Method for in-situ characterization of local strain by using photoelectric measurement

Abstract

The invention relates to the field of two-dimensional semiconductor detection, in particular to a method for in-situ characterization of local strain by photoelectric measurement, and aims to solve the problems that in-situ accurate characterization means for local strain are deficient, and local strain cannot be measured in an in-situ refined and quantitative manner. Compared with a traditional piezoelectric force microscope and an electrical measurement technology, a photocurrent imaging technology is adopted, so that a measurable system can be enriched, measurement materials are not limited to a traditional ferroelectric system any more, the localized strain engineering effect can be represented, the strain engineering test can be finer, and the measurement accuracy is improved. Compared with the prior art, the method is more effective in understanding a local strain regulation and control mechanism and testing strain engineering effects, and meanwhile, the photocurrent test generally applies zero bias voltage to a device, and the used exciting light power is lower, so that the sample is not easy to damage, and the method is more lossless compared with a piezoelectric force microscope or electrical measurement.

Description

Technical Field

[0001] The present invention relates to the field of two-dimensional semiconductor detection, and in particular to a method for in-situ characterization of local strain using 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 occurs inside the crystal, resulting in a potential difference at both ends of the material. The flexoelectric effect refers to the polarization phenomenon caused by the strain gradient when the material is bent or mechanically strained. Unlike the piezoelectric effect, the flexoelectric effect originates from the strain gradient. Even non-polar materials can produce changes in charge distribution and form an electric dipole moment when bent. Due to the difference in thermal expansion coefficients of different materials, there will be stress to be released at the interface when the device is subjected to temperature change operation, which ultimately easily introduces local strain in the device. It is also easy to introduce local strain in the process of preparing 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. It has important applications in flexible devices, optoelectronic devices, and non-volatile memory.

[0004] However, the existing piezoelectric force microscope and electrical measurement technology are limited to the characterization of local strain in ferroelectric materials, while electrical measurement can only obtain the contact resistance of the entire device, and cannot distinguish the localized strain engineering control effect. Therefore, the existing technology lacks in-situ precise characterization methods for local strain. In order to precisely and quantitatively measure the effect of local strain in-situ, a method for diagnosing local strain using confocal photocurrent imaging technology has been developed.

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

[0006] The photocurrent imaging technology used in the present invention can not only enrich the measurable system, so that the measured material is no longer limited to the traditional ferroelectric system, but also characterize the localized strain engineering effect, so that the strain engineering test can be more precise, which is more effective for understanding the local strain regulation mechanism and testing the strain engineering effect. It solves the problem that the in-situ accurate characterization means for local strain are relatively scarce and the local strain cannot be precisely and quantitatively measured in situ, and proposes a method for in-situ characterization of local strain using photoelectric measurement.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for in-situ characterization of local strain using photoelectric measurement, comprising the following steps:

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

[0010] Step 2: Build a confocal optoelectronic imaging device, place the device to be tested 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: The light source and the laser transmitting end emit light and a laser beam, which are reflected and refracted by a beam splitter and then irradiated to an area on the device to be measured;

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

[0013] 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.

[0014] 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;

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

[0016] As a preferred embodiment of the present invention, the confocal optoelectronic imaging device in step 2 includes a CMOS camera, and a plurality of groups of beam splitters are arranged under the lens of the CMOS camera, wherein one side of the upper two groups of beam splitters are respectively provided with a light source and a laser emitting end, and one side of the lowermost group of beam splitters is provided with a single photon counter, and the sample placement position is connected to an active meter, and the optoelectronic signal emitted by the device to be tested is collected through the source meter, and the source meter, the single photon counter and the CMOS camera are all connected to a control center.

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

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

[0019] 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;

[0020] 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.

[0021] As a preferred embodiment of the present invention, the method for processing the sample to be detected in step 1 is:

[0022] 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. Then, a metal electrode is transferred above the sample to be tested using the "method for electrode transfer using fluorphlogopite mica". The PMMA flexible substrate, the sample to be tested, and the electrode are connected to a base that is adapted to the sample placement position by means of silver glue leads to form a device to be measured.

