JP2007063623A - Method for manufacturing optical thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film deposition method, by which a transition state in reactive sputtering can be stably maintained for a long time. <P>SOLUTION: In a magnetron sputtering system, the transition sputtering is performed by supplying an inert gas and a reactive gas in respective desired flow rates into a vacuum chamber while adjusting the variation with time of discharge electric power or discharge admittance to be within ±10% and controlling the voltage of a sputter electric source. Further, the maximum magnetic field intensity of the surface of a target is adjusted to be 0.03-0.1 tesla so as to stabilize the discharge electric power or the discharge admittance for a long time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of depositing a film at a special operating point called a transition region when forming an optical thin film mainly used in the field of optical technology by a sputtering method, and in particular, a method of manufacturing an optical thin film capable of stably controlling a transition state. About.

  Optical thin films are widely used in various products such as display devices such as liquid crystal display elements, optical components for optical communication, optical discs, window glass for construction, and windshields for automobiles.

In optical multilayer films in which these optical thin films are laminated, an optical interference effect can be utilized by combining a transparent thin film having a high refractive index with a transparent thin film having a low refractive index, and sometimes a transparent thin film having an intermediate refractive index between them. . Examples of the material having a high refractive index include TiO ₂ , Ta ₂ O ₅ , SnO ₂ , ZnO, Nb ₂ O ₅ , ZrO ₂ , and HfO _2, and examples of the low refractive index material include MgF ₂ , SiO ₂ , and Al ₂ O. _As the intermediate refractive index material such as ₃ , materials such as Si ₃ N ₄ , WO ₃ and MgO are known and widely used.

  As a method for forming a thin film of these materials, a wet film forming method or a physical film forming method in a vacuum is used. However, an optical thin film requires a large number of layers or requires a highly accurate control of the film thickness. Therefore, a physical film formation method in a vacuum is suitable. Various methods such as vapor deposition, ion plating, and sputtering can be applied as the physical film formation method. However, when a film is uniformly formed on a large substrate such as a display device or an architectural window material. The sputtering method is the most suitable method.

  When forming an optical thin film by sputtering method, it can divide roughly and can use two types of methods. One is a method for obtaining a dielectric film by using a metal target such as Ti, Ta, Nb, Zr, Hf, Si, and Al and introducing a reactive gas such as oxygen or nitrogen into the sputtering gas (reactive sputtering method). The other is to obtain a dielectric film by sputtering in an atmosphere with a low reactive gas content (mainly a rare gas) using a dielectric such as an oxide or nitride as a target. Is the method.

  In the former method, since the surface of the metal target is coated with a dielectric compound except for a material having a high sputtering rate, the sputtering rate on the target surface is lowered and the deposition rate is reduced. The challenge is to become.

  In the latter method, when the target is not conductive and RF sputtering film formation is required, the film formation speed is generally slow. However, for a ceramic target having conductivity, a high film formation rate may be obtained by DC sputtering film formation.

However, with respect to SiO ₂ and Al ₂ O ₃ target for applying the conductivity is technically very difficult, DC sputtering using a SiO ₂ or Al ₂ O ₃ target is impossible.

On the other hand, a transition sputtering method is disclosed as a method for improving the deposition rate of SiO ₂ or Al ₂ O ₃ . In reactive sputtering, the metal target surface was coated with a dielectric compound, which caused a decrease in film formation speed and arcing. However, in the transition sputtering method, the target surface was not coated with a dielectric compound. In addition, since a dielectric compound can be deposited on the substrate, a high sputtering rate can be maintained, and almost no reduction in film formation rate is observed.

  However, the transition region where transition sputtering can be realized exists between the reactive sputtering region and the metal sputtering region (the ratio of the reactive gas and the target material chemically reacting is low, and the ratio of the dielectric compound as the film is small), and the discharge Since it is realized in an extremely unstable state (transition state) in which the region changes depending on the environment, it has been difficult to stably maintain this state for a long time. For this reason, in order to perform transition sputtering film formation stably, many studies have been made so far and various control methods have been proposed.

  A method capable of realizing transition sputtering with the simplest apparatus configuration is disclosed in Non-Patent Document 1, and details are discussed in Non-Patent Document 2. This method only controls the output of the sputtering power supply. That is, only a voltage is output so as to be constant, and no special device is required. For this reason, this method is the most excellent method from the viewpoint of apparatus cost.

