Optical thin film forming apparatus and method

Abstract

To improve a yield in the case of mass-producing a product of a multilayer optical thin film and to form a film closest to a design by judging an exact FOM minimum time in optimizing the film thickness of each layer and preventing the occurrence of a systematic error caused by slightly overcoating the optimum film thickness.SOLUTION: Provided is an optical thin film forming apparatus including a control unit that controls formation of an optical thin film, wherein the control unit performs fitting of a temporal change in transmittance for each wavelength point in the optical thin film to be formed, extrapolates a fitting curve of each wavelength point obtained by the fitting, predicts a future spectrum which is a transmittance of each wavelength at a future time, calculates a figure-of-merit (FOM) function for a spectrum prediction of each time point in the future obtained by the prediction, sets a time point at which the predicted FOM takes a minimum value as a film formation stop time, and executes film formation control of the optical thin film on the basis of the set film formation stop time.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an optical thin film forming apparatus and method, and more particularly to an optical thin film forming apparatus and method employing an optimal film thickness control apparatus by FOM control in a multilayer optical thin film.

Background Art

[0002] As an optical thin film widely applied in the field of optical devices, a multilayer optical thin film having a laminated structure in which a plurality of optical thin films are stacked on a substrate is known.

[0003] As film formation control in a multilayer optical thin film, direct vision broadband monitoring (BBM) is known. And one of the common control methods in direct vision broadband monitoring (BBM) is Figure-of-Merit (FOM) control.

[0004] 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 measurement value during film formation and the designed spectrum of each layer. And the control that stops film formation at the time when this FOM function becomes minimum and optimizes the film thickness of each layer is FOM control. Assuming that the film thickness configuration that gives the minimum value of this evaluation function is the optimal solution, the minimum value of this FOM function is obtained (see, for example, Document 1).

[0005]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] However, in the FOM control that stops film formation at the time when the conventional FOM function as described above becomes minimum and optimizes the film thickness of each layer, there are the following two problems. That is, the first problem is that in order to stop film formation at the time when the FOM function reaches its minimum and optimize the film thickness of each layer, it is impossible to determine where the FOM minimum time is unless the time at the minimum point is slightly exceeded. Therefore, since the time at the minimum point is slightly exceeded, overcoating will always be slightly more than the optimum film thickness, resulting in systematic errors.

[0007] The second problem is that measurement noise occurs in the direct-vision broadband monitoring (BBM) optical system for calculating the FOM function, and its adverse effects cannot be ignored. That is, since the FOM function is calculated independently at each time point, the information in the time direction cannot be utilized, and thus the measurement noise of the optical system at each time directly becomes a factor of accidental error, resulting in accidental errors due to noise. Due to the above two problems, the yield in mass-producing multilayer optical thin film products deteriorates.

[0008] The present invention has been made by paying attention to the above-described conventional problems. When optimizing the film thickness of each layer, it is an object of the present invention to obtain an optical thin film forming apparatus and method capable of accurately determining the FOM minimum time and preventing the occurrence of systematic errors caused by slightly overcoating the optimum film thickness. Another object of the present invention is to obtain an optical thin film forming apparatus and method that prevent the occurrence of accidental errors due to measurement noise caused by independent calculation of the FOM function at each time point and improve the yield in mass-producing multilayer optical thin film products.

Means for Solving the Problems

[0009] To achieve the above object, an optical thin film forming apparatus according to the present invention is an optical thin film forming apparatus for forming an optical thin film on a substrate to be film-formed. The apparatus includes a control unit that controls film formation on the substrate to be film-formed according to a received light signal obtained by receiving monitor light transmitted through the substrate to be film-formed. The control unit fits the change in transmittance over time at each wavelength point in the optical thin film to be formed, extrapolates the fitting curve at 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 the minimum value as the film formation stop time, and executes film formation control of the optical thin film based on the set film formation stop time.

