Preparation method of filter chip for SF6 gas identification

Abstract

The application relates to the technical field of infrared filter chip preparation, and discloses a preparation method of a filter chip for SF6 gas identification, which comprises the following steps: based on the detection wave band and the reference wave band of SF6 gas, corresponding film system theoretical stacking sequences are respectively designed, and standard spectral trajectories reflecting the expected spectral states of each film layer after deposition are simulated and generated accordingly; each film layer is sequentially deposited in an iterative mode, and after the deposition of each layer is completed, the measured spectral curve of the current film system is acquired, the characteristic parameters thereof are extracted, and the characteristic parameters are compared with the theoretical values of the corresponding positions in the standard spectral trajectories; the process parameters of the subsequent to-be-deposited film layers are dynamically adjusted according to the calculated deviation values and the change trends, so that a closed-loop control is formed. The application effectively overcomes the problem that the spectral performance deviates due to error accumulation in the traditional preparation process, can significantly improve the spectral accuracy and product consistency of the filter chip, and further enhances the accuracy and reliability of SF6 gas detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of infrared filter chip preparation, in particular to a preparation method of a filter chip for SF6 gas identification. BACKGROUND

[0002] In the field of power equipment safety monitoring, sulfur hexafluoride (SF6) gas is widely used due to its excellent insulation performance, but its leakage can pose a serious threat to equipment safety and the environment. Gas leak detection technology based on infrared imaging, especially the principle of using SF6 gas with strong absorption characteristics at a specific infrared wavelength (such as 10.55 μm), has become a key means to realize remote and visual detection under voltage. One of the core components of this technology is the infrared filter chip, which is like a precise spectral sieve. The filter chip is a dual-channel infrared filter chip that only allows light at the characteristic absorption wavelength of SF6 gas and a reference wavelength (such as 8.05 μm) for comparison to pass through, thereby making the invisible gas visible in the camera. Currently, such high-performance filter chips are mainly achieved by depositing dozens of thin films of different thicknesses and materials (i.e., film system structure) on a silicon substrate, and the preparation process directly determines the performance and reliability of the final product.

[0003] However, the preparation of this filter chip faces a serious challenge, which is how to ensure that the spectral performance of the final product is highly consistent with the initial theoretical design. During the complex multi-layer film deposition process, any slight process fluctuation, such as nanometer-level deviation in film thickness and slight changes in material refractive index, can cause cumulative errors between film layers.

[0004] The existing technology usually uses the extreme method of "depositing one layer and measuring one layer" to control the thickness of a single film. Although this method can control the thickness of a single film, it lacks overall monitoring of the entire spectral evolution process. This local and post-control method cannot compensate for the chain effects of previous film layer errors on subsequent film systems, resulting in problems such as center wavelength drift and transmittance reduction in the prepared filter chip. This reduces the contrast and signal-to-noise ratio of gas imaging, severely affecting the accuracy and sensitivity of SF6 leak detection. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to overcome the defect of spectral performance degradation caused by interlayer error accumulation during the preparation of an infrared filter chip in the prior art. The present application provides a preparation method of a filter chip for SF6 gas identification, which can dynamically correct the deposition process by introducing standard spectral trajectory closed-loop control, thereby obtaining a measured spectral curve that is highly consistent with the theoretical design, and improving the accuracy and reliability of gas detection.

[0006] To solve the above technical problems, the application provides a preparation method of a filter chip for SF6 gas identification, the filter chip comprising a first membrane system structure and a second membrane system structure deposited on a silicon substrate, the first membrane system structure corresponding to a detection waveband of SF6 gas, and the second membrane system structure corresponding to a reference waveband, the preparation method comprising the following steps:

[0007] Based on the detection waveband and the reference waveband, a theoretical stacking sequence of the first membrane system structure and the second membrane system structure is designed respectively;

[0008] Based on the theoretical stacking sequence, a real-time theoretical spectrum curve of the filter chip after the deposition of each membrane layer is simulated and calculated during the film plating process, and a feature parameter of each real-time theoretical spectrum curve is extracted, and all the feature parameters are arranged in the plating order to form a standard spectrum track;

[0009] According to the theoretical stacking sequence, the first membrane layer of the first membrane system structure or the second membrane system structure is deposited on the silicon substrate, and each subsequent membrane layer is deposited in an iterative manner, wherein after the deposition of each membrane layer is completed, the following operations are performed: a transmittance measurement of the currently deposited membrane system structure is performed by using an online spectrum measurement system to obtain a current measured spectrum curve, and a current measured feature parameter corresponding to the standard spectrum track is extracted; the current measured feature parameter is compared with a theoretical feature parameter at a position corresponding to the membrane layer in the standard spectrum track, a deviation value is calculated, and the deposition control parameter of the subsequent to-be-deposited membrane layer is dynamically adjusted according to the deviation value and its change trend;

[0010] The above iterative deposition process is repeated until the first membrane system structure and the second membrane system structure are completely deposited, so that the spectrum evolution of the entire membrane system structure in the deposition process follows the standard spectrum track generated by the simulation calculation.

