Method and system for locating weak spots in microelectronic devices based on reflectance thermography

Abstract

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

Description

TECHNICAL FIELD

[0001] The present application relates to the field of application thermal method testing technology, in particular to a microelectronic device weak part positioning method and system based on reflectivity thermal imaging. BACKGROUND

[0002] With the development of high-performance computing and other fields, the device to be tested evolves towards small size and high integration, and thermal management becomes the key to restricting its performance improvement and reliability. Under micro-nano scale, the transistor density increases greatly, and local hot spots and non-uniform heat flow are easily gathered, which can cause device performance degradation and failure. In actual operation, the local part of the device to be tested can produce thermal-induced defects under abnormal working conditions, which can cause abnormal temperature rise and is an early manifestation of failure. Therefore, it is very important to develop high-precision temperature imaging technology to achieve sub-micron scale resolution for health monitoring and weak part positioning of the device to be tested.

[0003] Currently, the main methods for positioning the weak part of the microelectronic device are as follows: using luminescence microscopic imaging to image the weak luminescence of the defect, which can identify some defects, but it cannot identify defects without obvious luminescence, the spatial resolution is often more than 1 μm, the signal-to-noise ratio is low, it is easily disturbed and has no temperature change information; another method is to use a scanning electron microscope, which has nanoscale resolution and can observe physical structure abnormalities, but it requires a high vacuum environment and destroys the sample, so it cannot be used for online detection and is not suitable for defect tracking in the running state; the latter is focused ion beam, which can be combined with analysis technology to deeply analyze the failure point, but it is highly destructive, complex to operate, high in cost, limited in detection range, and mainly used for post-validation.

[0004] The existing technology cannot simultaneously achieve sub-micron spatial and nanosecond temporal resolution under non-contact and non-destructive conditions, which cannot meet the monitoring requirements.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The existing microelectronic device weak part positioning technology cannot simultaneously achieve sub-micron spatial and nanosecond temporal resolution under non-contact and non-destructive conditions, which cannot meet the monitoring requirements. In view of the above technical problems, the purpose of the present application is to provide a microelectronic device weak part positioning method and system based on reflectivity thermal imaging.

[0007] In the first aspect of the present application, a method for locating weak parts of microelectronic devices based on reflectivity thermal imaging is provided. The method comprises: generating a periodic pulse signal based on device excitation and generating a synchronous reference signal; synchronously triggering at least one light source LED and at least one imaging acquisition device at the same frequency or an integer multiple of the frequency of the periodic pulse signal in the initial state; determining that the device under test is located on 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 to heat excite the device under test, and synchronously triggering an LED pulse through a preset delay time, wherein the delay time is the time interval between the start of the excitation pulse and the triggering of the LED pulse; measuring the reflectivity of the device under test at the heating delay time when the LED pulse is triggered, and calculating the transient temperature distribution of the device under test during the excitation process by the reflectivity change at multiple time points and the first coefficient.

[0008] In a further aspect of the present application, the method of synchronously triggering at least one light source LED and at least one imaging acquisition device at the same frequency or an integer multiple of the frequency of the periodic pulse signal in the initial state based on the device excitation and generating a synchronous reference signal comprises: generating a synchronous reference signal with the same frequency as the device excitation frequency through a TTI system according to the device excitation; wherein the triggering frequency of the light source LED and the synchronous excitation frequency of the synchronous reference signal are consistent, and the triggering frequency of the imaging acquisition device is set to n times the synchronous excitation frequency.

[0009] In a further aspect of the present application, the method of determining that the device under test is located on a sample stage further comprises: uniformly coating a heat-conducting silicone grease on the side of the device under test away from the measurement surface; and / or fixing the device under test to the sample stage with the aid of a pressing strip; and / or adjusting the knobs of the device under test in either of the X-axis and Y-axis to make the focusing of different regions consistent.

[0010] In a further aspect of the present application, the method of 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 comprises:

[0011] measuring the initial reflectivity R and the temperature rise induced ΔR of each component material region of the device under test, and calculating the corresponding first coefficient by the following formula ;

[0012]

[0013] wherein, The first coefficient of the reflectivity of the material at the point of the device to be measured at a specific wavelength in relation to temperature; ΔT represents the temperature change of a point on the surface of the device to be measured; ΔR is the change in reflectivity of the point of the device to be measured; and R0 is the initial reflectivity of the point of the device to be measured.