[0010] Another feature of the present invention is that the optical thin film forming apparatus includes a light projecting unit that projects monitor light onto a substrate to be film-formed on which a thin film multilayer is formed by film-forming a film-forming material supplied from a film-forming material supply unit disposed in a film-forming chamber, a light receiving unit that receives the monitor light transmitted through the substrate to be film-formed and outputs a received light signal, a temperature measuring unit that measures the temperature of the substrate during film formation, and a control unit that acquires the light transmittance of the substrate to be film-formed according to the received light signal and controls film formation of the thin film in association with the acquired light transmittance information. The control unit fits the change in transmittance over time at each wavelength point in the optical thin film to be formed, extrapolates the fitting curve at 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 the minimum value as the film formation stop time, and executes film formation control of the optical thin film based on the set film formation stop time.

[0011] Another feature of the present invention is that in an optical thin film forming apparatus that forms a thin film on a substrate to be film-formed and has a control unit that controls the film formation of the thin film on the substrate to be film-formed according to a light reception signal obtained by receiving monitor light that has passed through the substrate to be film-formed, an optical thin film forming method for forming an optical thin film on the substrate to be film-formed, comprising: a step of fitting, by the control unit, the change in transmittance over time at each wavelength point in the optical thin film to be formed; a step of extrapolating, by the control unit, the fitting curve at each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance at each wavelength at a future time; a step of calculating, by the control unit, a figure of merit (FOM) for the predicted spectrum at each future time obtained by the prediction, and setting the time at which the predicted FOM takes the minimum value as the film formation stop time; and a step of executing, by the control unit, the film formation control of the optical thin film based on the set film formation stop time.

[0012] Another feature of the present invention is that in an optical thin film forming apparatus that forms an optical thin film on a substrate to be film-formed and has a control unit comprising a computer that controls the film formation of a thin film on the substrate to be film-formed according to a light reception signal obtained by receiving monitor light that has passed through the substrate to be film-formed, it is a program for causing the computer to execute the following procedures. A procedure for fitting the change in transmittance over time at each wavelength point in the optical thin film to be formed. A procedure for extrapolating the fitting curve at each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance at each wavelength at a future time. A procedure for calculating a figure-of-merit (FOM) function for the predicted spectrum at each future time obtained by the prediction, and setting the time at which the predicted FOM takes the minimum value as the film formation stop time. A procedure for executing the film formation control of the optical thin film based on the set film formation stop time.

Effects of the Invention

[0013] According to the present invention, when optimizing the film thickness of each layer, an accurate FOM minimum time can be determined, and the occurrence of systematic errors due to slightly overcoating the optimal film thickness can be prevented. Furthermore, according to the present invention, the occurrence of accidental errors due to measurement noise caused by independent calculation of the FOM function at each time point can be prevented, and as a result, the yield in mass-producing products of multilayer optical thin films can be improved.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of a vacuum film forming apparatus as an optical thin film forming apparatus employing the optical film thickness control apparatus of the present invention and a vacuum film forming method using the same will be described in association with the drawings.

[0016] FIG. 1 is a configuration diagram schematically showing an ion beam assist vacuum evaporation apparatus which is a vacuum film forming apparatus employing the optical film thickness control apparatus according to an embodiment of the present invention.

[0017] In the vacuum evaporation apparatus 1 of the present embodiment, for example, an exhaust pipe and a vacuum pump (not shown) are connected to a vacuum chamber 10 which is a film forming chamber, and the inside can be depressurized to a predetermined pressure. The back pressure in the vacuum chamber 10 during film formation by vacuum evaporation is, for example, about 10-2 to 10-5 Pa.

[0018] Below the inside of the vacuum chamber 10, a first vacuum evaporation source 21 and a second vacuum evaporation source 22 are arranged 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 evaporation material 21 is, for example, SiO2, and the second evaporation material 23 is, for example, TiO2 or Ta2O5. Each of the vacuum evaporation sources 21, 22 is provided with heating means such as resistance heating, electron beam heating, laser beam heating, electron guns (not shown), etc. When the evaporation material is heated and vaporized in the vacuum evaporation source, the vapor of the evaporation material is ejected.

[0019] For example, inside the vacuum chamber 10, a substrate holder 31 that holds a film-forming target substrate 30, which is an optical substrate such as quartz glass, is provided in the direction in which the vapors of the deposition materials of the first vacuum evaporation source 21 and the second vacuum deposition source 22 are ejected, with the film-forming surface facing the film-forming material supply unit 20 side. For example, the substrate holder 31 is supported by a holder support portion 32 from above the vacuum chamber 10.

