CN101339816A - Two-dimensional micro-motion platform for atomic force microscope and micro-mechanical parameter testing method - Google Patents

Abstract

The invention relates to a two-dimensional micro-motion platform for an atomic force microscope and a method for measuring mechanical parameters. The moving range of the two-dimensional micro-motion platform in the horizontal direction is 3 multiplied by 3 square millimeters, and the maximum scanning displacement of the PZT scanning tube is 20 micrometers. The improved AFM microscope with two-dimensional micro-motion platform can be used for testing mechanical parameters of fixed points on a microstructure, and a good consistency result can be obtained by performing a mechanical-displacement function test and a micro-area continuous elastic coefficient test point by point.

Description

Two-dimensional micro-motion platform and micro-mechanical parameter testing method for atomic force microscope

technical field

The invention relates to a two-dimensional micro-movement platform for an atomic force microscope and a testing method for micro-mechanical parameters to detect and analyze the mechanical parameters of micro-structures produced by micro-processing, and belongs to the field of micro-mechanical testing and analysis.

Background technique

All kinds of tiny devices manufactured by MEMS are composed of basic structural units such as micro-cantilever beams and thin films. These tiny structural units can sense external vibrations, heat, etc. and transmit them as electrical or other forms of signals. go out. External effects such as vibration and heat will cause deformation of the microstructure, and the magnitude of the deformation determines the sensitivity and range of the device and other parameters. Therefore, in order to obtain the parameters required by the design, the manufacturing control process is very important. At the same time, the detection of the microstructure, especially the elastic coefficient of the microcantilever is indispensable, which directly provides extremely necessary data for design and processing. Generally speaking, the size of structural units such as micro-cantilever beams ranges from nanometers to hundreds of microns in length, and the prepared microstructures have three-dimensional structural characteristics. It is an important research content to carry out basic mechanical measurement of microstructure, including static and dynamic characteristic parameters such as elastic coefficient, resonance frequency, Young's modulus, fatigue characteristics and so on. The mechanical properties of microstructures have become a core content that people are most concerned about on the road to the practical application of micro-nano systems. At present, there are some equipment and instruments that can be used to characterize the mechanical properties of microstructures. In various microanalysis test systems, such as atomic force microscopes, nanoindenters, optical interferometers and other equipment have been used in the testing of mechanical properties of microstructures. , often requires equipment capable of giving nanometer-scale resolution accuracy. In a nanoindenter, the device can accurately give force from micronewtons to millinewtons and displacement in nanonewtons, but the accuracy is not high under nanonewton loads (nN) [Holbery J D and Eden V L, Acomparison of scanning microscopy cantilever force constants determined using ananoindentation testing apparatus. Journal of Micromechanics and Microengineering. 2000, 10: 85-92.]. The usual optical detection method has a large field of view but can only perform static testing and cannot actively apply force loads [O'Mahony C, Hill M, Brunet M, DuaneR and Mathewson A 2003 Characterization of micromechanical structures using white-light interferometry Meas, Sci. Technol. 14 1807-14]. The current test method based on atomic force microscope (AFM) can give nano-Newton nanoscale resolution accuracy. Using the parameters such as the displacement and resonance frequency that can be accurately given, and using the known structural parameters of the cantilever beam, etc., the elastic coefficient of the cantilever beam and other structures can be obtained [Comella B T, Scanlon M R, The determination of the elastic modulus of Microcantilever beams using atomic force microscopy, Journal of Materials Science, 2000, 35: 567-572].

The atomic force microscope is currently a widely used detection device for surface structure parameters. It has high lateral and longitudinal displacement resolution, and the longitudinal resolution can reach 0.01nm; through the Z-axis vertical drive mechanism piezoelectric ceramic PZT (PbZrTiO ₃ , lead zirconate titanate ceramic) scanning tube can apply a small force load to the scanning probe. When the microstructure to be tested is placed on the platform and placed under the scanning probe, the corresponding mechanical quantity can be measured through the elastic deformation of the contact between the probe and the microstructure. The atomic force microscope is an instrument with relatively high force and displacement resolution in scientific research at the micro-nano scale. Researchers have been using some of its functions for testing, but they cannot directly and effectively perform characterization and comprehensive analysis, and cannot automatically extract mechanical forces. parameter. Therefore, special test equipment and corresponding special test analysis software control system are required.