[0014] In a further aspect of the present application, the device to be measured is applied with a plurality of excitation pulses to cause the device to be measured to be thermally excited, and an LED pulse is triggered synchronously through a preset delay time, wherein the delay time is a time interval from the start of the excitation pulse to the triggering of the LED pulse, comprising: triggering the LED pulse through the delay time preset based on the synchronization reference signal, and gradually increasing the delay time between the LED pulse and the excitation pulse according to a preset delay step.

[0015] In a further aspect of the present application, the delay step is 20 microseconds; and / or the exposure period of the imaging acquisition device is 1 second.

[0016] In a further aspect of the present application, the wavelength light source is selected according to the material parameters, comprising: when the device to be measured is a GaN material, selecting an ultraviolet light source with a wavelength of 365 nm; and when the device to be measured is a Ti material and / or an Al device, selecting a green light source with a wavelength of 530 nm.

[0017] In a further aspect of the present application, after the transient temperature distribution of the device during the excitation process is calculated, further comprising: converting the reflectivity change in each frame of image into the corresponding temperature change according to the calibrated first coefficient and the initial reflectivity; and reconstructing the transient thermal distribution image sequence of the device during the excitation process according to the temperature change.

[0018] In a further aspect of the present application, the triggering time of the imaging acquisition device is set before the synchronization reference signal to compensate for the acquisition time of the imaging acquisition device.

[0019] The application constructs a lock-in signal synchronization mechanism for transient abnormal working conditions (such as high voltage stress, short circuit, etc.), which can realize nanosecond-level synchronization of the device excitation pulse, the light source LED, and the imaging acquisition device (such as CCD) through frequency multiplication and delay triggering technology, can acquire the reflectivity change signal at the key moment in real time when the device is subjected to a short-time high-power impact, and can improve the signal-to-noise ratio and time resolution by combining periodic averaging and delay scanning, which is a prerequisite for precise observation of transient thermal behavior; on the basis of the synchronously acquired transient thermal images, the application proposes a weak area positioning method combining thermal resistance abnormalities and cooling delay behaviors. Through dynamic monitoring of the temperature evolution of the device after multiple stress loads by the reflectivity thermal imaging system, the potential structural defects that may exist in the thermal diffusion abnormality or interface degradation are identified by using the criterion that the cooling rate of some areas in the thermal image is slowed down.

[0020] Other features and advantages of the present embodiments will be illustrated in the following detailed description of the embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the present application or prior art, the following will briefly introduce the drawings needed to be used in the description of the embodiments or prior art. Obviously, the drawings described below are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0022] Figure 1 The flow chart of the microelectronic device weak site positioning method based on reflectivity thermal imaging provided by the present application;

[0023] Figure 2 In the microelectronic device weak site positioning method based on reflectivity thermal imaging provided by the present application, the timing diagram of the reflectivity thermal imaging transient test working signal;

[0024] Figure 3 The temperature rise and fall curves of the gallium nitride HEMT before and after 3000 times of short circuit and 5000 times of short circuit are exemplified by the embodiments of the present application.

[0025] Figure 4 The thermal image at 1.5 ms before the gallium nitride HEMT short circuit 3000 times is exemplified by the embodiments of the present application.

[0026] Figure 5 The thermal image at 1.5 ms after the gallium nitride HEMT short circuit 5000 times is exemplified by the embodiments of the present application.

[0027] Figure 6 The schematic diagram of a microelectronic device weak site positioning system based on reflectivity thermal imaging provided by the embodiments of the present application. DETAILED DESCRIPTION

[0028] The terms "second direction", "first direction", "third direction", "inner", "outer" and the like appearing below indicate the description of the orientation or positional relationship, and if there is no special description, it is understood to be based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as a limitation on the present application. Indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0029] In addition, as the features appearing with the limitation of "first", "second" are only used for the purpose of description, it cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features. The features with the limitation of "first", "second" can explicitly or implicitly include at least one of the features limited.

[0030] In the present application, unless otherwise explicitly specified and limited, the terms such as "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense. For example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected, it can be directly connected, or it can be indirectly connected through an intermediate medium, it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0031] In the description of the present application, the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" and the like mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0032] Reference Figures 1 to 2 The present application first provides a microelectronic device weak part positioning method based on reflectivity thermal imaging, comprising the following steps:

[0033] Step S1, based on device excitation to generate periodic pulse signal and generate synchronization reference signal, at least one light source LED and at least one imaging acquisition device are respectively triggered with the same or integer multiple frequency of the periodic pulse signal in the initial state;

[0034] Step S2, determine the device to be measured at the sample table, receive the material parameters of the device to be measured, and select the wavelength light source according to the material parameters, and calibrate the first coefficient of reflectivity associated with temperature for the device to be measured;

[0035] Step S3, control to apply several excitation pulses to the device under test, so that the device under test is subjected to thermal excitation, and trigger the LED pulse through the preset delay time synchronously, wherein the delay time is the time interval from the start of the excitation pulse to the triggering of the LED pulse;

[0036] S4, measure the reflectivity of the device under test at the heating delay time when the LED pulse is triggered, and calculate the transient temperature distribution of the device during the excitation process by the reflectivity change at multiple time points and the first coefficient.

