JPH06128731A - Production of thin-film oxide - Google Patents

Abstract

PURPOSE:To efficiently form a thin-film oxide at the time of vapor-depositing an oxide on a substrate by ion plating by utilizing an arc discharge-type ion plating device having a pressure-gradient plasma producing means. CONSTITUTION:A vessel 6 having a rotary holder 18 as a cathode to which a specularly polished quartz glass substrate 12 is fixed and a vapor-deposition source holding means 7 as an anode contg. Si is evacuated to about 5X10<-4>Torr. An inert gas such as Ar as a discharge gas and a gaseous O2 reactant are supplied from a gas inlet 1 in the cathode part of an electron gun 50 as a plasma producing means, a plasma producing space 51 is controlled to about 1Torr, an Ar plasma current 13 is developed by the arc discharge of the electron gun 50, Si is irradiated with the current through a plasma converging magnet 8 and vaporized, and an SiO2 film is formed on the substrate 12 by the reaction with the gaseous O2. The pressure in the vessel 6 is held lower than that in the space 51 to efficiently form the SiO2 film on the substrate 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing (depositing) a thin film oxide using arc discharge type ion plating using plasma generated by a pressure gradient type plasma generating means.

[0002]

2. Description of the Related Art Conventionally, when manufacturing (forming) an optical thin film such as an antireflection film or a reflection increasing film, the thin film is formed by vacuum vapor deposition. In this vacuum vapor deposition, a vapor deposition source is heated in a vacuum to adsorb (deposit) vaporized molecules on a substrate to form a film. Further, in order to obtain a higher quality optical thin film (having excellent durability and optical characteristics), an ion plating method in which vapor deposition is performed in a plasma atmosphere is sometimes used. This method is a type of vacuum deposition,
Atoms evaporated from the vapor deposition source are ionized to generate plasma, and an electric field is applied to cause the ions to collide with the substrate to form a film on the substrate. There are several types of this ion plating method depending on the plasma generation method and the configuration of the evaporation source. For example, a high-frequency ion plating method that improves the properties of the thin film by applying a high-frequency excitation voltage in a vacuum container to cause glow discharge, or a hollow cathode ion that causes a hollow discharge by introducing a hollow cathode into the chamber. The plating method and the like are known.

Further, as another thin film manufacturing method, there is a case where a sputtering method is used in which ions are made to collide with a target to form a film by using a sputtering action of a target material generated thereby. As this sputtering method, a magnetron type sputtering method in which an electric field and a magnetic field are applied so as to be orthogonal to each other is known.

[0004]

However, according to the conventional method, an optical thin film (for example, silicon oxide (SiO ₂ )) having good durability is used.
And a titanium oxide (TiO ₂ ) thin film) could not be formed efficiently. For example, in vacuum deposition,
When the resistance heating or the electron beam heating method is used as the heating method of the vapor deposition source, the film formation under high vacuum (low pressure) is possible, but the film formation speed becomes slow. Further, since the vapor deposition material is not ionized, the formed film is likely to have a low density. Furthermore, in order to reduce the moisture contained in the formed thin film and improve the durability, the substrate is not
Must be heated to ~ 300 ° C. Therefore, heat resistance is required for the material of the substrate on which the thin film is formed, and the usable material is limited.

In the ion plating method, since the substrate is cleaned by plasma, it is easy to form a thin film having excellent adhesion without heating the substrate. However, when forming a high quality thin film as described above, it was necessary to heat the substrate. Further, in this method, since the film formation proceeds under a low vacuum (relatively high pressure), the formed thin film contains water, impurities, etc., and the purity of the thin film becomes low, resulting in poor environment resistance. . There is also a problem that the characteristics of the thin film are likely to change in the atmosphere. Further, since the pressure is high, there is a problem that the film forming rate (film forming rate) of the thin film is slower than that of the vacuum evaporation.

Since the magnetron type sputtering method can form a thin film having a relatively high density, a thin film having excellent durability can be obtained. However, since the use efficiency of the target is low and the film formation rate is slow, it was not possible to form a film with high efficiency. The present invention aims to solve such problems.