[0011] In an embodiment of the application, based on the detection waveband and the reference waveband, a theoretical stacking sequence of the first membrane system structure and the second membrane system structure is designed, comprising the following steps:

[0012] High-refractive-index materials and low-refractive-index materials are selected, and optical constants of the high-refractive-index materials and the low-refractive-index materials in the detection waveband and the reference waveband are determined;

[0013] A basic membrane system unit is constructed, comprising a resonant layer located at the center, and a plurality of reflection layers are symmetrically arranged on both sides of the resonant layer, and the reflection layers are formed by alternately stacking high-refractive-index materials and low-refractive-index materials with a quarter of the optical thickness;

[0014] The initial stacking sequence design of the first film system structure is performed by cascading the basic film system unit multiple times according to the target center wavelength of the detection waveband; and the initial stacking sequence design of the second film system structure is performed by cascading the basic film system unit multiple times according to the target center wavelength of the reference waveband;

[0015] The initial stacking sequences of the first film system structure and the second film system structure are respectively set as optimization starting points, and an optimization algorithm is run to iteratively adjust the thickness of each film layer in the two initial stacking sequences, with the passband rectangularity and the peak transmittance as optimization targets;

[0016] When the optimization results simultaneously satisfy the matching of the passband center of the first film system structure to the detection waveband, the matching of the passband center of the second film system structure to the reference waveband, and the passband rectangularity and the peak transmittance of the two film system structures reaching preset indicators, the final film layer thickness sequence obtained at this time is determined as the theoretical stacking sequence of the first film system structure and the second film system structure, respectively.

[0017] In an embodiment of the present application, the characteristic parameters include the center wavelength and the full width at half maximum, and the characteristic parameters of each real-time theoretical spectrum curve are extracted, specifically including:

[0018] The peak point with the highest transmittance in the real-time theoretical spectrum curve is identified, and the wavelength corresponding thereto is recorded as the center wavelength;

[0019] On the real-time theoretical spectrum curve, two wavelength points with a transmittance of half the peak transmittance are found, and the width between the two wavelength points is calculated as the full width at half maximum.

[0020] In an embodiment of the present application, after the standard spectrum trajectory is constructed, a dynamic tolerance range is further set for the theoretical characteristic parameters of each film layer position in the trajectory; the dynamic tolerance range is determined according to the sensitivity of the current film layer in the overall film system structure, and the higher the sensitivity, the smaller the tolerance range;

[0021] When the current measured characteristic parameters are compared with the theoretical characteristic parameters of the corresponding film layer position in the standard spectrum trajectory, if the deviation value exceeds the dynamic tolerance range, the operation of dynamically adjusting the deposition control parameters of the subsequent to-be-deposited film layer is triggered.

[0022] In an embodiment of the present application, the deposition control parameters of the subsequent to-be-deposited film layer are dynamically adjusted according to the deviation value and its change trend, specifically including:

[0023] When the deviation value indicates that the center wavelength of the current measured spectrum has a systematic drift relative to the theoretical value, the theoretical design thickness of all subsequent to-be-deposited film layers is increased or decreased in proportion according to the direction and amplitude of the drift, so as to macroscopically compensate for the systematic drift.

[0024] In one embodiment of the present application, the variation law of the deviation value after deposition of several continuous film layers is analyzed, if it is determined that the deviation trend is caused by a single film layer deposition failure and the influence is local, then the deposition control parameter of the subsequent one or several specific film layers with the highest optical coupling degree with the failure film layer is fine-tuned for localized correction.

[0025] In one embodiment of the present application, the deposition control parameter is the deposition rate, and the deposition control parameter of the subsequent film layer to be deposited is dynamically adjusted, specifically including:

[0026] If the deviation value indicates that the film layer density is insufficient, the deposition rate of the subsequent film layer to be deposited is reduced;

[0027] If the deviation value indicates that the film layer stress is too high, the deposition rate of the subsequent film layer to be deposited is increased.

[0028] In one embodiment of the present application, after the deposition of each film layer is completed, the fluctuation of the current measured spectrum curve is continuously monitored, and only when the fluctuation amplitude of the current measured spectrum curve tends to be stable, the feature parameter extraction and comparison operation is performed.

[0029] In one embodiment of the present application, before the deposition of the first film system structure and the second film system structure, the spectrum reference calibration is performed, and when the first film system structure and the second film system structure are deposited respectively, the same set of calibrated online spectrum measurement system is used to measure the transmittance of the current deposited film system structure.

[0030] In one embodiment of the present application, after all the film layers are deposited, the prepared filter chip is finally scanned by a high-precision Fourier transform infrared spectrometer in a constant temperature and humidity environment.

[0031] The final measured spectrum is compared with the theoretical design spectrum in the full wave band, and according to the coincidence degree of the comparison result, the filter chip is classified by performance level.

[0032] The above technical solutions of the present application have the following advantages compared with the prior art:

[0033] The preparation method of the filter chip for SF6 gas identification in the present application no longer considers the deposition of each layer of film in isolation, but considers the entire film deposition process as a complete growth process, and presets a standard growth track for it, that is, a standard spectrum track composed of the real-time theoretical spectrum curve after deposition of each layer simulated based on the theoretical film system sequence.

[0034] At the beginning of preparation, firstly, a first film layer is deposited on a silicon substrate, and then an iteration cycle is entered, after the deposition of each film layer is completed, the next layer is not started immediately, but the integrated online spectrum measurement system is used to perform a full body scan on the current semi-finished product to obtain the current measured spectrum curve; then, the measured curve is compared with the theoretical curve at the corresponding position on the standard growth track to calculate the deviation value of the characteristic parameter, which is no longer an isolated number, but reveals the degree and trend of the current film system structure deviating from the expected direction; based on this diagnostic result, the deposition control parameters of the subsequent to-be-deposited film layer are actively and prospectively adjusted, and the deviation generated in the front is compensated and corrected through subsequent operation, forming a self-correcting closed loop; through repeated iteration process until all film layers are deposited, the spectrum evolution of the film system structure is effectively constrained on the preset theoretical track.

