A pulsed laser irradiation experimental device

Abstract

The present invention relates to a pulsed laser irradiation experimental device. It comprises an optical parameter measurement platform, an optical coupling module, an optoelectronic test module, an electrical test platform, and a first control system and a second control system. The first control system is used to fit the ellipsometric state change parameters with a scanning model to obtain the refractive index and extinction coefficient of a single-layer thin film. The second control system is used to input the refractive index, extinction coefficient, reflectivity, and transmittance of the thin film into a device incident model to calculate the effective pulsed laser energy of pulsed lasers of different wavelengths when they pass through each layer of thin film and reach the active region in a wide bandgap power device to be tested. The equivalent heavy ion LET value is obtained based on the effective pulsed laser energy, and the optical coupling module, optoelectronic test module, and electrical test platform are controlled to perform closed-loop regulation of the pulsed laser energy. The present invention achieves accurate control and regulation of pulsed laser energy.

Description

Technical Field

[0001] The present invention belongs to the technical field of pulse laser irradiation of silicon carbide and gallium nitride based wide bandgap power devices and device irradiation characteristic parameter testing, and particularly relates to a pulse laser irradiation experimental device. Background Art

[0002] Third-generation wide-bandgap semiconductor materials, represented by silicon carbide (SiC) and gallium nitride (GaN), offer wider bandgap widths, higher breakdown electric fields, faster switching speeds, lower on-resistance, and higher thermal conductivity. These materials are capable of meeting the stringent operating temperature, breakdown voltage, and switching frequency requirements of power devices, and are therefore widely considered a core component for new power supplies and high-power conversion systems. Wide-bandgap power devices significantly reduce the size and weight of passive components and increase power density. Furthermore, their inherent resistance to displacement damage and total dose effects provides inherent advantages for space applications.

[0003] However, the application of wide-bandgap power devices faces challenges with space radiation damage and reliability, and their failure mechanisms require further investigation. Therefore, there is a need to develop an experimental setup for pulsed laser irradiation of wide-bandgap power devices to evaluate the performance degradation of devices after irradiation. Because actual experiments in space are prohibitively expensive and experimental cycles are difficult to determine, various experimental devices are typically used to simulate the radiation exposure of devices. Traditional irradiation experiments typically rely on neutron sources, proton sources, or heavy ion accelerators, but these are time-consuming, costly, and require long testing cycles. Operators must be kept away from the radiation source, resulting in limited real-time control, difficulty in data collection, and insufficient test accuracy. To this end, research using pulsed lasers to irradiate equivalent heavy ions for irradiation experiments is a commonly used testing method. However, existing pulsed laser irradiation experimental devices still have the following major shortcomings: 1. Existing devices lack real-time mapping and calibration of "pulsed laser energy and heavy ion LET," making it impossible to quantitatively calculate the pulsed laser energy equivalent to a specific heavy ion LET value; 2. Due to insufficient precision, the experimental device cannot automatically align with the sensitive area of ​​the device, resulting in an uncertain irradiation area; 3. Rapid evaluation of electrical characteristics before and after irradiation is difficult; and 4. The number of test items that can be performed by the experimental device is limited. Therefore, a pulsed laser irradiation experimental device is urgently needed to overcome these shortcomings. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies in the above-mentioned background technology and to provide a pulsed laser irradiation experimental device. This device is used to address the following issues: the inability to quantitatively calculate the pulsed laser energy equivalent to the LET value of a specific heavy ion, the inability to accurately adjust the pulsed laser energy, the inability to accurately locate the pulsed laser irradiation area, the inability to achieve real-time acquisition of device parameters before and after irradiation for different dynamic test items, poor device electrical performance after irradiation, degradation or failure of the device gate control capability, increased gate leakage current IGS and off-state drain-source current IDS, exacerbated gate voltage oscillation during the turn-on and turn-off processes, and impact on normal testing.

[0005] The technical solution adopted by the present invention is: a pulse laser irradiation experimental device, including an optical parameter measurement platform, an optical path coupling module, a photoelectric test module, an electrical test platform, and a first control system and a second control system;

[0006] The optical parameter measurement platform is used to measure the ellipsometric state change parameters, reflectivity and transmittance of a single-layer thin film grown on a substrate, corresponding to each layer of thin film material of a wide bandgap power device to be measured, within a full spectral range;

[0007] The optical path coupling module is used to incident the pulsed laser onto the surface of the wide bandgap power device to be measured through the optical path, control the wavelength, energy and incident position of the pulsed laser, and perform real-time imaging of the surface morphology of the wide bandgap power device to be measured and the pulsed laser irradiation position;

[0008] The photoelectric test module is electrically connected to the gate, drain, and source of the wide bandgap power device to be tested via a probe station, and is used to perform conventional electrical and photoelectric characteristic tests on the wide bandgap power device to be tested before and after irradiation;

[0009] The electrical test platform is connected to the test circuit via a reserved power line interface, and the wide bandgap power device to be tested is connected to the test circuit by plugging and unplugging, so as to perform dynamic switching characteristic testing on the wide bandgap power device to be tested before and after irradiation;

[0010] The first control system is used to fit the ellipsometric state change parameters with the scanning model to obtain the refractive index and extinction coefficient of the single-layer film and transmit the refractive index, extinction coefficient, reflectivity and transmittance of the single-layer film to the second control system;

[0011] The second control system is used to input the refractive index, extinction coefficient, reflectivity and transmittance of the thin film into the device incident model to calculate the effective pulse laser energy of pulse lasers of different wavelengths when they pass through each layer of thin film and reach the active area in the wide bandgap power device to be tested, obtain the equivalent heavy ion LET value based on the effective pulse laser energy, and control the optical path coupling module, optoelectronic test module and electrical test platform to close-loop adjust the pulse laser energy based on the equivalent heavy ion LET value.

[0012] In the above solution, the single-layer thin film is the thin film material of each layer in the actual wide bandgap power device to be tested, which is grown on a substrate such as sapphire by processes such as physical vapor deposition or plasma chemical vapor deposition.

