Method for measuring thickness of thin film through atomic force microscope assisted by low-power light mirror

Abstract

The invention discloses a method for measuring the thickness of a thin film through an atomic force microscope assisted by a low-power optical microscope, which comprises the following steps of: pre-aligning the tip of a probe of the atomic force microscope with a step of a sample to be measured by virtue of the low-power optical microscope, and then controlling the tip to descend to a first height of the surface of the step; the needle tip is lifted under real-time monitoring, the needle tip and the surface of the sample are located in the focal plane range of the low-power optical microscope, the position of the probe is adjusted, and the projection of the needle tip is located over the step to complete accurate positioning. Starting a linear scanning mode, carrying out single-line scanning in a direction perpendicular to the step extension direction, dynamically adjusting scanning range parameters until a scanning curve presents a step-shaped characteristic, adjusting the scanning curve to a view center, switching a line-by-line scanning mode to obtain three-dimensional shape data, and obtaining the film thickness of the to-be-detected sample based on the three-dimensional shape data. According to the method, the probe and sample positioning process is optimized, scanning parameters and a data processing method are reasonably set, and the problems of long time consumption and low precision of measuring the film thickness by the atomic force microscope under the assistance of the low-power light microscope are effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of film thickness measurement and relates to a method for measuring film thickness using an atomic force microscope assisted by a low-power optical microscope. Background Art

[0002] Precise measurement of thin film thickness is a core component supporting the development of modern high-end manufacturing and cutting-edge technologies, playing an irreplaceable role in fields such as semiconductors, display technology, optical coatings, photovoltaics, and flexible electronics. With the trend toward device miniaturization and functional integration, the accuracy of thin film thickness control is directly linked to the device's electrical performance, optical properties, and reliability. For example, in semiconductor manufacturing, errors in the thickness of a transistor's gate oxide exceeding the subnanometer level can lead to a surge in leakage current and device failure. In the display field, variations in the thickness of the light-emitting layer and electron transport layer in an OLED screen by just a few nanometers can significantly affect luminous efficiency and color uniformity. In particular, the measurement of nanometer-scale (1-100 nm) and submicron-scale (100-1000 nm) thin films involves critical parameter ranges across numerous fields, making high-precision, efficient, and non-destructive thickness measurement of these films crucial.

[0003] Atomic force microscopy (AFM) is a commonly used thin film thickness measurement technology in existing technologies. This technology directly obtains the height difference between the film and the substrate by scanning the surface morphology with a probe. Its core advantage lies in the nanometer-level resolution of three-dimensional morphology (vertical resolution can reach 0.1nm), and can directly measure the step height of any material (including insulators). It is particularly suitable for non-transparent, low-roughness or heterogeneous interface films. At the same time, AFM has high repeatability (accuracy better than 1%) and is authoritative in nanoscale thin film measurement.

[0004] However, when using an atomic force microscope to test thin film thickness, the AFM probe tip needs to be positioned at the step. Because the probe is very small, typically at the micrometer level, an optical microscope is required to magnify and observe the step and assist in positioning in order to measure the step's topography. However, for AFMs equipped with optical microscopes with low magnification (e.g., a maximum magnification of several dozen times), manual positioning requires operator experience, a time-consuming process that significantly impacts test efficiency. Furthermore, during the auxiliary positioning process, the probe surface is susceptible to contamination or mechanical wear, resulting in morphological distortion and affecting test accuracy. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a method for measuring film thickness using an atomic force microscope assisted by a low-magnification optical microscope, thereby solving the technical problems in the prior art of measuring film thickness using an atomic force microscope assisted by a low-magnification optical microscope, which is time-consuming and has low accuracy.

