Microelectronic device weak part positioning method and system based on reflectivity thermal imaging

Abstract

The invention relates to the technical field of application thermal method testing, in particular to a microelectronic device weak part positioning method and system based on reflectivity thermal imaging. The method for positioning the weak part of the microelectronic device comprises the following steps: generating a periodic pulse signal based on device excitation and generating a synchronous reference signal, and synchronously triggering at least one light source LED and at least one imaging acquisition device in an initial state at the frequency which is the same as or integral multiple of the periodic pulse signal; determining that the to-be-tested device is located at the sample table, receiving material parameters of the to-be-tested device, selecting a wavelength light source according to the material parameters, and calibrating a first coefficient of reflectivity associated with temperature for the to-be-tested device; a plurality of excitation pulses are controlled to be applied to the to-be-tested device, so that the to-be-tested device is subjected to thermal excitation, the LED pulses are triggered synchronously through preset delay time, and the delay time is the time interval from application of the excitation pulses to triggering of the LED pulses.

Description

Technical Field

[0001] The present application relates to the field of testing technology using thermal methods, and in particular to a method and system for locating weak points of microelectronic devices based on reflectivity thermal imaging. Background Art

[0002] With the development of fields such as high-performance computing, devices under test are evolving towards smaller sizes and higher integration. Thermal management has become a key constraint on their performance improvement and reliability. At the micro-nano scale, transistor density has greatly increased, and local hot spots and non-uniform heat flow have accumulated, which can easily lead to device performance degradation and failure. In actual operation, under abnormal conditions, thermally induced defects will occur locally in the device under test, causing abnormal temperature rise, which is an early manifestation of failure. Therefore, the development of high-precision temperature imaging technology to achieve sub-micron scale resolution is very important for health monitoring of devices under test and locating weak points.

[0003] Currently, there are several main methods for locating weak parts of microelectronic devices: for example, luminescence microscopy can identify some defects through weak luminescence imaging at the defect site, but it cannot identify defects without obvious luminescence, and the spatial resolution often exceeds 1μm, the signal-to-noise ratio is low, it is easily interfered with and has no temperature change information; the other is the use of scanning electron microscopes, which have nanometer-level resolution and can observe physical structural abnormalities, but require a high vacuum environment, destroy the sample, cannot be detected online, and are not suitable for defect tracking under operation; the latter focuses ion beams and can be combined with analytical technology to deeply analyze the failure point, but it is highly destructive, complex to operate, and expensive, with a limited detection range, and is mainly used for post-verification.

[0004] Existing technologies are unable to simultaneously achieve submicron spatial and nanosecond temporal resolution under non-contact and non-destructive conditions, making it difficult to meet monitoring needs.

[0005] Based on this, this application is filed. Summary of the Invention

[0006] Existing technologies for locating weak points in microelectronic devices cannot simultaneously achieve submicron spatial and nanosecond temporal resolution under non-contact and non-destructive conditions, making it difficult to meet monitoring needs. In response to the above technical problems, the purpose of this application is to provide a method and system for locating weak points in microelectronic devices based on reflectivity thermal imaging.

[0007] In a first aspect of the present application, a method for locating weak parts of microelectronic devices based on reflectivity thermal imaging is first provided. The method for locating weak parts of microelectronic devices based on reflectivity thermal imaging includes: generating a periodic pulse signal based on device excitation and generating a synchronous reference signal, and in an initial state, synchronously triggering at least one light source LED and at least one imaging acquisition device at the same frequency as or an integer multiple of the periodic pulse signal; determining that the device under test is located at a sample stage, receiving material parameters of the device under test, and selecting a wavelength light source based on the material parameters, and calibrating a first coefficient of reflectivity associated with temperature for the device under test; controlling the application of a plurality of excitation pulses to the device under test so that the device under test is thermally excited, and synchronously triggering the LED pulse through a preset delay time, wherein the delay time is the time interval from the start of the excitation pulse application to the triggering of the LED pulse; measuring the reflectivity of the device under test at the heating delay moment when the LED pulse is triggered, and calculating the transient temperature distribution of the device during the excitation process through the reflectivity changes at multiple moments and the first coefficient.

[0008] In a further solution of the present application, a periodic pulse signal is generated based on device excitation and a synchronization reference signal is generated. In the initial state, at least one light source LED and at least one imaging acquisition device are synchronously triggered at a frequency that is the same as or an integer multiple of the periodic pulse signal, including: based on the device excitation, a synchronization reference signal that is the same as the device excitation frequency is generated through the TTI system; wherein the trigger frequency of the light source LED is consistent with the synchronization excitation frequency of the synchronization reference signal, and the trigger frequency of the imaging acquisition device is set to n times the synchronization excitation frequency.

