A method for in-situ characterization of local strain by optoelectronic measurement

Abstract

The present invention relates to the field of two-dimensional semiconductor detection, and is used to solve the problem that there is a lack of in-situ precise characterization means for local strain and it is impossible to perform in-situ refined quantitative measurement of local strain. Specifically, it is a method for in-situ characterizing local strain using optoelectronic measurement. In the present invention, photocurrent imaging technology is adopted. Compared with traditional piezoresponse force microscopy and electrical measurement techniques, it can not only enrich the measurable systems, making the measured materials no longer limited to traditional ferroelectric systems, but also characterize the effects of localized strain engineering, making the testing of strain engineering more refined, more effective for understanding the local strain regulation mechanism and testing the strain engineering effects. At the same time, in the photocurrent test of the present invention, generally zero bias voltage is applied to the device, and the excitation light power used is also low, so it is not easy to damage the sample, and it is more non-destructive than piezoresponse force microscopy or electrical measurement.

Description

Technical Field

[0001] The present invention relates to the field of two-dimensional semiconductor detection, and specifically to a method for in-situ characterizing local strain by photoelectric measurement. Background Art

[0002] The piezoelectric effect refers to the phenomenon that when certain specific crystal materials are subjected to mechanical stress, charge separation will occur inside the crystal, and a potential difference will appear at both ends of the material. The flexoelectric effect refers to the phenomenon of electrode polarization caused by strain gradient when the material is bent or mechanically strained. Different from the piezoelectric effect, the flexoelectric effect originates from the strain gradient. Even non-polar materials can generate changes in charge distribution and form electric dipole moments when bent. Due to the difference in the thermal expansion coefficients of different materials, there will be stress to be released at the interface during the temperature change operation of the device, which is likely to introduce local strain into the device in the end. Local strain is also easily introduced during the process of fabricating micro-devices;

[0003] For electronic devices, local strain is ubiquitous. At the same time, the flexoelectric effect can be used to write ferroelectric domains, enhance the photovoltaic effect of the device, and reduce the contact resistance of the electrode, and has important applications in flexible devices, optoelectronic devices, non-volatile memories, etc.;

[0004] However, in the existing piezoresponse force microscopy and electrical measurement techniques, the former is limited to the characterization of local strain in ferroelectric materials, while electrical measurement can only obtain the overall contact resistance of the device and cannot distinguish the effect of localized strain engineering regulation. Therefore, there are relatively few in-situ precise characterization means for local strain in the existing technology. In order to in-situ finely and quantitatively measure the effect of local strain, a method for diagnosing local strain by using confocal photocurrent imaging technology has been developed;

[0005] In view of the above technical problems, the present application proposes a solution. Summary of the Invention

[0006] In the present invention, photocurrent imaging technology is adopted. Compared with the traditional piezoresponse force microscopy and electrical measurement techniques, it can not only enrich the measurable system, making the measured materials no longer limited to the traditional ferroelectric system, but also characterize the effect of localized strain engineering, making the test of strain engineering more refined, which is more effective for understanding the local strain regulation mechanism and testing the strain engineering effect, and solves the problem that there are relatively few in-situ precise characterization means for local strain and it is impossible to in-situ finely and quantitatively measure local strain, and thus a method for in-situ characterizing local strain by photoelectric measurement is proposed.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] A method for in-situ characterizing local strain by photoelectric measurement, comprising the following steps:

[0009] Step 1: Process the sample to be detected and combine it into a device to be measured;

[0010] Step 2: Set up a confocal optoelectronic imaging device, place the device to be detected in the sample placement position of the variable-temperature vacuum chamber, and evacuate or adjust the temperature of the sample test environment through the variable-temperature vacuum chamber;

[0011] Step 3: Emit light and a laser beam through the light source and the laser emission end, and after being reflected and refracted by the beam splitter, irradiate a region on the device to be measured;

[0012] Step 4: Obtain a reflected light image through the reflected light of the laser emission end, excite the sample to be detected through the laser beam, collect the optoelectronic signal through the source meter, and combine the reflected light image and the optoelectronic signal to obtain the local strain distribution;

[0013] Step 5: Determine whether time strain engineering is required. If it is required, proceed to Step 6. If it is not required, record the strain distribution and degree and end the test;

[0014] Step 6: Apply strain engineering to the device to be measured through the probe, and collect the optoelectronic signal and the reflected light image again to obtain the local strain distribution;

[0015] Step 7: Compare the local strain distribution in Step 4 with the local strain distribution in Step 6 to obtain the application effect of the strain engineering.

