JP2023158648A - Optical thin film and method for manufacturing the same - Google Patents

Abstract

To provide an optical thin film that is excellent in hydrophilicity and has photocatalytic function.SOLUTION: A method for manufacturing an optical thin film repeats a step of depositing a film with a vacuum deposition method using a silicon oxide as a vapor deposition material and a step of depositing a film with a sputtering method using titanium or a titanium oxide as a target constitution material to deposit an optical thin film having a 10° or less contact angle with respect to water and a photocatalytic function of decomposing a CH group. The acquired optical thin film comprises a mixed film of the silicon oxide and the titanium oxide, where an atomic number rate of the titanium oxide is 3-24% in which atomic number is measured using an X-ray photoelectron spectroscopy; and the balance silicon oxide.SELECTED DRAWING: Figure 1

Description

Application for application of Article 30, Paragraph 2 of the Patent Act Published on February 25, 2022, 2022 69th Japan Society of Applied Physics Spring Academic Conference Proceedings DVD Held on March 25, 2022, sponsored by the Japan Society of Applied Physics, 69th Japan Society of Applied Physics Spring Academic Conference

The present invention relates to an optical thin film and a method for manufacturing the same, and more particularly to an optical thin film that has excellent hydrophilicity and can suppress a decrease in hydrophilicity or restore hydrophilicity, and a method for manufacturing the same.

When a thin film made of titanium oxide is exposed to ultraviolet light, the titanium oxide is excited and the surface of the thin film is covered with hydrophilic groups (-OH), so that it becomes hydrophilic. Therefore, the water droplets adhering to the surface of the hydrophilic thin film made of titanium oxide form a thin layer of water, and fogging is prevented because the water droplets do not cause diffuse reflection of light. Furthermore, the hydrophilic thin film has a self-cleaning action in which dirt adhering to the surface is lifted and removed by the hydrophilized water. Furthermore, since hydrophilized water has a large evaporation area, the hydrophilic thin film evaporates while efficiently removing the latent heat of vaporization from the substance it comes into contact with, thereby also having a cooling effect that lowers the temperature of the substance. These hydrophilic thin films are used in a wide range of fields, including side mirrors for cars, curved mirrors for roads, exterior construction materials for buildings and houses, tiles, and blinds.

However, when a thin film made of titanium oxide is no longer irradiated with ultraviolet rays, the once excited titanium oxide returns to its original ground state, so the hydrophilic groups (-OH) on the surface decrease and the contact angle of water gradually increases. The hydrophilic state returns to the original hydrophobic state. In this hydrophobic state, the above-mentioned antifogging properties and self-cleaning effects can hardly be expected. Titanium oxide is also a high refractive index material.

On the other hand, it is known that a thin film made of silicon oxide with a low refractive index can be formed by repeating vapor deposition and sputtering (Patent Document 1). According to Patent Document 1, when the vacuum degree of the vapor deposition atmosphere decreases, the denseness of the film decreases, and the thin film becomes porous, thereby decreasing the refractive index.

Japanese Patent Application Publication No. 2018-123365

The thin film made of silicon oxide formed by the method described in Patent Document 1 is presumed to exhibit high hydrophilicity because the film structure is porous, but when exposed to high temperature and high humidity, the surface There is a problem that CH groups are attached and hydrophilicity is lost.

The problem to be solved by the present invention is to provide an optical thin film that is excellent in hydrophilicity and has a photocatalytic function.

The present invention solves the above problems with an optical thin film containing silicon, titanium, and oxygen, having a contact angle with water of 10° or less, and having a photocatalytic function.

In addition, the present invention repeats the process of forming a film by a vacuum evaporation method using silicon oxide as a vapor deposition material and the process of forming a film by a sputtering method using titanium or titanium oxide as a target constituent material. The above problem is solved by a method for manufacturing an optical thin film, which forms an optical thin film having an angle of 10° or less and having a photocatalytic function.

In the above invention, the photocatalytic function is more preferably a photocatalytic function that decomposes CH groups.

In the above invention, the atomic ratio of the silicon is 26% to 32%, the atomic ratio of the titanium is 1% to 8%, and the remainder is the oxygen, as determined by atomic number measurement using X-ray photoelectron spectroscopy. More preferred.

