A device for measuring the resistivity of isostatically pressed graphite

Abstract

The utility model provides a kind of resistivity measuring device of isostatic pressing graphite, including the sample table for placing sample to be measured and the measuring device for measuring the resistivity of sample to be measured;Measuring device includes six measuring units, data acquisition unit and control processing unit;Six orientations of sample table are equipped with one measuring unit respectively;Each measuring unit includes telescopic mechanism, probe seat and four probes;Four probes are installed in one side of probe seat, and telescopic mechanism is connected with the other side of probe seat, for driving probe seat to be close to or away from sample to be measured;All probes are connected with data acquisition unit communication, and control processing unit is connected with data acquisition unit, telescopic mechanism communication respectively.The utility model measures the resistivity of six faces of sample to be measured by six measuring units simultaneously, to greatly improve detection efficiency.In addition, by constant pressure contact control, the contact state of each probe even each needle and each measuring face can be kept consistent, and the measurement result can truly reflect the uniformity of graphite.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor measurement technology, specifically to a resistivity measuring device for isostatic graphite. Background Technology

[0002] Isostatically pressed graphite, a key material for semiconductor thermal field components, directly impacts the quality of silicon carbide epitaxial growth due to the uniformity of its graphite grain orientation. Isostatically pressed graphite is formed through cold isostatic pressing (pressure 100–200 MPa), causing microcrystalline particles to arrange themselves randomly in a liquid medium. Theoretically, this achieves isotropy, with the isotropy ratio (performance ratio in different directions) controllable within the range of 1.0–1.1. This uniform structural characteristic results in minimal resistivity differences across different directions, ideally <5%. However, in actual production, process fluctuations such as pressure transmission deviations or graphitization furnace temperature control deviations can lead to uneven grain size and pore distribution, resulting in localized resistivity fluctuations. This microstructural inhomogeneity can cause abnormal thermal gradients in the semiconductor thermal field, ultimately leading to defects and yield issues in silicon carbide epitaxial products.

[0003] Currently, the method for measuring the uniformity of isostatically pressed graphite is based on the national standard GB / T 24525-2009, using the four-probe method to measure resistivity. The uniformity of resistivity is used to characterize the uniformity of isostatically pressed graphite. While existing four-probe measuring instruments (such as the GEST-122A tester and the FTDZS-50KN multi-functional system) can achieve high-precision single-point measurements (error ±0.5%), they have the following drawbacks: Firstly, existing four-probe measuring instruments support resistivity detection at a single point or on a single surface, and the results only represent the conductivity of that surface. Secondly, when measuring multiple surfaces, the sample must be manually rotated and measured step-by-step on different surfaces, resulting in low measurement efficiency. Thirdly, because the flatness of graphite surfaces is inconsistent, step-by-step measurement of different surfaces leads to inconsistent contact states between the electrodes and each measurement surface. The contact resistance between the electrodes and the graphite surface is significantly affected by surface flatness, thus the measurement results cannot accurately reflect the uniformity of the graphite. Summary of the Invention

[0004] One objective of this invention is to solve the technical problem of low efficiency in existing four-probe measuring instruments. Another objective of this invention is to solve the technical problem that the measurement results of existing four-probe measuring instruments cannot accurately reflect the uniformity of graphite.

[0005] To achieve at least one of the above objectives, this utility model provides a resistivity measuring device for isostatically pressed graphite, comprising a sample stage for placing the sample to be tested and a measuring device for measuring the resistivity of the sample; the measuring device includes six measuring units, a data acquisition unit, and a control processing unit; each of the six positions of the sample stage is provided with one of the measuring units; each measuring unit includes a telescopic mechanism, a probe holder, and four probes; the four probes are mounted on one side of the probe holder, and the telescopic mechanism is connected to the other side of the probe holder for driving the probe holder closer to or further away from the sample to be tested; all probes are communicatively connected to the data acquisition unit, and the control processing unit is communicatively connected to the data acquisition unit and the telescopic mechanism respectively.

[0006] The four-probe resistivity meter is designed based on the current-voltage separation principle. It achieves high-precision resistivity measurement through four independent probes (arranged in a straight line or rectangle): the two outer probes are connected to a constant current source to inject a stable current, while the two inner probes are connected to a high-precision voltmeter to detect the potential difference, effectively eliminating interference from contact resistance and lead resistance. The instrument uses tungsten carbide probes with a spring pressure device to ensure contact stability. The digital voltmeter has a resolution of 0.1μV and supports automatic range switching. Its advantages include non-destructive measurement, adaptability to samples with different geometries (bulks, thin films), and a correction coefficient that can correct for edge effect errors. It is widely used for resistivity and sheet resistance testing of materials such as semiconductor wafers, metal thin films, and ceramics, and is particularly suitable for micro-area electrical characteristic analysis, such as quality control of photovoltaic silicon wafers or conductivity evaluation of lithium battery electrodes.