[0037] In this application, the device under test is a microelectronic device, that is, an electronic device with small volume and highly integrated electronic components, commonly used in various electronic equipment, such as integrated circuit device under test, etc. The periodic pulse signal in step S1 is an electrical signal that appears repeatedly according to a certain period, has periodicity and pulse characteristics, and can be used to excite the device under test. The synchronization reference signal is based on the device excitation, which is used as a reference signal for synchronizing other devices or signals, to ensure that the timing of 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. The imaging acquisition device is used to collect image information. In this application, it is used to collect images of the device under test under certain conditions to obtain reflectivity and other related information. By applying an excitation pulse to the device under test, a pulse signal is generated to respond to heat or other responses, which is used to stimulate the physical process inside the device. The delay time is the time interval from the start of the excitation pulse to the triggering of the LED pulse. By controlling this time interval, the reflectivity of the device under test can be measured at different time points, so as to obtain temperature information at different time points. The transient temperature distribution is the distribution of temperature in space at a certain moment or a short period of time, which reflects the dynamic process of temperature change of the device under excitation.

[0038] The following takes the measurement of the surface temperature distribution of the device under test as an example to explain the application of the above-mentioned phase-locked synchronization principle in the TTI system in detail:

[0039] The device under test generates heat during operation, and the surface temperature distribution has an important influence 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 It is very difficult to directly measure such a weak change, and special techniques are needed to stabilize the signal extraction.

[0040] In order to make the device to be tested to produce periodic temperature changes, the application adopts to apply periodic pulse current to the device to be tested as excitation; assuming that the frequency of 1 kHz pulse current is selected, which means that the device to be tested will experience 1000 complete heating to cooling cycles per second, the duty cycle of the pulse current (the ratio of pulse duration to period) is set to 30%, that is, in a period, the first 0.3 ms has current passing through the device to be tested to heat it, and the last 0.7 ms stops the current, and the device to be tested naturally cools down.

[0041] When the excitation effect is generated, such as when there is current passing through, the electronic motion in the device to be tested is intensified, generating Joule heat, and the temperature of the device to be tested rises; after the current stops, the device to be tested dissipates heat to the surrounding environment through heat conduction and convection, and the temperature gradually decreases. In this way, the surface temperature of the device to be tested will present periodic changes with the pulse current.

[0042] The trigger frequency of the light source LED is set to be synchronized with the excitation frequency of the device to be tested (note that here synchronization does not mean that the trigger frequency of the light source LED needs to be completely consistent with the excitation frequency of the device to be tested, as long as there is a certain correspondence in time, which can ensure the coordination of the measurement process, for example, it can be an integer multiple of the excitation frequency of the device to be tested). Using a special synchronization control circuit, ensure that at the moment when each pulse current starts to heat the device to be tested, the LED triggers to light up, providing stable light for the surface of the device to be tested. In this way, the change of the light intensity reflected by the surface of the device to be tested in each heating period is associated with the temperature change.

[0043] The trigger frequency of the CCD camera is set to be an integer multiple of the excitation frequency of the device to be tested, for example, if 3 kHz is selected, that is, in each excitation period of the device to be tested, the CCD camera itself collects multiple frames of images in three periods per cycle. Through precise timing control, the dynamic change process of the reflectivity of the surface of the device to be tested with temperature can be captured in detail.

[0044] Since the light source LED and the CCD camera are strictly synchronized with the excitation pulse of the device to be tested, the device to be tested is in the same thermal excitation stage when the CCD camera collects images each time, ensuring that the initial conditions of each sampling are consistent, and eliminating the influence of the difference in thermal state of the device to be tested on reflectivity measurement due to different sampling times.