[0013] More preferably, the optical parameter measurement platform includes an ellipsometer, a spectrophotometer and a custom test sample, wherein the custom test sample is used to provide a single-layer film; the ellipsometer is used to scan the custom test sample in the infrared to ultraviolet wavelength range to obtain the ellipsometric state change parameters of the single-layer film; the spectrophotometer is used to scan the custom test sample in the infrared to ultraviolet wavelength range to obtain the reflectivity and transmittance of the single-layer film.

[0014] Preferably, the optical path coupling module includes a pulse laser control unit, an energy control unit, a microscopic imaging unit and an electric scanning unit; the pulse laser control unit includes multiple groups of pulse lasers of different wavelengths, a pull-rod switch and an excitation light source coupling optical path, which is used to emit pulse lasers of different wavelengths and adjust the incident light direction; the energy control unit includes an optical path reflection module, a continuously adjustable attenuation plate and an OD3 filter, which is used to continuously control the pulse laser intensity over a large range and reflect the pulse laser into the microscopic imaging unit; the microscopic imaging unit includes a long working distance visible objective lens, a white lighting LED, an illumination filter, a microscopic camera, a microscopic coarse and fine adjustment bracket, an electric shutter and an imaging optical path, which is used to coaxially illuminate the wide bandgap power device to be tested, focus imaging and obtain high-resolution microscopic images in real time; the electric scanning unit includes a high-precision XY motor and photocurrent scanning imaging software, which is used to scan the surface of the wide bandgap power device to be tested point by point in a two-dimensional plane, collect and record the photocurrent signal of each scanning point in real time and generate a photocurrent distribution image.

[0015] More preferably, the photoelectric test module includes a transient photoelectric test unit, a custom source meter, a high-precision optical power meter and photoelectric test software. The transient photoelectric test unit includes a high-performance oscilloscope and a high-speed amplifier for collecting high-speed data and high-precision current preamplification; the custom source meter includes 2400 series and 2600 series source meters, which are used to provide power for the transient photoelectric test unit and the electrical test platform; the photoelectric test software is used to perform conventional electrical tests and photoelectric characteristic tests and record the results; the high-precision optical power meter is used to measure the intensity of the pulsed laser light source irradiated on the wide bandgap power device to be tested.

[0016] More preferably, the electrical testing platform includes a damped optical shockproof platform, a shielded electrical testing platform and a vacuum low-temperature platform. The damped optical shockproof platform is used to reduce environmental interference during high-power operation; the shielded electrical testing platform includes a precision probe platform, a custom sample platform, a vacuum pump and a photoelectric shielding cover, which are used to fix the wide bandgap power device to be tested in the central adsorption hole of the precision probe platform and the custom sample platform after turning on the vacuum pump; the vacuum low-temperature platform includes a low-temperature cold stage, cold stage electrical accessories, a liquid nitrogen dewar and a vacuum pump, which are used to monitor the ambient temperature and vacuum degree of the platform where the wide bandgap power device to be tested is located.

[0017] More preferably, the custom sample stage includes a sample stage and a custom PCB board, which is controlled by a custom source meter of the optoelectronic test module and is used to perform dynamic switching characteristic testing on the wide bandgap power device to be tested. The custom PCB board includes a power motherboard and a pluggable test sub-board. The power motherboard is fixed by the sample stage and connected to the custom source meter. The test sub-board is parallel to the power motherboard, fixed by the power motherboard and connected to the output end of the power motherboard. The test sub-board is connected to the gate, drain and source of the wide bandgap power device to be tested. The test sub-board integrates an isolated power supply, a PWM control unit, a gate drive module, a buffer layer circuit, a voltage regulator and a small-area active clamping circuit. The test sub-board is pluggable, and the corresponding test sub-board is selected according to different test items.

[0018] Preferably, the small-area active clamping circuit includes a voltage regulator diode, a comparator, a metal oxide semiconductor field effect transistor, a gate-source bleeder resistor, a turn-on resistor, a turn-off resistor, and a high-current magnetic bead connected in series. The output end of the driver in the gate drive module is connected to the gate node after passing through the turn-on resistor and the turn-off resistor in sequence; one end of the gate-source bleeder resistor is connected to the gate node, and the other end is grounded. The cathode of the voltage regulator diode is connected to the gate node and the anode is grounded. The inverting input end of the comparator is connected to the gate node, and the non-inverting input end is provided with an adjustable reference voltage by the voltage regulator. The output end of the comparator is connected to the gate of the metal oxide semiconductor field effect transistor, the drain of the transistor is connected to the gate node and the source is grounded, and the gate node is then connected to the gate end of the power device under test through a high-current magnetic bead; the source end of the power device under test is grounded, and its drain end serves as the power output end.

[0019] More preferably, the conventional electrical properties test and photoelectric properties test include at least one or more of IV curve, transfer curve, output curve and photocurrent test; the dynamic switching properties test includes at least one or more of dual-pulse dynamic switching, dynamic on-resistance and Buck circuit conversion efficiency test.

[0020] Preferably, the effective pulse laser energy that ultimately reaches the active region is calculated using the following formula:

[0021] ;

[0022] Among them, E eff is the effective pulse laser energy; E0 is the pulse laser energy at the surface of the wide bandgap power device to be measured; R i is the reflectivity between the i-th layer and the i-1-th layer; t i is the transmittance of the laser in the i-th layer; E' is the pulse laser energy that is reflected multiple times at the interface and finally reaches the active area; i is the number of layers; n is the total number of layers.

