, the deposited aluminum oxide (Al
_It is considered that the density of a thin film of an oxide such as ₂ O ₃ ) has a value close to the density of the oxide in the bulk state (a film quality close to that of the desired oxide can be obtained).

In the excimer laser wavelength range, the high-refractive index material and the low-refractive index material, which have little absorption in the ultraviolet wavelength range, are used as the material forming the multilayer structure excimer mirror (hereinafter, simply referred to as “multilayer film”). This is because it is easy to set the reflectance of. In particular, the reason why aluminum oxide and silicon oxide are used is that since the refractive index of aluminum oxide and that of silicon oxide are close to each other in the excimer laser wavelength range, the change in reflectance due to the number of laminated layers is small, so increase the number of laminated layers. This makes it easy to finely adjust the reflectance. As described above, in the present invention, the pressure at the time of forming each oxide including aluminum oxide is set to 8 × 10 ⁻⁴ Torr or less, so that the mixing of impurities is suppressed and the oxides in the bulk state of these oxides are suppressed. The excimer laser resistance close to the property was obtained.

Further, in the present invention, since it is not necessary to heat the substrate during film formation, the material of the substrate on which the oxide is formed is not limited by heat resistance. Therefore, the range of selection of the substrate material is widened. In the present invention, during film formation, an inert gas such as argon (Ar) or helium (He) used as a discharge gas of the plasma generating means introduced from the first vacuum space and a reaction gas (O ₂ gas). Etc.) are introduced into the second vacuum space. Therefore, the pressure in the second vacuum space during the film formation is determined depending on the sum of the partial pressures of the discharge gas and the reaction gas.

Further, the film substance of the present invention is not limited to aluminum oxide and silicon oxide.
Thorium fluoride (ThF ₄ ), barium fluoride (BaF ₂ ), magnesium oxide (MgO ₂ ) and the like can be preferably used. Hereinafter, the present invention will be specifically described by way of examples with reference to the drawings, but the present invention is not limited thereto.

[0017]

FIG. 1 is a schematic configuration diagram of a thin film forming apparatus (arc discharge type ion plating apparatus) used for carrying out the present invention. Hereinafter, the thin film manufacturing method of the present invention will be described with reference to FIG. This thin film forming apparatus includes an evaporative substance holding means (also serving as an anode) 7 on which an evaporative substance is placed, a plasma focusing permanent magnet 8 installed immediately below the retaining means 7, and a rotatable substrate holder for supporting a substrate 12. 18, a film thickness monitor 17 composed of a crystal oscillator for measuring the film thickness of a thin film formed on the substrate 12, a shutter 15 for preventing evaporating particles from evaporates from reaching the substrate 12, and these constituent elements are installed. Stainless steel (SUS3
It is equipped with a vacuum container 6 made of 04). Further, a plasma generating means (electron gun) 50 for generating the plasma is attached to the vacuum container 6 in order to heat the evaporate with a plasma containing electrons. An air-core coil 14 for externally applying a magnetic field to the plasma is arranged at a connection portion between the plasma generating means 50 and the vacuum container 6. Also,
The substrate holder 18 and the bias power source 11 for setting the potential of the substrate 12 placed on the substrate holder 18 to be a negative potential with respect to the potential of the evaporation material holding means 7.

The evaporation holding means 7 has a water cooling mechanism (not shown) and also serves as an anode of the plasma generating means 50. Further, as described above, the bias power supply 11 is configured to have a higher potential than that of the substrate holder 18. The evaporation material holding means 7 is provided with a holding portion (not shown) composed of a plurality of recesses so that a plurality of kinds of evaporation materials can be placed, and the evaporation material in each recess is selectively irradiated with plasma. And a selection means (not shown) for rotating the holding portion. The selection means may be provided with a shielding means such as a cover so that plasma is not irradiated to the evaporated material on which film formation is not performed. The vacuum container 6 is provided with an exhaust means (not shown) for setting the inside of the container 6 to a desired pressure, and a reaction gas supply port 10. A reaction gas supply means (not shown) for introducing the reaction gas into the container 6 is connected to the reaction gas supply port 10. A plasma generating means 50 is installed on the wall surface of the container 6, and the plasma flow generated by the generating means 50 is introduced into the space inside the container 6.

