Direct light control system and method for a coating apparatus

Abstract

The application relates to a direct light control system and method of a coating equipment, the laser light control light path of the system comprises a tunable laser light source and a first detector, the white light control light path comprises a white light source and a second detector, a first dichroic mirror performs light combination treatment on laser signals emitted by the tunable laser light source and visible light signals emitted by the white light source, a second dichroic mirror performs light splitting treatment on light signals passing through a product, the transmittance corresponding to a laser wavelength is obtained through the first detector, the transmittance corresponding to a visible light wavelength is obtained through the second detector, a work computer monitors the transmittance variation trend of the laser light control and the white light control on the product, and the optical thickness of a film layer is calculated and obtained. The white light control and the laser light control are combined, the time for switching the white light and the laser light control of the equipment is reduced, the signals of the white light control and the laser light control can be monitored simultaneously, different light controls are adopted for control according to different light control value signals, and a film layer with higher precision can be obtained.

Description

Technical Field

[0001] This invention relates to the field of coating equipment thickness control technology, and in particular to a direct light control system and method for coating equipment. Background Technology

[0002] Vacuum deposition technology is a method of physical vapor deposition. Its principle involves sublimating or sputtering the film material through thermal evaporation or ion beam bombardment, then directing it onto a substrate in a vacuum environment to ultimately deposit a solid thin film on the substrate surface. Methods for controlling film thickness include: 1. Time and power control; 2. Quartz crystal monitoring; 3. Optical monitoring. Time and power control utilizes the principle that thickness equals time multiplied by the speed, adjusting the power to maintain a near-constant speed, and then controlling the thickness through time. Quartz crystal monitoring detects the oscillation frequency of the crystal and calculates the current thickness based on the relationship between thickness and frequency. Optical monitoring directly measures the optical properties of the film system, and is categorized into direct and indirect optical control based on the measurement method, and white light and laser optical control based on the test wavelength.

[0003] Currently, optical monitoring methods offer higher control precision compared to other methods. Because they directly monitor the product, direct optical control is more direct than indirect optical control. Existing direct optical control systems generally only support white light or laser light control. During the manufacturing process, the monitoring wavelength is relatively limited, and under certain special light intensity conditions, the thickness accuracy achieved using existing optical control algorithms is relatively low. This leads to the continuous accumulation of processing errors and makes it impossible to achieve high-precision spectral accuracy. Summary of the Invention

[0004] To achieve the above-mentioned objectives and other advantages of the present invention, a first objective of the present invention is to provide a direct light control system for a coating equipment, comprising a laser light control optical path, a white light light control optical path, a first dichroic mirror, a second dichroic mirror, and an industrial control computer. The laser light control optical path includes a tunable laser source and a first detector. The white light light control optical path includes a white light source and a second detector. The first dichroic mirror is used to combine the laser signal emitted by the tunable laser source and the visible light signal emitted by the white light source. After the laser signal and the visible light signal are combined, they are incident on the product. The second dichroic mirror is used to separate the laser signal and the visible light signal passing through the product. The first detector receives the laser signal after the beam splitting and obtains the transmittance of the corresponding laser wavelength. The second detector receives the visible light signal after the beam splitting and obtains the transmittance of the corresponding visible light wavelength. The industrial control computer monitors the transmittance change trend of the product by the laser light control and the white light control by reading the signals from the first detector and the second detector, and calculates the optical thickness of the film layer.

[0005] Furthermore, the laser optical control path also includes an optical signal output collimator, which collimates the laser beam output by the tunable laser source, and the collimated laser beam passes through the first dichroic mirror.

[0006] Furthermore, the white light control optical path also includes a visible light signal output lens, which processes the visible light beam output by the white light source. The processed visible light beam passes through the first dichroic mirror, causing the laser beam and the visible light beam to combine.

[0007] Furthermore, the laser optical control path also includes an optical signal receiving collimator, which receives the laser signal split by the second dichroic mirror, and the laser signal received by the optical signal receiving collimator enters the first detector.

[0008] Furthermore, the white light control optical path also includes a visible light signal receiving lens, which receives the visible light signal split by the second dichroic mirror, and the visible light signal received by the visible light signal receiving lens enters the second detector.

[0009] Furthermore, the first dichroic mirror and the second dichroic mirror are 45-degree dichroic mirrors.