[0023] Preferably, the pulse laser equivalent heavy ion LET value is calculated by the following formula:

[0024] ;

[0025] Where ELET is the pulse laser equivalent heavy ion LET value; E Laser is the incident photon energy of the pulsed laser; LET ion is the LET value of heavy ions; LET laser is the LET value of pulsed laser in semiconductor materials; E ion is the ionization energy of the semiconductor material; λ is the pulse laser wavelength; ρ is the density of the semiconductor material; h is the Planck constant; c is the speed of light in vacuum; E(x) is the laser energy at a depth x injected into the semiconductor material; x is the depth injected into the semiconductor material.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention realizes the accurate control and regulation of pulsed laser energy. By collecting data through the optical parameter measurement platform, a pulsed laser front device incident model in the sensitive area is established in the second control system. The effective pulsed laser energy actually reaching the active area of ​​the device can be calculated and mapped with the LET value of the specified heavy ion to better simulate the experimental effect of heavy ion irradiation. The optical path coupling module can also realize large-scale continuous control of pulsed laser energy and switching of pulsed laser wavelength, meeting the comprehensive testing requirements of irradiation dose and depth.

[0028] 2. The present invention uses a high-precision XY motor with a minimum step size of 1 μm, combined with photocurrent scanning imaging software to scan and determine the position and characterize the surface morphology of the device, and can accurately locate the sensitive area of ​​the device to be tested for pulsed laser irradiation.

[0029] 3. The present invention can perform conventional electrical and photoelectric characteristic tests on devices before and after irradiation on a test platform, including conventional IV curve, transfer curve, output curve and photocurrent tests. It can also perform customizable test items such as dual-pulse dynamic switching, dynamic on-resistance, Buck circuit conversion efficiency test, etc. by switching test sub-boards, and record real-time test data to avoid the impact of device recovery after irradiation on test results when switching test platforms, thereby achieving compatibility of different electrical test items and timely monitoring of device degradation after irradiation.

[0030] 4. The small-area active clamping circuit added to the test sub-board of the present invention suppresses gate voltage oscillations when the device is turned on and off, avoiding invalid testing of the device due to aggravated gate voltage oscillations after irradiation. At the same time, the clamping voltage of the small-area active clamping circuit of the present invention is adjustable, and can be used for testing wide bandgap semiconductor devices with large differences in threshold voltages, including gallium nitride and silicon carbide devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the overall structure of a pulsed laser irradiation experimental device provided by the present invention;

[0032] Figure 2 A schematic diagram of the specific structure of a pulsed laser irradiation experimental device provided by the present invention;

[0033] Figure 3 This is a schematic diagram of the test daughter board drive circuit;

[0034] Figure 4 This is a schematic diagram of the small-area active clamping circuit of the driving circuit of the present invention. DETAILED DESCRIPTION

[0035] The following is a further description of specific embodiments of the present invention in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0036] like Figure 1 As shown, the present invention provides a pulsed laser irradiation experimental device, including an optical parameter measurement platform 100, an optical path coupling module 200, a photoelectric testing module 400, an electrical testing platform 300, and a first control system 500 and a second control system 600;

[0037] The optical parameter measurement platform 100 is used to measure the ellipsometric state change parameters, reflectivity and transmittance of a single-layer thin film grown on a substrate corresponding to each layer of the thin film material of the wide bandgap power device 700 to be measured within the full spectral range;

[0038] The optical coupling module 200 is used to inject a pulsed laser onto the surface of the wide bandgap power device 700 to be tested through an optical path, control the wavelength, energy, and incident position of the pulsed laser, and perform real-time imaging of the surface morphology and pulsed laser irradiation position of the wide bandgap power device 700 to be tested;

[0039] The photoelectric test module 400 is electrically connected to the gate, drain, and source of the wide bandgap power device 700 to be tested via a probe station, and is used to perform conventional electrical and photoelectric characteristic tests on the wide bandgap power device 700 to be tested before and after irradiation;

[0040] The electrical test platform 300 is connected to the test circuit via a reserved power line interface, and the wide bandgap power device 700 to be tested is connected to the test circuit by plugging and unplugging, so as to perform dynamic switching characteristic tests on the wide bandgap power device 700 to be tested before and after irradiation.

[0041] The first control system 500 is used to fit the ellipsometric state change parameters with the scanning model to obtain the refractive index and extinction coefficient of the single-layer film and transmit the refractive index, extinction coefficient, reflectivity and transmittance of the single-layer film to the second control system;

[0042] The second control system 600 is used to input the refractive index, extinction coefficient, reflectivity and transmittance of the thin film into the device incident model to calculate the effective pulse laser energy of pulse lasers of different wavelengths when they pass through each layer of the thin film to reach the active area in the wide bandgap power device 700 to be tested, obtain the equivalent heavy ion LET value based on the effective pulse laser energy, and control the optical path coupling module, optoelectronic test module and electrical test platform to close-loop adjust the pulse laser energy based on the equivalent heavy ion LET value.

[0043] In the above scheme, the refractive index and extinction coefficient of the single-layer film are obtained by fitting the ellipsometric state change parameters with the scanning model in the following way: first, the ellipsometric state change parameters describing the polarization change of the light beam are obtained using an ellipsometer under the set incident angle condition; then a scanning model of the optical structure of the air single-layer film substrate is established, and the complex refractive index of the film is characterized by the Cauchy dispersion formula in the transparent area of ​​the film and the Lorentz-Drude dispersion model in the absorption area; the theoretical reflectance is calculated using the Fresnel formula combined with the ABCD matrix method; the residual sum of squares between the experimental curve and the theoretical curve is used as the objective function, and the Levenberg-Marquardt nonlinear least squares algorithm is used to iteratively optimize the film thickness and dispersion model parameters until the residual converges to the preset threshold; finally, the refractive index and extinction coefficient curves that change with wavelength are output, and the fitting quality is tested by the residual spectrum or root mean square error, so as to achieve the purpose of obtaining the refractive index and extinction coefficient of the single-layer film by fitting the ellipsometric state change parameters with the scanning model.

[0044] In the above solution, the single-layer thin film is each layer of thin film material in an actual wide bandgap power device to be tested, grown on a substrate such as sapphire by processes such as physical vapor deposition or plasma chemical vapor deposition.