[0023] As a preferred embodiment of the present invention, the method for collecting the reflected light image in step 4 is:

[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. It is collected by the single photon counter to obtain a reflected light signal.

[0025] As a preferred embodiment of the present invention, the method for collecting the photoelectric signal in step 4 is:

[0026] The light emitted from the laser emitting end is refracted by the second group of beam-forming mirrors and projected by the third group of beam-forming mirrors before being irradiated on the device to be detected. After being excited by the laser, the device to be detected generates an electrical signal, which is then collected by the source meter.

[0027] As a preferred embodiment of the present invention, the method of applying strain engineering in step six includes bending a flexible substrate or a corrugated substrate, imprinting the device using an AFM tip or other tip, and changing the shape of the device to be tested using heat, force, electricity, and magnetism.

[0028] As a preferred embodiment of the present invention, the method for obtaining the local strain distribution in step 4 is:

[0029] 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.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. In the present invention, the photocurrent imaging technology is used. Compared with the traditional piezoelectric force microscope and electrical measurement technology, it can not only enrich the measurable system so that the measured material is no longer limited to the traditional ferroelectric system, but also characterize the localized strain engineering effect, so that the strain engineering test can be more precise, which is more effective for understanding the local strain regulation mechanism and testing the strain engineering effect.

[0032] 2. In the present invention, reflected light imaging is performed simultaneously with photocurrent imaging, achieving a one-to-one mapping between reflected light imaging and photocurrent imaging, and enabling high-resolution in-situ characterization of local strain, thereby being able to simultaneously apply a variety of strain engineering projects of different degrees or types, and characterize their effects accordingly, greatly improving the test efficiency.

[0033] 3. The present invention is more non-destructive than piezoelectric force microscopy or electrical measurement. Traditional electrical measurement requires the application of an external bias, which may burn out the device. Piezoelectric force microscopy measurement requires scanning in needle tip contact mode and also requires the application of an external bias, which may easily scratch the sample or cause the sample to bulge due to the needle tip voltage. The photocurrent test in the present invention generally applies zero bias to the device and uses a relatively low excitation light power, so it is not easy to cause damage to the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

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

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

[0037] Figure 3 This is a diagram for constructing a first device to be detected according to the present invention;

[0038] Figure 4 This is a diagram for constructing a second device to be detected according to 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

[0040] The technical scheme of the present invention will be described clearly and completely in conjunction with the embodiments below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Embodiment 1:

[0042] See also Figure 1 - Figure 4 As shown, a method for in-situ characterization of local strain using photoelectric measurement comprises the following steps:

[0043] Step 1: Process the sample to be tested, select a PMMA flexible substrate, and transfer a thin layer or a single layer of the sample to be tested on the PMMA flexible substrate using the PDMS dry transfer method, and then use the "method for electrode transfer using fluorphlogopite mica" to transfer the metal electrode above the sample to be tested, and connect the PMMA flexible substrate, the sample to be tested and the electrode to the base adapted to the sample placement position 5 through silver glue leads to form a device to be measured, such as Figure 3 As shown;

[0044] Alternatively, the PVA transfer method may be used to stack the graphene, the sample to be detected and the graphene layer by layer, and the whole is placed on the PMMA flexible substrate, and the electrode is transferred to the graphene after the sample to be detected is transferred, and the upper and lower graphenes can also be directly replaced by thin-layer metal electrodes, and the area where the sample to be detected overlaps with the upper and lower graphenes is imprinted with a needle tip, and the imprinted pattern can be a dot array, a line array or a surface imprint, and the combination of the substrate, the sample to be detected, the graphene and the electrode is connected to the base adapted in the sample placement position 5 by means of silver glue leads to form a device to be measured, such as Figure 4 As shown;

[0045] Step 2: Build 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;

[0046] Step 3: light and laser beam are emitted through the light source 2 and the laser emitting end 3, and are reflected and refracted by the beam splitter and then irradiated to an area on the device to be measured;