  However, when the discharge is controlled by the voltage, the discharge current or the discharge power fluctuates with the change of the discharge admittance (when the discharge admittance is the reciprocal of the discharge impedance and the voltage is constant, the discharge power is proportional to the discharge admittance). Therefore, in order to suppress time fluctuation of the film formation rate and time fluctuation of the film quality and realize stable sputtering, it is necessary that the discharge admittance is stable. However, in the transition state, the target surface state changes due to subtle changes in the sputtering environment (for example, substrate transport, target erosion, film deposition in the chamber, etc.), and the discharge admittance changes from moment to moment. For this reason, it is difficult to perform stable film formation in both the short term and the long term only by controlling the discharge voltage.

  When performing transition sputtering with voltage control, the set voltage is a variable used for controlling (selecting) the sputtering state. However, assuming that the discharge admittance is constant, if the discharge voltage is determined so that the sputtering state becomes the transition state, the discharge power is uniquely determined at the same time. For this reason, it is impossible to adjust the discharge power in order to adjust the film formation rate. That is, there is a problem that a new control item for adjusting the film forming speed is required.

  From the data published in Non-Patent Document 2, it can be seen that in the case of discharge by voltage control, the discharge power can be adjusted by adjusting the reactive gas supply rate. However, when the reactive gas supply rate is adjusted in a state where electric power is supplied under a constant discharge voltage condition, there are cases where the transition state is deviated. It is also predicted that there is a problem that the film quality varies even if the transition state is maintained. In order to avoid this problem, a means for changing the voltage set value when the oxygen supply rate is changed is necessary.

In Patent Document 1, it is assumed that light detection by a plasma emission monitor is effective, and a system for feeding back a signal of the emission monitor to a set value of a discharge voltage is proposed. However, in this method, there is a problem that when the electric discharge is performed for a long time, the window frame is contaminated and the emission intensity gradually changes. In addition, an expensive plasma emission monitor must be installed for system construction.
JP 2003-342725 A R. McMahon, 2 others, Journal of vacuum science & technology, 1982, A20, 3, p.376-378 J. et al. Affinito, R.I. R. Parsons, Journal of vacuum science & technology, 1984, Volume A2, No. 3, p. 1275-1284

  An object of the present invention is to provide a method for producing an optical thin film capable of stably controlling the transition state for a long period of time, and to obtain an optical thin film at a high film formation rate excellent in mass productivity.

  In order to achieve the above object, a first aspect of the present invention includes a target installed in a vacuum chamber, a sputtering power source for supplying power to the target, an inert gas and a reactive gas in the vacuum chamber. In a method for producing an optical thin film using a magnetron sputtering apparatus provided with a mechanism for supplying each at a desired flow rate, the time variation of discharge power or discharge admittance is controlled within ± 10%, and the voltage of the sputtering power supply The gist is to perform transition sputtering by controlling the above. If comprised in this way, the manufacturing method of the optical thin film which can control a transition state stably for a long term can be provided, and an optical thin film can be obtained with the high film-forming speed | rate excellent in mass productivity.

  According to the second aspect of the present invention, a target installed in the vacuum chamber, a sputtering power source for supplying electric power to the target, and an inert gas and a reactive gas are respectively supplied into the vacuum chamber at desired flow rates. An optical thin film using a magnetron sputtering apparatus having a mechanism, wherein the maximum magnetic field strength of the target surface is 0.03 Tesla or more and 0.1 Tesla or less, and the voltage of the sputtering power source is controlled. The gist is to perform transition sputtering. If comprised in this way, the manufacturing method of the optical thin film which can control a transition state stably for a long term can be provided, and an optical thin film can be obtained with the high film-forming speed | rate excellent in mass productivity.

  In addition, although the upper limit of the magnetic field intensity required for discharge admittance stabilization is not specifically defined, when the use of a commercially available permanent magnet is assumed, about 0.1 Tesla becomes a substantial upper limit. It is also known that the discharge mode changes if the magnetic field strength is increased too much.

  The invention of claim 3 controls the flow rate ratio of the inert gas and the reactive gas in claims 1 to 2 and sets the voltage value of the sputter power source in the transition region according to the flow rate ratio of the gas. The gist is to adjust. If comprised in this way, the manufacturing method of the optical thin film which can control a transition state stably for a long term can be provided, and an optical thin film can be obtained with the high film-forming speed | rate excellent in mass productivity.