[0045] In the above scheme, if Figure 2 As shown, the optical parameter measurement platform includes an ellipsometer, a spectrophotometer and a custom test sample. The custom test sample is used to provide a single-layer film; the ellipsometer is used to scan the custom test sample in the infrared to ultraviolet wavelength range to obtain the ellipsometric state change parameters of the single-layer film; the spectrophotometer is used to scan the custom test sample in the infrared to ultraviolet wavelength range to obtain the reflectivity and transmittance of the single-layer film.

[0046] In the above scheme, if Figure 2 As shown, the optical path coupling module includes a pulse laser control unit, an energy control unit, a microscopic imaging unit and an electric scanning unit; the pulse laser control unit includes multiple groups of pulse lasers with different wavelengths such as 266nm and 355nm, a pull-rod switch and an excitation light source coupling optical path, which is used to emit pulse lasers of different wavelengths and adjust the incident light direction; the energy control unit includes an optical path reflection module, a continuously adjustable attenuator and an OD3 filter, which is used to continuously control the pulse laser intensity over a large range and reflect the pulse laser into the microscopic imaging unit, adapting to different pulse laser wavelengths to select the attenuation intensity; the microscopic imaging unit includes a long working distance visible objective lens, a white lighting LED, an illumination filter, a microscopic camera, a microscopic coarse and fine adjustment bracket, an electric shutter and an imaging optical path, which is used to coaxially illuminate the wide bandgap power device to be tested, focus imaging and obtain high-resolution microscopic images in real time; the electric scanning unit includes a high-precision XY motor and photocurrent scanning imaging software, which is used to scan the surface of the wide bandgap power device to be tested point by point in a two-dimensional plane, collect and record the photocurrent signal of each scanning point in real time and generate a photocurrent distribution image.

[0047] In the above scheme, in the pulse laser control unit, the pulse laser, the pull-rod switch and the excitation light source coupling optical path are arranged in sequence on the same optical axis. The output ends of multiple groups of pulse lasers with different wavelengths face the pull-rod switch. The pull-rod switch mechanically switches between the pulse lasers. The pulse laser is selected according to the test requirements, so that the laser beam output by the selected pulse laser is colinear with the optical axis and introduced into the excitation light source coupling optical path. The excitation light source coupling optical path further collimates the laser beam and couples it to the subsequent energy control unit and the microscopic imaging unit, thereby realizing rapid switching of lasers of different wavelengths and shared optical path transmission.

[0048] In the energy control unit, the output end of the optical path reflection module is rigidly docked with the incident end of the continuously adjustable attenuator through a standard optical interface, and coaxial locking is achieved through a unified optical axis positioning hole. The output end of the continuously adjustable attenuator is directly fitted with the OD3 filter mounting frame, and the two are fastened so that the incident surface of the OD3 filter remains parallel to the output surface of the attenuator. The three are fixed in sequence on the common optical bracket of the energy control unit.

[0049] In the microscopic imaging unit, the light-emitting end of the white illumination LED faces the illumination filter, the light-emitting surface of the illumination filter is optically connected to the illumination entrance of the imaging light path, and the reflector arranged inside the imaging light path reflects the reflected light of the wide bandgap power device to be measured along the same optical axis to the incident end of the long working distance visible objective lens. The mechanical housing of the long working distance visible objective lens is fixed on the microscopic coarse and fine adjustment bracket. The microscopic coarse and fine adjustment bracket is kept coaxial with the sample stage through a spiral lifting mechanism and provides coarse and fine adjustment strokes. The output end of the objective lens is optically aligned with the light inlet of the electric shutter. The light outlet of the electric shutter is aligned with the photosensitive surface of the microscope camera and is hardware-fixed on the same optical axis. The microscope camera is connected to the second control system through a data cable to realize real-time image transmission and control command interaction. The components of the microscope imaging unit work together in the following order and functional relationship on the same imaging optical path: the light emitted by the white illumination LED first passes through the illumination filter to filter out the stray band and then illuminates the wide bandgap power device to be measured along the illumination channel of the imaging optical path, providing uniform visible light illumination. The reflected light or self-luminescence of the wide bandgap power device to be measured is reflected by the reflector built into the imaging optical path and the imaging beam is converged by the long working distance visible objective lens; the objective lens is fixed on the microscopic coarse and fine adjustment bracket, which provides coarse and fine adjustment strokes to accurately adjust the working distance between the objective lens and the device. The imaging light beam passes through the electric shutter, which opens and closes under the command of the second control system to control the exposure time and prevent stray light from entering. The imaging light beam passing through the shutter eventually falls on the image plane of the microscope camera, and the microscope camera transmits the acquired real-time image data to the second control system. The white illumination LED and the illumination filter together constitute the illumination sub-channel; the long working distance visible objective lens, the microscopic coarse and fine adjustment bracket, the electric shutter, the microscope camera and the imaging optical path constitute the coaxial imaging sub-channel in sequence. The two channels are coupled at the reflector in the imaging optical path to achieve illumination and imaging under the same optical axis.

[0050] In the electric scanning unit, a high-precision XY motor drives the sample stage to scan the wide bandgap power device to be tested. The photocurrent scanning imaging software is used to provide photocurrent and photocurrent waveform scanning functions, record the photocurrent at each scanning point and generate an image.

[0051] In the above scheme, if Figure 2As shown, the optoelectronic test module includes a transient optoelectronic test unit, a custom source meter, a high-precision optical power meter and optoelectronic test software. The transient optoelectronic test unit includes a high-performance oscilloscope and a high-speed amplifier for collecting high-speed data and high-precision current preamplification; the custom source meter includes 2400 series and 2600 series source meters, which are used to provide power for the transient optoelectronic test unit and the electrical test platform; the optoelectronic test software is used to perform routine electrical tests and optoelectronic characteristic tests and record the results; the high-precision optical power meter is used to directly measure the intensity of the pulsed laser light source irradiated on the wide bandgap power device to be tested.