[0007] The above scheme significantly improves detection efficiency by simultaneously measuring the resistivity of all six faces of the graphite sample using six measurement units. It should be noted that the control processing unit controls the telescopic mechanism and calculates the resistivity of the six faces of the sample based on data transmitted from the data acquisition unit. Resistivity ρ k The calculation formula is as follows:

[0008] ρ k =C*(V / I)*t;

[0009] Where C is the geometric correction factor, V is the voltage difference between adjacent electrodes, I is the injection current, and t is the electrode spacing.

[0010] The uniformity of resistivity can be evaluated using the spatial coefficient of variation (CVs).

[0011] CVs=(σ / ρ total )*100%;

[0012] In the formula, σ is the standard deviation of all measurement points, and ρ total The resistivity is the average value of the six surfaces of the sample to be tested.

[0013] The smaller the value of the spatial coefficient of variation (CVs), the better the uniformity. The above formula is common knowledge, and this invention does not involve any improvement to the measurement method.

[0014] To achieve another objective of the invention, in some embodiments, the probe includes an electrode base, a piezoelectric ceramic actuator, a pressure sensor, and a needle connected in sequence; the needle is electrically connected to the electrode base, and the electrode base is electrically connected to a power supply; the control processing unit is communicatively connected to the piezoelectric ceramic actuator and the pressure sensor, respectively.

[0015] A pressure sensor is used to acquire the contact pressure between the probe and the surface of the sample to be tested and send it to the control processing unit. When the contact pressure corresponding to a certain probe is inconsistent with the set threshold (e.g., due to surface micro-unevenness), the control processing unit controls the piezoelectric ceramic actuator to drive the probe forward or backward until the pressure sensor returns to the set threshold, thus achieving constant pressure contact control. Through the above constant pressure contact control, the contact state between each probe, or even each needle, and each measurement surface can be kept consistent, and the measurement results can truly reflect the uniformity of graphite.

[0016] Pressure sensors are devices that convert pressure signals into electrical signals. Based on their operating principle, they are classified into piezoresistive, piezoelectric, and capacitive types. Piezoresistive sensors utilize the change in resistance caused by strain gauge deformation (Wheatstone bridge output), suitable for industrial hydraulic systems; piezoelectric sensors are based on the positive piezoelectric effect of quartz / ceramic (pressure generates charge), suitable for dynamic pressure measurement; capacitive sensors change the capacitance value through changes in the distance between electrodes, commonly used for micro-pressure detection. Core parameters include measurement range (e.g., 0–100 MPa), accuracy (±0.5% FS), overload capacity, and operating temperature range. Applications are wide-ranging: industrial monitoring of pipeline pressure or compressor status; automotive tire pressure monitoring (TPMS); real-time blood pressure feedback in medical equipment; and measurement of cabin pressure changes in aerospace. Modern sensors integrate temperature compensation and digital output (I... 2 (C / SPI) improves reliability and integration.

[0017] Piezoelectric ceramic actuators operate using the inverse piezoelectric effect: when a voltage is applied to a piezoelectric ceramic (such as PZT), the internal lattice distortion generates nanoscale mechanical displacement. Their core characteristics include high precision (nanometer-level resolution), fast response (microsecond-level), and wide bandwidth (from a few hertz to hundreds of kilohertz), with high output force and stiffness. Engineering applications require addressing temperature drift (compensated by built-in sensors) and drive power supply stability. Typical applications include precision instrument positioning (such as probe movement in atomic force microscopes), optical system focusing, robotic micromanipulation (such as robotic arms in minimally invasive surgery), and high-frequency fine-tuning in active vibration control systems. Emerging fields such as semiconductor lithography alignment and space telescope mirror calibration are driving their development towards higher temperature stability and lead-free technology.

[0018] The above constant pressure contact control device is existing technology. This utility model only directly applies this existing technology and does not involve any improvement to the control method. References are as follows:

[0019] [1] K Sato, T. Watanabe. Development of a Piezoelectric-Driven ProbeSystem for Nanoscale Electrical Measurements with Active Contact ForceControl. Review of Scientific Instruments. Vol. 88, Issue 6, 2017.

[0020] [2]M.Chen et al.Multi-probe Electrical Testing System with ActiveContact Pressure Stabilization for Heterogeneous Materials.IEEE InternationalConference on Microelectronic Test Structures.IMTS, 2020.

[0021] In some embodiments, a support is also included, with the sample stage located in the center of the support; the measuring unit is provided on the periphery, top surface, and lower part of the support.