[0016] As a preferred embodiment of the present invention, the confocal optoelectronic imaging device in Step 2 includes a CMOS camera. Below the lens of the CMOS camera, there are multiple beam splitters. One side of the upper two beam splitters is respectively provided with a light source and a laser emission end, and one side of the lowermost beam splitter is provided with a single-photon counter. The sample placement position is connected to a source meter, and the source meter collects the optoelectronic signal emitted by the device to be detected. The source meter, the single-photon counter, and the CMOS camera are all connected to the control center.

[0017] As a preferred embodiment of the present invention, an optoelectronic measurement system is provided in the control center, and the optoelectronic measurement system can control the light source to emit light and control the laser emission end to emit a laser beam;

[0018] The optoelectronic measurement system obtains the approximate spot position through the CMOS camera, obtains the reflected light signal through the single-photon counter, and collects the optoelectronic signal excited by the device to be detected through the source meter;

[0019] The optoelectronic measurement system fuses the reflected light signal and the optoelectronic signal to obtain the local strain distribution and judges the local strain distribution;

[0020] The optoelectronic measurement system compares the local strain distributions before and after the stress application process, and makes a judgment based on the comparison result to confirm whether the effect of the strain process meets the standard.

[0021] As a preferred embodiment of the present invention, the method for processing the sample to be detected in step one is as follows:

[0022] Select a PMMA flexible substrate, transfer the thin layer or single layer of the sample to be detected on the PMMA flexible substrate by using the PDMS dry transfer method, then transfer the metal electrode above the sample to be detected by using the "method for electrode transfer using fluorophlogopite", and connect the PMMA flexible substrate, the sample to be detected, and the electrode to the matching base in the sample placement position by means of silver glue leads to form the device to be measured.

[0023] As a preferred embodiment of the present invention, the method for collecting the reflected light image in step four is as follows:

[0024] The light emitted from the laser emission end is refracted by the top beam splitter, transmitted through the two sets of beam splitters below, irradiated on the device to be detected, reflected by the device to be detected, and then refracted by the bottom set of beam splitters and collected by the single photon counter to obtain the reflected light signal.

[0025] As a preferred embodiment of the present invention, the method for collecting the optoelectronic signal in step four is as follows:

[0026] The light emitted from the laser emission end is refracted by the second beam splitter and projected by the third beam splitter, irradiated on the device to be detected. After being excited by the laser, the device to be detected generates an electrical signal, and the source meter collects the electrical signal.

[0027] As a preferred embodiment of the present invention, the method for applying the strain process in step six includes bending the flexible substrate and the corrugated substrate, imprinting the device with an AFM tip or other tip, and changing the shape of the device to be detected by using various means such as heat, force, electricity, and magnetism.

[0028] As a preferred embodiment of the present invention, the method for obtaining the local strain distribution in step four is as follows:

[0029] According to the obtained reflected light signal, a reflected light image is generated. According to the obtained optoelectronic signal, a photocurrent image is generated. The reflected light signal and the photocurrent image are overlapped so that the features in the reflected light signal image and the photocurrent image correspond one by one, and the local strain is characterized by the photocurrent image and the reflected light signal image together.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. In the present invention, the photocurrent imaging technology is adopted. Compared with the traditional piezoresponse force microscopy and electrical measurement techniques, it can not only enrich the measurable systems, making the measured materials no longer limited to the traditional ferroelectric systems, but also characterize the localized strain engineering effects, enabling the testing of strain engineering to be more precise and more effective for understanding the localized strain regulation mechanism and testing the strain engineering effects.

