Minority-carrier lifetime imaging system and method for semiconductor wafer

Abstract

A minority-carrier lifetime imaging system (100) and method for a semiconductor wafer. The system (100) comprises: a control module (110), which is used for generating a first electric pulse signal (Ep1) and a second electric pulse signal (Ep2); a light source module (120), which is used for generating a detection light beam (L1) and an excitation light beam (L2) on the basis of the first electric pulse signal (Ep1) and the second electric pulse signal (Ep2); a bearing module (130), which is used for fixing a wafer; a beam expansion module (140), which is used for enabling the detection light beam (L1) and the excitation light beam (L2) to be incident, by means of the beam expansion module (140), onto the wafer fixed on the bearing module (130), such that minority carriers on the wafer are converted from a ground state to an excited state under the excitation of the excitation light beam (L2), and the detection light beam (L1) detects the minority carriers in the excited state; and an imaging module (150), which is used for acquiring the minority carriers in the excited state that are detected by the detection light beam (L1), and generating a transient absorption image of the wafer, wherein the control module (110) is further used for generating a wafer minority-carrier lifetime image on the basis of the transient absorption image.

Description

Semiconductor wafer minority carrier lifetime imaging system and method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311703543.5, filed on December 11, 2023, entitled “A System and Method for Imaging Minority Carrier Lifetime of Semiconductor Wafers,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the field of wafer detection technology, and in particular relates to a semiconductor wafer minority carrier lifetime imaging system and method. Background Art

[0004] Third-generation semiconductor materials, typically represented by silicon carbide (SiC) and gallium nitride (GaN), possess unique properties such as wide bandgap, high breakdown voltage, high thermal conductivity, high electron saturation drift velocity, low dielectric constant, and excellent chemical stability. They hold great promise for application in high-power devices, high-temperature electronics, and optoelectronics. However, the wafer quality of third-generation semiconductors is significantly inferior to that of traditional silicon wafers. For example, due to the unique physical and chemical properties of SiC, such as its crystal structure, the crystal growth process is still immature, and the defect concentration in the crystal is several orders of magnitude higher than that of Si. This results in a very short minority carrier lifetime in SiC, which affects the performance of subsequent chip devices. Therefore, measuring the minority carrier lifetime of wafers for third-generation semiconductors is particularly important for optimizing the crystal growth process and improving wafer quality and yield.

[0005] At present, the conventional minority carrier lifetime test system is based on pulsed laser excitation of samples, microwave conductivity detection, the use of microwaves to scan the sample wafer from top to bottom, and the continuous acquisition of microwave intensity attenuation by an oscilloscope.

[0006] However, since the relevant technology can only be implemented by scanning samples, the imaging efficiency is low and testing the entire wafer takes a lot of time.

[0007] Summary of the Invention

[0008] Based on the above background, in order to solve at least one of the above problems, the purpose of this application is to provide a semiconductor wafer minority carrier lifetime imaging system and method, which can improve the imaging efficiency of minority carrier lifetime imaging.

[0009] An embodiment of the first aspect of the present application provides a semiconductor wafer minority carrier lifetime imaging system, the semiconductor wafer minority carrier lifetime imaging system comprising:

[0010] A control module is used to generate a first electric pulse signal and a second electric pulse signal, and there is a preset time interval between the starting moment of the enable level of the first electric pulse signal and the starting moment of the enable level of the second electric pulse signal; a light source module is electrically connected to the control module so that the light source module can generate a detection beam and an excitation beam according to the first electric pulse signal and the second electric pulse signal; a carrier module is used to fix the wafer; a beam expansion module is arranged between the light source module and the carrier module so that the detection beam and the excitation beam can be incident on the wafer fixed on the carrier module through the beam expansion module, so that the minority carriers on the wafer are converted from the ground state to the excited state under the excitation of the excitation beam, and the detection beam detects the minority carriers in the excited state; an imaging module is electrically connected to the control module, and the imaging module is used to obtain the minority carriers in the excited state detected by the detection beam to generate a transient absorption image of the wafer; the control module is also used to generate a wafer minority carrier lifetime image based on the transient absorption image.

[0011] According to the implementation of the first aspect of the present application, the beam expansion module includes: a first beam expansion module, which is arranged on the optical path of the detection beam reaching the wafer; and a second beam expansion module, which is arranged on the optical path of the excitation beam reaching the wafer.

[0012] According to any of the aforementioned embodiments of the first aspect of the present application, the first beam expanding module and the second beam expanding module are arranged on opposite sides of the carrier module in the thickness direction.

