JP7715411B2 - Optical thin film forming apparatus and method - Google Patents

Description

The present invention relates to an optical thin film forming apparatus and method, and in particular to an optical thin film forming apparatus and method that employs an optimal film thickness control device using FOM control for multilayer optical thin films.

A type of optical thin film widely used in the field of optical equipment is a multilayer optical thin film, which has a layered structure in which multiple optical thin films are stacked on a substrate.

Direct-view broadband monitoring (BBM) is known as a method for controlling the deposition of multilayer optical thin films. One of the common control methods used in direct-view broadband monitoring (BBM) is figure-of-merit (FOM) control.

The FOM function used in the Figure-of-Merit (FOM) control is an evaluation function that takes the integral of the difference between the spectrum measured during film formation and the design spectrum of each layer.
The FOM control is a control that stops film formation at the time when this FOM function is minimized and optimizes the film thickness of each layer.The film thickness configuration that gives the minimum value of this evaluation function is considered to be the optimal solution, and the minimum value of this FOM function is obtained (see, for example, Reference 1).

JP 2010-138463 A Japanese Patent Application Laid-Open No. 2003-279727

However, the conventional FOM control described above, which stops film formation at the time when the FOM function is minimized and optimizes the film thickness of each layer, has the following two problems.
In other words, the first problem is that in order to stop deposition at the time when the FOM function is at its minimum and optimize the film thickness of each layer, it is necessary to go slightly past the time at which the FOM function is at its minimum, in order to determine when the FOM function is at its minimum.
Therefore, the time at which the minimum point occurs is slightly exceeded, resulting in a systematic error, as the film thickness is always slightly overcoated rather than the optimum film thickness.

The second problem is that the measurement noise of the direct-view broadband monitoring (BBM) optical system affects the calculation of the FOM function, and its adverse effect cannot be ignored.
In other words, since the FOM function is calculated independently for each time point, information in the time direction cannot be utilized, and as a result, the measurement noise of the optical system at each time directly becomes a factor in random errors, resulting in random errors due to noise.
The above two problems result in a decrease in yield when multilayer optical thin film products are mass-produced.

The present invention has been made in response to the above-mentioned conventional problems, and aims to provide an optical thin film forming apparatus and method that can accurately determine the minimum FOM time when optimizing the film thickness of each layer, and that can prevent systematic errors caused by slightly overcoating the optimum film thickness.
Another object of the present invention is to provide an optical thin film forming apparatus and method that prevents the occurrence of accidental errors due to measurement noise caused by independent calculation of the FOM function for each time point, and improves the yield when mass-producing multilayer optical thin film products.

To achieve the above objective, the optical thin film formation apparatus of the present invention is an optical thin film formation apparatus that forms an optical thin film on a substrate to be formed, and includes a control unit that controls the formation of a thin film on the substrate to be formed in response to a light reception signal obtained by receiving monitor light that has passed through the substrate to be formed. The control unit fits the time change in transmittance at each wavelength point in the optical thin film to be formed, extrapolates the fitting curve for each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance at each wavelength at a future time, calculates a figure-of-merit (FOM) function for the predicted spectrum at each future time obtained by the prediction, sets the time at which the predicted FOM takes a minimum value as the film formation stop time, and controls the formation of the optical thin film based on the set film formation stop time.

Another feature of the present invention is that the optical thin film formation apparatus comprises a light-projecting unit that projects monitor light onto a substrate to be formed, on which a multilayer thin film is formed by depositing a film material supplied from a film-forming material supply unit disposed within a film-forming chamber; a light-receiving unit that receives the monitor light that has passed through the substrate to be formed and outputs a light-receiving signal; a temperature-measuring unit that measures the substrate temperature during film formation; and a control unit that acquires the light transmittance of the substrate to be formed in response to the light-receiving signal and controls the formation of the thin film in association with the acquired light transmittance information. The control unit fits the time change in transmittance for each wavelength point in the optical thin film to be formed, extrapolates the fitting curve for each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance for each wavelength at a future time, calculates a figure-of-merit (FOM) function for the predicted spectrum for each future time obtained by the prediction, sets the time at which the predicted FOM takes a minimum value as the film-forming stop time, and performs film-forming control of the optical thin film based on the set film-forming stop time.

