Pulse laser irradiation experimental device

Abstract

The invention relates to a pulse laser irradiation experimental device. Comprising an optical parameter measurement platform, an optical path coupling module, a photoelectric test module, an electrical test platform, a first control system and a second control system, the first control system is used for fitting the elliptic polarization state change parameters with a scanning model to obtain the refractive index and the extinction coefficient of the single-layer film; the second control system is used for inputting the refractive index, the extinction coefficient, the reflectivity and the transmissivity of the thin film into a device incidence model to calculate effective pulse laser energy when pulse laser with different wavelengths penetrates through each layer of thin film to reach an active region in the to-be-measured wide bandgap power device, and obtaining an equivalent heavy ion LET value according to the effective pulse laser energy; and the light path coupling module, the photoelectric test module and the electrical test platform are controlled to carry out closed-loop adjustment on pulse laser energy. According to the invention, accurate control and adjustment of pulse laser energy are realized.

Description

Technical Field

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

[0002] The third-generation wide bandgap semiconductor materials, represented by silicon carbide (SiC) and gallium nitride (GaN), can meet the stringent requirements of power devices in terms of operating temperature, breakdown voltage, and switching frequency due to their wider bandgap width, higher breakdown electric field, faster switching speed, lower on-resistance, and higher thermal conductivity. Therefore, they are widely regarded as the core devices of a new type of power supply and high-power conversion system. On the one hand, wide bandgap power devices can significantly reduce the volume and weight of passive components and improve power density; on the other hand, their inherent anti-displacement damage ability and anti-total dose effect ability provide inherent advantages for space applications.

[0003] However, the application of wide bandgap power devices faces problems such as space irradiation damage and reliability, and its irradiation failure mechanism needs to be further studied. Therefore, there is a need to develop an experimental device for pulse laser irradiation of wide bandgap power devices to evaluate the performance degradation of the devices after irradiation. Since the actual cost of experiments in outer space is too high and the experimental period is difficult to determine, various experimental devices are usually used to simulate the radiation received by the devices. Traditional irradiation experiments usually rely on neutron sources, proton sources, or heavy ion accelerators, but the machine time is tight, the cost is high, and the test period is long; the operators must stay away from the irradiation source, resulting in problems such as limited real-time control, difficult data acquisition, and insufficient test accuracy. Therefore, the research on using pulse laser irradiation to simulate heavy ion irradiation experiments is a commonly used test method at present. At present, the existing pulse laser irradiation experimental devices still have the following main deficiencies: 1. The existing devices lack real-time mapping and calibration means for "pulse laser energy and heavy ion LET", and cannot quantitatively calculate the pulse laser energy corresponding to the equivalent specific heavy ion LET value; 2. The experimental device cannot automatically align the sensitive area of the device due to insufficient accuracy, and the irradiation area is uncertain; 3. It is difficult to quickly evaluate the electrical characteristics before and after irradiation; 4. The number of test items that the experimental device can perform is limited. Therefore, there is an urgent need to provide a pulse laser irradiation experimental device to overcome the above deficiencies. Summary of the Invention

[0004] The object of the present invention is to solve the deficiencies existing in the above-mentioned background technology, and provide a pulsed laser irradiation experimental device, which is used to solve the problems that the pulsed laser energy for quantitatively calculating the equivalent specific heavy ion LET value cannot be calculated, the pulsed laser energy cannot be accurately adjusted, the irradiation area of the pulsed laser cannot be accurately positioned, the real-time acquisition of device parameters before and after irradiation for different dynamic test items cannot be achieved, the electrical performance of the device is poor after irradiation, the gate control ability of the device degenerates or fails, resulting in an increase in the gate leakage current IGS and the off-state drain-source current IDS, aggravating the gate voltage oscillation during the turn-on and turn-off processes, and affecting normal testing, etc.

[0005] The technical solution adopted by the present invention is: a pulsed laser irradiation experimental device, which includes an optical parameter measurement platform, an optical path coupling module, a photoelectric test module, an electrical test platform, 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 to-be-tested wide-bandgap power device in the full spectral range; The optical path coupling module is used to incident a pulsed laser onto the surface of the to-be-tested wide-bandgap power device through an optical path, control the pulsed laser wavelength, energy, incident position, and perform real-time imaging on the surface topography of the to-be-tested wide-bandgap power device and the pulsed laser irradiation position; The photoelectric test module is electrically connected to the gate, drain and source of the to-be-tested wide-bandgap power device through a probe station, and is used to perform conventional electrical tests and photoelectric characteristic tests on the to-be-tested wide-bandgap power device before and after irradiation; The electrical test platform is connected to the test circuit through a reserved power supply line interface, and the to-be-tested wide-bandgap power device is connected to the test circuit in a plug-and-play manner, and is used to perform dynamic switching characteristic tests on the to-be-tested wide-bandgap power device before and after irradiation; 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 the single-layer thin film, and transmit the refractive index, extinction coefficient, reflectivity and transmittance of the single-layer thin 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 a device incidence model to calculate the effective pulsed laser energy when pulsed lasers of different wavelengths pass through each layer of thin film in the to-be-tested wide-bandgap power device and reach the active region, obtain the equivalent heavy ion LET value according to the effective pulsed laser energy, and control the optical path coupling module, the photoelectric test module and the electrical test platform to close-loop adjust the pulsed laser energy according to the equivalent heavy ion LET value.