[0009] In a further solution of the present application, determining that the device under test is located at the sample stage also includes: evenly applying thermal grease on the surface of the device under test facing away from the measuring surface; and / or fixing the device under test to the sample stage with the assistance of a pressure strip; and / or adjusting the knob of either the X-axis or Y-axis of the device under test so that different areas thereof are focused uniformly.

[0010] In a further embodiment of the present application, receiving material parameters of the device under test, selecting a wavelength light source, and calibrating a first coefficient of reflectivity associated with temperature for the device under test includes: Measure the initial reflectivity R and ΔR caused by temperature rise of each component material area of ​​the device under test respectively, and calculate the corresponding first coefficient by the following formula ; in, is the first coefficient of the reflectivity of the material at that point of the device under test at a specific wavelength related to temperature; ΔT represents the temperature change at a point on the surface of the device under test; ΔR is the change in the reflectivity of the device at that point; and R0 is the initial reflectivity of the device at that point.

[0011] In a further scheme of the present application, a control is provided for applying a number of excitation pulses to the device under test so that the device under test is thermally stimulated and the LED pulse is synchronously triggered by a preset delay time, wherein the delay time is the time interval from the application of the excitation pulse to the triggering of the LED pulse, including: triggering the LED pulse by a delay time preset based on a synchronization reference signal, and gradually increasing the delay time between the LED pulse and the excitation pulse according to a preset delay step.

[0012] In a further embodiment of the present application, the delay step is 20 microseconds; and / or the exposure period of the imaging acquisition device is 1 second.

[0013] In a further solution of the present application, the wavelength of the light source is selected according to the material parameters, including: when the device under test is GaN material, selecting an ultraviolet light source with a wavelength of 365nm; when the device under test is Ti material and / or Al device under test, selecting a green light source with a wavelength of 530nm.

[0014] In a further scheme of the present application, after calculating the transient temperature distribution of the device during the excitation process, it also includes: converting the reflectivity change in each frame image into a corresponding temperature change based on the calibrated first coefficient and the initial reflectivity; and reconstructing the transient thermal distribution image sequence of the device during the excitation process based on the temperature change.

[0015] In a further solution of the present application, the triggering moment of the imaging acquisition device is set before the synchronization reference signal to compensate for the acquisition time of the imaging acquisition device.

[0016] The application constructs a phase-locked signal synchronization mechanism for transient abnormal working conditions (such as high voltage stress, short circuit, etc.). After the device excitation pulse, light source LED and imaging acquisition equipment (such as CCD) are synchronized at the nanosecond level through frequency multiplication and delayed triggering technology, it can collect the reflectivity change signal at the critical moment in real time when the device undergoes a short-term high-power shock, and combine periodic averaging and delayed scanning to improve the signal-to-noise ratio and time resolution. This mechanism is the prerequisite for achieving accurate observation of transient thermal behavior. Based on the synchronously collected transient thermal images, the present invention proposes a weak area positioning method that combines thermal resistance anomalies and cooling hysteresis behavior. The reflectivity thermal imaging system is used to dynamically monitor the temperature evolution of the device after multiple stress loadings. The slowdown in the cooling rate of some areas shown in the thermal image is used as a criterion to identify potential structural defects that may have thermal diffusion anomalies or interface degradation.

[0017] Other features and advantages of the embodiments of the present invention will be described in the subsequent specific implementation examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 This is a flow chart of the method for locating weak points of microelectronic devices based on reflectivity thermal imaging provided in this application; Figure 2 This is a timing diagram of the working signal of the reflectivity thermal imaging transient test in the method for locating weak points of microelectronic devices based on reflectivity thermal imaging provided by this application; Figure 3 The temperature rise and fall curves of the GaN HEMT before and after 3000 short circuits and 5000 short circuits in the embodiment of the present application are shown.

[0020] Figure 4 This is a thermal image of the gallium nitride HEMT exemplified in the embodiment of the present application 1.5ms before the short circuit 3000 times; Figure 5 This is a thermal image of the gallium nitride HEMT at 1.5ms after 5000 short circuits in an embodiment of the present application. Figure 6 A schematic diagram of a microelectronic device weak point locating system based on reflectivity thermal imaging provided in an embodiment of the present application. DETAILED DESCRIPTION

[0021] The terms "second direction", "first direction", "third direction", "inside", "outside" and the like that appear below to indicate directions or positional relationships, unless otherwise specified, are to be understood as being based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting this application.

[0022] Furthermore, the use of "first" or "second" in describing features is for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features identified. Features identified as "first" or "second" may explicitly or implicitly include at least one of the identified features. The use of the word "plurality" generally implies at least two, such as two or three, unless otherwise specifically defined.