Another feature of the present invention is an optical thin film formation method for forming an optical thin film on a substrate to be deposited, in an optical thin film formation apparatus having a control unit that controls the formation of a thin film on the substrate to be deposited in response to a light reception signal obtained by receiving monitor light transmitted through the substrate to form the optical thin film on the substrate to be deposited, the method comprising the steps of: fitting, by the control unit, the time change in transmittance for each wavelength point in the optical thin film to be deposited; extrapolating, by the control unit, the fitting curve for each wavelength point obtained by the fitting, to predict a future spectrum, which is the transmittance for each wavelength at a future time; calculating, by the control unit, the FOM for the predicted spectrum for each future time obtained by the prediction, and setting the time at which the predicted FOM takes a minimum value as the deposition stop time; and executing, by the control unit, deposition control of the optical thin film based on the set deposition stop time.

Another feature of the present invention is an optical thin film forming apparatus that forms an optical thin film on a substrate to be film-formed, the optical thin film forming apparatus having a control unit consisting of a computer that controls the formation of a thin film on the substrate to be film-formed in response to a light reception signal obtained by receiving monitor light that has passed through the substrate to be film-formed, and a program for causing the computer to execute the following steps:
A procedure for fitting the time change in transmittance for each wavelength point in the optical thin film to be formed;
A procedure of extrapolating the fitting curves at each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance of each wavelength at a future time;
calculating a figure-of-merit (FOM) function for the spectrum prediction for each time in the future obtained by the prediction, and setting the time at which the predicted FOM takes a minimum value as the deposition stop time;
a step of controlling the deposition of the optical thin film based on the set deposition stop time.

According to the present invention, when optimizing the film thickness of each layer, it is possible to determine an accurate minimum FOM time and prevent systematic errors caused by slightly overcoating the optimum film thickness.
Furthermore, according to the present invention, the independent calculation of the FOM function for each time point prevents the occurrence of accidental errors due to measurement noise, and as a result, the yield can be improved when multilayer optical thin film products are mass-produced.

FIG. 1 is a schematic diagram showing the configuration of an ion beam assisted vacuum deposition apparatus, which is a vacuum film forming apparatus that employs an optical film thickness control apparatus according to an embodiment of the present invention. FIG. 2 is a diagram schematically illustrating a film formation target substrate according to the embodiment shown in FIG. 1 and a multilayer film of thin films formed on the film formation target substrate. FIG. 3 is a block diagram showing the internal configuration of the control unit 60 shown in FIG. FIG. 4 is a diagram for explaining a figure-of-merit (FOM) function and its parameters related to optical film thickness control according to this embodiment. FIG. 5 is a flowchart of a process for predicting changes in the FOM curve in the future beyond the current time using a future FOM minimum time prediction algorithm. FIG. 6 is a graph showing an example of a fitting curve at each wavelength point. FIG. 7 is a graph showing an example of a curve (when λ=400 nm) obtained by extrapolating the fitting curves at each wavelength point shown in FIG. FIG. 8 is a graph showing an FOM prediction curve calculated using raw data during film formation according to the FOM function shown in FIG. FIG. 9 is an explanatory diagram illustrating the application of the FOM curve change prediction process using the FOM minimum time prediction algorithm to a color target. FIG. 10 is an explanatory diagram of a case where the physical characteristics of each layer are obtained in the process of fitting the time change in transmittance for each wavelength point.

Below, an embodiment of a vacuum film deposition apparatus as an optical thin film deposition apparatus employing the optical film thickness control device of the present invention and a vacuum film deposition method as an optical thin film deposition method using the same will be described with reference to the drawings.

Figure 1 is a schematic diagram showing the configuration of an ion beam assisted vacuum deposition apparatus, which is a vacuum film formation apparatus that employs an optical film thickness control device according to an embodiment of the present invention.

