Single-piezoelectric-layer micro-cantilever structure and application thereof

Abstract

The invention relates to a single-piezoelectric-layer micro-cantilever structure and application thereof.The single-piezoelectric-layer micro-cantilever structure comprises an arm beam and a monitoring assembly, a groove is formed in the upper surface of the arm beam, a cantilever is defined by the groove, a gap is formed between the peripheral side of the cantilever and the side wall of the groove, and a gap is also formed between the bottom face of the cantilever and the bottom face of the groove; a reference groove communicated with the groove is further formed in the upper surface of the cantilever beam, and the reference groove is used for judging the displacement of the cantilever under the action of gravity and stress; the monitoring assembly comprises a buffer layer, a bottom electrode layer, a piezoelectric film and a circuit layer which are sequentially stacked on the upper surface of the cantilever from bottom to top, the circuit layer comprises a driving circuit and a monitoring circuit, the driving circuit is used for driving the piezoelectric film to vibrate, and the monitoring circuit is used for monitoring vibration parameters of the piezoelectric film. According to the technical scheme, the step height difference between the tail end of the cantilever beam and the table top is measured through the reference groove and the SEM, the in-situ stress state can be judged, and the micro-cantilever beam structure with overlarge pressing / pulling stress can be rapidly screened out.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor technology, in particular to a single piezoelectric layer micro-cantilever structure and application thereof. BACKGROUND

[0002] Process Control Monitor (PCM) is a key technical means for monitoring the manufacturing quality and process stability of semiconductor devices. The PCM test structure needs to be highly compatible with the standard manufacturing process, can be produced synchronously with semiconductor devices, and thus can effectively and accurately reflect the actual process conditions, which is a key technology for improving the manufacturing yield and process stability of MEMS. Understanding the geometric parameters, electrical parameters and material characteristic parameters of MEMS devices helps to improve the efficiency of detection and analysis.

[0003] The key structure of a piezoelectric MEMS device with AlN as a piezoelectric material includes three parts: a MEMS movable mechanical structure, a piezoelectric brake and a piezoelectric sensor. The PCM test structure of the piezoelectric MEMS driven and sensed by the piezoelectric film is an essential part of process monitoring.

[0004] The MEMS process monitoring structure based on the piezoelectric micro-cantilever beam can provide evaluation for various key process qualities due to its electromechanical conversion characteristics, resonance characteristics, dynamic sensitivity and the like. Moreover, the process of the piezoelectric micro-cantilever beam structure is compatible with the MEMS process, and does not increase the additional process complexity or production cost.

[0005] From the perspective of function implementation, when the piezoelectric micro-cantilever beam PCM structure works as a sensor, environmental vibration or applied test signals will cause mechanical deformation of the cantilever beam, which is converted into a measurable electrical signal through the positive piezoelectric effect; as an actuator, the applied voltage induces mechanical movement of the cantilever beam through the inverse piezoelectric effect, and the amplitude and resonance frequency directly reflect the mechanical characteristics and material parameters of the structure. This bidirectional transduction capability enables a single test structure to comprehensively evaluate multiple process parameters, improving the monitoring efficiency.

[0006] The resonance frequency of the cantilever beam as a core monitoring index is extremely susceptible to process fluctuations. The geometric size, material parameters, stress state and interface characteristics of the cantilever beam will affect the frequency characteristics. Among them, the residual stress will change the equivalent stiffness, causing the resonance frequency to shift. Residual stress not only directly affects the performance of the device, but also affects the overall stress distribution of the wafer. When the warpage of the wafer exceeds 50 , it may affect the subsequent process and the performance and reliability of the device. SUMMARY

[0007] Based on the above description, the application provides a single piezoelectric layer micro-cantilever structure and its application, aiming to monitor the frequency response and stress state synchronously.

