JPH09291358A - Production of optical thin film and optical thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a MgF2 thin film substantially free from the absorption by a sputtering method. SOLUTION: At first, SiO2 is vapor depositied on a glass substrate. A target material 8 is placed on a glass made pan and installed on a magnetron sputtering cathode 7. The target 8 is sputtered on the glass substrate 11 by impressing RF voltage to the magnetron sputtering cathode 7 to generate plasma. A target shield is expressed by 9 and a shutter is expressed by 10 in Figure.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an optical thin film using a sputtering method and an optical thin film.

[0002]

2. Description of the Related Art Conventionally, when forming a thin film, a vacuum vapor deposition method has been widely used because of its easiness in the method and the speed of film formation. This is also the case when forming an optical thin film such as an antireflection film, a half mirror, or an edge filter.
On the other hand, in recent years, even for optical thin films and other thin films, there is an increasing demand for coating by a sputtering method, which is advantageous in terms of automation, labor saving, and applicability to a large area substrate as compared with the vacuum deposition method. .

However, due to the difference in principle between the vacuum vapor deposition method and the sputtering method, even a film which can be produced without problems by the vacuum vapor deposition method may have a problem by the sputtering method. A typical example is MgF ₂ . MgF ₂ is a substance that is chemically stable, has excellent insulating properties, and has a low refractive index that is difficult to obtain with other substances. For this reason, conventionally, it has been regarded as an indispensable material for forming an optical film, but when a thin film of MgF ₂ is manufactured by a usual sputtering method, a large light absorption occurs in the film in the visible region.

The absorption in the visible region repels the F ions in the plasma due to the negative plasma potential excited on the substrate holder side, so that the F ions taken into the thin film are absorbed.
The main cause is the lack of weight and MgO formed by the oxidation reaction of O ions and Mg ions excited by the dissociation of water in plasma. Several methods have been proposed as methods for suppressing absorption in the visible region due to these causes.

As the above method, for example, Japanese Patent Laid-Open No. 4-223
A method of mixing Si into a target disclosed in Japanese Patent No. 401, and a method of assisting fluorine gas or a fluorine-containing compound gas disclosed in Japanese Patent Laid-Open No. 4-289165 in sputtering can be mentioned. . According to each of the above methods, the absorption of the film itself is eliminated,
Or it can be smaller.

[0006]

However, JP-A-4-223401 and JP-A-4-2891 are known.
According to the method described in Japanese Patent Publication No. 65, the light absorption of the MgF ₂ film itself is reduced, but in the glass containing PbO, phosphoric acid, and other specific elements, the charge in the plasma during the formation of the MgF ₂ film is increased. The incidence of particles may damage the surface of the substrate and cause absorption at the boundary between the substrate and the film. This absorption can be a serious defect for an optical element, and must be suppressed in order to obtain an optical element having desired characteristics. Therefore, a technique for suppressing light absorption on the boundary surface is desired.

It is an object of claims 1 to 4 to provide a method for suppressing absorption at the boundary between the substrate and the film when producing an MgF ₂ optical thin film, and an optical thin film that does not generate absorption.

[0008]

According to a first aspect of the invention, an oxide thin film containing at least one of SiO ₂ , ZrO ₂ and Al ₂ O ₃ is formed on the surface of a substrate, and the oxide thin film is formed on the oxide thin film. A method for producing an optical thin film is characterized in that a MgF ₂ thin film is formed by sputtering.

According to the first aspect of the invention, many charged particles are present in the plasma generated during the film formation by the sputtering method. A part of them is incident on the substrate, but these have the action of dissociating or missing components in the substrate. As a result, light absorption occurs at the interface between the substrate and the film. Therefore, before the MgF ₂ thin film is formed on the optical element such as the lens by the sputtering method, the change in the optical characteristics due to the incident electrons on the substrate is small.
Alternatively, by forming a thin film of a material that does not exist at all, it is possible to suppress the occurrence of light absorption.

In fact, it has been confirmed in many experiments conducted by us that the above structure can effectively suppress the generation of the light absorption. In addition, as a material in which the optical characteristics are hard to change or not in the experiment, Si
It has also been found that O ₂ , ZrO ₂ and Al ₂ O ₃ are particularly effective, limiting the material of the thin film to the oxide.

According to a second aspect of the invention, the particle size is 0.1 to 10 mm.
A film raw material made of granular MgF ₂ is provided in the vicinity of the electrode,
Plasma is generated on the film raw material by applying an AC voltage to the electrode, the surface temperature of the film raw material is raised by the plasma, and the film raw material is sputtered to form a MgF ₂ thin film. The method for producing an optical thin film according to claim 1.

