Method for correcting narrow-band optical filter through online ion beam etching

Abstract

The invention relates to a method for correcting a narrow-band optical filter through online ion beam etching, and belongs to the technical field of optical communication. According to the invention, through on-line ion beam etching, correction of a film layer over-thickness error is realized, a film thickness monitoring signal is returned before the error occurs, correction of the error is realized, the rejection rate of a product is reduced, the rate of finished products of monitoring is improved, and the plating cost of an optical filter is reduced. And light quantity value reading is adopted, so that the method is more reliable than a time power method, and the over-etching amount can be ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of optical communication, and in particular relates to a method for correcting a narrow-band filter by online ion beam etching. Background Art

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

[0003] The narrower the bandwidth, the smaller the coating error tolerance of the Fabry-Perot filter. When the bandwidth is less than 40nm, the widely used quartz crystal monitoring method has a low coating yield, poor coating filter waveform, and low peak transmittance. The standard method is to use the central straight light 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 methods to improve the monitoring accuracy of optical thin films [4]-[8]. On the one hand, based on hardware [1], crystal control methods, eccentric straight light path transmission methods [2], and online ellipsometry methods [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 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, and a 0.01% change in light value can lead to an actual error of 5nm. When the ion source is turned off or the light value fluctuates abnormally, the algorithm defects in the automatic optical monitoring system will lead to misjudgment of extreme values ​​or failure to judge extreme values, and the current layer thickness exceeds the design, or automatically jumps to the next layer. The thickness error of the existing film layer can be solved by re-plating before the design thickness, but for special film systems such as filters, if the current layer thickness exceeds the design value, it is either scrapped or modified to increase the original film thickness to 3 times the original, which actually compresses the bandwidth of the filter, deviates from the original design, and reduces the effective area of ​​the filter. If the adjustment layer is plated with another material, it can only 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 thickness of structural color pigment optical film and coating machine [P]. Zhejiang Province: CN112981357A, 2021-06-18.

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

[0008] [4] Ma Zhiliang. Brief introduction to optical film automation control system[J]. Instrumentation and Analysis Monitoring, 2014(04):25-28.

[0009] [5] Cai Qingyuan, An optical monitoring and tracking method for rapid inversion of thin film growth thickness. Shanghai, 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 filter[J]. Laser Technology, 2007(04):412-415.

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

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

[0013] [9] Zhu Meiping, Yi Kui, Guo Shihai, Fan Zhengxiu, Shao Jianda. Effect of film thickness monitoring error and monitoring film non-uniformity 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 optical filter thin film coating process [J]. Journal of Infrared and Millimeter Waves, 2003(01):56-58. Summary of the invention

[0017] 1. Technical issues to be resolved

[0018] The technical problem to be solved by the present invention is: to design an online correction method for coating narrow-band filters, to perform etching correction on the over-positive and layer-jumping errors of the filters, to restore the filter monitoring signal to a normal state, and to improve the yield of the filters.

[0019] (II) Technical solution

[0020] In order to solve the above technical problems, the present invention provides a method for online ion beam etching correction of a narrow-band filter. The method utilizes a radio frequency ion source configured with an auxiliary narrow beam ion beam optical vacuum coating machine, and adjusts the radio frequency ion source to an etching working state by changing the working gas and parameters of the radio frequency ion source, thereby realizing direct physical etching of the optical film layer of the narrow-band filter, and online etching of another material whose optical film layer exceeds the designed film thickness error or is mistakenly plated, so that the film thickness monitoring signal returns to the state before the error occurs, thereby realizing error correction of the narrow-band filter.

[0021] The invention also provides a device for implementing the method.

[0022] (III) Beneficial effects

[0023] The present invention realizes online ion beam direct etching by adjusting parameters of the narrow beam auxiliary source and replacing the gas, thereby converting the ion beam auxiliary source into an etching source. Furthermore, according to the signal amplitude of the optically controlled amplifier, combined with the actual optical monitoring signal light value direction and amplitude, the over-positive and layer-jumping errors of the filter are etched and corrected, and the filter monitoring signal is restored to a normal state. The present invention realizes the correction of the error of excessive film thickness through online ion beam etching, and returns the film thickness monitoring signal to the state before the error occurs, thereby realizing the correction of the error, reducing the scrap rate of the product, improving the monitoring yield, and reducing the cost of filter plating. The use of light value readings is more reliable than the time power method and can guarantee the amount of over-etching. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 is the transmission curve distribution of the filter simulated by a random error of 0.002;

[0026] Figure 3 It is the 1380nm filter layer jump monitoring curve;

[0027] Figure 4 It is the light value before and after etching;

[0028] Figure 5 This is the etching diagram of the spacer layer exceeding the extreme value. DETAILED DESCRIPTION

[0029] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0030] The light value monitoring error of the ultra-narrowband filter is the main factor affecting the filter transmittance and waveform. During a long deposition process, the ion source flameout and the rotation signal jitter may cause misjudgment of the film layer extreme value and erroneous layer jump. The present invention adjusts the parameters of the narrow beam auxiliary source and replaces the gas to convert the ion beam auxiliary source into an etching source, thereby realizing online ion beam direct etching. Furthermore, according to the signal amplitude of the optically controlled amplifier, combined with the actual optical monitoring signal light value direction and amplitude, the over-positive and layer jump errors of the filter are corrected by etching, and the filter monitoring signal is restored to a normal state, thereby improving the filter yield.