In the vacuum deposition apparatus 1 of this embodiment, for example, an exhaust pipe and vacuum pump (not shown) are connected to the vacuum chamber 10, which serves as the film-forming chamber, so that the interior can be depressurized to a predetermined pressure. The back pressure within the vacuum chamber 10 during film formation by vacuum deposition is, for example, approximately 10-2 to 10-5 Pa.

A first vacuum evaporation source 21 and a second vacuum evaporation source 22 are arranged at the bottom inside the vacuum chamber 10 as a film forming material supply unit 20. A first evaporation material 211 is accommodated inside the first vacuum evaporation source 21, and a second evaporation material 221 is accommodated inside the second vacuum evaporation source 22.
The first deposition material 21 is, for example, SiO2, and the second deposition material 23 is, for example, TiO2 or Ta2O5.
Each vacuum evaporation source 21, 22 is provided with a heating means such as resistance heating, electron beam heating, laser beam heating, or an electron gun (not shown), and when the evaporation material is heated and vaporized in the vacuum evaporation source, the vapor of the evaporation material is ejected.

For example, within the vacuum chamber 10, a substrate holder 31 is provided that holds a film-forming target substrate 30, which is an optical substrate such as quartz glass, in the direction in which the vapor of the evaporation material from the first vacuum evaporation source 21 and the second vacuum evaporation source 22 is ejected, with the film-forming surface facing the film-forming material supply section 20.
For example, the substrate holder 31 is supported from above the vacuum chamber 10 by a holder support portion 32 .

Although FIG. 1 shows an example in which two vacuum deposition sources are provided to form a multilayer film of two types of thin films, various embodiments are possible, such as providing three vacuum deposition sources to form a multilayer film of three types of thin films.
In this embodiment, a case where a multilayer film is formed is described, but the present invention can also be implemented in the case of a single layer instead of a multilayer film.
When three vacuum evaporation sources are used, for example, the first evaporation material is SiO2, the second evaporation material is Si3N4, and the third evaporation material is a-SiN:H.

2A and 2B are diagrams schematically showing a film-formation target substrate 30 and a multilayer film of thin films formed on the film-formation target substrate according to the first embodiment.
FIG. 2(a) shows an example in which two substances are used as deposition materials, and FIG. 2(b) shows an example in which three substances are used as deposition materials.
Although examples in which two substances are used as deposition materials and examples in which three substances are used as deposition materials are shown here, the present invention is not limited to these examples.

When two substances are used as deposition materials, as shown in Figure 2(a), when the vapor of the deposition material ejected from each of the two vacuum deposition sources 21 and 22 reaches the surface of the substrate 30 to be deposited and solidifies, a multilayer film 310 of thin films 311 and 312 of the deposition material is formed on the surface of the substrate 30 to be deposited.
For example, an NBP filter is fabricated by alternately stacking 66 layers of SiO2/TiO2 on a film-forming target substrate 30 made of an optical glass substrate. For example, the center wavelength of the transmission band is 827 nm, and the bandwidth is 12 nm or less.

When three substances are used as deposition materials, as shown in Figure 2(b), when the vapor of the deposition material ejected from each of the three vacuum deposition sources reaches the surface of the substrate 30 to be deposited and solidifies, a multilayer film 320 of thin films 321, 322, and 323 of the deposition material is formed on the surface of the substrate 30 to be deposited.
For example, a BP filter is fabricated by alternately stacking 66 layers of SiO2/Si3N4/a-SiN:H on a film-forming target substrate 30 made of an optical glass substrate. For example, the center wavelength of the transmission band is 940 nm.