[0010] Furthermore, the 45-degree dichroic mirror is a long-pass dichroic mirror, which reflects visible light wavelengths and transmits laser wavelengths.

[0011] Furthermore, the 45-degree dichroic mirror is a short-pass dichroic mirror, which transmits light signals of visible wavelength and reflects light signals of laser wavelength.

[0012] Furthermore, the first detector is a power meter, and the second detector is a monochromator.

[0013] A second objective of this invention is to provide a direct light control method for a coating apparatus, comprising the following steps:

[0014] Determine whether the stopping point of the optical control curve of the laser wavelength is an extreme point;

[0015] If the stopping point of the optical control curve of the laser wavelength is an extreme point, then the laser optical control is used as the dominant control method. The derivative of the optical control curve of the laser wavelength is calculated, and the film thickness when the derivative is 0 is the target thickness of the film.

[0016] If the stopping point of the optical control curve of the laser wavelength is not an extreme point, then determine whether the optical control curve of the laser wavelength passes through an extreme point.

[0017] If the optical control curve of the laser wavelength passes through the extreme point, then it is determined whether the difference between the transmittance at the starting point of the film and the transmittance at the extreme point is within the preset range compared with the difference between the transmittance at the ending point of the film and the transmittance at the extreme point.

[0018] If the optical control curve of the laser wavelength passes through an extreme point and the difference between the transmittance at the beginning of the film and the transmittance at the extreme point is within a preset range compared to the difference between the transmittance at the end of the film and the transmittance at the extreme point, then the laser optical control is used as the dominant control method. The actual transmittance at the end of the film is calculated by the ratio of the difference between the transmittance at the end of the film and the transmittance at the extreme point to the difference between the transmittance at the beginning of the film and the transmittance at the extreme point, and the film thickness is obtained.

[0019] If the optical control curve of the laser wavelength does not pass through the extreme point, then switch to white light optical control as the dominant control mode. The actual transmittance at the end of the film layer is calculated by the ratio of the difference between the maximum transmittance of the visible light wavelength optical control curve and the transmittance at the end of the film layer to the difference between the maximum transmittance and the minimum transmittance, and the film layer thickness is obtained.

[0020] If the optical control curve of the laser wavelength passes through an extreme point and the difference between the transmittance at the start point of the film and the transmittance at the extreme point is not within the preset range compared to the difference between the transmittance at the end point of the film and the transmittance at the extreme point, then white light optical control is switched to the dominant control mode. The actual transmittance at the end of the film is calculated by the ratio of the difference between the transmittance at the end point of the film and the minimum transmittance to the difference between the maximum transmittance and the minimum transmittance of the optical control curve of the visible light wavelength, and the film thickness is obtained.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention combines direct light control of white light with direct light control of laser, reducing the time required for switching between white light and laser light control. It can also monitor the signals of both white light and laser light control simultaneously. By using different light control methods to control different light control signals, higher precision films can be obtained.

[0023] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Specific embodiments of the present invention are given in detail below with reference to the accompanying drawings. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0025] Figure 1 This is a schematic diagram of the direct light control system of the coating equipment in Example 1;

[0026] Figure 2 This is a schematic diagram of the transmittance spectral characteristics of the 45-degree dichroic mirror in Example 1.

[0027] Figure 3 This is a flowchart of the direct light control method for the coating equipment in Example 2;

[0028] Figure 4 This is a schematic diagram of the laser light control curve with the end point of the film being the extreme point under laser wavelength monitoring in Example 2;

[0029] Figure 5 This is a schematic diagram of the laser light control curve passing through the extreme point under laser wavelength monitoring in Example 2;

[0030] Figure 6 This is a schematic diagram of the laser light control curve for the film layer in Example 2 where the end point is not an extreme point;

[0031] Figure 7 This is a schematic diagram of the transmittance curve at a visible light wavelength of 530 nm in Example 2.

[0032] Figure 8 This is a schematic diagram of a white light control curve in Example 2 where the difference between the transmittance at the starting point of the film and the transmittance at the extreme point is not within a preset range compared to the difference between the transmittance at the ending point of the film and the transmittance at the extreme point.

[0033] Figure 9 This is a schematic diagram of the transmittance curve change at a visible light wavelength of 740nm in Example 2.