[0023] In this application, unless otherwise specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integration; mechanical connections, electrical connections, direct connections, or indirect connections through an intermediary; and internal connections between two components or interactions between two components. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0024] In the description of this specification, if the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" appear, it means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0025] Reference Figures 1 to 2 The present application first provides a method for locating weak points of microelectronic devices based on reflectivity thermal imaging, comprising the following steps: Step S1: Based on device excitation, a periodic pulse signal is generated and a synchronization reference signal is generated. In an initial state, at least one light source LED and at least one imaging acquisition device are synchronously triggered at a frequency that is the same as or an integer multiple of the periodic pulse signal. Step S2: determining that the device under test is located at the sample stage, receiving material parameters of the device under test, selecting a wavelength light source according to the material parameters, and calibrating a first coefficient of reflectivity associated with temperature for the device under test; Step S3, controlling the application of a plurality of excitation pulses to the device under test so that the device under test is thermally stimulated and the LED pulse is triggered synchronously with a preset delay time, wherein the delay time is the time interval between the application of the excitation pulse and the triggering of the LED pulse; S4. When the LED pulse is triggered, the reflectivity of the device under test at the heating delay moment is measured, and the transient temperature distribution of the device during the excitation process is calculated based on the reflectivity changes at multiple moments and the first coefficient.

[0026] In the present application, the device to be tested is a microelectronic device, that is, an electronic device with a tiny size and highly integrated electronic components, which is commonly used in various electronic devices, such as integrated circuit devices to be tested; the periodic pulse signal in step S1 is an electrical signal that repeats at a certain period, has periodic and pulse characteristics, and can be used to stimulate the device to be tested; the synchronization reference signal is generated based on the device excitation, and is used as a reference signal for synchronizing other devices or signals to ensure that the timing between each device or signal is consistent and coordinated; the light source LED is a light emitting diode, which is a semiconductor device that can convert electrical energy into light energy. Here it is used as a light source to provide illumination for reflectivity measurement. An imaging acquisition device is a device used to collect image information. In this application, it is used to collect images of the device under test under specific conditions to obtain relevant information such as reflectivity. By applying an excitation pulse to the device under test, it generates a pulse signal with a thermal response or other response, which is used to stimulate the physical process inside the device. The delay time is the time interval between the application of the excitation pulse and the triggering of the LED pulse. By controlling this time interval, the reflectivity of the device under test can be measured at different times, thereby obtaining temperature information at different times. The transient temperature distribution device is the spatial distribution of the temperature at a certain moment or in a short process, reflecting the dynamic process of temperature change of the device when it is stimulated.

[0027] The following uses the measurement of the surface temperature distribution of the device under test as an example to explain in detail the application of the above phase-locked synchronization principle in the TTI system: The device under test generates heat during operation, and its surface temperature distribution has a significant impact on the performance, reliability, and life of the device under test. However, for example, the reflectivity of the surface material of the device under test changes very slightly with temperature, ΔR / R≈10 -4 ~10 -6 In general, it is very difficult to directly measure such weak changes, and special techniques are needed to stably extract the signal.

[0028] In order to cause the device to produce periodic temperature changes, this application adopts the application of periodic pulse current to the device to be tested as excitation; assuming that a pulse current with a frequency of 1kHz is selected, this means that the device to be tested will undergo 1000 complete heating to cooling cycles per second, and the duty cycle of the pulse current (the ratio of the pulse duration to the period) is set to 30%, that is, in one cycle, current passes through the device to be tested for the first 0.3ms to cause it to heat up, and the current stops for the next 0.7ms, and the device to be tested cools down naturally.

[0029] When an excitation effect occurs, such as when current flows through it, the electron motion inside the DUT intensifies, generating Joule heating and causing the DUT temperature to rise. After the current stops, the DUT dissipates heat to the surrounding environment through conduction and convection, gradually cooling the temperature. Thus, the DUT surface temperature exhibits periodic changes with the pulsed current.

[0030] Set the trigger frequency of the light source LED to synchronize with the DUT excitation frequency. (Note that synchronization here does not mean that the trigger frequency of the light source LED must be completely consistent with the DUT excitation frequency. As long as there is a certain temporal correspondence between the two to ensure the coordination of the measurement process, it is sufficient. For example, it can be an integer multiple of the DUT excitation frequency.) Use a dedicated synchronization control circuit to ensure that the LED is triggered and illuminated at the moment each pulse current begins to heat the DUT, providing stable illumination to the DUT surface. In this way, the change in light intensity reflected from the DUT surface during each heating cycle is correlated with the temperature change.

[0031] The CCD camera's trigger frequency is set to an integer multiple of the DUT's excitation frequency. For example, if 3kHz is selected, the CCD camera captures three frames of images per DUT excitation cycle. Through precise timing control, the dynamic changes in the DUT's surface reflectivity with temperature can be captured in detail.