[0006] In the above solution, the single-layer thin film is each layer of thin film material in an actual to-be-tested wide-bandgap power device grown on a substrate such as sapphire by processes such as physical vapor deposition or plasma chemical vapor deposition.

[0007] More preferably, the optical parameter measurement platform includes an ellipsometer, a spectrophotometer, and a custom test sample, and 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 change parameters of the ellipsometric state 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.

[0008] More preferably, the optical path coupling module includes a pulsed laser control unit, an energy control unit, a microscopic imaging unit, and an electric scanning unit; the pulsed laser control unit includes multiple groups of pulsed lasers with different wavelengths, a pull rod switch, and an excitation light source coupling optical path, and is used to emit pulsed lasers with different wavelengths and adjust the incident light direction; the energy control unit includes an optical path reflection module, a continuously adjustable attenuation sheet, and an OD3 filter, and is used to continuously control the light intensity of the pulsed laser in a large range and reflect the pulsed laser into the microscopic imaging unit; the microscopic imaging unit includes a long working distance visible objective lens, a white illumination LED, an illumination filter, a microscopic camera, a microscopic coarse and fine adjustment bracket, an electric shutter, and an imaging optical path, and is used to perform coaxial illumination, focus imaging on the wide-bandgap power device to be tested, and obtain high-resolution microscopic images in real time; the electric scanning unit includes a high-precision XY motor and a photocurrent scanning imaging software, and 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 signals of each scanning point in real time, and generate a photocurrent distribution image.

[0009] More preferably, 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, and is used to collect high-speed data and perform high-precision current pre-amplification; the custom source meter includes 2400 series and 2600 series source meters, and is used to provide power for the transient optoelectronic test unit and the electrical test platform; the optoelectronic test software is used to perform conventional electrical tests and optoelectronic characteristic tests and record the results; the high-precision optical power meter is used to measure the light intensity of the pulsed laser light source irradiated on the wide-bandgap power device to be tested.

[0010] More preferably, the electrical test platform includes a damping optical anti-vibration platform, a shielded electrical test platform, and a vacuum cryogenic platform. The damping 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 housing, and is used to adsorb the wide-bandgap power device to be tested at the center adsorption holes of the precision probe platform and the custom sample stage after starting the vacuum pump; the vacuum cryogenic platform includes a cryogenic cold stage, cold stage electrical accessories, a liquid nitrogen dewar, and a vacuum pump, and is used to monitor the environmental temperature and vacuum degree of the platform where the wide-bandgap power device to be tested is located.

[0011] More preferably, 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 for dynamically testing the switching characteristics of the wide-bandgap power device to be tested. The custom PCB board includes a power supply motherboard and a pluggable test daughter board. The power supply motherboard is fixed by the sample stage and connected to the custom source meter. The test daughter board is parallel to the power supply motherboard, fixed by the power supply motherboard and connected to the output end of the power supply motherboard. The test daughter board accesses 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. The test daughter board can be plugged and unplugged, and the corresponding test daughter board is selected according to different test items.

[0012] More preferably, the small-area active clamping circuit includes a zener diode, a comparator, a metal-oxide-semiconductor field-effect transistor, a gate-source discharge resistor, a turn-on resistor, a turn-off resistor, and a series large-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 discharge resistor is connected to the gate node and the other end is grounded. The cathode of the zener 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 terminal of the power device under test through a large-current magnetic bead; the source terminal of the power device under test is grounded, and its drain terminal is used as the power output end.

[0013] More preferably, the conventional electrical test and optoelectronic characteristic test include at least one or more of an I-V curve, a transfer curve, an output curve, and a photocurrent test; the dynamic switching characteristic test includes at least one or more of a double-pulse dynamic switch, a dynamic on-resistance, and a Buck circuit conversion efficiency test.

[0014] More preferably, the effective pulsed laser energy reaching the active region finally is calculated by the following formula: ; wherein, E eff is the effective pulsed laser energy; E0 is the pulsed laser energy at the surface of the wide-bandgap power device to be tested; 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 pulsed laser energy that finally reaches the active region after multiple reflections at the interface; i is the number of layers; n is the total number of layers.

