CN116676582A - Direct light control system and method of coating equipment - Google Patents

Abstract

The application relates to a direct light control system and a method of coating equipment, wherein a 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 first detector obtains the transmittance of corresponding laser wavelength, the second detector obtains the transmittance of corresponding visible light wavelength, and an industrial personal computer monitors the transmittance change trend of the laser light control and the white light control on the product and calculates and obtains the optical thickness of a film. The application combines the light control of white light and the light control of laser, reduces the time for switching the white light and the light control of the laser by the equipment, can monitor the signals of the white light and the light control of the laser at the same time, and can obtain a film layer with higher precision by adopting different light control to control different light control value signals.

Description

Direct light control system and method of coating equipment

Technical Field

The application relates to the technical field of film thickness control of film coating equipment, in particular to a direct light control system and method of film coating equipment.

Background

The vacuum coating technology is one of the physical vapor deposition methods, and the principle is that the film material sublimates or splashes out by means of thermal evaporation or ion beam bombardment film material, and the film material is irradiated to the substrate in a vacuum environment, and finally a solid film is formed on the surface of the substrate by deposition. The mode of controlling the film thickness is as follows: 1. controlling the thickness of the film layer through time and power; 2. monitoring quartz crystal oscillator; 3. optical monitoring, and the like. The thickness of the film layer is controlled by time and power in a mode of multiplying the thickness by the speed according to the fact that the thickness is equal to the time, the speed is ensured to be close to a constant by changing power, and the thickness is controlled by time; the quartz crystal vibration monitoring mode is to calculate the current thickness to control according to the vibration frequency of the detection crystal vibration plate and the change relation between the thickness and the frequency; the optical monitoring mode is divided into a direct light control mode and an indirect light control mode according to the measurement mode according to the optical characteristics of a direct measurement film system, and a white light control mode and a laser light control mode according to the test wavelength.

At present, the control precision of the optical monitoring mode is higher than that of other modes; because the direct detection is a product, the direct light control is more direct than the indirect light control. The existing direct light control system generally has only white light control or only laser light control; in the processing and preparation process, the monitoring wavelength is relatively single, and under the condition of some special light intensity running values, the thickness precision realized by the existing light control algorithm is relatively low, so that the processing errors are accumulated continuously, and the high-precision spectrum cannot be realized.

Disclosure of Invention

To achieve the above and other advantages and in accordance with the purpose of the present application, a first object of the present application is to provide a direct light control system of a film plating apparatus, which includes a laser light control optical path, a white light control optical path, a first dichroic mirror, a second dichroic mirror, and an industrial personal computer, wherein the laser light control optical path includes a tunable laser light source, a first detector, the white light control optical path includes a white light source, a second detector, the first dichroic mirror is configured to combine a laser signal emitted from the tunable laser light source with a visible light signal emitted from the white light source, the laser signal and the visible light signal are combined and then enter a product, the second dichroic mirror is configured to split a laser signal and a visible light signal from the product, the first detector receives the split laser signal to obtain a transmittance of a corresponding laser wavelength, the second detector receives the split visible light signal to obtain a transmittance of a corresponding visible light wavelength, and the industrial personal computer calculates a trend of the transmittance of the white light control film by reading the first detector and the second detector, and the optical film thickness of the film.

Further, the laser light-controlled optical path further comprises an optical signal output collimator, the optical signal output collimator collimates the laser beam output by the tunable laser source, and the collimated laser beam passes through the first dichroic mirror.

Further, the white light control light path further comprises a visible light signal output lens, the visible light signal output lens processes the visible light beam output by the white light source, and the processed visible light beam passes through the first dichroic mirror, so that the laser beam and the visible light beam are combined.

Further, the laser light-controlled light path further comprises an optical signal receiving collimator, the optical signal receiving collimator 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.

Further, the white light control optical path further comprises a visible light signal receiving lens, the visible light signal receiving lens receives the visible light signal split by the second color direction mirror, and the visible light signal received by the visible light signal receiving lens enters the second detector.

Further, the first dichroic mirror and the second dichroic mirror are 45-degree dichroic mirrors.

Further, the 45-degree dichroic mirror is a long-wavelength dichroic mirror, and the long-wavelength dichroic mirror reflects the optical signal of the visible light wavelength and transmits the optical signal of the laser wavelength.