[0007]

To achieve the above object, in the present invention, plasma is generated by arc discharge in a first vacuum space set to a predetermined pressure, and the plasma is generated in the first vacuum space. Method for producing thin film oxide by arc discharge type ion plating in which film deposition is performed in the second vacuum space by irradiating a vapor deposition source installed in the second vacuum space set to a lower pressure In, the pressure during film formation in the second vacuum space was set to 5 × 10 ⁻⁴ Torr or less.

[0008]

According to the research conducted by the present inventors, plasma is generated by arc discharge in the first vacuum space set to a predetermined pressure, and the plasma is set to a pressure lower than that of the first vacuum space. In producing a thin film oxide by arc discharge type ion plating using a pressure gradient type plasma generating means introduced into the second vacuum space, the pressure during film formation in the second vacuum space is set to 5 It was found that a thin-film oxide having a good efficiency and a good durability was formed by setting it to be not more than × 10 ^-4 Torr. This is because the density of the plasma generated in the second vacuum space by the plasma generating means is high, and the ionization degree near the position where the thin film is formed (the position where the substrate is installed) in the second vacuum space is high. It is thought to be due to the high price. In addition, since the second vacuum space has a high vacuum, the inclusion of impurities (particles other than the thin film constituents) in the film of the thin film oxide to be formed is suppressed, and the thin film oxide is desired. It is thought that this is because the oxide has a value close to the bulk density of the oxide (which provides a film quality close to that of the desired oxide).

Further, according to the present invention, since it is not necessary to heat the substrate during film formation, the material of the substrate on which the thin film oxide is formed is not limited by heat resistance. Therefore, the range of selection of the substrate material is widened. During the film formation of the present invention, an inert gas such as Ar or He used as a discharge gas of the plasma generating means introduced from the first vacuum space,
A reaction gas (O ₂ gas or the like) is 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.

As the vapor deposition source, silicon (Si) or titanium (T
A simple substance such as i) can be used. Then, by reacting the particles evaporated from these evaporation sources with the reaction gas (O ₂ ), a thin film of silicon oxide (SiO ₂ ) or titanium oxide (TiO ₂ ) can be manufactured.

[0011]

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 ion plating method of the present invention will be described with reference to FIG. This thin film forming device
A vapor deposition source holding means 7 for mounting a vapor deposition source, a plasma focusing permanent magnet 8 installed in the vicinity of this holding means 7, a rotatable substrate holder 18 for supporting the substrate 12, and a thin film formed on the substrate 12. A film thickness monitor 17 made of a quartz oscillator for measuring the thickness, a shutter 15 for preventing vaporized particles from the vapor deposition source from reaching the substrate 12, and a stainless steel (SUS304) for vacuumizing the space in which these constituent elements are installed. And a vacuum container 6 made of metal. Further, a plasma generating means (electron gun) 50 for generating plasma containing electrons for heating the vapor deposition source attached to the vacuum container 6 and a plasma arranged at a connecting portion between the generating means 50 and the vacuum container 6 Bias power supply 11 for setting the air-core coil 14 for applying a magnetic field from the outside, the substrate holder 18 and the substrate 12 mounted thereon to have a negative potential with respect to the potential of the vapor deposition source holding means 7. And are equipped with.

The vapor deposition source 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 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 exhaust means is an oil diffusion pump provided with an exhaust port 9 provided in the vacuum container 6 and a trap connected to the exhaust port 6, an oil rotary pump, an auxiliary valve, and a roughing valve (both not shown). ) And the main valve 16 and the like. FIG. 2 is a schematic configuration diagram of the plasma generating means 50 of the thin film forming apparatus used in this embodiment. As the plasma generating means 50, a pressure gradient type plasma generating device using a composite cathode as described in "Vacuum No. 25, Vol. 10" was used.

The plasma generating means 50 has a cathode portion arranged at one end, a quartz tube 22, a first intermediate electrode 3 having a ring-shaped permanent magnet 52 built therein, and a second air core coil 53 having a second air core coil 53 built therein. It has an intermediate electrode 4, an insulating ring 26 made of Teflon, an anode 7 also serving as a vapor deposition source holding means (see FIG. 1), and a main discharge power source 5 (see FIG. 1). The permanent magnet 52 and the second air-core coil 53 are provided with a cooling means (such as a cooling water channel) not shown in the figure to prevent excessive heating.