[0032] Since both the light source LED and the CCD camera are strictly synchronized with the excitation pulse of the device under test, the device under test is in the same thermal excitation stage each time the CCD camera captures an image, ensuring the consistency of the initial conditions for each sampling. This eliminates the impact of differences in the thermal state of the device under test due to different sampling times on the reflectivity measurement.

[0033] Sampling at the same time point over multiple excitation cycles results in comparable and consistent reflectivity data. For example, assuming data is continuously collected over 1000 excitation cycles, the CCD camera captures multiple frames of images from three excitation cycles within each cycle, yielding multiple sets of data. In actual measurements, in addition to the reflectivity change signal caused by temperature changes in the device under test, various noise factors, such as electronic noise and optical noise, are present. This noise is randomly distributed and exhibits different behavior over multiple cycles. However, the reflectivity change signal caused by temperature changes in the device under test exhibits periodicity, and reflectivity changes at the same time point are similar.

[0034] Multiple sets of data are classified according to the time points of acquisition, and then the reflectivity change values ​​at the same time points are superimposed and averaged. For example, all reflectivity change values ​​acquired 0μs after the device under test starts heating are added together, and then the accumulated value is divided by the number of acquisition cycles 1000 to obtain the average reflectivity change value. The same processing is performed on the data acquired in 20μs. Through superposition and averaging, the positive and negative amplitudes of random noise will cancel each other out, and the amplitude of the signal will be enhanced, thereby improving the signal-to-noise ratio.

[0035] Based on the reflectivity-temperature relationship of the DUT material obtained through pre-calibrated experiments, the reflectivity change data with high signal-to-noise ratio is converted into temperature data. This allows for the acquisition of high-precision temperature distribution information at different locations and times on the DUT surface, enabling clear observation of the DUT's thermal dynamics during operation.

[0036] Generally speaking, step S1 generates a periodic pulse signal based on device excitation. This signal serves as the fundamental signal for stimulating the DUT throughout the entire test process. It also generates a synchronization reference signal for coordinating the operation of other devices: The trigger settings for the light source LED and imaging acquisition equipment are set. The trigger frequency of the light source LED is synchronized with the DUT excitation frequency.

[0037] Step S2 uses image recognition or other sensors to determine that the DUT is placed at a designated location on the sample stage. Material parameters of the DUT are then received. Due to the varying physical properties of different materials, the relationship between light reflection and temperature changes also varies. A light source with an appropriate wavelength is selected based on these material parameters to improve measurement accuracy and sensitivity. A first temperature-dependent coefficient of reflectivity is calibrated for the DUT, and a quantitative relationship between reflectivity and temperature is established experimentally. Step S3 controls the application of several excitation pulses to the DUT, causing thermal excitation and internal temperature changes. The excitation pulse parameters (such as amplitude and duty cycle) can be configured based on the DUT's characteristics and test requirements. An LED pulse is then triggered synchronously with a preset delay time, which is the interval between the application of the excitation pulse and the triggering of the LED pulse. By setting different delay times, the DUT's reflectivity can be measured at different times, thereby obtaining dynamic temperature information about the DUT during the excitation process. For example, setting a shorter delay time can measure the temperature change of the device in the early stage of excitation, and setting a longer delay time can observe the temperature distribution of the device in the later stage of excitation; when the LED pulse is triggered, the reflectivity of the device under test at the heating delay moment is measured. Since the first coefficient of reflectivity and temperature has been calibrated, the reflectivity change data at multiple moments and this coefficient can be used to obtain the transient temperature distribution of the device during the excitation process through mathematical calculation.

[0038] In summary, the present application constructs a phase-locked signal synchronization mechanism for transient abnormal working conditions (such as high voltage stress, short circuit, etc.). After the device excitation pulse, light source LED and imaging acquisition equipment (such as CCD) are synchronized at the nanosecond level through frequency multiplication and delayed triggering technology, it can collect the reflectivity change signal at the critical moment in real time when the device undergoes a short-term high-power shock, and combine periodic averaging and delayed scanning to improve the signal-to-noise ratio and time resolution. This mechanism is the prerequisite for achieving accurate observation of transient thermal behavior. Based on the synchronously collected transient thermal images, the present invention proposes a weak area positioning method that combines thermal resistance anomalies and cooling hysteresis behavior. The reflectivity thermal imaging system is used to dynamically monitor the temperature evolution of the device after multiple stress loadings. The slowdown in the cooling rate of some areas shown in the thermal image is used as a criterion to identify potential structural defects that may have thermal diffusion anomalies or interface degradation.