At present, the micro-nano-scale mechanical testing platform based on the atomic force microscope and the corresponding testing software system for in-situ extraction of mechanical parameters have always been blank, and research and development of mechanical-related testing systems based on atomic force microscopy has become a development trend. A more important problem is that the scanning area of the atomic force microscope is usually only on the scale of a few square microns, such as the atomic force microscope of DI company, the scanning area of the scanning tube PZT is about 5×5 square microns, and the observed surface is usually two-dimensional of. However, microstructure devices are generally tens, hundreds or even thousands of microns. Once the sample is placed on the test platform, the sample can only be moved manually to position the sample under the microprobe, which greatly limits its application Applications in mechanical testing of microstructures. Japan's Seiko II, SPA 400 system has a micro-motion platform structure, which can move between millimeters and centimeters. It is characterized in that the mobile platform is placed on the probe, that is, when the micro-motion platform moves, the probe moves with it. This can have a large range of moving space, which is convenient and practical, but the corresponding system only includes conventional scanning testing and surface analysis, without corresponding mechanical testing analysis and automatic data extraction functions. Therefore, the present invention attempts to develop a mobile platform and a micromechanical testing method based on the atomic force microscope for microstructure testing, so that it can complete larger-scale measurements while having higher micro-nano scale resolution accuracy.

Contents of the invention

The purpose of the present invention is to provide a two-dimensional micro-motion platform based on atomic force microscope and a micromechanical testing method. The present invention focuses on the development of a platform testing system based on atomic force microscopy and related mechanical testing methods suitable for micro-nano structure testing. The purpose of the present invention is to develop a mechanical testing micro-motion platform for micro-nano structures on the basis of the AJ-III model atomic force microscope produced by Shanghai Aijian Nano Technology Development Co., Ltd. Horizontal shift function in magnitude. Therefore, the present invention designs a two-dimensional micro-motion platform (2 in FIG. 1 ) on the hardware, so that it has a relatively large lateral displacement, so as to ensure that the micro-nano structure device can be easily moved and tested under the atomic force microscope. Fig. 2 is a schematic diagram of the structure of the two-dimensional micro-motion platform and the PZT linkage system of the scanning tube. In this way, the precise positioning requirements of the microstructure sample under the probe on the micro-movement platform can be adjusted conveniently, while the probe remains stationary. The test method established based on the main force-displacement curve and other test functions in the atomic force microscope is used to directly perform mechanical measurement and evaluation of microstructures and microdevices, directly extract the mechanical quantities of microstructures, and obtain elasticity for structures such as cantilever beams. Coefficient, Young's modulus, stress and other mechanical parameters. In this way, it is convenient, automatic and effective to test and analyze the mechanical properties of the microstructure and extract the parameters. It can implement the test functions such as the extraction of mechanical parameters at fixed points, the measurement of multi-point micro-area resolution, and the acquisition of elastic coefficients under single-line continuous scanning. The test has good consistency and usability, and can conveniently extract mechanical quantities. The developed algorithm for micro-area mechanical properties and parameter extraction has been solidified in the original test system to achieve precise analysis of micro-area mechanical properties under micro-force and micro-displacement, and has been applied on the MEMS processing platform.