Furthermore, for example, an ion source 23 for irradiating ions such as oxygen ions onto a substrate on which a film is to be formed is provided in the vacuum chamber 10, and ion beam assisted vacuum deposition can be performed.
By irradiating ions from the ion source 23 onto the film formation surface of the substrate 30 to be film-formed, a film can be formed while simultaneously carrying out two processes: a process in which a film is formed using a vapor deposition material supplied from the film-forming material supply unit 20, thereby increasing the film thickness, and a process in which a portion of the surface of the already formed film is sputtered by ions irradiated from the ion source 23, thereby decreasing the film thickness.
In this case, if a difference in film thickness occurs within the surface of the substrate 30 to be film-formed due to the density distribution of the film-forming substance supplied from the film-forming material supply unit 20, a multilayer film with a uniform in-plane film thickness distribution can be obtained by performing sputtering using ions irradiated from the ion source 23 under conditions that cancel out the difference in film thickness.

In this embodiment, a light projecting unit 40 is provided that projects monitor light L onto a film-forming target substrate 30 held by a substrate holder 31 .
The light projecting unit 40 is installed outside the vacuum chamber 10 and includes a light source 41 as a light projecting head that projects monitor light L onto the film formation target substrate 30. As the light source 40, for example, a halogen lamp can be used.

A light receiving section 50 is provided which receives monitor light L transmitted through the film formation target substrate 30 and the thin film and multilayer film being formed, and outputs a light reception signal SR.
The light receiving unit 50 is provided, for example, within the vacuum chamber 10, and is composed of a light receiving lens 51 as a light receiving head of the light receiving unit that receives monitor light L that has passed through the substrate on which a film is to be formed and the thin film or multilayer film being formed, a spectroscopic unit 52 consisting of a spectrophotometer that disperses the monitor light received by the light receiving lens 51, a light detection unit 53 that detects the light dispersed by the spectroscopic unit 52, and a light receiving optical system 54 such as an optical fiber that transmits the monitor light L received by the light receiving lens 51 to the spectroscopic unit 52.

For example, the light detection unit 53 has a configuration in which light receiving pixels that convert received light into optical signals are arranged in a matrix, and a CCD sensor or the like can be used as the light detection unit 53 .
The monitor light L transmitted through the film-forming substrate 30 is received by the light-receiving lens 51, transmitted to the spectroscopic section 52 by the light-receiving optical system 54, and dispersed, and the dispersed monitor light is detected by the light detection section 53.
The monitor light L transmitted through the film formation target substrate 30 is dispersed by the spectroscopic unit 52, and the dispersed light is detected by the photodetector unit 53, which has light-receiving pixels arranged in a matrix, and outputs a light-receiving signal SR. The photodetector unit 53 can acquire a continuous spectrum of the monitor light, i.e., can detect the monitor light at multiple wavelengths.

The light receiving signal SR detected by the light detecting section 53 is supplied to a control section 60 configured by a personal computer (PC) or the like.
The control unit 60 processes the light reception signal SR to obtain the light transmittance of the film formation target substrate 30. Furthermore, by obtaining the continuous spectrum of the monitor light as described above, the control unit 60 obtains the light transmission spectrum of the film formation target substrate 30.
The control unit 60 can provide feedback during film formation based on the obtained light transmittance or light transmission spectrum so as to change the film formation conditions so as to obtain desired optical characteristics.
In addition to the above configuration, the vacuum deposition apparatus 1 of this embodiment further includes a radiation thermometer 70 as a temperature measurement unit for measuring the substrate temperature during film formation, which is provided, for example, within the holder support portion 32 of the substrate holder 31 (above the substrate holder 31).

In this embodiment, the substrate temperature includes not only the temperature of the substrate itself, but also the temperature around the substrate, which is expected to be maintained at the same temperature as the substrate.

In this embodiment, the control unit 60 is configured to be able to make corrections to the film formation control based on the substrate temperature measured by the radiation thermometer 70 serving as the temperature measurement unit.

FIG. 3 is a block diagram showing the internal configuration of the control unit 60 shown in FIG.
3, the control unit 60 is a personal computer (PC) having a configuration in which a RAM 61, a ROM 62, a display monitor 64, a keyboard 65, and a mouse 66 are connected to a CPU 63, and the CPU 63 is configured to perform film formation control (described later) in accordance with a film formation control program stored in the ROM 62, based on instructions input by an operator via the keyboard 65 and the mouse 66. The film formation control by the CPU 63 is performed while the control content is displayed on the display monitor 64.
The film formation control program also includes an FOM control program for optimizing the film thickness of layers in the optical thin film, which will be described later, and this FOM control program is equipped with an FOM minimum time prediction algorithm, which will be described later.
The FOM control program equipped with the above-mentioned FOM minimum time prediction algorithm may be stored in various types of storage media and may be applied to and used in various optical thin film forming apparatuses.

