Method for online ion beam etching correction of narrow band optical filters

Abstract

The application relates to a method for modifying a narrow-band filter by an online ion beam etching, and belongs to the technical field of optical communication. The method realizes the modification of the over-thick error of a film layer through online ion beam etching, makes a film thickness monitoring signal return to before the error occurs, realizes the modification of the error, reduces the scrappage rate of products, improves the finished product rate of monitoring, and reduces the cost of filter plating. The light value reading is more reliable than the time power method, and can guarantee the over-etching amount.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, specifically relating to a method for online ion beam etching to correct narrowband filters. Background Technology

[0002] With the rapid development of information technologies such as 5G communication, the demand for ultra-narrowband filters used in optical communication has increased significantly, including wavelength division multiplexing filters and band separation filters for various channels. In the medical industry, various fluorescent narrowband filters are used; ultra-narrowband filters are used for laser ranging and lidar; and in smart wearable devices, large-angle incident narrowband filters are applied. The basic structure of these filters is that of a multi-wave Fabry-Perot filter.

[0003] The narrower the bandwidth, the smaller the tolerance of the coating error of the Fabry-Perot filter. After the bandwidth is less than 40nm, the widely used quartz crystal monitoring method has a low coating yield, poor waveform of the coated filter, and low peak transmittance. The standard method is to use the central straight optical path transmission method for monitoring and use the error compensation characteristics of the optical extreme value method to improve the monitoring accuracy by an order of magnitude. There are many ways to improve the monitoring accuracy of optical thin films [4]-[8]. On the one hand, based on hardware [1], crystal control method, eccentric straight optical path transmission method [2], and online ellipsometry method [3] are used. On the other hand, based on software algorithms [5]-

[12] , the focus is on data processing of hardware signals, smoothing extreme point data, and improving the monitoring accuracy. In the actual coating process of ultra-narrow band filters, the film thickness is not sensitive to the optical signal of the extreme point. A change of 0.01% in the light quantity value can lead to an actual error of 5nm. When the ion source shuts down or the light intensity fluctuates abnormally, algorithmic defects in the automatic optical monitoring system can lead to misjudgment or failure to recognize extreme values. This can cause the current layer thickness to exceed the design limit, or the system to automatically jump to the next layer. While existing technologies can address film thickness errors before reaching the designed thickness through re-plating, for special film systems like optical filters, if the current layer thickness exceeds the design value, the filter must either be scrapped or the design modified, increasing the original film thickness to three times its original value. This effectively compresses the filter's bandwidth, deviating from the original design and reducing the filter's effective area. If a different material is deposited during the re-plating process, the filter must be scrapped.

[0004] References

[0005] [1] Liu, Shuqin. An online film thickness monitoring system and method for optical thin film deposition [P]. Guangdong Province: CN113862629A, 2021-12-31.

[0006] [2] Ma Daoyuan. Monitoring method for the thickness of structural color pigment optical thin films and coating machine [P]. Zhejiang Province: CN112981357A, 2021-06-18.

[0007] [3] Hiroshi Masuda, Liwei He. A method for monitoring the thickness of optical filter films [P]. Jiangsu Province: CN112710244A, 2021-04-27.

[0008] [4] Ma Zhiliang. A brief introduction to automated control systems for optical thin films [J]. Instrumentation and Analysis Monitoring, 2014(04):25-28.

[0009] [5] Cai Qingyuan, An optical monitoring and tracing method for rapid inversion of thin film growth thickness. Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 2013-11-01.

[0010] [6] Zhao Rujin, Ma Zi, Yao Yuancheng, He Changtao. Optical film thickness monitoring signal processing based on generalized Kalman filtering [J]. Laser Technology, 2007(04):412-415.

[0011] [7] Zhao Rujin, Ma Zi, Yao Yuancheng, He Changtao. Digital phase-sensitive detection for monitoring optical film thickness based on V / F transformation [J]. Laser Journal, 2007(03):77-78.

[0012] [8] Zhu Meiping, Yi Kui, Guo Shihai, Fan Zhengxiu, Shao Jianda. Research on automatic control system for optical thin film thickness [J]. Acta Photonica Sinica, 2007(02):308-311.

[0013] [9] Zhu Meiping, Yi Kui, Guo Shihai, Fan Zhengxiu, Shao Jianda. Effects of film thickness monitoring error and unevenness of monitoring sheet on film thickness monitoring [J]. Acta Optica Sinica, 2006(07):1107-1111.

[0014]

[10] Ma Zi, Xiao Qi, Yao Dewu. Digital signal processing of thin-film optical monitoring signals [J]. Optical Instruments, 2004(02):95-98.

