Reference sample suitable for magnetic force microscope probe tip calibration and calibration method

Abstract

The invention discloses a reference sample suitable for magnetic force microscope probe tip calibration and a calibration method. The reference sample is formed on the surface of a substrate material, is made of a magnetic material, is provided with at least one group of magnetic micro-nano structures consisting of a plurality of substructures, and can generate a magnetic field with specific spatial distribution on the surface of the sample. The reference sample is used for calibrating the magnetic needle point of the magnetic force microscope. According to the invention, the substrate material is a silicon-containing or sapphire film growth substrate, the magnetic material is a single-layer or multi-layer film with perpendicular magnetic anisotropy, and the magnetization direction is perpendicular to the base surface of the substrate material. The magnetic material forms a magnetic micro-nano structure containing various spatial feature size patterns, and a stable magnetic field with specific spatial distribution can be generated on the surface of a sample. According to the invention, the spatial frequency range of magnetic probe calibration can be widened, and quantitative measurement of the magnetic force microscope on the surface magnetic fields of different magnetic micro-nano structures can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro-nano magnetic field testing, and particularly relates to a reference sample suitable for calibrating a probe tip of a magnetic force microscope and a calibration method. BACKGROUND

[0002] As an important branch of scanning force microscope, the test system of MFM mainly consists of a cantilever, a piezoelectric positioner and an optical cantilever motion detection device. When the needle tip plated with a magnetic film scans above a magnetic sample, the static magnetic interaction force between the magnetic needle tip and the surface magnetic field of the sample will change the vibration frequency and amplitude of the cantilever, and the contrast of the detection signal can realize the characterization of the magnetism of the material surface. However, the measurement results of the MFM under normal circumstances are only used to provide purely qualitative stray magnetic field images, instead of being used for quantitative data analysis. The reason is that the measurement signal is largely dependent on the magnetism of the needle tip, the mechanical performance of the cantilever and the sensitivity of the detection device. Only by understanding the shape and magnetization state of the magnetic needle tip and using a deconvolution algorithm, the accurate quantitative magnetic field map can be extracted from the MFM image. Therefore, accurate calibration of the magnetic needle tip determines the reliability of the quantitative magnetic field analysis of the MFM.

[0003] The magnetic needle tip transfer function method is usually calibrated by a vertically magnetized reference sample, so the magnetic field space frequency domain of the reference sample determines the space frequency domain of the magnetic needle that can be calibrated. For the needle calibration reference sample that cannot cover the full frequency domain, the spatial magnetic field distribution of the real magnetic needle cannot be obtained. In the calibration of MFM measurement, several different types of nanometer magnetic standard materials have been tested (for example, X.K. Hu et al. in 2020: Round robin comparison on quantitative nanometer scale magnetic field measurements by magnetic force microscopy (Round robin comparison on quantitative nanometer scale magnetic field measurements by magnetic force microscopy), Journal of Magnetism and Magnetic Materials; 511 / 2020: 166947.), but the periodic magnetic domain structure based on the intrinsic magnetic characteristics determines the singleness of the magnetic needle calibration space frequency domain, and the quantitative measurement of the magnetic field of the sample to be measured is also limited to the calibrated frequency domain range, which cannot cover the sufficient span of the feature size from microns to nanometers. Such a span is the overlapping measurement range required for the calibration from high-resolution magnetic force microscopy measurement to micron-level resolution technology (such as magneto-optical indicator film microscopy), which is an important link for establishing a complete quantitative magnetic field traceability chain from nanometers to microns and even millimeters. Therefore, the reference sample with variable magnetic pattern size covering the range from several microns to tens of nanometers is an effective way to expand the space frequency domain of the magnetic needle calibration. The patterned magnetic multilayer film with high vertical anisotropy is the preferred way to solve this problem. SUMMARY

[0004] In order to solve the above problems, the present application provides a reference sample suitable for magnetic force microscope probe tip calibration and a calibration method, which solves the problem of single space frequency domain of the reference sample existing in probe calibration and cannot effectively calibrate the surface magnetic field of micro-nano materials, and provides a reference sample for calibrating a magnetic force microscope magnetic probe and a use method.

[0005] The present application is realized by the following technical scheme: a reference sample suitable for magnetic force microscope probe tip calibration, comprising a substrate material, a magnetic micro-nano structure made of a magnetic material and having a predetermined size and shape.