[0045] In multiple excitation cycles, the reflectivity data obtained by sampling at the same time point has comparability and consistency; for example: assuming that 1000 excitation cycles of data are continuously collected, the CCD camera collects multiple frames of images under three excitation cycles in each cycle of itself, that is, multiple sets of data are obtained; in actual measurement, in addition to the reflectivity change signal caused by the temperature change of the device under test, there are various noises such as electronic noise, optical noise, etc. These noises are randomly distributed and behave differently in multiple cycles. The reflectivity change signal caused by the temperature change of the device under test has periodicity, and the reflectivity change at the same time point has similarity.

[0046] The multiple sets of data are classified according to the time points of collection, and then the reflectivity change values at the same time point are superimposed and averaged; for example, the reflectivity change values collected at 0 μs after the device under test starts heating are added, and then accumulated to be divided by the number of cycles collected 1000, to obtain the average reflectivity change value; similarly, the data collected at 20 μs is processed in the same way. Through superimposed 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.

[0047] According to the reflectivity-temperature relationship of the device under test material obtained by pre-experiment calibration, the high signal-to-noise ratio reflectivity change data is converted into temperature data. In this way, the high-precision temperature distribution information of the surface of the device under test at different positions and different times can be obtained, and the thermal dynamic characteristics of the device under test in the working process can be clearly observed.

[0048] Overall, step S1 generates a periodic pulse signal based on device excitation, which is used as the basic signal for exciting the device under test in the entire test process, and a synchronous reference signal is also generated to coordinate the operation of other equipment: the light source LED and the imaging acquisition equipment are triggered and set. The trigger frequency of the light source LED is set to be synchronized with the excitation frequency of the device under test.

[0049] Step S2 can adopt image recognition or other sensors to determine that the device under test is placed at the designated position of the sample table, receive the material parameters of the device under test, since different materials have different physical properties, the relationship between light reflection and temperature change also differs; according to these material parameters, a light source with a suitable wavelength is selected to improve the accuracy and sensitivity of the measurement; a first coefficient of the correlation between reflectivity and temperature is calibrated for the device under test, and a quantitative relationship between reflectivity and temperature is established through experimental methods. Step S3 controls the application of a plurality of excitation pulses to the device under test, so that the device under test is subjected to thermal excitation and internal temperature change; the parameters (such as amplitude, duty cycle, etc.) of the excitation pulse can be set according to the characteristics of the device under test and the test requirements. The LED pulse is triggered synchronously through a preset delay time, which is the time interval from the start of the excitation pulse to the triggering of the LED pulse. By setting different delay times, the reflectivity of the device under test at different times can be measured, thereby obtaining the dynamic temperature information of the device under test during the excitation process. For example, setting a short delay time can measure the temperature change of the device at the initial stage of excitation, and setting a long delay time can observe the temperature distribution of the device at the later stage of excitation; the reflectivity of the device under test at the heating delay time is measured when the LED pulse is triggered, since the first coefficient of the correlation between reflectivity and temperature has been calibrated, the reflectivity change data at multiple times and the coefficient can be used to obtain the transient temperature distribution of the device during the excitation process through mathematical calculation.

[0050] In summary, the application constructs a lock-in signal synchronization mechanism for transient abnormal operating conditions (such as high voltage stress, short circuit, etc.), which can realize nanosecond-level synchronization of device excitation pulse, light source LED and imaging acquisition device (such as CCD) through frequency multiplication and delay triggering technology. When the device is subjected to a short-time high-power impact, the reflectivity change signal at the key moment can be collected in real time, and the signal-to-noise ratio and time resolution can be improved by combining periodic averaging and delay scanning. This mechanism is the premise of accurate observation of transient thermal behavior. Based on the synchronous collection of transient thermal images, the application proposes a weak area positioning method combining thermal resistance abnormality and cooling delay behavior. Through dynamic monitoring of the temperature evolution of the device after multiple stress loads by the reflectivity thermal imaging system, the slowdown of the cooling rate in some areas in the thermal image is used as a criterion to identify potential structural defects that may have thermal diffusion abnormalities or interface degradation.

[0051] In the above step S1, a periodic pulse signal is generated based on device excitation, and a synchronous reference signal is generated, and in the initial state, at least one light source LED and at least one imaging acquisition device are respectively triggered at the same frequency or an integer multiple of the frequency of the periodic pulse signal, including:

[0052] According to the device excitation, a synchronous reference signal with the same frequency as the device excitation frequency is generated by the TTI system;

[0053] 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 of the synchronization excitation frequency.