Further, in the above invention, the optical thin film is made of a mixed film of silicon oxide and titanium oxide, and the atomic ratio of the titanium oxide as determined by atomic number measurement using X-ray photoelectron spectroscopy is 3% to 24%, and the remainder is the More preferably, it is silicon oxide.

Further, in the above invention, it is more preferable that the optical thin film has a refractive index of 1.44 or less for light with a wavelength of 550 nm. Further, in the above invention, it is more preferable that the optical thin film has a refractive index of 1.31 to 1.44 for light with a wavelength of 550 nm.

According to the present invention, it is possible to provide an optical thin film that is excellent in hydrophilicity and has a photocatalytic function.

1 is a longitudinal section showing an example of a film forming apparatus used in the method for manufacturing an optical thin film according to the present invention. FIG. 2 is a sectional view taken along line II-II in FIG. 1. FIG. 1 is a process diagram showing an embodiment of a film forming method according to the present invention. It is a graph showing the spectral characteristics of Examples and Comparative Examples of the present invention. 1 is a graph showing X-ray diffraction of Examples 1 to 3 of the present invention. It is a graph showing the photocatalytic function of Examples and Comparative Examples of the present invention. It is a photographic image showing the antifogging properties of Examples and Comparative Examples of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below based on the drawings. FIG. 1 is a schematic longitudinal cross-sectional view showing an example of a film forming apparatus 1 used in the method for manufacturing an optical thin film according to the present invention, and FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. Note that the method for manufacturing an optical thin film of the present invention is not limited to implementation using the film forming apparatus 1 shown in FIGS. 1 and 2, and any film forming apparatus that can realize the constituent elements of the present invention may be used.

The film forming apparatus 1 of this example includes a film forming chamber 2 configured to be able to reduce pressure from an atmospheric pressure atmosphere, an exhaust device 3 for reducing the pressure inside the film forming chamber 2, and a rotating shaft 4b rotated by a drive unit 4a. A disk-shaped substrate holder 5 that is rotatable around the substrate holding surface 5a and capable of holding the substrate S on the substrate holding surface 5a, and a part of the substrate holding surface 5a of the substrate holder 5 provided so as to face the sputtering part 5b. A differential pressure vessel 6, a sputtering mechanism 7 provided inside the differential pressure vessel 6, a gas introduction system 8 for introducing sputtering gas into the differential pressure vessel 6, and a substrate holding surface 5a inside the film forming chamber 2. and a vapor deposition mechanism 9 for vacuum vapor deposition provided so as to face the.

As shown in FIGS. 1 and 2, the substrate holder 5 of this example is formed into a disk shape, and a rotating shaft 4b that rotates in one direction by a drive section 4a is fixed to the center of the disk. The lower surface of the substrate holder 5 is a substrate holding surface 5a that fixes and holds the substrate S. An example of how the substrate S is mounted on the substrate holder 5 is shown in FIG. 2, but the method for manufacturing an optical thin film of the present invention is not limited to this mounting form, and various forms can be adopted.

In this example, a differential pressure area B inside the differential pressure vessel 6 and a high vacuum area A outside the differential pressure vessel 6 are provided between the substrate holding surface 5a of the substrate holder 5 and the upper end surface 6a of the differential pressure vessel 6. In order to provide a gap G that allows slight gas communication between the substrate holder 5 and the substrate holder 5, the substrate holder 5 is formed into a disk shape so that the gap G can be easily adjusted. However, as long as the gap G can be adjusted appropriately, the shape is not limited to a disk shape, but may be formed into a dome shape or a cylindrical shape used in a carousel type rotary film forming apparatus.

The substrate S to be film-formed is not particularly limited, and in addition to glass substrates, acrylic or other plastic substrates, metal plates, etc. can be used. In particular, when using a substrate for optical applications that requires high hydrophilicity that can exhibit antifogging performance, self-cleaning performance, or cooling performance, and has a high refractive index, it is necessary to suppress reflectance. The effects of this will be further demonstrated.

The differential pressure container 6 of this example is formed into a cylindrical shape, and has a bottomed cylindrical shape with one axial end surface 6b (bottom surface in FIG. 1) closed and the other end surface 6a (top surface in FIG. 1) open. It consists of a container body. The inside of the film forming chamber 2 is separated by the differential pressure container 6 into a high vacuum region A outside the differential pressure container 6 and a differential pressure region B inside the differential pressure container 6 .

