Method and device for measuring structural parameters of MEMS cantilever beam

Abstract

The invention discloses a method and device for measuring structural parameters of an MEMS cantilever beam, and the method comprises the steps: placing the MEMS cantilever beam on an objective table of a nanoprobe station, and guaranteeing that the thickness direction of the MEMS cantilever beam is perpendicular to a horizontal plane; measuring the length l and the width b of the MEMS cantilever beam by using a microscope; controlling a micro probe of the nano probe station to descend until the micro probe is in contact with the surface of the MEMS cantilever beam; continuously controlling the micro-probe to descend, and recording the displacement X and the loading stress F of the micro-probe at the same time; carrying out linear fitting by utilizing a preset calculation device displacement X and the loading stress F to obtain the deformation rigidity K of the MEMS cantilever beam; and calculating the thickness h of the MEMS cantilever beam based on the deformation stiffness K, the length l, the width b and the Young modulus E. The measuring method is wide in application range and low in testing cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS processing, and in particular relates to a method and device for measuring structural parameters of a MEMS cantilever beam. Background Art

[0002] MEMS (Micro-Electro-Mechanical Systems) processing technology is an advanced manufacturing technique that integrates mechanical structures and electronic circuits at the micron or even nanometer scale. This technology can construct three-dimensional movable structures on wafers through processes such as semiconductor lithography, thin film deposition, etching, and wafer bonding. Devices manufactured using MEMS processing technology are called MEMS devices. These devices offer advantages such as miniaturization, low power consumption, and low cost, and have been widely used in intelligent driving, medical equipment, geological exploration, and aerospace.

[0003] As a key functional unit in MEMS devices, the accuracy of cantilever beam structural parameters (especially thickness) directly affects device performance. However, due to the inherent precision of MEMS processing, the measured dimensions of the cantilever beam are often difficult to fully match the designed values. Therefore, accurate measurement of cantilever beam thickness has become a key step in achieving precise control of MEMS device performance. Currently, cantilever beam thickness measurement mainly relies on the following three methods: The first method involves cross-sectional observation using a scanning electron microscope (SEM). This method involves sealing the sample with epoxy resin and grinding it to the desired cross-section using a grinder. The SEM's high resolution allows for direct observation and measurement of the cantilever thickness at that cross-section. This method offers nanometer-level accuracy and intuitiveness, making it a relatively common method. However, its core drawback is that it is a destructive measurement, which is not only time-consuming (due to cumbersome sample preparation), but also generally unusable after measurement. Furthermore, the high cost of SEM equipment limits its economic viability for large-scale application.

[0004] The second method is three-dimensional X-ray (3D X-ray) observation: This method emits X-rays at the sample, capturing a two-dimensional image based on the energy attenuation of the rays as they penetrate the sample. Combined with a high-precision rotating platform and a three-dimensional reconstruction algorithm, a three-dimensional model of the sample is constructed, enabling intuitive measurement of cantilever thickness. Its non-contact measurement feature is a major advantage. However, its fatal drawback is that data acquisition and reconstruction are extremely time-consuming (often taking several hours), and the equipment (3D X-ray microscope) is extremely expensive, resulting in high measurement costs and failing to meet the requirements for efficient and economical measurement.

[0005] The third method is the resonant frequency estimation method. This method is based on the inherent relationship between a cantilever's undamped resonant frequency and its structural dimensions (including thickness) and material parameters. After measuring the cantilever's resonant frequency, its thickness can be estimated. This method has a certain theoretical basis. However, its implementation requires a complex resonant frequency measurement system. More importantly, to ensure accurate measurement results (and eliminate the effects of atmospheric damping), the cantilever must be measured in a high vacuum environment, which significantly increases the complexity of the measurement system and the difficulty of practical operation.