[0054] According to the device excitation, the device excitation can cause a specific physical change, and the TTI (Time-to-Interval, time interval measurement system, which is assumed to have the function of generating a synchronization signal according to the input excitation) can perceive and process the excitation. When the TTI system receiver receives the device excitation signal, a synchronization reference signal with the same frequency as the device excitation is generated, providing an accurate time reference for the subsequent synchronization triggering of the light source LED and the imaging acquisition device. In the above-mentioned "setting the trigger frequency of the light source LED to be consistent with the synchronization excitation frequency of the synchronization reference signal", the trigger time of the LED completely corresponds to the pulse of the synchronization reference signal, but it needs to be noted that the trigger time can be completely consistent or relatively advanced / lagged.

[0055] It needs to be noted that setting the trigger frequency of the light source LED to be consistent with the synchronization excitation frequency of the synchronization reference signal does not mean that the trigger time of the light source LED completely corresponds to the pulse time of the synchronization reference signal. The trigger time can be designed differently because there is a hardware delay between the driving circuit of the light source LED triggered by the synchronization reference signal and the actual light emission of the light source LED. For example, the transistor in the driving circuit needs a certain time to respond to the input signal and reach the appropriate conduction state, thereby providing sufficient current for the LED light source to emit light. This time delay can be in the nanosecond to microsecond level, but it is enough to cause the difference in the trigger time. Therefore, the application aims to match the trigger period of the light source LED with the period of the synchronization reference signal, but this does not guarantee that the trigger time of the light source LED completely corresponds to the pulse time of the synchronization reference signal.

[0056] The trigger frequency of the imaging acquisition device is set to n times of the synchronization excitation frequency, where n is a positive integer (such as n=2, 3, 4, etc.). Its role is that in one device excitation period, the imaging acquisition device can collect images multiple times. Since the reflectivity of the device under test changes over time during the excitation process, more reflectivity information of the device under test at different times can be obtained by collecting images multiple times.

[0057] In step S2, it further includes:

[0058] Uniformly applying a heat-conducting silicone grease on the side of the device under test away from the measurement surface; and / or fixing the device under test to the sample table with the aid of a pressing strip; and / or adjusting the knobs of the device under test in either the X-axis or the Y-axis to make the focusing of different regions consistent.

[0059] The device under test will generate heat when excited, and if the heat cannot be conducted out in time and effectively, it will cause uneven temperature distribution of the device itself, affecting the accuracy of reflectivity measurement, and then affecting the subsequent temperature distribution and weak part positioning results based on reflectivity calculation; coating with thermal conductive silicone grease can significantly reduce the contact thermal resistance between the device under test and the sample table, so that the heat can be transferred from the device under test to the sample table more quickly and uniformly, ensuring that the temperature state of the device under test during the measurement process is closer to its real working state; the device under test is pressed on the sample table by a pressing strip (usually made of materials with certain strength and rigidity, such as metal or hard plastic). The pressing strip can be firmly installed on the sample table by screws, clamps and other fixing devices, so that the device under test can maintain a stable position during the measurement process and will not move relative to the sample table; during the reflectivity thermal imaging measurement process, it is necessary to accurately record the reflectivity information of the device under test at different positions. If the device under test moves relative to the actual position, the measurement data will not match, which will affect the calculation of temperature distribution and the positioning accuracy of weak parts. With the aid of the pressing strip, the position of the device under test during the measurement process can be fixed, improving the accuracy and reliability of the measurement. At the same time, by rotating these knobs, the position of the device under test in the horizontal direction can be changed. In the microscopic imaging system, due to the unevenness of the surface of the device under test, different regions may not be on 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 objective lens of the microscope can focus on different regions of the device under test at the same time, realizing clear imaging in the entire field of view

[0060] Based on the foregoing, in step S2, a wavelength light source is selected according to the material parameters of the device under test, and a first coefficient of reflectivity associated with temperature is calibrated for the device under test, including:

[0061] The initial reflectivity R and the change ΔR caused by temperature rise of each component material region of the device under test are measured respectively, and the corresponding first coefficient is calculated by the following formula ;

[0062]

[0063] wherein, is the first coefficient of reflectivity associated with temperature of the material at the point of the device under test at a specific wavelength; ΔT represents the temperature change of a certain point on the surface of the device under test; ΔR is the change of reflectivity of the device under test at that point; R0 is the initial reflectivity of the device under test at that point.

[0064] A plurality of excitation pulses are applied to the device under test to heat excite the device under test, and an LED pulse is triggered synchronously through a preset delay time, wherein the delay time is the time interval from the start of the excitation pulse to the triggering of the LED pulse, including:

[0065] The LED pulse is triggered by a preset delay time based on a synchronization reference signal, and the delay time between the LED pulse and the excitation pulse is gradually increased according to a preset delay step.