[0008] The technical solution of the application to solve the above technical problems is as follows: The application provides a single piezoelectric layer micro-cantilever structure, comprising: The arm beam has a groove on the upper surface, the groove surrounds to form a cantilever, the gap between the side wall of the groove and the circumferential side of the cantilever, and the gap between the bottom surface of the cantilever and the bottom surface of the groove, and the upper surface of the arm beam is also provided with a reference groove connected with the groove, and the reference groove is used to judge the displacement of the cantilever under the action of gravity and stress. The monitoring assembly comprises, from bottom to top, a buffer layer, a bottom electrode layer, a piezoelectric film and a circuit layer on the upper surface of the cantilever, the circuit layer comprises a driving circuit and a monitoring circuit, the driving circuit is used to drive the piezoelectric film to vibrate, and the monitoring circuit is used to monitor the vibration parameters of the piezoelectric film.

[0009] Further, the driving circuit comprises a driving electrode, a power amplifier and a signal generator connected in an electric manner. The monitoring circuit comprises an induction electrode, a current amplifier and an oscilloscope connected in an electric manner.

[0010] Further, the driving circuit is provided with two groups. The induction electrode is arranged between the driving electrodes of the two groups of driving circuits.

[0011] Further, one side wall of the reference groove is coplanar with one side wall of the groove, and the width of the reference groove is equal to the gap between the groove and the cantilever.

[0012] The application also provides an application of the single piezoelectric layer micro-cantilever structure in monitoring the piezoelectric film.

[0013] The application also provides a detection method of the piezoelectric film, comprising: S1. obtaining a piezoelectric film to be detected, and preparing the piezoelectric film to be detected into the single piezoelectric layer micro-cantilever structure as described above. S2. turning on the signal generator to generate an electric signal, amplifying the signal through the power amplifier, and transmitting the signal to the driving electrode to drive the piezoelectric film to be detected to convert the electric signal into mechanical vibration. S3. the induction electrode induces the mechanical vibration and generates an electric signal corresponding thereto, amplifies the signal through the current amplifier, and transmits the signal to the oscilloscope to obtain parameters, and judges whether the piezoelectric film is qualified according to the parameters.

[0014] Further, step S2 comprises: S21. Turn on the signal generator to generate a transient square wave signal, and transmit the signal to the driving electrode after amplification by the power amplifier, to drive the piezoelectric film to be tested to convert the electrical signal into mechanical vibration; In step S3, the obtained parameters include the peak frequency.

[0015] Further, step S2 includes: S22. Turn on the signal generator to generate an electrical signal, adjust the start frequency, center frequency and end frequency of the signal generator, and transmit the signal to the driving electrode after amplification by the power amplifier, to drive the piezoelectric film to be tested to convert the electrical signal into mechanical vibration; In step S3, the obtained parameters include the frequency and amplitude.

[0016] The present application also provides a stress self-detection method for the single piezoelectric layer micro-cantilever structure as described above, comprising: S10. Record the vertex of the upper surface of one end of the cantilever extending into the groove as point A, record the vertex of the upper surface of the reference groove close to point A as point B, and place the single piezoelectric layer micro-cantilever structure on a sample stage; S20. Adjust the inclination angle of the sample stage to θ, vertically project A onto the inner side surface of B in the groove by SEM, record the projection of A point as a point, and measure the horizontal distance between a point and B point by SEM ; Calculate the deviation distance of the cantilever end by the formula ; S30. Calculate the deviation distance of the cantilever end under the premise of only being affected by gravity , and the calculation formula is as shown in formula (1)-(5), (1), (2), (3), (4), (5), Wherein, is the equivalent bending stiffness, is the distributed load caused by gravity, is the length of the cantilever beam, , , , , The film thickness, Young's modulus, density, Poisson's ratio and the distance from the center to the reference surface of the i-th layer are respectively, is the total thickness of the cantilever beam, For average density, The overall neutral axis position, It is the acceleration due to gravity; S40. According to and The stress state of the single piezoelectric layer microcantilever beam structure is obtained by calculating the magnitude relationship.