[0006] Therefore, how to provide a method for measuring the structural parameters of a MEMS cantilever beam with a wide range of applications, low measurement cost and high accuracy is one of the technical problems that those skilled in the art urgently need to solve. Summary of the Invention

[0007] The main purpose of the present invention is to overcome the shortcomings and deficiencies of the existing technology and provide a method and device for measuring the structural parameters of a MEMS cantilever beam. The present invention measures the length and width of the MEMS cantilever beam through a microscope, and then uses a microprobe to obtain the displacement and loading stress of the MEMS cantilever beam during the bending deformation process. The deformation stiffness is calculated in combination with a formula, and then the thickness of the MEMS cantilever beam is solved. This measurement method has a wide range of applications and low testing costs.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for measuring structural parameters of a MEMS cantilever beam, comprising the following steps: S1. Place the MEMS cantilever beam on the stage of the nanoprobe station, ensuring that the thickness direction of the MEMS cantilever beam is perpendicular to the horizontal plane; S2. Measure the length of the MEMS cantilever using a microscope l and width b ; S3, controlling the microprobe of the nanoprobe station to descend until it contacts the surface of the MEMS cantilever beam; S4, continue to control the microprobe to descend and record the displacement of the microprobe X and loading stress F ; S5. Using the preset calculation device displacement X and loading stress F Perform linear fitting to obtain the deformation stiffness of the MEMS cantilever beam K ; S5, based on deformation stiffness K ,length l ,width b and Young's modulus E , through the formula Calculate the thickness of the MEMS cantilever beam h .

[0009] As a preferred technical solution, in step S3, the landing point of the micro probe is set at the end center point of the MEMS cantilever beam.

[0010] As a preferred technical solution, in step S3, before the microprobe contacts the cantilever beam surface, a contact determination stiffness is set to 40-60 N / m to determine whether the microprobe contacts the MEMS cantilever beam surface.

[0011] As a preferred technical solution, in step S4, the microprobe is kept still for 5 to 15 seconds after contacting the surface, and then continues to press down by 800 to 1200 nm.

[0012] As a preferred technical solution, in step S5, the linear fitting is calculated based on the following formula: F = KX + ε ; in, K is the deformation stiffness of the MEMS cantilever beam, ε This is the overall offset caused by the measurement error of the nanoprobe station. This offset value is not involved in subsequent data processing.

[0013] As a preferred technical solution, in step S5, the linear fitting is automatically completed by a computing device, and the goodness of fit R 2 ≥0.95.

[0014] In a second aspect, the present invention provides a device for measuring structural parameters of a MEMS cantilever beam, which is used to implement the method for measuring structural parameters of a MEMS cantilever beam, and is characterized by comprising: Nanoprobe station, used to fix the MEMS cantilever sample and control the three-dimensional movement of the microprobe; Microscope equipped with an optical ruler for measuring the length of the MEMS cantilever l and width b ; A host computer is configured to control the movement of the microprobe of the nanoprobe station and collect displacement and loading stress data; a calculation device configured to fit the deformation stiffness based on the displacement and loading stress data and calculate the thickness; The device realizes the measurement of the thickness of the MEMS cantilever beam through the coordinated operation of the host computer, microscope, nanoprobe station and computing device.

[0015] As a preferred technical solution, the microscope is an optical microscope, whose field of view coincides with the working area of ​​the microprobe, and the measuring position is switched by translation of the stage.

[0016] As a preferred technical solution, the stage of the nanoprobe station is provided with a tilt adjustment mechanism to ensure that the thickness direction of the cantilever beam is perpendicular to the horizontal plane.

[0017] As a preferred technical solution, the computing device is integrated into the host computer, and the device is configured to be based on the formula Calculate the thickness of the MEMS cantilever beam h .

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: This technology proposes a testing device consisting of a host computer, a microscope, a nanoprobe station, and a computing device. Based on the mathematical relationship between bending deformation stiffness and thickness, it measures the structural parameters of a MEMS cantilever beam. This method addresses the high cost of observational methods, which generally require expensive specialized equipment such as SEM and 3D X-rays, and the limited applicability of resonant frequency estimation methods, which require vacuum packaging.

[0019] Because the measurement method proposed in this invention directly utilizes the mathematical relationship between the bending deformation stiffness and thickness of a MEMS cantilever beam, it can be applied to all types of MEMS cantilever beams. Furthermore, this measurement method only requires the testing equipment to be able to record the displacement and loading stress of the microprobe online, resulting in relatively low testing costs. Therefore, this measurement method has a wide range of applications, low testing costs, and high operational feasibility. This method can help MEMS device designers accurately measure the structural parameters of MEMS cantilever beams, thereby improving processing techniques and optimizing the performance consistency of MEMS devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 Schematic diagram of the structure of the MEMS cantilever beam; Figure 2 Schematic diagram of the structure of a device for measuring structural parameters of a MEMS cantilever beam according to an embodiment of the present invention; Figure 3 A schematic diagram of the structure of linear fitting according to an embodiment of the present invention; Figure 4 This is a flow chart of a method for measuring structural parameters of a MEMS cantilever beam according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0023] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0024] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. The specification and claims do not distinguish components based on differences in name, but rather on differences in their functions. For example, the term "including" used throughout the specification and claims is an open-ended term and should be interpreted as "including but not limited to"; "substantially" means that those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect.