[0039] In the above step S1, based on device excitation, a periodic pulse signal is generated and a synchronization reference signal is generated. In an initial state, at least one light source LED and at least one imaging acquisition device are synchronously triggered at a frequency that is the same as or an integer multiple of the periodic pulse signal, including: Based on the device stimulus, a synchronous reference signal with the same frequency as the device stimulus is generated through the TTI system; The trigger frequency of the light source LED is made consistent with the synchronous excitation frequency of the synchronous reference signal, and the trigger frequency of the imaging acquisition device is set to n times the synchronous excitation frequency.

[0040] Device excitation generates specific physical changes. The TTI (Time-to-Interval) system, assuming here that it generates synchronization signals based on input excitation, senses and processes this excitation. Upon receiving the device excitation signal, the TTI system generates a synchronization reference signal at the same frequency as the device excitation, providing a precise time reference for the subsequent synchronous triggering of the light source LED and imaging acquisition equipment. The aforementioned "setting the trigger frequency of the light source LED to be consistent with the synchronous excitation frequency of the synchronization reference signal" means that the triggering moment of the LED and the pulse of the synchronization reference signal completely correspond to each other. However, it should be noted that the triggering moments can be completely consistent or relatively advanced or delayed.

[0041] It should be noted that setting the trigger frequency of the light source LED to be consistent with the synchronous excitation frequency of the synchronization reference signal does not mean that the triggering moment of the light source LED completely corresponds to the pulse moment of the synchronization reference signal. The triggering moment can be designed differently because in almost any electronic system, there is a hardware-level delay from the time when the synchronization reference signal triggers the driving circuit of the light source LED to the time when the light source LED actually emits light. For example, the transistor in the driving circuit requires a certain amount of time to respond to the input signal and reach the appropriate conduction state, thereby providing sufficient current to the LED light source to make it emit light. This time delay may be at the nanosecond to microsecond level, but it is enough to cause a difference in the triggering moment. Therefore, the present application aims to match the triggering period of the light source LED with the period of the synchronization reference signal, but this does not guarantee that the triggering moment of the light source LED completely corresponds to the pulse moment of the synchronization reference signal.

[0042] Set the trigger frequency of the imaging acquisition device to n times the synchronous excitation frequency, where n is a positive integer (such as n=2, 3, 4, etc.). This allows the imaging acquisition device to capture images multiple times within a device excitation cycle. Since the reflectivity of the device under test changes over time during the excitation process, multiple image captures can provide reflectivity information of the device under test at more moments.

[0043] In step S2, the following is also included: Evenly apply thermal grease on the side of the DUT facing away from the measurement surface; and / or secure the DUT to the sample stage with the aid of a pressure strip; and / or adjust the knobs on either the X-axis or Y-axis of the DUT to ensure consistent focus across different areas.

[0044] When the device under test (DUT) is stimulated, it generates heat. If this heat cannot be transferred away promptly and effectively, the device's temperature distribution will be uneven, affecting the accuracy of the reflectivity measurement and, in turn, the subsequent temperature distribution and weak spot location results calculated based on the reflectivity. Applying thermal grease can significantly reduce the contact thermal resistance between the DUT and the sample stage, allowing heat to be transferred from the DUT to the sample stage more quickly and evenly, ensuring that the DUT's temperature during the measurement process is closer to its actual operating state. A pressure bar (usually made of a strong and rigid material such as metal or hard plastic) is used to press the DUT against the sample stage. The pressure bar can be securely attached to the sample stage using screws, clamps, or other fixing devices, ensuring that the DUT maintains a stable position relative to the sample stage during the measurement process, preventing it from moving relative to the sample stage. During reflectivity thermal imaging measurements, the reflectivity information of the DUT at different positions must be accurately recorded. If the DUT moves relative to the sample stage, the measured data will not match the actual position, affecting the temperature distribution calculation and the accuracy of weak spot location. Using a pressure bar to assist in fixing the DUT during the measurement can ensure that the position of the DUT remains fixed, improving the accuracy and reliability of the measurement. At the same time, by rotating these knobs, the horizontal position of the device under test can be changed. In the microscopic imaging system, due to the unevenness of the surface of the device under test, different areas are not in the same focal plane, resulting in blurred imaging. By adjusting the X-axis or Y-axis knobs, the position of the device under test can be fine-tuned, so that the microscope objective lens can focus on different areas of the device under test at the same time, achieving clear imaging in the entire field of view. Following the above, in step S2, the material parameters of the device under test are received, a wavelength light source is selected, and a first coefficient of reflectivity associated with temperature is calibrated for the device under test, including: Measure the initial reflectivity R and ΔR caused by temperature rise of each component material area of ​​the device under test respectively, and calculate the corresponding first coefficient by the following formula ; in, is the first coefficient of the reflectivity of the material at that point of the device under test at a specific wavelength related to temperature; ΔT represents the temperature change at a point on the surface of the device under test; ΔR is the change in the reflectivity of the device at that point; and R0 is the initial reflectivity of the device at that point.

