Film coating method based on wave band self-adaption wide spectrum film layer thickness monitoring

Abstract

The invention discloses a film coating method based on waveband self-adaption wide spectrum film layer thickness monitoring, aims to improve the film coating quality and efficiency of an optical thin film, and aims to evaluate the influence of thickness change on optical performance by designing an optical thin film structure layer by layer and calculating a transmittance spectrum by using film system design software. In the film coating process, the wave band self-adaptive monitoring technology is adopted, according to the characteristics of each layer of film and the performance of a film coating machine, the high-sensitivity monitoring wavelength is selected in a self-adaptive mode, and accurate monitoring of the film layer thickness in the wide spectrum range is achieved. According to the method, the influence degree of the current film layer thickness deviation on the current film layer transmittance is calculated by designing optical thin film layer-by-layer stacking, the sensitivity of the transmittance spectrum on the film layer thickness deviation is obtained layer by layer, the sensitivity threshold value is set, and the high-sensitivity wavelength is selected as the monitoring wavelength, so that the monitoring signal-to-noise ratio is inhibited, and the monitoring accuracy is improved. And the film thickness deposition precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum coating, and particularly relates to a coating method based on band adaptive wide-spectrum film thickness monitoring. Background Art

[0002] Since the birth of thin film deposition technology, the precise monitoring of thin film deposition thickness has always been a core issue of great concern. At present, the mainstream film thickness monitoring technologies include three categories: time monitoring, quartz crystal oscillation monitoring, and optical monitoring. However, these technologies all have their own limitations, which affect the accuracy and reliability of thin film deposition.

[0003] The time monitoring technology is essentially an open-loop film thickness control method. By artificially setting the deposition time of each layer, the corresponding film layer thickness is indirectly controlled. Its control accuracy completely depends on the deposition rate stability of the deposition technology itself and the accuracy of the designer's estimation of the deposition rate of the current material. It can only be applied to thin film deposition technologies with relatively stable deposition rates such as ion beam sputtering, magnetron sputtering, and atomic layer deposition, and cannot solve the problem of cumulative film thickness deviation caused by inaccurate deposition rate estimation, fluctuation, and drift.

[0004] The quartz crystal oscillation monitoring technology is mainly based on the piezoelectric effect and mass loading effect of quartz crystals. By measuring the corresponding relationship between the natural resonance frequency of the quartz crystal or related parameters and the film material deposition on the crystal surface, the film layer deposition thickness is deduced, but the achievable comprehensive film thickness monitoring accuracy only reaches 2% - 3%.

[0005] The optical monitoring technology has two principles: single wavelength monitoring and wide-spectrum fitting. Single wavelength monitoring judges the change of the current film layer thickness by measuring the change of the transmittance at the monitoring wavelength, and gradually develops various monitoring strategies such as differential monitoring and swing value monitoring from simple extreme value monitoring. Due to its advantage of high control accuracy for thin film thickness with a regular film system structure, it is widely used in the preparation of reflectors and FB filters. Wide-spectrum fitting is to monitor the spectral transmittance and reflectance curves within a certain wavelength range and compare them with the designed theoretical spectrum, calculate the remaining coating time through deviation, and when the deviation amount shrinks to the error tolerance, it is judged that the current film layer deposition is completed. Thanks to the miniaturization and performance improvement of spectrophotometers, spectrometers, and high-speed CCD cameras, the current wide-spectrum fitting can achieve a film thickness control accuracy of 0.1 - 0.3%.

[0006] Although closed-loop feedback control methods such as quartz crystal oscillation, single wavelength extreme value, and wide spectrum fitting can achieve high-precision closed-loop feedback control of thin film deposition thickness, various film thickness monitoring methods still have a series of inherent problems. For example, quartz crystal oscillation film thickness control is generally non-co-located indirect measurement. The deviation of the crystal control factor will cause a systematic deviation in the calculated film thickness. As the thickness of the film deposition increases, the signal-to-noise ratio of the film thickness monitoring will decrease, and switching the quartz crystal monitoring piece will destroy the continuity and consistency of the film thickness monitoring to a certain extent. Single-wavelength extreme value optical monitoring has high accuracy, but there is a problem that it cannot monitor the thickness of films with non-regular film structures. Although the monitoring of some complex film systems can be achieved by expanding the monitoring strategy, the relative accuracy is poor. Although there is no problem with the scope of application of wide spectrum fitting film thickness monitoring technology, there is a problem of non-unique solution through spectrum fitting thickness. The monitoring signal-to-noise ratio changes with the shape of the spectrum, and there will be extremely low signal-to-noise ratio points.