[0020] In FIG. 1, an example is shown in which two vacuum deposition sources are provided to form a multilayer film of two types of thin films. However, various modes are possible, such as providing three vacuum deposition sources to form a multilayer film of three types of thin films. In addition, in this embodiment, the case of forming a multilayer film is described. However, the present invention can also be implemented in the case of a single layer instead of a multilayer film. When using three vacuum deposition sources, for example, the first deposition material is SiO2, the second deposition material is Si3N4, and the third deposition material is a-SiN:H.

[0021] FIGS. 2(a) and (b) are diagrams schematically showing the film-forming target substrate 30 according to the first embodiment and the multilayer film of the thin films formed on the film-forming target substrate. FIG. 2(a) shows an example when two substances are used as the deposition materials, and FIG. 2(b) shows an example when three substances are used as the deposition materials. Here, examples when two substances are used as the deposition materials and examples when three substances are used as the deposition materials are shown. However, it is of course not limited thereto.

[0022] When two substances are used as the deposition materials, as shown in FIG. 2(a), when the vapors of the deposition materials ejected from the two vacuum deposition sources 21 and 22 reach the surface of the film-forming target substrate 30 and solidify, a multilayer film 310 of thin films 311 and 312 of the deposition materials is formed on the surface of the film-forming target substrate 30. For example, an NBP filter is fabricated by alternately laminating 66 layers of SiO2 / TiO2 on a film-forming target substrate 30 formed 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.

[0023] When three substances are used as the evaporation material, as shown in Fig. 2(b), when the vapors of the evaporation materials ejected from the three respective vacuum evaporation sources reach the surface of the substrate 30 to be formed and solidify, a multilayer film 320 of thin films 321, 322, and 323 of the evaporation material is formed on the surface of the substrate 30 to be formed. For example, a BP filter is fabricated by alternately laminating 66 layers of SiO2 / Si3N4 / a-SiN:H on a substrate 30 to be formed made of an optical glass substrate. For example, the center wavelength of the transmission band is 940 nm.

[0024] Also, for example, an ion source 23 for irradiating ions such as oxygen ions onto the substrate to be formed is provided in the vacuum chamber 10, and ion beam assisted vacuum evaporation can be performed. By irradiating ions from the ion source 23 onto the film formation surface of the substrate 30 to be formed, a process in which a film is formed by the evaporation substance supplied from the film formation material supply unit 20 and the film thickness becomes thick, and a part of the region near the surface of the already formed film is sputtered by the ions irradiated from the ion source 23 and the film thickness becomes thin can be simultaneously advanced while forming a film. At this time, when a film thickness difference occurs depending on the density distribution of the film formation substance supplied from the film formation material supply unit 20 within the plane of the substrate 30 to be formed, by performing sputtering with ions irradiated from the ion source 23 under conditions that cancel the film thickness difference, a multilayer film having a uniform in-plane film thickness distribution can be obtained.

[0025] In the present embodiment, a light projecting unit 40 for projecting monitor light L onto the substrate 30 to be formed held by the substrate holder 31 is provided. The light projecting unit 40 is installed outside the vacuum chamber 10 and includes a light source 41 as a light projecting head for projecting monitor light L onto the substrate 30 to be formed. As the light source 40, for example, a halogen lamp can be used.

[0026] A light receiving unit 50 for receiving the monitor light L that has passed through the substrate 30 to be formed and the thin film and multilayer film during film formation and outputting a light receiving signal SR is provided. The light receiving unit 50 is provided, for example, inside the vacuum chamber 10, and includes a light receiving lens 51 as a light receiving head of the light receiving unit that receives the monitor light L transmitted through the substrate to be film-formed and the thin film and multilayer film during film formation, a spectroscopic unit 52 composed of a spectrophotometer that spectroscopically analyzes the monitor light received by the light receiving lens 51, a light detection unit 53 that detects the light spectroscopically analyzed 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.

[0027] For example, the light detection unit 53 has a configuration in which light receiving pixels that convert the received light into an optical signal 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 substrate 30 to be film-formed is received by the light receiving lens 51, transmitted to the spectroscopic unit 52 by the light receiving optical system 54, spectroscopically analyzed, and the spectroscopically analyzed monitor light is detected by the light detection unit 53. The monitor light L transmitted through the substrate 30 to be film-formed is spectroscopically analyzed by the spectroscopic unit 52, and the spectroscopically analyzed light is detected by the light detection unit 53 in which light receiving pixels are arranged in a matrix, and a received light signal SR is output. The light detection unit 53 can acquire the continuous spectrum of the monitor light, that is, can detect the monitor light at multiple wavelengths.

