A film coating method based on waveband adaptive wide-spectrum film layer thickness monitoring

Abstract

A kind of coating method based on waveband adaptive wide spectrum film layer thickness monitoring, to improve the coating quality and efficiency of optical thin film, by layer by layer design optical thin film structure, and using film system design software to calculate transmittance spectrum, to evaluate the influence of thickness change on optical performance;In the coating process, waveband adaptive monitoring technology is used, according to the characteristics of each layer of film and the performance of coating machine, to adaptively select high sensitivity monitoring wavelength, to realize accurate monitoring of film layer thickness in wide spectral range.The present application calculates the influence of current film thickness deviation on current film transmittance for layer by layer design of optical thin film, obtains the sensitivity of transmittance spectrum to film thickness deviation layer by layer, sets the sensitivity threshold, selects high sensitivity wavelength as monitoring wavelength, to improve the signal-to-noise ratio of suppression monitoring, to improve the deposition accuracy of film layer thickness.

Description

Technical Field

[0001] This invention relates to the field of vacuum coating technology, and in particular to a coating method based on band-adaptive broadband film thickness monitoring. Background Technology

[0002] Since the inception of thin film deposition technology, precise monitoring of thin film thickness has been a core issue of great concern. Currently, the mainstream film thickness monitoring technologies include three main categories: time monitoring, quartz crystal oscillation monitoring, and optical monitoring. However, each of these technologies has its own limitations, affecting the accuracy and reliability of thin film deposition.

[0003] Time monitoring technology is essentially an open-loop film thickness control method. It indirectly controls the corresponding film thickness by manually setting the deposition time of each layer. Its control accuracy depends entirely on the stability of the deposition rate 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. Furthermore, it cannot solve the problem of cumulative film thickness deviation caused by inaccurate, fluctuating, or drifting deposition rate estimation.

[0004] Quartz crystal oscillation monitoring technology is mainly based on the piezoelectric effect and mass loading effect of quartz crystal. By measuring the inherent resonant frequency of quartz crystal or the corresponding relationship between it and the film material when it is deposited on the crystal surface, the film deposition thickness can be estimated. However, the overall film thickness monitoring accuracy can only reach 2% to 3%.

[0005] Optical monitoring technology employs two principles: single-wavelength monitoring and broadband fitting. Single-wavelength monitoring determines the current film thickness variation by measuring the transmittance change at the monitored wavelength. It has evolved from simple extreme value monitoring to various monitoring strategies such as difference monitoring and oscillation value monitoring. Due to its high precision in controlling the thickness of films with regular film structures, it is widely used in the fabrication of mirrors and FB filters. Broadband fitting, on the other hand, monitors the spectral transmittance and reflectance curves within a certain wavelength range and compares them with the designed theoretical spectrum. The remaining coating time is calculated based on the deviation, and the film deposition is considered complete when the deviation decreases to the error tolerance. Thanks to the miniaturization and performance improvement of spectrophotometers, spectrometers, and high-speed CCD cameras, broadband fitting can currently achieve a film thickness control accuracy of 0.1% to 0.3%.

[0006] While combining closed-loop feedback control methods such as quartz crystal oscillation, single-wavelength extremum, and broadband spectral 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 an indirect measurement method, and deviations in the crystal control factor can lead to systematic deviations in the calculated film thickness. Furthermore, the signal-to-noise ratio (SNR) of film thickness monitoring decreases with increasing film deposition thickness, and switching quartz crystal monitoring chips can disrupt the continuity and consistency of film thickness monitoring to some extent. Single-wavelength extremum optical monitoring offers high precision but cannot monitor the thickness of films with irregular film structures. Although extended monitoring strategies can monitor some complex film systems, the relative accuracy is poor. While broadband spectral fitting film thickness monitoring technology does not have an applicability issue, the solution for thickness fitting through spectral means is not unique, and the monitoring SNR varies with the spectral shape, resulting in extremely low SNR points.