[0007] In summary, although the wide spectrum fitting film thickness monitoring technology has certain potential in terms of application range and film thickness control accuracy, the existing various film thickness monitoring technologies have inherent problems, which limit the further improvement of thin film deposition accuracy. Therefore, the development of more accurate, stable and widely applicable film thickness monitoring technology is still a key issue to be solved in the current vacuum coating technology field. Summary of the invention

[0008] The purpose of the present invention is to solve the problem of reduced monitoring signal-to-noise ratio caused by the insensitivity of some monitoring bands to film thickness errors during the preparation of precision optical thin film deposition using a wide-spectrum film thickness monitoring method, and propose a monitoring band adaptive wide-spectrum film thickness monitoring method. The influence of the current film thickness deviation on the current film transmittance is calculated for the design of optical thin film stacking layer by layer, the sensitivity of the transmittance spectrum to the film thickness deviation is obtained layer by layer, and the sensitivity threshold is set, and a high-sensitivity wavelength is selected as the monitoring wavelength, thereby improving the suppression of monitoring signal-to-noise ratio and improving the film thickness deposition accuracy.

[0009] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0010] A coating method based on band-adaptive wide-spectrum film thickness monitoring, characterized in that the method comprises the following steps:

[0011] S1. Design optical thin films and calculate transmittance spectra

[0012] According to the target optical performance requirements T x (λ), design the structure of the optical film, including determining the total number of film layers N, and the physical thickness of each film layer is P n ;

[0013] The transmittance spectrum of only the first n thin films is calculated using the film system design software as T n (λ), where n is the current deposition layer number and n ≤ N;

[0014] For the nth thin film, calculate the transmittance spectra T n1 (λ) and T n2 (λ) when its physical thickness increases by ΔP and decreases by -ΔP respectively;

[0015] S2. Layer-by-layer adaptive correction of the monitoring band:

[0016] Set the wide-spectrum monitoring band interval [λ1, λ2];

[0017] For each layer of the designed optical thin film, starting from λ1, calculate T n1 (λ) and T n2 (λ) in the interval [λ1, λ2] at intervals of Δλ;

[0018] Calculate the sensitivity ES n (λ) of the spectral corresponding film thickness deviation, and the formula is as follows:

[0019]

[0020] Select the wavelength when ES n (λ) ≤ ES n as the effective monitoring wavelength, where ES n is the preset sensitivity threshold;

[0021] For each layer of thin film, obtain an effective monitoring wavelength set Λ n = {λ|λ ∈ [λ1, λ2], ES n (λ) ≤ ES n};

[0022] S3. Set the effective monitoring wavelength of the wide-spectrum film layer thickness and coat the film:

[0023] Input the designed optical thin film structure into the coating machine;

[0024] Adopt a wide-spectrum fitting film layer thickness monitoring system and layer-by-layer set the effective monitoring wavelength Λ n as the wide-spectrum film layer thickness monitoring wavelength of the nth layer;

[0025] Put the monitoring substrate, the substrate to be coated, and the target into the vacuum chamber of the coating machine for pretreatment;

[0026] Start the coating machine to coat the film and use the effective monitoring wavelength to monitor the change of the film layer thickness in real time.

[0027] Further, in the step S1, the target optical performance requirement Tx(λ) includes at least one of specific transmittance, reflectance or phase difference.

[0028] Further, the physical thickness P of the nth layer in the step S1 n changes by ΔP and -ΔP respectively, where ΔP ranges from 0.1 nm to 50 nm.

[0029] Further, in the step S2, the spectral monitoring band interval [λ1, λ2] is set according to the characteristics of the designed optical thin film and the performance of the coating machine.

[0030] Further, in the step S2, the preset sensitivity threshold ES n is preset according to the coating accuracy requirements and the performance of the monitoring equipment.

[0031] Further, in the step S3, the coating machine is one of an ion beam sputtering coating machine, an electron beam evaporation coating machine, and a magnetron sputtering coating machine.