Further, the 45-degree dichroic mirror is a short-wave dichroic mirror, and the short-wave dichroic mirror transmits the optical signal of the visible light wavelength and reflects the optical signal of the laser wavelength.

Further, the first detector is a power meter, and the second detector is a monochromator.

The second object of the present application is to provide a direct light control method of a coating apparatus, comprising the steps of:

judging whether a stopping point of a light control curve of the laser wavelength is an extreme point or not;

if the stopping point of the light control curve of the laser wavelength is an extreme point, controlling the laser light control as a leading control mode, deriving the light control curve of the laser wavelength, and calculating to obtain the film thickness when the derivative is 0 as the target thickness of the film;

if the stopping point of the light control curve of the laser wavelength is not an extreme point, judging whether the light control curve of the laser wavelength passes through the extreme point;

if the light control curve of the laser wavelength passes through the extreme point, judging whether the difference value of the transmittance of the starting point of the film layer and the transmittance of the extreme point is in a preset range or not compared with the difference value of the transmittance of the ending point of the film layer and the transmittance of the extreme point;

if the light control curve of the laser wavelength passes through the extreme point and the difference value between the transmittance of the film starting point and the transmittance of the extreme point is in a preset range compared with the difference value between the transmittance of the film ending point and the transmittance of the extreme point, controlling the laser light control as a leading control mode, and calculating the actual transmittance of the film ending by the ratio of the difference value between the transmittance of the film ending point and the transmittance of the extreme point to the difference value between the transmittance of the film starting point and the transmittance of the extreme point to obtain the film thickness;

if the light control curve of the laser wavelength does not pass through the extreme point, switching the white light control as a dominant control mode, and calculating the actual transmittance of the film ending by the ratio of the difference value of the maximum transmittance of the light control curve of the visible wavelength and the transmittance of the film ending point to the difference value of the maximum transmittance and the minimum transmittance to obtain the film thickness;

if the light control curve of the laser wavelength passes through the extreme point and the difference value between the transmittance of the film starting point and the transmittance of the extreme point is not in the preset range compared with the difference value between the transmittance of the film ending point and the transmittance of the extreme point, switching the white light control as a leading control mode, and calculating the actual transmittance of the film ending by the ratio of the difference value between the transmittance of the film ending point of the light control curve of the visible wavelength and the minimum transmittance to the difference value between the maximum transmittance and the minimum transmittance to obtain the film thickness.

Compared with the prior art, the application has the beneficial effects that:

the application combines the direct light control of the white light with the direct light control of the laser, reduces the time for switching the white light control and the laser light control by the equipment, can monitor the signals of the white light control and the laser light control at the same time, and can obtain a film layer with higher precision by adopting different light control to different light control value signals.

The foregoing description is only an overview of the present application, and is intended to provide a better understanding of the present application, as it is embodied in the following description, with reference to the preferred embodiments of the present application and the accompanying drawings. Specific embodiments of the present application are given in detail by the following examples and the accompanying drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a limitation on the application. In the drawings:

FIG. 1 is a schematic diagram of a direct light control system of the coating apparatus of example 1;

FIG. 2 is a graph showing the transmittance spectrum characteristic of the 45 degree dichroic mirror of example 1;

FIG. 3 is a flow chart of a direct light control method of the coating apparatus of example 2;

fig. 4 is a schematic diagram of a laser light control curve with the ending point of the film layer as the extreme point under the laser wavelength monitoring of example 2;

FIG. 5 is a schematic diagram of a laser light control curve passing through an extreme point under laser wavelength monitoring in example 2;

FIG. 6 is a schematic view of a laser light control curve with the end point of the film layer of example 2 not being the extreme point;

FIG. 7 is a graph showing the change in transmittance at 530nm of visible light wavelength in example 2;

FIG. 8 is a graph showing a white light control curve of example 2, wherein the transmittance at the start point of the film layer and the transmittance at the end point of the film layer are different from each other in the preset range;

FIG. 9 is a graph showing the change in transmittance at 740nm in the visible light wavelength of example 2.

In the figure: 1. a first dichroic mirror; 2. a second dichroic mirror; 3. a film material container; 4. a glass substrate; 5. an optical signal output collimator; 6. an optical signal receiving collimator; 7. a visible light signal output lens; 8. a visible light signal receiving lens.

Detailed Description

The present application will be further described with reference to the accompanying drawings and detailed description, wherein it is to be understood that, on the premise of no conflict, the following embodiments or technical features may be arbitrarily combined to form new embodiments.