The evacuation means is an oil diffusion pump having an exhaust port 9 provided in the vacuum container 6 and a trap connected to the exhaust port 9, an oil rotary pump, an auxiliary valve, and a roughing valve (both not shown). ) And the main valve 16 and the like. Further, the plasma generating means 50 of the present embodiment divides the space between the cathode and the anode into the cathode side and the anode side by disposing the intermediate electrodes 3 and 4 between the cathode part and the anode 7, and It is configured to generate plasma while maintaining the pressure on the side higher than that on the anode side. Therefore, for example, it is possible to generate plasma by setting the pressure on the cathode side to about 1 Torr and the pressure on the anode side to desired values of about 10 ^-1 to 10 ^-4 Torr. The plasma generating means having such a configuration is called a pressure gradient type plasma generating means. When this pressure gradient type plasma generating means is used, high vacuum (low pressure) is applied to the inside of the vacuum container 6 where the film is formed.
It is possible to carry out stable discharge for plasma generation while maintaining the temperature. Also, since there is almost no backflow of ions to the main cathode 2 due to the pressure difference, damage to the cathode due to collision of ions can be prevented, thermionic emission from the cathode is less likely to decrease, the life of the cathode is prolonged, and large current discharge occurs. It has advantages such as being possible. Furthermore, even if a reaction gas is introduced into the vacuum container 6, there is no possibility that this gas will enter the plasma generation chamber 51.

Here, a process of manufacturing (film forming) a half mirror for an excimer having a multi-layer structure using the thin film forming apparatus (arc discharge type ion plating apparatus) of this embodiment will be described. First, as the substrate 12, optically polished circular quartz glass having a diameter of 30 mm is prepared, and the substrate 12 is attached to the substrate holder 18. Then, aluminum (Al) and silicon (Si) are placed in the respective recesses of the evaporated material holding means 7 (also serving as the anode of the plasma generation means 50). After that, while adjusting the opening of the main valve 16, the pressure in the vacuum container 6 is set to 8 × 10 ⁻⁶ Torr by the exhaust means. In this state, a DC voltage of about 600 V is applied between the cathode section 51 and the anode (holding means) 7 by the main discharge electrode 5 to generate plasma. At this time, in the plasma generating means 50, the gas pressure in the region near the cathode part 51 (the first vacuum space) is about 1 Torr due to the introduction of the discharge gas (Ar) from the gas introduction port 1 of the cathode part 51. Maintained at. Also, the pressure in the region near the anode (holding means) 7 in the vacuum container 6 is set to about 2 × 10 −3 Torr by the exhaust means. Thereby, the plasma generating means 5
Arc discharge is generated in the vicinity of the cathode portion 51 of 0, and the discharge gas is turned into plasma. The generated plasma is extracted from the plasma generation chamber to the anode 7 side (inside the vacuum container 6) by the first intermediate electrode 3 and the second intermediate electrode 4. The plasma is converged into a cylindrical shape by the intermediate electrode and the air-core coil 14, and the plasma flow 13 forms the vacuum vessel 6
Be guided inside. The course can be changed by the magnetic field of the plasma focusing magnet 8 installed near the anode (holding means) 7. At this time, the exhaust means is controlled so that the opening of the main valve 16 is adjusted so that the pressure in the vacuum container 6 becomes 8 × 10 ⁻⁴ Torr. On the other hand, oxygen gas (O ₂ ) is introduced into the container 6 from the reaction gas supply port 10 at a desired flow rate (85 CC / min) by the reaction gas supply means to react with the substance (aluminum) evaporated from the evaporated material. . The opening of the main valve 16 is adjusted so that the pressure inside the container 6 is maintained at 8 × 10 ⁻⁴ Torr even after the introduction of the reaction gas. afterwards,
When the shutter 15 is opened, the evaporated material (aluminum)
The reaction gas (oxygen gas) is ionized by passing through the plasma and reaches the substrate 12. As a result, thin film aluminum oxide (Al ₂ O ₃ ) is formed on the surface of the substrate 12. During the formation of the thin film, the film thickness of the thin film and the film forming rate (evaporation rate) can be measured by the film thickness monitor 17, and therefore the film forming may be stopped when the predetermined film thickness is reached. Thus, one layer of the multilayer film is used as the substrate 12
Formed on.

Next, the other evaporated material (here, silicon)
By irradiating plasma to the layer, a layer made of silicon oxide (SiO ₂ ) is formed on the layer made of aluminum oxide (Al ₂ O ₃ ) in the same process. In this way, the aluminum and the silicon placed on the evaporation material holding means 7 are alternately irradiated with plasma, and 17 layers of aluminum oxide and 17 layers of silicon oxide are alternately laminated on the substrate 12. A multilayer film was manufactured (deposited). The film thickness of each layer of the multilayer film was set to be λ / 4 (λ = 248 nm in this embodiment), where λ is the wavelength of the light used. The film forming conditions of this example are shown below.

SiO ₂ Al ₂ O ₃ Arc discharge voltage 50 V 35 V Arc discharge current 50 A 25 A Evaporate Si Al Film formation rate 0.2 nm / sec 0.3 nm / sec Ultimate pressure (vacuum degree) in the vacuum vessel 8 × 10 ^{− 6} Torr Pressure (vacuum degree) in vacuum chamber during film formation 8 × 10 ⁻⁴ Torr Discharge gas Ar flow rate 20 SCCM (CC / min) Reaction gas O ₂ flow rate 85 SCCM (CC / min) Manufactured in this example ( The reflection, the change with time, and the excimer laser resistance of the multilayer film (half mirror) composed of the formed aluminum oxide layer and the silicon oxide layer were measured.