[0006] The present invention is achieved through the following technical solutions: A method for measuring film thickness using an atomic force microscope assisted by a low-magnification optical microscope comprises the following steps: S1: Pre-aligning the probe tip of the atomic force microscope with the step of the sample to be measured through low-magnification optical microscopy observation, and then controlling the probe tip to descend to a position at a first height on the step surface; S2: Raise the probe tip so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification optical microscope. Under the real-time monitoring of the low-magnification optical microscope, adjust the position of the probe so that the projection of the probe tip is located directly above the step of the sample to be tested, thus completing precise positioning; S3: Starting the linear scanning mode of the atomic force microscope, performing a single-line scan perpendicular to the step extension direction, dynamically adjusting the scanning range parameters until a step-like feature appears in the real-time feedback scanning curve, and adjusting the area corresponding to the step-like feature to the center position of the scanning field of view, then switching to the line-by-line scanning mode to obtain three-dimensional morphology data; S4: Obtaining the film thickness of the sample to be measured based on the three-dimensional morphology data.

[0007] Preferably, the first height is 5-20 nm.

[0008] Preferably, the first height is 10-15 nm.

[0009] Preferably, in step S2, the probe tip is raised so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope. Specifically, the probe tip is raised so that the distance between the probe tip and the surface of the sample to be tested is 100-300 μm, so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope.

[0010] Preferably, in step S2, the probe tip is raised so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope. Specifically, the probe tip is raised so that the distance between the probe tip and the surface of the sample to be tested is 100-200 μm, so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope.

[0011] Preferably, in step S3, the scanning range parameters are dynamically adjusted, specifically: first set the initial scanning range to 5% to 10% of the probe tip motion limit, perform linear scanning, and then gradually increase the scanning range until the upper and lower platforms of the step of the sample to be tested are completely displayed in the scanning curve.

[0012] Preferably, in the process of gradually increasing the scanning range, the amplitude of each increase in the scanning range does not exceed 50% of the current value.

[0013] Preferably, in the process of gradually increasing the scanning range, if the height difference of the step-shaped feature in the scanning curve changes by more than 10% after increasing the scanning range twice in succession, the scanning range is returned to the previous time and manual intervention is triggered.

[0014] Preferably, in step S3, when performing linear scanning mode, when the scanning range exceeds 50% of the atomic force microscope scanner range, the scanning range is narrowed to 30%~40% of the scanner range, and it is ensured that the upper and lower platforms of the step of the sample to be tested are both within the scanning field of view.

[0015] Preferably, in step S4, the film thickness of the sample to be tested is obtained based on the three-dimensional morphology data, specifically: first, the three-dimensional morphology data is leveled and the noise lines are removed, and then at least 3 to 10 measurement points are selected, the step heights are measured respectively, and the average value is taken as the film thickness.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention discloses a method for measuring thin film thickness using an atomic force microscope (AFM) assisted by a low-magnification optical microscope. This method first performs pre-alignment through low-magnification optical microscopy observation. The probe tip is then controlled to descend to a first height above a step surface. Under real-time monitoring by the low-magnification optical microscope, the probe tip is raised to achieve confocal alignment between the probe tip and the sample surface under the microscope, followed by fine positioning. This method of lowering the probe tip to the appropriate height before raising it for fine positioning ensures that both the probe tip and the sample surface are clearly focused under the microscope. Furthermore, the tip's movement prevents scratching the sample surface, making the positioning process more efficient and avoiding repeated attempts due to positioning difficulties, thereby reducing positioning time. Furthermore, regarding parameter setting, the method sets the initial scan range (Size) to a small value to protect the probe and sample. After the probe is lowered, the probe scans back and forth along a line, gradually adjusting the parameters. Once a step-like profile is observed in the scanned line and the step position is adjusted to the center, line-by-line scanning is resumed. This gradual parameter adjustment method avoids repeated scans caused by blindly setting parameters, enabling faster identification of appropriate scanning parameters, thereby shortening scanning time and improving measurement efficiency. This method effectively solves the technical problem of long time consumption and low accuracy in measuring film thickness using atomic force microscope with the assistance of low-magnification optical microscope in the existing technology by optimizing the probe and sample positioning process, reasonably setting scanning parameters and data processing methods.