The original equipment includes base visible CCD (coupled charge device, charge-coupled device) system, PZT scanning tube and corresponding optical detection system. The scanning tube PZT can move in the three directions of X, Y and Z under the voltage drive. The maximum scanning displacement of the PZT scanning tube is 5 microns. Because the original scanning tube PZT is fixed on the base, the base cannot be placed on the Move in the horizontal direction, therefore, the original PZT scanning tube system can only move, observe and scan a small area. The base includes an automatic motor screw fixing slot (4 in Figure 2) and a manual needle insertion screw fixing slot (3 in Figure 2). The cantilever beam probe for scanning detection is installed in the probe fixture, and the laser light is reflected on the cantilever beam. into the optical detector. The two-dimensional micro-moving platform provided by the present invention is made of steel, and the opening in the center is used to install the PZT scanning tube (7 in Fig. 2); wherein on the horizontal X and Y positions perpendicular to each other, there are two X, Y Direction adjustment knobs (5, 6 in Figure 1), the two knobs are connected to two driving rods (not visible outside), and the two driving rods are fixedly connected to the PZT scanning tube. When the X and Y adjustment knobs are rotated, the knobs drive the connecting rod to drive the scanning tube to move in the horizontal direction. Part of the structural device of the optical feedback principle and the micro-force testing principle is shown in Figure 3.

The manufactured two-dimensional micro-movement platform has been debugged, and its movement range in the horizontal direction can reach 3×3 square millimeters, which meets the test of the general micro-device structure size. A standard scanning test was carried out on the two-dimensional micro-motion platform installed on the AFM system, including the detection of gratings and DNA molecules, to investigate resolution, drift, etc. The resolution of the system hardware can be achieved by scanning the grating or scanning the DNA sample. The system can repeatedly obtain DNA images, and the resolution meets the requirements of the original AFM test; the stability of the system can be achieved by scanning the fixed features of the sample surface for a long time. The degree of drift of the point image, within 40 minutes of the scanning interval, the feature point drifts about 0.5 microns in the X direction and less than 0.1 microns in the Y direction, which indicates that the system is very stable. Tests show that the introduction of the mobile platform did not cause system instability. The processed micro-motion platform system has good anti-seismic effect, and the system has good stability and repeatability after passing the test. That is to say, the performance of the AFM system is not affected after the system is installed with a two-dimensional micro-mobility platform.

In terms of testing, based on the original operating system platform, a mechanical characteristic test control program is designed, which can extract mechanical parameters in situ. It mainly includes mechanical test functions in the following aspects: mechanical parameter test of fixed points on the microstructure; continuous test analysis of points in the micro-area and mechanical tests of continuous points in the micro-area, etc., to realize the elastic constant k, Young's modulus The extraction of parameters such as quantity E. The main data involved include: the elastic coefficient of the reference cantilever beam, the length, width and thickness dimensions of the tested cantilever and the position parameters for selecting the length on the cantilever beam. The reference cantilever fixed point on the hard substrate, the slope of the point-by-point force curve of the micro-area, and the constant force and scanning length (X, Y) and deformation data in the Z direction under continuous point scanning in the micro-area; The fixed point on the beam and the slope of the point-by-point force curve in the micro-area, as well as the constant force and scan length (X, Y) at continuous points in the micro-area, and the deformation data of the cantilever beam in the Z direction. From this, data such as the Young's modulus of the fixed point of the tested cantilever beam, the point-by-point elastic coefficient in the micro-area, the elastic coefficient and deformation of the continuous points in the micro-area are obtained.

The main mechanical testing methods of the system are briefly described as follows: Based on the force-displacement control function of the scanning tube PZT and the cantilever in the atomic force microscope, the reference cantilever with known elastic coefficient is used to apply a force load to the tested cantilever to perform cantilever compression. In the contact test of the beam, the mechanical parameters of the unknown cantilever beam are obtained from the data such as the deformation of the cantilever beam and the applied force load. The test is completed in two steps. Firstly, the known reference cantilever beam with elastic coefficient k _ref is brought into contact with a smooth surface hardness or a sample surface with a large elastic coefficient (such as a flat silicon surface, called a hard substrate). Obtain its total deformation δ _tot , and then contact the reference cantilever with the cantilever with unknown elastic coefficient k (equivalent to a soft structure) to obtain the deformation δ _test data on the unknown cantilever; considering the cantilever in the atomic force microscope Placed at a certain inclination angle θ, θ is the angle between two cantilever beams, as shown in Figure 3(a)(b), where (a) is the test process of a cantilever beam on a hard substrate, ( b) is the test process of one cantilever beam on another cantilever beam. The PSD in the figure is a four-quadrant position sensitive detector. After appropriate derivation, the elastic coefficient of the unknown cantilever beam can be obtained as:

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}\frac{{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; test</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}{{\text{<span class="notranslate"> \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; tot</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; test</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the above formula, k is the elastic coefficient of the unknown cantilever beam to be tested, k _ref is the elastic coefficient of the known cantilever beam, δ _tot is the total deformation of the reference cantilever, and δ _test is the deformation on the tested cantilever ,

For a cantilever beam with thickness t, width w, and length L, the relationship between the elastic coefficient in the normal direction, structural parameters and Young's modulus E is:

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="Ew\; t"\; filenames="A20081004151700141.png"\; state="\{\{state\}\}">Ew</figure-callout></span><figure-callout\; id="3"\; label="Ew\; t"\; filenames="A20081004151700141.png"\; state="\{\{state\}\}">\; </figure-callout>}{\mathrm{<span\; class="notranslate">\; </span>}}^{}{\mathrm{<span\; class="notranslate">t</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}^{\text{<span class="notranslate"> 3</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In general, when a force load ΔF is applied to the cantilever beam (the differential force ΔF is the magnitude of the applied force, which is the difference between two different forces), the cantilever beam will deform ΔZ in the normal Z direction, and ΔZ can be called differential Displacement, depending on the position on the cantilever beam, when the same load is applied, ΔZ is different. In the elastic range, the elastic coefficient is expressed as:

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;F</span>}}{\text{<span class="notranslate"> \&Delta;z</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Specific implementation steps:

The original AJ-III type test system does not have the function of horizontal movement. According to the existing AJ-III type structure, the scheme of installing the scanning tube on the mobile platform is adopted, which is an update to the original equipment system. The scanning tube is moved by the moving platform to achieve the purpose of accurately moving the sample on the scanning tube on the XY plane. The structure diagram of the designed XY plane micro-motion platform is shown in Figure 1. It mainly includes the two-dimensional micro-motion platform 2 fixed on the base, and two screw rods perpendicular to each other for connecting and driving the two-dimensional micro-motion platform. The two screw rods are controlled by two corresponding adjustment knobs (5 in Fig. 1). and 6), turn the screw knob to move the platform horizontally in the X and Y directions. Both the two-dimensional micro-motion platform and the base are made of steel. Fix the PZT scanning tube 7 (7 in FIG. 2 ) to the central hole of the two-dimensional micro-motion platform with epoxy glue, and then fix the two-dimensional micro-motion platform containing the PZT scanning tube to the original AFM system. In this way, when the screw knob is rotated, the screw knob drives the connecting rod to drive the scanning tube to move in the horizontal direction to obtain a large range of movement. The movement displacement of the micro-motion platform in the X and Y directions is 3 mm, and the PZT scanning tube The maximum scanning displacement is 20 microns to ensure that the cantilever beam probe can move in a large range on the microstructure. Both manual needle entry and motor needle entry control screw slots included in the original structure are installed at the lower part of the base, and a vibration-reducing device is also included under the base to avoid vibration interference during horizontal displacement and needle insertion. Figure 4 is the micro-motion platform with PZT installed.

For the AFM system equipped with a two-dimensional micro-motion platform, the performance of resolution, drift and positioning are mainly tested. On the micron scale, the reference cantilever probe can be successfully positioned at a specific location on the cantilever. The resolution of the system hardware can be achieved by scanning the raster or scanning the DNA sample. The test results show that the system can repeatedly obtain DNA images, which meets the requirements for use. The stability of the system can be tested by testing the drift degree of the image of fixed feature points on the surface of the sample during long-term scanning. In the scanning range of 10 microns × 10 microns, the scanning interval is 40 minutes. The X-direction drift of the feature points is about 0.5 microns, and the Y-direction drift is less than 0.1 microns, the results show that the system is very stable.