[0035] Through the synergistic effect of a series of technical features, the present application can fundamentally overcome the problem of spectral performance degradation caused by error accumulation in the prior art, and its most significant beneficial effect is to greatly improve the preparation precision and product consistency of the filter chip, and to ensure that the final measured spectrum curve is highly consistent with the theoretical design. The filter chip prepared based on this method can more accurately separate the characteristic information of SF6 gas, thereby significantly improving the signal-to-noise ratio and recognition accuracy of the subsequent binocular imaging system when detecting SF6 gas; at the same time, this forward-looking adjustment strategy also reduces the dependence on extremely harsh initial conditions of the film deposition process, improves the robustness and yield of the process, and lays a solid foundation for core components for realizing high-performance and low-cost SF6 gas leak detection equipment. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to make the content of the present application easier to be clearly understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings, in which:

[0037] Figure 1 is a step flow chart of the preparation method of the filter chip for SF6 gas recognition of the present application;

[0038] Figure 2 is a step flow chart of the theoretical stacking sequence of the first film system structure and the second film system structure designed by the present application. DETAILED DESCRIPTION

[0039] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting to the present application.

[0040] In the prior art, the preparation process of the infrared filter chip mainly adopts the extreme value method of layer-by-layer plating film combined with single-layer thickness control. This method terminates the deposition by monitoring the single-layer film thickness to reach the preset threshold. Although it can ensure the thickness accuracy of a single film layer, it cannot globally track the optical performance evolution of the overall film system structure. Due to the complex coupling effect of the optical characteristics of the multilayer film, a small error of the previous film layer will have a superimposed influence on the spectral response of the subsequent film layer through optical interference, eventually leading to defects such as passband shift and transmittance drop of the finished product. Such defects are particularly evident in a dual-channel filter chip. The spectral coupling effect between the two channels will further amplify the process error, causing the signal-to-noise ratio of the gas detection system to deteriorate.

[0041] Through experimental analysis of the optical superposition mechanism of the multilayer film, it is found that controlling only the single-layer thickness is not enough to offset the error accumulation effect. In order to solve this problem, the following two ideas are proposed:

[0042] Establish a spectral evolution trajectory model to dynamically compare the real-time optical response in the plating process with the theoretical prediction;

[0043] Further imagine that through a closed-loop feedback mechanism, the process parameters are corrected in real time during the deposition process, so that the optical characteristics of the actual plating process always develop along the preset trajectory. This idea breaks through the passive control mode of the traditional process and instead adopts an active optical performance tracking strategy.

[0044] Therefore, based on the above ideas, referring to Figure 1 The present application proposes an iterative deposition method based on standard spectral trajectory tracking. This method first establishes a standard spectral trajectory through theoretical simulation, measures the spectral characteristics in real time after each layer is deposited and compares them with the trajectory nodes, dynamically adjusts the subsequent process parameters according to the deviation, and through closed-loop control makes the spectral evolution of the actual plating process always approach the theoretical trajectory, thereby eliminating the error accumulation effect.

[0045] Among them, the theoretical stacking sequence refers to the sequence of film layer materials and thickness determined by optical simulation. Specifically, it can be designed by using the transfer matrix method combined with an optimization algorithm, and is used to construct a film system structure with a target spectral response. The standard spectral trajectory refers to the set of theoretical spectral characteristic parameters at each stage of the plating process. Specifically, it can be generated by time-domain spectral simulation technology and serves as the benchmark for the optical performance evolution of the plating process. The dynamic adjustment of the deposition control parameters refers to the correction of the subsequent process conditions according to the real-time spectral deviation. Specifically, it can be realized by using an adaptive control algorithm to compensate for the process deviation that has occurred and suppress error propagation.

[0046] Specifically, the preparation process is first based on the detection waveband and the reference waveband, respectively designs the theoretical stacking sequence of the first film system structure and the second film system structure, and then establishes a theoretical model of the double-channel film system through optical simulation. Based on the theoretical stacking sequence, the real-time theoretical spectral curve of the filter chip after the deposition of each film layer is simulated and calculated during the coating process, and the characteristic parameters of each real-time theoretical spectral curve are extracted. All the characteristic parameters are arranged in the order of coating to form a standard spectral trajectory. After starting the deposition on the silicon substrate, the transmission spectrum is measured after the deposition of each film layer, and the characteristic parameters of the current spectrum are extracted. The measured characteristics are compared with the theoretical values of the corresponding nodes in the standard trajectory. When the characteristic parameters deviate from the predetermined range, the deposition rate or thickness design of the subsequent film layer is automatically adjusted. For example, when the center wavelength continuously drifts to the long wave direction, the theoretical thickness value of the subsequent film layer can be proportionally reduced to pull back the spectral response to the predetermined trajectory by changing the optical interference conditions. This closed-loop control runs through the entire coating process to ensure that the optical performance of the overall film system after the deposition of dozens of thin films can still accurately match the design requirements.

[0047] Compared with the prior art, the traditional process only focuses on the static control of the thickness of a single layer, while the present scheme establishes a dynamic tracking mechanism for the optical performance throughout the process. The prior art is like building a wall block by block according to the drawing without detecting the overall inclination of the wall body, while the present scheme dynamically adjusts the construction scheme by real-time monitoring of the center of gravity change of the building structure. This change from local control to global regulation effectively suppresses the chain transmission of film layer errors and solves the spectral coupling problem in the preparation of the double-channel filter chip.

[0048] Through the above technical scheme, the present application effectively controls the optical performance drift in the coating process, reduces the deviation of the actual passband center wavelength of the double-channel filter chip from the design value by an order of magnitude, and at the same time guarantees the spectral isolation degree between the two channels, controls the crosstalk between the channels within a negligible range. The preparation method significantly improves the transmittance uniformity and passband edge steepness of the filter chip, and provides a core optical element with stable spectral characteristics for the SF6 gas detection system.