[0013] According to any of the aforementioned embodiments of the first aspect of the present application, the first beam expansion module is a beam expansion and homogenization device, including an integrating sphere.

[0014] According to any of the aforementioned embodiments of the first aspect of the present application, a first light homogenizing device is provided between the second beam expansion module and the carrier module. According to any of the aforementioned embodiments of the first aspect of the present application, the carrier module includes a carrier plate, the carrier plate is provided with a first light through hole and a second light through hole, the first light through hole is used to fix the wafer, and the second light through hole is used to fix the filter.

[0015] According to any of the aforementioned embodiments of the first aspect of the present application, the semiconductor wafer minority carrier lifetime imaging system also includes: a first optical path adjustment device, which is arranged on the optical path of the detection light beam arriving at the first beam expansion module; and a second optical path adjustment device, which is arranged on the optical path of the excitation light beam arriving at the second beam expansion module.

[0016] According to any of the aforementioned embodiments of the first aspect of the present application, the control module includes: an industrial computer, electrically connected to the imaging module, and the industrial computer is used to generate a first electrical signal; a timing controller, electrically connected to the light source module, and the timing controller is used to generate a first electrical pulse signal and a second electrical pulse signal based on the first electrical signal; the industrial computer is also used to receive and process the transient absorption image sent by the imaging module to obtain a minority carrier lifetime image of the wafer.

[0017] According to any of the aforementioned embodiments of the first aspect of the present application, the semiconductor wafer minority carrier lifetime imaging system also includes a second light homogenizing device and a third light homogenizing device arranged in an array, the second light homogenizing device is arranged between the integrating sphere and the third light homogenizing device, and the third light homogenizing device is arranged between the second light homogenizing device and the carrier module.

[0018] According to any of the aforementioned embodiments of the first aspect of the present application, the detection light beam and the excitation light beam are lasers.

[0019] According to any of the aforementioned embodiments of the first aspect of the present application, the repetition frequency of the detection beam is greater than the repetition frequency of the excitation beam.

[0020] The second aspect of the present application provides a semiconductor wafer minority carrier lifetime imaging method, which uses the semiconductor wafer minority carrier lifetime imaging system of the first aspect. The semiconductor wafer minority carrier lifetime imaging method includes:

[0021] The control module generates a first electric pulse signal and a second electric pulse signal, and there is a preset time interval between the starting time of the enable level of the first electric pulse signal and the starting time of the enable level of the second electric pulse signal; the light source module generates a detection beam and an excitation beam according to the first electric pulse signal and the second electric pulse signal, and the detection beam and the excitation beam are incident on the wafer fixed on the supporting module through the beam expansion module, so that the minority carriers on the wafer are converted from the ground state to the excited state under the excitation of the excitation beam, and the detection beam detects the minority carriers in the excited state; the imaging module obtains the minority carriers in the excited state detected by the detection beam, generates a transient absorption image of the wafer, and transmits the transient absorption image to the control module; the control module generates a wafer minority carrier lifetime image based on the transient absorption image.

[0022] In the semiconductor wafer minority carrier lifetime imaging system and method of the embodiment of the present application, the first electric pulse signal and the second electric pulse signal generated by the control module in the system are both trigger signals. The trigger light source module generates a detection beam and an excitation beam. Since there is a preset time interval between the starting moment of the enable level of the first electric pulse signal and the starting moment of the enable level of the second electric pulse signal, there is also a preset time interval between the detection beam and the excitation beam. The excitation beam can convert the wafer minority carriers from the ground state to the excited state. The detection beam detects the wafer minority carriers in the excited state and transmits the detected wafer transient absorption image to the control module. The control module processes the transient absorption image to obtain the wafer minority carrier lifetime image. Since the beam expansion module is used to expand the detection beam and the excitation beam, combined with the use of the homogenization device, the imaging module can collect the excitation beam passing through the wafer sample over a large area without scanning from top to bottom, which greatly improves the detection efficiency of semiconductor wafer minority carrier lifetime imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0024] FIG1 is a schematic structural diagram of a semiconductor wafer minority carrier lifetime imaging system provided in an embodiment of the present application;

[0025] FIG2 is a schematic diagram of pulse time delay of a detection beam and an excitation beam provided in an embodiment of the present application;

[0026] FIG3 is another structural schematic diagram of a semiconductor wafer minority carrier lifetime imaging system provided in an embodiment of the present application;

[0027] FIG4 is a schematic structural diagram of a carrier plate provided in an embodiment of the present application;

[0028] FIG5 is a schematic diagram of another structure of a semiconductor wafer minority carrier lifetime imaging system provided in an embodiment of the present application;

[0029] FIG6 is a schematic diagram of transient absorption imaging provided by an embodiment of the present application;

[0030] FIG7 is a schematic diagram of processing transient absorption imaging provided by an embodiment of the present application;

[0031] FIG8 is a schematic diagram of a kinetic curve provided in an embodiment of the present application;

[0032] FIG9 is a schematic diagram of minority carrier lifetime imaging provided in an embodiment of the present application;

[0033] FIG10 is a flow chart of a method for imaging minority carrier lifetime of a semiconductor wafer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present application by illustrating the examples of the present application.