[0047] Step 4: The light emitted by the laser emitting end 3 is converted into parallel light by a lens, refracted by the top beam splitter 9, and transmitted through the two groups of beam splitters 9 below, and then irradiated on the device to be detected, and reflected by the device to be detected, and then refracted by the bottom group of beam splitters 9, and then attenuated by a filter or an attenuation plate, focused by a lens, and covered by a small hole in turn, and finally collected by a single photon counter 7 to obtain a reflected light signal, thereby obtaining a reflected light image through the reflected light of the laser emitting end 3, and the light emitted by the laser emitting end 3 is refracted by the second group of beam splitters 9, and projected by the third group of beam splitters 9, and then irradiated on the device to be detected. After the device to be detected is excited by the laser, an electrical signal is generated, and the electrical signal is collected through the source meter 6, and then a reflected light image is generated according to the acquired reflected light signal, and a photocurrent image is generated according to the acquired photoelectric signal, and 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, and the photocurrent image and the reflected light signal image are jointly characterized by the local strain;

[0048] 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.

[0049] Step 6: applying strain engineering to the device to be measured, wherein the step of applying strain engineering includes bending a flexible substrate or a corrugated substrate, using an AFM tip or other tips to imprint the device, using heat, force, electricity, and magnetism to change the shape of the device to be detected, and collecting photoelectric signals and reflected light images again after the strain engineering is completed to obtain 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 strain engineering application effect;

[0051] At the same time, by adjusting the degree of applied strain engineering, multiple experiments are conducted on the effects of strain engineering of different degrees 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] See also Figure 1 - Figure 4 As shown, the confocal optoelectronic imaging device includes a CMOS camera 1, and a plurality of groups of beam mirrors 9 are arranged below the lens of the CMOS camera 1, wherein one side of the upper two groups of beam mirrors are respectively provided with a light source 2 and a laser emitting end 3, and one side of the lowest group of beam mirrors 9 is provided with a single photon counter 7, and a sample placement position 5 is connected to an active meter 6, and the optoelectronic 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;

[0054] The illumination light emitted by the light source 2 is converted into parallel light through the lens, and is focused by the objective lens onto the device to be detected through reflection by the top beam splitter 9 and transmission by the two groups of beam splitters 9 at the bottom. The reflected light then passes through three groups of beam splitters 9 to reach the CMOS camera 1, and finally an optical image of the device is taken, which helps to find the approximate position of the sample and the electrode.

[0055] The control center 8 is provided with a photoelectric measurement system, which can control the light source 2 to emit light and the laser emitting end 3 to emit a laser beam;

[0056] The photoelectric measurement system obtains the approximate spot position 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 make a judgment on the local strain distribution;

[0058] 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 results to confirm whether the strain engineering effect meets the requirements.

[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 invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only 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 effect of strain engineering application.

2. The method for in-situ characterization of local strain using photoelectric measurement according to claim 1, characterized in that: The confocal photoelectric 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 provided with a light source (2) and a laser emitting end (3), respectively, 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).

3. The method for in-situ characterization of local strain using photoelectric measurement according to claim 2, characterized in that: The control center (8) is provided with a photoelectric measurement system, and the photoelectric measurement system is capable of controlling the light source (2) to emit light and controlling the laser emitting end (3) to emit a laser beam; The photoelectric measurement system obtains 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.

4. 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 single layer or a preset number of layers of the sample to be tested is transferred onto the PMMA flexible substrate using the PDMS dry transfer method. A metal electrode is then transferred above the sample to be tested using the "method for electrode transfer using fluorphlogopite mica". 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.

5. The method of 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 top beam splitter (9), and is transmitted through the two groups of beam splitters (9) below, before being irradiated on the device to be detected, and is reflected by the device to be detected, and is refracted by the bottom group of beam splitters (9), before being collected by the single photon counter (7) to obtain a reflected light signal.

6. The method of 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) before being irradiated on the device to be detected. After being excited by the laser, the device to be detected generates an electrical signal, which is then collected by the source meter (6).

7. The method of in-situ characterization of local strain using photoelectric measurement according to claim 4, 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.

8. The method for in-situ characterization of local strain using photoelectric measurement according to claim 5, 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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