[0032] Further, in the step S3, the pretreatment steps include steps such as vacuum pumping and substrate baking to ensure the smooth progress of the coating process.

[0033] Compared with the prior art, the technical effects of the present invention are as follows:

[0034] 1) Traditional coating monitoring methods often rely on fixed monitoring wavelengths or bands and cannot be flexibly adjusted according to the film layer characteristics and changes during the coating process. However, the present invention realizes the dynamic selection and optimization of the monitoring wavelength by introducing the band adaptive monitoring technology. During the coating process, according to the characteristics of each thin film layer and the performance of the coating machine, the monitoring wavelength with high sensitivity is adaptively selected, thereby improving the monitoring signal-to-noise ratio and the deposition accuracy of the film layer thickness.

[0035] 2) The wide-spectrum fitting film layer thickness monitoring technology is adopted, and the change of the film layer thickness is accurately monitored by calculating and analyzing the change of the transmittance spectrum in the wide-spectrum range. Compared with the traditional single-point or narrow-band monitoring methods, the wide-spectrum monitoring technology has higher sensitivity and accuracy and can more comprehensively reflect the change of the film layer thickness.

[0036] 3) In the design stage before coating, the method of layer-by-layer design and calculation optimization is adopted. According to the target optical performance requirements, the structure and parameters of each thin film layer are accurately designed, and the transmittance spectrum is calculated using the film system design software. By comparing the transmittance spectra under different thickness changes, the influence of the thickness change on the optical performance can be evaluated, and the thickness and refractive index and other parameters of each thin film layer can be optimized, making the coating process more accurate and controllable, and contributing to the preparation of higher-quality optical thin films. Description of the Drawings

[0037] Figure 1 This is the flow chart of the coating method based on band - adaptive wide - spectrum film thickness monitoring of the present invention;

[0038] Figure 2 Design the optical thin - film structure for the first embodiment of the present invention;

[0039] Figure 3 Design the transmittance spectrum of the optical thin - film for the first embodiment of the present invention;

[0040] Figure 4 Design the transmittance spectrum when the first 3 layers of the optical thin - film are stacked, and the transmittance spectra when the physical thickness of the 3rd layer changes by 3nm and - 3nm respectively for the first embodiment of the present invention;

[0041] Figure 5 Design the transmittance spectrum sensitivity when the first 3 layers of the optical thin - film are stacked for the first embodiment of the present invention;

[0042] Figure 6 Design the test spectrum after the optical thin - film is prepared for the first embodiment of the present invention; Detailed implementation manners

[0043] The following will explain the embodiments of the present invention in detail with reference to the drawings, but the protection scope of the present invention should not be limited thereby.

[0044] This embodiment provides a coating method based on band - adaptive wide - spectrum film thickness monitoring. This method is based on the wide - spectrum fitting film thickness monitoring technology. By depositing the optical thin - film layer by layer and adaptively selecting the monitoring wavelength with high sensitivity, the monitoring signal - to - noise ratio and the deposition accuracy of the film thickness are improved. The specific steps are as follows:

[0045] Step 1. Design the optical thin - film and calculate the transmittance spectrum:

[0046] First, according to the target optical performance requirements T x (λ) (such as specific transmittance, reflectance or phase difference, etc.), design the structure of the optical thin - film, including determining the total number of layers N of the thin - film, the physical thickness P n of each layer of material and the refractive index, etc.;

[0047] Then, use film system design software (such as TFCalc, Macleod or Optilayer) to calculate the transmittance spectrum T n (λ) of only the first n layers of the thin - film. In order to evaluate the influence of thickness change on the transmittance spectrum, it is also necessary to calculate the transmittance spectra T n1 (λ) and T n2 (λ) when the physical thickness of the nth layer increases by ΔP and decreases by ΔP respectively (the value range of ΔP is 0.1nm - 50nm).

[0048] Step 2. Layer-by-layer Adaptive Correction of Monitoring Bands:

[0049] First, set the spectral monitoring band interval [λ1, λ2]. Then, for each layer of the designed optical thin film, starting from λ1, calculate T n1 (λ) and T n2 (λ) within the interval [λ1, λ2] at intervals of Δλ.