[0017] Furthermore, the length L of the cantilever is not less than 300 μm.

[0018] Compared with the prior art, the technical solution of this application has the following beneficial technical effects: The structure described in this invention, under static conditions, allows for the measurement of the distance between the end of the cantilever beam and its original plane using in-line SEM sidewall ranging. This enables the determination of the cantilever beam's stress state and rapid screening of cantilever beam structures prone to buckling due to excessive compressive / tensile stress, thus achieving in-situ online monitoring of residual stress. Under dynamic conditions, by utilizing the electromechanical conversion characteristics of piezoelectric materials and the frequency response characteristics of the micro-cantilever beam structure, the amplitude and resonant frequency of the output electrical signal are analyzed to monitor the piezoelectric MEMS process. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a testing device for the piezoelectric coefficient of a piezoelectric thin film in the prior art; Figure 2 This is a schematic diagram of an embodiment of the single piezoelectric layer microcantilever beam structure in this application; Figure 3 This is a plan view of an embodiment of the single piezoelectric layer microcantilever beam structure in this application; Figure 4 For this application Figure 3 Cross-sectional view at point AB of a microcantilever beam structure with a single piezoelectric layer; Figure 5 This is a schematic diagram of the cross alignment mark in one embodiment of the single piezoelectric layer microcantilever beam structure in this application; Figure 6 This is a schematic diagram of the stress detection structure of an embodiment of the single piezoelectric layer microcantilever beam structure in this application; Figure 7 This is a schematic diagram of the height difference projected onto a horizontal plane in an embodiment of the single piezoelectric layer microcantilever beam structure in this application; Figure 8 This is a schematic diagram of the rounded corner effect of an embodiment of the single piezoelectric layer microcantilever beam structure in this application.

[0020] The attached diagram lists the components represented by each number as follows: 1000. Single piezoelectric layer microcantilever beam structure; 100. Cantilever beam; 101. Buffer layer; 102. Bottom electrode layer; 103. Piezoelectric thin film; 104. Driving electrode; 105. Sensing electrode; 106. Groove; 107. Signal generator; 108. Power amplifier; 109. Switch; 110. Current amplifier; 111. Oscilloscope. Detailed Implementation

[0021] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0023] In existing technologies, the resonant frequency of a cantilever beam, as a core monitoring indicator, is highly susceptible to process fluctuations. Factors such as the cantilever beam's geometry, material parameters, stress state, and interface characteristics all affect frequency characteristics. Residual stress, in particular, can alter the equivalent stiffness, causing a shift in the resonant frequency. This residual stress not only directly affects device performance but also influences the overall stress distribution on the wafer. When the wafer warpage exceeds 50°... This could affect the performance and reliability of subsequent processes and devices.

[0024] According to standard IEC 62047-42-2022, the testing apparatus for the piezoelectric coefficient of piezoelectric films is as follows: Figure 1 As shown, the resonant frequency of the cantilever beam was measured by a Doppler vibration meter (LDV), which could not analytically determine the specific effect of residual stress on the frequency response. The resonant frequency of the cantilever beam is related to its stiffness and mass distribution. Tensile stress increases the effective stiffness of the beam, raising the resonant frequency; compressive stress reduces stiffness, potentially leading to a decrease in frequency or even buckling instability. Therefore, the resonant frequency of the cantilever beam will shift under different residual stress states. This frequency shift directly affects the measurement accuracy of the piezoelectric coefficient, causing deviations in the measurement results due to changes in residual stress. Precise control of residual stress is necessary during manufacturing to accurately measure the resonant frequency and piezoelectric coefficient.