  When the oxygen supply rate is increased while the voltage is kept constant in the voltage control mode, the discharge power increases, but the film formation rate per unit power decreases. In the worst case, the discharge state shifts from the transition mode to the oxide mode. Conversely, when the oxygen supply rate is decreased, the film formation rate per unit power increases. In the worst case, the discharge state shifts from the transition mode to the metal mode. It is disclosed in Non-Patent Document 1 that there is such a problem.

  Therefore, for example, an automatic control circuit is provided so that the voltage set value when discharging is performed by voltage control can be changed by the oxygen flow rate. In other words, this circuit automatically increases the voltage set value when the oxygen flow rate is increased, and automatically decreases the voltage set value when the oxygen flow rate is decreased. The slope of the set voltage with respect to the oxygen supply rate is determined in advance. That is, the change in discharge power is measured with the oxygen supply rate kept constant and the voltage as a variable. This measurement is carried out for oxygen supply rates of two or more levels. From this result, the discharge voltage in the transition state is plotted against the oxygen flow rate, and the slope of this figure is obtained. This inclination is input in advance to the control circuit described above, and the set voltage value is changed when the oxygen supply rate is changed according to this inclination.

  The invention of claim 4 comprises means for measuring the reactive gas partial pressure in the vacuum chamber in real time in claims 1 to 2, wherein the voltage of the sputtering power source is a variable, and the logarithm of the reactive gas partial pressure is The gist is to control the voltage of the sputtering power supply so that the reactive gas partial pressure is constant in a plateau region (see FIG. 8) appearing in the plotted diagram. If comprised in this way, the manufacturing method of the optical thin film which can control a transition state stably for a long term can be provided, and an optical thin film can be obtained with the high film-forming speed | rate excellent in mass productivity.

  By means of measuring the reactive gas partial pressure in real time, it is possible to effectively suppress the change in the sputtering state when the oxygen supply rate is changed. The plateau region is a region where the oxygen partial pressure is less dependent on the discharge voltage, and is a region where the deposition rate is less dependent on the discharge voltage.

  The stability of the film quality and the stability of the deposition rate in sputtering in the transition region largely depend on the surface state of the target. The main factor that determines this surface state is the oxygen partial pressure in the chamber. That is, if this oxygen partial pressure can be controlled stably, the film forming speed, film quality, etc. can be controlled stably. From this point of view, the plateau region is the region in which the oxygen partial pressure can be most easily controlled by the discharge voltage control because the fluctuation range of the oxygen partial pressure with respect to the discharge voltage is small.

  The gist of the invention of claim 5 is that a pulse voltage of 40 kHz or more and 350 kHz or less is applied to the target in claims 1 to 4. If comprised in this way, the manufacturing method of the optical thin film which can control a transition state stably for a long term can be provided, and an optical thin film can be obtained with the high film-forming speed | rate excellent in mass productivity.

The power source of the present invention is not particularly limited, but when an insulating film such as SiO ₂ or Al ₂ O ₃ is formed, the insulating film attached to the periphery of the target is prevented from being charged and arced. It is necessary to suppress it. In this case, the DC pulse power supply is effective, and an inversion frequency of at least 40 kHz or more is necessary to effectively prevent charging of the insulating film. In addition, when the inversion frequency is higher than 350 kHz, the plasma diffuses and the film formation rate decreases. For this reason, the frequency of the pulse voltage is particularly preferably 40 kHz or more and 350 kHz or less.

  A sixth aspect of the present invention is that, in the first to fourth aspects, the target is a set of two targets, and a voltage that is alternately switched at a cycle of 20 kHz or more and 100 kHz or less is applied to each set of targets. It is a summary. If comprised in this way, the manufacturing method of the optical thin film which can control a transition state stably for a long term can be provided, and an optical thin film can be obtained with the high film-forming speed | rate excellent in mass productivity.

The power source of the present invention is not particularly limited, but when an insulating film such as SiO ₂ or Al ₂ O ₃ is formed, the insulating film attached to the periphery of the target is prevented from being charged and arced. It is necessary to suppress it. In this case, it is desirable that two negative voltages are alternately supplied to a set of targets, and the voltage at each target is a sine wave or a square wave whose polarity is inverted. An inversion frequency of 20 kHz or higher is necessary to effectively prevent charging of the insulating film. In addition, since each target is in an anode / cathode relationship, the plasma diffuses at a lower frequency than when the single target is pulse-driven, so that the deposition rate decreases at an inversion frequency higher than 100 kHz. Become. For this reason, the switching frequency is particularly preferably 20 kHz or more and 100 kHz or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and sputtering apparatus of an optical thin film which can control a transition state stably for a long period can be provided, and an optical thin film can be obtained with the high film-forming speed | rate excellent in mass productivity.