Example 1

A direct light control system of coating equipment is shown in figure 1, and comprises a laser light control light path, a white light control light path, a first dichroic mirror 1, a second dichroic mirror 2 and an industrial personal computer, wherein the laser light control light path comprises a tunable laser light source (TLS light source in figure 1) and a first detector, the tunable laser light source is used for emitting laser with specific wavelength, and the laser wavelength is 1260-1640nm; in this embodiment, the first detector is a power meter. The white light control light path comprises a white light source and a second detector, in the embodiment, the second detector is a monochromator, the white light source is a halogen lamp source, the light emission is realized by utilizing an optical fiber lens, and the visible light wavelength is 380-900nm. The first dichroic mirror 1 is used for carrying out light combination treatment on a laser signal emitted by the tunable laser source and a visible light signal emitted by the white light source, the laser signal and the visible light signal are incident into a product after light combination treatment, the second dichroic mirror 2 is used for carrying out light splitting treatment on the laser signal and the visible light signal of the product, the first detector receives the laser signal after light splitting treatment to obtain the transmittance of the corresponding laser wavelength, the second detector receives the visible light signal after light splitting treatment to obtain the transmittance of the corresponding visible light wavelength, and the industrial personal computer monitors the transmittance change trend of the laser light control and the white light control on the product by reading the signals of the first detector and the second detector and calculates to obtain the optimal optical thickness of the film layer.

In this embodiment, the first dichroic mirror 1 and the second dichroic mirror 2 are 45-degree dichroic mirrors. The light combination of white light and laser wavelength is realized by using a 45-degree dichroic mirror, so that the product positions monitored by the two optical signal systems are the same product position; after the combined light signal passes through the product, the 45-degree dichroic mirror is utilized to split light;

the 45-degree dichroic mirror may be a long-wavelength dichroic mirror, which reflects the optical signal of the visible wavelength and transmits the optical signal of the laser wavelength. The 45-degree dichroic mirror can also be a short-wave dichroic mirror, which transmits the optical signal of visible light wavelength and reflects the optical signal of laser wavelength.

The laser light-controlled light path further comprises a light signal output collimator 5, the light signal output collimator 5 collimates the laser beam output by the tunable laser light source, and the collimated laser beam passes through the first dichroic mirror 1.

The white light control light path further comprises 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, the signals of the communication wave band are cut off on one hand, the white light is collimated on the other hand, and the processed visible light beam passes through the first dichroic mirror 1, so that the laser beam and the visible light beam are combined.

The laser light-controlled optical path further comprises an optical signal receiving collimator 6, the optical signal receiving collimator 6 receives the laser signal which is split by the second dichroic mirror 2, and the laser signal received by the optical signal receiving collimator 6 enters the first detector.

The optical signal receiving collimator 6 can be changed into a large-spot detector, so that the difficulty in adjusting the optical path of the optical signal receiving collimator 6 is reduced.

The white light control optical path further comprises a visible light signal receiving lens 8, the visible light signal receiving lens 8 receives the visible light signal split by the second dichroic mirror 2, and the visible light signal received by the visible light signal receiving lens 8 enters the second detector.

The embodiment adopts a long-wave-path dichroic mirror, the transmittance spectrum curve of which is shown in figure 2, the abscissa is 380-1700nm of the wavelength range, the ordinate is 0-100%, the transmittance is less than 0.1% in the visible light 380-900nm wave band range, and the reflectivity is more than 99%; the transmittance of the optical communication within the 1260-1650nm range is more than 99%. The collimated laser beam passes through the first dichroic mirror 1, and the processed visible light beam is reflected by the dichroic mirror at 45 degrees, so that the light with the laser wavelength and the white light are combined. After the light with the laser wavelength and the white light are combined, the light enters the glass substrate, then passes through a 45-degree dichroic mirror, and the light with the laser wavelength is received by the light signal receiving collimator 6 and enters the power meter; the white light is reflected by the dichroic mirror and is received by the visible light signal receiving lens 8 to be introduced into the monochromator. By reading signals of the power meter and the monochromator, the industrial personal computer can obtain two groups of different light control curves, one group is a light control curve of communication wavelength, and the other group is a light control curve of visible light wavelength.

