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 optimum film thickness control device using FOM control for a multi-layer optical thin film. [Background technology]

[0002] 2. Description of the Related Art Multilayer optical thin films having a laminated structure in which a plurality of optical thin films are laminated on a substrate are known as optical thin films that are widely used in the field of optical instruments.

[0003] 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 for direct-view broadband monitoring (BBM) is the figure-of-merit (FOM) control.

[0004] The Figure-of-Merit (FOM) function used in the FOM control is an evaluation function that calculates the integral of the difference between the spectrum measured during film formation and the design spectrum of each layer. The FOM control involves stopping deposition at the time when this FOM function is minimized and optimizing 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 sought (see, for example, reference 1).

[0005] [Patent Document 1] JP 2010-138463 A [Patent Document 2] JP 2003-279727 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0006] However, the conventional FOM control described above, which stops deposition 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 overshot, resulting in a systematic error since the coating is always slightly overcoated rather than at the optimum thickness.

[0007] The second problem is that the measurement noise of the direct-view broadband monitoring (BBM) optical system occurs in 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 of random error, resulting in random error due to noise. The above two problems result in poor yields when multilayer optical thin film products are mass-produced.

[0008] The present invention has been made in view of the above-mentioned problems in the conventional technology, and has as its object to provide an optical thin film formation apparatus and method that can determine an accurate minimum FOM time when optimizing the film thickness of each layer, and 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 which 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. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the optical thin film forming apparatus of the present invention is an optical thin film forming apparatus that forms an optical thin film on a substrate to be formed, and has a control unit that controls the formation of a thin film on the substrate to be formed in response to a received light signal obtained by receiving monitor light that has passed through the substrate to be formed, and the control unit fits the change in transmittance over time 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 of each wavelength at a future time, calculates a figure-of-merit (FOM) function for the spectrum prediction for each future time obtained by the prediction, sets the time at which the predicted FOM takes a minimum value as the deposition stop time, and performs deposition control of the optical thin film based on the set deposition stop time.

[0010] Another feature of the present invention is that an optical thin film forming apparatus includes a light projecting unit that projects monitor light onto a substrate on which a thin multilayer film is formed by depositing a film material supplied from a film forming material supply unit arranged in a film forming chamber, a light receiving unit that receives the monitor light that has passed through the substrate 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 on which a film is formed in response to the light receiving signal and controls the formation of a thin film in association with the acquired light transmittance information, wherein 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 of each wavelength at a future time, calculates a figure-of-merit (FOM) function for the spectrum prediction for 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 performs film formation control of the optical thin film based on the set film formation stop time.

[0011] Another feature of the present invention is an optical thin film formation method for forming an optical thin film on a substrate to be film-formed, in an optical thin film formation apparatus having a control unit that controls formation of a thin film on the substrate to be film-formed in response to a received light signal obtained by receiving monitor light transmitted through the substrate to be film-formed, the method comprising the steps of: fitting, by the control unit, a time change in transmittance for each wavelength point in the optical thin film to be formed; extrapolating, by the control unit, a fitting curve for each wavelength point obtained by the fitting, to predict a future spectrum, which is the transmittance of each wavelength at a future time; calculating, by the control unit, an FOM 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; and executing, by the control unit, film-formation control of the optical thin film based on the set film-formation stop time.

[0012] 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 receiving signal obtained by receiving monitor light that has passed through the substrate to be film-formed, the optical thin film forming apparatus comprising: a computer; 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 step of extrapolating the fitting curves of 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 future time 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 deposition of the optical thin film based on the set deposition stop time. Effect of the Invention

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

[0014] [Figure 1] FIG. 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 thickness control apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram 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. [Diagram 3] FIG. 3 is a block diagram of the internal configuration of the control unit 60 shown in FIG. [Figure 4] FIG. 4 is a diagram for explaining a figure-of-merit (FOM) function and its parameters related to the optical thickness control according to the present embodiment. [Diagram 5] FIG. 5 is a flowchart of a process for predicting changes in an FOM curve in the future beyond the current time using a future FOM minimum time prediction algorithm. [Figure 6] FIG. 6 is a graph showing an example of a fitting curve at each wavelength point. [Figure 7] 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. [Figure 8] 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. [Figure 9] FIG. 9 is an explanatory diagram of the application of the prediction process of the FOM curve change using the FOM minimum time prediction algorithm to a color target. [Figure 10]FIG. 10 is a diagram illustrating the case where the physical characteristics of each layer are obtained in the process of fitting the time change in transmittance for each wavelength point. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of a vacuum film deposition apparatus as an optical thin film forming apparatus employing an optical thickness control device of the present invention and a vacuum film deposition method as an optical thin film forming method using the same will be described with reference to the drawings.