Both the intermediate electrodes 3 and 4 are formed in a ring shape, and a space connected to the vacuum container 6 is formed by the intermediate electrodes 3 and 4, the insulating ring 26 and the quartz tube 22. Of this space, a space inside the quartz tube 22 which is in contact with the cathode portion is defined as a plasma generation chamber (first vacuum space) 51. The plasma generating means 50 and the vacuum container 6 are connected by fixing the first intermediate electrode 3, the second intermediate electrode 4, and the flange 27 provided on the vacuum container 6 with intermediate electrode mounting bolts 29. . An insulating coating is formed on the mounting bolt 29 to prevent a short circuit.

The insulating ring 26 is arranged between the first intermediate electrode 3 and the second intermediate electrode 4 and between the second intermediate electrode 4 and the flange 27 via O-rings 28, respectively. In addition, the cathode part, the quartz tube 22, and the quartz tube 2
An O-ring 28 is also arranged at a connecting portion between the second intermediate electrode 3 and the second intermediate electrode 3. As a result, the plasma generation chamber 51 can be maintained in a sealed state.

The cathode part protects the pipe-shaped auxiliary cathode 23 made of Ta (tantalum) having a small heat capacity, the disc-shaped main cathode 2 made of LaB ₆ (lanthanum hexaboride), and both cathodes from plasma. A disk-shaped cathode protection plate 25 made of W (tungsten), a cylinder (cathode tube) 24 made of Mo (molybdenum) for housing both cathodes, and a cooling means (cooling water channel) 21. It is supported. The auxiliary cathode 23 is connected to the gas inlet 1.

Here, the discharge by the plasma generating means 50
Explain the process. Discharge gas from the gas inlet 1 of the cathode part
Ar gas is introduced as a carrier (carrier gas) so that it is close to the cathode.
The gas pressure in the side area (the first vacuum space) is set to about 1 Torr
maintain. On the other hand, by the exhaust means,
The pressure in the region near the anode (deposition source holding means) 7 is 2 × 10. ^-3
Set it to about Torr. And in this state
600 V between the cathode part and the anode 7 by the discharge power source 5
The subsequent DC voltage is applied. With this, first, the auxiliary cathode
Glow discharge (1 A or less) is generated at the tip of 23. This
Of the auxiliary cathode 23 by the glow discharge (initial discharge) of
Edge heated by ionization of Ar gas by collision of countercurrent ions
To be done. As a result, the tip of the auxiliary cathode 23 emits thermoelectrons.
The discharge voltage gradually decreases and the discharge current increases.
Add The tip of the auxiliary cathode 23 is heated to 2000 ° C or higher.
And the discharge voltage is around 70V and the discharge current reaches over 30A.
It becomes possible. After 2-3 minutes in this state, the auxiliary shadow
The main cathode 2 is indirectly heated to about 1700 ° C by the radiation heat at the tip of the pole 23.
Is heated. A large amount of heat is generated from the heated main cathode 2.
Since the electron emission occurs, the main cathode 2 is not discharged.
To function as a cathode. At this point, discharge
Arc discharge (up to about 250 A), and the auxiliary cathode 23
The temperature will drop. Therefore, the heat of the auxiliary cathode 23
Damage (wear) caused by this is avoided.

The reason why the main cathode 2 is not directly heated by Ar countercurrent ions of glow discharge from the beginning is that LaB ₆ constituting the main cathode 2 is a low density substance (specific gravity 4.6) and may be sputtered by the fast countercurrent ions. Because there is. However, LaB ₆ has very good thermoelectron emission characteristics and can emit thermoelectrons with a large current density even at a temperature significantly lower than the melting point, so that it has the advantages of small thermal consumption and long life even with a large current discharge. On the other hand, Ta, which constitutes the auxiliary cathode 23, is a high-density material (specific gravity: 16.7) and has durability against the sputtering action caused by the initial discharge, but is extremely resistant to the temperature rise due to the thermionic emission with a large current density. weak. Therefore, it has a drawback that it is thermally consumed and has a short life. Therefore, in the plasma generating means 50 used in the present embodiment, the cathode portion includes the auxiliary cathode 23 made of Ta which is strong against the sputtering action at the time of initial discharge, and the main cathode 2 made of LaB ₆ which is strong against the final thermionic emission temperature. To form a composite LaB ₆ cathode.