[0052] In the above scheme, if Figure 2 As shown, the electrical test platform includes a damped optical anti-vibration platform, a shielded electrical test platform, and a vacuum cryogenic platform. The damped optical anti-vibration platform is used to reduce environmental interference during high-magnification operations. The shielded electrical test platform includes a precision probe platform, a custom sample stage, a vacuum pump, and an optoelectronic shielding cover. After the vacuum pump is turned on, the wide bandgap power device to be tested is fixed to the central adsorption holes of the precision probe platform and the custom sample stage. The custom sample stage is rigidly docked with the central opening of the precision probe platform via locating pins and shares the same vacuum adsorption channel. A vacuum interface is provided at the bottom of the precision probe platform, which is connected to the air inlet of the vacuum pump through a vacuum hose to form a closed suction circuit. The optoelectronic shielding cover is placed outside the precision probe platform and the custom sample stage. Its bottom edge fits into the positioning grooves around the probe platform and is fixed with screws (or magnetic rings) to achieve overall light shielding and electromagnetic shielding. The optoelectronic shielding cover is used to reduce stray light interference in the test environment and improve the shielding effect of electrical performance testing. The vacuum cryogenic platform includes a low-temperature cold stage, cold stage electrical accessories, a liquid nitrogen dewar, and a vacuum pump. It is used to monitor the ambient temperature and vacuum level of the platform where the wide bandgap power device to be tested is located.

[0053] In the above scheme, if Figure 2 As shown, the custom sample stage includes a sample stage and a custom PCB board, which is controlled by the custom source meter of the optoelectronic test module and is used to perform dynamic switching characteristic tests on the wide bandgap power device to be tested. The sample stage is controlled by a fine-tune handwheel and can move along the XYR three axes with a movement accuracy of 2μm. The custom PCB board includes a power motherboard and a pluggable test daughter board. The power motherboard is fixed through the sample stage and connected to the custom source meter. The test daughter board is parallel to the power motherboard, fixed through the power motherboard and connected to the output terminal of the power motherboard. The test daughter board is connected to the gate, drain and source of the wide bandgap power device to be tested, as shown in FIG. Figure 3As shown, the test daughterboard integrates an isolated power supply, PWM control unit, gate driver module, buffer layer circuit, voltage regulator, and a small-area active clamp circuit. The test daughterboard is pluggable and removable, allowing selection of the appropriate test daughterboard based on the test item. The isolated power supply electrically isolates the driver circuit from the external test system to prevent signal interference. The custom source meter connects to the isolated power supply and voltage regulator in the driver circuit via a reserved interface on the power motherboard, providing programmable voltage input. The PWM control unit generates an adjustable pulse width signal from a signal generator based on preset parameters, which is converted into a high-precision drive signal by the gate driver module. The buffer layer circuit suppresses switching transient voltage spikes, ensuring a stable drive waveform. The signal generator can be adjusted in real time via a secondary control system. A small-area active clamp circuit dynamically limits the gate voltage, ultimately applying the drive signal to the gate of the device under test. The synergistic effect of the isolated power supply and buffer layer circuit effectively reduces the impact of parasitic parameters. Combined with the shielded electrical test platform, electromagnetic interference is further suppressed, ensuring low-noise, high-fidelity drive signal output even in vacuum and low-temperature environments or high-power conditions, providing highly reliable drive support for device electrical performance evaluation before and after irradiation.

[0054] like Figure 4 As shown, the small-area active clamping circuit includes a voltage regulator diode, a comparator, a metal oxide semiconductor field effect transistor, a gate-source bleeder resistor, a turn-on resistor, a turn-off resistor, and a series high-current magnetic bead. The output end of the driver in the gate drive module is connected to the gate node after passing through the turn-on resistor and the turn-off resistor in sequence; one end of the gate-source bleeder resistor is connected to the gate node, and the other end is grounded. The cathode of the voltage regulator diode is connected to the gate node and the anode is grounded. The inverting input end of the comparator is connected to the gate node, and the non-inverting input end is provided with an adjustable reference voltage by the voltage regulator. The output end of the comparator is connected to the gate of the metal oxide semiconductor field effect transistor, the drain of the transistor is connected to the gate node and the source is grounded, and the gate node is then connected to the gate end of the power device under test through a high-current magnetic bead; the source end of the power device under test is grounded, and its drain end serves as the power output end.

[0055] During the turn-on process of the wide bandgap power device to be tested, a Zener diode connected in parallel between the gate and the source limits the gate-source voltage. When the wide bandgap power device to be tested is turned off, a comparator compares the gate-source voltage with an adjustable reference voltage provided by the voltage regulator in real time. When the gate-source voltage is higher than the reference value, the metal oxide semiconductor field effect transistor is driven to turn on, short-circuiting the gate and the source to suppress false turn-on caused by the discharge of the Miller capacitor. The clamping threshold is set by adjusting the output of the voltage regulator to adapt to gallium nitride power devices or silicon carbide power devices with different thresholds. At the same time, the gate of the wide bandgap power device to be tested is connected to a large current magnetic bead to suppress gate voltage oscillation during turn-on and turn-off.

[0056] Conventional electrical and photoelectric characteristic tests include at least one or more of IV curve, transfer curve, output curve and photocurrent test; dynamic switching characteristic test includes at least one or more of double-pulse dynamic switching, dynamic on-resistance and Buck circuit conversion efficiency test.

[0057] For the above experimental setup, a pulsed laser irradiation experiment includes the following steps:

[0058] S1: The first control host, ellipsometer, and spectrophotometer in the first control system are turned on, and the tester manually places the prepared single-layer thin film material in the measuring device. For the spectrophotometer, the material is fixed vertically on the barium sulfate substrate, and the test parameters and scanning wavelength range are set in the operating software of the first control host. The test instructions are sent to the spectrophotometer through the data line. During the scanning process of the spectrophotometer, the reflectivity and transmittance of the material are transmitted to the first control host in real time; for the ellipsometer, a scanning model of the test material is established in the operating software of the first control host, the corresponding dispersion formula is selected according to the type of material, the scanning wavelength range and wavelength are set, and the test instructions are sent to the ellipsometer through the data line. The ellipsometer automatically performs the scanning process to obtain the ellipsometric state change parameters. After the end, the scanning data is transmitted back to the first control host, and fitted with the established scanning model to obtain the refractive index and extinction coefficient of the material.

