A film layer detection method
By obtaining the second harmonic intensity information of the film layer through optical characterization methods, the problem of the inability to quickly and non-destructively monitor the doping characteristics of the film layer in the existing technology is solved, and online detection is realized in the semiconductor device fabrication process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGDONG GREATER BAY AREA INST OF INTEGRATED CIRCUIT & SYST
- Filing Date
- 2024-11-28
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies cannot achieve rapid, non-destructive online monitoring of film doping characteristics during semiconductor device fabrication, and electrical characterization methods lack flexibility.
A non-destructive optical characterization method is used to determine the doping concentration and type by focusing a test laser within the film and obtaining the intensity information of the second harmonic. The film is then tested in conjunction with the intensity variation information of the second harmonic.
It enables rapid and non-destructive monitoring of film doping characteristics, allowing for online analysis during device fabrication and improving the flexibility and accuracy of detection.
Smart Images
Figure CN122109771A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductors, and in particular to a method for film detection. Background Technology
[0002] Currently, semiconductor device characterization is typically performed using electrical characterization techniques. These techniques allow for the characterization and analysis of the overall electrical performance of the device. However, this work can only be performed after the device fabrication is complete, making online monitoring during the fabrication process impossible. Furthermore, electrical characterization requires connecting metal electrodes and probes for electrical testing after the device structure is fabricated. While the test results are highly accurate, this approach lacks convenience. Moreover, extracting the doping characteristics within the film layers requires understanding their impact on other parameters such as threshold voltage and mobility, and there is no direct extraction method available. In short, while electrical characterization, as a contact-based and destructive method, offers highly accurate results, it lacks flexibility and cannot enable rapid analysis and online monitoring during device fabrication. Summary of the Invention
[0003] In view of this, the purpose of this application is to provide a film detection method that can monitor the interior of the film under test based on non-destructive optical characterization.
[0004] This application provides a method for film detection, the method comprising:
[0005] Provide the film layer to be tested;
[0006] The test laser is focused onto a first target position within the film layer to be tested and continuously irradiated for a first preset time period to obtain the first intensity information of the second harmonic generated at the first target position.
[0007] The doping concentration information of the first target location is determined based on the initial intensity value in the first intensity information; the doping type of the first target location is determined based on the intensity change information in the first intensity information.
[0008] Optionally, the method further includes:
[0009] The test laser is focused onto the second target position within the film layer to be tested and continuously irradiated for a second preset time period to obtain the second intensity information of the second harmonic generated at the second target position;
[0010] The doping concentration information of the second target location is determined based on the initial intensity value in the second intensity information; the doping type of the second target location is determined based on the intensity change information in the second intensity information.
[0011] The doping uniformity of the film under test is determined based on the doping concentration information at the first target location and the doping concentration information at the second target location.
[0012] Optionally, the device under test includes a substrate, a buried oxide layer and a channel layer sequentially stacked on the substrate, wherein the film layer under test is the channel layer.
[0013] Optionally, the channel layer includes a core layer and a shell layer, the upper surface of the core layer has a groove, and the shell layer is located in the groove; the doping concentration of the shell layer is less than the doping concentration of the core layer.
[0014] Optionally, the method further includes:
[0015] The test laser is focused onto the third target position in the reference film layer on the buried oxide layer and continuously irradiated for a third preset time period to obtain the third intensity information of the second harmonic generated at the third target position. The position of the third target position in the reference film layer is consistent with the position of the first target position in the film layer under test. The structure of the reference film layer is the same as that of the channel layer, and the material of the reference film layer is the same as that of the core layer.
[0016] The first intensity information is calibrated using the third intensity information.
[0017] Optionally, focusing the test laser onto a third target position within a reference film layer on the buried oxide layer and continuously irradiating it for a third preset time period to obtain the third intensity information of the second harmonic generated at the third target position includes:
[0018] A core material layer is formed on the buried oxide layer. Before etching a groove on the upper surface of the core material layer, the core material layer is used as a reference film layer on the buried oxide layer. A laser is focused on a third target position within the reference film layer on the buried oxide layer for a third preset time period to obtain the third intensity information of the second harmonic generated by the third target position during the third preset time period.
[0019] Optionally, the method further includes:
[0020] The test laser is focused at a preset position at the interface between the core layer and the shell layer, and continuously irradiated for a fourth preset time period to obtain the fourth intensity information of the second harmonic generated at the preset position.
[0021] The defect density information at the preset location is determined based on the initial intensity value in the fourth intensity information; the defect type at the preset location is determined based on the intensity change information in the fourth intensity information.