[0007] In summary, although broadband fitting film thickness monitoring technology has certain potential in terms of applicability and film thickness control accuracy, existing film thickness monitoring technologies all have inherent problems that limit further improvements in thin film deposition accuracy. Therefore, developing a more accurate, stable, and widely applicable film thickness monitoring technology remains a key issue that urgently needs to be addressed in the field of vacuum coating technology. Summary of the Invention

[0008] The purpose of this invention is to address the problem of reduced signal-to-noise ratio (SNR) in the deposition of precision optical thin films using broadband film thickness monitoring methods, where certain monitoring bands are insensitive to film thickness errors. This invention proposes an adaptive broadband film thickness monitoring method. It calculates the impact of current film thickness deviations on the transmittance of each layer during the stacking of the designed optical thin films, obtains the sensitivity of the transmittance spectrum to film thickness deviations layer by layer, sets a sensitivity threshold, and selects highly sensitive wavelengths as monitoring wavelengths. This improves the suppression of the monitoring SNR and enhances the accuracy of film thickness deposition.

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

[0010] A coating method based on band-adaptive broadband film thickness monitoring is characterized by the following steps:

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

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

[0013] The transmittance spectrum of a thin film containing only the first n layers was calculated using membrane design software. n (λ), where n is the current deposition layer number, and n≤N;

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

[0015] S2. Monitoring band layer-by-layer adaptive correction:

[0016] Set the broadband monitoring band interval [λ1,λ2];

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

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

[0019]

[0020] Select ES n (λ)≤ES n The wavelength at time is used as the effective monitoring wavelength, where ES n Set a preset sensitivity threshold;

[0021] For each thin film layer, an effective set of monitoring wavelengths is obtained. ;

[0022] S3. Set the effective monitoring wavelength for broadband film thickness and apply the coating:

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

[0024] A broadband fitting film thickness monitoring system was adopted, and effective monitoring wavelengths Λ were set layer by layer. n As a broadband film thickness monitoring wavelength for the nth layer;

[0025] The monitoring substrate, the substrate to be coated, and the target material are placed in the vacuum chamber of the coating machine for pretreatment;

[0026] Start the coating machine to perform coating, and use an effective monitoring wavelength to monitor the changes in film thickness in real time.

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

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

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

[0030] Furthermore, in step S2, a preset sensitivity threshold ES is set. n The settings are preset according to the coating accuracy requirements and the performance of the monitoring equipment.

[0031] Furthermore, in step S3, the coating machine is one of the following: ion beam sputtering coating machine, electron beam evaporation coating machine, and magnetron sputtering coating machine.

[0032] Furthermore, in step S3, the pretreatment step includes steps such as vacuuming and baking the substrate 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, which cannot be flexibly adjusted according to film characteristics and changes during the coating process. This invention, however, introduces band-adaptive monitoring technology to achieve dynamic selection and optimization of the monitoring wavelength. During the coating process, a highly sensitive monitoring wavelength is adaptively selected based on the characteristics of each thin film and the performance of the coating machine, thereby improving the monitoring signal-to-noise ratio and the deposition accuracy of the film thickness.

[0035] 2) A broadband fitting film thickness monitoring technique was employed. By calculating and analyzing transmittance spectral changes over a wide spectral range, variations in film thickness were precisely monitored. Compared to traditional single-point or narrow-band monitoring methods, broadband monitoring technology offers higher sensitivity and accuracy, and can more comprehensively reflect changes in film thickness.

[0036] 3) In the design phase before coating, a layer-by-layer design and computational optimization method was adopted. Based on the target optical performance requirements, the structure and parameters of each thin film layer were precisely designed, and the transmittance spectrum was calculated using film system design software. By comparing the transmittance spectra under different thickness variations, the impact of thickness changes on optical performance could be evaluated, and parameters such as the thickness and refractive index of each thin film layer could be optimized. This makes the coating process more precise and controllable, contributing to the fabrication of higher-quality optical thin films. Attached Figure Description

[0037] Figure 1 This is a flowchart of the coating method based on band-adaptive broadband film thickness monitoring according to the present invention;

[0038] Figure 2 An optical thin film structure was designed for Embodiment 1 of the present invention;

[0039] Figure 3 Design of optical thin film transmittance spectrum for Embodiment 1 of the present invention;

[0040] Figure 4 The transmittance spectrum of the first three layers of the optical thin film designed for Embodiment 1 of the present invention, and the transmittance spectrum of the third layer when the physical thickness is changed by 3 nm and -3 nm respectively;

[0041] Figure 5 The transmittance spectral sensitivity of the first three layers of the optical thin film designed in Embodiment 1 of the present invention.