[0017] Furthermore, in step S2, the probe tip is raised so that the probe tip and the surface of the sample to be measured are within the focal plane range of the low-magnification microscope. Specifically, the probe tip is raised so that the distance between the probe tip and the surface of the sample to be measured is 100~300μm, which can ensure that both the probe and the sample surface can be clearly imaged under the low-magnification microscope, facilitate precise positioning adjustment, and improve measurement efficiency. Within this range, it can ensure that there is a suitable height difference between the probe tip and the sample, and avoid inaccurate positioning due to excessive height or deviation of the probe during the falling process, thereby improving measurement accuracy and efficiency.

[0018] Furthermore, in step S3, the scanning range parameters are dynamically adjusted, specifically: first set the initial scanning range to 5%~10% of the probe tip movement limit, perform linear scanning, and then gradually increase the scanning range until the upper and lower platforms of the step of the sample to be tested are completely displayed in the scanning curve. Setting the initial scanning range can protect the probe and the sample, and avoid damage to the probe or sample due to an excessively large initial scanning range. At the same time, gradually increasing the scanning range can more accurately find the appropriate scanning range, ensuring that the upper and lower platforms of the step can be completely scanned, laying the foundation for subsequent acquisition of accurate three-dimensional morphology data.

[0019] Furthermore, in the process of gradually increasing the scanning range, the amplitude of each increase in the scanning range shall not exceed 50% of the current value. This limitation can avoid the scanning range from increasing too quickly, resulting in distortion of the scanning curve or inability to accurately capture step-like features. By controlling the amplitude of each increase, the scanning process can be made smoother and more accurate, thereby improving the reliability of the measurement results.

[0020] Furthermore, in the process of gradually increasing the scanning range, if the height difference of the step-shaped feature in the scanning curve changes by more than 10% after increasing the scanning range twice in succession, the system will regress to the previous scanning range and trigger manual intervention. This process can promptly detect abnormal situations that may occur during the scanning process, such as abnormal height difference changes caused by unreasonable scanning range settings, interference on the sample surface, etc. By regressing to the previous scanning range and triggering manual intervention, inaccurate measurement results due to abnormal situations can be avoided, thereby ensuring the quality of the measurement.

[0021] Furthermore, in step S3, when performing the linear scanning mode, when the scanning range exceeds 50% of the atomic force microscope scanner range, the scanning range is reduced to 30%~40% of the scanner range, and it is ensured that the upper and lower platforms of the step of the sample to be measured are both within the scanning field of view. This process can protect the scanner and avoid inaccurate measurement results due to excessive scanning range. At the same time, it is ensured that the upper and lower platforms of the step are both within the scanning field of view, which can ensure that complete step morphology data is obtained, providing an accurate basis for the subsequent calculation of the film thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Schematic diagram of the probe structure of the atomic force microscope used in Example 2 of the present invention, wherein (a) is a top view and (b) is a side view; Figure 2 This is a low-magnification microscope photo of the sample step and the probe microcantilever after precise alignment in the prior art; Figure 3 This is a photo of the sample step and the probe microcantilever after the needle is inserted in the prior art under a low-magnification microscope; Figure 4 It is the sample profile obtained after precise alignment in the prior art; Figure 5 A two-dimensional topography image of the sample to be measured obtained by using existing technology; Figure 6 This is a photograph of the sample step and the probe microcantilever pre-aligned using the method of the present invention in Example 2 of the present invention under a low-magnification microscope; Figure 7 This is a photograph of the probe tip and the sample under a low-magnification optical microscope when the probe tip is raised after the needle is inserted using the solution of the present invention so that the distance between the probe tip and the surface of the sample is 100 μm; Figure 8 This is a schematic diagram of Example 2 of the present invention in which the projection of the probe tip is positioned directly above the step of the sample to be tested using the solution of the present invention; Figure 9 This is a photograph of the probe and sample step under a low-magnification optical microscope after fine alignment using the solution of the present invention; Figure 10 This is a cross-sectional view of the sample to be tested after fine alignment using the solution of the present invention; Figure 11 The topography of the steps of the sample to be measured using the solution of the present invention, wherein (a) is a two-dimensional topography of the sample, and (b) is a three-dimensional topography of the sample; Figure 12 For Figure 11 Select 4 measurement points on the 2D topography image in order to measure the subsequent step thickness; Figure 13 for Figure 12 The step thickness test results between points A and B; Figure 14 for Figure 12 The step thickness test results between points C and D; Figure 15 for Figure 12 The step thickness test results between points E and F; Figure 16 for Figure 12 The step thickness test results between points G and H.