[0045] Controlling the application of a plurality of excitation pulses to the device under test so as to thermally excite the device under test and synchronously triggering an LED pulse with a preset delay time, wherein the delay time is the time interval between the application of the excitation pulse and the triggering of the LED pulse, and includes: The LED pulse is triggered by a delay time preset based on the synchronization reference signal, and the delay time between the LED pulse and the excitation pulse is gradually increased according to a preset delay step.

[0046] By accurately calibrating this coefficient, a reliable quantitative relationship model between reflectivity and temperature was established. In subsequent reflectivity thermal imaging measurements, simply measuring the reflectivity of the device surface under test allows this model to accurately calculate the temperature at that location, ultimately providing the temperature distribution across the entire device surface.

[0047] The weak parts of the device under test are often prone to abnormal temperature increases during operation. By accurately calculating the temperature distribution on the surface of the device under test, abnormal points or areas with higher temperatures than the surrounding areas can be clearly identified.

[0048] Furthermore, in step S3, a plurality of excitation pulses are applied to the device under test so that the device under test is thermally stimulated and the LED pulse is triggered synchronously with a preset delay time, wherein the delay time is the time interval between the application of the excitation pulse and the triggering of the LED pulse, including: The LED pulse is triggered by a delay time preset based on the synchronization reference signal, and the delay time between the LED pulse and the excitation pulse is gradually increased according to a preset delay step.

[0049] After thermal stimulation, the temperature change of the device under test is a dynamic process that evolves over time. By gradually increasing the delay between the LED pulse and the excitation pulse, reflectivity information of the device under test can be obtained at different time points, thereby comprehensively understanding the device's temperature state and thermal response characteristics at different moments, providing rich data support for accurate analysis of the device's thermal performance. In the optional solution of this application, the delay step size is 20 microseconds; and / or the exposure period of the imaging acquisition device is 1 second.

[0050] The preset delay step is 20 microseconds. The delay time between the LED pulse and the excitation pulse is increased by 20 microseconds each time. The delay time is increased by 20 microseconds in sequence, that is, 40 microseconds, 60 microseconds, 80 microseconds..., and the process of applying the excitation pulse, triggering the LED pulse and acquiring the image is repeated until the preset maximum delay time (for example, 1 millisecond) is reached.

[0051] The entire steps of S3 can be explained as follows: Before conducting transient thermal testing, you need to first set the parameters such as the heating duration and duty cycle of the device excitation pulse. Then, in the initial state before the excitation pulse is applied, turn on the LED pulse light source to illuminate the device surface and collect its initial reflectivity value. , as a reference baseline for temperature changes; after each excitation pulse is formally applied, the system will follow the set delay time Accurately trigger the LED pulse and measure the reflectivity of the device at this heating delay moment .

[0052] In order to improve the system's sensitivity to weak reflectivity changes and the signal-to-noise ratio, the test needs to be repeated at each time point and the data is averaged. As the test progresses, the time interval between the LED pulse and the excitation pulse is gradually increased according to the preset delay step. At each delay moment (such as ) and repeatedly collect the corresponding reflectance values Finally, the reflectivity changes at multiple moments and the pre-calibrated reflectivity-temperature coefficient By using them together, the transient temperature distribution of the device during the excitation process can be calculated, thereby achieving dynamic tracking of the device's thermal response process and high-precision thermal imaging.

[0053] Furthermore, the wavelength of the light source is selected according to the material parameters, including: when the device under test is GaN material, a UV light source with a wavelength of 365nm is selected; when the device under test is Ti material and / or Al device under test, a green light source with a wavelength of 530nm is selected to obtain the maximum values ​​and stronger temperature response signals.

[0054] After calculating the transient temperature distribution of the device during the excitation process based on the above step S4, the method further includes: Step S5: Based on the calibrated first coefficient and initial reflectivity , convert the reflectivity change in each frame of image into the corresponding temperature change ΔT; Step S6: reconstructing a transient thermal distribution image sequence of the device during the excitation process according to the temperature change ΔT.

[0055] After completing the transient thermal test and obtaining the reflectivity images at different delay times, the system calculates the reflectivity-temperature coefficient based on the calibrated reflectivity-temperature coefficient. and initial reflectivity , converting the reflectivity change ΔR in each image frame into a corresponding temperature change ΔT, thereby reconstructing a sequence of transient thermal distribution images of the device during the excitation process. By analyzing this sequence frame by frame, the dynamic evolution of the device surface temperature over time can be intuitively observed.