Before testing, place the sample on the PZT surface containing the micro-motion platform, and then adjust the two-dimensional micro-motion platform under the view of the visible CCD to move the reference cantilever beam probe to the micro-cantilever beam under test. Once selected, mechanical testing can be performed.

The mechanical parameter test mainly includes the following aspects: the mechanical parameter test of the fixed point on the microstructure; the continuous test analysis of each point in the micro-area and the mechanical test of each continuous point in the micro-area, etc., to realize the elastic constant k, Young's modulus Extraction of parameters such as E. The main data parameters involved are as follows. The main parameters input include: the elastic coefficient of the reference cantilever beam and the position parameters for selecting the length on the cantilever beam, and the length, width and thickness dimensions of the tested cantilever. The data for the implementation of the test include: the reference cantilever fixed point on the hard substrate, the slope of the point-by-point force curve of the micro-area, and the constant force and scanning length (X, Y) and deformation data in the Z direction under continuous point scanning in the micro-area; The slope of the cantilever beam at the fixed point on the tested cantilever beam and the point-by-point force curve in the micro-area, as well as the constant force and scan length (X, Y) at continuous points in the micro-area, and the deformation data of the cantilever beam in the Z direction. The output data include: parameters such as Young's modulus of the fixed point of the tested cantilever beam, point-by-point elastic coefficient in the micro-area, elastic coefficient and deformation of continuous points in the micro-area, etc.

The mechanical parameter test at a fixed point on the microstructure is actually a single point single force curve test. The test process is shown in Figure 4. First, use a reference cantilever probe with known elastic coefficient to conduct the first force-displacement curve test on a hard substrate to obtain its slope data; then, on the cantilever to be tested, under the observation of the CCD field of view, move the two-dimensional micro Move the platform, select the position to be tested, place the reference cantilever on the selected position on the micro-cantilever to be tested, and perform the second force-displacement curve test to obtain the corresponding slope. Given the elastic coefficient of the reference cantilever beam, use the formula (1) to calculate the elastic coefficient of the cantilever beam to be tested; given the structural parameters of the cantilever beam to be tested, then directly obtain the unknown The Young's modulus of the cantilever beam and the stress at the root of the cantilever beam, etc.

The point-by-point force-displacement function test in the micro-area is to obtain the force resolution of different points on the micro-nano scale in a certain micro-area in the micro-structure. The automatic mobile measurement avoids the error caused by the inaccurate positioning of manual measurement. First select the scanning area, and then set several points to be tested. The basic sequence of operations is the same as for fixed point. Then execute the force-displacement test and perform point-by-point automatic testing to obtain point-by-point force-curve data on the cantilever beam, extract its slope data, and calculate according to the given formula (1). After testing and calculation, the elastic coefficient corresponding to each position point is obtained.

The micro-area continuous elastic coefficient test is actually a reference to the cantilever beam probe to analyze and test the continuous elastic coefficient in a small area on the tested cantilever beam. It is a single-line force scanning method. The test process is shown in Figure 6. First select an area on the hard base, then set the force load and scan size, perform continuous scanning of the reference cantilever beam on the hard base, and obtain the scanning position under constant force (the X and Y directions of the cantilever beam, as shown in the internal coordinates of Figure 3) , Z-direction deformation data; then under the CCD field of view and the operation of the micro-motion platform, place the reference cantilever beam in the micro-area on the cantilever beam to be tested, set several force loads of different levels and the same scan size, and perform the scan test. The program automatically changes the load (differential force) to apply the force to the cantilever beam, so that the displacement change (deformation) of the cantilever beam under different loads can be obtained. According to formula (3), the differential force and displacement can be obtained in the cantilever beam The relationship between the elastic coefficient of the microstructure and the scanning length in the direction of the scanning length. Figure 8 is a test result.