[0035] The acquisition, storage, use, and processing of data in this application's technical solution comply with relevant national laws and regulations.

[0036] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, the elements defined by the phrase "comprising..." do not exclude the presence of other identical elements in the process, method, article, or device comprising the elements.

[0037] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0038] It will be apparent to those skilled in the art that various modifications and variations can be made in this application without departing from the spirit or scope of this application. Therefore, this application is intended to cover modifications and variations of this application that fall within the scope of the corresponding claims (technical solutions claimed for protection) and their equivalents. It should be noted that the embodiments provided in the examples of this application can be combined with each other without contradiction.

[0039] Third-generation semiconductor materials, typically represented by silicon carbide (SiC) and gallium nitride (GaN), possess unique properties such as wide bandgap, high breakdown voltage, high thermal conductivity, high electron saturation drift velocity, low dielectric constant, and excellent chemical stability. They hold great promise for application in high-power devices, high-temperature electronics, and optoelectronics. However, the wafer quality of third-generation semiconductors is significantly inferior to that of traditional silicon wafers. For example, due to the unique physical and chemical properties of SiC, such as its crystal structure, the crystal growth process is still immature, and the defect concentration in the crystal is several orders of magnitude higher than that of Si. This results in a very short minority carrier lifetime in SiC, which affects the performance of subsequent chip devices. Therefore, measuring the minority carrier lifetime of wafers for third-generation semiconductors is particularly important for optimizing the crystal growth process and improving wafer quality and yield.

[0040] At present, the conventional minority carrier lifetime test system is based on pulsed laser excitation of samples, microwave conductivity detection, the use of microwaves to scan the sample wafer from top to bottom, and the continuous acquisition of microwave intensity attenuation by an oscilloscope.

[0041] However, because the technology can only be implemented by scanning the sample, the imaging efficiency is low and testing the entire wafer is time-consuming. Secondly, the long wavelength of microwaves used in microwave conductivity detection results in low temporal and spatial resolution of minority carrier lifetime imaging systems.

[0042] In order to solve the problems of the prior art, the embodiments of the present application provide a semiconductor wafer minority carrier lifetime imaging system and method. The semiconductor wafer minority carrier lifetime imaging system provided by the embodiments of the present application is first introduced below.

[0043] Figure 1 is a schematic diagram of a semiconductor wafer minority carrier lifetime imaging system according to an embodiment of the present invention. As shown in Figure 1 , semiconductor wafer minority carrier lifetime imaging system 100 may include a control module 110 , a light source module 120 , a carrier module 130 , a beam expander module 140 , and an imaging module 150 .

[0044] The control module 110 can be used to generate a first electrical pulse signal Ep1 and a second electrical pulse signal Ep2, wherein there is a preset time interval ΔT between the start time of the enable level of the first electrical pulse signal Ep1 and the start time of the enable level of the second electrical pulse signal Ep2. The range of the preset time interval ΔT can be taken from a set of data within the pulse light time interval range of the detection beam L1. The preset time interval ΔT can select different ΔT values ​​within this range based on the wafer minority carrier lifetime value. For silicon carbide semiconductor wafer samples, a set of data between 0 and 1 us and with an interval of 10 ns is generally preferred as the range of the preset time ΔT.

[0045] The light source module 120 is electrically connected to the control module 110 so that the light source module 120 can generate the detection beam L1 and the excitation beam L2 according to the first electrical pulse signal Ep1 and the second electrical pulse signal Ep2. The carrier module 130 can be used to fix the wafer.

[0046] The control module 110 is used to ensure that there is a preset time interval △T between the starting moments of the enable levels of the generated first electrical pulse signal Ep1 and the second electrical pulse signal Ep2, so that there is also a preset time interval △T between the detection light beam L1 and the excitation light beam L2, as shown in Figure 2, which is a schematic diagram of the pulse time delay of the detection light beam L1 and the excitation light beam L2 provided in an embodiment of the present application; when the detection light beam L1 arrives at the wafer before the excitation light beam L2, △T is defined as negative. At this time, there is no difference between the two adjacent detection light pulses, so no transient absorption signal is generated.