The open end surface 6a of the differential pressure container 6 is, for example, circular, and is spaced apart from the substrate holding surface 5a of the substrate holder 5 by a predetermined gap G. This gap G is caused by the fact that when sputter gas is introduced into the differential pressure area B from the gas introduction system 8, the sputter gas leaks through the gap G into the high vacuum area A. The interval can be adjusted to a predetermined pressure higher than the high vacuum area A (in other words, a degree of vacuum lower than the high vacuum area A). The suitable size of the gap G can be determined mainly by the volume of the differential pressure container 6, the flow rate of the sputtering gas, and the pressures in the high vacuum region A and the differential pressure region B to be adjusted.

Note that the differential pressure container 6 faces a part of the substrate holder 5 and has communication parts such as holes and gaps that allow slight gas communication between it and the other high vacuum area A inside the film forming chamber 2. It may have any shape as long as it can be physically isolated, and is not limited to the illustrated cylindrical body. For example, the differential pressure region B may be formed by providing a shielding wall or the like on the inner wall of the film forming chamber 2. Further, instead of providing the gap G between the end surface 6a and the substrate holding surface 5a, the end surface 6a and the substrate holding surface 5a may be arranged close to each other, and a gas communication hole may be provided in the differential pressure container 6.

The differential pressure container 6 is provided with a sputtering mechanism 7. The sputtering mechanism 7 of this example includes a target 7a arranged inside a differential pressure container 6, a sputtering electrode 7b on which the target 7a is set, a sputtering power source 7c supplying power to the sputtering electrode 7b, and a sputtering power source 7c that connects the target 7a and the substrate. A shutter 7d is arranged between the target 7a and the holder 5 and covers or opens the target 7a. The sputtering mechanism 7 of this example uses a DC (direct current) or RF (high frequency) sputtering method.

The target 7a is made of a membrane raw material formed into a flat plate, and is arranged inside the differential pressure vessel 6 so as to face the substrate holding surface 5a of the substrate holder 5. As the target 7a in this example, a metal target of titanium (Ti) can be used, and in addition to this, a metal oxide target such as titanium oxide (TiO ₂ ) may also be used.

Inside the differential pressure vessel 6, a gas introduction system 8 for introducing sputtering gas into the differential pressure region B is provided. The gas introduction system 8 includes gas cylinders 8a and 8d for storing sputtering gas, valves 8b and 8e provided corresponding to the gas cylinders 8a and 8d, mass flow controllers 8c and 8f for adjusting the flow rate of the sputtering gas, and gas cylinders 8a and 8d for storing sputtering gas. A pipe 8g serving as a supply path is provided.

The gas cylinder 8a, valve 8b, and mass flow controller 8c are used to supply oxygen gas, and the gas cylinder 8d, valve 8e, and mass flow controller 8f are used to supply argon gas. In this example, an inert gas such as argon or helium and a reactive gas such as oxygen are introduced as sputtering gases.

In order to increase the film formation rate in sputtering film formation, DC (direct current) sputtering using a metal target is effective. When obtaining a dielectric film or an oxide film, it is necessary to react with oxygen, nitrogen, etc., but the reaction may not necessarily proceed, resulting in an incomplete state. In this example, a metal target is used, and the amount of reactive gas such as oxygen is set to a very small amount, for example, reactive gas: inert gas = 1:80, relative to the amount of inert gas such as argon gas, to form a film. do. Thereby, by supplying complete oxide in the high vacuum region A where vacuum evaporation film formation is performed, which will be described later, it is possible to obtain a film close to a complete oxide as a whole. As a result, a film can be obtained that has a fast film formation rate, high adhesion, low stress, and no optical absorption. Note that the ratio of the reactive gas to the inert gas introduced into the differential pressure region B is preferably 0.5% to 15%, preferably 0.5% to 8%.

The vapor deposition mechanism 9 consists of an electron beam vapor deposition source, and includes a crucible 9a filled with vapor deposition material, and an electron gun 9b that irradiates the vapor deposition material filled in the crucible 9a with an electron beam. Further, above the crucible 9a, a shutter 9c is movably provided to open and close the upper opening of the crucible 9a. Silicon oxide (SiO ₂ ) can be used as the vapor deposition material in this example.