The film plating machine equipment is a vacuum film plating machine for preparing a medium material, the vacuum film plating machine utilizes a vacuum environment to realize a film with specific spectral characteristics in a mode of preparing a superimposed film layer of a high-low refractive index material, the film layer material in the film layer material container 3 can be sputtered and deposited on the glass substrate 4 by means of an electron gun, evaporation resistance, ion beam sputtering, magnetron sputtering and the like, and the glass substrate 4 rotates along an axis at a high speed so as to ensure the film layer deposition uniformity on the glass substrate 4. And monitoring the light intensity running value trend of the laser light control and the white light control by using the industrial personal computer, judging the finishing time of the film layer, and sending a signal for switching the film layer to the film plating machine to finish the preparation of different film layer materials.

The application provides a direct light control system of coating equipment, wherein the laser light control system is combined with a white light control system, a 45-degree dichroic mirror is utilized to carry out light combination treatment on the laser wavelength of a communication wave band and the light of a visible light wavelength, a product is vertically incident, and the light intensity signal change of the product in the coating process is tested; after the optical signal passes through the product, the optical signal separation of the laser wavelength signal and the white light is realized after the optical signal passes through the 45-degree dichroic mirror again, the laser wavelength is directly received by the first detector, the white light is introduced into the monochromator, the light intensity signal variation of the laser wave band and the visible light wave band are respectively obtained, the preparation of the film thickness with higher precision is obtained by comprehensively considering the two signal variation, and the problem that the monitoring precision of the specific film in the prior art is insufficient is solved. The application combines the direct light control of white light with the direct light control of laser, and combines the comprehensive consideration of a computer processing system to two signals, thereby greatly improving the preparation precision of the film thickness.

Example 2

The light control method of the direct light control system of the film plating device provided in embodiment 1 may refer to the corresponding description in the above system embodiment for the detailed description of the system, and will not be repeated here. As shown in fig. 3, the light control method includes the steps of:

the monochromaticity of the laser wavelength is superior to that of a white light monochromator, and the transmittance precision of the obtained laser light control is higher than that of white light. In the following case, the laser wavelength is preferentially used as the monitoring wavelength.

Judging whether a stopping point of a light control curve of the laser wavelength is an extreme point or not;

if the stopping point of the light control curve of the laser wavelength is an extreme point, controlling the laser light control as a leading control mode, deriving the light control curve of the laser wavelength, and calculating to obtain the film thickness when the derivative is 0 as the target thickness of the film; as shown in fig. 4, when the end point of the film is monitored by the laser wavelength, the laser wavelength is 1530nm, 1 Ta2O5 with 1/4 wavelength thickness is prepared, the refractive index of Ta2O5 is 2.12795, the completed target stopping point is the extreme point, the target thickness of the film is reached when the derivative is 0 by deriving the simulated curve of the optical data; on the other hand, the extreme values are all taken by direct light control, so that the compensation effect is achieved; in the case of this light control curve, the laser wavelength is used as a monitoring means.

If the stopping point of the light control curve of the laser wavelength is not an extreme point, judging whether the light control curve of the laser wavelength passes through the extreme point;

if the light control curve of the laser wavelength passes through the extreme point, judging whether the difference value of the transmittance of the starting point of the film layer and the transmittance of the extreme point is in a preset range or not compared with the difference value of the transmittance of the ending point of the film layer and the transmittance of the extreme point;

if the light control curve of the laser wavelength passes through the extreme point and the difference between the transmittance of the film starting point and the transmittance of the extreme point is within a preset range compared with the difference between the transmittance of the film ending point and the transmittance of the extreme point, if the difference between the transmittance of the film starting point and the transmittance of the extreme point is larger or is close to the difference between the transmittance of the film ending point and the transmittance of the extreme point, the specific range can be set according to the actual requirement, the laser light control is controlled as a dominant control mode, and the actual transmittance of the film ending is calculated according to the ratio of the difference between the transmittance of the film ending point and the transmittance of the extreme point to the difference between the transmittance of the film starting point and the transmittance of the extreme point, so as to obtain the film thickness;

as shown in fig. 5, when monitoring with the laser wavelength, the light control curve passes through the extreme point, the difference between the transmittance of the extreme point (Tmin in fig. 5) and the transmittance of the film starting point (Tstart in fig. 5) is greater than or close to the difference between the transmittance of the film ending point (Tend in fig. 5) and the transmittance of the extreme point, and the actual measurement error is reduced by the factor (Tstart-Tmin) > (Tend-Tmin), so that the actual transmittance of the film ending is estimated by the factor (Tend-Tmin)/(Tstart-Tmin), thereby obtaining the film thickness with high precision; the laser wavelength is 1290nm, and the film material with the refractive index of 2.13443 and the thickness of 226.64nm is prepared.