In the invention of claim 2, the particle size of the granular MgF ₂ particles as the target is numerically limited to 0.1 to 10 mm for the following reason. First, if the size of the granules is too small, they rise up in the chamber and become particles, so the particle size is preferably 0.1 mm or more, and more preferably 0.5 mm or more. In addition, if the granules are too large, the number of edge portions decreases, and when the plasma is generated, the electric field / magnetic field is not concentrated in the edge portions, and as a result, the effect of increasing the temperature of the surface of the film raw material decreases. The diameter is 10 mm or less, preferably 5 mm or less. Granules do not have to be uniform in size or shape.

There are several methods for forming the MgF ₂ film according to the first aspect of the present invention by the sputtering method, but most of them generate a large amount of Mg ions and F ions during sputtering. These ions may cause damage to the substrate in addition to the charged particles, and it is preferable to take a method of generating less ions to form MgF ₂ .

In the method of forming the MgF ₂ thin film according to the _second aspect of the present invention, the film raw material is in the form of granules having a particle size of 0.1 to 10 mm, so that the film raw material is easily heated by plasma and the film raw material is sputtered. In this case, the bond between Mg and F is not broken and the MgF ₂ molecule or molecule group is popped out into the space, so that the existence probability of Mg ion and F ion in the atmosphere becomes relatively small. Therefore, by applying the method recited in claim 2 as the method of forming the MgF ₂ , it is possible to further increase the effect of suppressing light absorption on the substrate surface.

According to a third aspect of the present invention, the oxide thin film is formed by a reactive sputtering method in which Si or a metal is used as a target and sputtering is performed while introducing at least O ₂ gas. It is a method of manufacturing a thin film.

In the invention of claim 3, several methods including the vacuum deposition method can be mentioned as the method of forming the oxide film described in claim 1, but an oxide thin film is formed on the surface of the substrate. MgF by sputtering after forming
Considering the formation of _two films, it is preferable that the oxide thin film is also formed by a sputtering method because it is possible to simplify the production equipment and production process.

Further, when Si or a metal is used as a sputtering target and reactive sputtering is performed while introducing at least oxygen gas, S is more preferable than oxide.
Since a metal such as i or Zr or Al has a better sputtering rate, the film forming rate becomes faster, and the disadvantage of the conventional sputtering method that the film forming rate is slower can be eliminated. Therefore, the reactive sputtering method is preferable from the viewpoint of production efficiency. As mentioned above, when considering industrial production,
By applying the method of claim 3 as the method of forming the oxide thin film of claim 1, the production efficiency in a broad sense can be improved.

As the sputtering gas, at least oxygen gas is introduced to form an oxide thin film by reactive sputtering. In addition to oxygen gas, Ar gas or the like may be introduced together for the purpose of increasing the film formation rate. Further, the sputtering method here may be a DC reactive sputtering method which is performed while applying a DC voltage (hereinafter referred to as DC voltage), or a high frequency voltage (hereinafter referred to as RF voltage) which is a kind of AC voltage is applied. Alternatively, the RF reactive sputtering method may be performed. However, when an AC voltage is used, an oxide thin film having high light absorption is easily formed, and charged particles are likely to enter the substrate and damage the substrate. Therefore, it is preferable to use a DC voltage.

According to a fourth aspect of the invention, the first layer is a MgF ₂ thin film formed by sputtering from the air side, and the second layer is at least one of SiO ₂ , ZrO ₂ and Al ₂ O _3. An optical thin film is characterized in that an oxide thin film containing one of them is provided.

According to the fourth aspect of the invention, when an optical film such as an antireflection film or an optical filter having good performance is to be produced, the difference in the optical impedance is reduced so that the first layer is separated from the air. It is often effective to use a substance having a low refractive index. In that sense, it is significant to use the MgF ₂ film having a low refractive index (about 1.38), which is not found in other substances, for the air-side first layer.

[0021] However, when manufacturing the MgF ₂ film by sputtering, the surface forming the MgF ₂ has for example a PbO as its components, when the MgF ₂ is deposited by sputtering, is generated in the plasma PbO is reduced by heat and electrons to form an altered layer, which causes absorption. In addition, even when a film containing phosphoric acid is present on the film-forming surface, MgF ₂ is affected by plasma.
Absorption often occurs inside the substrate rather than on itself, rather than MgF ₂ , and tends to be defective as an optical element.