[0022] In some embodiments, the measuring unit further includes a guide member; the guide member includes a first crossbeam and two parallel guide rails spaced apart, the two ends of the first crossbeam being fixedly connected to one end of each of the two guide rails, and the other ends of the two guide rails being fixedly connected to the bracket; the bottom of the probe holder is provided with a second crossbeam, the second crossbeam being movably connected to the guide rails; one end of the telescopic mechanism is fixedly connected to the first crossbeam, and the other end is fixedly connected to the second crossbeam.

[0023] In some embodiments, a groove is provided on the guide rail along its length, and a slider that cooperates with the groove is provided on the second crossbeam.

[0024] In some embodiments, the power supply is a multi-channel constant current source.

[0025] In some embodiments, the data acquisition unit is a 24-channel voltage synchronous acquisition card.

[0026] In some embodiments, for each measurement unit, the spacing between two adjacent probes is 5 mm.

[0027] In some embodiments, the needle tip is provided with a diamond coating.

[0028] This invention has at least the following technical effects or advantages: by simultaneously measuring the resistivity of the six surfaces of the graphite under test through six measuring units, the detection efficiency is greatly improved. Furthermore, through constant pressure contact control, the contact state between each probe, and even each needle tip, and each measuring surface can be kept consistent, ensuring that the measurement results accurately reflect the uniformity of the graphite. Attached Figure Description

[0029] Figure 1 This is a front view of a resistivity measuring device for isostatically pressed graphite according to an embodiment of the present invention;

[0030] Figure 2 This is a top view of a resistivity measuring device for isostatically pressed graphite according to an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the working state of an isostatic graphite resistivity measuring device in one embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram of the probe structure in one embodiment of the present invention;

[0033] Figure 5 This is an exploded view of the measuring unit in one embodiment of the present invention;

[0034] Figure 6 This is a circuit connection diagram of an isostatic graphite resistivity measuring device according to one embodiment of the present invention. Detailed Implementation

[0035] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0036] See Figures 1-6 A resistivity measuring device for isostatically pressed graphite includes a sample stage 1 for placing a sample 10 to be tested and a measuring device for measuring the resistivity of the sample 10. In this embodiment, the sample 10 to be tested is a cubic isostatically pressed graphite sample with a side length of 2 cm. The sample stage 1 is a flat plate with a through hole in the middle.

[0037] The measuring device includes six measuring units 2, a data acquisition unit 3, and a control and processing unit 4. A measuring unit 2 is located at each of the six positions of the sample stage 1. Each measuring unit 2 includes a telescopic mechanism 5, a probe holder 6, and four probes 7. The four probes 7 are mounted on one side of the probe holder 6, and the telescopic mechanism 5 is connected to the other side of the probe holder 6 to drive the probe holder 6 closer to or further away from the sample 10 to be tested. All probes 7 are communicatively connected to the data acquisition unit 3, and the control and processing unit 4 is communicatively connected to both the data acquisition unit 3 and the telescopic mechanism 5. The data acquisition unit 3 can be a 24-channel voltage synchronous acquisition card. In this embodiment, the four probes 7 can be arranged linearly or in a matrix, with a spacing of 5 mm between adjacent probes 7.

[0038] As a preferred embodiment, the probe 7 includes an electrode base 71, a piezoelectric ceramic actuator 72, a pressure sensor 73, and a needle tip 74 connected in sequence. The needle tip 74 is electrically connected to the electrode base 71, and the electrode base 71 is electrically connected to a power supply 9, which can be a multi-channel constant current source. The control processing unit 4 is communicatively connected to the piezoelectric ceramic actuator 72 and the pressure sensor 73, respectively. More preferably, the needle tip 74 is provided with a diamond coating.

[0039] As a preferred embodiment, this invention also provides a bracket 8 for mounting the measuring unit 2. The sample stage 1 is located in the center of the bracket 8. The measuring unit 2 is provided on the surrounding walls, top surface, and lower part of the bracket 8.

[0040] As a preferred embodiment, the measuring unit 2 further includes a guide component. The guide component includes a first crossbeam 211 and two parallel guide rails 212 arranged at intervals. Both ends of the first crossbeam 211 are fixedly connected to one end of each of the two guide rails 212, and the other ends of the two guide rails 212 are fixedly connected to the bracket 8. A second crossbeam 213 is provided at the bottom of the probe holder 6, and the second crossbeam 213 is movably connected to the guide rails 212. One end of the telescopic mechanism 5 is fixedly connected to the first crossbeam 211, and the other end is fixedly connected to the second crossbeam 213. More preferably, a groove 214 is provided on the guide rail 212 along its length. More preferably, the length of the groove 214 is half that of the guide rail 212. A slider 215 is provided on the second crossbeam 213 to cooperate with the groove 214. The slider 215 is embedded in the groove 214, thereby allowing the second crossbeam 213 to move along the guide rail 212. The telescopic mechanism 5 can be an electric telescopic rod with a thrust of 500N and a stroke of 20mm. It can extend and retract under the control of the control processing unit 4.