[0049] Reference Figure 2As shown, the present application further proposes a method for designing theoretical stacking sequences of the first and second film system structures based on the detection and reference wavebands, including the following steps: selecting high and low refractive index materials and determining their optical constants in the detection and reference wavebands; constructing a basic film system unit, including a resonant layer in the center, and a plurality of reflection layers symmetrically arranged on both sides of the resonant layer, the reflection layers being formed by alternately stacking the high and low refractive index materials in quarter optical thickness; designing the initial stacking sequence of the first film system structure by cascading the basic film system unit multiple times based on the target central wavelength of the detection waveband; designing the initial stacking sequence of the second film system structure by cascading the basic film system unit multiple times based on the target central wavelength of the reference waveband; setting the two initial stacking sequences as the optimization starting points, respectively, and running the optimization algorithm with the passband rectangularity and peak transmittance as the optimization targets to iteratively adjust the thicknesses of the film layers in the two initial stacking sequences; and determining the final film layer thickness sequence as the theoretical stacking sequence when the optimization results simultaneously satisfy the matching of the passband center of the first film system structure to the detection waveband, the matching of the passband center of the second film system structure to the reference waveband, and the passband rectangularity and peak transmittance reaching the preset indicators.

[0050] The high and low refractive index materials refer to two kinds of coating materials with significant refractive index difference, which can be realized by using the combination of zinc sulfide and yttrium fluoride, and the differentiated optical properties thereof can form an effective optical interference structure; the basic film system unit refers to a periodic film layer combination with a symmetric reflection layer structure, which can be realized by alternately depositing high and low refractive index material layers with quarter optical thickness on both sides of the resonant layer, and this structure can enhance the transmission selectivity of specific wavelengths. The multiple cascades refer to repeatedly stacking the basic film system unit according to a specific rule, which can be calculated by using a mathematical recursive model to determine the number of cascades, thereby expanding the passband width and improving the spectral response sharpness. The optimization algorithm refers to a calculation method for iteratively adjusting the film layer thickness based on the target function, which can be realized by using a genetic algorithm or a particle swarm optimization algorithm to achieve global optimization of the passband performance indicators through multi-parameter collaborative optimization.

[0051] Specifically, after the optical constants of the high and low refractive index materials are determined, a basic film system unit containing a resonant layer and symmetric reflection layers is first constructed. For example, when the central wavelength of the detection waveband is 10.55 μm, the resonant layer thickness corresponding to the quarter wavelength can be calculated, and the reflection layers are formed by alternately stacking the high and low refractive index materials, with the thickness of each layer being set to the quarter optical thickness of the corresponding material at the target wavelength. The basic film system unit is cascaded multiple times to form an initial stacking sequence, and then the optimization algorithm is run with the passband rectangularity and peak transmittance as the optimization targets to fine-tune the thicknesses of the film layers in the initial stacking sequence. When the optimized film system structure simultaneously satisfies the matching of the passband center wavelength, the steepness of the passband edges, and the transmittance requirements, the theoretical stacking sequence is obtained.

[0052] Compared with the prior art, the conventional method only calculates the film layer thickness by an empirical formula without considering multi-target collaborative optimization, resulting in insufficient steepness of the passband edge and large transmittance fluctuation, and the scheme realizes synchronous improvement of the passband rectangularity and the transmittance while ensuring the accuracy of the passband center wavelength by introducing a basic film system unit and an optimization algorithm, and solves the problem that the spectral performance indicators are difficult to balance in the prior art.

[0053] Through the above technical solution, the film layer stacking structure of the dual-channel filter chip can be accurately controlled, the passband centers of the two film system structures are strictly matched with the SF6 gas absorption peak and the reference waveband respectively, high rectangularity passband shape and stable peak transmittance are obtained, and a reliable theoretical design basis is provided for subsequent coating process.

[0054] Specifically, the feature parameters described in the embodiment include a center wavelength and a full width at half maximum, and the feature parameters of each real-time theoretical spectrum curve are extracted, specifically including: identifying a peak point with the highest transmittance in the real-time theoretical spectrum curve, recording the wavelength corresponding to the peak point as the center wavelength; finding two wavelength points with a transmittance of half the peak transmittance on the real-time theoretical spectrum curve, and calculating the width between the two wavelength points as the full width at half maximum.

[0055] The center wavelength is the wavelength corresponding to the peak point with the highest transmittance in the real-time theoretical spectrum curve, and can be realized by automatically identifying the highest point of the transmittance curve and recording the wavelength coordinate through a spectrum analysis algorithm. This parameter is used to represent the center position of the passband under the current deposition state of the filter chip, and ensures that it is matched with the target waveband. The full width at half maximum is the width between the two wavelength points corresponding to the transmittance of half the peak value, and can be realized by searching for the position with a transmittance of 50% of the peak value on the real-time theoretical spectrum curve and calculating the wavelength difference. This parameter is used to quantify the passband width and reflect the control accuracy of the spectral shape by the film layer stacking.

[0056] Specifically, after the deposition of each film layer is completed in the coating process, the real-time theoretical spectrum curve is simulated, and the identification of the peak point is completed by traversing the transmittance data points, for example, the wavelength value corresponding to the highest transmittance is locked by using a local maximum value detection algorithm. For the calculation of the full width at half maximum, first determine the 50% threshold of the peak transmittance, then search for the wavelength points on both sides of the real-time theoretical spectrum curve where the transmittance first falls below the threshold, and the difference between the two points is the full width at half maximum. The two parameters are continuously recorded and arranged in the order of the coating process to form a standard spectrum trajectory, which provides a benchmark for real-time deviation analysis in the subsequent deposition process.

[0057] Compared with the prior art, the traditional method only monitors whether the single-layer film thickness reaches the preset value, and the scheme can directly reflect the dynamic evolution of the passband characteristics in the multi-layer film stacking process by extracting the two key spectral characteristics of the center wavelength and the full width at half maximum. The prior art cannot capture the cumulative error caused by the optical coupling effect between the film layers, and the scheme can discover systematic deviations in the early stage and trigger adjustments by tracking the global changes of the standard spectral trajectory, thereby avoiding the transmission of errors to subsequent film layers.