However, the film on the substrate side of MgF ₂ is Si
It has been found from experiments that, in the case of a film containing at least one of O ₂ , ZrO ₂ and Al ₂ O ₃ , the generation of an altered layer that causes this absorption is small. From such a fact, it is understood that the optical thin film recited in claim 4 is effective in forming a high performance optical film.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) In this embodiment, a vapor deposition apparatus for forming a SiO ₂ film and a sputtering apparatus for forming a MgF ₂ film are used. These configurations will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic configuration diagram showing an internal configuration of a vacuum chamber of the vapor deposition apparatus.

Reference numeral 1 is a vapor deposition source, and SiO ₂ is deposited on the vapor deposition source 1 as a vapor deposition material. The SiO ₂ is stably heated by the electron beam heating method. 2 is a shutter. Reference numeral 3 denotes a glass substrate on which a film is formed, and in particular, here, it is BPH50 (manufactured by OHARA CORPORATION). Since BPH50 contains PbO in its composition, if a MgF ₂ film is formed on the surface as it is by the sputtering method, PbO on the surface is reduced and absorption occurs in the adhesion layer of the film. For example, it should be noted that when quartz glass is used for this glass substrate, absorption in the adhesion layer of the film does not occur at all.

The glass substrate 3 is mounted on the rotary dome 4 and is rotated about the axis directly above the vapor deposition source 1 by the rotation of the rotary dome 4 during vapor deposition. Reference numeral 5 is a heater for heating the glass substrate 3 to a constant temperature during vapor deposition. Reference numeral 6 is a crystal oscillator type film thickness meter for monitoring and controlling the film thickness on the glass substrate 3.

FIG. 2 is a schematic diagram showing the internal structure of the vacuum chamber of the sputtering apparatus. 7 is a magnetron sputtering cathode. Reference numeral 8 is a target material of granular MgF ₂ particles having a diameter of the sputtering material of about 1 to 3 mm. The target material 8 is placed on a glass dish and placed on the magnetron sputtering cathode 7. Reference numeral 9 is a target shield which surrounds the magnetron sputtering cathode 7 and the target material 8 and whose potential is always at the ground level. 10 is a shutter.

Reference numeral 11 denotes a glass substrate for forming a film, and the glass substrate 11 is held by 12 substrate holders. The center of rotation of the substrate holder 12 is not located directly above the magnetron sputtering cathode 7 but in an eccentric position. The substrate holder 12 rotates during film formation. Due to the effect of this rotation and the eccentricity, the film is uniformly formed on the glass substrate 11.

A manufacturing method using the apparatus having the above structure will be described below. First, the surface of the glass substrate 3 is cleaned. After that, the glass substrate 3 is placed in a state as shown in FIG. 1, that is, at a position on the lower surface of the rotary dome 4 of the vapor deposition device and displaced from the center of rotation of the rotary dome 4, and then the vacuum chamber is evacuated. Simultaneously with the start of evacuation, heating of the glass substrate 3 by the heater 5 for heating the substrate and rotation of the rotary dome 4 are started. As a result, the temperature of the glass substrate 3 is stabilized at about 300 ° C.

After a degree of vacuum of about 10 ⁻⁴ Pa is obtained and a sufficient time has passed for the temperature of the glass substrate 3 to stabilize, heating of the vapor deposition material SiO _{2 in} the evaporation source 1 is started. Here, it is assumed that the shutter 2 is closed. When SiO ₂ which is the vapor deposition material is sufficiently heated and stabilized, the shutter 2 is opened to start vapor deposition. The thickness of the deposited film is monitored by the film thickness meter 6. When the value of the film thickness meter shows a desired value, the shutter 2 is closed. Here, it is assumed that SiO ₂ having a physical film thickness of 20 nm is formed on the glass substrate 3. Immediately after the shutter 2 is closed, the heating of the vapor deposition material, the heating of the glass substrate 3 and the rotation of the rotary dome 4 are stopped, and a series of film forming work by vapor deposition is completed.

Next, in order to take out the glass substrate 3 on which SiO ₂ is formed from the vacuum chamber of the vapor deposition apparatus, the vacuum chamber is leaked. Then, the taken out glass substrate 3 is transferred to the vacuum chamber of the sputtering apparatus. At that time, the glass substrate 3 (= 11) is attached in a state as shown in FIG. 2, that is, at a position displaced from the rotation center of the substrate holder 12 on the lower surface of the substrate holder 12. Immediately thereafter, the vacuum chamber of the sputtering apparatus is evacuated.
When the degree of vacuum of about 10 ⁻⁴ Pa is obtained, the substrate holder 12
To rotate. At the same time, O ₂ gas is introduced into the vacuum chamber to obtain a pressure of 0.4 Pa.