[0022] Optionally, the pulse width of the test laser is on the order of hundreds of femtoseconds, the wavelength range of the test laser is 700-850nm, and the wavelength of the second harmonic is half the wavelength of the test laser.
[0023] Optionally, focusing the test laser onto a first target position within the film layer under test and continuously irradiating it for a first preset time period to obtain the first intensity information of the second harmonic generated at the first target position includes:
[0024] The test laser is focused onto a first target position within the film layer to be tested and continuously irradiated for a first preset time period to obtain the emitted signal generated at the first target position.
[0025] The emitted signal is filtered and detected to obtain the first intensity information of the second harmonic.
[0026] Optionally, the method further includes:
[0027] Before focusing the test laser, the test laser is adjusted to a preset polarization state;
[0028] The outgoing signal is adjusted to a preset polarization state before filtering.
[0029] This application provides a film layer detection method. A test laser is provided to a first target position within the film layer and continuously irradiated for a first preset time period. First intensity information of the second harmonic generated at the first target position is obtained. The doping concentration information at the first target position is determined based on the initial intensity value in the first intensity information. The doping type at the first target position is determined based on the intensity change information in the first intensity information. This allows for the determination of the doping type and concentration within the film layer based on the intensity information of the second harmonic, enabling monitoring of the film layer under test. The monitoring timing and methods are flexible, do not cause physical damage to the film layer under test, and do not require the fabrication of a complete device structure including electrodes. Therefore, rapid analysis and online monitoring of the film layer under test can be achieved. Attached Figure Description
[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0031] Figure 1 A flowchart of a film detection method provided in an embodiment of this application is shown;
[0032] Figure 2This is a schematic diagram of the structure of a device under test provided in an embodiment of this application;
[0033] Figure 3 This is a schematic diagram of another device under test provided in an embodiment of this application;
[0034] Figure 4 A schematic diagram of a testing process provided in an embodiment of this application;
[0035] Figure 5 This application provides a schematic diagram illustrating the effect of doping concentration on the initial intensity value of a second harmonic.
[0036] Figure 6 A schematic diagram illustrating the intensity variation trend of the second harmonic under different doping types, provided for an embodiment of this application;
[0037] Figure 7 This is a schematic diagram of another test process according to an embodiment of this application;
[0038] Figure 8 This is a schematic diagram of another test process according to an embodiment of this application. Detailed Implementation
[0039] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.
[0040] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.
[0041] This application is described in detail with reference to the schematic diagrams. When detailing the embodiments of this application, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of this application. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.
[0042] To better understand the technical solution and effects of this application, the specific embodiments will be described in detail below with reference to the accompanying drawings.
[0043] refer to Figure 1The diagram shown is a flowchart of a film detection method provided in an embodiment of this application. The method may include:
[0044] S101 provides the film to be tested.
[0045] The film under test (DUT) is the film layer that needs to be monitored. It can be a film layer in a complete device or a film layer in an incomplete device during manufacturing. The DUT can be a film layer in the device under test.
[0046] For details, please refer to Figure 2 The diagram shown is a schematic representation of a device under test (DUT) provided in an embodiment of this application. The DUT may include a substrate 100, a buried oxide (BOX) layer 110 and a channel layer 130 sequentially stacked on the substrate 100. The DUT may be the channel layer 130, which is used to form the gate and source / drain on both sides of the gate. The test on the channel layer 130 can be performed before the gate and source / drain are formed. Since the doping of the channel layer 130 directly affects the current characteristics of the device, controlling the doping concentration of the channel layer 130 during the manufacturing process is more conducive to controlling the overall quality of the device and reducing the probability of defective devices.
[0047] In this embodiment, the substrate 100 can be a semiconductor substrate to provide support for the film layer thereon, such as a silicon substrate or a germanium substrate. The buried oxide layer 110 is an insulating layer used to isolate the channel layer 130 and the substrate 100, and to prevent the carriers in the channel layer 130 from leaking from the substrate during device operation. The buried oxide layer 110 can be, for example, silicon oxide or germanium oxide.
[0048] The channel layer 130 may include a core and a shell, see reference. Figure 3 The diagram shows another device under test (DUT) provided in this embodiment. The upper surface of the core layer 131 has a groove, and the shell layer 132 is located within the groove. The doping concentration of the shell layer 132 is less than that of the core layer 131, meaning the DUT can be a core-shell junction-less (CS-JL) transistor. The core-shell junction-less transistor is a novel junction-less transistor based on FDSOI technology. Compared to traditional junction-less transistors, the core-shell structure uses the heavily doped top silicon layer of the traditional FDSOI wafer as the core layer, and adds an ultra-thin lightly doped or undoped shell layer on top. This allows for a positive threshold voltage and high on-state current, retaining the strong short-channel effect suppression capability of JL transistors, and possessing complete CMOS functionality, as well as advantages such as simple fabrication, multiple threshold adjustment, and low noise. It avoids the disadvantages of JL transistors, such as low mobility, high contact resistance, and negative threshold voltage.