  As described above, the most simple and reliable method for realizing the transition sputtering is the voltage control method disclosed in Non-Patent Document 1, but it is stable by suppressing the time fluctuation of the film forming speed and the time fluctuation of the film quality. In order to realize proper sputtering, stabilization of discharge admittance is a problem.

In view of this, the short-term fluctuation of the discharge admittance was investigated by paying attention to the substrate transport that shows a remarkable change in the discharge admittance during the SiO ₂ film forming process which is one of the optical thin films in the in-line sputtering apparatus.

  The apparatus configuration of the present invention is not particularly limited, such as an in-line type sputtering apparatus, a carousel type sputtering apparatus, or a single wafer type sputtering apparatus, but a batch that opens the chamber to the atmosphere for substrate replacement every film formation batch. In the mold processing equipment, the residual gas components in vacuum differ from batch to batch, so it is necessary to remeasure the voltage curve with the discharge voltage as a variable for each film forming batch, and it takes a lot of labor to determine the conditions. A sputtering apparatus that includes a load lock chamber and can replace the substrate while the film formation chamber is maintained in a vacuum state is preferable.

  In the following examples and comparative examples, a contact-type step meter is used for measuring the film thickness, and optical characteristics are measured with a spectrophotometer (transmittance, reflectance, color tone) and an ellipsometer (refractive index, extinction coefficient). Measured.

<Examples 1 and 2 and Comparative Example 1>
Sputtering device: In-line type sample (substrate): Soda lime glass target: Boron (B) added silicon (Si) x 1 set (2 sheets)
Ultimate vacuum: 4 × 10 ⁻⁴ Pa or less Argon (Ar) gas flow rate: 130 SCCM
Oxygen (O2) gas flow rate: 20 SCCM
Gas pressure: 0.4Pa
Target switching frequency: 40 kHz

  FIG. 1 shows the time variation of the discharge power when the discharge voltage is kept constant at 550 V, which is the transition region, under the above film forming conditions (this is referred to as Comparative Example 1). When the substrate transfer is started, the discharge power immediately before the substrate tray passes over the target was 4.0 kW, while the discharge power decreased by 15% to 3.4 kW while passing over the target, Immediately after passing, it recovered to 4.0 kW again. When the film thickness of the obtained sample was measured, the film thickness in the front and rear of the substrate traveling direction was thicker than that in the central portion, resulting in a film thickness difference of ± 15% and a difference in optical characteristics. At this time, the distance between the substrate trays was 50 mm.

  Next, under the same film forming conditions, a plurality of substrate trays were connected without gaps, and then the substrate was transported (this is referred to as Example 1). This is to effectively suppress the change in discharge admittance due to the substrate transport blocking the discharge space. FIG. 2 shows how the discharge power varies with time.

  Before the first substrate tray passed over the target and immediately after the last substrate tray passed, a large time fluctuation of the discharge power as described above was observed. The time fluctuation of electric power was about 2%. When the film thickness distribution was confirmed except for the substrates placed on the first tray and the last tray, it was within about ± 5% and the optical characteristics were uniform.

  Further, a similar experiment was performed with the interval between the substrate trays set to 10 mm (referred to as Example 2). These results are shown in Table 1. From Table 1, it was found that when the time variation of the discharge admittance exceeds 10%, the discharge shifts from the transition mode, affects the film characteristics, and the desired optical characteristics cannot be obtained.

<Examples 3 and 4, Comparative Examples 2 and 3>
Next, in order to confirm long-term fluctuations in the discharge admittance, four types of targets having different cumulative use times (erosion states) were prepared, and the relationship between the discharge voltage and the discharge output was measured. This is because if the target surface magnetic field strength is weak, the discharge admittance varies greatly depending on the target surface state, and therefore, when using targets with different erosion depths, the film formation speed, film quality, etc. may not be reproduced. At this time, the maximum magnetic field strength was 0.015 Tesla in the magnetic field direction of the target surface shown in FIG.