As described above, the film forming apparatus 1 used in this example is provided with the sputtering mechanism 7 and the vapor deposition mechanism 9 inside the single film forming chamber 2. In this film-forming apparatus 1, the configuration is such that the two film-forming methods, sputtering and vacuum evaporation, which require significantly different degrees of vacuum, are compatible. be.

By introducing sputtering gas into the differential pressure container 6, the pressure in the differential pressure region B of the differential pressure container 6 is made higher than the high vacuum region A inside the film forming chamber 2, thereby creating a vacuum that allows sputtering. The temperature can be adjusted to 1 to 10 ⁻¹ Pa. At this time, the pressure in the differential pressure region B is controlled by adjusting the flow rate of the sputtering gas and the dimensions of the gap G. That is, if the gap G is set to a small width, a large amount of gas will not flow from the differential pressure container 6 into the high vacuum region A inside the film forming chamber 2, so the degree of vacuum near the evaporation source of the evaporation mechanism 9 can be adjusted to The degree of vacuum can be set to 10 ⁻¹ to 10 ⁻⁶ Pa to allow vacuum evaporation. This configuration allows sputtering film formation and vacuum evaporation film formation to be performed inside the same film formation chamber 2. Furthermore, while switching between sputtering film formation and vacuum evaporation film formation, there is no need to adjust the internal pressure of the film formation chamber 2 to a pressure suitable for each film formation method. Film formation can be continuously repeated.

Further, the film forming apparatus 1 used in this example includes a rotary substrate holder 5 that holds the substrate S and rotates. Therefore, during film formation, the substrate S rotates inside the film formation chamber 2 around the rotation axis 4b. As a result, the substrate S moves between the differential pressure region B for sputtering film formation and the high vacuum region A for vacuum evaporation film formation. The time spent in A and B can be adjusted to any desired time. This indicates that a film formed by the sputtering method and a film formed by the vacuum evaporation method can be formed in the same film forming chamber 2.

Furthermore, according to this example, sputtering film formation is performed while the substrate S is passed through the high vacuum region A, which has a pressure higher than the pressure suitable for the sputtering method, by rotating the substrate holder 5. Adhesion to the substrate S can be suppressed, leading to the production of a high-quality film.

When sputtering film formation and vacuum evaporation film formation are performed simultaneously or alternately, the residence time of the substrate S in the differential pressure region B of sputtering film formation and the high vacuum region A of vacuum evaporation film formation, the sputtering By adjusting the film forming conditions of the mechanism 7 or the vapor deposition mechanism 9, the ratio of the film weight by sputtering to the film weight by vacuum evaporation and the total film forming amount (film thickness) can be set to desired values. .

It is also possible to realize regions with different degrees of vacuum using a differential pumping device, but when a differential pumping device is used, two pumping systems are required, and the piping system thereof becomes complicated. In contrast, in this example, regions A and B having different degrees of vacuum can be realized with a simple structure of the differential pressure vessel 6, and the entire apparatus is simplified and downsized.

Next, an embodiment of the method for manufacturing an optical thin film according to the present invention will be described. FIG. 3 is a process diagram showing an embodiment of the method for manufacturing an optical thin film according to the present invention. In this embodiment, a titanium-based thin film is formed on one side of a glass substrate S by a sputtering method using titanium as a target 7a, and a silicon oxide-based thin film is formed by a vacuum evaporation method using silicon oxide as an evaporation material. This is an example of a film forming method in which the steps of forming a thin film are successively and alternately repeated. In addition, in the method for manufacturing an optical thin film of the present invention, it is not necessarily necessary to alternately repeat sputtering film formation and vapor deposition film formation once each, and one may be repeated multiple times and then the other performed.

As a preliminary preparation, the substrate S is set on the substrate holder 5 and attached to the film forming chamber 2. Further, after setting titanium as the target 7a and filling the crucible 9a with silicon oxide as a vapor deposition material, the process shown in FIG. 3 is started.