[0034] In the figure: 1. First dichroic mirror; 2. Second dichroic mirror; 3. Film material container; 4. Glass substrate; 5. Optical signal output collimator; 6. Optical signal receiving collimator; 7. Visible light signal output lens; 8. Visible light signal receiving lens. Detailed Implementation

[0035] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0036] Example 1

[0037] A direct light control system for a coating apparatus, such as Figure 1As shown, it includes a laser light control optical path, a white light light control optical path, a first dichroic mirror 1, a second dichroic mirror 2, and an industrial control computer. The laser light control optical path includes a tunable laser source ( Figure 1 The tunable laser source emits laser light of a specific wavelength (1260-1640nm); in this embodiment, the first detector is a power meter. The white light control optical path includes a white light source and a second detector. In this embodiment, the second detector is a monochromator, and the white light source is a halogen lamp light source that emits light using a fiber optic lens, with a visible light wavelength of 380-900nm. A first dichroic mirror 1 is used to combine the laser signal emitted by the tunable laser source and the visible light signal emitted by the white light source. After the laser signal and visible light signal are combined, they are incident on the product. A second dichroic mirror 2 is used to separate the laser signal and visible light signal passing through the product. The first detector receives the laser signal after the separation process and obtains the transmittance of the corresponding laser wavelength. The second detector receives the visible light signal after the separation process and obtains the transmittance of the corresponding visible light wavelength. The industrial control computer reads the signals from the first and second detectors to monitor the transmittance change trend of the laser light control and white light control on the product and calculates the optimal optical thickness of the film.

[0038] In this embodiment, the first dichroic mirror 1 and the second dichroic mirror 2 are 45-degree dichroic mirrors. The 45-degree dichroic mirrors are used to combine white light and laser wavelengths, ensuring that the product positions monitored by the two optical signal systems are the same. After the combined light signal passes through the product, the 45-degree dichroic mirrors are used again to separate the light.

[0039] A 45-degree dichroic mirror can be a long-pass dichroic mirror, which reflects visible light wavelengths and transmits laser light wavelengths. Alternatively, a 45-degree dichroic mirror can be a short-pass dichroic mirror, which transmits visible light wavelengths and reflects laser light wavelengths.

[0040] The laser optical control path also includes an optical signal output collimator 5, which collimates the laser beam output from the tunable laser source. The collimated laser beam then passes through the first dichroic mirror 1.

[0041] The white light control optical path also includes a visible light signal output lens 7. The visible light signal output lens 7 processes the visible light beam output by the white light source. On the one hand, it cuts off the signal in the communication band, and on the other hand, it collimates the white light. The processed visible light beam passes through the first dichroic mirror 1, so that the laser beam and the visible light beam are combined.

[0042] The laser optical control path also includes an optical signal receiving collimator 6, which receives the laser signal split by the second dichroic mirror 2. The laser signal received by the optical signal receiving collimator 6 enters the first detector.

[0043] The optical signal receiving collimator 6 can be replaced with a detector with a large light spot, which reduces the difficulty of adjusting the optical path of the optical signal receiving collimator 6.

[0044] The white light control optical path also includes a visible light signal receiving lens 8, which receives the visible light signal split by the second dichroic mirror 2. The visible light signal received by the visible light signal receiving lens 8 enters the second detector.

[0045] This embodiment uses a long-pass dichroic mirror, and its transmittance spectrum curve is as follows: Figure 2 As shown, the horizontal axis represents the wavelength range of 380-1700nm, and the vertical axis represents 0-100%. In the visible light band (380-900nm), the transmittance is less than 0.1%, and the reflectivity is greater than 99%; in the optical communication band (1260-1650nm), the transmittance is greater than 99%. The collimated laser beam passes through the first dichroic mirror 1. The processed visible light beam is reflected by a 45-degree dichroic mirror, causing the laser wavelength light to combine with white light. The combined laser wavelength light and white light then enter the glass substrate, pass through the 45-degree dichroic mirror, and are received by the optical signal receiving collimator 6 before entering the power meter. The white light is reflected by the dichroic mirror and received by the visible light signal receiving lens 8, then introduced into the monochromator. By reading the signals from the power meter and monochromator, the industrial control computer can obtain two different sets of optical control curves: one for the communication wavelength and the other for the visible light wavelength.