Description of drawings

Figure 1, the structure diagram of the 2D mobile platform

Figure 2, Schematic diagram of the structure of the two-dimensional micro-motion platform and the PZT linkage system;

Figure 3, the probe-based mechanical testing method under the atomic force microscope, where (a) is a deformation test of a probe on a hard substrate, and (b) is a deformation test of this probe on another cantilever beam;

Figure 4, Fixed-point test flow.

Figure 5, micro-area point-by-point force resolution test process.

Fig. 6, the micro-area continuous point single-line scanning process.

Fig. 7. Schematic diagrams of the force curves of the reference cantilever beam on the hard substrate (left) and micro-cantilever beam (right).

Figure 8, Displacement and deflection resolution of the micro-cantilever beam under the action of force load, the single-line force curve scanning diagram of the cantilever beam probe on the hard substrate, the longitudinal displacement and deformation of the initial scanning point and the final scanning point do not change (a), (b) ) is the deformation analysis near the roots and tails within a scanning range of 10 μm. where the upper half is the deformation at different force load set points, and the lower half is the change in the elastic coefficient in the length direction (only one set of them was calculated).

In the figure: 1 indicates the base, 2 indicates the two-dimensional micro-motion platform, 3 indicates the fixing groove of the manual needle insertion screw, 4 indicates the fixing groove of the automatic motor screw, 5 and 6 respectively indicate the corresponding two screw buttons 5 and 6 (and mutually perpendicular driving screw), 7 represents the PZT scanning tube, 8 represents the sample or the cantilever to be tested, 9 represents the incident laser, 10 represents the reference cantilever, and 11 represents the photodetector.

Detailed ways

Embodiment 1, the implementation of two-dimensional micro-mechanical platform

The two-dimensional micro-motion platform is shown in Figures 1 and 2. It mainly includes the two-dimensional micro-motion platform 2 fixed on the base, and the PZT scanning tube is fixed in the center hole of the two-dimensional micro-motion platform 2 through epoxy glue. The micro-motion platform is controlled by two adjustment knobs (5 in Fig. 1) and (6 in Fig. 1) driving screws perpendicular to each other. Both the two-dimensional micro-motion platform and the base are made of steel, and the PZT scanning tube 7 is fixedly installed on the two-dimensional micro-motion device, and the adjustment knobs 5 and 6 are connected to the driving rod, and the driving rod is fixed to the two-dimensional micro-moving platform and the PZT scanning tube Connect to move the position of the scan tube and corresponding sample. Then place the micro-movement platform on the base 8 and fix it. When the knob is adjusted, the knob drives the connecting rod to drive the scanning tube to move in the X and Y horizontal directions to obtain a large range of movement. The movement displacement of the micro-motion platform in the X and Y directions is 3 mm, and the PZT scanning tube The maximum scanning displacement is 20 microns to ensure that the cantilever probe can move on the microstructure. Both the manual needle entry and the motor needle entry control screw slots in the structure diagram are installed at the lower part of the chassis of the head. The chassis also includes a vibration-reducing device to avoid vibration interference during horizontal displacement and needle insertion.

Embodiment 2, the test of the mechanical parameters of the cantilever beam under the three situations of fixed point, micro-zone point by point and continuous point:

The test is carried out in a clean room environment at room temperature, with a temperature of 25°C and a humidity of 40-60%. Test according to the program in Figure 4, on the silicon (100) surface with a length of 100 μm, a width of 40 μm, and a thickness of 1.55 μm, the micro-cantilever structure prepared along the <110> crystal direction, using a cantilever with an elastic coefficient k=16N/m Beam test (provided by the manufacturer), the elastic coefficient of the tail end of the cantilever beam to be measured is 6.2N/m. The Young's modulus E=165GPa of monocrystalline silicon is obtained by calculation, which is close to the currently recognized 169GPa. According to the theoretical calculation, by the formula $k=\frac{1}{4}\mathrm{Ew}{\left(\frac{t}{l}\right)}^3$ The elastic coefficient can be obtained by calculation, where E is the Young's modulus of silicon, w is the width of the cantilever beam, t is the thickness, and l is the length. If the Young's modulus of single crystal Si is taken as 169GPa, the elastic coefficient is 6.3N/m. Compared with the test value, the estimated error is 2%. Theoretical calculations show that the maximum error of the elastic coefficient in the lateral direction of the cantilever beam is not more than 2%. Therefore, the resolution test of the micro-area elastic coefficient is mainly reflected in the length direction of the cantilever beam. Figure 7 shows an example of the test, the force-displacement curves of a reference cantilever on a hard substrate and an unknown cantilever.