[0024] Among them, 1. cantilever, 2. probe tip, 3. step. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of 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. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0027] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0028] In the description of the embodiments of the present invention, it should be noted that if the terms "upper," "lower," "horizontal," "inner," etc. appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the inventive product is typically placed when in use. These terms are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0029] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0030] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0031] The present invention is described in further detail below with reference to the accompanying drawings: The present invention discloses a method for measuring film thickness using an atomic force microscope assisted by a low-magnification optical microscope, comprising the following steps: S1: Pre-aligning the probe tip of the atomic force microscope with the step of the sample to be measured through low-magnification optical microscopy observation, and then controlling the probe tip to descend to a position at a first height on the step surface; In a preferred embodiment, the first height is 5-20 nm, preferably 10-15 nm, and more preferably 10 nm.

[0032] S2: Raise the probe tip so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification optical microscope. Under the real-time monitoring of the low-magnification optical microscope, adjust the position of the probe tip so that the projection of the probe tip is located directly above the step of the sample to be tested, thereby completing precise positioning; In a specific embodiment, the probe tip is raised so that the distance between the probe tip and the surface of the sample to be tested is 100-300 μm, so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-power microscope. The raised distance is preferably 100-200 μm, more preferably 100 μm.

[0033] S3: Starting the linear scanning mode of the atomic force microscope, performing a single-line scan perpendicular to the step extension direction, dynamically adjusting the scanning range parameters until a step-like feature appears in the real-time feedback scanning curve, and adjusting the area corresponding to the step-like feature to the center position of the scanning field of view, then switching to the line-by-line scanning mode to obtain three-dimensional morphology data; When dynamically adjusting the scanning range parameters, specifically: first set the initial scanning range to 5%~10% of the probe tip motion limit, perform linear scanning, and then gradually increase the scanning range until the upper and lower platforms of the step of the sample to be tested are completely displayed in the scanning curve.

[0034] During the process of gradually increasing the scanning range, the amplitude of each increase in the scanning range shall not exceed 50% of the current value. In addition, if the height difference of the step-like feature in the scanning curve changes by more than 10% after two consecutive increases in the scanning range, the scanning range will be retracted to the previous one and manual intervention will be triggered.

[0035] When performing linear scanning mode, when the scanning range exceeds 50% of the AFM scanner range, the scanning range is reduced to 30%~40% of the scanner range, and it is ensured that the upper and lower platforms of the step of the sample to be measured are within the scanning field of view.

[0036] S4: Leveling and noise filtering the three-dimensional topography data, selecting multiple measurement points in the step area to calculate the average height difference and obtain the film thickness result. The measurement points can be 3 to 10, preferably 5.

[0037] Example 2 In order to further explain the technical solution of the present invention, the method is described by taking the Bruker NCHV-A atomic force microscope probe as an example. The Bruker NCHV-A atomic force microscope probe has a structure as shown in FIG. Figure 1 As shown, the Bruker NCHV-A atomic force microscope probe includes a cantilever 1 and a probe tip 2 located at the free end of the cantilever 1. The cantilever 1 and the probe tip 2 are designed as an integrated whole. The specific test process is as follows: S1: Pre-alignment. Specifically, the tip of the atomic force microscope probe 2 is pre-aligned with the step of the sample to be measured through low-magnification optical microscopy observation; In the existing technology, the pre-alignment during the test is also called fine alignment. The main process is to make the probe as close to the sample step as possible under a low-power microscope before inserting the needle. Figure 2 shown.