[0056] Understandably, in a typical thermal image, the defective area usually shows a higher local temperature rise than the surrounding area. This is because the material interface structure or heat conduction path abnormalities caused by the defects lead to a significant increase in local thermal resistance, thereby accumulating more heat per unit time and forming a prominent "hot spot" area. In addition, in the subsequent cooling stage, the temperature in the normal area drops rapidly, while the area with abnormal thermal resistance often shows a slow cooling feature due to the obstruction of heat dissipation. By comparing the evolution trends of thermal images at different time points, potential structural defects or failure risk points inside the device can be accurately identified and located, providing a key basis for reliability analysis and thermal design optimization.

[0057] In the present application, the triggering moment of the imaging acquisition device is set before the synchronization reference signal to compensate for the acquisition time of the imaging acquisition device.

[0058] After receiving a trigger signal, an imaging acquisition device doesn't immediately begin capturing image data. Instead, it requires a certain amount of time to complete operations such as activating internal circuits, initializing sensors, and establishing data transmission channels. This period is called the acquisition time. The synchronization reference signal coordinates the operating rhythm of various devices in the measurement system (such as the light source LED and excitation source), ensuring that each device performs its corresponding actions at a specific time for precise, synchronized measurement. Setting the imaging acquisition device's triggering time ahead of the synchronization reference signal allows sufficient acquisition time for the device to complete its preparations by the time the image is needed (the time corresponding to the activation of other devices, as determined by the synchronization reference signal), ensuring accurate image data acquisition. If the imaging acquisition device is not triggered in advance and only begins acquisition when the synchronization reference signal arrives, the device under test may have already changed state during the acquisition time, resulting in the captured image not accurately reflecting the device's state at the time corresponding to the synchronization reference signal.

[0059] A specific application example is as follows: like Figure 3 Figure 2 shows the thermal ramp curves of a GaN HEMT after various short-circuit stress cycles. The test conditions were Vgs = 5V, Vds = 200V, a short-circuit stress duration of 200μs, and a short-circuit interval of 200ms. The curve in the figure depicts the device channel region's thermal ramp within 1.6ms of a typical short-circuit pulse, along with a thermal image of the 1.5ms timeframe using reflectivity thermal imaging.

[0060] The heating and cooling curves show that before 3000 short-circuit cycles, the device channel region rapidly heats up after pulse excitation and then gradually cools down within 1.6ms, exhibiting typical thermal diffusion behavior. However, as the number of stress cycles increases to 5000, the device rapidly heats up under the same excitation, but the cooling rate slows significantly, demonstrating a typical increase in local thermal resistance.

[0061] like Figure 4 and Figure 5 The corresponding thermal images further verified this change. Before the short circuit was 3000 times, the short circuit thermal image at 1.5ms showed that most areas had experienced a significant temperature drop (such as Figure 4 After 5000 short circuits, a local high temperature appears and the temperature drops slowly, indicating that there may be abnormal thermal diffusion inside the device due to material degradation, structural stress concentration or interface delamination, forming a potential thermal structural weak area (such as Figure 5 ).

[0062] The experimental results fully demonstrate the ability of reflectivity thermal imaging technology to identify thermal anomalies inside devices under stress conditions, enabling early perception of thermal structure degradation trends and providing effective support for device reliability assessment and failure risk location.

[0063] like Figure 6 On the other hand, the present application further provides a microelectronic device weak point positioning system 100 based on reflectivity thermal imaging, which includes a sample stage 10, an imaging acquisition device 20, a device excitation device 30, a light source LED 40, and a prism 50; the sample stage 10 is used to place the device under test; the imaging acquisition device 20 is used to capture images of the device under test; the device excitation device 30 is used to generate a periodic pulse signal; the light source LED 40 is used to emit LED pulses to trigger reflection; the prism 50 is arranged between the device excitation device and the device under test, and the LED pulse passes through the prism and is incident on the device under test.

[0064] The microelectronic device weak point locating system 100 further includes a controller (not shown), which is configured to execute at least part of or all of the steps of the above-mentioned microelectronic device weak point locating method based on reflectivity thermal imaging.

[0065] This system is applicable to various types of microelectronic devices. Using an imaging acquisition device 20 to capture images of the device under test, it can detect subtle changes in the device's surface reflectivity. When a weak part of a microelectronic device is stimulated (e.g., thermally), its physical properties (such as thermal expansion and heat conduction) differ from those of normal parts. These differences are reflected in the reflectivity. By precisely measuring changes in reflectivity, weak parts can be accurately identified, with positioning accuracy reaching micrometers or even nanometers, meeting high-precision testing requirements.

[0066] The system uses non-destructive testing, allowing multiple tests on the device under test to track performance changes at different stages of use or under different environmental conditions. Long-term monitoring enables timely identification of potential device problems, enabling appropriate maintenance measures to be implemented and extending the device's lifespan.

[0067] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and are not to be construed as limiting the present invention. The present invention is provided with a parameter entry, and the parameters can be changed at will for analysis, optimization and verification. Those skilled in the art can change, modify, replace and modify the above embodiments within the scope of the present invention.