First, in step ST1, the film forming chamber 2 is sealed, and the inside of the film forming chamber 2 is evacuated (depressurized) using the exhaust device 3. In the following step ST2, using the pressure gauge 10 provided so as to face the high vacuum region A of the film forming chamber 2, the pressure inside the film forming chamber 2 is set to a predetermined pressure in the range of 10 ^-1 to 10 ^-6 Pa. It is determined whether the pressure has reached, for example, 7×10 ⁻⁴ Pa. If the internal pressure of the film forming chamber 2 has not reached a predetermined pressure, for example 7×10 ⁻⁴ Pa, the process returns to step ST1, and evacuation is repeated until the pressure reaches 7×10 ⁻⁴ Pa.

When the inside of the film forming chamber 2 reaches a predetermined pressure, it is assumed that the pressure has been reduced to a degree of vacuum suitable for vacuum evaporation by the evaporation mechanism 9, and the process proceeds to step ST3, where the rotation of the substrate holder 5 is started. Note that in this embodiment, the rotation of the substrate holder 5 in step ST3 is started before the introduction of the gas in step ST4, but it is also possible to start the rotation of the substrate S during or after the introduction of the gas. Good too. However, since the rotation of the substrate holder 5 affects the flow rate of gas leaking to the outside of the differential pressure container 6 from the gap G between the substrate holder 5 and the differential pressure container 6, the rotation of the substrate holder 5 It is preferred to start before or during the introduction of the gas.

In step ST4, the valves 8b and 8e are opened to introduce oxygen gas and argon gas into the differential pressure region B inside the differential pressure vessel 6 from the gas cylinders 8a and 8d, respectively. When oxygen gas and argon gas are introduced into the differential pressure region B, the pressure in the differential pressure region B, which had been reduced to about 7×10 ⁻⁴ Pa by the exhaust device 3, is locally reduced to oxygen gas and argon gas. Gases are introduced, and a small amount of these gases leaks to the outside of the differential pressure container 6 through the gap G at a constant flow rate.

When the amount of gas introduced into differential pressure region B and the amount of gas leaking from differential pressure region B through gap G reach a predetermined balance, the pressure in differential pressure region B becomes the desired pressure, In this embodiment, the pressure is 1 to 10 ⁻¹ Pa, which is suitable for sputtering film formation. The pressure in the differential pressure region B may be detected by installing a pressure gauge inside the differential pressure container 6, but the inventors have discovered that plasma is generated when the pressure reaches 1 to 10 ⁻¹ Pa. This was confirmed by experiments by et al. Therefore, in this embodiment, when plasma is generated inside the differential pressure vessel 6, it is determined that the predetermined pressure of 1 to 10 ⁻¹ Pa has been reached. Note that in step ST4, if plasma is not generated even after waiting for a while, the inside of the differential pressure vessel 6 is It is expected that the pressure has not increased enough. Therefore, by adjusting the mass flow controllers 8c and 8f, the flow rates of oxygen gas and argon gas are increased.

In step ST5, the shutter 7d that had previously covered the target 7a is opened to start sputtering film formation, and the shutter 9c that had previously closed the crucible 9a is opened, and an electron beam is emitted from the electron gun 9b to the crucible 9a. is irradiated to start vacuum evaporation film formation.

In step ST6, the non-contact film thickness sensor 11 determines whether the film thickness of the thin film formed on the substrate S has reached a predetermined required film thickness. If the thickness of the thin film formed on the substrate S does not reach the predetermined required thickness, step ST5 is repeated until the required thickness is reached.

When the film thickness of the thin film formed on the substrate S reaches the predetermined required film thickness, in step ST7, the target 7a is covered with the shutter 7d, the valves 8b and 8e are closed, and the sputtering process is completed. At the same time as finishing the film, the electron gun 9b is turned off and the shutter 9c is closed to complete the vacuum evaporation film formation. Thereafter, the internal pressure of the film forming chamber 2 is returned to atmospheric pressure, and the substrate holder 5 is taken out from the film forming chamber 2.

As described above, the method for manufacturing an optical thin film of this embodiment includes the steps of forming a film of silicon oxide as a vapor deposition material on the surface of the substrate S by vacuum evaporation method, and titanium (or titanium oxide as a target constituent material). By continuously repeating the step of forming a film using a sputtering method, an optical thin film having excellent hydrophilicity and a photocatalytic function for decomposing CH groups can be obtained.