[0025] In view of this, see Figures 2 to 4The application provides a single piezoelectric layer micro-cantilever structure 1000, which comprises an arm beam 100 and a monitoring assembly, a groove 106 is formed on the upper surface of the arm beam 100, the groove 106 surrounds to form a cantilever, a gap is formed between the side wall of the groove 106 and the circumferential side of the cantilever, and a gap is also formed between the bottom surface of the cantilever and the bottom surface of the groove 106, and a reference groove is formed on the upper surface of the arm beam 100 and is connected with the groove 106, the reference groove is used to judge the displacement of the cantilever under the action of gravity and stress; the monitoring assembly comprises, from bottom to top, a buffer layer 101, a bottom electrode layer 102, a piezoelectric film 103 and a circuit layer on the upper surface of the cantilever, the circuit layer comprises a driving circuit and a monitoring circuit, the driving circuit is used to drive the piezoelectric film 103 to vibrate, and the monitoring circuit is used to monitor the vibration parameters of the piezoelectric film 103; by arranging the reference groove, an alignment point and a reference line are provided for measuring the height difference between the end of the cantilever beam and the table top, the actual position offset of the free end of the cantilever under the action of stress can be clearly observed, the In-line SEM is facilitated to measure, in the SEM vacuum environment, the influence of gravity is relatively constant and can be modeled, by comparing the actual projection position of the cantilever under no external load with the theoretical neutral position, the stress state in situ can be judged, and the micro-cantilever structure with excessive compression / tension stress can be quickly screened out.

[0026] In the technical scheme of the application, the groove 106 is arranged on the upper surface of the arm beam 100 to form an independent cantilever structure, and gaps are arranged on the circumferential side and the bottom surface, so that the leakage of vibration energy of external support structures is effectively isolated, and the boundary effect interference is reduced, the arm beam 100 serves as a substrate and has key functions such as mechanical support, stress transmission and resonance characteristic regulation; specifically, in some embodiments of the application, the materials of the arm beam 100 and the cantilever are silicon to form a silicon substrate, the material of the bottom electrode layer 102 is molybdenum, and an aluminum nitride (AlN) layer is grown between the silicon substrate and the bottom electrode layer 102 as the buffer layer 101, so that the interface stress accumulation can be effectively relieved, the interface lattice mismatch degree is reduced, the risk of device warping is reduced, and meanwhile the AlN buffer layer 101 can absorb the surface defects (such as oxide layer and scratch) of the Si substrate, avoid the defects from being transmitted to the functional layer, and improve the reliability of the device.

[0027] And, by integrating the piezoelectric film 103 to be tested in the cantilever region of the micro-cantilever beam, and cooperating with the driving circuit and the monitoring circuit, an experimental platform is constructed, which can apply excitation to the piezoelectric film 103 at the micro scale and synchronously collect the response signal of the piezoelectric film 103, and the intrinsic performance of the piezoelectric film 103 is directly and controllably tested; the driving circuit in the monitoring assembly can apply a controllable voltage signal to the piezoelectric film 103 to excite the piezoelectric film 103 to generate a slight deformation or vibration; at the same time, the monitoring circuit can collect the voltage / current response, vibration frequency, amplitude, phase and other parameters of the piezoelectric film 103 under excitation in real time, and in combination with the driving input and the response output, the electromechanical coupling coefficient, the resonance characteristic, the loss behavior and the nonlinear response of the piezoelectric film 103 can be dynamically analyzed, and the in-situ evaluation of the material performance is realized.

[0028] Further, the driving circuit comprises a driving electrode 104, a power amplifier 108 and a signal generator 107 which are electrically connected; The monitoring circuit comprises an induction electrode 105, a current amplifier 110 and an oscilloscope 111 which are electrically connected.