In the following case, the variable light is preferentially used as the monitoring wavelength.

If the light control curve of the laser wavelength does not pass through the extreme point, the white light control is switched to be used as a dominant control mode, and the white light control passes through the extreme point, so that the ending point can be calculated by using a ratio method. Specifically, the actual transmittance of the film ending is calculated through the ratio of the difference value between the maximum transmittance of the light control curve of the visible light wavelength and the transmittance of the film ending point to the difference value between the maximum transmittance and the minimum transmittance, so as to obtain the film thickness;

as shown in FIG. 6, when Ta2O5 with 0.8 1/4 wavelength thickness is prepared by taking 1550nm as a reference wavelength, the refractive index of Ta2O5 is 2.12677, the theoretical light-operated curve does not pass through an extreme point, the light-operated curve does not have a corresponding reference point, and the thickness is difficult to accurately control in a light-operated algorithm. By adopting white light to control and select 532nm as the monitoring wavelength, the Ta2O5 refractive index of the film layer is 2.23572, the optical thickness of the film layer is 2.4595 1/4 wavelength thicknesses, as shown in FIG. 7, the thickness of the film layer is monitored by using the white light wavelength of 530nm, and a corresponding stopping point can be obtained by calculating by a (Tmax-Tend)/(Tmax-Tmin) ratio method; wherein Tmax is the maximum transmittance in the light control curve of FIG. 7, tmin is the minimum transmittance in the light control curve of FIG. 7, tend is the transmittance of the end point in the light control curve of FIG. 7, and the film thickness with higher precision can be obtained by a ratio method.

If the light control curve of the laser wavelength passes through the extreme point and the difference between the transmittance of the film starting point and the transmittance of the extreme point is not within the preset range compared with the difference between the transmittance of the film ending point and the transmittance of the extreme point, for example, the difference between the transmittance of the film starting point and the transmittance of the extreme point is much smaller than the difference between the transmittance of the film ending point and the transmittance of the extreme point, the specific range can be set according to the actual requirement, the white light control is switched to be used as a dominant control mode, and the actual transmittance of the film ending is calculated according to the ratio of the difference between the transmittance of the film ending point of the light control curve of the visible wavelength and the difference between the maximum transmittance and the minimum transmittance, so as to obtain the film thickness.

As shown in FIG. 8, the monitoring wavelength was 1420nm when SiO2 was prepared in the 111.63nmTA2O5/210.69nmSiO2 film system; when the light control curve passes through the extreme point and the difference between the transmittance of the extreme point (Tmin in FIG. 8) and the transmittance of the film starting point (Tstart in FIG. 8) is much smaller than the difference between the transmittance of the extreme point and the transmittance of the film ending point (Tend in FIG. 8), the actual measurement error is amplified by the coefficient, so that the actual transmittance of the film ending is estimated by the coefficient (Tend-Tmin)/(Ttart-Tmin) to obtain a larger actual transmittance error. By obtaining a transmittance curve change at a visible wavelength of 740nm, a curve passing through an extreme point, tmax-Tmin > Tend-Tmin, can be obtained as shown in fig. 9.

It should be noted that, in addition to the above integrated algorithm of white light control and laser light control, a conventional laser light control algorithm and a white light control algorithm may be used alone.

It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article or apparatus that comprises an element.

In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments.

The foregoing is illustrative of the embodiments of the present disclosure and is not to be construed as limiting the scope of the one or more embodiments of the present disclosure. Various modifications and alterations to one or more embodiments of this description will be apparent to those skilled in the art. Any modifications, equivalent substitutions, improvements, or the like, which are within the spirit and principles of one or more embodiments of the present disclosure, are intended to be included within the scope of the claims of one or more embodiments of the present disclosure.

Claims (10)

1. A direct light control system of a coating device, characterized in that: the device comprises a laser light control light path, a white light control light path, a first dichroic mirror, a second dichroic mirror and an industrial personal computer, wherein the laser light control light path 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, the first dichroic mirror is used for carrying out light combination treatment on a laser signal emitted by the tunable laser light source and a visible light signal emitted by the white light source, the laser signal and the visible light signal are subjected to light combination treatment and then enter a product, the second dichroic mirror is used for carrying out light splitting treatment on the laser signal and the visible light signal of the product, the first detector receives the laser signal subjected to light splitting treatment to obtain the transmittance of a corresponding laser wavelength, the second detector receives the visible light signal subjected to light splitting treatment to obtain the transmittance of a corresponding visible light wavelength, and the industrial personal computer monitors the transmittance change of the laser light control and the white light control to the product through reading signals of the first detector and the second detector, and the optical thickness of the film layer is obtained through calculation.