Hydrophilicity here means that the contact angle with water is 10° or less. When a film is formed using the film forming apparatus 1 described above, the degree of vacuum in the high vacuum area A decreases due to gas leaking from the differential pressure container 6 (differential pressure area B), so the density of the film decreases and the film becomes porous. This is because it becomes easier for moisture to enter. In addition, it exhibits high hydrophilicity due to the chemical action of the OH group of the silicon oxide component.

On the other hand, hydrophilic thin films made of silicon oxide have the problem that when exposed to high temperature and high humidity, CH groups attach to the surface and the hydrophilicity disappears. , a photocatalytic function for decomposing CH groups is imparted to the resulting optical thin film. That is, even if hydrophilicity is reduced or lost due to CH groups attached to the surface, upon irradiation with ultraviolet rays, the photocatalytic function of titanium oxide decomposes and removes the CH groups attached to the surface of the optical thin film. Thereby, a decrease in hydrophilicity can be suppressed and the lost hydrophilicity can be restored.

The optical thin film of this example contains silicon, titanium, and oxygen as main components. In order to exhibit the above-mentioned hydrophilicity and photocatalytic function, the atomic ratio of silicon must be 26% to 32% and the ratio of titanium atoms must be 1% to 8%, as determined by atomic number measurement using X-ray photoelectron spectroscopy. %, and the remainder is more preferably oxygen. When the silicon atomic ratio exceeds 32%, the titanium atomic ratio decreases, resulting in insufficient photocatalytic function. On the other hand, if the ratio of silicon atoms is less than 26%, hydrophilicity decreases. Furthermore, when the proportion of titanium atoms exceeds 8%, the proportion of silicon atoms decreases, resulting in a decrease in hydrophilicity. Conversely, if the atomic ratio of titanium is less than 1%, the photocatalytic function will be insufficient.

The optical thin film of this example contains silicon, titanium, and oxygen as main components, but the film is composed of a mixed film of silicon oxide and titanium oxide, and is a laminated film in which a thin film of silicon oxide and a thin film of titanium oxide are laminated. isn't it. It is more preferable that the atomic ratio of titanium oxide as determined by atomic number measurement using X-ray photoelectron spectroscopy is 3% to 24%, with the remainder being silicon oxide. When the atomic ratio of titanium oxide exceeds 24%, the atomic ratio of silicon oxide decreases, resulting in a decrease in hydrophilicity. Conversely, if the atomic ratio of titanium oxide is less than 3%, the photocatalytic function will be insufficient.

In the optical thin film of this example, the degree of vacuum in the high vacuum region A decreases due to the gas leaking from the differential pressure container 6 (differential pressure region B), so the denseness of the film decreases and becomes porous. Therefore, the optical thin film has a low refractive index, and the refractive index for light with a wavelength of 550 nm is preferably 1.44 or less, more preferably 1.31 to 1.44. Having such a low refractive index makes it possible to suppress light reflection on the substrate surface, thereby preventing flare, ghosting, reflection of external light, etc. In addition, since the film is formed using a material with a higher refractive index than glass, the desired refractive index can be freely selected without being constrained by the refractive index of existing materials, giving greater freedom in the design of optical thin films. can be increased.

The optical thin film of this example may be formed as a single layer on the surface of a substrate made of metal, plastic, or inorganic material, or may be included as one or more thin films of a laminated multilayer film.

<<Examples and Comparative Examples>> A glass substrate S (N-BK7 manufactured by SCHOTT, plate thickness 1.0 mm, 40 x 40 mm, A mixed film of silicon oxide and titanium oxide was formed on one side of the substrate (refractive index n _d : 1.5168) with a target film thickness of 500 nm, and the spectral transmission was measured using a spectrophotometer (V-670 manufactured by JASCO Corporation). The refractive index (550 nm wavelength light) of the film after film formation was calculated from the transmittance, and the contact angle θ was determined for the same film based on the wettability test method for the substrate glass surface (JIS R3257). , hydrophilicity was evaluated. The contact angle was measured immediately after film formation and after the high-temperature and high-humidity test by irradiating the sample with an ultraviolet lamp (Funakoshi UVGL-58, 6W, peak wavelength 254 nm, 150 μW/cm ² ) from a distance of 2 cm. I went there a total of 3 times. The high temperature and high humidity test was conducted at 85° C., 85%, for 24 hours using an environmental tester (SH-641 manufactured by ESPEC). The film forming conditions of the film forming apparatus 1 at this time are as follows.