[0025] MEMS cantilever beams are a key sensitive structure in MEMS devices. Their deformation response characteristics make them widely used to sense changes in external physical quantities. For example, a MEMS accelerometer has two anchor points on the substrate of the sensitive chip, connected by a MEMS microbeam. A proof mass is suspended in the center of the MEMS beam. When external linear acceleration occurs, the proof mass is subjected to inertial forces, causing the MEMS cantilever beam to deform. By measuring the deformation displacement of the proof mass, the magnitude of the external linear acceleration can be determined.

[0026] The structural dimensions of a MEMS cantilever beam can significantly affect its deformation characteristics, which in turn directly impact the performance of the MEMS device. Therefore, accurate evaluation of MEMS device performance requires measurement of the structural dimensions of the MEMS cantilever beam. Because MEMS cantilevers are typically fabricated using processes such as semiconductor photolithography and (wet / dry) etching, the cross-section of the MEMS cantilever beam is often perpendicular to the top surface of the wafer. While the length and width of a MEMS cantilever beam can be measured directly using an electron microscope, the thickness of the MEMS cantilever beam is difficult to directly measure.

[0027] This paper designs a method for measuring the thickness of a MEMS cantilever beam, offering wide applicability, low testing costs, and high accuracy. This method primarily utilizes hardware such as a host computer, microscope, nanoprobe station, and computing device. Using a microprobe on the nanoprobe station, the paper acquires the strain-stress curve of the MEMS cantilever beam and calculates its thickness.

[0028] like Figure 2 FIG. 1 is a schematic diagram of a device for measuring the structural parameters of a MEMS cantilever beam according to the present embodiment, including a host computer, a microscope, a nanometer probe station, and a computing device; The nanoprobe station is used to fix the MEMS cantilever beam sample and control the three-dimensional movement of the microprobe; specifically, the nanoprobe station is used to build a test environment for the test sample and collect test data such as the displacement and loading stress of the microprobe.

[0029] The microscope is equipped with an optical ruler for measuring the length of the MEMS cantilever beam. l and width b ; When measuring, the length and width of the MEMS cantilever beam are measured directly.

[0030] A host computer is configured to control the movement of the microprobe of the nanoprobe station and collect displacement and loading stress data; A computing device configured to fit the deformation stiffness based on the displacement and loading stress data and calculate the thickness; specifically, the computing device is used to fit the loading stress-deformation curve of the MEMS cantilever beam to obtain the deformation stiffness, and calculate the thickness of the MEMS cantilever beam based on the length and width measured by the microscope The device realizes the measurement of the thickness of the MEMS cantilever beam through the coordinated operation of the host computer, microscope, nanoprobe station and computing device.

[0031] During the test, the test sample is first fixed on the stage of the nanoprobe station, and the length of the MEMS cantilever is measured using an optical microscope. l and width b Then, the landing point of the microprobe is set at the midpoint of the end of the MEMS cantilever beam, and the microprobe is controlled to descend vertically until it contacts the MEMS cantilever beam. The microprobe then continues to press down, and the upper computer records the displacement of the microprobe during the pressing process after it contacts the MEMS cantilever beam. and the corresponding loading stress , at this time the two sets of data should have good linearity, such as Figure 3 shown.

[0032] By using a computing device to perform linear fitting on the deformation displacement and loading stress of the microprobe, the following mathematical model can be obtained: F = KX + ε ; (1) In formula (1), K is the deformation stiffness of the MEMS cantilever beam; ε This is the overall offset caused by the measurement error of the nanoprobe station. This value is not involved in subsequent data processing.