[0058] Through the above technical scheme, the present application realizes real-time tracking and quantitative evaluation of the spectral characteristics in the filter chip coating process, wherein: continuous monitoring of the center wavelength can timely discover the passband shift caused by the thickness or refractive index deviation of the film layer, and dynamic analysis of the full width at half maximum can effectively identify the spectral broadening caused by the asymmetric stacking of the film layer or the interface scattering. This dual-parameter monitoring mechanism based on spectral characteristics provides a reliable basis for dynamically adjusting the deposition process, thereby improving the spectral performance consistency of the filter chip.

[0059] In actual preparation processes, in order to avoid excessive sensitivity of adjustment, a dynamic tolerance mechanism is introduced to realize hierarchical control of the sensitivity of the film layer, thereby reducing the process cost of non-critical film layers while ensuring the precision of critical film layers. Specifically, the following methods are used: a dynamic tolerance range is set for the theoretical characteristic parameter of each film layer position in the trajectory; the dynamic tolerance range is determined according to the sensitivity of the current film layer in the overall film system structure, and the higher the sensitivity, the smaller the tolerance range; when comparing the current measured characteristic parameter with the theoretical characteristic parameter of the corresponding film layer position in the standard spectral trajectory, if the deviation value exceeds the dynamic tolerance range, the operation of dynamically adjusting the deposition control parameters of the subsequent to-be-deposited film layer is triggered.

[0060] The dynamic tolerance range refers to the maximum interval allowed for the measured characteristic parameter to deviate from the theoretical characteristic parameter, and the width of the interval is dynamically set according to the optical contribution weight of the film layer in the overall film system. Specifically, the sensitivity coefficient can be realized by statistical deposition data or optical simulation model. The sensitivity refers to the influence degree of a specific film layer on the overall spectral performance, and the disturbance amplitude of the final passband characteristics caused by different film layer thickness deviations can be quantitatively evaluated by using an optical transfer matrix.

[0061] Specifically, during the deposition of the film system, after the deposition of each film layer is completed, the in-line spectral measurement system will collect the transmittance curve of the current film system in real time, and extract the center wavelength and full width at half maximum as characteristic parameters. These measured characteristic parameters are immediately compared with the theoretical characteristic parameters at the corresponding position in the standard spectral trajectory. When the deviation exceeds the preset dynamic tolerance range, the system will automatically adjust the deposition rate or thickness design value of the subsequent film layer according to the sensitivity level of the current film layer; for example, for high-sensitivity film layers located in the core position of the resonant cavity, the tolerance range is set to ±0.5 nanometers, while the tolerance range of the edge reflection layer can be widened to ±2 nanometers. This differential tolerance control allows the process fluctuations of key film layers to be corrected in time, avoiding the transmission of errors to subsequent film layers.

[0062] Through the above technical solutions, the present application effectively solves the problem of spectral performance degradation caused by error accumulation during the deposition of multi-layer films. By dynamically adjusting the process tolerance of different sensitivity film layers, the overall process stability can be optimized while ensuring the precision of key film layers, thereby improving the spectral consistency and production yield of the filter chip.

[0063] Specifically, the present application dynamically adjusts the deposition control parameters of the subsequent to-be-deposited film layers according to the deviation value and its trend, specifically including the following two dynamic adjustment strategies:

[0064] The first dynamic adjustment strategy: when the deviation value indicates that the center wavelength of the current measured spectrum has a systematic drift relative to the theoretical value, then according to the direction and amplitude of the drift, the theoretical design thickness of all subsequent to-be-deposited film layers is increased or decreased in proportion to compensate for the systematic drift macroscopically.

[0065] Wherein, the systematic drift refers to the phenomenon that the center wavelength continuously deviates from the theoretical value caused by the parameter offset of the film deposition equipment or environmental factors. It can be specifically identified by detecting the wavelength drift trend after the deposition of multiple film layers by the in-line spectral measurement system, for example, when the center wavelengths of three consecutive film layers are all shifted more than a threshold value in the long wave direction, it is determined as a systematic drift. The theoretical design thickness refers to the target thickness value of each film layer calculated by the film system structure optimization algorithm. It can be specifically calculated by iterative simulation using optical thin film design software, for example, by adjusting the thickness ratio of high refractive index material layer and low refractive index material layer to optimize the passband characteristics.

[0066] Specifically, in the coating process, when the online spectral measurement system detects a continuous same-direction deviation of the central wavelength of the deposited film layer, it is determined that there is a systematic error caused by temperature drift or evaporation source rate abnormality in the coating cavity. At this time, according to the proportional relationship between the measured deviation and the theoretical value, the thickness of all subsequent un-deposited film layers is scaled as a whole. For example, if the measured central wavelength is 2% shorter than the theoretical value, the design thickness of each subsequent film layer is increased by 2%. By globally adjusting the film layer thickness sequence, the overall optical performance of the finally formed film system structure is returned to the theoretical design track, avoiding the amplification of errors in the multi-layer stacking process.

[0067] Compared with the prior art, the traditional extreme value method only corrects the error of a single film layer thickness, and cannot eliminate the cumulative error caused by the drift of the coating process parameters. The present scheme realizes error correction from the overall structure of the film system by monitoring the spectral evolution trend in real time and compensating the thickness of subsequent film layers when a systematic deviation is detected, effectively suppressing the influence of central wavelength drift on the final filtering performance.

[0068] The second dynamic adjustment strategy is: when analyzing the change rule of the deviation value after the deposition of several continuous film layers, if it is determined that the deviation trend is caused by a single film layer deposition failure and its influence is local, then only the subsequent one or several specific film layers with the highest optical coupling degree with the failed film layer are fine-tuned for localized correction.