[0050] Next, calculate the sensitivity ES n (λ) of the spectral corresponding film thickness deviation. This sensitivity reflects the sensitivity of the transmittance spectrum to the film layer thickness deviation at a given wavelength λ. The formula is as follows:

[0051]

[0052] By comparing the sensitivity ES n (λ) with the preset sensitivity threshold ES n , select the wavelengths that meet the conditions as the effective monitoring wavelengths, that is, select the wavelengths when ES n (λ) ≤ ES n as the effective monitoring wavelengths.

[0053] For each layer of the thin film, a set of effective monitoring wavelengths will be obtained, that is, the set of effective monitoring wavelengths corresponding to the nth layer of the thin film, denoted as Λ n = {λ|λ ∈ [λ1, λ2], ES n (λ) ≤ ES n}. These effective monitoring wavelengths will be used to monitor the change of the film layer thickness during the subsequent coating process.

[0054] Step 3. Set the Effective Monitoring Wavelengths and Coat the Film

[0055] Input the designed optical thin film structure into a coating machine (such as an ion beam sputtering coating machine, an electron beam evaporation coating machine, or a magnetron sputtering coating machine), and layer by layer set the set of effective monitoring wavelengths Λ n as the wide-spectrum film layer thickness monitoring wavelength for the nth layer.

[0056] Then, put the monitoring substrate, the substrate to be coated, and the target into the vacuum chamber of the coating machine, and perform pre-treatment steps such as vacuum pumping and substrate baking to ensure the smooth progress of the coating process.

[0057] Finally, start the coating machine to coat the film, and at the same time use the wide-spectrum fitting technology and the set effective monitoring wavelengths to monitor the change of the film layer thickness in real time to ensure that the finally obtained thin film meets the design requirements.

[0058] Example:

[0059] Objective: To fabricate an anti-reflection film (i.e., anti-reflection coating) with an average component at an incident angle of 0 degrees at a wavelength of 800 nm on a quartz material substrate to improve the light transmittance at this wavelength.

[0060] Material selection:

[0061] The quartz material is used as the substrate, SiO2 is the low refractive index material, and Ta2O5 is the high refractive index material to achieve the anti-reflection effect.

[0062] Step 1. Design the optical thin film and calculate the transmittance spectrum:

[0063] 1.1 Film system structure design: As Figure 2 shown, a designed film system structure of an 800 nm anti-reflection film with a total of 5 layers is designed. The corresponding transmittance spectrum is as Figure 3 shown.

[0064] 1.2 Transmittance spectrum calculation: Calculate the transmittance spectrum when the first n layers of the designed optical thin film are stacked layer by layer, and the transmittance spectra when the physical thickness of the nth layer changes by 3 nm and -3 nm respectively. Figure 4 Shows the transmittance spectrum when the first 3 layers are stacked and the transmittance spectra when the physical thickness of the 3rd layer changes by 3 nm and -3 nm.

[0065] Step 2. Layer-by-layer adaptive correction for the monitoring band:

[0066] Set the wide-spectrum monitoring band interval as [300 nm, 1000 nm]. For each layer of the designed optical thin film, starting from 300 nm, calculate the sensitivity ES n (λ) of the spectral corresponding film thickness deviation in the interval [300 nm, 1000 nm] at an interval of 1 nm. Select the wavelength that satisfies ES n (λ) less than or equal to the sensitivity threshold of 0.005 1 / nm as the effective monitoring wavelength, and count all the effective monitoring wavelengths corresponding to the nth layer as the set Λ n ={λ|λ∈[λ1,λ2], ES n (λ)≤ES n}, which is used as the monitoring wavelength for the wide-spectrum monitoring of each layer.

[0067] Step 3. Set the effective monitoring wavelength and deposit the film

[0068] In this embodiment, a dual-ion beam sputtering coater is used. The quartz substrate to be coated and the monitoring substrate are ultrasonically cleaned to remove surface dirt and impurities. After drying, they are placed in the vacuum chamber of the coater.

[0069] The vacuum is pumped to a vacuum degree of 5×10 -6 Pa to reduce gas pollution during the film deposition process. The substrate is heated until the temperature reaches 100 degrees Celsius and kept at a constant temperature to improve the film deposition quality and adhesion.

[0070] Coat the substrate with a dual ion beam sputtering coater. The main ion source voltage is 1200V, and argon is used as the main ion source gas. The auxiliary ion source voltage is 550V, and argon and oxygen are used as the ion source gases. Select metal Ta and SiO2 as the sputtering targets for high and low refractive index materials.