[0042] Figure 6 The test spectrum after the optical thin film was prepared according to Embodiment 1 of the present invention. Detailed Implementation

[0043] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0044] This embodiment provides a coating method based on band-adaptive broadband film thickness monitoring. This method utilizes broadband fitting film thickness monitoring technology, depositing optical thin films layer by layer and adaptively selecting highly sensitive monitoring wavelengths to improve the monitoring signal-to-noise ratio and the deposition accuracy of the film thickness. The specific steps are as follows:

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

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

[0047] Then, the transmittance spectrum T of only the first n layers of the film is calculated using film system design software (such as TFCalc, Macleod, or Optilayer). n (λ). To evaluate the effect of thickness variation on the transmittance spectrum, it is also necessary to calculate the transmittance spectrum T when the physical thickness of the nth layer increases by ΔP and decreases by ΔP (ΔP ranges from 0.1 nm to 50 nm). n1 (λ) and T n2 (λ).

[0048] Step 2. Monitor bands for layer-by-layer adaptive correction:

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

[0050] Next, the sensitivity ES of the spectrum to film thickness deviation is calculated. n (λ), this sensitivity reflects the degree to which the transmittance spectrum is sensitive to film thickness deviation at a given wavelength λ, and is expressed by the following formula:

[0051]

[0052] By comparing sensitivity ES n (λ) and the preset sensitivity threshold ES n Select the wavelength that meets the conditions as the effective monitoring wavelength, that is, select ES. n (λ)≤ES n The wavelength at that time is used as the effective monitoring wavelength.

[0053] For each thin film layer, a set of effective monitoring wavelengths is obtained, namely, the set of effective monitoring wavelengths corresponding to the nth thin film, denoted as . These effective monitoring wavelengths will be used to monitor changes in film thickness during subsequent coating processes.

[0054] Step 3. Set the effective monitoring wavelength and apply the coating.

[0055] The designed optical thin film structure is input 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 an effective monitoring wavelength set Λ is set layer by layer. n Used as the wavelength for monitoring the thickness of the broadband film layer n.

[0056] Then, the monitoring substrate, the substrate to be coated, and the target material are placed into the vacuum chamber of the coating machine for pretreatment steps such as vacuuming and baking the substrate to ensure the smooth progress of the coating process.

[0057] Finally, the coating machine is started to coat the film, while broadband fitting technology and the set effective monitoring wavelength are used to monitor the change in film thickness in real time to ensure that the final film meets the design requirements.

[0058] Example:

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

[0060] Material selection:

[0061] Quartz material is used as the substrate, with SiO2 being a low-refractive-index material and Ta2O5 being a high-refractive-index material, to achieve an anti-reflective effect.

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

[0063] 1.1 Membrane system structure design: such as Figure 2 As shown, a 5-layer antireflection membrane structure for an 800nm ​​antireflection coating was designed. Its corresponding transmittance spectrum is shown below. Figure 3 As shown.

[0064] 1.2 Transmittance Spectrum Calculation: The transmittance spectrum of the first n layers of the designed optical thin film was calculated layer by layer, as well as the transmittance spectrum when the physical thickness of the nth layer changed by 3 nm and -3 nm respectively. Figure 4 The transmittance spectra of the first three layers are shown, as well as the transmittance spectra of the third layer when the physical thickness changes by 3 nm and -3 nm.

[0065] Step 2. Monitor bands for layer-by-layer adaptive correction:

[0066] The broadband monitoring band is set to [300nm, 1000nm]. For each layer of the designed optical thin film, starting from 300nm, the sensitivity ES of the film thickness deviation corresponding to the spectrum in the [300nm, 1000nm] interval is calculated at 1nm intervals. n (λ), select the one that satisfies ES n (λ) is less than or equal to the sensitivity threshold of 0.005 The wavelength at 1 / nm is taken as the effective monitoring wavelength, and all effective monitoring wavelengths corresponding to the nth layer are counted into a set. , which serves as the monitoring wavelength for each layer of broadband monitoring.