[0049] The core layer 131, as part of the channel layer, can be made of silicon or germanium, and its thickness can range from 3 to 10 nm, specifically 3 to 5 nm, for example, 3 nm. The doping concentration of the core layer 131 is greater than or equal to 10. 19 cm -3 The shell 132, as part of the channel layer, can be made of silicon or germanium, and its thickness can range from 3 to 10 nm, specifically 3 to 5 nm, for example, 4 nm. The doping concentration of the shell 132 is less than that of the core layer, and it can be lightly doped or undoped.
[0050] The core layer 131 and the shell layer 132 are usually two parts made of the same material but with different doping types and concentrations. Together they form the channel layer. The doping type and concentration of the two directly affect the device performance. Therefore, it is necessary to monitor the internal doping of the core layer 131 and the shell layer 132 to ensure the quality of the film layers. However, current electrical characterization methods cannot quickly and non-destructively characterize the doping characteristics inside the film layer.
[0051] S102, the test laser is focused onto the first target position within the film layer to be tested and continuously irradiated for a first preset time period to obtain the first intensity information of the second harmonic generated at the first target position.
[0052] In this embodiment, the test laser can be focused onto a first target position within the film layer to be tested and continuously irradiated for a first preset time period, for reference. Figure 4 The diagram shown is a schematic of a testing process provided in an embodiment of this application. The first target position generates a second harmonic wave under the irradiation of the test laser. In addition to the advantages of traditional optical characterization methods, the second harmonic wave also has interface specificity. It only generates a second harmonic wave at lattice mismatch and lattice defects. In other words, there is no signal response in the bulk material of intrinsic semiconductors, but there will be a second harmonic wave response at locations that disrupt symmetry, such as interfaces, defects, and doping. The intensity of the second harmonic wave is affected by the doping concentration, type, and interface properties. Based on the above characteristics, the film layer to be tested can be detected.
[0053] Therefore, by irradiating the first target position with a test laser, the first intensity information of the second harmonic generated at the first target position can be obtained. The first intensity information indicates the intensity information of the second harmonic within a first preset time period, thereby obtaining the doping information.
[0054] The pulse width of the test laser is on the order of hundreds of femtoseconds, the wavelength range of the test laser is 700-850 nm, and the wavelength of the second harmonic is half the wavelength of the test laser. The power of the test laser is approximately 400 mW.
[0055] The test laser can be emitted through the test equipment. By initializing the test equipment, various parameters can be adjusted to achieve the minimum spot size and optimal focus, focusing on the first target position where the spot size is minimized and the light intensity per unit area is maximized. When the test laser is focused on the first target position and continuously irradiated for a first preset time period, the test laser induces the generation of a second harmonic. The emitted signal generated at the first target position is collected. The emitted signal is located at the reflection angle of the test laser, i.e., the angle between the incident direction of the test laser and the normal perpendicular to the surface of the film under test, and the angle between the emitted direction and the emitted signal. The first intensity information of the second harmonic is obtained from the emitted signal.
[0056] Specifically, the emitted signal can be filtered and detected to obtain the first intensity information of the second harmonic. Filtering removes background light, which is beneficial to the fundamental frequency laser (i.e., the test laser), thus obtaining the second harmonic. Specifically, before focusing the test laser, it can be adjusted to a preset polarization state, i.e., the polarization state of the test laser is determined, so that the first target position is illuminated by the preset polarization state; before filtering the emitted signal, the emitted signal can also be adjusted to a preset polarization state, i.e., the polarization state of the emitted signal is determined, so that the second harmonic of the preset polarization state is detected, making the acquisition of the second harmonic intensity information more accurate. When determining the polarization state of the test laser, it can also be collimated to reduce the spot size of the test laser and improve the test accuracy; before determining the polarization state of the emitted signal, it can also be focused.
[0057] S103, determine the doping concentration information of the first target location based on the initial intensity value in the first intensity information; determine the doping type of the first target location based on the intensity change information in the first intensity information.