[0006] The magnetic material has a perpendicular magnetic anisotropy characteristic, and a preferred magnetization direction is perpendicular to the substrate plane. The main material includes, but is not limited to, Co-based and CoFeB-based single-layer and / or multi-layer films, and has a clear saturation magnetization. The magnetic micro-nano structure is patterned, and the upper surface of the magnetic micro-nano structure and the substrate plane preferably have a small surface roughness. The surface roughness of a better thin film is preferably about 1 nm. To avoid interference with the measurement of the nanoscale magnetic probe tip, the height of the particle impurities on the surface is preferably less than 30 nm. The upper surface of the magnetic micro-nano structure is parallel to the substrate plane, and the distance between the upper surface of the magnetic micro-nano structure and the substrate plane in the z direction is less than or equal to 100 nm, and preferably less than or equal to 50 nm.

[0007] The magnetic micro-nano structure includes at least one group of substructures. The width of the substructure varies in the range of 100 nm to 10 μm. The substructures are separated by a certain distance. The starting spatial frequency and the ending spatial frequency corresponding to the substructure vary in the range of 1 / 200 nm -1 to 1 / 20 μm -1 .

[0008] According to a first embodiment of the present application, the structure includes at least one group of structures. The substructure of each group of structures is a line structure. Each line structure has a different line structure width. The spatial frequency corresponding to the line structure width continuously and linearly varies with the distance. The line edge position of the line structure gradually changes according to the linear relationship. The line edge positions of the line structure correspond to the zero-crossing points of a chirp curve in turn. The frequency of the chirp curve is a part of 1 / 200 nm -1 to 1 / 20 μm -1 . When the structure is only one group, the frequency range needs to cover 1 / 200 nm -1 to 1 / 20 μm -1 . When there are more than one group of structures, the frequency range of each group of structures needs to partially overlap.

[0009] According to another advantageous embodiment of the present application, the structure includes at least one group of structures. The substructure of each group of structures is a circular ring structure. Each circular ring structure has a different circular ring width. The radial spatial frequency corresponding to the circular ring width continuously and linearly varies with the circular ring radius. The circular ring edge position of the circular ring structure gradually changes according to the linear relationship. The circular ring edge positions of the circular ring structure correspond to the zero-crossing points of a chirp curve in turn. The frequency of the chirp curve is a part of 1 / 200 nm -1 to 1 / 20 μm -1 . When the structure is only one group, the frequency range needs to cover 1 / 200 nm -1 to 1 / 20 μm -1 . When there are more than one group of structures, the frequency range of each group of structures needs to partially overlap.

[0010] According to another advantageous embodiment of the present application, it comprises at least one set of structures, each set of structures is a periodic arrangement of sector structures in the circumferential direction, the sector structures have a fixed central angle, the central angle of the area between the edges of adjacent sector structures is the same as the central angle of the sector structure. Each circumference contains an integer number of sector periodic structures, each substructure is a sector structure with a continuous linear change in radial spatial frequency with radius, when the structure is only one set, the spatial frequency at the minimum and maximum radius of the circular ring covers 1 / 200nm -1 to 1 / 20μm -1 When there are more than one set of structures, the frequency range of each set of structures needs to have some overlap.

[0011] The use of the reference sample for calibrating the specific spatial frequency characteristics of the magnetic force microscope needle tip, comprising the following steps:

[0012] (1) providing the reference sample on the magnetic force microscope test platform to be calibrated, wherein at least one set of substructures of the selected structures of the reference sample is introduced into the test range of the magnetic probe;

[0013] (2) acquiring magnetic force phase image data of the at least one set of substructures at a specified probe-sample distance by means of the magnetic force microscope test system;

[0014] (3) evaluating the acquired image data and storing the evaluation results in a retrievable form to obtain the magnetic probe needle tip transfer function in a specific frequency range.

[0015] A method for constructing a wide spatial frequency domain magnetic probe needle tip calibration, comprising the following steps:

[0016] (1) fixing the reference sample on the magnetic force microscope test platform to be calibrated, wherein one set of substructures of the selected structures of the reference sample is introduced into the test range of the magnetic probe;

[0017] (2) acquiring magnetic force phase image data of the at least one set of substructures at a specified probe-sample distance by means of the magnetic force microscope test system, preferably the probe-sample distance is within 30nm-100nm;

[0018] (3) evaluating the acquired image data and storing the evaluation results as the first evaluation results;

[0019] (4) introducing another set of substructures of the selected structures of the reference sample into the test range of the magnetic probe;

[0020] (5) acquiring magnetic force phase image data of the other set of substructures at the same probe-sample distance as step (2) by means of the magnetic force microscope test system;

[0021] (6) evaluate the acquired image data and store the evaluation results as second evaluation results;

[0022] (7) repeat steps (1)-(3), evaluate the acquired image data, and store all evaluation results meeting the specific spatial frequency requirement;

[0023] (8) data fusion is performed on the stored results to obtain a wide spatial frequency domain magnetic probe tip transfer function, and the magnetic probe tip calibration is completed.