[0038] In the present invention, pre-alignment is to roughly align the sample step with the sample. First, ensure that the Shimadzu SPM-9700HT atomic force microscope is in normal working condition, place the sample to be tested on the sample stage, and fix it to avoid movement during the test. Turn on the low-power optical microscope and observe the step structure on the surface of the sample to be tested through the eyepiece of the microscope or the connected display screen. Adjust the focal length, magnification, brightness and other parameters of the low-power optical microscope so that it can form a clear image. At the same time, adjust the low-power microscope so that the probe enters the field of view to observe the relative position of the probe tip and the step of the sample to be tested.

[0039] Then, according to the observed positions of the probe tip and the step, the sample is moved and adjusted so that the step of the sample is close to the probe tip, such as Figure 6 location.

[0040] S2: Fine alignment. The existing technology is to perform pre-alignment before the probe is inserted, that is, precise alignment, that is, to complete Figure 2 However, in the prior art, the probe after pre-alignment is placed and the sample step is shown in the photo under a low-power microscope. Figure 3 It can be seen that the tip of the probe microcantilever in the prior art cannot be effectively aligned with the sample step after the needle is lowered. In this case, when testing, the sample profile line obtained is as follows Figure 4 As shown in the figure, it can be seen that the step surface of the sample cannot be effectively observed under the test window. At the same time, during the test process, the morphology image obtained cannot effectively observe the step surface of the sample, such as Figure 5 shown.

[0041] The fine alignment process of the present invention is as follows: After pre-alignment, the control system of the atomic force microscope is used to precisely control the probe tip to descend to a position 5-20nm above the step surface (fast approach process of the atomic force microscope). The height sensor of the atomic force microscope or the height feedback function of the control system can be used to monitor the height change of the probe tip in real time to ensure that it accurately descends to a height of 5-20nm. The probe tip is then raised so that the distance between the probe tip and the surface of the sample to be tested is 100μm. At this time, the probe tip and the sample step are photographed under a low-magnification optical microscope. Figure 7 At this time, the sample step and the probe can be focused at the same time, and then under the real-time monitoring of the low-power optical microscope, the relative position of the needle tip and the step can be finely adjusted so that the projection of the probe tip is located just above the step 3 of the sample to be tested, as shown in the figure. Figure 8 As shown, the precise positioning of the probe is completed. The aligned probe and sample step are shown in the photo under a low-magnification optical microscope. Figure 9 ,Depend on Figure 9 It can be seen that after the above operations, the rapid and accurate alignment of the probe and the sample step position is effectively achieved.

[0042] In step S2, with the help of real-time monitoring of a low-magnification optical microscope, the control system of the atomic force microscope is operated to slowly raise the probe tip so that the distance between the probe tip and the surface of the sample to be measured reaches 100 μm.

[0043] After the probe tip is raised to a height of 100μm, the relative position of the probe tip and the step of the sample to be measured is observed again using a low-magnification optical microscope. At this point, due to the appropriate height difference between the probe tip and the sample surface, both can be clearly imaged under the optical microscope. Based on the observed image, the control system of the atomic force microscope is used to finely move and adjust the probe tip so that its projection is directly above the step of the sample to be measured. This adjustment process requires great patience and precision, as even slight deviations may lead to inaccurate subsequent measurement results. The fine-tuning function of the control system can be used to gradually move the probe tip while observing the changes in the image in the low-magnification optical microscope until the projection of the probe tip is accurately located directly above the step. During the adjustment process, the operation needs to be slow to avoid collision between the probe tip and the sample surface. During the movement, the image in the low-magnification optical microscope is continuously observed to ensure that the probe tip does not deviate from the expected movement path.