[0015]

[11] Lin Yuxiang, Zhang Yueguang, Gu Peifu, Tang Jinfa. Real-time optical monitoring system for thin film filter deposition process [J]. Optical Instruments, 2004(02):105-108.

[0016]

[12] Zhang Rongjun, Chen Dayu, Zheng Yuxiang, Wu Yunhua, Li Li, Zhou Peng, Chen Liangyao. Simulation analysis of monitoring technology in the thin film deposition process of optical filter[J]. Journal of Infrared and Millimeter Waves, 2003(01):56-58. Summary of the Invention

[0017] (a) Technical problems to be solved

[0018] The technical problem to be solved by this invention is to design an online correction method for depositing narrowband filters, which can be used to etch and correct over-correction and skip-layer errors of the filter, restore the filter monitoring signal to a normal state, and improve the yield of the filter.

[0019] (II) Technical Solution

[0020] To address the aforementioned technical problems, this invention provides a method for online ion beam etching to correct narrowband filters. This method utilizes an RF ion source configured with an auxiliary narrowband ion beam optical vacuum coating machine. By changing the working gas and parameters of the RF ion source, it is adjusted to an etching state, enabling direct physical etching of the optical film layer of the narrowband filter. This allows for online etching of another material whose optical film layer exceeds the designed film thickness error or is mistakenly deposited, thus restoring the film thickness monitoring signal to its state before the error occurred and achieving error correction of the narrowband filter.

[0021] The present invention also provides an apparatus for implementing the method.

[0022] (III) Beneficial Effects

[0023] This invention transforms the ion beam auxiliary source into an etching source by adjusting parameters and replacing the gas, achieving direct online ion beam etching. Furthermore, based on the signal amplitude of the optical amplifier and combined with the direction and amplitude of the actual optical monitoring signal, over-correlation and layer skipping errors of the filter are corrected through etching, restoring the filter monitoring signal to a normal state. This invention, through online ion beam etching, corrects excessive film thickness errors, returning the film thickness monitoring signal to its state before the error occurred, thus reducing product scrap rates, increasing the yield of monitored products, and lowering the cost of filter deposition. Using light intensity readings is more reliable than the time-power method and can guarantee the amount of over-etching. Attached Figure Description

[0024] Figure 1 It is the transmission monitoring curve of a 3-half-wave ultra-narrowband filter;

[0025] Figure 2 This is the distribution of the filter transmission curve simulated with a random error of 0.002.

[0026] Figure 3 This is the monitoring curve for the 1380nm filter skipping layer;

[0027] Figure 4 These are the light intensity values ​​before and after etching;

[0028] Figure 5 It is an extreme value etching pattern of the spacer layer. Detailed Implementation

[0029] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0030] The monitoring error of the light intensity value of ultra-narrowband filters is a major factor affecting the filter's transmittance and waveform. During long-term deposition, ion source shutdown and rotation signal jitter can cause misjudgment of film extrema and incorrect layer skipping. This invention transforms the ion beam auxiliary source into an etching source by adjusting the parameters and changing the gas, achieving online direct ion beam etching. Furthermore, based on the signal amplitude of the optical amplifier and combined with the actual optical monitoring signal light intensity value direction and amplitude, etching corrections are made for overcorrection and layer skipping errors of the filter, restoring the filter monitoring signal to a normal state and improving the filter yield.

[0031] The Fabry-Perot narrowband filter is the most effective film structure for ultra-narrowband filter design. Taking a 1065nm half-wavelength filter as an example, the structure is denoted as G / (HL). 4 H4LH(LH) 4 L(HL) 4 H6LH(LH) 4 L(HL) 4 H4LH(LH) 3 L0.6H0.8L / A, where H represents Ta₂O₅ with an optical thickness of 1 / 4 wavelength, L represents SiO₂ with an optical thickness of 1 / 4 wavelength, G represents glass, and A represents air. The designed full width at half maximum (FWHM) bandwidth is 5 nm. This design is highly sensitive to monitoring errors; a random thickness error of 0.002 nm can cause waveform collapse in the filter. HAMacleod analyzed the monitoring error of the filter and found that the compensation effect of optical monitoring can improve the monitoring accuracy by an order of magnitude. The transmission monitoring curve of the filter was calculated using Essential Macleod software as follows: Figure 1 Analysis was performed using a random thickness error of 0.002, and the transmission spectrum distribution is shown in the figure. Figure 2 The characteristics of this film system are: the thickness of each layer is an integer number of quarter wavelengths, and the stopping point is the maximum or minimum value of the light intensity.