[0059] S2: The first control host transmits the measured reflectivity, transmittance, refractive index, and extinction coefficient via the server to the second control host within the second control system. The second control host then uses a pre-programmed program or MATLAB script file to establish a device incident model. This model includes the reflectivity, transmittance, and thickness of each layer of the device under test, as well as the wavelength and pulse energy of the pulsed laser. This model is used to quantitatively calculate the energy loss during the pulsed laser incident process, establish a mapping between the energy of a pulsed laser of a known wavelength and the LET value of heavy ions, and determine the required pulsed laser energy.

[0060] Calculate the effective pulse laser energy E eff :

[0061] ;

[0062] Where E0 is the pulse laser energy at the surface of the wide bandgap power device to be measured; R i is the reflectivity between the i-th layer and the i-1-th layer (the 0th layer is air); t i is the transmittance of the laser in the i-th layer; E' is the pulse laser energy that is reflected multiple times at the interface and finally reaches the active area; i is the number of layers; n is the total number of layers.

[0063] A pulsed laser is incident vertically on a certain GaN device. Assuming that during the laser energy transmission process, the laser passes through the passivation layer, the insulating layer and the AlGaN barrier layer in sequence, since the laser is incident vertically, the main loss mechanism of the pulse energy is the reflection between the layers and the absorption inside the film, and the effective pulse energy E that finally reaches the active area is eff It can be expressed as:

[0064] ;

[0065] Among them, E0 is the pulse laser energy at the device surface. Testers can easily obtain the E0 value using the high-precision optical power meter of the photoelectric test module; R1 is the reflectivity between the passivation layer and the air; R2 is the reflectivity between the passivation layer and the insulating layer; R3 is the reflectivity between the insulating layer and the AlGaN barrier layer; t1 is the transmittance of the laser in the passivation layer; t2 is the transmittance of the laser in the insulating layer; t3 is the transmittance of the laser in the AlGaN barrier layer; E' is the pulse laser energy that is reflected multiple times at the interface and finally reaches the active area.

[0066] Since the reflectivity between the layers of materials is usually very small, the energy of the pulse laser reflected from material a to material b and then reflected back by material b is only the original R a (1-R b ), while the number of reflections in actual scenes is higher than two. The pulsed laser energy reaching the active area after multiple reflections is extremely weak, so E' can be ignored in most cases. This can determine the actual pulsed laser energy reaching the active area of ​​the device. For vertically incident pulsed lasers, the Fresnel formula is used to calculate the reflectivity R between each interface. Due to the presence of an absorptive medium, light will attenuate when passing through the material, resulting in a change in the ratio of reflection and transmission. The complex refractive index needs to be used for calculation. The complex refractive index is n=n r +ik,n r is the refractive index, k is the extinction coefficient, and the reflectivity is calculated using the formula Calculate and compare with spectrophotometer measurements. For two adjacent layers of material, n1 is the complex refractive index of the upper layer, and n2 is the complex refractive index of the lower layer. i indicates that the complex refractive index is a complex number, which is the square root of -1. Since light energy attenuation within a material can be calculated based on the extinction coefficient and material thickness, the transmittances t1 to t3 can be verified by comparing the extinction coefficient and material thickness calculations with spectrophotometer measurements. Once the transmittance and reflectance measurements are consistent with the theoretical calculations, proceed to the next step.

[0067] The use of pulsed laser equivalent heavy ion LET, that is, a pulsed laser is equivalent to the LET of a heavy ion, is mainly based on the fact that the pulsed laser and heavy ions produce the same amount of ionized charge per unit length in the sensitive area of ​​the device. Assuming that the light is fully absorbed between the semiconductor bands, one photon generates one free carrier, and the pulsed laser and heavy ions produce the same number of electron-hole pairs, that is, , E ion is the ionization energy of the semiconductor material, E Laser is the incident photon energy of the pulsed laser, LET ion is the LET value of heavy ions, LET laser is the LET value of the pulsed laser in the semiconductor material, defined as , where ρ is the density of the semiconductor material, E(x) is the laser energy at the depth x of the semiconductor material, and the equivalent heavy ion LET value of the pulsed laser injected into the semiconductor material at the depth x is obtained as follows:

[0068] ;

[0069] Where λ is the wavelength of the pulsed laser, h is the Planck constant, and c is the speed of light in vacuum.

[0070] It is known that the attenuation of laser power density I(x) with incident depth satisfies , where α is the single-photon absorption coefficient and β is the two-photon absorption coefficient. For GaN devices, if a 266nm ultraviolet pulsed laser is used, the single-photon energy is about 4.66eV, which is greater than the band gap of GaN material 3.39eV. Single-photon absorption occurs, and two-photon absorption can be ignored (β≈0). At this time, the attenuation of laser power density I(x) with incident depth can be expressed as , where I0 is the laser power density on the semiconductor surface, α is the linear absorption coefficient, and the laser energy E(x) is proportional to the laser power density I(x). The attenuation law of the laser energy is the same as that of the laser power density, and it decays exponentially with the increase of the incident depth, so: , the expression of pulse laser equivalent LET is obtained as For GaN devices, the sensitive area is the two-dimensional electron gas formed at the interface between GaN and AlGaN. The depth is only a few nanometers, which is much smaller than the penetration depth of the laser. The LET attenuation in this area is not obvious, so the equivalent LET value at the surface can be regarded as the equivalent LET value of the entire sensitive area. The equivalent LET value is: .

[0071] The above calculation process is a simplification of the actual device. During actual testing, the device incident model should be re-established according to the actual structure of the device, and the equivalent relationship between the pulsed laser and the heavy ion LET should be calculated based on the device material and the pulsed laser wavelength.