Such a composite type LaB ₆ cathode has already been proposed as an efficient and simple discharge cathode (Japanese Patent Laid-Open No. 5057/1990).
No. 7), which also has the advantage of good ion accumulation efficiency. Further, the plasma generating means 50 of the present embodiment has the intermediate electrodes 3, 4 between the cathode part and the anode 7.
Is arranged to divide the space between the cathode and the anode into the cathode side and the anode side, and generate plasma while maintaining the pressure on the cathode side higher than that on the anode side. Therefore, for example, the pressure on the cathode side is 1 To
It is possible to generate plasma by setting the pressure on the anode side to a desired value of about 10 ^-1 to 10 ^-4 Torr or about rr. The plasma generating means having such a configuration is called a pressure gradient type plasma generating means. By using this pressure gradient type plasma generation means, stable discharge can be performed for plasma generation while maintaining a high vacuum (low pressure) in the vacuum container 6 in which film formation is performed. Further, 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. Further, thermionic emission from the cathode is less likely to decrease, and the life of the cathode is extended,
It has an advantage that a large current can be discharged. 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.

Next, a thin film forming process in this thin film forming apparatus will be described. First, while adjusting the opening of the main valve 16, the pressure in the vacuum container 6 (second vacuum space) is set to 1 × 10 ⁻⁶ Torr by the exhaust means.
Then, the vapor deposition source is placed on the vapor deposition source holding means (also serving as the anode) 7, and a DC voltage of about 600 V is applied between the cathode portion and the anode 7 by the main discharge power source 5 to generate plasma. At this time, as described above, the plasma generating means (electron gun)
In No. 50, the discharge gas (Ar) was introduced from the gas inlet 1 of the cathode part, so that the region near the cathode part (the first part
The gas pressure in the vacuum space) is maintained at about 1 Torr. Further, the pressure in the region near the anode (deposition source holding means) 7 is about 2
The pressure in the vacuum container 6 is set by the exhaust means so that the pressure becomes × 10 ^-3 Torr. As a result, arc discharge is generated near the cathode portion of the plasma generating means (electron gun) 50, and the discharge gas is turned into plasma. The generated plasma is drawn from the plasma generation chamber 51 to the anode 7 side (inside the vacuum container 6) by the first intermediate electrode 3 and the second intermediate electrode 4. This plasma is cylindrically converged by the permanent magnet 52 built in the intermediate electrode, the second air-core coil 53, and the air-core coil 14, and is introduced into the vacuum container 6 as the plasma flow 13. And this plasma flow 13
Is changed in course by the magnetic field of the plasma focusing permanent magnet 8 installed near the lower part of the anode (deposition source holding means) 7, reaches the evaporation source in the evaporation source holding means 7, and evaporates this evaporation source. At this time, the opening of the main valve 16 is adjusted so that the pressure in the vacuum container 6 is 5 × 10 ⁻⁴ To by the exhaust means.
Control to be rr. On the other hand, the reaction gas supply means introduces a reaction gas (O ₂ gas) from the reaction gas supply port 10 at a desired flow rate to react with the substance evaporated from the vapor deposition source. The opening of the main valve 16 is adjusted so that the pressure in the vacuum container 6 is maintained at 5 × 10 ⁻⁴ Torr even after the introduction of the reaction gas. After that, when the shutter 15 is opened,
The evaporated substance is ionized by passing through the plasma 13 and reaches the substrate 12 kept at a negative potential by the bias power source 11. As a result, a thin oxide film is formed on the surface of the substrate 12. During the formation of this thin film, the film thickness and the film pressure rate (evaporation rate) of the thin film can be measured by the film thickness monitor 17, so that the film formation can be completed when the predetermined film thickness is reached.