[0016] FIG. 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 thickness control apparatus according to an embodiment of the present invention.

[0017] In the vacuum deposition 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 formation chamber, so that the inside can be depressurized to a predetermined pressure. The back pressure in the vacuum chamber 10 during film formation by vacuum deposition is, for example, about 10-2 to 10-5 Pa.

[0018] A first vacuum evaporation source 21 and a second vacuum evaporation source 22 are disposed in the lower interior portion of 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 of the vacuum evaporation sources 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.

[0019] 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, with the film-forming surface facing the film-forming material supply section 20 in the direction in which the vapor of the deposition material from the first vacuum evaporation source 21 and the second vacuum deposition source 22 is sprayed. For example, the substrate holder 31 is supported by a holder support 32 from above the vacuum chamber 10 .

[0020] Although Figure 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 practiced in the case of a single layer film instead of a multilayer film. When three vacuum deposition sources are used, for example, the first deposition material is SiO2, the second deposition material is Si3N4, and the third deposition material is a-SiN:H.

[0021] 2(a) and (b) are diagrams that diagrammatically show 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 an example in which two substances are used as the deposition material and an example in which three substances are used as the deposition material are shown here, the present invention is not limited to this.

[0022] 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, 22 reaches the surface of the substrate 30 on which a film is to be formed and solidifies, a multilayer film 310 of thin films 311, 312 of the deposition material is formed on the surface of the substrate 30 on which a film is to be formed. For example, an NBP filter is fabricated by alternately stacking 66 layers of SiO2 / TiO2 on a deposition target substrate 30 formed of an optical glass substrate. For example, the central wavelength of the transmission band is 827 nm, and the bandwidth is 12 nm or less.

[0023] 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 on which a film is to be formed 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 on which a film is to be formed. 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 formed of an optical glass substrate. For example, the central wavelength of the transmission band is 940 nm.

[0024] Furthermore, for example, an ion source 23 for irradiating a substrate on which a film is to be formed with ions such as oxygen ions is provided in the vacuum chamber 10, so that ion beam assisted vacuum deposition can be performed. By irradiating the film formation surface of the substrate 30 with ions from the ion source 23, a film can be formed by simultaneously carrying out a process in which a film is formed using the deposition material supplied from the film formation material supply unit 20, thereby increasing the thickness of the film, and a process in which a portion of the surface of the already formed film is sputtered by the ions irradiated from the ion source 23, thereby decreasing the thickness of the film. In this case, if a difference in film thickness occurs within the surface of the substrate 30 on which the film is to be formed due to the density distribution of the film forming substance supplied from the film forming material supply unit 20, a multilayer film having 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.

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

[0026] A light receiving section 50 is provided for receiving monitor light L transmitted through the film-formation target substrate 30 and the thin film or multilayer film being formed, and outputting 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 formed and the thin film and 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.

[0027] 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 and transmitted to the spectroscopic section 52 by the light-receiving optical system 54 where it is dispersed. The dispersed monitor light is detected by the light detection section 53. The monitor light L transmitted through the film-forming target substrate 30 is split by the spectroscopic section 52, and the split light is detected by the photodetector section 53, which has light-receiving pixels arranged in a matrix, and outputs a light-receiving signal SR. The photodetector section 53 can obtain a continuous spectrum of the monitor light, i.e., 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 performs signal processing on the light receiving signal SR to obtain the light transmittance of the film-forming target substrate 30. In addition, the control unit 60 obtains the light transmission spectrum of the film-forming target substrate 30 by obtaining the continuous spectrum of the monitor light as described above. 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, in the vacuum deposition apparatus 1 of this embodiment, a radiation thermometer 70 as a temperature measurement unit that measures the substrate temperature during film formation is provided, for example, within the holder support portion 32 of the substrate holder 31 (above the substrate holder 31).

[0029] 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.