[0032] 2. In the present invention, while performing photocurrent imaging, reflected light imaging is carried out, realizing a one-to-one mapping between the reflected light imaging and the photocurrent imaging, enabling high-resolution in-situ characterization of the localized strain. Thus, multiple different degrees or types of strain engineering can be applied simultaneously, and their effects can be characterized accordingly, greatly improving the testing efficiency.

[0033] 3. In the present invention, compared with piezoresponse force microscopy or electrical measurement, it is more non-destructive. Traditional electrical measurement requires the application of an external bias voltage, which poses a risk of burning out the device. While piezoresponse force microscopy measurement requires scanning in the tip contact mode and also requires the application of an external bias voltage, which is likely to scratch the sample or cause the sample to bulge due to the tip voltage. In the photocurrent test of the present invention, generally a zero bias voltage is applied to the device, and the excitation light power used is also relatively low. Therefore, it is not easy to damage the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] For the convenience of those skilled in the art to understand, the present invention will be further described below with reference to the accompanying drawings.

[0035] Figure 1 is the system flow chart of the present invention;

[0036] Figure 2 is the schematic diagram of the principle of the confocal photoelectric imaging device of the present invention;

[0037] Figure 3 is the construction diagram of the first device to be detected of the present invention;

[0038] Figure 4 is the construction diagram of the second device to be detected of the present invention.

[0039] In the figure: 1. CMOS camera; 2. Light source; 3. Laser emission end; 4. Variable-temperature vacuum chamber; 5. Sample placement position; 6. Source meter; 7. Single-photon counter; 8. Control center; 9. Beam splitter. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0041] Example 1:

[0042] Please refer to Figure 1 - Figure 4 As shown in the figure, a method for in-situ characterization of local strain using photoelectric measurement includes the following steps:

[0043] Step 1: Process the sample to be detected. Select a PMMA flexible substrate, and use the PDMS dry transfer method to transfer a thin layer or a single layer of the sample to be detected on the PMMA flexible substrate. Then, use the "method for electrode transfer using fluorophlogopite" to transfer a metal electrode above the sample to be detected. Connect the PMMA flexible substrate, the sample to be detected, and the electrode to the matching base in the sample placement position 5 through silver glue leads to form a device to be measured, as Figure 3 shown;

[0044] It is also possible to stack graphene, the sample to be detected, and graphene layer by layer using the PVA transfer method, and place them on the PMMA flexible substrate as a whole. After transferring the sample to be detected, transfer the electrode to the graphene. The upper and lower graphene can also be directly replaced by thin-layer metal electrodes. Use a tip to imprint the area where the sample to be detected overlaps with the upper and lower graphene. The imprinted pattern can be a dot array, a line array, or a surface imprint. Connect the combination of the substrate, the sample to be detected, graphene, and the electrode to the matching base in the sample placement position 5 through silver glue leads to form a device to be measured, as Figure 4 shown;

[0045] Step 2: Build a confocal photoelectric imaging device. Place the device to be detected in the sample placement position 5 of the variable-temperature vacuum chamber 4, and evacuate or adjust the temperature of the sample test environment through the variable-temperature vacuum chamber 4;

[0046] Step 3: Emit light and a laser beam through the light source 2 and the laser emission end 3, and after reflection and refraction by the beam splitter, irradiate a region on the device to be measured;

[0047] Step 4: The light emitted by the laser emission end 3 is changed into parallel light by a lens, refracted by the top beam splitter 9, transmitted through the two sets of beam splitters 9 below, irradiated on the device to be detected, reflected by the device to be detected, refracted by the bottom set of beam splitters 9, attenuated by a filter or an attenuator, focused by a lens, and masked by a small hole in sequence, and finally collected by the single photon counter 7 to obtain a reflected light signal. Thus, a reflected light image is obtained from the reflected light of the laser emission end 3. The light emitted by the laser emission end 3 is refracted by the second beam splitter 9 and projected by the third beam splitter 9, and then irradiated on the device to be detected. After being excited by the laser, the device to be detected generates an electrical signal, and the source meter 6 collects the electrical signal. Then, according to the obtained reflected light signal, a reflected light image is generated, and according to the obtained optoelectronic signal, a photocurrent image is generated. The reflected light signal and the photocurrent image are overlapped so that the features in the reflected light signal image and the photocurrent image correspond one by one. The local strain is characterized by the photocurrent image and the reflected light signal image;