[0015] Preferably, 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 wavelength of the pulsed laser; ρ is the density of the semiconductor material; h is the Planck constant; c is the speed of light in a 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.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention realizes accurate control and regulation of pulse laser energy. By collecting data through the optical parameter measurement platform, a pulse laser front device incident model in the sensitive area is established in the second control system. The effective pulse 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 heavy ion irradiation experiment effect. The optical path coupling module can also realize large-scale continuous control of pulse laser energy and switching of pulse laser wavelength to meet the comprehensive testing requirements of irradiation dose and depth.

[0017] 2. The present invention uses a high-precision XY motor with a minimum step length 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.

[0018] 3. The present invention can perform conventional electrical tests and photoelectric characteristic tests on devices before and after irradiation on a test platform, including conventional IV curves, transfer curves, output curves 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.

[0019] 4. The small-area active clamping circuit added to the test sub-board of the present invention suppresses the gate voltage oscillation when the device is turned on and off, avoiding invalid testing of the device due to aggravated gate voltage oscillation 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

[0020] Figure 1 Schematic diagram of the overall structure of a pulsed laser irradiation experimental device provided by the present invention; Figure 2 Schematic diagram of the specific structure of a pulsed laser irradiation experimental device provided by the present invention; Figure 3 Schematic diagram of the test daughter board drive circuit; Figure 4 Schematic diagram of the small-area active clamping circuit of the drive circuit of the present invention. Specific embodiments

[0021] The following further describes the specific embodiments of the present invention with reference to the accompanying drawings. It should be noted here that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the following specific embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0022] As Figure 1 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 test module 400, an electrical test platform 300, and a first control system 500 and a second control system 600; 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 thin film material of the wide-bandgap power device 700 to be measured within the full spectral range; The optical path coupling module 200 is used to incident pulsed laser onto the surface of the wide-bandgap power device 700 to be measured through an optical path, control the pulsed laser wavelength, energy, incident position, and perform real-time imaging on the surface topography of the wide-bandgap power device 700 to be measured and the pulsed laser irradiation position; The photoelectric test module 400 is electrically connected to the gate, drain, and source of the wide-bandgap power device 700 to be measured through a probe station, and is used to perform conventional electrical tests and photoelectric characteristic tests on the wide-bandgap power device 700 to be measured before and after irradiation; The electrical test platform 300 is connected to the test circuit through a reserved power supply interface, and the wide-bandgap power device 700 to be measured is connected to the test circuit in a plug-and-play manner, and is used to perform dynamic switching characteristic tests on the wide-bandgap power device 700 to be measured before and after irradiation; The first control system 500 is used to fit the ellipsometric state change parameters with a scanning model to obtain the refractive index and extinction coefficient of the single-layer thin film and transmit the refractive index, extinction coefficient, reflectivity, and transmittance of the single-layer thin film to the second control system; The second control system 600 is used to input the refractive index, extinction coefficient, reflectivity, and transmittance of the thin film into the device incidence model to calculate the effective pulsed laser energy when pulsed lasers of different wavelengths pass through each layer of the thin film and reach the active region in the wide-bandgap power device 700 to be measured. According to the effective pulsed laser energy, the equivalent heavy ion LET value is obtained, and based on the equivalent heavy ion LET value, the optical path coupling module, the optoelectronic test module, and the electrical test platform are controlled to adjust the pulsed laser energy in a closed loop.

[0023] In the above solution, the refractive index and extinction coefficient of a single-layer thin film can be obtained by fitting the ellipsometric state change parameters with the scanning model in the following way: First, under the condition of a set incident angle, an ellipsometric state change parameter describing the polarization change of the light beam is obtained using an ellipsometer; Subsequently, a scanning model of the optical structure of an air-single-layer thin film substrate is established, and the Cauchy dispersion formula is used in the transparent region of the thin film and the Lorentz-Drude dispersion model is used in the absorption region to characterize the complex refractive index of the thin film; The theoretical reflectance is calculated using the Fresnel formula in combination with the ABCD matrix method; Taking the sum of the squares of the residuals between the experimental curve and the theoretical curve as the objective function, the Levenberg-Marquardt nonlinear least squares algorithm is used to iteratively optimize the thin film thickness and dispersion model parameters until the residual converges to a preset threshold; Finally, the refractive index and extinction coefficient curves varying with wavelength are output, and the fitting quality is tested through the residual spectrum or root mean square error, thereby achieving the purpose of obtaining the refractive index and extinction coefficient of a single-layer thin film by fitting the ellipsometric state change parameters with the scanning model.

[0024] In the above solution, the single-layer thin film is each layer of thin film material in the actual wide-bandgap power device to be measured grown on a substrate such as sapphire through processes such as physical vapor deposition or plasma-enhanced chemical vapor deposition.

[0025] In the above solution, as Figure 2 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 thin 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 thin 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 thin film.