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

[0031] FIG. 3 is a block diagram of 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 contents are displayed on the display monitor 64. The film formation control program also includes an FOM control program for optimizing the 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. Incidentally, 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.

[0032] The control unit 60 in this embodiment acquires the light transmittance of the substrate 30 on which a film is formed in response to the light receiving signal SR, and performs film formation control in association with the acquired light transmittance information to control the formation of a thin film, more specifically, the film thickness of the current thin film (current layer) being formed. Here, in the present invention, the Figure-of-Merit (FOM) function is used to take 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 deposition is stopped at the time when the FOM function is minimized and the thickness of each layer is optimized, as described in the problem that the invention aims to solve, in order to stop deposition at the time when the FOM function is minimized and optimize the 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 minimum time is. As a result, the time at which the minimum point occurs is slightly exceeded, resulting in a systematic error, since the coating is always slightly overcoated rather than at the optimum thickness.

[0033] Therefore, in the present invention, a future FOM minimum time prediction algorithm, which will be described later, is used to predict changes in the FOM curve for the optical thin film being deposited further in time than the current time, and the time at which the predicted future FOM curve will be at its minimum point is set as the deposition stop time.

[0034] Next, the deposition control by the above-mentioned 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, in which the integral of the difference between the measured value of the optical transmittance spectrum during film formation and the design value of the optical transmittance spectrum is calculated. FIG. 4 is a diagram for explaining a figure-of-merit (FOM) function and its parameters related to the optical thickness control according to the present embodiment.

[0035] Next, a process of predicting changes in the FOM curve future than 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 an FOM curve in the future beyond the current time using a future FOM minimum time prediction algorithm.

[0036] First, in step ST1 in FIG. 5, an FOM minimum time prediction algorithm is started, and 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 measured wavelength points. 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 of transmittance for each wavelength point, for example, a fitting curve such as that shown in Fig. 6 can be obtained. Here, 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 is time (sec) and the vertical axis is transmittance (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 already-formed multilayer film and the substrate are equated with a certain film and defined as an equivalent film, the square root of the reflectance between the two materials (r = √R) is defined as the reflection amplitude, and a fitting function T(t) is adopted 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.

[0037]

number

[0038] 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 uses the measurement information at each time, so random errors due to noise are suppressed more than in conventional FOM control. That is, in the conventional FOM control, the measurement noise of the direct-view broadband monitoring (BBM) optical system occurs in the calculation of the FOM function, and the effect of this noise cannot be ignored. To explain in more detail, 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 of random error, causing random error due to noise, which deteriorates the yield when multilayer optical thin film products are mass-produced. In contrast, according to the present 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.

[0039] Next, in step ST3, extrapolation is performed on each fitting curve for each wavelength point obtained in step ST2, and the curves are superimposed for all wavelength points to predict the transmittance of each wavelength at a future time, i.e., the future spectrum. Here, a spectrum is a set of transmittances at wavelength points arranged 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, 0 nm to 500 nm in FIG. 6 is the measured raw data, and 500 nm to 600 nm is the fitting curve. When each of the fitting curves is extrapolated, a graph as 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. It should be noted that here, curve graphs similar to those in FIG. 7 are obtained for each of the cases of λ=500 nm, λ=600 nm, and λ=700 nm.

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

[0041] In FIG. 7, at λ=400 nm, the current time is about 600 sec, the curve before about 600 sec (solid line) is the actual fitting curve, and the curve after about 600 sec (dotted line) is the extrapolated portion. The above-mentioned current time (approximately 600 seconds) is an arbitrary current time, and is obviously determined by the causal laws of various conditions and the like.

[0042] 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 deposition stop time. That is, the FOM curve is calculated using the raw data during film formation by 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 take 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 with the FOM function shown in FIG. 4, where the horizontal axis represents time (sec) and the vertical axis represents the merit function value. As shown in FIG. 8, the merit function of this FOM curve reaches a minimum value at approximately 620 seconds, just after 600 seconds, and then increases. Therefore, the time when this merit function has a minimum value is set as the deposition stop time, which is set to 620 seconds in this case.