[0024] Compared with the prior art, the present application provides a reference sample for calibrating a magnetic force microscope probe and a use method, which has the following beneficial effects: the present application can realize the calibration of the spatial magnetic field component of the magnetic probe tip within a certain spatial frequency range by constructing a magnetic micro-nano structure capable of generating a spatial magnetic field with different spatial frequencies, obtain more spatial magnetic field distribution information of the magnetic probe tip, widen the spatial frequency range of the magnetic probe tip calibration, make the quantitative measurement between the magnetic force microscope and other scanning magnetic field measurement systems such as a scanning Hall sensor and a magneto-optical indicator film microscope comparable, and establish a traceability chain for the quantitative measurement of the spatial magnetic field from the nanometer to the millimeter scale. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0026] Figure 1 a side view of the reference sample for calibrating the magnetic force microscope probe;

[0027] Figure 2 a top view of the reference sample for calibrating the magnetic force microscope probe;

[0028] Figure 3 a schematic diagram of the reference sample with a line structure as a substructure;

[0029] Figure 4 a schematic diagram of the reference sample with a circular structure as a substructure;

[0030] Figure 5 a schematic diagram of the edge position of the reference sample with a line structure and a circular structure as substructures;

[0031] Figure 6 a schematic diagram of the reference sample with a fan-shaped structure as a substructure.

[0032] Wherein: 1, base material; 2, micro-nano magnetic structure; 2a, a group of sub-structures; 3, reference sample upper surface; 4, surface of base supporting micro-nano magnetic structure; 5, reference sample for calibrating magnetic probe tip. DETAILED DESCRIPTION

[0033] All features disclosed in this specification, and / or all steps of any methods or processes disclosed in this specification, can be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0034] Any feature disclosed in this specification, unless stated otherwise, can be replaced by alternative features serving the same, equivalent or similar purpose, to achieve the same, equivalent or similar result.

[0035] Figure 1 and Figure 2 A reference sample 5 for calibrating magnetic probe tip according to the present application is schematically shown. It comprises a base material 1 having an upper surface 4 for supporting a magnetic micro-nano structure 2. The upper surface 3 of the magnetic micro-nano structure 2 is parallel to the upper surface 4 of the base.

[0036] The base material 1 can be a semiconductor single crystal material or other material capable of growing thin film, including but not limited to silicon (Si or Si / SiO x ) substrate, silicon carbide (SiC), sapphire (Al2O3).

[0037] The magnetic micro-nano structure 2 is obtained by patterning a magnetic thin film. The magnetic thin film has perpendicular magnetic anisotropy, with the preferred magnetization direction perpendicular to the substrate plane. The main material includes but is not limited to Co-based and CoFeB-based single-layer and / or multi-layer films, with a clear saturation magnetization. The upper surface of the thin film has a surface roughness as low as nanometer level with the substrate plane, and the thin film surface is clean, with no particle-type foreign matter higher than 30 nm. The upper surface of the magnetic micro-nano structure is parallel to the substrate plane, with a distance in the z direction from the substrate plane less than or equal to 100 nm, preferably less than or equal to 50 nm.

[0038] Figure 3 An exemplary embodiment of the calibration sample 5 is given, which contains at least one group of structures 2a in the magnetic micro-nano structure, the structure 2a is composed of linear sub-structures with different widths, the width of the sub-structure varies in the range of 100 nm to 10 μm, and the adjacent sub-structures are separated by a certain distance. The spatial frequency corresponding to each sub-structure changes continuously and linearly with the distance, and the position of the edge of the linear structure changes gradually according to the linear relationship. Figure 5The one-to-one correspondence between the edge position of the line structure and the zero-crossing point of the chirp curve is given as an example. In this embodiment, the starting spatial frequency and the ending spatial frequency corresponding to the linear substructure vary within 1 / 200nm. -1 to 1 / 20μm -1 When the structure is only one group, the frequency range must cover 1 / 200nm -1 to 1 / 20μm -1 When there are more than one set of structures, the frequency range of each set of structures must overlap.