[0066] By accurately calibrating the coefficient, a reliable quantitative relationship model between reflectivity and temperature is established. In subsequent reflectivity thermal imaging measurement, only the reflectivity of the surface of the device to be measured needs to be measured, and the temperature of the corresponding position can be accurately calculated by using this model, and then the temperature distribution of the entire device surface is obtained.

[0067] The weak part of the device to be measured is prone to abnormal temperature rise during operation. By accurately calculating the temperature distribution of the surface of the device to be measured, the abnormal points or regions with higher temperature than the surrounding regions can be clearly identified.

[0068] Further, in step S3, a plurality of excitation pulses are applied to the device to be measured to heat the device to be measured, and an LED pulse is triggered by a preset delay time at the same time, wherein the delay time is the time interval from the start of the excitation pulse to the triggering of the LED pulse, including:

[0069] The LED pulse is triggered by a preset delay time based on a synchronization reference signal, and the delay time between the LED pulse and the excitation pulse is gradually increased according to a preset delay step.

[0070] After the device to be measured is heated, the temperature change of the device to be measured is a dynamic development process with time. By gradually increasing the delay time between the LED pulse and the excitation pulse, the reflectivity information of the device to be measured at different time points can be obtained, so that the temperature state and thermal response characteristics of the device at different time points can be comprehensively understood, and rich data support is provided for accurately analyzing the thermal performance of the device. In an optional scheme of the present application, the delay step is 20 microseconds; and / or the exposure period of the imaging acquisition device is 1 second.

[0071] 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, and the delay time is increased by 20 microseconds in turn, i.e. 40 microseconds, 60 microseconds, 80 microseconds, …, the processes of applying excitation pulses, triggering LED pulses and image acquisition are repeated until the preset maximum delay time (for example, 1 millisecond) is reached.

[0072] The whole step of S3 can be explained as follows:

[0073] Before performing the transient thermal test, the heating time and duty cycle of the device excitation pulse and the like parameters need to be set first. Subsequently, in the initial state before the excitation pulse is applied, the LED pulse light source is turned on to irradiate the device surface and collect the initial reflectivity value , as a reference baseline for temperature variation; after each excitation pulse is formally applied, the system will follow a set delay time Precise triggering of LED pulses, measuring reflectivity of the device at this heating delay time .

[0074] To improve the sensitivity and signal-to-noise ratio of the system to weak reflectivity changes, the test needs to be repeated multiple times at each time point, and the data is averaged. As the test progresses, according to the preset delay step, gradually increase the time interval between the LED pulse and the excitation pulse, and repeat the collection of the corresponding reflectivity value at each delay time (such as ). Finally, by using the reflectivity changes at multiple times and the pre-calibrated reflectivity-temperature coefficient jointly, the transient temperature distribution of the device during the excitation process is calculated, thereby realizing dynamic tracking and high-precision thermal imaging of the device's thermal response process.

[0075] Further, according to the material parameter selection wavelength light source, including: the device to be measured is GaN material, select the wavelength of 365nm ultraviolet light source; the device to be measured is Ti material and / or Al device to be measured, select the wavelength of 530nm green light source, to obtain the maximum value and stronger temperature response signal.

[0076] After calculating the transient temperature distribution of the device during the excitation process based on the above step S4, it further includes:

[0077] Step S5, according to the calibrated first coefficient and the initial reflectivity , convert the reflectivity change in each frame of image into the corresponding temperature change ΔT;

[0078] Step S6, according to the temperature change ΔT, reconstruct the transient thermal distribution image sequence of the device during the excitation process.

[0079] After completing the transient thermal test and obtaining the reflectivity images at different delay times, the system converts the reflectivity change ΔR in each frame of image into the corresponding temperature change ΔT according to the calibrated reflectivity-temperature coefficient and the initial reflectivity , thereby reconstructing the transient thermal distribution image sequence of the device during the excitation process. By frame-by-frame analysis of the sequence, the dynamic evolution process of the device surface temperature with time can be directly observed.

[0080] It can be understood that in a typical thermal image, a defect region usually appears as a higher local temperature rise compared to the surrounding region. This is because the defect causes abnormal material interface structure or heat conduction path, resulting in a significant increase in local thermal resistance, thereby accumulating more heat in a unit of time, forming a prominent "hot spot" region. In addition, in the subsequent cooling stage, the temperature of the normal region falls rapidly, while the thermal resistance abnormal region tends to show a slow cooling characteristic due to the obstruction of heat dissipation. By comparing the evolution trend of thermal images at different time points, potential structural defects or failure risk points inside the device can be accurately identified and located, providing key basis for reliability analysis and thermal design optimization.