[0044] This process ensures that the height difference between the needle tip and the sample surface is only 100μm. Under an optical microscope, the two can be clearly focused at the same time, and the needle tip will not scratch the sample surface when moving. The most important thing is to align the needle tip and the sample before lowering the needle. The needle tip will not deviate significantly during the falling process. If the needle tip is aligned when it is far away from the sample surface, the needle tip and the sample surface cannot be focused at the same time. Even if the needle tip is moved to the step position on the sample surface during testing, the probe will not move vertically downward when it approaches the sample surface. Therefore, the probe will deviate from the step position when it hits the sample surface, and the step height cannot be obtained. S3: Parameter setting, needle test. Start the linear scanning mode of the atomic force microscope, perform a single line scan along the direction perpendicular to the step extension, and dynamically adjust the scanning range parameters until the real-time feedback scanning curve shows a step-like feature, such as Figure 10 As shown, after adjusting the area corresponding to the step-shaped feature to the center position of the scanning field of view, switching to the line-by-line scanning mode to obtain three-dimensional topography data; In step S3, first, enable the scanning function of the atomic force microscope and set the initial value of the scanning range Size to a small value, such as approximately 10% of the probe tip's motion limit. The main purpose of this setting is to protect the probe and sample, avoiding damage to the probe or sample surface due to an excessively large scanning range during the initial scanning process. At the same time, other relevant scanning parameters are set, such as the scanning speed and scanning frequency. The scanning speed should not be too fast to avoid affecting the accuracy of the scan; the scanning frequency should be reasonably selected based on the characteristics of the sample and the measurement requirements.

[0045] Then, control the probe tip to descend to the sample surface and start a single-line scan. During the scanning process, observe the changes in the scanning curve or image in real time. You can view the scanning data through the software interface to observe whether the profile line of the scanning line has step-like features. If the profile line of the scanning line does not have obvious step-like features, or the step position is not in the center, you need to adjust the scanning parameters. You can gradually adjust the value of the scanning range Size to gradually increase the scanning range until a clear step shape can be seen on the profile line. After seeing the step shape, start adjusting the value of offset X. The adjustment of offset X is to make the step position in the middle position of the profile line, so that the height information of the step can be obtained more accurately. By fine-tuning the value of offset X, observe the changes in the step position on the profile line until the step is in the middle position.

[0046] After adjusting offset X, consider whether the scanning range needs to be further reduced. If the current scanning range is large and exceeds half of the measurement range of the scanner, the Size value needs to be reduced. When reducing the Size value, make sure that the upper and lower platforms of the step can be fully seen to ensure the integrity of the measurement data. When all parameters are adjusted to the appropriate position, switch the scanning mode to the line-by-line scanning mode. During the line-by-line scanning process, the atomic force microscope will scan the sample surface line by line according to the set scanning range and parameters to obtain complete three-dimensional morphological image data. The morphology of the step of the sample to be measured is as follows: Figure 11 During the scanning process, pay close attention to the scanning progress and data accuracy. If any abnormalities occur, such as distortion of the scanning curve or large fluctuations in the data, stop scanning immediately, check the parameter settings and device status, and then continue scanning after troubleshooting.

[0047] S4: Process the data to obtain the step height (i.e., film thickness) result. Specifically, data processing software is required to perform operations such as flattening and removing noise lines. Then, multiple locations are selected, the step height is measured separately, and the average is calculated.

[0048] In step S4, the saved 3D topography image data is imported into data processing software. This software can be the AFM's own software or a third-party professional data processing software. In the data processing software, the data is first flattened. The purpose of flattening is to remove any overall topographical variations, such as tilt or curvature, that may exist on the sample surface, ensuring that the data more accurately reflects step height information. The software's leveling function allows you to select an appropriate leveling method, such as plane leveling or polynomial leveling, to process the data.

[0049] After leveling is complete, remove noise from the data. Noise can be caused by factors such as equipment noise and environmental interference, affecting the accuracy of step height measurements. Filtering functions in data processing software, such as Gaussian filtering and median filtering, can be used to filter the data and remove noise. During the filtering process, appropriate filtering parameters should be selected based on the data characteristics and noise type to avoid data distortion caused by excessive filtering.

[0050] After removing the noise lines, select multiple measurement points in the step area, such as Figure 12 As shown in Figure 1, four measurement points are selected. The selection of measurement points should be representative and cover different positions of the steps to ensure the accuracy of the measurement results. Measure the height of each measurement point separately, as shown in Figure 1. Figures 13-16 As shown, the height value of each measurement point can be obtained through the measurement function in the data processing software. Then, the average of these height values ​​is calculated. This average is the height of the step, which is also the thickness of the film.