[0026] In the above solution, as Figure 2As shown, the optical path coupling module includes a pulsed laser control unit, an energy control unit, a microscopic imaging unit, and an electric scanning unit; the pulsed laser control unit includes multiple groups of pulsed lasers with different wavelengths such as 266nm and 355nm, a pull rod switcher, and an excitation light source coupling optical path, which is used to emit pulsed lasers with different wavelengths and adjust the incident light direction; the energy control unit includes an optical path reflection module, a continuously adjustable attenuation sheet, and an OD3 filter, which is used to continuously control the intensity of the pulsed laser over a wide range and reflect the pulsed laser into the microscopic imaging unit, and adapt the attenuation intensity according to different pulsed laser wavelengths; the microscopic imaging unit includes a long working distance visible objective lens, a white illumination 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 coaxial illuminate, focus and image the wide bandgap power device to be measured and obtain high-resolution microscopic images in real time; the electric scanning unit includes a high-precision XY motor and a photocurrent scanning imaging software, which is used to scan the surface of the wide bandgap power device to be measured point by point in a two-dimensional plane, collect and record the photocurrent signals of each scanned point in real time and generate a photocurrent distribution image.

[0027] In the above solution, in the pulsed laser control unit, the pulsed laser, the pull rod switcher, and the excitation light source coupling optical path are arranged in sequence on the same optical axis. The output end faces of multiple groups of pulsed lasers with different wavelengths face the pull rod switcher. The pull rod switcher mechanically switches between the pulsed lasers and selects the pulsed laser according to the test requirements, so that the laser beam output by the selected pulsed laser is collinear with the optical axis and is introduced into the excitation light source coupling optical path. The excitation light source coupling optical path further collimates and couples the laser beam to the subsequent energy control unit and microscopic imaging unit, realizing the rapid switching of different wavelength lasers and the common optical path transmission.

[0028] In the energy control unit, the output end of the optical path reflection module is rigidly docked with the input end of the continuously adjustable attenuation sheet through a standard optical interface, and is coaxially locked through a unified optical axis positioning hole. The output end of the continuously adjustable attenuation sheet is directly attached to the OD3 filter mounting frame, and the two are fixed tightly, so that the incident surface of the OD3 filter is parallel to the output surface of the attenuation sheet. The three are sequentially fixed on the common optical support of the energy control unit.

[0029] 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 docked with the illumination inlet of the imaging optical path. The mirror disposed inside the imaging optical 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 coaxial with the sample stage through a screw lifting mechanism and provides coarse and fine adjustment strokes. The exit 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 microscopic camera and is hardware-fixed on the same optical axis. The microscopic camera is communicatively connected to the second control system through a data line to achieve real-time image transmission and control command interaction. Each component of the microscopic imaging unit cooperates and works 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, and after filtering out the stray wavelength bands, it irradiates 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-emitted light of the wide-bandgap power device to be measured is folded back by the mirror built in the imaging optical path and converged into an imaging beam by the long working distance visible objective lens. The objective lens is fixed on the microscopic coarse and fine adjustment bracket, and the bracket provides coarse and fine adjustment strokes to precisely adjust the working distance between the objective lens and the device. The imaging beam output by the objective lens passes through the electric shutter. The shutter opens and closes under the command of the second control system to control the exposure time and prevent stray light from entering. The imaging beam passing through the shutter finally falls on the image plane of the microscopic camera. The microscopic 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 microscopic camera, and the imaging optical path successively constitute the coaxial imaging sub-channel. The two channels are coupled at the mirror in the imaging optical path to achieve illumination and imaging under the same optical axis.

[0030] In the electric scanning unit, the high-precision XY motor drives the sample stage to scan the wide-bandgap power device to be measured. The photocurrent scanning imaging software is used to provide photocurrent and photocurrent waveform scanning functions, record the photocurrent at each scanning point, and generate pictures.

[0031] In the above solution, as Figure 2 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, which are used for collecting high-speed data and high-precision current pre-amplification. 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 conventional electrical tests and optoelectronic characteristic tests and record the results. The high-precision optical power meter is used to directly measure the light intensity of the pulsed laser light source irradiating the wide-bandgap power device to be measured.

[0032] In the above solution, asFigure 2 As shown in the figure, the electrical test platform includes a damping optical anti-vibration platform, a shielded electrical test platform, and a vacuum cryogenic platform. The damping 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 shield housing, which is used to adsorb the wide-bandgap power device to be tested at the central adsorption holes of the precision probe platform and the custom sample stage after starting the vacuum pump. The custom sample stage is rigidly docked with the central opening of the precision probe platform through a positioning pin and shares the same vacuum adsorption channel. The bottom of the precision probe platform is provided with a vacuum interface, which is connected to the air inlet of the vacuum pump through a vacuum hose to form a closed suction circuit. The optoelectronic shield housing covers the outside of the precision probe platform and the custom sample stage, and its bottom edge is fitted with the peripheral positioning groove of the probe platform and fixed with screws (or magnetic suction rings) to achieve overall light shielding and electromagnetic shielding. The optoelectronic shield housing is used to reduce the stray light interference in the test environment and improve the shielding effect of electrical performance testing. The vacuum cryogenic platform includes a cryogenic cold stage, cold stage electrical accessories, a liquid nitrogen dewar, and a vacuum pump, which is used to monitor the environmental temperature and vacuum degree of the platform where the wide-bandgap power device to be tested is located.