The ratio of the volume of the vacuum container 2 to the volume of the differential pressure container 6 is 1:0.02, the vertical distance H between the crucible 9a of the vacuum evaporation mechanism 9 shown in FIG. 1 and the substrate S is 35 to 50 cm, and the height is The target degree of vacuum for vacuum region A was 7×10 ⁻⁴ Pa, and the target degree of vacuum for differential pressure region B was 1 to 10 ⁻¹ Pa. Regarding sputtering film formation, DC sputtering was performed using a DC power source as the sputter power source 7c, and the DC power of the sputter power source 7c was 1500W. A titanium target (manufactured by USTRON) was used as the target 7a, and as sputtering gases, 100 sccm of oxygen gas and 500 sccm of argon gas were introduced from the lower part of the target 7a to perform reactive sputtering.

Furthermore, for vacuum deposition film formation, silicon oxide (manufactured by Merck) was used as the deposition material. Furthermore, no reactive gas such as oxygen gas was introduced into the high vacuum region A. Further, the substrate S was heated to 200°C. In Examples 1 to 3 in Table 1 below, the deposition conditions for sputtering deposition (the DC power of the sputtering power source 7c is 1500 W) are fixed, and the deposition rate for evaporation deposition, specifically, the electron gun By setting the current amount of 9b to three levels: 150 mA (Example 1), 180 mA (Example 2), and 200 mA (Example 3), Examples 1 to 3 with different mixing ratios of silicon oxide and titanium oxide It was made into an optical thin film. Comparative Example 1 shows an example in which the same film forming apparatus 1 was used, the DC power was set to 0, the sputtering gas flow rate was set to 0, and film formation was performed only by vacuum evaporation.

The atomic ratios of the constituent elements Si, Ti, and O, and the atomic ratios of silicon oxide and titanium oxide constituting each of the optical thin films of Examples 1 to 3 were analyzed by X-ray photoelectron spectroscopy (XPS). . Table 1 shows the atomic ratio and refractive index of Examples 1 to 3 and Comparative Example 1.

FIG. 4 shows the results of measuring the spectral transmittance of Examples 1 to 3, Comparative Example 1, and the glass substrate using a spectrophotometer (V-670, manufactured by JASCO Corporation). As shown in FIG. 4, no optical absorption was observed in any of Examples 1 to 3 and Comparative Example 1.

Further, the crystal structure of each optical thin film of Examples 1 to 3 was analyzed by X-ray diffraction (XRD). The results are shown in FIG. From the analysis results by X-ray photoelectron spectroscopy (XPS) shown in Table 1, it is understood that all the optical thin films of Examples 1 to 3 were produced as mixed films of silicon oxide and titanium oxide. Further, from the analysis results by X-ray diffraction (XRD) shown in FIG. 5, no difference was observed in the crystal structure of any of the optical thin films of Examples 1 to 3.

Next, evaluation of hydrophilicity will be explained. First, when the contact angle of each of the optical thin films of Examples 1 to 3 with water was measured immediately after the film was formed, they were all 10° or less, and no difference was observed. Next, each of the optical thin films of Examples 1 to 3 was placed in an environmental tester (SH-641 manufactured by ESPEC) set at a temperature of 85° C. and a humidity of 85% for 24 hours to conduct a high temperature and high humidity test. When the contact angle of water was measured immediately after this high temperature and high humidity test, the optical thin film of Example 1 had θ=49°, the optical thin film of Example 2 had θ=53°, and the optical thin film of Example 3 had θ =58°. It was confirmed that all of the optical thin films of Examples 1 to 3 lost their hydrophilicity when subjected to a high temperature and high humidity test.