[0039] Figure 4 Another example of reference sample 5 is given. Its magnetic micro-nanostructure contains at least one group of structures 2a. Structure 2a is composed of circular substructures with different widths. The width of the substructure varies in the range of 100nm to 10μm, and adjacent circular structures are separated by a certain distance. The spatial frequency corresponding to each substructure varies continuously and linearly with distance. The edge position of each line of the circular structure gradually changes according to the linear relationship, following Figure 5 The one-to-one correspondence between the edge position of the ring structure and the zero-crossing point of the chirp curve is given in FIG. In this embodiment, the starting spatial frequency and the ending spatial frequency corresponding to the ring-shaped substructure vary within 1 / 200 nm. -1 to 1 / 20μm -1 When the structure is only one group, the frequency range must cover 1 / 200nm -1 to 1 / 20μm -1 When there are more than one set of structures, the frequency range of each set of structures must overlap.

[0040] Figure 6 Another embodiment of Reference Sample 5 is presented. Its magnetic micro-nanostructure contains at least one group of structures 2a. Structure 2a is composed of fan-shaped substructures with different central angles arranged periodically along the circumference. The fan-shaped structures have a fixed central angle, and the central angle of the area between the edges of adjacent fan-shaped structures is the same as the central angle of the fan-shaped structure. Each circle contains an integer number of fan-shaped periodic structures. Each substructure is a fan-shaped structure with a radial spatial frequency that varies continuously and linearly with the radius. When there is only one group of structures, the spatial frequency at the minimum and maximum points of the ring radius covers 1 / 200nm. -1 to 1 / 20μm -1 When there are more than one set of structures, the frequency range of each set of structures must overlap.

[0041] The following describes the measurement process of the magnetic probe tip calibration sample 5 in this embodiment when used for magnetic force microscope tip calibration:

[0042] This embodiment provides a method for calibrating a specific spatial frequency of a magnetic probe tip of a magnetic force microscope based on one of the reference samples, comprising the following steps:

[0043] (1) providing the reference sample 5 on the magnetic force microscope test bench to be calibrated, wherein at least one set of sub-structures 2a of the selected structure of the reference sample is introduced into the test range of the magnetic probe;

[0044] (2) acquiring magnetic force phase image data of the at least one set of sub-structures 2a by means of the magnetic force microscope test system at a specified probe-to-surface 3 distance of the reference sample 5;

[0045] (3) evaluating the acquired image data and storing the evaluation results in a retrievable form to obtain a magnetic probe tip transfer function in a specific frequency range.

[0046] The embodiment also provides a method for constructing a wide spatial frequency domain magnetic probe tip calibration, comprising the following steps:

[0047] (1) fixing the reference sample 5 on the magnetic force microscope test bench to be calibrated, wherein one set of sub-structures 2a of the selected structure of the reference sample is introduced into the test range of the magnetic probe;

[0048] (2) acquiring magnetic force phase image data of the at least one set of sub-structures 2a by means of the magnetic force microscope test system at a specified probe-to-surface 3 distance of the reference sample 5, preferably within a probe-sample distance of 30-100 nm;

[0049] (3) evaluating the acquired image data and storing the evaluation results as first evaluation results;

[0050] (4) introducing another set of sub-structures 2a of the selected structure of the reference sample into the test range of the magnetic probe;

[0051] (5) acquiring magnetic force phase image data of the other set of sub-structures by means of the magnetic force microscope test system at the same probe-to-surface 3 distance of the reference sample 5 as in step 2;

[0052] (6) evaluating the acquired image data and storing the evaluation results as second evaluation results;

[0053] (7) repeating steps (1)-(3), evaluating the acquired image data, and storing all evaluation results that meet specific spatial frequency requirements;

[0054] (8) data fusion of the stored results to obtain a wide spatial frequency domain magnetic probe tip transfer function, completing the magnetic probe tip calibration.

[0055] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any change or replacement without creative labor should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be limited by the protection scope defined in the claims.

Claims

1. A reference sample suitable for calibrating a magnetic force microscope probe tip, comprising a substrate material and a magnetic micro-nanostructure made of a magnetic material thereon, wherein the magnetic material is capable of generating a magnetic field with a specific spatial distribution on the sample surface, characterized in that: The reference sample substrate material is a semiconductor single crystal material; The magnetic material is a magnetic film having perpendicular magnetic anisotropy characteristics; The magnetic micro-nanostructure comprises at least one group of magnetic micro-nanostructures, each group of magnetic micro-nanostructures comprises at least one group of substructures, the substructures are composed of a plurality of substructures of predetermined size and shape, the substructures are spaced a certain distance apart, and a single magnetic domain is formed in the structure with a magnetization direction perpendicular to the sample surface, wherein the width of the substructure varies within the range of 100 nm to 10 μm, and the corresponding starting spatial frequency and ending spatial frequency vary within 1 / 200 nm. -1 to 1 / 20μm -1 within the range.