[0033] In the above solution, as Figure 2 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 can be controlled by a micrometer head handwheel and can move along the X, Y, and R axes with a movement accuracy of 2 μm. The custom PCB board includes a power supply motherboard and a pluggable test daughter board. The power supply motherboard is fixed by the sample stage and is connected to the custom source meter. The test daughter board is parallel to the power supply motherboard, is fixed by the power supply motherboard, and is connected to the output end of the power supply motherboard. The test daughter board is connected to the gate, drain, and source of the wide-bandgap power device to be tested. As Figure 3As shown in the figure, 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. The test daughter board can be plugged in and unplugged, and the corresponding test daughter board can be selected according to different test items. The isolated power supply realizes the electrical isolation between the drive circuit and the external test system, avoiding signal interference; the custom source meter is connected to the isolated power supply and the voltage regulator in the drive circuit through the reserved interface of the power supply motherboard, providing a programmable voltage input; the PWM control unit generates an adjustable pulse width signal by the signal generator based on preset parameters, which is converted into a high-precision drive signal by the gate drive module, and the switching transient voltage spike is suppressed through the buffer layer circuit to ensure the stability of the drive waveform, and the signal generator can be adjusted in real time through the second control system; the gate voltage is dynamically limited and protected by the small-area active clamping circuit, and finally the drive signal acts on the gate of the device under test. Through the coordinated work of the isolated power supply and the buffer layer circuit, the influence of parasitic parameters is effectively reduced, and the electromagnetic interference is further suppressed by combining with the shielded electrical test platform, ensuring that a low-noise and high-fidelity drive signal can still be output in a vacuum low-temperature environment or a high-power working condition, providing a highly reliable drive support for the electrical performance evaluation of the device before and after irradiation.

[0034] As Figure 4 As shown in the figure, the small-area active clamping circuit includes a zener diode, a comparator, a metal-oxide-semiconductor field-effect transistor, a gate-source discharge resistor, a turn-on resistor, a turn-off resistor, and a series large-current magnetic bead. The output end of the driver in the gate drive module is connected to the gate node through the turn-on resistor and the turn-off resistor in sequence; one end of the gate-source discharge resistor is connected to the gate node and the other end is grounded. The cathode of the zener 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 terminal of the power device under test through a large-current magnetic bead; the source terminal of the power device under test is grounded, and its drain terminal is used as the power output terminal.

[0035] During the turn-on process of the wide-bandgap power device under test, the zener diode connected in parallel between the gate and the source limits the gate-source voltage; during the turn-off of the wide-bandgap power device under test, the comparator compares the gate-source voltage with the 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 conduct, short-circuiting the gate and the source to suppress the mis-conduction caused by the discharge of the Miller capacitance; by adjusting the output of the voltage regulator, the clamping threshold is set 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 under test is connected to a large-current magnetic bead to suppress the gate voltage oscillation during turn-on and turn-off.

[0036] The conventional electrical tests and optoelectronic property tests include at least one or more of I-V curve, transfer curve, output curve, and photocurrent test; the dynamic switching property tests include at least one or more of double-pulse dynamic switching, dynamic on-resistance, and Buck circuit conversion efficiency test.

[0037] For the above experimental device, the single-pulse laser irradiation experiment includes the following steps: S1: Turn on the first control host, ellipsometer, and spectrophotometer in the first control system. The tester manually places the prepared single-layer thin film material in the measuring device. For the spectrophotometer, fix the material vertically on the barium sulfate substrate, set the test parameters and scanning wavelength range in the operation software of the first control host, send the test instruction to the spectrophotometer through the data cable, and the spectrophotometer transmits the reflectivity and transmittance of the material to the first control host in real time during the scanning process; for the ellipsometer, establish a scanning model of the test material in the operation software of the first control host, select the corresponding dispersion formula according to the material type, set the scanning wavelength range and wavelength, send the test instruction to the ellipsometer through the data cable, the ellipsometer automatically obtains the ellipsometric state change parameters during the scanning process, and after the end, transmits the scanning data back to the first control host and fits it with the established scanning model to obtain the refractive index and extinction coefficient of the material.