[0047] When the excitation beam L2 reaches the wafer before the detection beam L1, ΔT is defined as positive. At this time, the excitation beam L2 reaches the wafer first, converting the minority carriers in the wafer from the ground state to the excited state. After the detection beam L1 arrives, the wafer minority carriers in the excited state are detected.

[0048] When both beams reach the wafer simultaneously, ΔT is zero. At this point, the transient absorption signal begins to generate and quickly reaches its maximum value. As the delay time ΔT increases, the minority carrier population continues to decay, and the signal gradually decreases. This curve follows a single exponential decay pattern.

[0049] Typically, the test time points are evenly distributed between the time before zero and the time when the decay is complete. To minimize test duration, the number of test time points is typically limited to approximately 10. For example, if the preset time interval ΔT is set to 10.1 microseconds, the number of test time points is 10, and each test time point can last for a specific period of time, such as a 90-second test.

[0050] In some embodiments, both the probe beam L1 and the excitation beam L2 can be lasers, and can be emitted by a laser. Preferably, the lasers emitting the probe beam L1 and the excitation beam L2 can be nanosecond lasers equipped with a laser frequency doubling device that can adjust the output to different wavelengths. By adjusting the different output wavelengths, different wavelengths of detection and excitation can be achieved, allowing for more comprehensive characterization of the wafer carrier lifetime and wafer quality. The output wavelength of the probe beam L1 can be 266nm-1064nm, with an energy range of 10uJ to 500mJ and a repetition rate of 1Hz-1000Hz; the output wavelength of the excitation beam L2 can be 266nm-1064nm, with an energy range of 10uJ-500mJ and a repetition rate of 1Hz-1000Hz. Because the pulse width of the nanosecond laser is less than 10ns, in this embodiment, the temporal resolution of the semiconductor wafer minority carrier lifetime imaging system is less than 15ns, improving the temporal resolution of the semiconductor wafer minority carrier lifetime imaging system and enabling accurate detection of the wafer carrier lifetime.

[0051] Based on the above embodiment, preferably, the output wavelength of the probe beam L1 is 532 nm, the energy is approximately 10 mJ, and the repetition frequency is 100 Hz. The output wavelength of the excitation beam L2 is 355 nm, the energy is approximately 90 mJ, and the repetition frequency of the probe beam L1 must be greater than the repetition frequency of the excitation beam L2. Preferably, the repetition frequency of the excitation beam L2 can be half that of the probe beam L1, 50 Hz. This allows for high efficiency in detecting the transition of minority carriers from the ground state to the excited state in the wafer using the probe beam L1.

[0052] In some preferred embodiments, the carrier module 130 can be mounted on a two-axis movable scanning stage, or can be mounted on the two-axis movable scanning stage via an automatically changing turntable, thereby enabling automatic sample movement and automatic sample replacement. The two-axis movable scanning stage and the automatically changing turntable are commonly used in the art and will not be described in detail.

[0053] Continuing to refer to Figure 1, the beam expansion module 140 is arranged between the light source module 120 and the carrier module 130, so that the detection beam L1 and the excitation beam L2 can be incident on the wafer fixed on the carrier module 130 through the beam expansion module 140, and the expanded detection beam L1 and the excitation beam L2 can completely cover the surface of the wafer, so that the minority carriers on the wafer are converted from the ground state to the excited state under the excitation of the excitation beam L2, and the detection beam L1 detects the minority carriers in the excited state.

[0054] The imaging module 150 is electrically connected to the control module 110 and is used to acquire the minority carriers in the excited state detected by the detection beam L1 and generate a transient absorption image of the wafer.

[0055] In some embodiments, the imaging module 150 may include an area array camera. The detection light beam L1 and the excitation light beam L2 can be expanded by the beam expansion module 140, and the expanded light beams can be homogenized in conjunction with a homogenizing device so that the two light beams cover a large area when irradiating the wafer, realizing one-time excitation and detection in a large field of view at the wafer level, and stimulating the detection mode of the area array camera instead of the sample scanning mode, which greatly improves the imaging efficiency. The area array camera is used to collect the wafer image of the detection light to realize the imaging of the carrier decay dynamics. By measuring the imaging data under a series of preset time intervals △T, the spatiotemporal evolution information of the minority carrier distribution can be obtained. The imaging data includes pixel coordinates and light intensity values. Using a high-resolution fast area array camera for imaging, a spatial resolution of 0.1mm can be achieved, which improves the spatial resolution of the minority carrier lifetime of the semiconductor wafer and can accurately characterize the distribution of the carrier lifetime of the wafer.