The control unit 60 in this embodiment acquires the light transmittance of the substrate 30 to be film-formed in accordance with the light receiving signal SR, and performs film formation control in association with the acquired light transmittance information to form a thin film, more specifically, to control the film thickness of the current thin film (current layer) being formed.
In the present invention, the Figure-of-Merit (FOM) function is used to calculate the integral of the difference between the measured value of the light transmission spectrum during film formation obtained as described above and the design value of the light transmission spectrum, and film formation is stopped at the time when this FOM function is minimized, thereby performing FOM control to optimize the film thickness of each layer.
However, in conventional FOM control, in which film formation is stopped at the time when the FOM function is minimized and the film thickness of each layer is optimized, as described in the problem that the invention aims to solve, in order to stop film formation at the time when the FOM function is minimized and optimize the film thickness of each layer, there was a problem in that it was not possible to determine when the FOM minimum time was, unless the time at which the FOM function was minimized was slightly exceeded.
Therefore, the time at which the minimum point is reached is slightly exceeded, resulting in a slight overcoating beyond the optimum film thickness, which results in a systematic error.

The present invention therefore further predicts future changes in the FOM curve for the optical thin film being deposited beyond the current time using a future FOM minimum time prediction algorithm, which will be described later, and sets the time at which the predicted future FOM curve reaches its minimum point as the deposition stop time.

Next, the film formation control using the future FOM minimum time prediction algorithm will be described.
The FOM function used in this future FOM minimum time prediction algorithm is expressed, for example, by Equation 1 shown in FIG. 4, which calculates the integral of the difference between the measured light transmittance spectrum during film formation and the design value of the light transmittance spectrum.
FIG. 4 is a diagram for explaining a figure-of-merit (FOM) function and its parameters related to optical film thickness control according to this embodiment.

Next, a process for predicting changes in the FOM curve in the future beyond the current time using the above-mentioned future FOM minimum time prediction algorithm will be described.
FIG. 5 is a flowchart of a process for predicting changes in the FOM curve in the future beyond the current time using a future FOM minimum time prediction algorithm.

First, in step ST1 of FIG. 5, the FOM minimum time prediction algorithm is started, and then in step ST2, fitting is performed on the time change in transmittance for each wavelength point in the optical thin film to be formed.
This is because fitting the time series data of only one wavelength only allows prediction of the future transmittance at that one wavelength, so fitting is performed independently at all wavelength points being measured.
The time change in transmittance for each wavelength is independent and unrelated to the time change in transmittance for other wavelengths.
That is, by fitting the time change in transmittance for each wavelength point, for example, a fitting curve such as that shown in Fig. 6 can be obtained. Fig. 6 shows fitting curves at wavelength points of 400 nm, 500 nm, 600 nm, and 700 nm, and in the graph for each wavelength point, the horizontal axis represents time (sec) and the vertical axis represents transmittance (%).
Here, as a fitting function for fitting the time change in transmittance for each wavelength point, the following fitting function can be used.
That is, for the multilayer film to be formed, the multilayer film and the substrate that have already been formed are equated with a certain film and defined as an equivalent film, and the square root of the reflectance between the two materials (r = √R) is defined as the reflection amplitude. A fitting function T(t) is employed that relates the (equivalent) reflection amplitude r between the equivalent film and the current layer, the (current) reflection amplitude r0 between the current layer and air (vacuum), and the phase δ.
The fitting function T(t) is shown below.