[0069] The change rule of the deviation value after the deposition of several continuous film layers refers to identifying the evolution mode of the deviation by monitoring the deviation sequence of the characteristic parameters of multiple adjacent film layers after deposition, which can be realized by using a sliding window algorithm to trend fit the deviation values of adjacent film layers, and is used to distinguish between systematic errors and local errors. The local influence caused by a single film layer deposition failure refers to the fact that after the thickness or refractive index of a film layer deviates from the theoretical value, its optical effect only has significant interference with specific subsequent film layers. This can be quantified by establishing an optical coupling matrix between film layers to quantify the mutual influence between film layers, and is used to accurately locate the subsequent film layers that need to be corrected. The subsequent specific film layer with the highest optical coupling degree refers to the subsequent film layer that has strong optical interference with the failed film layer in the multi-layer film structure, which can be determined by calculating the electric field intensity distribution or transmission phase matching degree between film layers, and is used to select the most sensitive correction target for error. Fine-tuning the deposition control parameters refers to fine adjustment of the deposition rate or deposition time of the selected subsequent film layer, which can use a PID control algorithm to generate compensation instructions according to the deviation amplitude, and is used to eliminate local errors with minimal intervention.

[0070] Specifically, when the online spectral measurement system detects that the spectral characteristic parameters of a certain film layer after deposition deviate abnormally, firstly, the deviation data of the previous three film layers are traced back, and whether a single-point sudden increase trend is presented is judged by calculating the deviation change rate. If it is confirmed that the abnormality is caused by the deposition failure of the current film layer, the pre-stored optical coupling model is called to screen out the subsequent two film layers that have strong coupling relationship with the film layer. For example, when the fifth layer of high refractive index film is deposited too thick, the model identifies that the optical phase of the seventh layer of low refractive index film will be most disturbed. At this time, only the deposition time of the seventh layer is shortened by a predetermined proportion, while the parameters of other subsequent film layers remain unchanged. This local correction operation avoids excessive adjustment of the overall film system structure by suppressing the transmission of errors between specific film layers.

[0071] Compared with the prior art, the traditional extreme value method only makes post-correction for single-layer film thickness and cannot identify the error source and propagation path, often resulting in new cumulative errors by using a global compensation strategy. The scheme can accurately locate the subsequent film layers affected by errors by establishing a coupling relationship model between film layers, reducing the correction range from the entire film system to a specific local area, and significantly reducing the process adjustment cost while ensuring the spectral performance.

[0072] In the embodiment, the deposition control parameter is the deposition rate, and the deposition control parameter of the subsequent film layer to be deposited is dynamically adjusted, specifically including: if the deviation value indicates that the film layer density is insufficient, the deposition rate of the subsequent film layer to be deposited is reduced; if the deviation value indicates that the film layer stress is too high, the deposition rate of the subsequent film layer to be deposited is increased.

[0073] The deposition rate refers to the deposition amount of material on the substrate surface per unit time, which can be realized by adjusting the sputtering power or gas flow in the ion beam sputtering process. The deposition rate directly affects the density and internal stress distribution of the film layer microstructure. Insufficient film layer density refers to the existence of pores or loose structure in the film, which can be identified by the increase of scattering loss of non-characteristic wavelength in transmission spectrum; and the film layer stress is too high refers to the internal stress between the film and the substrate due to the difference in thermal expansion coefficient or lattice mismatch, which can be judged by the film edge warping or cracking phenomenon.

[0074] Specifically, in the coating process, when the online spectral measurement system detects that the central wavelength or full width at half maximum of the current film layer deviates from the theoretical value, the physical cause of the film layer defect can be judged by analyzing the deviation type; for example, if the measured spectral curve abnormally increases in transmittance outside the target waveband, it indicates that the film layer is not dense enough, at this time, by reducing the deposition rate of the subsequent film layer, the migration time of the material particles on the substrate surface can be prolonged, and a more compact accumulation structure can be formed; on the contrary, if micro-cracks appear on the surface of the film layer or the substrate is deformed, it indicates that the stress of the film layer is too high, at this time, increasing the deposition rate can reduce the heat accumulation in the film growth process and relieve the stress concentration phenomenon, and by adjusting the deposition rate in real time, different compensation can be implemented for different defect types, so that the optical performance of the film system structure gradually returns to the theoretical track.

[0075] By dynamically adjusting the deposition rate, the film layer quality can be corrected in real time without interrupting the coating process, so that the dual-channel filter chip has stable transmittance and spectral resolution in the SF6 characteristic absorption waveband and the reference waveband.

[0076] In actual process, after the physical vapor deposition of each film layer is completed, the temperature distribution in the vacuum cavity has not been completely balanced, and the microstructure of the newly deposited film layer is still in a metastable state, at this time, if feature extraction and comparison are performed, measurement errors are likely to occur due to transient changes in the film layer surface, in order to solve this problem, the application further proposes that after the deposition of each film layer is completed, the fluctuation of the current measured spectral curve is continuously monitored, and only when the fluctuation amplitude of the current measured spectral curve tends to be stable, the feature parameter extraction and comparison operation is performed.

[0077] The continuous monitoring of the fluctuation of the current measured spectral curve refers to that after the deposition of a single film layer is completed, the transmittance is continuously sampled for multiple times by the online spectral measurement system to form a spectral data change trajectory in time sequence, which can be realized by using a high sampling rate spectral sensor in cooperation with a data acquisition module, for example, 10 times of transmittance data are collected per second and the wavelength-transmittance curve is recorded; the monitoring process is used to capture the transient changes of optical performance caused by the release of thermal stress or the material crystallization process after coating. The fluctuation amplitude tends to be stable, which means that the form parameter change amount of the measured spectral curve is reduced to within a preset threshold range, which can be realized by using a standard deviation calculation method, for example, when the standard deviation of the central wavelength of 5 continuous samplings is less than 0.2 nanometers, it is determined that the state is stable, and the determination condition is used to exclude the short-term interference caused by the temperature fluctuation in the coating cavity or the adsorption of residual gas.