The reflectance was measured with a spectrophotometer at a wavelength of 248 nm. The change with time was measured by measuring the change in reflectance at a wavelength of 248 nm for one month immediately after film formation. The wavelength of the laser used to measure excimer laser resistance is 248n.
m, pulse width 30 ns. The excimer laser resistance was evaluated by using the above laser until irradiation energy was gradually increased until the multilayer mirror was damaged, and the maximum irradiation energy at which damage was not generated was determined.

FIG. 2 is a graph showing the spectral reflectance of the multilayer film (half mirror) manufactured in this example. As is clear from the figure, the reflectance is 80% at the design wavelength (248 nm).
Met. Multilayer film (half mirror) obtained in this example
No change in reflectance with time was observed at all, and no damage was observed in excimer laser resistance up to an irradiation energy of 7.1 J / cm 2.

[Comparative Example] Using an electron gun heating type vacuum vapor deposition apparatus that heats an evaporated material with an electron gun, the following film forming conditions were set, and a layer made of aluminum oxide and an oxide film were formed on the same substrate as in the example. A multilayer film was manufactured (formed) by alternately stacking 17 layers each made of silicon. Ultimate pressure (vacuum degree) in the vacuum container: 5 × 10 ^-6 Torr Pressure (vacuum degree) in the vacuum container during film formation: 5 × 10 ^-5 Torr Evaporated substances: SiO ₂ , Al ₂
O ₃ substrate temperature: 320 ° C. Film formation rate: 0.2 nm / sec For a multilayer film composed of a layer made of aluminum oxide and a layer made of silicon oxide manufactured (formed) in this comparative example,
The reflectance, the change with time, and the excimer laser resistance were measured in the same manner as in the examples.

The reflectance of the multilayer film obtained in this comparative example was 80% (248 nm), which is the same as that in the example. The multilayer film (half mirror) obtained in this comparative example is ± 3.0% in one month.
Was observed over time. With respect to excimer laser resistance, damage was confirmed at an irradiation energy of 3.0 J / cm 2.

[0027]

As described above, according to the present invention, since a high density film containing few impurities can be formed, a multilayer film having excellent excimer laser resistance can be efficiently manufactured (film formed). Further, since it is not necessary to heat the substrate during film formation, the multilayer film can be formed even on the substrate made of a material weak against heat.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a thin film forming apparatus (arc discharge type ion plating apparatus) used in an embodiment of the present invention.

FIG. 2 is a graph showing the spectral reflectance of an excimer half mirror manufactured according to an embodiment of the present invention.

[Explanation of symbols]

 1 Gas Inlet 2 Main Cathode 3 First Intermediate Electrode 4 Second Intermediate Electrode 5 Main Discharge Electrode 6 Vacuum Container 7 Evaporation Retaining Means (Also Anode) 8 Plasma Focusing Permanent Magnet 9 Exhaust Port 10 Reactive Gas Supply Port 11 Bias power supply 12 Substrate 14 Air-core coil 15 Shutter 16 Main valve 17 Film thickness monitor 18 Substrate holder 50 Plasma generation means (electron gun) 51 Plasma generation chamber Above

Claims (4)

[Claims] 1. A multilayer structure in which a first layer made of a high refractive index substance having a small absorption in the ultraviolet wavelength region and a second layer made of a low refractive index substance having a small absorption in the ultraviolet wavelength region are alternately laminated. In the method of manufacturing a mirror for excimer laser, the step of forming each of the first and second layers includes: (a) generating plasma by arc discharge in a first vacuum space set to a predetermined pressure; (B) a step of installing an evaporated material corresponding to the film to be formed in a second vacuum space whose pressure is lower than that of the first vacuum space; (c) the second
Irradiating the plasma to the evaporate placed in the vacuum space, and forming the first layer or the second layer while introducing a reaction gas in the second vacuum space. A method for manufacturing an excimer laser mirror, comprising: 2. The manufacturing method according to claim 1, wherein the pressure of the second vacuum space is set to 8 × 10 ⁻⁴ Torr or less when the first or second layer is formed. And a method for manufacturing an excimer laser mirror. 3. The evaporation gas for forming the thin film of the high refractive index material is aluminum (Al), the evaporation material for forming the thin film of the low refractive index material is silicon (Si), and the reaction gas There the oxygen (O ₂₎ according to claim 1 or 2 excimer method for producing laser mirrors according to, characterized in that. 4. The excimer laser mirror manufactured by the method for manufacturing an excimer laser mirror according to claim 3, wherein the high refractive index material is aluminum oxide and the low refractive index material is silicon oxide. .