[0072] S3: After the tester determines the required pulse laser energy based on the test needs, he or she turns on the pulse laser and, using the integrated control software of the second control host, drives the motor to switch the attenuator and filter in the optical coupling module to adjust the pulse laser energy. The tester can manually use a high-precision optical power meter to confirm the adjustment effect. During the test, the second control host drives the high-precision XY motor under the sample stage to move the sample and controls the electric shutter of the microscopic imaging unit to collect image information. The microscopic camera transmits the image information back to the second control host and displays it on a second display. Based on the surface morphology or electrical property degradation of the device under test after irradiation, the tester evaluates and modifies the scanning model established when using the ellipsometer in S1. The results of the modified model can be repeated until a suitable model is obtained. The electric scanning unit receives operating instructions from the photocurrent scanning imaging software of the second control host, generates the photocurrent waveform, and the scanned image and test data are automatically extracted and sent to the second control host. During subsequent test operations, the second control host is used to control the pulse laser on and off to irradiate the device under test, i.e., the wide bandgap power device under test.

[0073] S4: The tester opens the optoelectronic test software and manually connects the custom source meter and oscilloscope required for the test to the second control host and transient optoelectronic test unit. The wide bandgap power device to be tested is fixed to the sample stage of the transient optoelectronic test unit and electrically connected to the source meter via a probe. The custom source meter and oscilloscope are then uniformly controlled by the optoelectronic test software. After the tester sets test conditions such as gate voltage, drain voltage, and drain current limit in the optoelectronic test software, the selected conventional electrical and optoelectronic characteristic tests are automatically performed. Depending on the test item, the optoelectronic test software collects the test data required by the tester in real time, creates test curves, and saves the test data. When testing the transfer curve, the drain-source voltage and gate current are collected; when testing the output curve, the gate-source voltage and source current are collected; when testing the device's photoelectric response It, the photocurrent variation over time data is collected; when testing the device's photoelectric response Vt, the photovoltage variation over time data is collected.

[0074] S5: The tester manually connects the custom source meter and oscilloscope required for the test to the vacuum low-temperature platform and the shielded electrical test platform. If the vacuum low-temperature platform needs to be used for testing, the temperature range to be tested is set on the second control host. The temperature control unit in the vacuum low-temperature platform changes different temperatures. The reserved test interface is connected to the oscilloscope to collect the gate and drain currents of the device at different wavelengths to determine the test temperature. The tester installs the power motherboard on the shielded electrical test platform and connects the test daughter board according to the test needs. The test daughter board is connected to the gate, drain and source of the device to be tested in a plug-in manner, and is connected to the high-precision oscilloscope through an isolation probe. The tester clicks the test switch, and the test software controls the source meter to perform a single test, while the oscilloscope captures the waveform. For example, for the dual-pulse test sub-board, the gate-source voltage, drain-source voltage, and drain-source current of the device under test are collected during the test; for the dynamic on-resistance test sub-board, the drain-source clamping voltage, actual drain-source voltage, and drain-source current of the device under test are collected during the test; for the switching efficiency test sub-board, the input voltage, input current, output voltage, and output current of the test sub-board are collected during the test, and the collected data and test waveforms are saved in the second control host.

[0075] S6: After completing the connection work, the tester can complete all the above test processes and view the experimental data through the control system, so as to determine the radiation resistance and degradation of the wide bandgap power device under pulse laser.

[0076] The above are only specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be covered by the scope of protection of the present invention. Matters not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims

1. A pulsed laser irradiation experimental device, characterized in that: It includes an optical parameter measurement platform, an optical path coupling module, a photoelectric test module, an electrical test platform, and a first control system and a second control system; The optical parameter measurement platform is used to measure the ellipsometric state change parameters, reflectivity and transmittance of a single-layer thin film grown on a substrate, corresponding to each layer of thin film material of a wide bandgap power device to be measured, within a full spectral range; The optical path coupling module is used to incident the pulsed laser onto the surface of the wide bandgap power device to be measured through the optical path, control the wavelength, energy and incident position of the pulsed laser, and perform real-time imaging of the surface morphology of the wide bandgap power device to be measured and the pulsed laser irradiation position; The photoelectric test module is electrically connected to the gate, drain, and source of the wide bandgap power device to be tested via a probe station, and is used to perform conventional electrical and photoelectric characteristic tests on the wide bandgap power device to be tested before and after irradiation; The electrical test platform is connected to the test circuit via a reserved power line interface, and the wide bandgap power device to be tested is connected to the test circuit by plugging and unplugging, so as to perform dynamic switching characteristic testing on the wide bandgap power device to be tested before and after irradiation; The first control system is used to fit the ellipsometric state change parameters with the scanning model to obtain the refractive index and extinction coefficient of the single-layer film and transmit the refractive index, extinction coefficient, reflectivity and transmittance of the single-layer film to the second control system; The second control system is used to input the refractive index, extinction coefficient, reflectivity and transmittance of the thin film into the device incident model to calculate the effective pulse laser energy of pulse lasers of different wavelengths when they pass through each layer of thin film and reach the active area in the wide bandgap power device to be tested, obtain the equivalent heavy ion LET value based on the effective pulse laser energy, and control the optical path coupling module, optoelectronic test module and electrical test platform to close-loop adjust the pulse laser energy based on the equivalent heavy ion LET value.

2. The pulse laser irradiation experimental device according to claim 1, characterized in that: The optical parameter measurement platform includes an ellipsometer, a spectrophotometer and a custom test sample, wherein the custom test sample is used to provide a single-layer film; the ellipsometer is used to scan the custom test sample in the infrared to ultraviolet wavelength range to obtain the ellipsometric state change parameters of the single-layer film; and the spectrophotometer is used to scan the custom test sample in the infrared to ultraviolet wavelength range to obtain the reflectivity and transmittance of the single-layer film.