[0071] As Figure 6 shown, the preparation result of the designed optical thin film is basically consistent with the designed spectrum, indicating that the coating process is well controlled and the expected anti-reflection effect is achieved.

[0072] In this embodiment, through precise design, calculation and coating process control, an anti-reflection film with an average component at 0-degree incidence at a wavelength of 800nm is successfully prepared on a quartz substrate. The film structure effectively improves the light transmittance and provides strong support for the performance improvement of optical devices. At the same time, through wide-spectrum monitoring and sensitivity analysis, the precision control during the coating process is ensured, providing a reliable method for the preparation of high-quality optical thin films.

[0073] The present invention calculates the influence degree of the current film thickness deviation on the transmittance of the current film layer layer by layer for the designed optical thin film, obtains the sensitivity of the transmittance spectrum to the film thickness deviation layer by layer, sets a sensitivity threshold, and selects the high-sensitivity wavelength as the monitoring wavelength, so as to improve the suppression of the monitoring signal-to-noise ratio and improve the deposition precision of the film layer thickness.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A coating method based on monitoring the thickness of a band - adaptive wide - spectrum film layer, characterized in that: The method includes the following steps: S1. Design an optical thin film and calculate the transmittance spectrum According to the target optical performance requirement T x (λ), design the structure of the optical thin film, including determining the total number of layers N of the thin film and the physical thickness P of each layer of the thin film n ; Use the film system design software to calculate the transmittance spectrum of only the first n layers of thin films as T n (λ), where n is the current deposition layer number and n ≤ N; For the nth layer of the film, calculate the transmittance spectra T n1 (λ) and T n2 (λ) when its physical thickness increases by ΔP and decreases by -ΔP, respectively; n1 (λ) and T n2 (λ); S2. Layer-by-layer adaptive correction for the monitored band: Set the wide-spectrum monitored band interval [λ1, λ2]; For each layer of the designed optical thin film, starting from λ1, calculate T n1 (λ) and T n2 (λ) within the interval [λ1, λ2] at intervals of Δλ. n1 (λ) and T n2 (λ); Calculate the sensitivity ES of the spectral corresponding film thickness deviation n (λ), the formula is as follows: Select ES n λ(λ) ≤ ES n When the wavelength is used as the effective monitoring wavelength, where ES n is the preset sensitivity threshold; For each layer of the film, an effective monitoring wavelength set Λ is obtained n ={λ|λ∈[λ1,λ2], ES n (λ)≤ES n}; S3. Set the effective monitoring wavelength of the wide-spectrum film layer thickness and deposit the film: Input the designed optical thin film structure into the coating machine; Adopt a wide-spectrum fitting film thickness monitoring system, and set the effective monitoring wavelength Λ layer by layer n as the wide-spectrum film thickness monitoring wavelength of the nth layer; Put the monitoring substrate, the substrate to be coated, and the target into the vacuum chamber of the coating machine for pretreatment; Start the coating machine to deposit the film, and use the effective monitoring wavelength to monitor the change of the film layer thickness in real time.

2. The coating method based on band adaptive wide-spectrum film thickness monitoring according to claim 1, wherein: In the step S1, the target optical performance requirement Tx(λ) includes at least one of a specific transmittance, reflectance, or phase difference.

3. The coating method based on band adaptive wide-spectrum film layer thickness monitoring according to claim 1, characterized in that: The physical thickness P of the nth layer in the step S1 n are respectively changed by ΔP and -ΔP, where ΔP ranges from 0.1 nm to 50 nm.

4. The coating method based on band adaptive wide-spectrum film thickness monitoring according to claim 1, characterized in that: In the step S2, the spectral monitoring band interval [λ1, λ2] is set according to the characteristics of the designed optical thin film and the performance of the coating machine.

5. The coating method based on band adaptive wide-spectrum film layer thickness monitoring according to claim 1, characterized in that: In the step S2, a preset sensitivity threshold ES n is preset according to the coating accuracy requirement and the performance of the monitoring device.

6. The coating method based on band adaptive wide-spectrum film layer thickness monitoring according to claim 1, wherein: In the step S3, the coating machine is one of an ion beam sputtering coating machine, an electron beam evaporation coating machine, and a magnetron sputtering coating machine.

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