[0056] The control module 110 is further configured to generate a wafer minority carrier lifetime image based on the transient absorption image.

[0057] The control module 110 generates a wafer minority carrier lifetime image based on the transient absorption image, which will be described in detail below and will not be elaborated here.

[0058] In the semiconductor wafer minority carrier lifetime imaging system and method of the embodiment of the present application, the first electric pulse signal and the second electric pulse signal generated by the control module in the system are both trigger signals. The trigger light source module generates a detection beam and an excitation beam. Since there is a preset time interval between the start time of the enable level of the first electric pulse signal and the start time of the enable level of the second electric pulse signal, there is also a preset time interval between the detection beam and the excitation beam. The excitation beam can convert the wafer minority carriers from the ground state to the excited state. The detection beam detects the wafer minority carriers in the excited state and transmits the detected wafer transient absorption image to the control module. The control module processes the transient absorption image to obtain the wafer minority carrier lifetime image. Since the beam expansion module is used to expand the detection beam and the excitation beam, and the beam is homogenized in conjunction with the homogenization device, the imaging module can collect the excitation beam passing through the wafer sample over a large area without scanning from top to bottom, which greatly improves the detection efficiency of semiconductor wafer minority carrier lifetime imaging.

[0059] FIG3 is another structural diagram of a semiconductor wafer minority carrier lifetime imaging system provided in an embodiment of the present application. As shown in FIG3 , the beam expansion module 140 may include: a first beam expansion module 141 and a second beam expansion module 142 .

[0060] The first beam expansion module 141 is provided on the optical path of the detection beam L1 to the wafer, and the second beam expansion module 142 is provided on the optical path of the excitation beam L2 to the wafer. The first beam expansion module 141 and the second beam expansion module 142 are provided on opposite sides of the carrier module in the thickness direction.

[0061] In some embodiments, the first beam expansion module 141 can select a beam expansion device with a light homogenizing effect, including an integrating sphere S1. The diameter of the integrating sphere S1 can include 50mm-500mm, and the outlet diameter of the integrating sphere S1 can include 50mm-500mm. Preferably, the diameter of the integrating sphere S1 is 300mm, and the outlet diameter of the integrating sphere S1 is 170mm. The light can be expanded and homogenized by the integrating sphere S1.

[0062] Continuing to refer to FIG. 3 , a first light homogenizing device 302 is disposed between the second beam expanding module 142 and the carrying module 130 .

[0063] In some embodiments, the second beam expansion module 142 may include a concave lens with a focal length ranging from -30 mm to -500 mm. The first light homogenizing device 302 may include a light homogenizer, which may be a refractive or diffractive light homogenizer with a divergence angle of 5-50 degrees.

[0064] Continuing to refer to Figure 3, the semiconductor wafer minority carrier lifetime imaging system 100 can also include a second light homogenizing device 303 and a third light homogenizing device 304 arranged in an arranged manner, the second light homogenizing device 303 is arranged between the integrating sphere and the third light homogenizing device 304, and the third light homogenizing device 304 is arranged between the second light homogenizing device 303 and the carrier module 130.

[0065] In some embodiments, the second light homogenizing device 303 may include frosted glass, and the third light homogenizing device may include an emulsified light homogenizing plate. The detection beam L1 first passes through the frosted glass at the exit of the integrating sphere S1 and then passes through the emulsified light homogenizing plate to make the light more uniform. Finally, the uniform detection beam passes through the wafer.

[0066] Figure 4 is a structural schematic diagram of a carrier plate provided in an embodiment of the present application. As shown in Figure 4, the carrier module 130 may include a carrier plate, and the carrier plate is provided with a first light hole K1 and a second light hole K2. The first light hole is used to fix the wafer, and the second light hole is used to fix the filter.

[0067] In some embodiments, the second light hole K2 is located at a corner of the carrier plate, and a neutral density filter is placed in the second light hole. Preferably, the carrier plate body is made of opaque metal material, and the wafer is placed in the first light hole K1. The shape of the first light hole K1 is adapted to the shape of the wafer. The wafer is translucent and can be a 6-inch, i.e., 150 mm wafer. A neutral density filter is placed in the second light hole K2 as a reference light area. The neutral density filter can be 1 inch, and the optical density value (OD) can be 0.3. It is also translucent, and the transmittance at the wavelength of the corresponding detection beam L1 is basically the same as that of the wafer. Because the neutral density filter area and the wafer area are derived from the same detection beam, they have consistent volatility, and the detection light fluctuation of the initial imaging data of the wafer can be corrected by the imaging data of the neutral density filter. Specifically, the light intensity values ​​in the imaging data of the neutral density filter are averaged, and then the light intensity value of each pixel in the initial imaging data of the wafer is divided by the average value. This can eliminate the intensity fluctuations of the detection light itself and obtain corrected imaging data with a higher signal-to-noise ratio.