In this embodiment, a mirror-polished circular quartz glass having a diameter of 30 mm was prepared as the substrate 12, and a thin film of SiO ₂ (film thickness 0.3 μm) was produced (formed) on the substrate 12. The film forming conditions at that time are shown below. Ultimate pressure (vacuum degree) in the vacuum vessel: 1 × 10 ^-6 Torr Pressure (vacuum degree) in the vacuum vessel during film formation: 5 × 10 ^-4 Torr Arc discharge voltage: 70 V Arc discharge current: 93 A Discharge gas Ar Flow rate: 20 SCCM (CC /
Min) Reaction gas O ₂ flow rate: 85 SCCM (CC /
Min) Evaporation source: Si substrate temperature: 120 ° C. Film formation rate: 0.6 nm / sec The spectrum near the absorption band (about 3400 cm ⁻¹ ) of the (OH) bond of the SiO ₂ thin film produced (formed) in this example. Infrared spectrophotometer (PERKIN ELMER983G INF
RAND SPECTROPHOTOMETER). The measurement result is shown in FIG. The SiO ₂ thin film obtained in this example showed almost no influence of absorption by water in the measurement region.

[Comparative Example] As a comparative example, an electron gun heating type vacuum vapor deposition apparatus was used, the following film forming conditions were set, and a thin film of SiO ₂ (film thickness 0 .
3 μm) was manufactured (film formation). Ultimate pressure (vacuum degree) in the vacuum container: 5 × 10 ^-5 Torr Pressure (vacuum degree) in the vacuum container during film formation: 3 × 10 ^-4 Torr Deposition source: SiO ₂ Substrate temperature: 320 ℃ Deposition rate : 0.6 nm / sec The spectrum in the vicinity of the absorption band (about 3400 cm ^-1 ) of the (OH) bond of the SiO ₂ thin film produced (formed) in this comparative example was measured in the same manner as in the example. The measurement result is shown in FIG. The SiO ₂ thin film obtained in this comparative example has a thickness of 3400-35 as shown in FIG.
At around 00 cm ^-1 , there is remarkable absorption, which is thought to be due to the moisture in the thin film.

[0024]

As described above, according to the present invention, a thin film oxide having almost no water in the film can be produced (formed), so that the durability of the thin film can be improved. It will be possible. Therefore, by forming this thin film oxide as an optical thin film on an optical element, the durability of this element can be improved.

Further, since it is not necessary to heat the substrate at the time of film formation, the oxide thin film can be formed on the substrate made of a material weak against heat. Further, there is an advantage that the structure of the thin film forming apparatus used for film formation becomes simple.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional configuration diagram of a thin film forming apparatus (arc discharge type ion plating apparatus) used for carrying out the present invention.

FIG. 2 is a schematic vertical cross-sectional configuration diagram of a plasma generating means used in the thin film forming apparatus of FIG.

FIG. 3 is a diagram showing infrared absorption spectra of SiO ₂ thin films obtained in Examples and Comparative Examples.

[Explanation of symbols for main parts]

 1 Gas Inlet 2 Main Cathode 3 First Intermediate Electrode 4 Second Intermediate Electrode 5 Main Discharge Electrode 6 Vacuum Container 7 Deposition Source Holding 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 20 Cathode mount 21 Cooling means 22 Quartz tube 23 Auxiliary cathode 24 Cylinder (cathode tube) 25 Cathode protection plate 26 Insulation ring 27 Flange 28 O-ring 29 Intermediate electrode mounting bolt 50 Plasma generation means (electron gun) 51 Plasma generation chamber 52 Permanent magnet 53 Second air-core coil

Claims (2)

[Claims] 1. A plasma is generated by arc discharge in a first vacuum space set to a predetermined pressure, and the plasma is transferred to a second vacuum space set to a pressure lower than that of the first vacuum space. In the method for producing a thin film oxide by arc discharge type ion plating for forming a film in the second vacuum space by irradiating an installed vapor deposition source, the pressure during the film formation in the second vacuum space. Is set to 5 × 10 ⁻⁴ Torr or less. 2. The method for producing a thin film oxide according to claim 1, wherein the oxide is silicon oxide (SiO ₂ ).