2. A direct light control system for a coating apparatus as set forth in claim 1, wherein: the laser light-operated light path further comprises a light 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. A direct light control system for a coating apparatus as set forth in claim 2, wherein: the white light control light path further comprises a visible light signal output lens, the visible light signal output lens processes the visible light beam output by the white light source, and the processed visible light beam passes through the first dichroic mirror, so that the laser beam and the visible light beam are combined.

4. A direct light control system for a coating apparatus as set forth in claim 3, wherein: the laser light-operated light path further comprises an optical signal receiving collimator, the optical signal receiving collimator receives the laser signals which are split by the second dichroic mirror, and the laser signals received by the optical signal receiving collimator enter the first detector.

5. A direct light control system for a coating apparatus as set forth in claim 4 wherein: the white light-operated light path further comprises a visible light signal receiving lens, the visible light signal receiving lens receives the visible light signal which is split by the second dichroic mirror, and the visible light signal received by the visible light signal receiving lens enters the second detector.

6. A direct light control system for a coating apparatus as set forth in claim 1, wherein: the first dichroic mirror and the second dichroic mirror are 45-degree dichroic mirrors.

7. A direct light control system for a coating apparatus as set forth in claim 6, wherein: the 45-degree dichroic mirror is a long-wavelength dichroic mirror, and reflects the optical signal of the visible light wavelength and transmits the optical signal of the laser wavelength.

8. A direct light control system for a coating apparatus as set forth in claim 6, wherein: the 45-degree dichroic mirror is a short-wave dichroic mirror, and the short-wave dichroic mirror transmits optical signals of visible light wavelengths and reflects optical signals of laser wavelengths.

9. A direct light control system for a coating apparatus as set forth in claim 1, wherein: the first detector is a power meter, and the second detector is a monochromator.

10. A method for direct light control of a coating apparatus of a system according to any one of claims 1 to 9, comprising the steps of:

judging whether a stopping point of a light control curve of the laser wavelength is an extreme point or not;

if the stopping point of the light control curve of the laser wavelength is an extreme point, controlling the laser light control as a leading control mode, deriving the light control curve of the laser wavelength, and calculating to obtain the film thickness when the derivative is 0 as the target thickness of the film;

if the stopping point of the light control curve of the laser wavelength is not an extreme point, judging whether the light control curve of the laser wavelength passes through the extreme point;

if the light control curve of the laser wavelength passes through the extreme point, judging whether the difference value of the transmittance of the starting point of the film layer and the transmittance of the extreme point is in a preset range or not compared with the difference value of the transmittance of the ending point of the film layer and the transmittance of the extreme point;

if the light control curve of the laser wavelength passes through the extreme point and the difference value between the transmittance of the film starting point and the transmittance of the extreme point is in a preset range compared with the difference value between the transmittance of the film ending point and the transmittance of the extreme point, controlling the laser light control as a leading control mode, and calculating the actual transmittance of the film ending by the ratio of the difference value between the transmittance of the film ending point and the transmittance of the extreme point to the difference value between the transmittance of the film starting point and the transmittance of the extreme point to obtain the film thickness;

if the light control curve of the laser wavelength does not pass through the extreme point, switching the white light control as a dominant control mode, and calculating the actual transmittance of the film ending by the ratio of the difference value of the maximum transmittance of the light control curve of the visible wavelength and the transmittance of the film ending point to the difference value of the maximum transmittance and the minimum transmittance to obtain the film thickness;

if the light control curve of the laser wavelength passes through the extreme point and the difference value between the transmittance of the film starting point and the transmittance of the extreme point is not in the preset range compared with the difference value between the transmittance of the film ending point and the transmittance of the extreme point, switching the white light control as a leading control mode, and calculating the actual transmittance of the film ending by the ratio of the difference value between the transmittance of the film ending point of the light control curve of the visible wavelength and the minimum transmittance to the difference value between the maximum transmittance and the minimum transmittance to obtain the film thickness.