[0068] In some embodiments, the imaging module 150 may include an area array camera, and the shape detected by the area array camera corresponds to the structure of the carrier module 300. Because the neutral density filter area and the wafer area are derived from the same detection light source, they have consistent fluctuations. The intensity values ​​of 10,000 pixels in the neutral density filter area are averaged into a single light intensity value (i.e., the light intensity value of the reference light area). The light intensity values ​​of all other pixels are then divided by the light intensity value of the reference light area to obtain a light intensity value that eliminates its own intensity fluctuations, thereby achieving a higher signal-to-noise ratio for the corrected imaging data. The area array camera can use a high-speed camera with 2048*2048 pixels and an acquisition rate of 100Hz.

[0069] Figure 5 is another structural schematic diagram of the semiconductor wafer minority carrier lifetime imaging system provided in an embodiment of the present application. As shown in Figure 5, the semiconductor wafer minority carrier lifetime imaging system may further include: a first optical path adjustment device 510 and a second optical path adjustment device 520.

[0070] The first optical path adjustment device 510 is disposed on the optical path of the detection beam L1 arriving at the first beam expansion module 141; the second optical path adjustment device 520 is disposed on the optical path of the excitation beam L1 arriving at the second beam expansion module 142. The excitation beam L2 is adjusted by the second optical path adjustment device, expanded by the second beam expansion device 142, and homogenized by the first homogenization device 302. The excitation beam is shaped into a uniform flat-top-shaped uniform light spot and irradiated onto the wafer. The spot diameter can be 150 mm. The detection beam L1 is adjusted by the first optical path adjustment device 510 and passes through the first beam expansion device 141. Preferably, a beam expansion device with a homogenizing function is used for beam expansion and homogenization. In some embodiments, a second device 303 and a third homogenization device 304 may be added to further homogenize the detection beam L1, shaping it into a uniform flat-top-shaped uniform light spot, irradiating the wafer, and passing through the wafer into the imaging module 150.

[0071] In some embodiments, the first optical path adjustment device 510 may include a first high-reflective mirror M1 and a second high-reflective mirror M2. The wavelength of the first high-reflective mirror M1 may range from 343 nm to 1064 nm, the wavelength of the second high-reflective mirror M2 may range from 343 nm to 1064 nm, and the wavelength of the first and second high-reflective mirrors is preferably 532 nm. The second optical path adjustment device 520 may include a third high-reflective mirror M3 and a fourth high-reflective mirror M4. Preferably, the wavelength of the third high-reflective mirror M3 may range from 266 nm to 532 nm, the wavelength of the fourth high-reflective mirror M2 may range from 266 nm to 532 nm, and the wavelength of the third and fourth high-reflective mirrors is preferably 532 nm.

[0072] Continuing to refer to FIG. 5 , the control module 110 may include an industrial computer 111 and a timing controller 112 .

[0073] The industrial computer 111 is electrically connected to the imaging module 150 and is used to generate a first electrical signal E1; the timing controller 112 is electrically connected to the light source module 120 and is used to generate a first electrical pulse signal Ep1 and a second electrical pulse signal EP2 according to the first electrical signal E1;

[0074] The industrial computer 111 is further configured to receive and process the transient absorption image sent by the imaging module 150 to obtain a minority carrier lifetime image of the wafer.

[0075] The process of the industrial computer 111 processing the transient absorption image to obtain the minority carrier lifetime image of the wafer may include: the industrial computer calculates the transient absorption signal of the sample at each test time point based on the corrected imaging data of the wafer at all test time points. The transient absorption signal is calculated according to the following formula:

[0076] Where ΔA(λ) represents the transient absorption signal, A(λ) pump Indicates the absorbance of the wafer when there is excitation light, A(λ) unpump Indicates the wafer absorbance when there is no excitation light, I 0-pump Indicates the light intensity in front of the excitation light wafer, I 1-pump Indicates the light intensity behind the excitation light wafer, I 0-unpump Indicates the light intensity in front of the wafer without excitation light, I 1-unpu mp Indicates the light intensity behind the wafer without excitation light, I 0-pump =I 0-unpump .

[0077] The relative delay between the excitation beam L2 and the detection beam L1 is achieved through the timing controller 112. The control program controls the laser to emit light using the preset timing information through the timing controller 112. By measuring the imaging data under a series of delay conditions, the spatiotemporal evolution information of the minority carrier distribution can be obtained.