When the pressure in the vacuum chamber is stabilized and an RF voltage is applied to the magnetron sputtering cathode 7, plasma is generated on the target material 8 and the target material 8 is sputtered by positive ions. At this time, the shutter 10 is still closed and the so-called pre-sputtering state is set. Ordinary pre-sputtering is performed mainly for the purpose of stabilizing the sputter by removing oxides or the like on the target surface. Here, in addition to the above-mentioned purpose, the target material 8 easily jumps in the state of molecules or molecule groups during sputtering. To raise the target temperature.

When the temperature of the target material 8 rises and the plasma state stabilizes, the shutter 10 is opened and the MgF ₂ thin film is formed on the surface of the glass substrate 11. When the physical film thickness reaches 100 nm, the shutter 1 is pressed again.
Close 0. At this time, the film forming speed is measured in advance, and the film thickness is controlled by the time for opening and closing the shutter 10. The sputtering conditions are such that when a film is formed on a quartz glass substrate, absorption does not occur in the film.

After closing the shutter 10, the RF voltage applied to the magnetron sputtering cathode 7 is gradually decreased to extinguish the plasma. At the same time, the rotation of the substrate holder 12 is stopped and the vacuum chamber is leaked. At this point, on the glass substrate 11, a SiO ₂ film having a physical film thickness of 20 nm is formed as the first layer from the substrate side and a physical film thickness of 10 nm is formed as the second layer.
A 0 nm MgF ₂ film is formed. The absorption of the substrate provided with this two-layer thin film is 0.1% or less with respect to light having a wavelength of 400 nm. For comparison, SiO _{2 on} the same substrate
When MgF ₂ was formed under the same conditions as those shown here without attaching a film, absorption of 6% or more occurred at 400 nm.

According to this embodiment, M is formed on the glass substrate.
gF_TwoBefore forming the thin film by sputtering._Two
By forming the film, MgF_TwoOccurs during film formation
Minimize the absorption that occurs at the boundary between the glass substrate and the film
I was able to. Also, depending on the material of the glass substrate,
It is possible to minimize the difference in the quality of the film. Further
And here SiO_TwoThe thickness of the film was reduced to 20 nm
From approximately SiO _TwoIgnoring the film, MgF_TwoSingle layer anti
It can be treated as an anti-reflection film. Actually, BPH50
Has a large refractive index of 1.74, so MgF has a low refractive index.
_TwoIs a film material, an antireflection film with a large effect even in a single layer
Becomes

(Embodiment 2) In the present embodiment, a sputtering apparatus having two magnetron sputtering cathodes is used. FIG. 3 is a schematic configuration diagram showing the internal configuration of the vacuum chamber of the sputtering apparatus.

Reference numeral 21 is a glass substrate of BPH50 (manufactured by OHARA CORPORATION), and a multilayer film is formed on the glass substrate 21. The glass substrate 21 is attached to the substrate holder 22 as shown in FIG. 3, that is, on the lower surface of the substrate holder 22 while being displaced from the center of rotation of the substrate holder 22. The substrate holder 22 is eccentrically positioned with respect to the two magnetron sputtering cathodes 23 and 28, and the substrate holder 22 rotates during film formation to make the film thickness distribution uniform.

The material of the target 24 attached to one of the magnetron sputtering cathodes 23 is Zr. 26 is a magnetron sputtering cathode 23
And a target shield surrounding the target 24. 27 is a shutter for the target 24. The target 29 attached to the other magnetron sputtering cathode 28 is porous MgF ₂ ,
The thermal conductivity of the membrane material itself is poor. 30 is a magnetron sputtering cathode 28 and a target 29
Is a target shield that surrounds. Reference numeral 31 is a shutter of the target 29.

The two shutters 27 and 31 are opened only when film formation is performed, and the target film thickness is obtained by controlling the opening time. Two target shields 2
The potentials of the shutters 6, 30 and the two shutters 27, 31 are always kept at the ground level. Further, the two targets 24 and 29 are bonded to the backing plates attached to the magnetron sputtering cathodes 23 and 28, respectively.