[0068] The various technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification as long as such combination does not conflict.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still adjust the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these adjustments or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for locating weak points of microelectronic devices based on reflectivity thermal imaging, characterized in that: include: Based on the device excitation, a periodic pulse signal is generated and a synchronization reference signal is generated. In the initial state, at least one light source LED and at least one imaging acquisition device are synchronously triggered at the same frequency as the periodic pulse signal or an integer multiple thereof; Determining that a device under test is located at a sample stage, receiving material parameters of the device under test, selecting a wavelength light source according to the material parameters, and calibrating a first coefficient of reflectivity associated with temperature for the device under test; Controlling the application of a plurality of excitation pulses to the device under test so that the device under test is thermally stimulated and the LED pulse is triggered synchronously with a preset delay time, wherein the delay time is the time interval between the application of the excitation pulse and the triggering of the LED pulse; When the LED pulse is triggered, the reflectivity of the device under test at the heating delay moment is measured, and the transient temperature distribution of the device during the excitation process is calculated based on the reflectivity changes at multiple moments and the first coefficient.

2. The method for locating weak points of a microelectronic device according to claim 1, wherein: The device excitation generates a periodic pulse signal and a synchronization reference signal, and in an initial state, synchronously triggers at least one light source LED and at least one imaging acquisition device at a frequency that is the same as or an integer multiple of the periodic pulse signal, including: Based on the device stimulus, a synchronous reference signal with the same frequency as the device stimulus is generated through the TTI system; The trigger frequency of the light source LED is made consistent with the synchronous excitation frequency of the synchronous reference signal, and the trigger frequency of the imaging acquisition device is set to n times the synchronous excitation frequency.

3. The method for locating weak points of a microelectronic device according to claim 2, wherein: The determining that the device under test is located at the sample stage further includes: Evenly apply thermal conductive silicone grease on the surface of the device under test that is away from the measuring surface; and / or Fixing the device under test on the sample stage with the aid of a pressure strip; and / or Adjust any one of the knobs on the X-axis and the Y-axis of the device under test to make different areas thereof focus on the same level.

4. The method for locating weak points of a microelectronic device according to claim 1, wherein: The receiving of the material parameters of the device under test, selecting a wavelength light source, and calibrating a first coefficient of reflectivity associated with temperature for the device under test includes: Measure the initial reflectivity R and ΔR caused by temperature rise of each component material area of ​​the device under test respectively, and calculate the corresponding first coefficient by the following formula ; in, is the first coefficient of the reflectivity of the material at that point of the device under test at a specific wavelength related to temperature; ΔT represents the temperature change at a point on the surface of the device under test; ΔR is the change in the reflectivity of the device under test at that point; and R0 is the initial reflectivity of the device under test at that point.

5. The method for locating weak points of a microelectronic device according to claim 4, characterized in that: The control applies a plurality of excitation pulses to the device under test so that the device under test is thermally stimulated and synchronously triggers an LED pulse with a preset delay time, wherein the delay time is the time interval between the application of the excitation pulse and the triggering of the LED pulse, including: The LED pulse is triggered by a delay time preset based on the synchronization reference signal, and the delay time between the LED pulse and the excitation pulse is gradually increased according to a preset delay step.

6. The method for locating weak points of a microelectronic device according to claim 5, characterized in that: The delay step is 20 microseconds; and / or The exposure period of the imaging acquisition device is 1 second.

7. The method for locating weak points of a microelectronic device according to claim 1, wherein: The step of selecting a wavelength light source according to the material parameters comprises: When the device under test is made of GaN material, 365nm ultraviolet light is selected. When the device under test is made of Ti material and / or Al material, 530 nm green light is selected.

8. The method for locating weak points of a microelectronic device according to claim 4, wherein: After the transient temperature distribution of the device during the excitation process is obtained by calculation, the method further includes: Convert the reflectivity change ΔR in each frame of image into a corresponding temperature change based on the calibrated first coefficient and the initial reflectivity; The transient thermal distribution image sequence of the device during the excitation process is reconstructed based on the temperature change ΔT.

9. The method for locating weak points of a microelectronic device according to claim 1, wherein: include: The triggering moment of the imaging acquisition device is set before the synchronization reference signal to compensate for the acquisition time of the imaging acquisition device.

10. A microelectronic device weak point positioning system based on reflectivity thermal imaging, characterized in that: include: Sample stage, used to place the device under test; An imaging acquisition device, used for acquiring an image of the device under test; Device excitation equipment, used to generate periodic pulse signals; Light source LED, used for emitting LED pulses; A prism is provided between the device excitation device and the device under test, and the LED pulse is incident on the device under test after passing through the prism; A controller configured to execute the method for locating weak points of a microelectronic device as claimed in any one of claims 1 to 9.

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