[0067] Step 3. Set the effective monitoring wavelength and apply the coating.

[0068] This embodiment uses a dual-ion beam sputtering coating machine, and ultrasonically cleans the quartz substrate and monitoring substrate to be coated to remove surface dirt and impurities. After drying, they are placed in the vacuum chamber of the coating machine.

[0069] Evacuate to a vacuum level of 5×10 -6 Pa is used to reduce gas contamination during the coating process. The substrate is heated until it reaches 100 degrees Celsius and maintained at a constant temperature to improve coating quality and adhesion.

[0070] The substrate was coated using a dual-ion-beam sputtering coating machine with a main ion source voltage of 1200V and argon as the main ion source gas. The auxiliary ion source voltage was 550V and argon and oxygen were used as the ion source gases. Metallic Ta and SiO2 were selected as sputtering targets for high and low refractive index materials, respectively.

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

[0072] This embodiment successfully fabricated an average component antireflective coating on a quartz substrate at an 800nm ​​wavelength with 0-degree incident light through precise design, calculation, and coating process control. This film structure effectively improves light transmittance, providing strong support for enhancing the performance of optical devices. Simultaneously, broadband monitoring and sensitivity analysis ensured precise control during the coating process, providing a reliable method for preparing high-quality optical thin films.

[0073] This invention addresses the impact of current film thickness deviation on the transmittance of an optical thin film by stacking it layer by layer. It obtains the sensitivity of the transmittance spectrum to the film thickness deviation layer by layer, sets a sensitivity threshold, and selects a highly sensitive wavelength as the monitoring wavelength, thereby improving the suppression monitoring signal-to-noise ratio and enhancing the film thickness deposition accuracy.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A coating method based on band-adaptive broadband film thickness monitoring, characterized in that: The method includes the following steps: S1. Design optical thin films and calculate transmittance spectra. Based on the target optical performance requirements T x (λ), design the structure of the optical thin film, including determining the total number of layers N and the physical thickness P of each layer. n ; The transmittance spectrum of a thin film containing only the first n layers was calculated using membrane design software. n (λ), where n is the current deposition layer number, and n≤N; For the nth thin film, calculate the transmittance spectrum T when its physical thickness increases by ΔP and decreases by -ΔP. n1 (λ) and T n2 (λ); S2. Monitoring band layer-by-layer adaptive correction: Set the broadband monitoring band interval [λ1,λ2]; For each layer of the designed optical thin film, starting from λ1, calculate T within the interval [λ1,λ2] at intervals of Δλ. n1 (λ) and T n2 (λ); Calculate the sensitivity ES of the spectrum to film thickness deviation n (λ), the formula is as follows: Select ES n (λ)≤ES n The wavelength at time is used as the effective monitoring wavelength, where ES n Set a preset sensitivity threshold; For each thin film layer, an effective set of monitoring wavelengths is obtained. ; S3. Set the effective monitoring wavelength for broadband film thickness and apply the coating: Input the designed optical thin film structure into the coating machine; A broadband fitting film thickness monitoring system was adopted, and effective monitoring wavelengths Λ were set layer by layer. n As a broadband film thickness monitoring wavelength for the nth layer; The monitoring substrate, the substrate to be coated, and the target material are placed in the vacuum chamber of the coating machine for pretreatment; Start the coating machine to perform coating, and use an effective monitoring wavelength to monitor the changes in film thickness in real time.

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

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

4. The coating method based on band-adaptive broadband film thickness monitoring according to claim 1, characterized in that: In step S2, the spectral monitoring band range [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 broadband film thickness monitoring according to claim 1, characterized in that: In step S2, a preset sensitivity threshold ES is defined. n The settings are preset according to the coating accuracy requirements and the performance of the monitoring equipment.

6. The coating method based on band-adaptive broadband film thickness monitoring according to claim 1, characterized in that: In step S3, the coating machine is one of the following: ion beam sputtering coating machine, electron beam evaporation coating machine, or magnetron sputtering coating machine.

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