[0041] During operation, the sample 10 to be tested is first placed in the center of the sample stage 1. Then, the control processing unit 4 controls all telescopic mechanisms 5 to extend synchronously until the tips 74 of all probes 7 contact the sample 10. After the tips 74 contact the sample 10, the pressure sensor 73 acquires the contact pressure between the tips 74 and the surface of the sample 10 and sends it to the control processing unit 4. If the contact pressure corresponding to a certain tip 74 is inconsistent with the set threshold (e.g., due to surface micro-unevenness), the control processing unit 4 controls the piezoelectric ceramic actuator 72 to drive the tip 74 to advance or retract until the pressure sensors 73 of all probes 7 reach the set threshold. Finally, orthogonal current injection is performed in the X / Y / Z axes, and the voltage difference between adjacent electrodes in the same plane is synchronously acquired in each excitation cycle. Four sets of voltage values ​​can be obtained from a single surface, and a total of 24 sets of raw data are obtained from six surfaces, that is, the six measurement units 2 simultaneously collect the resistivity data of six surfaces.

[0042] Similarly, it should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, the inventive aspect lies in fewer than all features of a single foregoing disclosed embodiment. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0043] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of this invention and form different embodiments.

[0044] As used herein, unless otherwise specified, the use of ordinal numbers such as “first,” “second,” “third,” etc., to describe ordinary objects merely indicates different instances of similar objects and is not intended to imply that the objects being described must have a given order in time, space, ordering, or any other manner.

[0045] Although the present invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the present invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and edibility purposes, and not for interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. Regarding the scope of the invention, the disclosure made is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0046] Finally, it should be noted that this utility model does not explain in detail the common knowledge recognized by those skilled in the art. The above description is only a specific embodiment of this utility model and is not intended to limit this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. An apparatus for measuring the resistivity of isostatically pressed graphite, comprising a sample stage for placing a sample to be measured and a measuring device for measuring the resistivity of the sample to be measured; characterized in that: The measuring device comprises six measuring units, a data acquisition unit and a control processing unit; one of the measuring units is arranged at each of the six positions of the sample table; each of the measuring units comprises an extension mechanism, a probe base and four probes; the four probes are mounted on one side of the probe base, and the extension mechanism is connected with the other side of the probe base and used to drive the probe base to approach or move away from the sample to be measured; all the probes are in communication connection with the data acquisition unit, and the control processing unit is in communication connection with the data acquisition unit and the extension mechanism.

2. The apparatus for measuring the resistivity of isostatic graphite according to claim 1, characterized by: The probe comprises an electrode base, a piezoelectric ceramic driver, a pressure sensor and a needle head which are connected in sequence; the needle head is electrically connected with the electrode base, and the electrode base is electrically connected with a power supply; the control processing unit is in communication connection with the piezoelectric ceramic driver and the pressure sensor.

3. The apparatus for measuring the resistivity of isostatic graphite according to claim 1 or 2, characterized by: The device further comprises a support, and the sample table is located in the middle of the support; the measuring units are arranged around the support, on the top surface of the support and in the lower part of the support.

4. The apparatus for measuring the resistivity of isostatic graphite according to claim 3, characterized by: The measuring unit further comprises a guide; the guide comprises a first cross beam and two parallelly arranged guide rails, the two ends of the first cross beam are fixedly connected with one ends of the two guide rails respectively, and the other ends of the two guide rails are fixedly connected with the support; the bottom of the probe base is provided with a second cross beam, the second cross beam is movably connected with the guide rails; one end of the extension mechanism is fixedly connected with the first cross beam, and the other end is fixedly connected with the second cross beam.

5. The apparatus for measuring the resistivity of isostatic graphite according to claim 4, characterized by: A sliding groove is formed on the guide rail along the length direction of the guide rail, and a sliding block matched with the sliding groove is arranged on the second cross beam.

6. The apparatus for measuring the resistivity of isostatically pressed graphite according to claim 2, characterized by: The power supply is a multi-channel constant current source.

7. The apparatus for measuring the resistivity of isostatic graphite according to claim 1 or 2, characterized by: The data acquisition unit is a 24-channel voltage synchronous acquisition card.

8. The apparatus for measuring the resistivity of isostatic graphite according to claim 1 or 2, characterized by: For each of the measuring units, the distance between two adjacent probes is 5 mm.

9. The apparatus for measuring the resistivity of isostatically pressed graphite according to claim 2, characterized by: The needle head is provided with a diamond coating.

Images