Each of the samples of Examples 1 to 3 that underwent these high temperature and high humidity tests was exposed to ultraviolet light from a distance of 2 cm using an ultraviolet lamp (Funakoshi UVGL-58, 6W, peak wavelength 254 nm, 150 μW/cm ² ). Irradiated. The contact angle of each of the optical thin films of Examples 1 to 3 with respect to water was measured every hour after the UV irradiation began. The results are shown in FIG. In the optical thin film of Comparative Example 1, which does not contain titanium oxide, the contact angle did not decrease even when irradiated with ultraviolet rays, and restoration of hydrophilicity was not observed. On the other hand, it was confirmed that in all of the optical thin films of Examples 1 to 3, the contact angle decreased and the hydrophilicity was restored by irradiation with ultraviolet rays. At the same time, it was confirmed that when the irradiation time (irradiation light amount) was the same, the contact angle decreased more markedly in Example 1, which had a higher titanium oxide content. It was also confirmed that all of the optical thin films of Examples 1 to 3 recovered to their original contact angles of 10° or less, despite differences in irradiation time (irradiation light amount).

Immediately after the optical thin films of Example 1 and Comparative Example 1 were formed, they were placed in a desiccator and stored indoors for one year, after which a fogging test was conducted in which each sample was exposed to water vapor. The results are shown in FIG. It was confirmed that the optical thin film of Example 1 maintained high hydrophilicity even one year after the film was formed, whereas the optical thin film of Comparative Example 1 lost its hydrophilicity.

A... High vacuum area B... Differential pressure area G... Gap S... Substrate 1... Film deposition device 2... Film deposition chamber 3... Exhaust device 4a... Drive unit 4b... Rotation shaft 5... Substrate holder 5a... Substrate holding surface 5b... Sputtering Part 6...Differential pressure vessel 6a, 6b...End face 7...Sputter mechanism 7a...Target 7b...Sputter electrode 7c...Sputter power source 7d...Shutter 8...Gas introduction system 8a, 8d...Gas cylinder 8b, 8e...Valve 8c, 8f...Mass flow controller 8g... Piping 9... Vapor deposition mechanism 9a... Crucible 9b... Electron gun 9c... Shutter 10... Pressure gauge 11... Film thickness sensor

Claims (12)

Contains silicon, titanium and oxygen,
An optical thin film that has a contact angle with water of 10° or less and has a photocatalytic function. The optical thin film according to claim 1, wherein the photocatalytic function is a photocatalytic function that decomposes CH groups. According to claim 1 or 2, the atomic ratio of the silicon is 26% to 32%, the atomic ratio of the titanium is 1% to 8%, and the remainder is the oxygen, as determined by atomic number measurement using X-ray photoelectron spectroscopy. The optical thin film described. Consisting of a mixed film of silicon oxide and titanium oxide,
The optical thin film according to claim 1 or 2, wherein the atomic ratio of the titanium oxide as determined by atomic number measurement using X-ray photoelectron spectroscopy is 3% to 24%, with the remainder being the silicon oxide. The optical thin film according to claim 1 or 2, wherein the optical thin film has a refractive index of 1.44 or less for light with a wavelength of 550 nm. Consisting of a mixed film of silicon oxide and titanium oxide,
An optical thin film in which the atomic ratio of the titanium oxide is 3% to 24%, as determined by atomic number measurement using X-ray photoelectron spectroscopy, and the remainder is the silicon oxide. The contact angle with water is 10° or less,
The refractive index for light with a wavelength of 550 nm is 1.44 or less,
The optical thin film according to claim 6, which has a photocatalytic function to decompose CH groups. Repeating the step of forming a film by a vacuum evaporation method using silicon oxide as a vapor deposition material, and the step of forming a film by a sputtering method using titanium or titanium oxide as a target constituent material,
A method for producing an optical thin film, which forms an optical thin film having a contact angle with water of 10° or less and having a photocatalytic function. The optical thin film according to claim 8, wherein the photocatalytic function is a photocatalytic function that decomposes CH groups. According to claim 8 or 9, the atomic ratio of the silicon as determined by atomic number measurement using X-ray photoelectron spectroscopy is 26% to 32%, the atomic ratio of the titanium is 1% to 8%, and the remainder is the oxygen. The method for producing the optical thin film described above. The optical thin film is made of a mixed film of silicon oxide and titanium oxide,
The method for producing an optical thin film according to claim 8 or 9, wherein the atomic ratio of the titanium oxide as determined by atomic number measurement using X-ray photoelectron spectroscopy is 3% to 24%, with the remainder being the silicon oxide. 10. The method for manufacturing an optical thin film according to claim 8, wherein the optical thin film has a refractive index of 1.44 or less for light with a wavelength of 550 nm.

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