The physical parameters of this fitting function T(t) are as follows:
The parameter r indicates the (equivalent) reflection amplitude between the equivalent film 330 and the current layer 340 .
The parameter r0 indicates the (current) reflection amplitude between the current layer 340 and the air (vacuum).
The parameter ω indicates the angular velocity that forms the phase information.
Here, there is a relationship of ωt=4πnd/λ, where n represents the refractive index, d represents the physical film thickness, and λ represents the monitoring wavelength.
The parameter φ0 indicates the initial phase, that is, the phase of a certain layer at the start of deposition.
The parameter Ψ represents a proportionality constant, which represents the systematic error of the absorption or transmittance measurement of the film (a value that would be 1 if they were absent).

Of the above physical parameters r, r0, ω, Ψ, and φ0, the current reflection amplitude r0 is a fixed value, and the remaining physical parameters r, ω, Ψ, and φ0 are determined by fitting using a fitting function.
In this way, the fitting process utilizes measurement information at each time point, which reduces random errors caused by noise more effectively than conventional FOM control.
In other words, in conventional FOM control, measurement noise from the direct-view broadband monitoring (BBM) optical system occurs in the calculation of the FOM function, and its influence cannot be ignored.
To explain in more detail, because the FOM function is calculated independently for each time point, information in the time direction cannot be utilized, and as a result, measurement noise from the optical system at each time directly becomes a factor in random errors, causing random errors due to noise and resulting in a decrease in yield when multilayer optical thin film products are mass-produced.
In contrast, according to this embodiment, measurement information at each time is used in the fitting process, so that random errors due to noise can be suppressed more effectively than in conventional FOM control.

Next, in step ST3, extrapolation is performed on each fitting curve for each wavelength point obtained in step ST2, and the results are superimposed for all wavelength points to predict the transmittance of each wavelength at a future time, i.e., the future spectrum.
Here, the spectrum is an arrangement of transmittances at each wavelength point in order of wavelength.
An example of predicting the future spectrum will be described below with reference to FIGS.
FIG. 6 is a graph showing an example of a fitting curve at each wavelength point.
That is, the range from 0 nm to 500 nm shown in FIG. 6 is the measured raw data, and the range from 500 nm to 600 nm is the fitting curve. When each of the fitting curves is extrapolated, a graph such as that shown in FIG. 7 is obtained.
7 is a graph showing an example of a curve obtained by extrapolating the fitting curve at each wavelength point, where λ=400 nm, where the horizontal axis represents time (sec) and the vertical axis represents transmittance (%).
Then, all of the curves obtained by extrapolating the fitting curves at each wavelength point are combined to predict the spectrum for each time period.
Here, curve graphs similar to those in FIG. 7 are obtained for each of the cases where λ=500 nm, λ=600 nm, and λ=700 nm.

Here, extrapolation refers to the process of using known numerical data to find predicted values outside the range of that data.
In this embodiment, extrapolating the fitting curve at each wavelength point means an operation of predicting data from 600 seconds onward from known numerical data, that is, the measured raw data from 0 seconds to 500 seconds shown in FIG. 6 and the fitting curve from 500 seconds to 600 seconds.
It should be noted that various prediction methods are conceivable and are adopted as appropriate.

In FIG. 7, when λ=400 nm, the current time is approximately 600 seconds, the curve before approximately 600 seconds (solid line) is the actual fitting curve, and the curve after approximately 600 seconds (dotted line) is the extrapolated portion.
The current time (approximately 600 seconds) is an arbitrary current time, and is obviously determined by the causal laws of various conditions.

Next, in step ST4, the FOM is calculated for the spectrum prediction (see FIG. 7) for each future time obtained in step ST3, and the time at which the curve of the predicted FOM takes the minimum value is set as the film formation stop time.
That is, the FOM curve is calculated using the raw data during film formation using the FOM function shown in FIG.
Here, the FOM function for calculating the FOM curve is expressed, for example, by the evaluation function of Equation 1 shown in FIG. 4, and this evaluation function is used to calculate the integral of the difference between the measured value of the light transmission spectrum during film formation and the design value of the light transmission spectrum.
FIG. 8 is a graph showing an FOM curve calculated using raw data during film formation by the FOM function shown in FIG. 4, with the horizontal axis representing time (sec) and the vertical axis representing the merit function value.
As shown in FIG. 8, the merit function of this FOM curve reaches a minimum value at approximately 620 seconds, slightly over 600 seconds, and then increases.
Therefore, the time when this merit function has a minimum value is set as the film formation stop time, which in this case is set to 620 seconds.