[0029] In the technical scheme of the present application, the signal generator 107 generates a voltage signal, which is amplified by the power amplifier 108 and applied to the driving electrode 104, so as to generate an electric field along the driving direction of the piezoelectric film 103, so that the piezoelectric film 103 generates piezoelectric deformation, while the silicon substrate of the cantilever beam remains unchanged, due to the strain difference between the two materials, a torque is generated, so that the whole cantilever beam structure bends in the vertical direction at the free end. The vibration of the cantilever beam changes the surface stress of the piezoelectric film 103, generating a small voltage signal. After being amplified by the current amplifier 110, the signal is received by the oscilloscope 111, which improves the capture ability of the weak dynamic response signal. Through the current, the amplitude and frequency characteristics of the cantilever beam can be obtained, so as to ensure that the real vibration state and electromechanical conversion characteristics of the piezoelectric film 103 can be accurately reflected.

[0030] Specifically, in some embodiments of the present application, a switch 109 is further arranged between the power amplifier 108 and the driving electrode 104; the bottom electrode layer 102 is grounded, keeping the electric potential at zero, providing a stable electric potential reference for the system, and the top electrode layer (molybdenum) is patterned to form the driving electrode 104 and the induction electrode 105, the driving electrode 104 is symmetrically distributed to improve the driving force, and the AlN piezoelectric film 103 is located between the bottom electrode 102 and the top electrode layer, which functions as: ① converting the applied electric signal into mechanical vibration; ② converting the mechanical vibration into an electric signal output through the upper and lower electrodes.

[0031] Further, the driving circuit is provided with two groups; The induction electrode 105 is arranged between the driving electrodes 104 of the two groups of driving circuits.

[0032] In the technical solution of the present application, two groups of symmetrically arranged driving circuits are used to apply the same or differential excitation signals on both sides of the piezoelectric film 103, forming a symmetric electric field distribution. This structure effectively balances the stress loading on the cantilever beam, avoiding the torsion, uneven bending or local stress concentration phenomenon caused by unilateral driving, ensuring that the piezoelectric film 103 generates a more uniform and controllable strain field during vibration, improving the accuracy and repeatability of performance testing.

[0033] Further, one side wall of the reference slot is coplanar with one side wall of the groove 106, and the width of the reference slot is equal to the gap between the groove 106 and the cantilever.

[0034] In the technical solution of the present application, by providing a reference slot, an alignment point and a reference line are provided for the measurement of the height difference between the cantilever beam end and the mesa, the actual position offset of the free end of the cantilever under stress can be clearly observed, which facilitates In-line SEM measurement. In the SEM vacuum environment, the influence of gravity is relatively constant and can be modeled. By comparing the actual projection position of the cantilever under no external load with the theoretical neutral position, the stress state in situ can be determined, and micro-cantilever beam structures with excessive compression / tension stress can be quickly screened out. Residual stress causes the equivalent stiffness of the cantilever beam to change, resulting in a shift in the resonant frequency. The resonant frequency of the cantilever beam is measured by electrical testing, and an in-situ relationship between residual stress and resonant frequency is established, realizing stress-frequency combined feedback.

[0035] In some embodiments of the present application, two crossing structures are etched on the mesa corresponding to the end of the cantilever beam along the sidewall gap direction of the groove 106, which have the same width as the sidewall gap and a crossing angle of 90°, as shown in Figure 5 The crossing structures provide an alignment point and a reference line for the measurement of the height difference between the cantilever beam end and the mesa, facilitating In-line SEM measurement.

[0036] The present application also proposes an application of the single piezoelectric layer micro-cantilever beam structure 1000 as described above in monitoring the piezoelectric film 103.

[0037] The present application also proposes a detection method of the piezoelectric film 103, comprising: S1. Obtain a piezoelectric film 103 to be tested, and prepare a single piezoelectric layer micro-cantilever beam structure 1000 as described above, wherein the piezoelectric film 103 is the piezoelectric film 103 to be tested; S2. Turn on the signal generator 107 to generate an electrical signal, which is amplified by the power amplifier 108 and transmitted to the driving electrode to drive the piezoelectric film 103 to be tested to convert the electrical signal into mechanical vibration; S3. The inductive electrode 105 induces mechanical vibration and generates corresponding electrical signal, which is amplified by the current amplifier 110 and transmitted to the oscilloscope 111 to obtain parameters, and whether the piezoelectric film 103 is qualified is determined according to the parameters.