[0032] Currently, radio frequency (RF) ion sources are widely used in the deposition process of optical thin films. After ion acceleration, they are neutralized by a neutralizer, and kinetic gas is incident on the film surface, triggering cascade collisions. When the ion source acceleration voltage is below 800V, the bombardment effect mainly makes the film more compact, resulting in increased refractive index, increased aggregation density, and increased stress. When the ion source acceleration voltage is above 1000V, under the surface collision effect, some film molecules gain higher energy, and atoms are sputtered off the film surface. In normal electron beam deposition and ion beam assisted deposition, the divergence angle of the aspherical grid is large, the ion current density on the umbrella is low, the main working gas is oxygen, the deposition rate of oxide films is high, and the sputtering effect is not obvious. However, on a dedicated filter coating machine, the ion source divergence angle is small and the workpiece disk size is small. Under the condition of changing the ion source parameters, the sputtering effect of heavy ion argon gas is more obvious. When the electron gun is not turned on, the ion source working mode is changed to direct physical etching mode, which can sputter away the previously deposited film layer and realize online correction of the actual film thickness exceeding the design value.

[0033] This invention relates to an online correction method for depositing narrowband filters, typically Fabry-Perot structures with peak half-bandwidth between 0.5 nm and 60 nm. Radio frequency ion beam assisted deposition and direct optical monitoring via transmission methods are used. However, optical signal jitter is caused by factors such as ion source shutdown, rotation signal jitter, electrical interference, and reduced monitoring signal due to multiple deposition layers. This leads to misjudgment of the film's stopping point due to monitoring algorithm malfunction, resulting in deviations in film thickness or structure from theoretical extreme points. This invention corrects these errors through direct online ion beam etching.

[0034] This invention utilizes an RF-assisted ion source equipped with an auxiliary narrow-beam ion beam optical vacuum coating machine. By changing the working gas and parameters of the ion source, the ion source is adjusted to an etching working state, realizing direct physical etching of optical films. It can also perform online etching correction of optical films that exceed the design thickness error or are mistakenly deposited with another material, and apply it to various ultra-narrow band coating processes, thereby improving the yield of optical filters.

[0035] The specific etching strategy is as follows: Due to interference from the electron gun, rotational jitter, and ion source shutdown, optical signal jitter occurs. The etching process stops when the film signal exceeds its extreme point. The following manual interventions are performed: Argon is added to the working gas of the RF ion source of the coating machine, oxygen is gradually reduced, and the process is switched to full argon. The ion source baffle is opened for etching. The light intensity reading of the optical amplifier is manually recorded, combined with... Figure 1Using similar theoretical light intensity values ​​and directions, estimate the actual light intensity value stop value after etching. Control the light intensity value by reversing the signal by 1%-10% to keep the over-etching amount around 1%-10%. The selection of the over-etching amount is mainly determined by the stability of the light intensity value and the amount of light intensity value drift after opening the ion source baffle. Select an amount greater than the corresponding drift, close the ion source baffle, switch the coating machine back to oxygen working mode, manually stop the current layer using the extreme value method, and then continue automatic coating.

[0036] See Figure 1 According to the present invention, a method for correcting narrowband filters by online ion beam etching comprises the following steps:

[0037] (1) Based on the design structure of the filter, each half-wave usually has a reflector-spacer-reflector-coupling layer structure, such as (HL). 4 HmLH(LH) 4 L. m is the number of spacer layer periods, which is an even number. Based on this membrane structure, automatic control is performed using a direct monitoring method.

[0038] (2) When an extreme point is misjudged, the coating is paused and the control software is manually switched to pause mode. The sputtering mode is manually switched to the control software. The reference values ​​are in Table 1 (which can be adjusted according to the actual equipment).

[0039] Table 1. Reference parameters for RF source

[0040]

[0041] (3) For films with deposition errors within one-quarter wavelength thickness, a typical example is... Figure 3 As shown, the 1380nm narrowband filter has 36 layers. The 34th layer is low-refractive-index SiO2. The monitoring signal should move down to its minimum value, causing a layer jump to the 35th layer, Ta2O5, where a 13.7nm layer is deposited. Checking the coating data, the current light intensity value TH = 71.17 for the 35th layer, the light intensity value TL = 78.81 for the layer jump from the 34th layer, and the current optical amplifier signal SH = 73.01mV.