Then, in step ST5, film formation control is executed based on the film formation stop time set in step ST4.
As described above, according to this embodiment, a future FOM minimum time prediction algorithm is used to predict the change in the FOM curve beyond the current time, and the minimum point in the predicted FOM is set as the film formation stop time.
Therefore, since film formation can be stopped at the predicted minimum point, the problem that occurs in existing technologies, in which it is not possible to determine when the FOM minimum time is, can be solved unless the time at which the minimum point is reached is slightly exceeded.
This makes it possible to eliminate the systematic error that occurs when the time to reach the minimum point is slightly exceeded, resulting in slightly overcoating more than the optimum film thickness.

Furthermore, the prediction process of the FOM curve change using the above-mentioned FOM minimum time prediction algorithm can also be applied to color targets.
In other words, depending on the film, the color seen by the human eye may be more important than the transmittance spectrum itself. In such cases, if a slight error occurs in the spectrum due to film thickness errors during film formation, it is better to control the spectrum to minimize the error from the color design (dE) rather than the error from the transmittance design (FOM).
This is the reason for its application to color targets. When targeting "colors visible to the human eye," some kind of function must be used to convert the transmittance spectrum into a numerical value that represents "color," and one example of such a "numerical value that represents color" is the CIE L*a*b* color space.
Therefore, after predicting the spectrum of the future time using the method of the present invention, the future color is calculated as L*a*b* instead of FOM, and the error dE is minimized.
More specifically, by using the future spectrum predicted in step ST3, it is possible to set the CIE L*a*b* and other colors as targets as well. Furthermore, weights can be set arbitrarily for each of L*, a*, and b* depending on the product requirements.
FIG. 9 is an explanatory diagram of the application of the prediction process of the FOM curve change by the FOM minimum time prediction algorithm to a color target.

Furthermore, in step ST2, by fitting the time change in transmittance for each wavelength point, if the measurement error of the BBM optical system is sufficiently small, the physical properties of each layer are naturally derived as a by-product of the fitting process.
Here, physical parameters that can be measured in principle include the refractive index dispersion of each layer, the initial phase, the reflection amplitude, and the deposition rate of the physical film thickness, and these physical properties of each layer can be usefully used for controlling the deposition.
FIG. 10 is an explanatory diagram of a case where the physical characteristics of each layer are obtained in the process of fitting the time change in transmittance for each wavelength point.

Although the present embodiment has been described, the description and drawings forming part of this disclosure should not be understood as limiting, and various embodiments not described herein are included.
That is, in this embodiment, a case where a multilayer film is formed is described, but the present invention can also be implemented in the case of a single layer instead of a multilayer film.
The FOM control program equipped with the above-mentioned FOM minimum time prediction algorithm may be stored in various types of storage media and may be applied to and used in various optical thin film forming apparatuses.

10: Vacuum chamber; 20: Film forming material supply unit; 21: First vacuum evaporation source;
211: First evaporation material, 22: Second vacuum evaporation source, 221: Second evaporation material,
23: Ion source; 30, 310-320: Film formation target substrate;
31: substrate holder, 32: holder support portion, 40: light projecting portion, 41: light source,
50: Light receiving unit, 51: Light receiving lens, 52: Spectroscopic unit, 53: Light detection unit,
54: Light receiving optical system, 60: Control unit, 61: RAM, 62: ROM,
63: CPU, 64: display monitor, 65: keyboard, 66: mouse,
70... Radiation thermometer, 80-87... Display screen, SR... Light reception signal,
ST1 to ST5...each step

Claims (11)