[0051] After obtaining the film thickness results, analyze and verify them. Compare the measured results with theoretical values ​​and those obtained using other measurement methods to verify that they are within a reasonable range. If there are significant deviations in the measured results, analyze the possible causes, such as improper parameter settings, inappropriate data processing methods, or surface defects on the sample. Based on the analysis results, adjust and improve the test process and data processing methods accordingly, and repeat the measurement until accurate and reliable results are obtained.

[0052] Through the comparison of Example 2, the efficiency of the technical solution of the present invention is effectively demonstrated. On the one hand, the existing technology cannot ensure whether the step surface can be tested, and the test is time-consuming. However, after the present invention optimizes the test process, the accurate test of the sample step surface can be effectively achieved within more than ten minutes, which greatly improves the efficiency and accuracy of the test.

[0053] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for measuring film thickness using an atomic force microscope assisted by a low-power optical microscope, characterized in that: The following steps are involved: S1: Pre-aligning the probe tip of the atomic force microscope with the step of the sample to be measured through low-magnification optical microscopy observation, and then controlling the probe tip to descend to a position at a first height on the step surface; S2: Raise the probe tip so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification optical microscope. Under the real-time monitoring of the low-magnification optical microscope, adjust the position of the probe so that the projection of the probe tip is located directly above the step of the sample to be tested, thus completing precise positioning; S3: Starting the linear scanning mode of the atomic force microscope, performing a single-line scan perpendicular to the step extension direction, dynamically adjusting the scanning range parameters until a step-like feature appears in the real-time feedback scanning curve, and adjusting the area corresponding to the step-like feature to the center position of the scanning field of view, then switching to the line-by-line scanning mode to obtain three-dimensional morphology data; S4: Obtaining the film thickness of the sample to be measured based on the three-dimensional morphology data.

2. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 1, wherein: The first height is 5-20 nm.

3. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 1, wherein: The first height is 10-15 nm.

4. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 1, wherein: In step S2, the probe tip is raised so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope. Specifically, the probe tip is raised so that the distance between the probe tip and the surface of the sample to be tested is 100-300 μm, so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope.

5. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 1, characterized in that: In step S2, the probe tip is raised so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope. Specifically, the probe tip is raised so that the distance between the probe tip and the surface of the sample to be tested is 100-200 μm, so that the probe tip and the surface of the sample to be tested are within the focal plane of the low-magnification microscope.

6. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 1, characterized in that: In step S3, the scanning range parameters are dynamically adjusted, specifically: first set the initial scanning range to 5% to 10% of the probe tip motion limit, perform linear scanning, and then gradually increase the scanning range until the upper and lower platforms of the step of the sample to be tested are completely displayed in the scanning curve.

7. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 6, characterized in that: In the process of gradually increasing the scanning range, the amplitude of each increase in the scanning range does not exceed 50% of the current value.

8. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 6, characterized in that: During the process of gradually increasing the scanning range, if the height difference of the step-shaped feature in the scanning curve changes by more than 10% after the scanning range is increased twice in succession, the scanning range is returned to the previous time and manual intervention is triggered.

9. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 1, characterized in that: In step S3, when performing linear scanning mode, when the scanning range exceeds 50% of the AFM scanner range, the scanning range is reduced to 30% to 40% of the scanner range, and it is ensured that the upper and lower platforms of the step of the sample to be tested are both within the scanning field of view.

10. The method for measuring film thickness using a low-power optical microscope-assisted atomic force microscope according to claim 1, characterized in that: In step S4, the film thickness of the sample to be measured is obtained based on the three-dimensional morphology data. Specifically, the three-dimensional morphology data is first leveled and the noise lines are removed. Then, at least 3 to 10 measurement points are selected, the step heights are measured respectively, and the average value is taken as the film thickness.

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