[0033] Since the cross section of the MEMS cantilever beam is generally rectangular, its moment of inertia can be calculated by formula (2). Then, the deformation displacement of the MEMS cantilever beam when loaded with stress F can be calculated based on formula (3). The calculation formula is as follows: ; (2) ; (3) Therefore, the thickness of the MEMS cantilever beam can be obtained by formula (4): ; (4) in, l、b They are the length and width of the MEMS cantilever, which can be directly measured using a microscope; K is the deformation stiffness of the MEMS cantilever beam, obtained by fitting formula (1); E is the Young's modulus of the MEMS cantilever beam, which can be obtained by looking up the material parameter table.

[0034] The basic principle of the MEMS cantilever thickness measurement in the present invention is: the host computer controls the micro-probe of the nanoprobe station so that it contacts the surface of the MEMS cantilever and then continues to move slowly, forcing the MEMS cantilever to bend and deform. The host computer obtains the displacement and loading stress of the micro-probe during the bending and deformation of the MEMS cantilever, and then uses a computing device to fit the deformation stiffness of the MEMS cantilever. Finally, the thickness of the MEMS cantilever is calculated based on a theoretical model between the deformation stiffness of the MEMS cantilever and the length, width, and thickness of the MEMS cantilever.

[0035] like Figure 4 As shown, in another embodiment of the present invention, a method for measuring the structural parameters of a MEMS cantilever beam based on an apparatus for measuring the structural parameters of a MEMS cantilever beam includes the following steps: S1. Place the MEMS cantilever beam on the stage of the nanoprobe station, ensuring that the thickness direction of the MEMS cantilever beam is perpendicular to the horizontal plane; S2. Measure the length of the MEMS cantilever using a microscope l and width b ; S3, controlling the microprobe of the nanoprobe station to descend until it contacts the surface of the MEMS cantilever beam; Furthermore, the landing point of the micro probe is set at the center point of the end of the MEMS cantilever beam.

[0036] Furthermore, before the microprobe contacts the cantilever beam surface, a contact determination stiffness is set to 40-60 N / m to determine whether the microprobe contacts the MEMS cantilever beam surface.

[0037] S4, continue to control the microprobe to descend and record the displacement of the microprobe X and loading stress F ; Furthermore, the microprobe remained stationary for 5 to 15 seconds after contacting the surface, and then continued to press down by 800 to 1200 nm.

[0038] S5. Using the preset calculation device displacement X and loading stress F Perform linear fitting to obtain the deformation stiffness of the MEMS cantilever beam K ; Furthermore, the linear fitting is calculated based on the following formula: F = KX + ε ; in, K is the deformation stiffness of the MEMS cantilever beam, ε This is the overall offset caused by the measurement error of the nanoprobe station. This offset value is not involved in subsequent data processing.

[0039] S5, based on deformation stiffness K ,length l ,width b and Young's modulus E , through the formula Calculate the thickness of the MEMS cantilever beam h .

[0040] Furthermore, the linear fitting is automatically completed by a computing device, and the goodness of fit R 2 ≥0.95.

[0041] In a more specific application scenario, the thickness of a MEMS cantilever beam is measured using the above-mentioned measuring device and method, which specifically includes the following steps: 1. Make the thickness direction of the MEMS cantilever beam perpendicular to the horizontal plane and place it on the stage of the nanoprobe station; 2. Turn on the nanoprobe station and move the MEMS cantilever beam under the microscope through the host computer; 3. Use the optical ruler of the microscope to measure the length of the MEMS cantilever beam l and width b ; 4. Control the MEMS cantilever beam to move under the microprobe and set the contact stiffness (determining whether it contacts the sample) to 50N / m; 5. Control the microprobe to descend, stop after touching the surface of the MEMS cantilever, and remain stationary for 10 seconds; 6. Control the microprobe to continue to descend 1000 nm and record the displacement X and loading stress F during the descent of the microprobe; 7. Based on formula (1), linear fitting is performed on the displacement X and the loading stress F to obtain the stiffness K of the MEMS cantilever beam; 8. Based on formula (4), calculate the thickness of the MEMS cantilever beam.