[0081] In the present application, the trigger time of the imaging acquisition device is set before the synchronization reference signal to compensate for the acquisition time of the imaging acquisition device.

[0082] After receiving the trigger signal, the imaging acquisition device does not start collecting image data immediately, but needs a certain time to complete the startup of the internal circuit, the initialization of the sensor, and the establishment of the data transmission channel, etc. This period of time is the acquisition time. The synchronization reference signal is a reference for coordinating the work rhythm of various devices (such as light source LED, excitation source, etc.) in the entire measurement system, ensuring that each device performs corresponding actions at a specific time point to achieve accurate synchronous measurement. The trigger time of the imaging acquisition device is set in advance of the synchronization reference signal, in order to reserve sufficient acquisition time for the imaging acquisition device, so that it can complete the preparation work at the time when image acquisition is needed (the time corresponding to the action of other devices determined by the synchronization reference signal), and can normally collect accurate image data. If the imaging acquisition device is not triggered in advance, and starts the acquisition process when the synchronization reference signal arrives, then within the acquisition time, the device under test may have undergone a state change, resulting in the collected image not accurately reflecting the device state at the time corresponding to the synchronization reference signal.

[0083] A specific application implementation is as follows:

[0084] For example, Figure 3 , are the temperature rise and fall curves of a gallium nitride HEMT after different numbers of short-circuit stress, with test conditions of Vgs=5V, Vds=200V, short-circuit stress time 200μs, and short-circuit interval 200ms. The curves in the figure are the temperature rise and fall process of the device channel region within 1.6ms after a typical short-circuit pulse, and the 1.5ms time thermal distribution image displayed in combination with the reflectance thermal imaging result.

[0085] From the temperature rise and fall curves, it can be seen that before 3000 short-circuit times, the device channel region can quickly rise in temperature after pulse excitation and gradually cool down within the subsequent 1.6 ms, showing a typical thermal diffusion behavior. However, as the stress cycle number rises to 5000, the device quickly rises in temperature under the same excitation, but the cooling rate is significantly slowed down, showing a typical local thermal resistance increase feature.

[0086] As Figure 4 and Figure 5 , the corresponding thermal images also further verify this change. Before 3000 short-circuit times, the short-circuit thermal image at the 1.5 ms time point shows that most of the region has obviously cooled down (as Figure 4 ); and after 5000 short-circuit times, local high temperature appears and cools down slowly, indicating that there may be abnormal thermal diffusion in the device due to material degradation, structural stress concentration or interface delamination, etc., forming a potential thermal structure weak area (as Figure 5 ).

[0087] The experimental results fully demonstrate the ability of the reflectivity thermal imaging technology to identify internal thermal abnormalities of the device under stress conditions, which can realize early perception of the thermal structure degradation trend and provide effective support for device reliability evaluation and failure risk positioning.

[0088] As Figure 6 , based on another aspect of the present application, a microelectronic device weak part positioning system 100 based on reflectivity thermal imaging is also provided, which comprises a sample table 10, an imaging acquisition device 20, a device excitation device 30, a light source LED 40 and a prism 50; the sample table 10 is used for placing a device to be tested; the imaging acquisition device 20 is used for acquiring an image of the device to be tested; the device excitation device 30 is used for generating a periodic pulse signal; the light source LED 40 is used for emitting an LED pulse to trigger reflection; and the prism 50 is arranged between the device excitation device and the device to be tested, and the LED pulse is incident on the device to be tested after passing through the prism.

[0089] The microelectronic device weak part positioning system 100 further comprises a controller (not shown), which is configured to perform at least part of the steps or all of the steps of the above-mentioned microelectronic device weak part positioning method based on reflectivity thermal imaging.

[0090] The system can be applied to various types of microelectronic devices, and the system uses the imaging acquisition device 20 to acquire images of the devices to be tested, which can capture subtle changes in reflectivity of the device surface. Since the weak parts of the microelectronic device differ from the normal parts in physical properties (such as thermal expansion, thermal conductivity, etc.) when they are excited (such as thermal excitation), these differences will be reflected in the reflectivity. By accurately measuring the reflectivity changes, the weak parts can be accurately identified, and the positioning accuracy can reach microns or even nanometers, meeting the high-precision detection requirements.

[0091] Moreover, the system uses non-destructive testing, and the device to be tested can be detected multiple times to track the performance changes of the device at different use stages or under different environmental conditions. Through long-term monitoring, potential problems of the device can be found in time, and appropriate maintenance measures can be taken to prolong the service life of the device.