[0042] Based on the linear scaling factor, and selecting a positive value of 0.03, the light intensity value stop point signal SL after etching is:

[0043] SL = (TL / TH) * 1.03 * SH = 83.3mV

[0044] After the actual baffle was opened, the light intensity value was 79.95, slightly higher than 78.81 before the layer skipping. The light intensity values ​​of the 34th and 35th layers before etching and after re-plating are shown in [reference needed]. Figure 4 (Draw according to the light intensity recorded by the coating machine).

[0045] (4) Figure 5 This is the actual monitoring signal for the 1065nm filter coating. When the extreme value of the 6L spacer layer SiO2 (red) in the 10th layer did not meet the normal value, the etching stopped. It reached 5.0mV and the light intensity value was 11.64. The etching stopped when it reached the minimum value of 3.5mV and then reversed to 3.7mV. After re-deposition, the light intensity jumped to 8.52. After the etching was completed, the ion source was gradually switched back to oxygen. The extreme value of the current layer was manually determined to stop at 8.16, and the software continued to perform the next coating.

[0046] (5) When the error thickness exceeds one 1 / 4 wavelength layer, the etching amount needs to be manually calculated on the optical amplifier, and finally the etching stop point is determined according to method (3) or (4).

[0047] As can be seen, the method for correcting narrowband filters by online ion beam etching provided by this invention replaces oxygen with argon in the radio frequency ion source of the coating machine, realizing online ion beam etching to remove deposited film layers exceeding the theoretical thickness or layers of another film material after skipping layers. For film layers with deposition errors within 1 / 4 of the reference wavelength thickness, regardless of whether there is a next layer of film material, the etching stop point is calculated linearly using the signal from the optical amplifier combined with the theoretical monitoring signal, with over-etching of 1-10%, and the number of extreme values ​​of etching is calculated manually. For film thickness errors exceeding the extreme values, the extreme points are used as characteristic points, with over-etching of 1-10%. After over-etching, the film is re-deposited to the extreme point, and the process is stopped manually or manually depending on the type of optical amplifier, thus completing the corresponding film system.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for online ion beam etching to correct narrowband filters, characterized in that, This method utilizes an RF ion source configured with an auxiliary narrow-beam ion beam optical vacuum coating machine. By changing the working gas and parameters of the RF ion source, the RF ion source is adjusted to an etching working state, enabling direct physical etching of the optical film layer of the narrow-band filter. It also performs online etching of another material whose optical film layer exceeds the design thickness error or is mistakenly deposited, allowing the film thickness monitoring signal to revert to the state before the error occurred, thus achieving error correction of the narrow-band filter. The specific etching strategy in this method is as follows: When a misjudgment of an extreme point occurs during the coating process, the coating process is paused, and then the following processing is performed: Argon is added to the working gas of the radio frequency ion source of the narrow beam ion beam optical vacuum coating machine, while oxygen is reduced. The oxygen is gradually and completely replaced with argon. The ion source baffle is opened for etching, and the light intensity value reading of the optical control amplifier is recorded. Based on the light intensity value and direction, the actual light intensity value stop value after etching is estimated. The over-etching amount is controlled based on the stability of the light intensity value and the light intensity value drift after the ion source baffle is opened, and the change in light intensity value caused by the over-etching amount is greater than the corresponding light intensity value drift. The extreme value method is used to determine the stop, and then the ion source baffle is closed. The narrow beam ion beam optical vacuum coating machine is switched back to the oxygen working mode, and then automatic coating continues. During the correction process, for optical films with deposition errors within 1 / 4 of the reference wavelength thickness, regardless of whether there is a next layer of film material, the signal of the optical amplifier is used in conjunction with the film thickness monitoring signal to calculate the etching stop point linearly, with over-etching of 1-10%, and the number of etching extrema is calculated. After etching, automatic coating is used to replenish the coating to the extreme point, and the process is stopped manually or manually depending on the type of optical amplifier to complete the corresponding film system.

2. The method as described in claim 1, characterized in that, The specific method for controlling the over-etching amount is as follows: control the over-etching amount by reverse-stepping the light intensity signal according to the 1%-10% range, so that the over-etching amount is within the range of 1%-10%.

3. The method as described in claim 1, characterized in that, This method involves switching the operating mode of the radio frequency ion source to a direct physical etching mode when the electron gun is not turned on, thereby correcting errors in the narrowband filter.

4. The method as described in claim 1, characterized in that, During the correction process, for film thickness errors that exceed extreme values, the extreme points are used as characteristic points, and 1-10% of the film thickness is over-etched.

5. The method as described in claim 1, characterized in that, The narrowband filter is a Fabry-Perot structure narrowband filter.

6. The method as described in claim 1, characterized in that, This method is applied in the field of optical communication technology.

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