[0031] The narrowband filter of Fabry-Perot structure is the most effective film structure for ultra-narrowband filter design. Taking the reference wavelength 1065nm three half-wave filter as an example, the structure is recorded 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, A represents air, and the half-height bandwidth is designed to be 5nm. Such a design is very sensitive to monitoring errors. A random thickness error of 0.002 can cause the filter waveform to collapse. 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 is calculated using Essential Macleod software. Figure 1 , using 0.002 random thickness error for analysis, the transmission spectrum distribution is shown in Figure 2 The characteristics of this film system are: the thickness of each layer is an integer of 1 / 4 wavelength, and the stopping point is the maximum or minimum value of the light value.

[0032] At present, radio frequency (RF) ion sources are widely used in the deposition process of optical thin films. After ions are accelerated, they are neutralized by the neutralizer, and the kinetic gas is incident on the surface of the film layer, causing cascade collisions. When the ion source acceleration voltage is lower than 800V, the effect of the bombardment is mainly to make the film layer more compact, which is manifested as an increase in the refractive index of the film layer, an increase in the aggregation density, and an increase in stress; when the ion source acceleration voltage is higher than 1000V, under the collision effect on the surface of the film layer, some of the film layer molecules obtain higher energy, and atoms are sputtered out of the film layer surface. In normal electron beam film formation and ion beam assisted deposition, the divergence angle of the aspheric grid is large, the ion flow density on the umbrella frame is small, the main working gas is oxygen, the deposition rate of the oxide film layer is high, and the sputtering effect is not obvious. However, in the filter-specific coating machine, the ion source divergence angle is small and the workpiece disk size is small. When the ion source parameters are changed, the sputtering effect of heavy ion argon 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 off the previously deposited film layer and realize online correction of the actual film thickness exceeding the design value.

[0033] The present invention relates to an online correction method for coating a narrow-band filter. The filter is usually the above-mentioned Fabry-Perot structure, with a peak half-bandwidth between 0.5nm and 60nm. Radio frequency ion beam assisted coating and transmission method are used for direct optical monitoring. Due to the ion source flameout, rotation signal jitter, electrical interference, and reduction of the deposition layer multi-mode monitoring signal, optical signal jitter is caused, and the monitoring algorithm is out of control, resulting in misjudgment of the film stop point, and the film thickness or structure deviates from the theoretical extreme point. The present invention performs error correction through direct online ion beam etching.

[0034] The present invention utilizes a radio frequency auxiliary ion source equipped with an auxiliary narrow beam ion beam optical vacuum coating machine, and adjusts the ion source to an etching working state by changing the working gas and parameters of the ion source, thereby realizing direct physical etching of the optical film layer, performing online etching correction on another material whose optical film layer exceeds the designed thickness error or is mistakenly plated, and applying it to various ultra-narrow band plating processes, thereby improving the yield rate of the filter.

[0035] The specific etching strategy is: due to the interference of the electron gun, the jitter of the machine, the flameout of the ion source, etc., the optical signal jitter, the film layer signal exceeds the extreme point to stop, the coating process is suspended, and the following processing is performed manually: argon is added to the working gas of the RF ion source of the coating machine, oxygen is reduced and gradually switched to all argon, the ion source baffle is opened for etching, and the light value reading of the optical control amplifier is manually recorded, combined with Figure 1Similar theoretical light intensity values ​​and directions are used to estimate the actual stop value of the light intensity after etching, and the over-etching amount is controlled according to the reverse value of the 1%-10% light intensity signal, so that the over-etching amount is around 1%-10%. The selection of the over-etching amount is mainly determined by the stability of the light intensity value and the light intensity drift after opening the ion source baffle. A value greater than the corresponding drift is selected, the ion source baffle is closed, the coating machine is switched back to the oxygen working mode, the current layer is manually stopped using the extreme value method, and then automatic coating continues.

[0036] See also Figure 1 According to the present invention, a method for online ion beam etching to correct a narrow-band filter is divided into the following steps:

[0037] (1) According to 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 interval layers, which is an even number. According to this film structure, direct monitoring method is used for automatic control.

[0038] (2) When an extreme point misjudgment occurs, the coating is suspended, and the control software is manually switched to the pause mode and manually switched to the sputtering mode. The reference value is shown in Table 1 (can be adjusted according to the actual equipment).