[0038] S2: The first control host transmits the measured reflectivity, transmittance, refractive index, and extinction coefficient to the second control host in the second control system through the server. In the second control host, use the pre-written program or MATLAB script file to establish a device incident model, which includes the reflectivity, transmittance, thickness of each layer of the device to be measured, as well as the wavelength and pulse energy of the pulsed laser. It is used to quantitatively calculate the energy loss during the pulsed laser incidence process, establish the mapping relationship between the pulsed laser energy with a known wavelength and the heavy ion LET value, and determine the required pulsed laser energy.

[0039] Calculate the effective pulsed laser energy E eff : ; where, E0 is the pulsed 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 0-th layer is air); t i is the transmittance of the laser in the i-th layer; E' is the pulsed laser energy that finally reaches the active region after multiple reflections at the interface; i is the layer number; n is the total number of layers.

[0040] A pulsed laser is incident perpendicularly from the front on a certain gallium nitride device. Assuming that during the laser energy transmission process, the laser passes through the passivation layer, the insulating layer, and the aluminum gallium nitride barrier layer successively. Since the laser is perpendicularly incident, the main loss mechanisms of the pulsed energy are the reflections between the thin films of each layer and the absorption inside the thin films. The effective pulsed energy E that finally reaches the active region eff can be expressed as: ; where E0 is the pulsed laser energy at the device surface, and the tester can easily obtain the value of E0 using the high-precision optical power meter of the optoelectronic test module; R1 is the reflectivity between the passivation layer and air; R2 is the reflectivity between the passivation layer and the insulating layer; R3 is the reflectivity between the insulating layer and the aluminum gallium nitride 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 aluminum gallium nitride barrier layer; E' is the pulsed laser energy that reaches the active region after multiple reflections at the interfaces.

[0041] Since the reflectivity between the materials of each layer is usually very small, for the pulsed laser reflected from material a to material b and then reflected back by material b, the energy is only R a (1 - R b ) of the original. And in the actual scenario, the number of reflections is higher than two, and the pulsed laser energy reaching the active region after multiple reflections is extremely weak. So E' can be ignored in most cases. Thus, the pulsed laser energy actually reaching the device active region can be determined. For the perpendicularly incident pulsed laser, the Fresnel formula is used to calculate the reflectivity R between the interfaces of each layer. Since there is an absorbing medium, the light will attenuate when passing through the material, resulting in a change in the ratio of reflection and transmission, and the complex refractive index needs to be used for calculation. The complex refractive index is n = n r + ik, where n r is the refractive index and k is the extinction coefficient. Then the reflectivity is calculated using the formula . Compare with the measurement results of the spectrophotometer. For two adjacent layers of materials, n1 is the complex refractive index of the upper layer material and n2 is the complex refractive index of the lower layer material. i indicates that the complex refractive index is a complex number, which is the square root of -1. Since the energy attenuation of the light inside the material can be calculated according to the extinction coefficient and the material thickness, the transmittances t1~t3 can be verified by calculating the extinction coefficient and the material thickness and comparing with the measurement results of the spectrophotometer. After the measurement results of the transmittance and reflectivity are consistent with the theoretical calculation results, the next operation is carried out.

[0042] Using the pulsed laser to be equivalent to the LET of heavy ions, that is, a pulsed laser is equivalent to the LET of a heavy ion. It is mainly based on that the pulsed laser and the heavy ion generate equal amounts of ionized charge per unit length in the sensitive region of the device. Assuming that the light is fully absorbed between the semiconductor bands and one photon generates one free carrier, the pulsed laser and the heavy ion generate the same number of electron-hole pairs, that is , E ion is the ionization energy of the semiconductor material, and E Laser is the incident photon energy of the pulsed laser, and LET ion is the LET value of the heavy ion, and LET laser is the LET value of the pulsed laser in the semiconductor material, and is defined as , where ρ is the density of the semiconductor material, and E(x) is the laser energy at the depth x of the incident semiconductor material. From this, the equivalent heavy ion LET value of the pulsed laser at the depth x of the incident semiconductor material can be obtained as: ; where λ is the wavelength of the pulsed laser, h is Planck's constant, and c is the speed of light in vacuum.

[0043] It is known that the attenuation of the laser power density I(x) with the incident depth satisfies , where α is the single-photon absorption coefficient and β is the two-photon absorption coefficient. For a gallium nitride device, if a 266 nm ultraviolet pulsed laser is used, the single-photon energy is about 4.66 eV, which is greater than the bandgap width of the gallium nitride material, 3.39 eV. Single-photon absorption occurs, and two-photon absorption can be ignored (β≈0). At this time, the attenuation of the laser power density I(x) with the incident depth can be expressed as , where I0 is the laser power density on the semiconductor surface and α is the linear absorption coefficient. The laser energy E(x) is proportional to the laser power density I(x). Then, the attenuation law of the laser energy is the same as that of the laser power density, showing exponential attenuation with the increase of the incident depth. Therefore, there is: , and the expression of the equivalent LET of the pulsed laser can be obtained as . For a gallium nitride device, the sensitive region is the two-dimensional electron gas formed at the interface between gallium nitride and aluminum gallium nitride, and the depth is only a few nanometers, which is much smaller than the penetration depth of the laser. The attenuation of LET in this region is not obvious. Therefore, the equivalent LET value at the surface can be regarded as the equivalent LET value of the entire sensitive region. Then, the equivalent LET value is: .