Carrying out similar micro-area force resolution function tests according to the program in Figure 5 is to obtain the force resolution of different points on a certain micro-area in the microstructure, such as automatic measurement of different positions within the scale of less than 1 micron, to avoid manual measurement and positioning. error due to accuracy. After the test, the elastic coefficient corresponding to each position point is obtained through calculation. Select a scanning area of 1 micron × 1 micron, and then select 3 points along the length direction of the cantilever beam for testing, for example, the uniform point spacing is 200nm. From the root to the end of the cantilever beam, three points are selected continuously for testing, and the elastic coefficients are 9.04N/m, 8.40N/m, and 8.15N/m respectively. By comparison, the result deviation is between 3.5% and 7%.

The test is carried out according to the flow chart in Figure 6, and the probe is continuously and automatically moved on the microstructure under the action of a constant force. By setting several reference points of different forces, the system automatically changes the load (differential force) to apply the force to the cantilever beam, so that the displacement change of the cantilever beam under different loads, that is, the deformation, can be obtained through the differential force and deformation. The relationship between the elastic coefficient of the microstructure and the scanning length in the scanning length direction of the cantilever beam can be obtained. An example is shown in Figure 8.

The cantilever beam with an elastic coefficient of 0.8N/m was selected for the test, its length was 200 μm, its width was 40 μm, and its thickness was 1.55 μm. A reference cantilever beam with an elastic coefficient of 16N/m is pressed at a place 70-80 μm near the root of the cantilever, the scanning length is 10 μm, and the scanning rate of the probe in the experiment is 1 Hz. The displacement resolution of the test reaches 2nm. Except at the root of the cantilever, there is a large error. In the entire length of the test, the relationship between the elastic coefficient of the cantilever beam and the length is obtained. The results are consistent with the theory. The elastic coefficient k is inversely proportional to the cube of the length L, and the elasticity The coefficient varies from 14.20N/m to 11.39N/m. The elastic coefficient becomes significantly smaller away from the root, and the fluctuations in the test result curve can be clearly observed. This is because, even if there is no external noise, the contact motion of the two cantilever beams during the scanning process produces a result similar to the resonance effect. After the single-line scan test, keep the probe in place, and switch the test mode to the single-shot mode to perform a single-point elastic coefficient test, which is used to compare with the elastic coefficient obtained in the single-line scan mode. The elastic coefficient obtained by in-situ measurement is 13.40N/m, which is between 14.20N/m and 11.39N/m in the single-line scanning mode. The results show that the system has good consistency.

Claims (7)