  When the discharge power was measured when the discharge voltage was increased or decreased in the range of 230 to 630 V, the result of FIG. 4 was obtained.

In these waveforms, the peak position is the boundary between the reactive sputtering region and the transition region, and the bottom position is the boundary between the transition region and the metal sputtering region. In the oxide mode, an SiO ₂ film can be obtained, but the film formation rate is slow. In the metal mode, the film formation rate is high, but the resulting film is a suboxide having optical absorption.

  As a result of the four measurements, the boundary between the oxide mode and the transition mode is in the range of 460 to 520 V, and the boundary from the transition mode to the metal mode varies in the range of 580 to 640 V, and the controllable range in the transition region is narrow. That is, when target erosion progresses after long-term use, the discharge admittance changes even in constant voltage drive, and the sputter state may change to another mode, so there is a problem in controllability in transition mode. It was confirmed that there was.

  Next, the position of the magnet was adjusted so that the maximum magnetic field intensity on the target surface was 0.03 Tesla, and the same measurement was performed. The results are shown in FIG.

  Although the waveform has shifted to the lower voltage side as a result of increasing the magnetic field strength, this is not an essential problem. The boundary between the oxide mode and the transition mode is in the range of 380 to 400 V, the boundary from the transition mode to the metal mode is in the range of 530 to 580 V, and the measurement variation between the four measurements is improved, and the controllable range in the transition region Is getting wider. That is, in a cathode whose magnetic field intensity on the target surface is adjusted to 0.03 tesla or more, even if the target erodes after long-term use, the discharge admittance hardly changes in constant voltage driving, and the film formation speed, film quality, etc. It was found that the change of can be suppressed.

  One type of target was selected, continuous discharge was carried out for 10 hours under the conditions shown in Table 1, and changes in film formation speed and film quality were measured (Example 3 with a target surface magnetic field strength of 0.03 Tesla). 4 and the same strength of 0.015 Tesla was designated as Comparative Examples 2 and 3. The results are shown in Table 2. From Table 2, it was found that when the maximum magnetic field strength on the target surface was less than 0.03 Tesla, a stable high-speed film formation or a desired optical film could not be obtained.

<Examples 5, 6, 7, 8>
Next, in performing constant voltage control in the transition region, the oxygen concentration dependency in the relationship between voltage and power was examined in order to use the oxygen concentration as a means for adjusting the film formation rate. The maximum magnetic field intensity on the target surface was 0.03 Tesla, the total flow rate of argon gas and oxygen gas was constant at 150 SCCM, and the oxygen concentration was changed to 6.7, 10, 13, 17%. The results are shown in FIG.

  This result reproduces the contents described in Non-Patent Document 2, and the discharge power in the transition state increases with an increase in the supply rate of the reactive gas. However, it can be seen that the transition region is not only simply increased but also shifted to the high voltage side due to the increase in oxygen concentration. Therefore, there is a problem that switching to the oxide mode or the metal mode occurs in the worst case due to the increase or decrease of the oxygen flow rate.

  Thus, a film formation experiment was performed by providing a control circuit that automatically changes the set value of the discharge voltage according to the oxygen concentration. For the relationship between the oxygen concentration and the set voltage, the following relational expression obtained from FIG. 6 was used.

  Discharge voltage (V) = 4.3 × oxygen concentration (%) + 400 (V) (1)

Since this relational expression is specific to the apparatus, it is necessary to determine it by conducting an experiment for each apparatus, but this time, the above expression was used. A control circuit in which the voltage control value is changed by changing the oxygen concentration of the supply gas was connected. In this state, the oxygen concentration was changed again to 6.7, 10, 13, and 17%, and the discharge power was measured (these are referred to as Examples 5, 6, 7, and 8, respectively). The results are shown in FIG. When the deposition rate was determined at each measurement point plotted in FIG. 7, the dynamic deposition rate per unit power was constant at 7 nm · m / min. That is, it was confirmed that the deposition rate was proportional to the power. The obtained film had a refractive index n = 1.46 and an extinction coefficient k ≦ 1 × 10 ⁻⁶ at a wavelength λ = 632.8 nm, and an excellent SiO ₂ film was obtained as an optical film.