[0028] The received light signal SR detected by the light detection unit 53 is supplied to a control unit 60 constituted by a personal computer (PC) or the like. The control unit 60 processes the received light signal SR to obtain the light transmittance of the substrate 30 to be film-formed. Also, by acquiring the continuous spectrum of the monitor light as described above, the light transmission spectrum of the substrate 30 to be film-formed is obtained. The control unit 60 can perform feedback during film formation so as to change the film formation conditions so that desired optical characteristics can be obtained from the obtained light transmittance or light transmission spectrum. Further, in the vacuum evaporation apparatus 1 of the present embodiment, in addition to the above configuration, a radiation thermometer 70 as a temperature measurement unit for measuring the temperature of the substrate during film formation is provided, for example, inside the holder support portion 32 of the substrate holder 31 (above the substrate holder 31).

[0029] In addition, in this embodiment, the substrate temperature shall include not only the temperature of the substrate itself but also the temperature of the periphery of the substrate that is predicted to be maintained at the same temperature as the substrate.

[0030] In this embodiment, the control unit 60 is configured to be able to correct film formation control based on the substrate temperature measured by the radiation thermometer 70 as a temperature measurement unit.

[0031] FIG. 3 is a block diagram of the internal configuration of the control unit 60 shown in FIG. 1. As shown in FIG. 3, the control unit 60 is a personal computer (PC) configured such that a RAM 61, a ROM 62, a display monitor 64, a keyboard 65, and a mouse 66 are connected to a CPU 63. The CPU 63 is configured to perform film formation control described later according to 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. Note that the film formation control by this CPU 63 is performed while displaying the control content on the display monitor 64. Further, the film formation control program includes an FOM control program for optimizing the film thickness of the layers in the optical thin film described later, and this FOM control program is provided with an FOM minimum time prediction algorithm described later. Note that the FOM control program provided with the FOM minimum time prediction algorithm may be stored in storage media in various forms and applied and used in various optical thin film forming apparatuses.

[0032] The control unit 60 according to this embodiment acquires the light transmittance of the film formation target substrate 30 in response to the received light signal SR, and performs film formation control for controlling the film thickness of the thin film, more specifically, the current thin film (current layer) being formed, in association with the acquired light transmittance information. Here, in the present invention, by using the Figure-of-Merit (FOM) function, the integral of the difference between the measured value of the light transmission spectrum during film formation obtained as described above and the designed value of the light transmission spectrum is taken, and the film formation is stopped at the time when this FOM function becomes minimum, and FOM control is performed to optimize the film thickness of each layer. However, in the conventional FOM control where the film formation is stopped at the time when the conventional FOM function becomes minimum to optimize the film thickness of each layer, as described in the problems to be solved by the invention, in order to stop the film formation at the time when the FOM function becomes minimum and optimize the film thickness of each layer, there is a problem that it is impossible to determine where the FOM minimum time is unless the time at the minimum point is slightly exceeded. Therefore, since the time at the minimum point is slightly exceeded, it always results in slightly overcoating compared to the optimum film thickness, causing a systematic error.

[0033] Therefore, in the present invention, further, by using a future FOM minimum time prediction algorithm described later, the change in the FOM curve in the future rather than the current time in the optical thin film to be formed is predicted, and the time at the minimum point in the predicted future FOM curve is set as the film formation stop time.

[0034] Next, the film formation control by the above future FOM minimum time prediction algorithm will be described. The FOM function used in this future FOM minimum time prediction algorithm is represented by, for example, Equation 1 shown in FIG. 4, and here, the integral of the difference between the measured value of the light transmission spectrum during film formation and the designed value of the light transmission spectrum is taken. FIG. 4 is a diagram for explaining the Figure-of-Merit (FOM) function and its parameters related to the optical film thickness control according to the present embodiment.