[0044] The above calculation process is a simplification of the actual device. When actually testing, the device incident model needs to be re-established according to the actual structure of the device, and the equivalent relationship between the pulsed laser and the heavy ion LET needs to be calculated according to the device material and the pulsed laser wavelength.

[0045] S3: After the tester determines the required pulsed laser energy according to the test needs, turn on the pulsed laser. In the integrated control software of the second control host, drive the motor to switch the attenuation sheet and filter in the optical path coupling module to adjust the magnitude of the pulsed laser energy. The tester can manually use a high-precision optical power meter to confirm the adjustment effect. During the test, drive the high-precision XY motor under the sample stage by the second control host to move the sample, control the electric shutter of the microscopic imaging unit to collect image information, and the microscopic camera transmits the image information back to the second control host and displays it on the second display. According to the surface morphology or electrical property degradation of the device under test after irradiation, the tester evaluates and corrects the scanning model established when using the ellipsometer in S1. The results obtained after model correction can repeat the above operations until a suitable model is obtained. The electric scanning unit receives the operation instructions of the photocurrent scanning imaging software of the second control host, and the photocurrent waveform, scanned pictures, and test data will be automatically extracted and sent to the second control host. When performing subsequent test operations, use the second control host to control the turning on and off of the pulsed laser to irradiate the device under test, i.e., the wide-bandgap power device under test.

[0046] S4: The tester turns on the optoelectronic test software and manually connects the custom source meter, oscilloscope, second control host, and transient optoelectronic test unit required for the test. The wide-bandgap power device under test is fixed on the sample stage of the transient optoelectronic test unit and forms an electrical connection with the source meter through the probe. Then, the custom source meter and oscilloscope are uniformly controlled by the optoelectronic test software. After the tester sets test conditions such as gate voltage, drain voltage, and drain current limit on the optoelectronic test software, automatic selected conventional electrical tests and optoelectronic characteristic tests are performed. According to different test items, the optoelectronic test software real-time collects the test data required by the tester, establishes test curves, and saves the test data. When testing the transfer curve, collect the drain-source voltage and gate current; when testing the output curve, collect the gate-source voltage and source current; when testing the optoelectronic response I-t of the device, collect the change data of the photocurrent over time; when testing the optoelectronic response V-t of the device, collect the change data of the optical voltage over time.

[0047] S5: The tester manually connects the custom source table, oscilloscope, vacuum cryogenic platform, and shielded electrical test platform required for testing. If it is necessary to use the vacuum cryogenic platform for testing, set the temperature range to be tested on the second control host. The temperature control unit in the vacuum cryogenic platform changes to different temperatures, and the reserved test interface is connected to the oscilloscope to collect the magnitudes of the gate and drain currents of the device at different wavelengths to determine the test temperature. The tester installs the power supply motherboard on the shielded electrical test platform and connects the test daughter board according to the test requirements. The test daughter board is connected to the gate, drain, and source of the device under test in a plug-and-play form 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 waveforms. For example, for the double-pulse test daughter board, collect the gate-source voltage, drain-source voltage, and drain-source current of the device under test during the test; for the dynamic on-resistance test daughter board, collect the drain-source clamped voltage, actual drain-source voltage, and drain-source current of the device under test during the test; for the switching efficiency test daughter board, collect the input voltage, input current, output voltage, and output current of the test daughter board during the test, and save the collected data and test waveforms to the second control host.

[0048] 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 judge the radiation resistance and degradation of the wide-bandgap power device under test under pulsed laser.

[0049] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. The content not described in detail in this specification belongs to the prior art well 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, 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 film grown on a substrate corresponding to each layer of thin film material of the wide-bandgap power device under test in the full spectral range; The optical path coupling module is used to incident pulsed laser on the surface of the wide-bandgap power device under test through the optical path, control the pulsed laser wavelength, energy, incident position, and perform real-time imaging on the surface topography of the wide-bandgap power device under test 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 under test through a probe station, and is used to perform conventional electrical tests and photoelectric characteristic tests on the wide-bandgap power device under test before and after irradiation; The electrical test platform is connected to the test circuit through a reserved power supply line interface, and the wide-bandgap power device under test is connected to the test circuit in a plug-and-play manner, and is used to perform dynamic switching characteristic tests on the wide-bandgap power device under test 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 pulsed laser energy when pulsed lasers of different wavelengths pass through each layer of thin film and reach the active region in the wide-bandgap power device under test, obtain the equivalent heavy ion LET value according to the effective pulsed laser energy, and control the optical path coupling module, the photoelectric test module and the electrical test platform to close-loop adjust the pulsed laser energy according to the equivalent heavy ion LET value.