[0092] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application. The present application has a parameter entry, and the parameters can be changed for analysis, optimization and verification. Those skilled in the art can make changes, modifications, replacements and modifications to the above embodiments within the scope of the present application.

[0093] The technical features described above can be combined arbitrarily. Although all possible combinations of these technical features are not described, any combination of these technical features should be considered to be covered by the present specification, as long as such a combination does not contradict.

[0094] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still adjust the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to part or all of the technical features; and these adjustments or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for locating weak points in microelectronic devices based on reflectivity thermal imaging, characterized in that, include: Based on the device excitation to generate a periodic pulse signal and generate a synchronization reference signal, 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. The device under test is located on the sample stage. The material parameters of the device under test are received, and a wavelength light source is selected according to the material parameters. A first coefficient relating the reflectivity to temperature is calibrated for the device under test. The system controls the application of several excitation pulses to the device under test (DUT) to thermally excite the DUT and simultaneously triggers LED pulses through a preset delay time, where the delay time is the time interval between the application of the excitation pulses and the triggering of the LED pulses. The reflectivity of the device under test is measured at the heating delay time when the LED pulse is triggered. The transient temperature distribution of the device during the excitation process is calculated by the reflectivity changes at multiple times and the first coefficient. The method of generating a periodic pulse signal based on device excitation and generating a synchronization reference signal, in the initial state, involves 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, including: Based on the device excitation, a synchronization reference signal with the same frequency as the device excitation is generated by the TTI system; 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. Selecting a wavelength light source based on the material parameters of the device under test (DUT), and calibrating a first coefficient relating the reflectivity of the DUT to temperature, including: The initial reflectivity R and the temperature rise-induced ΔR of each component material region of the device under test are measured respectively, and the corresponding first coefficient is calculated using the following formula. ; ； in, The first coefficient relating the reflectance of the material at a specific wavelength of the device under test to temperature is given by the coefficient; ΔT represents the temperature change at a certain point on the surface of the device under test; ΔR is the change in reflectance at that point of the device under test; and R0 is the initial reflectance at that point of the device under test.

2. The method for locating weak points in microelectronic devices according to claim 1, characterized in that, The step of determining that the device under test is located at the sample stage also includes: A thermally conductive silicone grease is uniformly applied to the side of the device under test that is away from the measurement surface. and / or The device under test is fixed to the sample stage with the aid of a pressure strip; and / or Adjust the knob on either the X-axis or Y-axis of the device under test to make different areas focus in a consistent manner.

3. The method for locating weak points in microelectronic devices according to claim 1, characterized in that, The control applies several excitation pulses to the device under test (DUT) to thermally excite the DUT, and simultaneously triggers LED pulses after a preset delay time. The delay time is the time interval from the application of the excitation pulses to the triggering of the LED pulses, including: The LED pulse is triggered by a preset delay time based on the synchronization reference signal, and the delay time between the LED pulse and the excitation pulse is gradually increased according to the preset delay step size.

4. The method for locating weak points in microelectronic devices according to claim 3, characterized in that, The delay step is 20 microseconds; and / or The exposure cycle of the imaging acquisition device is 1 second.

5. The method for locating weak points in microelectronic devices according to claim 1, characterized in that, The step of selecting a wavelength light source based on the material parameters includes: 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, 530nm green light is selected.

6. The method for locating weak points in microelectronic devices according to claim 1, characterized in that, After calculating the transient temperature distribution of the device during the excitation process, the method further includes: Based on the calibrated first coefficient and initial reflectance, the reflectance change ΔR in each frame of the image is converted into the corresponding temperature change; The transient thermal distribution image sequence of the device during the excitation process is reconstructed based on the temperature change ΔT.

7. The method for locating weak points in microelectronic devices according to claim 1, characterized in that, include: The trigger time of the imaging acquisition device is set before the synchronization reference signal to compensate for the acquisition time of the imaging acquisition device.

8. A system for locating weak points in microelectronic devices based on reflectivity thermal imaging, characterized in that, include: Sample stage, used to place the device under test; An imaging acquisition device, used to acquire images of the device under test; Device excitation equipment used to generate periodic pulse signals; LED light source, used to emit LED pulses; A prism is positioned between the device excitation device and the device under test (DUT), through which the LED pulse is incident on the DUT. The controller is configured to perform the method for locating weak points in a microelectronic device as described in any one of claims 1 to 7.

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