[0035] Next, the prediction process of the change in the FOM curve in the future rather than the current time by the above-described future FOM minimum time prediction algorithm will be explained. FIG. 5 is a flowchart of a prediction process of changes in the FOM curve in the future from the current time by a future FOM minimum time prediction algorithm.

[0036] First, in step ST1 of FIG. 5, when the FOM minimum time prediction algorithm is activated, in step ST2, the transmittance time change for each wavelength point in the optical thin film to be formed is fitted. This is because even if the time-series data of only one wavelength is fitted, only the future transmittance at that one wavelength can be predicted. Therefore, fitting is performed independently at all the measured wavelength points. Note that the transmittance time change for each wavelength is independent and has no relation to the transmittance changes of other wavelengths. That is, when the transmittance time change for each wavelength point is fitted, for example, as an example, a fitting curve as shown in FIG. 6 is obtained. Here, in FIG. 6, the fitting curves at each wavelength point of 400 nm, 500 nm, 600 nm, and 700 nm are shown. In the graph of each wavelength point, the horizontal axis is time (sec), and the vertical axis is transmittance (Transmittance; %). Here, as a fitting function for fitting the transmittance time change for each of the above wavelength points, the following fitting functions can be used. That is, regarding the multilayer film to be formed, the already formed multilayer film and the substrate are regarded as equivalent to one film, and the square root of the reflectance (r = √R) between two substances is defined as the reflection amplitude. A fitting function T(t) associated with 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 is adopted. The fitting function T(t) is shown below.

[0037]

Equation

[0038] Among the above physical parameters r, r0, ω, Ψ, φ0, the current reflection amplitude r0 is a fixed value, and the remaining physical parameters r, ω, Ψ, φ0 are determined by fitting using the fitting function. Thus, in the above fitting process, the measurement information at each time is utilized. Therefore, the accidental error caused by noise is suppressed more than in the conventional FOM control. That is, in the conventional FOM control, measurement noise of the direct vision broadband monitoring (BBM) optical system for the calculation of the FOM function occurs, and its influence cannot be ignored. More specifically, since the FOM function is calculated independently at each time point, the information in the time direction cannot be utilized. As a result, the measurement noise of the optical system at each time directly becomes a factor of accidental error, causing accidental error due to noise, and deteriorating the yield when mass-producing multilayer optical thin film products. In contrast, according to this embodiment, in the above fitting process, the measurement information at each time is utilized, so the accidental error caused by noise can be suppressed more than in the conventional FOM control.

[0039] Next, in step ST3, extrapolation is performed on each of the fitting curves at each wavelength point obtained in step ST2, and by overlapping all of them for all wavelength points, the transmittance at each wavelength at future times, that is, the future spectrum, is predicted. Here, the spectrum is an arrangement of the transmittances at each wavelength point in the order of wavelengths. An example of predicting the above future spectrum will be described below with reference to FIGS. 6 to 8. FIG. 6 is a graph showing an example of the fitting curve at each wavelength point. That is, 0 nm to 500 nm shown in FIG. 6 are the measured raw data, 500 nm to 600 nm are the fitting curves, and when extrapolation is performed on each of the fitting curves, a graph as shown in FIG. 7 is obtained. FIG. 7 shows an example of the curve obtained by extrapolating the fitting curve at each wavelength point, and it is a graph in the case of λ = 400 nm. Here, the horizontal axis represents time (sec), and the vertical axis represents transmittance (%). Then, by combining all the curves obtained by extrapolating the fitting curves at each wavelength point, the spectrum for each time is predicted. Here, a curve graph similar to FIG. 7 is obtained for each of the cases of λ = 500 nm, λ = 600 nm, and λ = 700 nm.

[0040] Here, extrapolation refers to obtaining a numerical value expected outside the range of a certain known numerical data based on that data. In this embodiment, extrapolating the fitting curve at each wavelength point means the operation of predicting data after 600 sec from the measured raw data from 0 sec to 500 sec and the fitting curve from 500 sec to 600 sec shown in FIG. 6, which are known numerical data. Regarding this prediction method, various prediction methods can be considered and adopted as appropriate.

[0041] In FIG. 7, at λ = 400 nm, about 600 sec is the current time, the curve (solid line) before about 600 sec becomes the actual fitting curve, and the curve (dotted line) after about 600 sec is the extrapolated part. Note that the above-described current time (about 600 sec) is an arbitrary current time and is self-evidently determined by the law of causality such as various conditions.