A manufacturing method using the apparatus having the above structure will be described below. First, the surface of the glass substrate 21 is cleaned. After that, the glass substrate 21 is placed in a state as shown in FIG. 3, that is, at a position on the lower surface of the substrate holder 22 of the sputtering apparatus, which is displaced from the rotation center of the substrate holder 22, and then the vacuum chamber is evacuated. After the degree of vacuum of about 10 ⁻⁴ Pa is obtained, the substrate holder 22 is rotated, and at the same time, a mixed gas of oxygen and argon is introduced into the vacuum chamber to obtain an appropriate pressure.

When the pressure in the vacuum chamber is stabilized, a DC voltage is applied to the magnetron sputtering cathode 23 to generate plasma on the target 24. At this time, the shutter 27 is still closed and the pre-sputtering state is set. When enough time has passed to remove the oxides on the surface of the target 24 and the plasma stabilizes, the shutter 27
Open. The sputtered Zr is combined with oxygen molecules in the atmosphere until it reaches the glass substrate 21 or immediately after the glass substrate 21, and becomes ZrO ₂ .

When the time when the optical film thickness (nd) becomes 111 nm has elapsed, the shutter 27 is closed again. At this time, the film forming speed is measured in advance, and the film thickness is controlled by the time for opening and closing the shutter 27. Further, the magnetron sputtering cathode 2 is gradually closed after the shutter 27 is closed.
The DC voltage applied to 3 is dropped to extinguish the plasma. At this point, a film thickness of 111 n is formed on the glass substrate 21.
Thus, a ZrO ₂ film of m is formed.

Next, the gas to be introduced is changed to oxygen, and 0.4
Obtain the pressure of Pa. When the pressure in the vacuum chamber becomes stable, an RF voltage is applied to the magnetron sputtering cathode 28 to generate plasma on the target 29. At this time, the shutter 31 is still closed and the so-called pre-sputtering state is set. Normal pre-sputtering is performed mainly for the purpose of stabilizing oxides by removing oxides on the target surface.
The temperature of the target 29 is increased so that the target 29 easily jumps in the state of molecules or groups of molecules during sputtering.

When the temperature of the target 29 rises and stabilizes, the shutter 31 is opened. The sputtering conditions at this time are such that the MgF ₂ film does not absorb when formed on a quartz glass substrate. Optical film thickness (nd) is 111
When the time of nm has passed, the shutter 31 is closed again. At this time, the film forming speed is measured in advance, and the film thickness is controlled by the time for opening and closing the shutter 31. Further, after closing the shutter 31, the RF voltage applied to the magnetron sputtering cathode 28 is gradually reduced to extinguish the plasma. At this point, a Mg film having a film thickness of 111 nm is further formed on the glass substrate 21 having the ZrO ₂ film formed thereon.
An F ₂ film is formed.

By repeating the above steps, ZrO ₂ films and MgF ₂ films are alternately formed on the glass substrate 21, and finally a multilayer film of 17 layers as shown in FIG. 4 is formed. After the completion of the multilayer film, the vacuum chamber is leaked to take out the glass substrate having the multilayer film formed on its surface. The multilayer film has a wavelength of 444n
It becomes a high-reflectivity mirror showing the maximum reflectance (99% or more) at m. Since ZrO ₂ and MgF ₂ do not have absorption at 443 nm, a laser (Cd
It can be used as a laser emitting mirror for ion laser).

According to the present embodiment, since the ZrO ₂ film is first formed on the glass substrate, absorption due to the damage on the glass substrate side that occurs when forming MgF ₂ does not occur.
Furthermore, since both sputtering was used when forming ZrO ₂ and MgF ₂ , the apparatus used for film formation is common, and a multilayer film can be formed extremely simply in the same vacuum chamber. Further, since both targets are adhered to the backing plate, it is not necessary to keep the targets horizontal as in the first embodiment, and the magnetron sputtering cathode position in the vacuum chamber can be freely changed. is there.

(Embodiment 3) In this embodiment, a sputtering apparatus is used. FIG. 5 is a schematic configuration diagram showing the internal configuration of the vacuum chamber of the sputtering apparatus. 41 is BS
A multi-layer film is formed on the glass substrate 41 using a glass substrate of L7 (manufactured by OHARA CORPORATION). The glass substrate 41 is transferred to the substrate holder 42 as shown in FIG.
The lower surface of the substrate holder 42 is mounted at a position deviated from the center of rotation of the substrate holder 42.