[0078] Through the above technical solution, this application solves the problem of measurement data distortion caused by material phase transition hysteresis during the coating process, ensuring that the optical performance evaluation of each film layer is based on real data under stable conditions. This technical means can significantly reduce the risk of misadjustment of control parameters due to improper measurement timing and improve the control accuracy of the film structure deposition process.

[0079] Specifically, this application further proposes to perform spectral reference calibration before depositing the first and second film structures, and to use the same calibrated online spectral measurement system to measure the transmittance of the currently deposited film structure when depositing the first and second film structures respectively.

[0080] Spectral benchmark calibration refers to calibrating the wavelength accuracy and transmittance linearity of the online spectral measurement system using standard samples. Specifically, a standard filter with known optical constants can be used as a benchmark. Before deposition, the measured data of the online spectral measurement system is compared with the calibrated spectrum of the standard filter, and the system parameters are adjusted until the measurement error is below a preset threshold. A calibrated online spectral measurement system refers to the same spectral measurement equipment after a unified calibration process, where the optical probe, light source, and detector maintain fixed installation positions and parameter configurations during both film deposition processes, thereby ensuring consistency of the measurement conditions between the two measurements.

[0081] Specifically, before depositing the first film structure, a standard filter is placed on the silicon substrate, and an online spectral measurement system is activated for scanning. If the measured center wavelength of the spectrum deviates from the calibration value of the standard filter, the wavelength calibration parameters of the system are adjusted until the deviation is eliminated. After calibration, the system is locked as the sole device for subsequent film layer measurements. When depositing the second film structure, the same system under the same calibration state is directly used for transmittance measurement, avoiding additional errors introduced by changing equipment or adjusting the optical path. For example, when depositing the first film structure, the system may experience detector response drift due to changes in ambient temperature. In this case, calibration can correct the drift in real time, and the deposition process of the second film structure directly inherits the corrected parameters, thereby maintaining the consistency of the measurement reference for the two channels.

[0082] This application ensures that the transmittance measurement data of the dual-channel membrane structure is based on the same reference, avoiding the spectral response mismatch of the two channels due to differences in the measurement system, thereby improving the dual-channel contrast accuracy of the filter chip in SF6 gas identification.

[0083] Specifically, after all film layers are deposited, the prepared filter chip is subjected to a final spectral scan using a high-precision Fourier transform infrared spectrometer in a constant temperature and humidity environment. The final measured spectrum is compared with the theoretically designed spectrum across the entire band, and the filter chip is classified into performance levels based on the degree of agreement between the comparison results.

[0084] The constant temperature and humidity environment refers to a stable test condition in which the temperature is controlled at 20±0.5°C and the relative humidity is maintained at 45%±3%, and the condition can be achieved by using a constant temperature box and a humidity adjusting device in linkage control. The environment can eliminate the spectral measurement error caused by temperature and humidity fluctuation, and ensure the consistency of the data acquisition benchmark. The full-waveband comparison refers to the point-by-point calculation of the transmittance deviation value of the measured spectrum and the theoretical spectrum in the range of 8-12 μm, and the similarity index of the two curves can be calculated by using the least square method. The performance grade classification refers to setting multiple quality thresholds according to the deviation value distribution, for example, when the center wavelength deviation is less than 0.1% and the passband transmittance fluctuation is less than 2%, the product is determined as A grade, so as to establish an objective screening standard.

[0085] Specifically, after the deposition of the double-channel membrane system is completed, the filter chip is transferred to a constant temperature and humidity test cabin and is left to stand for two hours. After the internal stress of the chip is released and the temperature of the substrate is balanced with the environment, the spectrometer is started to perform full-waveband scanning. During the scanning process, a step-by-step measurement mode is used, and a transmittance data point is collected every 0.1 μm to generate a continuous measured spectrum curve. Then the measured data is imported into the analysis software, and the point-by-point matching degree calculation is performed with the theoretical design spectrum. The three core parameters of the passband center wavelength, the full width at half maximum and the stopband suppression ratio are evaluated. According to the preset error tolerance interval, the products are divided into A, B and C grades. The A grade product can be directly used for high-precision gas detection equipment, the B grade product needs to be calibrated twice before use, and the C grade product is determined as unqualified product for rework.

[0086] The application further establishes a full-waveband performance verification mechanism for the final product, which can accurately identify the defects of the membrane system structure caused by process fluctuation, and avoid the flow of products with hidden optical distortion into the subsequent assembly link. The grading screening mechanism significantly improves the batch consistency of the filter chip, and ensures that each product can meet the strict requirements of the SF6 gas detection system on spectral selectivity.