[0042] Next, in step ST4, for the spectrum prediction at each future time obtained in step ST3 (see FIG. 7), the FOM is calculated, and the time at which the curve of the predicted FOM takes the minimum value is set as the film deposition stop time. That is, according to the FOM function shown in FIG. 4, the FOM curve is calculated using the raw data during film deposition. Here, the FOM function for calculating the FOM curve is represented by, for example, the evaluation function of Equation 1 shown in FIG. 4. By this evaluation function, the integral of the difference between the measured value of the light transmission spectrum during film deposition and the designed value of the light transmission spectrum is taken. FIG. 8 is a graph showing the FOM curve calculated using the raw data during film deposition according to the FOM function shown in FIG. 4. The horizontal axis represents time (sec), and the vertical axis represents the merit function value. As shown in FIG. 8, this FOM curve has the merit function taking the minimum value at about 620 sec, which is a little over 600 sec, and then the merit function increases. Therefore, the time at which this merit function takes the minimum value is set as the film deposition stop time. In this case, 620 sec is set as the film deposition stop time.

[0043] Then, in step ST5, film deposition control based on the film deposition stop time set in step ST4 is executed. Thus, according to the present embodiment, by the future FOM minimum time prediction algorithm, prediction processing of the change in the FOM curve in the future from the current time is performed, and the minimum point in the predicted FOM is set as the film deposition stop time. Therefore, since film formation can be stopped at the predicted minimum point, it is possible to solve the problem that it is impossible to determine where the FOM minimum time is, as long as the time at the minimum point, which is a problem in the existing technology, does not go too far. As a result, it is possible to eliminate systematic errors in which the time at the minimum point is slightly exceeded and always slightly over-coated compared to the optimum film thickness.

[0044] In addition, the prediction process of the FOM curve change by the above-described FOM minimum time prediction algorithm can also be applied to the color target. That is, depending on the film, the color appearance visible to the human eye may be more important than the transmittance spectrum itself. In such a case, when a slight error occurs in the spectrum due to a film thickness error or the like during film formation, it is better to control to minimize the error (dE) with the color design rather than the error (FOM) with the transmittance design. This is the reason for the application to the color target. Here, when targeting the "color appearance visible to the human eye", it is necessary to convert the transmittance spectrum into a numerical value representing "color" using some function. As an example of the "numerical value representing color", there is the CIE L*a*b* color space. Therefore, after predicting the spectrum in the future by 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, when using the future spectrum predicted in step ST3, colors such as CIE L*a*b* can also be set as targets. Furthermore, according to the requirements of the product, weights can be arbitrarily set for each of L*, a*, and b*. FIG. 9 is an explanatory diagram when the prediction process of the FOM curve change by the FOM minimum time prediction algorithm is applied to the color target.

[0045] Also, in the above step ST2, when the measurement error of the BBM optical system is sufficiently small by fitting the time change of the transmittance at each wavelength point, the physical properties of each layer are naturally derived as by-products in the fitting process. Here, the physical parameters that can be measured in principle include the refractive index dispersion, initial phase, reflection amplitude, film formation rate of the physical film thickness, etc. of each layer, and the physical properties of these layers can be usefully used for film formation control. FIG. 10 is an explanatory diagram of the case where the physical properties of each layer are obtained in the process of fitting the time change of the transmittance at each wavelength point.

[0046] Note that although this embodiment has been described, the description and drawings forming part of this disclosure should not be understood as restrictive. Various embodiments and the like not described here are included. That is, in this embodiment, the case of forming a multilayer film is described, but the present invention can also be implemented in the case of a single layer instead of a multilayer film. Note that the FOM minimum time prediction algorithm may be provided with an FOM control program stored in various forms of storage media and applied to various optical thin film forming apparatuses for use.