<Example 9>
Similarly, in performing constant voltage control in the transition region, the relationship between the voltage and the oxygen partial pressure was investigated in order to use the measured value of the reactive gas partial pressure in real time as another means for adjusting the film formation rate. The maximum magnetic field intensity on the target surface was 0.03 Tesla, and the total flow rate of argon gas and oxygen gas was constant at 150 SCCM. The results are shown in FIG.

As a result of the measurement, it was found that a plateau region having an oxygen partial pressure exists in the vicinity of 400 to 500V. When film formation was performed at the center of this region, that is, with the discharge voltage adjusted to 450 V (this is referred to as Example 9), the dynamic film formation rate per unit power is as high as 5.9 nm · m / min. Met. The obtained film had a refractive index n = 1.46 and an extinction coefficient k ≦ 1 × 10 ⁻⁶ at a wavelength λ = 632.8 nm, and an excellent SiO ₂ film was obtained as an optical film.

<Examples 10, 11, 12, 13 and Comparative Example 4>
Sputtering device: In-line type sample (substrate): Soda lime glass Target: Boron (B) added silicon (Si)
Ultimate vacuum: 4 × 10 ⁻⁴ Pa or less Argon (Ar) gas flow rate: 90 SCCM
Oxygen (O2) gas flow rate: 10 SCCM
Gas pressure: 0.4Pa
Maximum magnetic field strength: 0.03 Tesla

  Under the above conditions, film formation was performed by changing the pulse frequency of the power source or the target switching frequency. The results are shown in Tables 3 and 4. When using a pulse power source from Table 3, it is preferable to use 40 kHz to 350 kHz so as not to cause a decrease in the film forming rate and to prevent arcing. From Table 4, when performing target switching, 20 kHz to It can be seen that it is preferable to use 100 kHz.

It is a figure which shows the mode of the time fluctuation | variation of the discharge power in the comparative example 1. FIG. It is a figure which shows the mode of the time fluctuation | variation of the discharge power in Example 1. FIG. It is a figure which shows the magnetic field direction of a target surface. It is a figure which shows the voltage dependence of the discharge electric power when the target maximum magnetic field strength is 0.015 Tesla. It is a figure which shows the voltage dependence of the discharge electric power when the target maximum magnetic field intensity | strength is 0.03 Tesla. It is a figure which shows the oxygen concentration dependence in the relationship between a voltage and electric power. It is a figure which shows the relationship between the oxygen concentration in Examples 5-8, and discharge electric power. It is a figure which shows the voltage dependence of the oxygen partial pressure in the method of Claim 4.

Explanation of symbols

11 Target 12 Magnet 13 Base 14 Magnetic flux line (The direction of the arrow is the magnetic field direction)

Claims (6)

A magnetron comprising a target installed in a vacuum chamber, a sputtering power source for supplying power to the target, and a mechanism for supplying an inert gas and a reactive gas to the target at a desired flow rate. In the method for producing an optical thin film using a sputtering apparatus,
A method for producing an optical thin film, wherein transition sputtering is performed by controlling discharge power or discharge admittance over time within ± 10% and controlling the voltage of the sputtering power source. A magnetron comprising a target installed in a vacuum chamber, a sputtering power source for supplying power to the target, and a mechanism for supplying an inert gas and a reactive gas to the target at a desired flow rate. In the method for producing an optical thin film using a sputtering apparatus,
A method for producing an optical thin film, wherein the maximum magnetic field strength of the target surface is set to 0.03 Tesla or more and 0.1 Tesla or less, and transition sputtering is performed by controlling the voltage of the sputtering power source.   The flow rate ratio between the inert gas and the reactive gas is controlled, and the voltage value of the sputtering power source is adjusted in the transition region according to the flow rate ratio of the gas. The manufacturing method of the optical thin film of description. Means for measuring the reactive gas partial pressure in the vacuum chamber in real time;
Using the sputtering power supply voltage as a variable, controlling the sputtering power supply voltage so that the reactive gas partial pressure is constant in a plateau region appearing in a graph plotting the logarithm of the reactive gas partial pressure. 3. The method for producing an optical thin film according to claim 1, wherein the optical thin film is produced.   The method for producing an optical thin film according to claim 1, wherein a pulse voltage of 40 kHz or more and 350 kHz or less is applied to the target. 5. The optical thin film according to claim 1, wherein the target is a set of two targets, and a voltage that is alternately switched at a cycle of 20 kHz or more and 100 kHz or less is applied to each of the pair of targets. Manufacturing method.

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