The substrate holder 42 is located eccentrically with respect to the magnetron sputtering cathode 43 and rotates during film formation to make the film thickness distribution uniform. On the magnetron sputtering cathode 43 is placed a dish 44 for placing the film material. The dish 44 has a plurality of recesses for mounting the film material, and by rotating about the shaft 45, the magnetron sputtering cathode 43
You can change the membrane material that comes on top of. The plate 44 has MgF ₂ powder, ZrO ₂ powder and Al ₂ O as film materials.
₃ powders are listed. Further, the material of the dish 44 is ceramics having a high electric insulation property, and has a structure in which there is no problem even if a high voltage is applied to the magnetron sputtering cathode 43.

A target shield 46 surrounds the magnetron sputtering cathode 43 and the target in the dish 44. Reference numeral 47 denotes a target shutter in the dish 44. The potentials of the target shield 46 and the shutter 47 are kept at the ground level. Further, reference numeral 48 is an adhesion preventing plate for preventing the material being sputtered from adhering to other film materials.

A manufacturing method using the apparatus having the above structure will be described below. First, the surface of the glass substrate 41 is cleaned. After that, the glass substrate 41 is placed in a state as shown in FIG. 5, that is, at a position on the lower surface of the substrate holder 42 of the sputtering apparatus which is displaced from the rotation center of the substrate holder 42, and then the vacuum chamber is evacuated. Here, by rotating the dish 44, the film material on the magnetron sputtering cathode 43 is changed to Al ₂ O ₃ . After the degree of vacuum of about 10 ⁻⁴ Pa is obtained, the substrate holder 42 is rotated and at the same time,
Ar gas is introduced into the vacuum chamber to obtain a pressure of about 0.5 Pa.

When the pressure in the vacuum chamber is stabilized, an RF voltage is applied to the magnetron sputtering cathode 43 to generate plasma on the film material (Al ₂ O ₃ ). At this time, the shutter 47 is still closed and the pre-sputtering state is set. When enough time has passed to remove the oxide on the target surface and the plasma stabilizes, the shutter 47
Open. When the optical film thickness (nd) reaches 125 nm, the shutter 47 is closed again. Here, it is assumed that the film forming speed is measured in advance, and the film thickness is controlled by the time for which the shutter 47 is opened and closed. This also applies to the subsequent film formation.

After closing the shutter 47, the RF voltage applied to the magnetron sputtering cathode 43 is gradually decreased to extinguish the plasma. At this point, an optical film having an optical film thickness (nd) of 125 nm is formed on the glass substrate 41 by A.
An l ₂ O ₃ film is formed. Here, by rotating the dish 44, the magnetron sputtering cathode 43
The film material above is changed to ZrO ₂ and the gas pressure is changed to a pressure of about 0.4 Pa. When the pressure in the vacuum chamber becomes stable, an RF voltage is applied to the magnetron sputtering cathode 43 to generate plasma on the film material (ZrO ₂ ). At this time, the shutter 47 is still closed and the pre-sputtering state is set.

The shutter 47 is opened when a sufficient time has passed to remove oxides and the like on the target surface and the plasma becomes stable. When the optical film thickness (nd) reaches 250 nm, the shutter 47 is closed again. After closing the shutter 47, the RF voltage applied to the magnetron sputtering cathode 43 is gradually decreased to extinguish the plasma. At this point, an Al ₂ O ₃ film having an optical film thickness of 125 nm and an optical film thickness of 250 are formed on the glass substrate 41.
nm ZrO ₂ is formed.

Next, by rotating the plate 44, the film material on the magnetron sputtering cathode 43 is changed to MgF ₂ and the gas to be introduced is changed to oxygen so that the pressure is about 0.4 Pa. Once the pressure in the vacuum chamber has stabilized, the magnetron sputtering cathode 4
An RF voltage is applied to 3 to generate plasma on the target. At this time, the shutter 47 is still closed, and the so-called pre-sputtering state is set.

Normal pre-sputtering is performed mainly for the purpose of stabilizing the sputter by removing oxides or the like on the target surface. Here, in addition to the above-mentioned purpose, the target material is a molecule or a group of molecules at the time of sputtering. Raise the target temperature to make it easier to jump. When the temperature of the target rises and becomes stable, the shutter 47 is opened. The sputtering conditions at this time are such that absorption does not occur in the MgF ₂ film when the film is formed on a quartz glass substrate.

When the time when the optical film thickness (nd) reaches 125 nm has elapsed, the shutter 47 is closed again. Further, after closing the shutter 47, the RF voltage applied to the magnetron sputtering cathode 43 is gradually decreased to extinguish the plasma. At this point, Al ₂ O ₃ , ZrO ₂
Thus, a three-layer antireflection film of MgF ₂ is formed. The three-layer film formed here is an antireflection film having a reflectance of 0.8% or less in the entire visible region, and particularly 0.1% or less for light having a wavelength of 500 nm.