2. The pulsed 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, and 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.

3. The pulsed laser irradiation experimental device according to claim 1, wherein: The optical path coupling module includes a pulsed laser control unit, an energy control unit, a microscopic imaging unit, and an electric scanning unit; the pulsed laser control unit includes multiple groups of pulsed lasers with different wavelengths, a pull rod switcher, and an excitation light source coupling optical path, which is used to emit pulsed lasers with different wavelengths and adjust the incident light direction; the energy control unit includes an optical path reflection module, a continuously adjustable attenuation sheet, and an OD3 filter, which is used to continuously control the intensity of the pulsed laser in a large range and reflect the pulsed laser into the microscopic imaging unit; the microscopic imaging unit includes a long working distance visible objective lens, a white illumination 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 coaxial illuminate, focus and image the wide bandgap power device to be tested and obtain high-resolution microscopic images in real time; the electric scanning unit includes a high-precision XY motor and a 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 signals of each scanning point in real time, and generate a photocurrent distribution image.

4. The pulsed laser irradiation experimental device according to claim 1, wherein: 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, which are used to collect high-speed data and perform high-precision current pre-amplification; 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 conventional electrical tests and optoelectronic 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 pulsed laser irradiation experimental device according to claim 1, characterized in that: The electrical test platform includes a damping optical anti-vibration platform, a shielded electrical test platform, and a vacuum cryogenic platform. The damping optical anti-vibration platform is used to reduce environmental interference during high-magnification operation; the shielded electrical test platform includes a precision probe platform, a custom sample stage, a vacuum pump, and an optoelectronic shielding housing, which is used to adsorb the wide bandgap power device to be tested at the center adsorption holes of the precision probe platform and the custom sample stage after starting the vacuum pump; the vacuum cryogenic platform includes a cryogenic cold stage, cold stage electrical accessories, a liquid nitrogen dewar, and a vacuum pump, which is used to monitor the environmental temperature and vacuum degree of the platform where the wide bandgap power device to be tested is located.

6. The pulsed laser irradiation experimental device according to claim 5, characterized in that: 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 custom PCB board includes a power supply motherboard and a pluggable test daughter board. The power supply motherboard is fixed through the sample stage and connected to the custom source meter. The test daughter board is parallel to the power supply motherboard, fixed through the power supply motherboard, and connected to the output end of the power supply 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. An experimental device for pulsed laser irradiation according to claim 6, characterized in that: The small-area active clamping circuit includes a zener diode, a comparator, a metal-oxide-semiconductor field-effect transistor, a gate-source discharge resistor, a turn-on resistor, a turn-off resistor, and a series large-current magnetic bead. The output terminal 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 discharge resistor is connected to the gate node and the other end is grounded. The cathode of the zener diode is connected to the gate node and the anode is grounded. The inverting input terminal of the comparator is connected to the gate node, and the non-inverting input terminal is provided with an adjustable reference voltage by a voltage regulator. The output terminal of the comparator is connected to the gate of the metal-oxide-semiconductor field-effect transistor. The drain of this transistor is connected to the gate node and the source is grounded. The gate node is then connected to the gate terminal of the power device under test through a large-current magnetic bead; the source terminal of the power device under test is grounded, and its drain terminal is used as the power output terminal.

8. The pulsed laser irradiation experimental device according to claim 1, wherein: The conventional electrical test and optoelectronic characteristic test include at least one or more of an I-V curve, a transfer curve, an output curve, and a photocurrent test; the dynamic switching characteristic test includes at least one or more of a double-pulse dynamic switch, a dynamic on-resistance, and a Buck circuit conversion efficiency test.

9. The pulsed laser irradiation experimental device according to claim 1, characterized in that: Calculate the effective pulsed laser energy finally reaching the active region through the following formula: ； Among them, E eff is the effective pulsed laser energy; E0 is the pulsed 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 pulsed laser energy that reaches the active region after multiple reflections at the interface; i is the number of layers; n is the total number of layers.

10. The pulsed laser irradiation experimental device according to claim 1, characterized in that: Calculate the pulsed laser equivalent heavy-ion LET value through the following formula: ； Among them, ELET is the equivalent heavy-ion LET value of the pulsed laser; E Laser is the incident photon energy of the pulsed laser; LET ion is the heavy-ion LET value; LET laser is the LET value of the pulsed laser in the semiconductor material; E ion is the ionization energy of the semiconductor material; λ is the wavelength of the pulsed laser; ρ is the density of the semiconductor material; h is Planck's constant; c is the speed of light in vacuum; E(x) is the laser energy at the depth x of the semiconductor material; x is the depth of the semiconductor material into which the laser is incident.

Images