[0078] The imaging module 150 can collect I 1-unpump and I 1-pump, that is, the intensity of the detection beam with the excitation beam and the intensity of the detection beam without the excitation light, the transient absorption intensity can be calculated according to formula (1). Because in some embodiments, the imaging module 150 is a planar array camera, the transient absorption intensity is an imaging mode, that is, transient absorption imaging (TA Mapping), as shown in Figure 6. Figure 6 is a schematic diagram of transient absorption imaging provided by an embodiment of the present application. The delay time is 10.1us, the horizontal axis and the vertical axis are pixel values, and the color represents the signal intensity. As the preset time interval △T between the detection beam L1 and the excitation beam L2 gradually increases, the corresponding TA Mapping will be calculated at each preset time interval. After collecting a series of TA Mappings at the preset time interval △T, the industrial computer 111 will process the data. Take the intensity value △A at the same pixel point in the TA Mapping at each preset time interval △T, as shown in Figure 7. Figure 7 is a schematic diagram of processing transient absorption imaging provided by an embodiment of the present application. A kinetic curve as shown in Figure 8 can be drawn with the delay time. The kinetic curve is fitted with a single exponential. The fitting formula is:

[0079] Where y is a function of the intensity of ΔA changing over time, a is the initial intensity, and t is the preset time interval ΔT. The corresponding carrier lifetime τ can be obtained by reverse calculation. The corresponding carrier lifetime is calculated for the kinetic curves under all pixels, and TA mapping can be converted into carrier lifetime mapping (Lifetime Mapping), as shown in Figure 9. In some embodiments, after acquiring imaging data, the industrial computer 111 processes the imaging data and eliminates fluctuations in the detection beam through a neutral density filter to obtain corrected imaging data with a higher signal-to-noise ratio.

[0080] FIG10 is a flow chart of a semiconductor wafer minority carrier lifetime imaging method provided in an embodiment of the present application. As shown in FIG10 , the semiconductor wafer minority carrier lifetime imaging method may include: S1001 to S1004.

[0081] S1001: A control module generates a first electrical pulse signal and a second electrical pulse signal.

[0082] There is a preset time interval ΔT between the start time of the enable level of the first electrical pulse signal and the start time of the enable level of the second electrical pulse signal.

[0083] S1002: The light source module generates a detection beam and an excitation beam according to the first electrical pulse signal and the second electrical pulse signal. The detection beam and the excitation beam are incident on a wafer fixed to the carrier module through a beam expansion module.

[0084] The minority carriers on the wafer are converted from the ground state to the excited state under the excitation of the excitation beam, so that the detection beam can detect the minority carriers in the excited state.

[0085] S1003: The imaging module acquires the minority carriers in the excited state detected by the detection beam, generates a transient absorption image of the wafer, and transmits the transient absorption image to the control module.

[0086] S1004: The control module generates a wafer minority carrier lifetime image based on the transient absorption image.

[0087] In the semiconductor wafer minority carrier lifetime imaging system and method of the embodiment of the present application, the first electric pulse signal and the second electric pulse signal generated by the control module in the system are both trigger signals. The trigger light source module generates a detection beam and an excitation beam. Since there is a preset time interval between the start time of the enable level of the first electric pulse signal and the start time of the enable level of the second electric pulse signal, there is also a preset time interval between the detection beam and the excitation beam. The excitation beam can convert the wafer minority carriers from the ground state to the excited state. The detection beam detects the wafer minority carriers in the excited state and transmits the detected wafer transient absorption image to the control module. The control module processes the transient absorption image to obtain the wafer minority carrier lifetime image. Since the beam expansion module is used to expand the detection beam and the excitation beam, and the beam is homogenized in conjunction with the homogenization device, the imaging module can collect the excitation beam passing through the wafer sample over a large area without scanning from top to bottom, which greatly improves the detection efficiency of semiconductor wafer minority carrier lifetime imaging.

[0088] It should be understood that the present application is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, a detailed description of known methods is omitted here. In the above embodiments, several specific steps are described and illustrated as examples. However, the method process of the present application is not limited to the specific steps described and illustrated. Those skilled in the art can make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of the present application.

[0089] It should also be noted that the exemplary embodiments described in this application describe methods or systems based on a series of steps or apparatuses. However, this application is not limited to the order of the steps described above. In other words, the steps may be performed in the order described in the embodiments, or in a different order, or several steps may be performed simultaneously.