[0048] Step 5: Determine whether time strain engineering is required. If it is required, go to Step 6; if not, record the strain distribution and degree, and end the test;

[0049] Step 6: Steps for applying strain engineering to the device to be measured, where the steps for applying strain engineering include bending a flexible substrate or a corrugated substrate, imprinting the device with an AFM tip or other tips, changing the shape of the device to be detected by various means such as heat, force, electricity, and magnetism, and collecting the optoelectronic signal and the reflected light image again after the strain engineering is applied to obtain the local strain distribution;

[0050] Step 7: Compare the local strain distribution in Step 4 with the local strain distribution in Step 6 to obtain the effect of applying the strain engineering;

[0051] Meanwhile, by adjusting the degree of the applied strain engineering, experiments are conducted multiple times on the effects generated by different degrees of strain engineering at the same position of the device to be detected, and the effects brought by various different strain engineering are obtained.

[0052] Embodiment 2:

[0053] Please refer to Figure 1 - Figure 4 As shown, the confocal optoelectronic imaging device includes a CMOS camera 1. Below the lens of the CMOS camera 1, there are multiple sets of beam splitters 9. One side of the two upper sets of beam splitters is respectively provided with a light source 2 and a laser emission end 3. One side of the bottom set of beam splitters 9 is provided with a single photon counter 7. The sample placement position 5 is connected to a source meter 6, and the source meter 6 collects the optoelectronic signal emitted by the device to be measured. The source meter 6, the single photon counter 7, and the CMOS camera are all connected to the control center 8;

[0054] The illumination light emitted by the light source 2 becomes parallel light after passing through the lens, and after being reflected by the top beam splitter 9 and transmitted through the two sets of beam splitters 9 below, it is focused on the device to be detected by the objective lens. The reflected light then passes through the three beam splitters 9 and reaches the CMOS camera 1, finally performing optical imaging on the device, and its function is to assist in finding the approximate positions of the sample and the electrodes.

[0055] A photoelectric measurement system is provided in the control center 8. The photoelectric measurement system can control the light source 2 to emit light and control the laser emission end 3 to emit a laser beam;

[0056] The photoelectric measurement system obtains the approximate position of the light spot through the CMOS camera 1, obtains the reflected light signal through the single-photon counter 7, and collects the photoelectric signal excited by the device to be detected through the source meter 6;

[0057] The photoelectric measurement system fuses the reflected light signal and the photoelectric signal to obtain the local strain distribution and judges the local strain distribution;

[0058] The photoelectric measurement system compares the local strain distributions before and after applying the stress engineering, and makes a judgment according to the comparison result to confirm whether the effect of the strain engineering meets the standard.