According to the present embodiment, the absorption due to the damage of the substrate that occurs when forming MgF ₂ is less likely to occur on the substrate side than MgF ₂ is Al ₂ O ₃ and ZrO.
_It does not occur because the film of ₂ is formed. The same magnetron sputtering cathode is used for forming each film, and a device used for film formation including a power supply is common, and the number of components of the device is reduced.

(Embodiment 4) This embodiment uses a sputtering apparatus having two magnetron sputtering cathodes having the same structure as that of Embodiment 2. The difference from the second embodiment is only that the Zr target 4 in the second embodiment is replaced with Si. Therefore, this embodiment will be described with reference to FIG.

A manufacturing method using the apparatus having the above structure will be described below. First, the surface of the glass substrate 21 is cleaned. After that, the glass substrate 21 is placed in a state as shown in FIG. 3, that is, at a position on the lower surface of the substrate holder 22 of the sputtering apparatus, which is displaced from the rotation center of the substrate holder 22, and then the vacuum chamber is evacuated. After the degree of vacuum of about 10 ⁻⁴ Pa is obtained, the substrate holder 22 is rotated and at the same time, oxygen gas is introduced into the vacuum chamber to obtain a pressure of 0.6 Pa.

When the pressure in the vacuum chamber becomes stable, use the magnetro
DC voltage is applied to the sputtering sputtering cathode 23.
Plasma is generated on the get 24. At this time, still
The shutter 27 is closed and the pre-sputtering state is not set.
You. Open the shutter 27 as soon as the plasma stabilizes.
You. Sputtered Si and SiO_XStick to the board
Oxygen immediately in the atmosphere until or about the substrate
Bound to molecules, SiO _TwoBecomes

When the time when the optical film thickness (nd) reaches 20 nm has elapsed, the shutter 27 is closed again. At this time, the film forming speed is measured in advance, and the film thickness is controlled by the time for opening and closing the shutter 27. In addition, the magnetron sputtering cathode 23 is gradually closed after the shutter 27 is closed.
The DC voltage applied to the plasma is dropped to extinguish the plasma. At this point, a SiO ₂ film having a physical film thickness of 20 nm is formed on the glass substrate 21.

Next, the introduction amount of oxygen (oxygen) is changed,
A pressure of 0.4 Pa is obtained. When the pressure in the vacuum chamber becomes stable, an RF voltage is applied to the magnetron sputtering cathode 28 to generate plasma on the target 29. At this time, the shutter 31 is still closed and the so-called pre-sputtering state is set. Ordinary pre-sputtering is performed mainly for the purpose of stabilizing the sputter by dropping oxides or the like on the target surface, but here, in addition to the above-mentioned purpose, the target material 29 easily jumps in the state of molecules or molecule groups during sputtering. To raise the target temperature.

When the temperature of the target 29 rises and becomes stable, the shutter 31 is opened. The sputtering conditions at this time are as follows:
A condition is used in which absorption does not occur in the MgF ₂ film when the film is formed on a quartz glass substrate. Physical film thickness is 100 nm
After a lapse of time, the shutter 31 is closed again.
At this time, the film formation speed was previously measured, and the shutter 31
The film thickness is controlled by the time of opening and closing.

Further, after closing the shutter 31, the RF voltage applied to the magnetron sputtering cathode 28 is gradually decreased to extinguish the plasma. At this point, further thickness onto a glass substrate 21 formed of SiO ₂ film is formed MgF ₂ film of 100 nm. After the film is completed, the vacuum chamber is leaked and the glass substrate having the multilayer film formed on its surface is taken out. The two-layer film formed here has the same film structure as the film formed in the first embodiment.

According to the present embodiment, by first forming the SiO ₂ film on the glass substrate, it is possible to minimize absorption due to damage on the substrate side that occurs when forming MgF ₂ . In addition to the above, the same effect as that of the first embodiment can be obtained, but since the respective films are formed by the sputtering method as compared with the first embodiment, the tact time is greatly shortened. Further, since both targets are bonded to the backing plate, it is not necessary to keep the targets in a horizontal position as in the first embodiment, and the magnetron sputtering cathode position in the vacuum chamber can be freely changed. Is.