3. The pulse laser irradiation experimental device according to claim 1, characterized in that: The optical path coupling module includes a pulse laser control unit, an energy control unit, a microscopic imaging unit and an electric scanning unit; the pulse laser control unit includes multiple groups of pulse lasers with different wavelengths, a pull-rod switch and an excitation light source coupling optical path, which is used to emit pulse lasers of different wavelengths and adjust the incident light direction; the energy control unit includes an optical path reflection module, a continuously adjustable attenuation plate and an OD3 filter, which is used to continuously control the pulse laser intensity over a large range and reflect the pulse laser into the microscopic imaging unit; the microscopic imaging unit includes a long working distance visible objective lens, a white lighting LED, an illumination filter, a microscopic camera, a microscopic coarse and fine adjustment bracket, an electric shutter and an imaging optical path, which is used to coaxially illuminate the wide bandgap power device to be tested, focus imaging and obtain high-resolution microscopic images in real time; the electric scanning unit includes a high-precision XY motor and photocurrent scanning imaging software, which is used to scan the surface of the wide bandgap power device to be tested point by point in a two-dimensional plane, collect and record the photocurrent signal of each scanning point in real time and generate a photocurrent distribution image.

4. The pulse laser irradiation experimental device according to claim 1, characterized in that: The photoelectric test module includes a transient photoelectric test unit, a custom source meter, a high-precision optical power meter and photoelectric test software. The transient photoelectric test unit includes a high-performance oscilloscope and a high-speed amplifier for collecting high-speed data and high-precision current preamplification; the custom source meter includes 2400 series and 2600 series source meters, which are used to provide power for the transient photoelectric test unit and the electrical test platform; the photoelectric test software is used to perform conventional electrical tests and photoelectric characteristic tests and record the results; the high-precision optical power meter is used to measure the intensity of the pulsed laser light source irradiated on the wide bandgap power device to be tested.

5. The pulse laser irradiation experimental device according to claim 1, characterized in that: The electrical testing platform includes a damped optical anti-vibration platform, a shielded electrical testing platform and a vacuum low-temperature platform. The damped optical anti-vibration platform is used to reduce environmental interference during high-power operation; the shielded electrical testing platform includes a precision probe platform, a custom sample stage, a vacuum pump and a photoelectric shielding cover, which are used to fix the wide bandgap power device to be tested on the central adsorption hole of the precision probe platform and the custom sample stage after turning on the vacuum pump; the vacuum low-temperature platform includes a low-temperature cold stage, cold stage electrical accessories, a liquid nitrogen dewar and a vacuum pump, which are used to monitor the ambient temperature and vacuum degree of the platform where the wide bandgap power device to be tested is located.

6. The pulse laser irradiation experimental device according to claim 5, characterized in that: The custom sample platform includes a sample platform and a custom PCB board, which is controlled by a custom source meter of a photoelectric test module and is used to perform dynamic switching characteristic testing on a wide bandgap power device to be tested. The custom PCB board includes a power motherboard and a pluggable test daughter board. The power motherboard is fixed by the sample platform and connected to the custom source meter. The test daughter board is parallel to the power motherboard, fixed by the power motherboard and connected to the output end of the power motherboard. The test daughter board is connected to the gate, drain and source of the wide bandgap power device to be tested. The test daughter board integrates an isolated power supply, a PWM control unit, a gate drive module, a buffer layer circuit, a voltage regulator and a small-area active clamping circuit.

7. The pulse laser irradiation experimental device according to claim 6, characterized in that: The small-area active clamping circuit includes a voltage-stabilizing diode, a comparator, a metal oxide semiconductor field effect transistor, a gate-source bleeder resistor, a turn-on resistor, a turn-off resistor, and a high-current magnetic bead connected in series. The output end of the driver in the gate drive module is connected to the gate node after passing through the turn-on resistor and the turn-off resistor in sequence. One end of the gate-source bleeder resistor is connected to the gate node, and the other end is grounded. The cathode of the voltage-stabilizing diode is connected to the gate node, and the anode is grounded. The inverting input end of the comparator is connected to the gate node, and the non-inverting input end is provided with an adjustable reference voltage by the voltage regulator. The output end of the comparator is connected to the gate of the metal oxide semiconductor field effect transistor, the drain of the transistor is connected to the gate node, and the source is grounded. The gate node is then connected to the gate end of the power device under test through a high-current magnetic bead. The source end of the power device under test is grounded, and its drain end serves as the power output end.

8. The pulse laser irradiation experimental device according to claim 1, characterized in that: The conventional electrical test and photoelectric characteristic test include at least one or more of IV curve, transfer curve, output curve and photocurrent test; the dynamic switching characteristic test includes at least one or more of double-pulse dynamic switching, dynamic on-resistance and Buck circuit conversion efficiency test.

9. The pulse laser irradiation experimental device according to claim 1, characterized in that: The effective pulse laser energy that finally reaches the active region is calculated by the following formula: ； Among them, E eff is the effective pulse laser energy; E0 is the pulse laser energy at the surface of the wide bandgap power device to be measured; R i is the reflectivity between the i-th layer and the i-1-th layer; t i is the transmittance of the laser in the i-th layer; E' is the pulse laser energy that is reflected multiple times at the interface and finally reaches the active area; i is the number of layers; n is the total number of layers.

10. The pulse laser irradiation experimental device according to claim 1, characterized in that: The pulse laser equivalent heavy ion LET value is calculated by the following formula: ； Where ELET is the pulse laser equivalent heavy ion LET value; E Laser is the incident photon energy of the pulsed laser; LET ion is the LET value of heavy ions; LET laser is the LET value of pulsed laser in semiconductor materials; E ion is the ionization energy of the semiconductor material; λ is the pulse laser wavelength; ρ is the density of the semiconductor material; h is the Planck constant; c is the speed of light in vacuum; E(x) is the laser energy at a depth x injected into the semiconductor material; x is the depth injected into the semiconductor material.

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