[0059] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the present invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. This specification selects and specifically describes these embodiments to better explain the principle and practical application of the present invention, so that those skilled in the art in the relevant technical field can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for in-situ characterization of local strain using photoelectric measurement, characterized in that: The following steps are involved: Step 1: Process the sample to be tested and combine it into the device to be measured; Step 2: construct a confocal optoelectronic imaging device, place the device to be tested in the sample placement position (5) of the variable temperature vacuum chamber (4), and evacuate or adjust the temperature of the sample test environment through the variable temperature vacuum chamber (4); Step 3: The light source (2) and the laser emitting end (3) emit light and a laser beam, which are reflected and refracted by a beam splitter and then irradiated onto an area on the device to be measured; Step 4: Obtain a reflected light image through the reflected light from the laser emitting end (3), excite the sample to be tested through the laser beam, collect the photoelectric signal through the source meter (6), combine the reflected light image and the photoelectric signal, and obtain the local strain distribution; Step 5: Determine whether time strain engineering is needed. If so, proceed to step 6. If not, record the strain distribution and degree and end the test. Step 6: Apply strain engineering to the device to be measured through the probe, and collect the photoelectric signal and reflected light image again to obtain the local strain distribution; Step 7: Compare the local strain distribution in step 4 with the local strain distribution in step 6 to obtain the strain engineering application effect; The confocal optoelectronic imaging device in step 2 comprises a CMOS camera (1), wherein a plurality of groups of beam splitters (9) are arranged below the lens of the CMOS camera (1), wherein one side of the two upper groups of beam splitters is respectively provided with a light source (2) and a laser emitting end (3), and one side of the lowermost group of beam splitters (9) is provided with a single photon counter (7), and the sample placement position (5) is connected to an active meter (6), and the photoelectric signal emitted by the device to be tested is collected through the source meter (6), and the source meter (6), the single photon counter (7) and the CMOS camera are all connected to a control center (8); The control center (8) is provided with a photoelectric measurement system, and the photoelectric measurement system can control the light source (2) to emit light and control the laser emitting end (3) to emit a laser beam; The photoelectric measurement system acquires the approximate light spot position through a CMOS camera (1), obtains the reflected light signal through a single photon counter (7), and collects the photoelectric signal excited by the device to be detected through a source meter (6); The photoelectric measurement system fuses the reflected light signal and the photoelectric signal to obtain the local strain distribution, and makes a judgment on the local strain distribution; The photoelectric measurement system compares the local strain distribution before and after the stress engineering is applied, and makes a judgment based on the comparison result to confirm whether the strain engineering effect meets the standard.

2. The method for in-situ characterization of local strain using photoelectric measurement according to claim 1, characterized in that: The method for processing the sample to be detected in step 1 is: A PMMA flexible substrate is selected, and a thin layer or a single layer of the sample to be tested is transferred onto the PMMA flexible substrate using the PDMS dry transfer method, and then a metal electrode is transferred above the sample to be tested using the "method for electrode transfer using fluorphlogopite mica", and the PMMA flexible substrate, the sample to be tested and the electrode are connected to a base adapted to the sample placement position (5) by means of silver glue leads to form a device to be measured.

3. The method for in-situ characterization of local strain using photoelectric measurement according to claim 1, characterized in that: The method for collecting the reflected light image in step 4 is: Light emitted from the laser emission end (3) is refracted by the uppermost beam splitter (9), and is transmitted through the two lower groups of beam splitters (9), irradiated on the device to be detected, and is reflected by the device to be detected, and is refracted by the lowermost group of beam splitters (9), and is collected by the single photon counter (7) to obtain a reflected light signal.

4. The method for in-situ characterization of local strain using photoelectric measurement according to claim 1, characterized in that: The method for collecting the photoelectric signal in step 4 is: The light emitted by the laser emitting end (3) is refracted by the second group of beam-forming mirrors (9), and projected by the third group of beam-forming mirrors (9), and then irradiated on the device to be detected. After being excited by the laser, the device to be detected generates an electrical signal, and the electrical signal is collected by the source meter (6).

5. The method of in-situ characterization of local strain using photoelectric measurement according to claim 1, characterized in that: The method of applying strain engineering in step six includes bending a flexible substrate or a corrugated substrate, using an AFM tip or other tips to imprint the device, and using heat, force, electricity, and magnetism to change the shape of the device to be tested.

6. The method of in-situ characterization of local strain using photoelectric measurement according to claim 1, characterized in that: The method for obtaining the local strain distribution in step 4 is: A reflected light image is generated based on the acquired reflected light signal, and a photocurrent image is generated based on the acquired photoelectric signal. The reflected light signal and the photocurrent image are overlapped so that the features in the reflected light signal image and the photocurrent image correspond one to one. The local strain is jointly characterized by the photocurrent image and the reflected light signal image.

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