[0042] This invention proposes a device for measuring the structural parameters of a MEMS cantilever beam, consisting of a host computer, a microscope, a nanoprobe station, and a computing device. This device is then used to measure these parameters. Its core innovation lies in leveraging the inherent mathematical relationship between the bending deformation stiffness and thickness of a MEMS cantilever beam to accurately measure its structural parameters. This method effectively addresses the shortcomings of existing measurement technologies: traditional observation methods (such as SEM or 3D X-ray) are expensive, resulting in high testing costs, while estimation methods based on resonant frequency require vacuum packaging, limiting their applicability. Compared to these methods, the present invention offers significant advantages: First, because it directly relies on the bending stiffness-thickness relationship of the cantilever beam, this method is universal and applicable to all types of MEMS cantilever beams. Second, its testing equipment requirements are relatively simple, requiring only the ability to online record the microprobe displacement and applied stress, significantly reducing testing costs. Consequently, this measurement method offers the combined advantages of wide applicability, low testing costs, and high operational feasibility. The present invention helps MEMS device designers to accurately obtain key structural parameters of the cantilever beam, thereby optimizing the processing technology and ultimately improving the performance consistency of the MEMS device.

[0043] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0044] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for measuring structural parameters of a MEMS cantilever beam, characterized in that: The following steps are involved: S1. Place the MEMS cantilever beam on the stage of the nanoprobe station, ensuring that the thickness direction of the MEMS cantilever beam is perpendicular to the horizontal plane; S2. Measure the length of the MEMS cantilever using a microscope l and width b ; S3, controlling the microprobe of the nanoprobe station to descend until it contacts the surface of the MEMS cantilever beam; S4, continue to control the microprobe to descend and record the displacement of the microprobe X and loading stress F ; S5. Using the preset calculation device displacement X and loading stress F Perform linear fitting to obtain the deformation stiffness of the MEMS cantilever beam K ; S5, based on deformation stiffness K ,length l ,width b and Young's modulus E , through the formula Calculate the thickness of the MEMS cantilever beam h .

2. The method for measuring the structural parameters of a MEMS cantilever beam according to claim 1, wherein: In step S3 , the landing point of the micro probe is set at the center point of the end of the MEMS cantilever beam.

3. The method for measuring the structural parameters of a MEMS cantilever beam according to claim 1, wherein: In step S3, before the microprobe contacts the cantilever beam surface, the contact determination stiffness is set to 40-60 N / m to determine whether the microprobe contacts the MEMS cantilever beam surface.

4. The method for measuring structural parameters of a MEMS cantilever beam according to claim 1, wherein: In step S4, the microprobe is kept still for 5 to 15 seconds after contacting the surface, and then pressed down by 800 to 1200 nm.

5. The method for measuring structural parameters of a MEMS cantilever beam according to claim 1, wherein: In step S5, the linear fitting is calculated based on the following formula: F = KX + ε ； in, K is the deformation stiffness of the MEMS cantilever beam, ε This is the overall offset caused by the measurement error of the nanoprobe station. The offset value is not involved in subsequent data processing.

6. The method for measuring structural parameters of a MEMS cantilever beam according to claim 1, characterized in that: In step S5, the linear fitting is automatically completed by the computing device, and the goodness of fit R 2 ≥0.

95.

7. A device for measuring structural parameters of a MEMS cantilever beam, used to implement a method for measuring structural parameters of a MEMS cantilever beam according to any one of claims 1 to 6, characterized in that: include: Nanoprobe station, used to fix the MEMS cantilever sample and control the three-dimensional movement of the microprobe; Microscope equipped with an optical ruler for measuring the length of the MEMS cantilever l and width b ; A host computer is configured to control the movement of the microprobe of the nanoprobe station and collect displacement and loading stress data; a calculation device configured to fit the deformation stiffness based on the displacement and loading stress data and calculate the thickness; The device realizes the measurement of the thickness of the MEMS cantilever beam through the coordinated operation of the host computer, microscope, nanoprobe station and computing device.

8. The device for measuring structural parameters of a MEMS cantilever beam according to claim 7, characterized in that: The microscope is an optical microscope, whose field of view coincides with the working area of ​​the microprobe, and the measuring position is switched by translation of the stage.

9. The device for measuring structural parameters of a MEMS cantilever beam according to claim 7, characterized in that: The loading platform of the nanoprobe station is provided with an inclination adjustment mechanism to ensure that the thickness direction of the cantilever beam is perpendicular to the horizontal plane.

10. The device for measuring structural parameters of a MEMS cantilever beam according to claim 7, characterized in that: The computing device is integrated into the host computer and is configured to be based on the formula Calculate the thickness of the MEMS cantilever beam h .

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