[0043] 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 prediction process of the change in the FOM curve in the future from the current time is performed using a future FOM minimum time prediction algorithm, and the minimum point in the predicted FOM is set as the film formation stop time. Therefore, since the deposition can be stopped at the predicted minimum point, the problem that occurs in the existing technology 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 exceeded by a little, which occurs in the existing technology. This makes it possible to eliminate the systematic error that occurs when the time to reach the minimum point is exceeded slightly, resulting in constant overcoating slightly beyond the optimum film thickness.

[0044] In addition, the prediction process of the change in the FOM curve using the above-mentioned FOM minimum time prediction algorithm can also be applied to color targets. That is, for some films, the color tone as 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 function must be used to convert the transmittance spectrum into a numerical value that represents "color." 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 colors such as CIE L*a*b* as targets as well. Furthermore, weights can be set arbitrarily for L*, a*, and b* depending on the product requirements. FIG. 9 is an explanatory diagram of the application of prediction processing of FOM curve changes using the FOM minimum time prediction algorithm to a color target.

[0045] Furthermore, in step ST2 above, 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 during the fitting process. Here, physical parameters that can in principle be measured include the refractive index dispersion, initial phase, reflection amplitude, and deposition rate of physical film thickness of each layer, and these physical properties of each layer can be usefully used for film deposition control. FIG. 10 is a diagram illustrating the case where the physical characteristics of each layer are obtained in the process of fitting the time change in transmittance for each wavelength point.

[0046] Although the present embodiment has been described, the description and drawings forming a part of this disclosure should not be understood as limiting. Various embodiments not described here are included. That is, in this embodiment, a case where a multilayer film is formed is described, but the present invention can also be practiced in the case of a single layer instead of a multilayer film. Incidentally, 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. [Explanation of symbols]

[0047] 10 Vacuum chamber, 20 Film forming material supply unit, 21 First vacuum deposition source, 211: first deposition material; 22: second vacuum deposition source; 221: second deposition material; 23: Ion source; 30, 310 to 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~ST5...each step

Claims

1. 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 substrate in response to a light reception signal obtained by receiving monitor light transmitted through the deposition target substrate; The control unit: Fitting the time change in transmittance for each wavelength point in the optical thin film to be formed, 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.

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

3. 3. The optical thin film forming apparatus according to claim 1, wherein the future spectrum is predicted by extrapolating each of the fitting curves for each wavelength point and superimposing the curves for all wavelength points.

4. a light projection unit that projects monitor light onto a film-forming target substrate on which a thin multilayer film is formed by depositing a film-forming material supplied from a film-forming material supply unit disposed in the film-forming 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 a substrate temperature during film formation; a control unit that acquires the light transmittance of the film-forming 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: Fitting the time change in transmittance for each wavelength point in the optical thin film to be formed, 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.

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

6. 6. The optical thin film forming apparatus according to claim 1, wherein the future spectrum is predicted by extrapolating each of the fitting curves for each wavelength point and superimposing the curves for all wavelength points.

7. 1. An optical thin film forming method for forming an optical thin film on a film formation target substrate, the method comprising: forming an optical thin film on the film formation target substrate in an optical thin film forming apparatus having a control unit for controlling formation of a thin film 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, the method comprising: fitting a time change in transmittance for each wavelength point in the optical thin film to be formed by the control unit; A step of predicting a future spectrum, which is a transmittance of each wavelength at a future time, by the control unit by extrapolating the fitting curve of each wavelength point obtained by the fitting; calculating an FOM for the spectrum prediction for each future time obtained by the prediction, and setting a time at which the predicted FOM has a minimum value as a deposition stop time by the control unit; and executing, by the control unit, control of the deposition of the optical thin film based on the set deposition stop time.

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

9. 9. The method for forming an optical thin film according to claim 7, further comprising the steps of: extrapolating each of the fitting curves for each wavelength point; and superimposing the resulting curves for all wavelength points to predict the future spectrum.

10. An optical thin film forming apparatus having a control unit made of a computer that controls thin film formation on a film formation target substrate in response to a light reception signal obtained by receiving monitor light transmitted through the film formation target substrate, the optical thin film forming apparatus forming an optical thin film on 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 step of extrapolating the fitting curves of 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 future time obtained by the prediction, and setting the time at which the predicted FOM has a minimum value as the deposition stop time; A procedure for controlling deposition of the optical thin film based on the set deposition stop time.

11. A storage medium storing the program according to claim 10.

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