[0039] Table 1 Reference parameters for RF source

[0040]

[0041] (3) For films with a deposition error within 1 / 4 wavelength thickness, a typical example is Figure 3 As shown, the 1380nm narrowband filter has 36 layers in total. The 34th layer is low-refractive-index SiO2. The monitoring signal should go down to the minimum value, jump to the 35th layer Ta2O5, and be plated with 13.7nm. Checking the coating record data, the current light value TH of the 35th layer is 71.17, the light value TL of the 34th layer when jumping layers is 78.81, and the current light-controlled amplifier signal SH is 73.01mV.

[0042] According to the linear proportional value calculation, the positive value 0.03 is selected, and the light value stop point signal SL after etching is:

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

[0044] After the baffle is opened, the light intensity value is 79.95, slightly higher than 78.81 before the layer jump. The light intensity values ​​of the 34th and 35th layers before etching and after re-plating are shown in Figure 2. Figure 4 (Draw according to the light intensity recorded by the coating machine).

[0045] (4) Figure 5 It is the actual monitoring signal of 1065nm filter coating. It stops when the extreme value of SiO2 (red) in the 6L spacer layer of the 10th layer is not normal. It goes over to 5.0mV and the light value is 11.64. It is etched to the minimum value of 3.5mV and stops etching when it reverses to 3.7mV. After re-plating, the light value jumps to 8.52. After etching is completed, the ion source is gradually switched back to oxygen, and the current layer's extreme value of 8.16 is manually completed to stop, and the software continues with the following coating.

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

[0047] It can be seen that the method of online ion beam etching to correct narrow-band filters provided by the present invention replaces oxygen with argon in the radio frequency ion source of the coating machine, thereby realizing online ion beam etching, and etching away the film layer deposited exceeding the theoretical thickness or another film layer of film material after layer skipping. For film layers with a deposition error within 1 1 / 4 reference wavelength thickness, regardless of whether there is a next layer of film material, the signal of the optically controlled amplifier is used in combination with the theoretical monitoring signal to perform linear proportional calculation of the etching stop point, over-etching 1-10%, and manually calculating the number of extreme values ​​of etching. For film thickness errors exceeding the extreme value, the extreme point is used as the characteristic point, and over-etching is 1-10%. After over-etching, the corresponding film system is completed by re-plating to the extreme point and stopping manually or manually judging according to the type of optically controlled amplifier.

[0048] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for online ion beam etching correction of narrow band filters, characterized in that: The method utilizes a radio frequency ion source configured with an auxiliary narrow beam ion beam optical vacuum coating machine. By changing the working gas and parameters of the radio frequency ion source, the radio frequency ion source is adjusted to an etching working state, thereby realizing direct physical etching of the optical film layer of the narrow band filter, and online etching of another material whose optical film layer exceeds the designed film layer thickness error or is mistakenly plated, so that the film thickness monitoring signal returns to the state before the error occurs, thereby realizing error correction of the narrow band filter.

2. The method according to claim 1, characterized in that In the method, the specific etching strategy is: during the coating process, when an extreme point misjudgment occurs, 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, and oxygen is reduced at the same time, and the oxygen is gradually and completely replaced with argon, the ion source baffle is opened for etching, and the light value reading of the optically controlled amplifier is recorded, and the stop value of the light value after actual etching is estimated based on the light value and direction, and the over-etching amount is controlled based on the stability of the light value and the light value drift after opening the ion source baffle, and the over-etching amount is made greater than the corresponding drift amount, and the extreme value method is used to judge the stop, and then the ion source baffle is closed, and the narrow beam ion beam optical vacuum coating machine is switched back to the oxygen working mode, and then the automatic coating is continued.

3. The method according to claim 2, characterized in that The method for controlling the over-etching amount is specifically as follows: controlling the over-etching amount in the range of 1%-10% according to the reverse value of the light intensity value signal of 1%-10%.

4. The method according to claim 2, characterized in that The method is to convert the working mode of the radio frequency ion source into a direct physical etching mode when the electron gun is not turned on, so as to realize the error correction of the narrow band filter.

5. The method according to claim 2, characterized in that During the correction process, for optical film layers with a deposition error within 1 / 4 of the reference wavelength thickness, regardless of whether there is a next layer of film material, the signal of the optically controlled amplifier is used, combined with the film thickness monitoring signal, to perform linear proportional calculation of the etching stop point, over-etching by 1-10%, and calculating the extreme number of etching.

6. The method according to claim 2, characterized in that During the correction process, for the film thickness error exceeding the extreme value, the extreme value point is used as the characteristic point and over-etched by 1-10%.

7. The method according to claim 2, characterized in that After over-etching, the film is automatically re-plated to the extreme point, and the corresponding film system is completed by manual or manual stop according to the type of optically controlled amplifier.

8. The method according to claim 1, characterized in that The narrow-band filter is a narrow-band filter with a Fabry-Perot structure.

9. The method according to claim 1, characterized in that The method is applied in the field of optical communication technology.

10. An apparatus for implementing the method according to any one of claims 1 to 9.

Images