[0087] Obviously, the above embodiments are only examples for clarity and do not limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments are not enumerated, and the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for preparing a filter chip for SF6 gas identification, the filter chip comprising a first membrane stack structure and a second membrane stack structure deposited on a silicon substrate, the first membrane stack structure corresponding to a detection wavelength band of SF6 gas, and the second membrane stack structure corresponding to a reference wavelength band, characterized in that, The preparation method comprises the following steps: The preparation method comprises the following steps: Based on the detection waveband and the reference waveband, the theoretical stacking sequences of the first film system structure and the second film system structure are designed respectively; including: selecting high refractive index materials and low refractive index materials, and determining the optical constants of the high refractive index materials and the low refractive index materials in the detection waveband and the reference waveband; a basic film system unit is constructed, including a resonant layer located at the center, and a plurality of reflection layers are symmetrically arranged on both sides of the resonant layer, and the reflection layers are formed by alternately stacking the high refractive index materials and the low refractive index materials with a quarter of the optical thickness; the initial stacking sequence design of the first film system structure is carried out by cascading the basic film system unit multiple times according to the target central wavelength of the detection waveband; the initial stacking sequence design of the second film system structure is carried out by cascading the basic film system unit multiple times according to the target central wavelength of the reference waveband; the initial stacking sequences of the first film system structure and the second film system structure are respectively set as the optimization starting points, the passband rectangular degree and the peak transmittance are taken as the optimization targets, and the optimization algorithm is run to iteratively adjust the thickness of each film layer in the two initial stacking sequences; When the optimization results meet the matching of the passband center of the first film system structure and the detection waveband, the matching of the passband center of the second film system structure and the reference waveband, and the passband rectangular degree and the peak transmittance of the two film system structures reach the preset indicators, the final film layer thickness sequence obtained at this time is determined as the theoretical stacking sequence of the first film system structure and the second film system structure respectively Based on the theoretical stacking sequence, the real-time theoretical spectrum curve of the filter chip is simulated and calculated after the deposition of each film layer in the coating process, and the characteristic parameters of each real-time theoretical spectrum curve are extracted, and all the characteristic parameters are arranged in the coating order to form a standard spectrum track; According to the theoretical stacking sequence, the first film layer of the first film system structure or the second film system structure is deposited on the silicon substrate, and each subsequent film layer is sequentially deposited in an iterative manner, wherein after the deposition of each film layer is completed, the following operations are performed: the transmittance of the current deposited film system structure is measured by using an online spectrum measurement system to obtain a current measured spectrum curve, and the current measured characteristic parameters corresponding to the standard spectrum track are extracted; the current measured characteristic parameters are compared with the theoretical characteristic parameters of the corresponding film layer position in the standard spectrum track, the deviation value is calculated, and the deposition control parameters of the subsequent to-be-deposited film layer are dynamically adjusted according to the deviation value and the change trend thereof; 2. The preparation method of the filter chip for SF6 gas identification according to claim 1, characterized in that: The above iterative deposition process is repeated until the first film system structure and the second film system structure are completely deposited, so that the spectrum evolution of the entire film system structure in the deposition process follows the standard spectrum track generated by simulation calculation. The characteristic parameters include the central wavelength and the full width at half maximum, and the characteristic parameters of each real-time theoretical spectrum curve are extracted, specifically including: A peak point with the highest transmittance in the real-time theoretical spectrum curve is identified, and the wavelength corresponding to the peak point is recorded as the central wavelength; On the real-time theoretical spectrum curve, two wavelength points with a transmittance of half of the peak transmittance are found, and the width between the two wavelength points is calculated as the full width at half maximum.

3. The preparation method of the filter chip for SF6 gas identification according to claim 1, characterized in that: After the standard spectral trajectory is constructed, a dynamic tolerance range is set for the theoretical characteristic parameter of each film layer position in the trajectory; the dynamic tolerance range is determined according to the sensitivity of the current film layer in the overall film system structure, and the higher the sensitivity, the smaller the tolerance range; When the current measured characteristic parameter is compared with the theoretical characteristic parameter of the corresponding film layer position in the standard spectral trajectory, if the deviation value exceeds the dynamic tolerance range, the operation of dynamically adjusting the deposition control parameter of the subsequent to-be-deposited film layer is triggered.

4. The preparation method of the filter chip for SF6 gas identification according to claim 1, characterized in that: According to the deviation value and its change trend, the deposition control parameter of the subsequent to-be-deposited film layer is dynamically adjusted, specifically including: When the deviation value indicates that the center wavelength of the current measured spectrum has a systematic drift relative to the theoretical value, the theoretical design thickness of all subsequent to-be-deposited film layers is increased or decreased in proportion according to the direction and amplitude of the drift, so as to macroscopically compensate for the systematic drift.

5. The preparation method of the filter chip for SF6 gas identification according to claim 4, characterized in that: The change rule of the deviation value after deposition of continuous several film layers is analyzed, if it is determined that the deviation trend is caused by a single film layer deposition error and its influence is local, only the deposition control parameter of the subsequent one or several specific film layers with the highest optical coupling degree with the error film layer is fine-tuned for localized correction.

6. The preparation method of the filter chip for SF6 gas identification according to claim 1, characterized in that: The deposition control parameter is the deposition rate, and the deposition control parameter of the subsequent to-be-deposited film layer is dynamically adjusted, specifically including: If the deviation value indicates that the film layer density is insufficient, the deposition rate of the subsequent to-be-deposited film layer is reduced; If the deviation value indicates that the film layer stress is too high, the deposition rate of the subsequent to-be-deposited film layer is increased.

7. The preparation method of the filter chip for SF6 gas identification according to claim 1, characterized in that: After the deposition of each film layer is completed, the fluctuation of the current measured spectrum curve is continuously monitored, and only when the fluctuation amplitude of the current measured spectrum curve tends to be stable, the characteristic parameter extraction and comparison operation is performed.

8. The preparation method of the filter chip for SF6 gas identification according to claim 1, characterized in that: Before depositing the first film system structure and the second film system structure, spectral benchmark calibration is performed, and when the first film system structure and the second film system structure are deposited respectively, the same set of calibrated online spectral measurement system is used to measure the transmittance of the current deposited film system structure.

9. The preparation method of the filter chip for SF6 gas identification according to claim 1, characterized in that: After all the film layers are deposited, the prepared filter chip is finally scanned by a high-precision Fourier transform infrared spectrometer in a constant temperature and humidity environment; The final measured spectrum is compared with the theoretical design spectrum in the full wave band, and according to the coincidence degree of the comparison result, the filter chip is classified by performance level. The final measured spectrum is compared with the theoretical design spectrum in the full wave band, and according to the coincidence degree of the comparison result, the filter chip is classified by performance level.

Images