[0038] In the technical scheme of the present application, the piezoelectric film 103 to be tested is directly integrated as a functional layer in the single piezoelectric layer micro-cantilever beam structure 1000, and the vibration behavior thereof is completely determined by the intrinsic electromechanical coupling characteristics of the piezoelectric film 103 to be tested. The parameters obtained by driving the vibration and monitoring the response can truly and directly reflect the piezoelectric activity, response sensitivity and energy conversion efficiency of the sample to be tested, avoiding errors caused by indirect calculation or model assumption. By applying controllable excitation through the signal generator 107, the piezoelectric film 103 is driven to produce mechanical vibration, and the dynamic response signal thereof is captured in real time by the inductive electrode 105. The whole process can be completed within milliseconds, and the frequency, amplitude, phase and waveform integrity of the response signal are displayed and analyzed in real time by the oscilloscope 111, so that the dynamic performance of the piezoelectric film 103 is quickly evaluated.

[0039] Further, step S2 comprises: S21. Turn on the signal generator 107 to generate a transient square wave signal, which is amplified by the power amplifier 108 and transmitted to the driving electrode to drive the piezoelectric film 103 to be tested to convert the electrical signal into mechanical vibration; In step S3, the obtained parameters include the peak frequency.

[0040] In the technical scheme of the present application, under the action of transient excitation, the piezoelectric micro-cantilever beam will produce free decay vibration. After the response signal is collected by the inductive electrode 105 and displayed by the oscilloscope 111, the time domain signal can be converted into a frequency domain spectrum by Fourier transform (FFT). The maximum amplitude in the spectrum corresponds to the frequency, which is the "peak frequency". The frequency is highly close to or equal to the first-order resonance frequency of the structure, and is a core parameter for evaluating the elastic modulus, mass distribution and overall stiffness of the piezoelectric film 103.

[0041] Further, step S2 comprises: S22. Turn on the signal generator 107 to generate an electrical signal, adjust the start frequency, center frequency and end frequency of the signal generator 107, amplify the signal by the power amplifier 108, and transmit it to the driving electrode to drive the piezoelectric film 103 to be tested to convert the electrical signal into mechanical vibration; In step S3, the obtained parameters include the frequency and amplitude.

[0042] In the technical solution of this invention, by adjusting the start frequency, center frequency, and end frequency of the signal generator 107, a continuously adjustable sinusoidal sweep signal can be applied to the piezoelectric film 103, covering its expected operating frequency band or resonant region. This allows for the systematic excitation of the microcantilever beam's response state at different frequencies, fully depicting its frequency-amplitude response curve. During the sweep process, when the excitation frequency approaches the natural frequency of the microcantilever beam system, the structure resonates, and the amplitude of the response signal output by the sensing electrode 105 reaches its maximum; this point is the resonant frequency (fr). Near the anti-resonant point, the impedance is at its maximum, which may also manifest as a very small amplitude or a sudden phase change. By recording the response amplitude at different frequencies, these key characteristic frequencies can be accurately identified for calculating core performance parameters of the piezoelectric material, such as the electromechanical coupling coefficient and mechanical quality factor.