[0090] The above description is only a specific embodiment of the present application. Those skilled in the art will clearly understand that for the convenience and brevity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the scope of protection of the present application.

Claims

1. A semiconductor wafer minority carrier lifetime imaging system, comprising: A control module, configured to generate a first electrical pulse signal and a second electrical pulse signal, wherein there is a preset time interval between a start time of an enable level of the first electrical pulse signal and a start time of an enable level of the second electrical pulse signal; A light source module is electrically connected to the control module so that the light source module can generate a detection light beam and an excitation light beam according to the first electrical pulse signal and the second electrical pulse signal; A carrier module, used to fix the wafer; A beam expansion module is arranged between the light source module and the carrier module, so that the detection beam and the excitation beam can be incident on the wafer fixed on the carrier module through the beam expansion module, so that the minority carriers on the wafer are converted from the ground state to the excited state under the excitation of the excitation beam, and the detection beam detects the minority carriers in the excited state; An imaging module, electrically connected to the control module, and used to acquire minority carriers in an excited state detected by the detection beam to generate a transient absorption image of the wafer; The control module is also used to generate a wafer minority carrier lifetime image based on the transient absorption image.

2. The semiconductor wafer minority carrier lifetime imaging system according to claim 1, wherein: The beam expansion module comprises: A first beam expansion module is arranged on an optical path where the detection beam reaches the wafer; The second beam expansion module is arranged on the optical path where the excitation light beam reaches the wafer.

3. The semiconductor wafer minority carrier lifetime imaging system according to claim 2, wherein: The first beam expanding module and the second beam expanding module are arranged on two opposite sides of the carrier module in a thickness direction.

4. The semiconductor wafer minority carrier lifetime imaging system according to claim 3, wherein: The first beam expansion module is a beam expansion and homogenization device, including an integrating sphere.

5. The semiconductor wafer minority carrier lifetime imaging system according to claim 3, wherein: The second beam expansion module includes a first light homogenizing device disposed between the second beam expansion module and the carrier module.

6. The semiconductor wafer minority carrier lifetime imaging system according to claim 1, wherein: The carrying module comprises a carrying plate, and the carrying plate is provided with a first light through hole and a second light through hole, wherein the first light through hole is used for fixing the wafer, and the second light through hole is used for fixing the filter.

7. The semiconductor wafer minority carrier lifetime imaging system according to claim 2, further comprising: A first optical path adjustment device is arranged on the optical path where the detection light beam reaches the first beam expansion module; The second optical path adjustment device is arranged on the optical path where the excitation light beam reaches the second beam expansion module.

8. The semiconductor wafer minority carrier lifetime imaging system according to claim 1, wherein: The control module comprises: An industrial computer, electrically connected to the imaging module, and configured to generate a first electrical signal; a timing controller, electrically connected to the light source module, and configured to generate the first electrical pulse signal and the second electrical pulse signal according to the first electrical signal; The industrial computer is also used to receive and process the transient absorption image sent by the imaging module to obtain the minority carrier lifetime image of the wafer.

9. The semiconductor wafer minority carrier lifetime imaging system according to claim 4, wherein: The semiconductor wafer minority carrier lifetime imaging system also includes a second light homogenizing device and a third light homogenizing device arranged in an arranged manner, wherein the second light homogenizing device is arranged between the integrating sphere and the third light homogenizing device, and the third light homogenizing device is arranged between the second light homogenizing device and the carrier module.

10. The semiconductor wafer minority carrier lifetime imaging system according to claim 1, wherein: The detection light beam and the excitation light beam are lasers.

11. The semiconductor wafer minority carrier lifetime imaging system according to claim 1, wherein: The repetition frequency of the detection light beam is greater than the repetition frequency of the excitation light beam.

12. A semiconductor wafer minority carrier lifetime imaging method, using the semiconductor wafer minority carrier lifetime imaging system according to any one of claims 1 to 11, the method comprising: The control module generates a first electrical pulse signal and a second electrical pulse signal, and there is a preset time interval between the start time of the enable level of the first electrical pulse signal and the start time of the enable level of the second electrical pulse signal; The light source module generates a detection light according to the first electrical pulse signal and the second electrical pulse signal The detection beam and the excitation beam are incident on the wafer fixed on the carrier module through the beam expansion module, so that the minority carriers on the wafer are converted from the ground state to the excited state under the excitation of the excitation beam, and the detection beam detects the minority carriers in the excited state; The imaging module acquires the minority carriers in the excited state detected by the detection beam, generates a transient absorption image of the wafer, and transmits the transient absorption image to the control module; The control module generates a wafer minority carrier lifetime image according to the transient absorption image.

Images