1. A two-dimensional micro-motion platform for atomic force microscope, comprising a base, a charge-coupled device system, and a PZT scanning tube, characterized in that the central opening of the two-dimensional micro-motion platform (2) is used to install a PZT scanning tube ( 7), wherein there are two adjustment knobs (5), (6) respectively on mutually perpendicular X and Y positions, the two adjustment knobs are connected with two drive rods, and the two drive rods are connected with the PZT scanning tube, the described The two-dimensional micro-motion platform is fixed on the base (1). 2. The two-dimensional micro-motion platform for atomic force microscope according to claim 1, characterized in that the displacement range of the two-dimensional micro-motion platform in the horizontal direction is 3×3 square millimeters. 3. The two-dimensional micro-motion platform for atomic force microscope according to claim 1, characterized in that the two-dimensional micro-motion platform and the base are made of steel. 4. The two-dimensional micro-motion platform for atomic force microscope according to claim 1, characterized in that the PZT scanning tube is fixed in the central hole of the two-dimensional micro-motion platform by epoxy glue, and the two-dimensional micro-motion platform comprising the PZT scanning tube The micro-motion platform is fixed in the atomic force microscope system. 5. The two-dimensional micro-motion platform for atomic force microscope according to claim 1 or 4, characterized in that the maximum scanning displacement of the PZT scanning tube is 20 microns. 6. The method for testing mechanical parameters using the improved two-dimensional micro-motion platform for atomic force microscope according to any one of claims 1-5, characterized in that the elastic coefficient and Young's modulus of the cantilever beam are extracted in situ The parameter test of the quantity can be divided into any of the following three situations: A. The mechanical parameter test of a fixed point on the microstructure, that is, the single-point single-time force curve test, the test steps are: first use a reference cantilever beam probe with a known elastic coefficient to perform the first force-displacement on a hard substrate Curve test to obtain its slope data; then, on the cantilever to be tested, under the observation of the CCD field of view, move the two-dimensional micro-motion platform, select the position to be tested, and place the reference cantilever on the micro-cantilever to be tested Carry out the second force-displacement curve test at the selected position above to obtain the corresponding slope, and use the formula (1) to calculate the elastic coefficient of the cantilever beam to be tested from the given reference cantilever beam elastic coefficient; The structural parameters of the cantilever beam are then calculated by the corresponding formula (2) to directly obtain the Young's modulus of the unknown cantilever beam to be tested and the stress at the root of the cantilever beam; B. Carry out the force-displacement function test point by point in the micro area, first select the scanning area, and then set several points to be tested, the basic operation sequence is the same as the fixed point described in A, and then carry out the force-displacement test, and carry out step by step Point-by-point automatic test, obtain point-by-point force-curve data on the cantilever beam, extract its slope data, calculate according to the given formula (1), and obtain the elastic coefficient corresponding to each position point after testing and calculation; C. Micro-area continuous elastic coefficient test, that is, refer to the cantilever beam probe to analyze and test the continuous elastic coefficient in a small area on the tested cantilever beam. It is a single-line force scanning method. The steps are: first select the area on the hard substrate , and then set the force load and scanning size, conduct continuous scanning of the reference cantilever beam on the hard substrate, and obtain the scanning position and deformation data of the cantilever beam in the X and Y directions under constant force, and the deformation data in the Z direction; then under the CCD field of view and the micro-motion platform Under the operation of , place the reference cantilever beam in the micro-area of the tested cantilever beam, set several force loads of different levels and the same scan size, and execute the scan test. The program automatically changes the load and applies the differential force to the cantilever beam to obtain the cantilever The deformation of the displacement of the beam under different loads, according to the formula (3), the relationship between the elastic coefficient of the microstructure and the scanning length in the scanning length direction of the cantilever beam can be obtained through the differential force and displacement; Described formula (1), (2), (3) are $\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}\frac{{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; test</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; tot</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; test</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ $\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; Ewt</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ $\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;F</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;z</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ In the formula, k is the elastic coefficient of the unknown cantilever beam to be tested, k _ref is the elastic coefficient of the known reference cantilever beam, δ _tot is the total deformation of the reference cantilever beam, and δ _test is the shape of the tested cantilever beam variable, θ is the angle between the two cantilever beams; Thickness t, width w, and length L are structural parameters of the cantilever beam to be tested, and E is Young's modulus; ΔF is the differential force, and ΔZ is the deformation of the cantilever beam in the normal Z direction, also known as the differential displacement; The hard substrate refers to a flat silicon surface, and the field of view of the CCD is the field of view of a visible charge-coupled device system. 7. The method for testing the mechanical parameters of the two-dimensional micro-motion platform used in the atomic force microscope according to claim 6, characterized in that in the case of B, it corresponds to the automatic movement measurement of different positions in the micro-area with a scale of less than 1 micron.

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