An optical thin film forming apparatus for forming an optical thin film on a film formation target substrate,
a control unit that controls the deposition of a thin film on the deposition target plate in response to a light reception signal obtained by receiving monitor light transmitted through the deposition target substrate;
The control unit
The time change in transmittance for each wavelength point in the optical thin film to be formed is fitted.
The fitting curves for each wavelength point obtained by the fitting are extrapolated to predict a future spectrum, which is the transmittance of each wavelength at a future time;
A figure-of-merit (FOM) function is calculated for the spectrum prediction for each future time obtained by the prediction, and the time at which the predicted FOM takes a minimum value is set as the deposition stop time;
The optical thin film forming apparatus controls the formation of the optical thin film based on the set film formation stop time. The optical thin film forming apparatus of claim 1, wherein the process of setting the film formation stop time is performed using an activated FOM minimum time prediction algorithm. An optical thin film forming apparatus as described in claim 1 or 2, which predicts the future spectrum by extrapolating each fitting curve for each wavelength point and superimposing the curves for all wavelength points. a light projection unit that projects monitor light onto a film formation target substrate on which a thin multilayer film is formed by depositing a film formation material supplied from a film formation material supply unit disposed in the film formation chamber;
a light receiving section that receives the monitor light transmitted through the film formation target substrate and outputs a light receiving signal;
a temperature measuring unit for measuring the substrate temperature during film formation;
a control unit that acquires the light transmittance of the film formation target substrate in response to the light receiving signal and controls the formation of a thin film in association with the acquired light transmittance information,
The control unit
The time change in transmittance for each wavelength point in the optical thin film to be formed is fitted.
The fitting curves for each wavelength point obtained by the fitting are extrapolated to predict a future spectrum, which is the transmittance of each wavelength at a future time;
A figure-of-merit (FOM) function is calculated for the spectrum prediction for each future time obtained by the prediction, and the time when the predicted FOM takes a minimum value is set as the deposition stop time;
The optical thin film forming apparatus controls the formation of the optical thin film based on the set film formation stop time. The optical thin film forming apparatus of claim 4, wherein the process of setting the film formation stop time is performed using an activated FOM minimum time prediction algorithm. An optical thin film forming apparatus as described in claim 1 or 5, which predicts the future spectrum by extrapolating each of the fitting curves for each wavelength point and superimposing them for all wavelength points. An optical thin film forming method for forming an optical thin film on a film formation target substrate in an optical thin film forming apparatus having a control unit that controls thin film formation on the film formation target substrate in response to a light reception signal obtained by receiving monitor light that has transmitted through the film formation target substrate, the method comprising:
fitting the time change in transmittance for each wavelength point in the optical thin film to be formed by the control unit;
a step of extrapolating the fitting curves of the wavelength points obtained by the fitting by the control unit to predict a future spectrum, which is the transmittance of each wavelength at a future time;
calculating a figure-of-merit (FOM) function for the spectrum prediction for each future time obtained by the prediction, and setting the time at which the predicted FOM takes a minimum value as a film formation stop time by the control unit;
and controlling the deposition of the optical thin film by the control unit based on the set deposition stop time. The optical thin film formation method described in claim 7, wherein the process of setting the film formation stop time is performed using an activated FOM minimum time prediction algorithm. The optical thin film formation method described in claim 7 or 8, wherein the future spectrum is predicted by extrapolating each of the fitting curves for each wavelength point and superimposing the results for all wavelength points. An optical thin film forming apparatus for forming an optical thin film on a film formation target substrate, the apparatus comprising: a control unit made of a computer that controls thin film formation on the film formation target substrate in response to a light reception signal obtained by receiving monitor light transmitted through the film formation target substrate;
A program for causing the computer to execute the following steps:
A procedure for fitting the time change in transmittance for each wavelength point in the optical thin film to be formed;
A procedure of extrapolating the fitting curves at each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance of each wavelength at a future time;
calculating a figure-of-merit (FOM) function for the spectrum prediction for each time in the future obtained by the prediction, and setting the time at which the predicted FOM takes a minimum value as the deposition stop time;
A procedure for controlling the deposition of the optical thin film based on the set deposition stop time. A storage medium storing the program according to claim 10.