[0046] The coating machine is a vacuum coating machine used to prepare dielectric materials. Utilizing a vacuum environment, it achieves thin films with specific spectral characteristics by stacking high and low refractive index materials. Film materials in container 3 can be sputtered and deposited onto a glass substrate 4 using methods such as electron gun, anti-evaporation, ion beam sputtering, and magnetron sputtering. The glass substrate 4 rotates at high speed along its axis to ensure uniform film deposition. An industrial control computer monitors the intensity trends of laser-controlled and white-light-controlled light, determines the completion time of the film layer, and sends a signal to the coating machine to switch between different film materials, thus completing the preparation of different film materials.

[0047] This invention provides a direct light control system for a coating equipment, combining a laser light control system with a white light light control system. A 45-degree dichroic mirror combines laser wavelengths in the communication band with visible light wavelengths, perpendicularly incident on the product, and measures the change in light intensity signal during the coating process. After passing through the product, the light signal passes again through the 45-degree dichroic mirror to separate the laser wavelength signal from the white light signal. The laser wavelength is directly received by a first detector, while the white light is introduced into a monochromator to obtain the changes in light intensity signals in the laser and visible light bands respectively. By comprehensively considering the changes in these two signals, a higher precision in film thickness preparation is achieved, solving the problem of insufficient monitoring accuracy for specific film layers in existing technologies. This invention, by combining direct light control of white light with direct light control of laser light, and using a computer processing system to comprehensively consider the two signals, significantly improves the precision of film thickness preparation.

[0048] Example 2

[0049] Example 1 provides a light control method for a direct light control system of a coating apparatus. For a detailed description of the system, please refer to the corresponding description in the above system embodiments; it will not be repeated here. Figure 3 As shown, the light control method includes the following steps:

[0050] Laser wavelengths have better monochromaticity than white light monochromators, and the transmittance accuracy obtained from laser-controlled light is higher than that from white light. Laser wavelengths should be preferred as the monitoring wavelength in the following situations.

[0051] Determine whether the stopping point of the optical control curve of the laser wavelength is an extreme point;

[0052] If the stopping point of the laser wavelength optical control curve is an extreme point, then laser optical control is used as the dominant control method. The derivative of the laser wavelength optical control curve is calculated, and the film thickness at which the derivative is 0 is the target film thickness. Figure 4 As shown, when monitoring with laser wavelength, the end point of the film is the extreme point. The laser wavelength is 1530nm. When preparing a Ta2O5 with a thickness of 1 / 4 wavelength, the refractive index of Ta2O5 is 2.12795. The target stopping point is the extreme point. By differentiating the simulated curve of the spectral data, when the derivative is 0, the target thickness of the film is reached. On the other hand, direct optical control always goes to the extreme point and has a compensation effect. Therefore, under this optical control curve, the laser wavelength is used as the monitoring method.

[0053] If the stopping point of the optical control curve of the laser wavelength is not an extreme point, then determine whether the optical control curve of the laser wavelength passes through an extreme point.

[0054] If the optical control curve of the laser wavelength passes through the extreme point, then it is determined whether the difference between the transmittance at the starting point of the film and the transmittance at the extreme point is within the preset range compared with the difference between the transmittance at the ending point of the film and the transmittance at the extreme point.

[0055] If the optical control curve of the laser wavelength passes through an extreme point and the difference between the transmittance at the beginning of the film and the transmittance at the extreme point is within a preset range compared to the difference between the transmittance at the end of the film and the transmittance at the extreme point, such as the difference between the transmittance at the beginning of the film and the transmittance at the extreme point being larger or closer than the difference between the transmittance at the end of the film and the transmittance at the extreme point (the specific range can be set according to actual needs), then laser optical control is used as the dominant control method. The actual transmittance at the end of the film is calculated by the ratio of the difference between the transmittance at the end of the film and the transmittance at the extreme point to the difference between the transmittance at the beginning of the film and the transmittance at the extreme point, and the film thickness is obtained.

[0056] like Figure 5 As shown, when monitored with laser wavelength, the light control curve passes through an extreme point, and the transmittance at the extreme point ( Figure 5 Tmin) and the transmittance at the film initiation point ( Figure 5 The difference between Tstart and the transmittance at the end of the membrane layer (Tstart) is compared. Figure 5 When the difference between the transmittance at the end of the film (Tend) and the transmittance at the extreme point is large or close, the actual measurement error is reduced by the coefficient because (Tstart-Tmin)>(Tend-Tmin). Therefore, the actual transmittance at the end of the film is estimated by the coefficient (Tend-Tmin) / (Tstart-Tmin), thereby obtaining a film thickness with high accuracy. The laser wavelength is 1290nm, and a film material with a refractive index of 2.13443 and a thickness of 226.64nm is prepared.