Explanation of Reference Numerals

[0047] 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 to 320... film forming target substrates, 31... substrate holder, 32... holder support part, 40... light projecting part, 41... light source, 50... light receiving part, 51... light receiving lens, 52... spectroscopic part, 53... light detection part, 54... light receiving optical system, 60... control part, 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 - ST5 ··· Each step

Claims

1. An optical thin film forming apparatus for forming an optical thin film on a substrate to be formed, comprising a control unit that controls the film formation on the film formation target substrate according to a light reception signal obtained by receiving monitor light transmitted through the substrate to be formed, wherein the control unit fits the change in transmittance over time at each wavelength point in the optical thin film to be formed (Fitting), extrapolates the fitting curve at each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance of 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, and sets the time at which the predicted FOM takes the minimum value as the film formation stop time, and an optical thin film forming apparatus that executes film formation control of the optical thin film based on the set film formation stop time.

2. The optical thin film forming apparatus according to claim 1, wherein the setting process of the film formation stop time is performed by a started FOM minimum time prediction algorithm.

3. The optical thin film forming apparatus according to claim 1 or 2, wherein extrapolation is performed for each of the fitting curves at each wavelength point, and the future spectrum is predicted by overlapping all of them for all wavelength points.

4. A light projecting unit that projects monitor light onto a substrate to be formed on which a multilayer film of a thin film is formed by depositing a deposition material supplied from a deposition material supply unit disposed in a film formation chamber, a light receiving unit that receives the monitor light transmitted through the substrate to be formed and outputs a light reception signal, a temperature measurement unit that measures the temperature of the substrate during film formation, and a control unit that acquires the light transmittance of the substrate to be formed according to the light reception signal and controls the film formation of the thin film in association with the acquired light transmittance information, wherein the control unit fits the change in transmittance over time at each wavelength point in the optical thin film to be formed (Fitting), extrapolates the fitting curve at each wavelength point obtained by the fitting to predict a future spectrum, which is the transmittance of 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, and sets the time at which the predicted FOM takes the minimum value as the film formation stop time, and an optical thin film forming apparatus that executes film formation control of the optical thin film based on the set film formation stop time.

5. The optical thin film forming apparatus according to claim 4, wherein the setting process of the film formation stop time is performed by the activated FOM minimum time prediction algorithm.

6. The optical thin film forming apparatus according to claim 1 or 5, wherein extrapolation is performed on each of the fitting curves at each wavelength point, and the future spectrum is predicted by overlapping them for all wavelength points.

7. An optical thin film forming apparatus having a control unit that controls film formation of a thin film on a substrate to be film-formed in accordance with a light reception signal obtained by receiving monitor light transmitted through the substrate to be film-formed, and forming an optical thin film on the substrate to be film-formed, wherein an optical thin film forming method for forming an optical thin film on the substrate to be film-formed, a step of fitting, by the control unit, the change in transmittance over time for each wavelength point in the optical thin film to be formed; a step of extrapolating, by the control unit, the fitting curve at each wavelength point obtained by the fitting to predict a future spectrum that is the transmittance at each wavelength at a future time; a step of calculating, by the control unit, a Figure-of-Merit (FOM) function for the predicted spectrum prediction at each future time obtained by the prediction, and setting the time at which the predicted FOM takes a minimum value as the film formation stop time; a step of executing, by the control unit, film formation control of the optical thin film based on the set film formation stop time. An optical thin film forming method having these steps.

8. The optical thin film forming method according to claim 7, wherein the setting process of the film formation stop time is performed by the activated FOM minimum time prediction algorithm.

9. The optical thin film forming method according to claim 7 or 8, wherein extrapolation is performed on each of the fitting curves at each wavelength point, and the future spectrum is predicted by overlapping them for all wavelength points.

10. An optical thin film forming apparatus having a control unit comprising a computer that controls film formation of a thin film on a substrate to be film-formed in accordance with a light reception signal obtained by receiving monitor light transmitted through the substrate to be film-formed, and forming an optical thin film on the substrate to be film-formed, a program for causing the computer to execute the following procedure. A procedure for fitting the change in transmittance over time for each wavelength point in the optical thin film to be formed, A procedure for extrapolating the fitting curves at each wavelength point obtained by the fitting to predict the future spectrum, which is the transmittance at each wavelength at future times. A procedure for calculating the Figure-of-Merit (FOM) function for the spectrum prediction at each future time obtained by the prediction and setting the film deposition stop time as the time at which the predicted FOM takes the minimum value. A procedure for performing film deposition control of the optical thin film based on the set film deposition stop time.

11. A storage medium storing the program described in Claim 10.

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