2. The reference sample for magnetic force microscope probe tip calibration according to claim 1, characterized in that: The upper surface of the magnetic micro-nano structure is parallel to the surface of the substrate material, and the distance from the upper surface of the magnetic micro-nano structure to the substrate plane in the z direction is less than or equal to 100 nm.

3. The reference sample for magnetic force microscope probe tip calibration according to claim 1, characterized in that: The magnetic micro-nanostructure comprises several groups of structures, wherein the substructures of at least one group are line structures.

4. The reference sample for magnetic force microscope probe tip calibration according to claim 3, characterized in that: The line structure is a line structure in which the spatial frequency changes continuously and linearly with distance, and the edge position of each line structure gradually changes with the linear relationship, and the edge position of the line structure corresponds to the zero-crossing point of the chirp curve in sequence, wherein the frequency of the chirp curve corresponding to each group of line structures is 1 / 200nm -1 to 1 / 20μm -1 In the case of multiple groups of structures, the frequency ranges of each group partially overlap with each other.

5. The reference sample for magnetic force microscope probe tip calibration according to claim 1, characterized in that: The magnetic micro-nano structure comprises several groups of structures, wherein the substructure of at least one group is a circular ring structure.

6. The reference sample suitable for magnetic force microscope probe tip calibration according to claim 5, characterized in that: The circular ring structure is a circular structure whose radial spatial frequency changes continuously and linearly with the circular ring radius, and the edge position of each circular structure gradually changes with the linear relationship, and the edge position of the circular ring structure corresponds to the zero-crossing point of the chirp curve in sequence, wherein the frequency of the chirp curve corresponding to each group of circular ring structures is 1 / 200nm -1 to 1 / 20μm -1 In the case of multiple groups of structures, the frequency ranges of each group partially overlap with each other.

7. The reference sample for magnetic force microscope probe tip calibration according to claim 1, characterized in that: The magnetic micro-nano structure comprises several groups of structures, wherein the substructures of at least one group are fan-shaped structures periodically arranged along the circumferential direction.

8. The reference sample for magnetic force microscope probe tip calibration according to claim 7, characterized in that: The fan-shaped structure has a fixed central angle, the central angle of the area between the edges of adjacent fan-shaped structures is the same as the central angle of the fan-shaped structure, and each circle contains an integer number of fan-shaped periodic structures. Each substructure is a fan-shaped structure in which the radial spatial frequency changes continuously and linearly with the radius, wherein the period corresponding to the minimum radius and the maximum radius of each group of structures is respectively a part of the range of 200nm to 20μm, and when there are multiple groups of structures, the period ranges of each group partially overlap with each other.

9. Use of the reference sample according to claim 1 for calibrating the specific spatial frequency characteristics of a magnetic force microscope probe tip, characterized in that: The following steps are involved: (1) placing the reference sample on a test bench of a magnetic force microscope to be calibrated so that at least one group of substructures selected from the reference sample is within the test range of the magnetic probe; (2) acquiring magnetic phase image data of the at least one group of substructures at a predetermined probe-sample distance using a magnetic force microscope testing system; (3) Evaluate the acquired image data and store it in a retrievable form to obtain the magnetic probe tip transfer function within a specific frequency range.

10. A method for constructing a wide spatial frequency domain magnetic probe tip calibration, characterized in that: The following steps are involved: (1) The reference sample of claim 1 is fixedly placed on a test bench of a magnetic force microscope to be calibrated, wherein at least one group of substructures in the reference sample is selected to be within the test range of the magnetic probe; (2) acquiring magnetic phase image data of the at least one group of substructures at a certain probe-sample distance, preferably a probe-sample distance of 30 nm to 100 nm; (3) evaluating the acquired image data and storing the data as a first evaluation result; (4) selecting another set of substructures of the reference sample and introducing them into the test range of the magnetic probe, repeating steps (2) and (3), and storing them as subsequent evaluation results; (5) All evaluation results are fused to obtain the magnetic probe tip transfer function covering a wide spatial frequency domain to complete the calibration of the magnetic probe tip.

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