[0057] In the following situations, the variable light wavelength should be used as the preferred monitoring wavelength.

[0058] If the optical control curve of the laser wavelength does not pass through an extreme point, then white light optical control is switched to the dominant control mode. White light optical control does pass through an extreme point, and the end point can be calculated using the ratio method. Specifically, the actual transmittance at the end of the film is estimated by using the ratio of the difference between the maximum transmittance of the visible light wavelength optical control curve and the transmittance at the end point of the film to the difference between the maximum transmittance and the minimum transmittance, thus obtaining the film thickness.

[0059] like Figure 6As shown, when preparing a Ta₂O₅ film with a thickness of 0.8 quarter wavelengths using 1550 nm as the reference wavelength, the refractive index of Ta₂O₅ is 2.12677. Its theoretical optical control curve does not pass through an extreme point, and there is no corresponding reference point, making it difficult to precisely control its thickness using optical control algorithms. By using white light optical control and selecting 532 nm as the monitoring wavelength, the refractive index of Ta₂O₅ in this film becomes 2.23572, and its optical thickness becomes 2.4595 quarter wavelengths. Figure 7 As shown, the thickness of this film is monitored using a white light wavelength of 530 nm. The corresponding stop point can be calculated using the ratio method of (Tmax-Tend) / (Tmax-Tmin); where Tmax is... Figure 7 The maximum transmittance, Tmin, in the light control curve is Figure 7 The minimum transmittance in the light control curve, Tend is Figure 7 The transmittance at the end point of the light control curve can be used to obtain the film thickness with high accuracy through the ratio method.

[0060] If the optical control curve of the laser wavelength passes through an extreme point and the difference between the transmittance at the beginning of the film and the transmittance at the extreme point is not within the preset range compared to the difference between the transmittance at the end of the film and the transmittance at the extreme point, for example, the difference between the transmittance at the beginning of the film and the transmittance at the extreme point is much smaller than the difference between the transmittance at the end of the film and the transmittance at the extreme point (the specific range can be set according to actual needs), then switch to white light optical control as the dominant control mode. The actual transmittance at the end of the film is calculated by the ratio of the difference between the transmittance at the end of the film and the minimum transmittance to the difference between the maximum transmittance and the minimum transmittance of the optical control curve of the visible light wavelength, and the film thickness is obtained.

[0061] like Figure 8 As shown, in the 111.63nm Ta2O5 / 210.69nm SiO2 film system, when preparing SiO2, the monitoring wavelength is 1420nm; when monitored with laser wavelength, when the optical control curve passes through the extreme point, the transmittance at the extreme point ( Figure 8 Tmin) and the transmittance at the film initiation point ( Figure 8 The difference between Tstart and the transmittance at the extreme point is compared with the transmittance at the end point of the film layer. Figure 8When the difference between (Tmax-Tmin) and (Tstart-Tmin) is much smaller, the actual measurement error is amplified by the coefficient because (Tstart-Tmin) << (Tend-Tmin). Therefore, the actual transmittance obtained by estimating the actual transmittance at the end of the film layer using the coefficient (Tend-Tmin) / (Tstart-Tmin) will have a larger error. By obtaining the transmittance curve at a visible light wavelength of 740nm, we can obtain the curve that passes through the extreme point where Tmax-Tmin > Tend-Tmin, as shown below. Figure 9 As shown.

[0062] It should be noted that, in addition to using the combined algorithm of white light control and laser light control, conventional laser light control algorithm and white light control algorithm can also be used separately.

[0063] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0064] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0065] The above are merely embodiments of this specification and are not intended to limit the scope of one or more embodiments of this specification. Various modifications and variations can be made to one or more embodiments of this specification by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of one or more embodiments of this specification should be included within the scope of the claims of one or more embodiments of this specification.