[0043] This invention also proposes a stress self-detection method for the single piezoelectric layer microcantilever beam structure 1000 as described above, see reference. Figure 6 ,include: S10. Let point A be the vertex of the upper surface of the end of the cantilever that extends into the groove 106, and let point B be the vertex of the upper surface of the reference groove that is close to point A. Place the single piezoelectric layer micro cantilever beam structure 1000 on the sample stage. S20. Adjust the tilt angle of the sample stage to θ, and use SEM to vertically project point A onto the inner surface of point B in the groove 106. Record the projection of point A as point a, and use SEM to measure the horizontal distance between point a and point B. Through formula The offset distance at the end of the cantilever was calculated. See Figure 7 ; S30. Calculate the deviation distance of the cantilever end under the condition of gravity alone. The calculation formulas are shown in equations (1)-(5). (1), (2), (3), (4), (5), in, For equivalent bending stiffness, The distributed load caused by gravity, The length of the cantilever beam. , , , , the film thickness, Young's modulus, density, Poisson's ratio, the distance from the center to the reference surface of the i-th layer, respectively, the total thickness of the cantilever beam, the average density, the position of the neutral axis of the whole, the acceleration of gravity; S40. According to and the stress state of the single piezoelectric layer micro-cantilever beam structure is calculated.

[0044] It should be noted that the inner side surface where the point B is located is always perpendicular to the sample table. Before step S20, the sample table is kept horizontal, and the inclination angle thereof is 0. At this time, the inner side surface where the point B is located is in the vertical direction, Specifically, in some embodiments of the present application, the inclination angle θ of the sample table is 5°-10°, the horizontal resolution of the in-line SEM is 1 nm, and according to the above formula, when θ = 10°, the height resolution is 5.759 nm.

[0045] Further, the length L of the cantilever is not less than 100 μm.

[0046] In some embodiments of the present application, the beam length of the cantilever beam is L 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, and the thickness of each layer is h Si 2 μm, h AlN1 0.5 μm, h Mo1 0.2 μm, h AlN2 1 μm, h Mo2 0.2 μm, the distance of the end of the cantilever beam of different beam length from the original plane under the action of gravity only is calculated , and the results are shown in Table 1, wherein, h Si is the thickness of the silicon substrate, i.e., the thickness of the cantilever, h AlN1 is the thickness of the buffer layer, h Mo1 is the thickness of the bottom electrode layer, h AlN2 is the thickness of the piezoelectric thin film, h Mo2 is the thickness of the circuit layer. When the beam length is 100 μm, the distance of the end of the cantilever beam from the original plane under the action of gravity only is , which is greater than the high resolution of the scanning electron microscope 5.759 nm, and can be measured by the in-line SEM in theory.

[0047] Table 1 L- delta gravity Relationship table

[0048] Preferably, the length L of the cantilever is not less than 300 μm.

[0049] It should be noted that, referring to Figure 8 In the actual manufacturing process, due to the limitations of photolithography, etching or deposition process steps, the pattern edge cannot completely maintain the ideal right angle or sharp shape, but forms a fillet or slope, which is called rounding effect.

[0050] The secondary electron signal of the SEM is sensitive to the surface topography of the sample. When the pattern edge is rounded due to the rounding effect, the signal contrast will be reduced, resulting in blurred edge positioning and affecting the measurement accuracy. When the rounding radius of the pattern edge of the sample is about 250 nm due to the rounding effect, the measurement accuracy of the SEM may be reduced to 25 nm. According to Table 1, when the length of the beam is not less than 300 μm, the distance between the cantilever beam and the original plane can be accurately measured delta gravity At the same time, when the cantilever beam is longer, the displacement of the end thereof can more accurately and sensitively reflect the small changes in stress.

[0051] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0052] In summary, the technical scheme of the present application has the following beneficial technical effects: The structure described in the present application can measure the distance between the cantilever beam and the original plane by in-line SEM side wall ranging in static state, so as to judge the stress state of the cantilever beam, quickly screen out the cantilever beam structure with excessive compression / tension stress leading to device buckling, and realize in-situ online monitoring of residual stress. In dynamic state, the piezoelectric material is used to realize the monitoring of the piezoelectric MEMS process by analyzing the amplitude and resonance frequency of the output electric signal and other information.

Claims

1. A single piezoelectric layer micro-cantilever structure, characterized by, The application relates to a single piezoelectric layer micro-cantilever structure for monitoring a piezoelectric film. The application relates to a single piezoelectric layer micro-cantilever structure for monitoring a piezoelectric film. The driving circuit comprises a driving electrode, a power amplifier and a signal generator which are electrically connected.