According to the above description, the following inventions can be understood. That is, (1) A method for producing an optical thin film, which comprises forming an oxide thin film on a surface of a substrate and forming a MgF ₂ thin film on the oxide thin film by a sputtering method. (2) A film raw material made of granular MgF ₂ having a particle diameter of 0.1 to 10 mm is provided in the vicinity of the electrode, and a high frequency voltage is applied to the electrode to generate plasma on the film raw material. The method for producing an optical thin film according to item (1), wherein the surface temperature of the film raw material is raised and the film raw material is sputtered to form an MgF ₂ thin film. (3) The oxide thin film is formed by a DC reactive sputtering method in which a metal such as Si or Zr or Al is used as a target, and sputtering is performed while introducing at least O ₂ gas. Thin film manufacturing method. (4) M formed on the air side by the sputtering method
An optical thin film comprising a gF ₂ thin film and an oxide thin film on the substrate side of the MgF ₂ thin film. (5) The optical thin film as described in (4), which is an oxide thin film containing at least one of SiO ₂ , ZrO ₂ and Al ₂ O ₃ . (6) The optical film according to (4), which is an oxide thin film formed by a DC reactive sputtering method in which a metal such as Si or Zr or Al is used as a target and sputtering is performed while introducing at least O ₂ gas. Thin film. (7) A film raw material made of granular MgF ₂ having a particle size of 0.1 to 10 mm is provided in the vicinity of the electrode, and a high frequency voltage is applied to the electrode to generate plasma on the film raw material. MgF formed by sputtering the film material while raising the surface temperature of the film material
Characterized in that it is a ₂ thin film (4) The optical thin film according to claim. (8) The optical thin film as described in the item (4), which is an antireflection film. (9) The optical thin film according to item (4), which is a mirror film. (10) A thin film manufacturing apparatus for forming a thin film on a substrate surface by a sputtering method using a granular material as a target, comprising a rotatable plate having a plurality of storage units for the granular material. An apparatus for manufacturing a thin film.

[0066]

INDUSTRIAL APPLICABILITY The present invention can suppress absorption at the boundary between the substrate and the film, which occurs when the MgF ₂ optical thin film is manufactured by the sputtering method. As a result, it is possible to manufacture a MgF ₂ thin film which has virtually no absorption by the sputtering method.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment.

FIG. 2 is a schematic configuration diagram showing the first embodiment.

FIG. 3 is a schematic configuration diagram showing a second embodiment.

FIG. 4 is a chart showing a second embodiment.

FIG. 5 is a schematic configuration diagram showing a third embodiment.

[Explanation of symbols]

 1 Vapor Deposition Source 2, 10 Shutter 3, 11 Glass Substrate 4 Rotating Dome 5 Heater 6 Film Thickness Meter 7 Magnetron Sputtering Cathode 8 Target Material 9 Target Shield 12 Substrate Holder

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location G02B 5/08 G02B 5/26 5/26 1/10 A (72) Inventor Hiroshi Ikeda Shibuya, Tokyo 2-43-2 Hatagaya-ku, Olympus Optical Co., Ltd. (72) Inventor Nobuyoshi Toyohara 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Norikazu Urata Tokyo 2-43-2 Hatagaya, Shibuya Olympus Optical Industry Co., Ltd. (72) Inventor Toshiaki Ikumizu 2-43-2 Hatagaya Shibuya-ku, Tokyo Olympus Optical Industry Co., Ltd.

Claims (4)

[Claims] 1. An oxide thin film containing at least one of SiO ₂ , ZrO ₂ and Al ₂ O ₃ is formed on the surface of a substrate, and M is formed on the oxide thin film by a sputtering method.
A method for producing an optical thin film, which comprises forming a gF ₂ thin film. 2. Granular MgF having a particle size of 0.1 to 10 mm.
_A film raw material consisting of ₂ is provided in the vicinity of the electrode, plasma is generated on the film raw material by applying an AC voltage to this electrode, and the surface temperature of the film raw material is raised by this plasma and the film raw material is sputtered. Mg
The method for producing an optical thin film according to claim 1, wherein an F ₂ thin film is formed. 3. The method for producing an optical thin film according to claim 1, wherein the oxide thin film is formed by a reactive sputtering method in which Si or a metal is used as a target and sputtering is performed while introducing at least O ₂ gas. 4. The first layer from the air side is a MgF ₂ thin film formed by a sputtering method, and the second layer is Si.
An optical thin film provided with an oxide thin film containing at least one of O ₂ , ZrO ₂ and Al ₂ O ₃ .