Claims

1. A direct light control system for a coating apparatus, characterized in that: The system includes a laser light control optical path, a white light light control optical path, a first dichroic mirror, a second dichroic mirror, and an industrial control computer. The laser light control optical path includes a tunable laser source and a first detector. The white light light control optical path includes a white light source and a second detector. The first dichroic mirror is used to combine the laser signal emitted by the tunable laser source and the visible light signal emitted by the white light source. After the laser signal and the visible light signal are combined, they are incident on the product. The second dichroic mirror is used to separate the laser signal and the visible light signal passing through the product. The first detector receives the laser signal after the beam splitting and obtains the transmittance of the corresponding laser wavelength. The second detector receives the visible light signal after the beam splitting and obtains the transmittance of the corresponding visible light wavelength. The industrial control computer monitors the transmittance change trend of the laser light control and white light control on the product by reading the signals from the first detector and the second detector, and calculates the optical thickness of the film layer.

2. The direct light control system for a coating apparatus as described in claim 1, characterized in that: The laser optical control path also includes an optical signal output collimator, which collimates the laser beam output by the tunable laser source, and the collimated laser beam passes through the first dichroic mirror.

3. The direct light control system for a coating apparatus as described in claim 2, characterized in that: The white light control optical path also includes a visible light signal output lens, which processes the visible light beam output by the white light source. The processed visible light beam passes through the first dichroic mirror, causing the laser beam and the visible light beam to combine.

4. The direct light control system for a coating apparatus as described in claim 3, characterized in that: The laser optical control path further includes an optical signal receiving collimator, which receives the laser signal split by the second dichroic mirror, and the laser signal received by the optical signal receiving collimator enters the first detector.

5. The direct light control system for a coating apparatus as described in claim 4, characterized in that: The white light control optical path also includes a visible light signal receiving lens, which receives the visible light signal split by the second dichroic mirror, and the visible light signal received by the visible light signal receiving lens enters the second detector.

6. The direct light control system for a coating apparatus as described in claim 1, characterized in that: The first dichroic mirror and the second dichroic mirror are dichroic mirrors at a 45-degree angle.

7. The direct light control system for a coating apparatus as described in claim 6, characterized in that: The 45-degree dichroic mirror is a long-pass dichroic mirror, which reflects visible light wavelengths and transmits laser light wavelengths.

8. The direct light control system for a coating apparatus as described in claim 6, characterized in that: The 45-degree dichroic mirror is a short-pass dichroic mirror, which transmits light signals of visible wavelength and reflects light signals of laser wavelength.

9. The direct light control system for a coating apparatus as described in claim 1, characterized in that: The first detector is a power meter, and the second detector is a monochromator.

10. A method for controlling the light in a direct light control system of a coating apparatus as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Determine whether the stopping point of the optical control curve of the laser wavelength is an extreme point; If the stopping point of the optical control curve of the laser wavelength is an extreme point, then the laser optical control is used as the dominant control method. The derivative of the optical control curve of the laser wavelength is calculated, and the film thickness when the derivative is 0 is the target thickness of the film. If the stopping point of the optical control curve of the laser wavelength is not an extreme point, then determine whether the optical control curve of the laser wavelength passes through an extreme point. If the optical control curve of the laser wavelength passes through the extreme point, then it is determined whether the difference between the transmittance at the starting point of the film and the transmittance at the extreme point is within the preset range compared with the difference between the transmittance at the ending point of the film and the transmittance at the extreme point. If the optical control curve of the laser wavelength passes through an extreme point and the difference between the transmittance at the beginning of the film and the transmittance at the extreme point is within a preset range compared to the difference between the transmittance at the end of the film and the transmittance at the extreme point, then the laser optical control is used as the dominant control method. The actual transmittance at the end of the film is calculated by the ratio of the difference between the transmittance at the end of the film and the transmittance at the extreme point to the difference between the transmittance at the beginning of the film and the transmittance at the extreme point, and the film thickness is obtained. If the optical control curve of the laser wavelength does not pass through the extreme point, then switch to white light optical control as the dominant control mode. The actual transmittance at the end of the film layer is calculated by the ratio of the difference between the maximum transmittance of the visible light wavelength optical control curve and the transmittance at the end of the film layer to the difference between the maximum transmittance and the minimum transmittance, and the film layer thickness is obtained. If the optical control curve of the laser wavelength passes through an extreme point and the difference between the transmittance at the start point of the film and the transmittance at the extreme point is not within the preset range compared to the difference between the transmittance at the end point of the film and the transmittance at the extreme point, then white light optical control is switched to the dominant control mode. The actual transmittance at the end of the film is calculated by the ratio of the difference between the transmittance at the end point of the film and the minimum transmittance to the difference between the maximum transmittance and the minimum transmittance of the optical control curve of the visible light wavelength, and the film thickness is obtained.

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