2. The single piezoelectric layer micro-cantilever structure according to claim 1, wherein, The monitoring circuit comprises an inductive electrode, a current amplifier and an oscilloscope which are electrically connected. The driving circuit comprises two groups.

3. The single piezoelectric layer micro-cantilever structure according to claim 2, wherein, The inductive electrode is arranged between the driving electrodes of the two groups of driving circuits. The side wall of the reference groove is coplanar with the side wall of the groove, and the width of the reference groove is equal to the gap between the groove and the cantilever.

4. The single piezoelectric layer micro-cantilever structure according to claim 1, wherein, 5. The single piezoelectric layer micro-cantilever structure according to any one of claims 1 to 4 is applied to monitoring a piezoelectric film. S1. A piezoelectric film to be detected is obtained, and a single piezoelectric layer micro-cantilever structure according to any one of claims 1 to 4 is prepared, wherein the piezoelectric film is the piezoelectric film to be detected.

6. A method of detecting a piezoelectric thin film, characterized by S2. The signal generator is started to generate an electric signal, the signal is amplified by the power amplifier and then transmitted to the driving electrode, the piezoelectric film to be detected is driven to convert the electric signal into mechanical vibration. S3. The inductive electrode senses the mechanical vibration and generates an electric signal corresponding to the mechanical vibration, the signal is amplified by the current amplifier and then transmitted to the oscilloscope, parameters are obtained, and whether the piezoelectric film is qualified is determined according to the parameters. S21. The signal generator is started to generate a transient square wave signal, the signal is amplified by the power amplifier and then transmitted to the driving electrode, the piezoelectric film to be detected is driven to convert the electric signal into mechanical vibration. In step S3, the obtained parameters include a peak frequency.

7. The method of detecting a piezoelectric thin film according to claim 6, wherein S22. The signal generator is started to generate an electric signal, the initial frequency, the center frequency and the terminal frequency of the signal generator are adjusted, the signal is amplified by the power amplifier and then transmitted to the driving electrode, the piezoelectric film to be detected is driven to convert the electric signal into mechanical vibration. In step S3, the obtained parameters include a frequency and an amplitude. S10. The top point of the upper surface of one end of the cantilever extending into the groove is recorded as point A, the top point of the upper surface of the reference groove close to point A is recorded as point B, and the single piezoelectric layer micro-cantilever structure is placed on a sample table.

8. The method of detecting a piezoelectric thin film according to claim 6, wherein The length L of the cantilever is not less than 300 microns. ​ ​ 9. A stress self-sensing method of a single piezoelectric layer micro-cantilever structure according to claim 1, wherein, ​ ​ S20. Adjust the tilt angle of the sample stage to θ, and use SEM to vertically project point A onto the inner surface of point B in the groove. Record the projection of point A as point a, and use SEM to measure the horizontal distance between point a and point B. Through formula The offset distance at the end of the cantilever was calculated. ; S30. Calculate the deflection distance of the cantilever tip under the condition of only gravity The calculation formula is shown in equations (1) to (5). （1）， （2）， （3）， （4）， （5）， wherein, is the equivalent bending stiffness, is the distributed load due to gravity, is the cantilever beam length, , , , , is the film thickness, Young's modulus, density, Poisson's ratio, center-to-reference plane distance of the i-th layer, respectively, is the total thickness of the cantilever beam, is the average density, is the overall neutral axis position, is the acceleration due to gravity; S40. The method of any one of S40-S39, wherein the stress state of the single piezoelectric layer microcantilever structure is calculated based on a size relationship of the first and second piezoelectric layers. and the stress state of the single piezoelectric layer microcantilever structure.

10. The stress self-sensing method of a single piezoelectric layer micro-cantilever structure according to claim 9, wherein, ​

Images