[0058] Different levels of doping introduce different interface charges or electric fields, which affect the initial intensity value of the second harmonic signal (i.e., the intensity value at the initial moment in the first preset time period) and the saturation rate. Especially with heavy doping, the initial intensity value of the second harmonic signal is significantly enhanced. (Refer to...) Figure 5The diagram illustrates the effect of doping concentration on the initial intensity value of the second harmonic wave (HSWHW) according to an embodiment of this application. The horizontal axis represents the doping concentration, and the vertical axis represents the initial intensity value of the HSWHW (SHG at t=0s). As can be seen from the diagram, the initial intensity value of the HSWHW generated by both p-type doped Si and n-type doped Si materials increases with increasing doping concentration. Therefore, after obtaining the first intensity information, the doping concentration information at the first target location can be determined based on the initial intensity value in the first intensity information. The doping concentration information includes the doping concentration. There can be a correspondence between the initial intensity value and the doping concentration, allowing the doping concentration information at the first target location to be determined based on this correspondence. This correspondence between the doping concentration and the initial intensity value can be predetermined.
[0059] Different types of doped carriers have different interface excitation mechanisms, which in turn cause the second harmonic to exhibit different variation trends. (Refer to...) Figure 6 The diagram shows the intensity variation trend of the second harmonic under different doping types according to an embodiment of this application. The horizontal axis represents the duration, and the vertical axis represents the intensity of the second harmonic. (a) and (b) represent the intensity variation trend of the second harmonic under p-type doping and n-type doping, respectively. The end of the test is marked as the laser blocking time. The lines of different colors represent the intensity of the second harmonic under different doping concentrations. It can be seen from (a) that under p-type doping, the intensity of the second harmonic will show a non-monotonic variation trend, which is to decrease first and then increase. It can be seen from (b) that under n-type doping, the second harmonic will show a monotonically increasing trend.
[0060] Therefore, after obtaining the first intensity, the doping type of the first target location can be determined based on the intensity change information in the first intensity information. Specifically, if the intensity change in the first intensity information is monotonically increasing, the doping type at the first target location is determined to be n-type doping; if the intensity change in the first intensity information is first decreasing and then increasing, the doping type at the first target location is determined to be p-type doping.
[0061] After determining the doping concentration and doping type at the first target location, doping concentration and doping type information at other locations can be obtained through detection at other locations. This allows for the determination of the doping uniformity of the film under test. The process for determining the doping concentration and doping type at other locations is similar to that for the first target location and will not be detailed here. Specifically, the initial intensity value of the second harmonic can be determined through rapid scanning, thereby determining the doping concentration. Detecting the doping concentration at different locations allows for the determination of the doping uniformity of the film under test. The obtained doping concentration information can assist in electrical testing. Quantitative analysis of the doping degree can be achieved through a dual electrical-optical inspection. Furthermore, continuous monitoring at a fixed point using a time-varying scanning method can determine the doping type at that specific location.
[0062] Specifically, a test laser can be focused onto a second target position within the film layer under test and continuously irradiated for a second preset time period to obtain the second intensity information of the second harmonic generated at the second target position; the doping concentration information of the second target position can be determined based on the initial intensity value in the second intensity information (i.e., the intensity value at the initial moment in the second preset time period); the doping type of the second target position can be determined based on the intensity change information in the second intensity information; and the doping uniformity of the film layer under test can be determined based on the doping concentration information of the first target position and the doping concentration information of the second target position.
[0063] In this embodiment, a reference film layer on the buried oxide layer can also be detected. The first intensity information is calibrated based on the detection results of the reference film layer, and the second intensity information can also be calibrated, thus improving the accuracy of the first and second intensity information. When the film layer to be tested is a channel layer, and the channel layer includes a core layer and a shell layer, the reference film layer can have the same structure as the channel layer, and the material of the reference film layer can be the same as the core layer. That is, the reference film layer is equivalent to the shell layer before the formation of the shell layer and the groove containing the shell layer.
[0064] Specifically, the test laser is focused onto a third target position within a reference film layer on the buried oxide layer and continuously irradiated for a third preset time period. The third intensity information of the second harmonic generated at the third target position is obtained. The position of the third target position in the reference film layer is consistent with the position of the first target position in the film layer under test. The first intensity information is calibrated using the third intensity information. The third preset time period can be shorter than the first preset time period to achieve rapid testing of the reference film layer. Obtaining the initial intensity value of the second harmonic (i.e., the intensity value at the initial moment within the third preset time period) is sufficient. Moving the test laser allows for the acquisition of third intensity information at different locations across the entire wafer.
[0065] In a specific implementation, a core material layer can be formed on the buried oxide layer. Before etching the groove on the upper surface of the core material layer, the core material layer is used as a reference film layer on the buried oxide layer. The test laser is focused on the third target position in the reference film layer on the buried oxide layer and continuously irradiated for a third preset time period to obtain the third intensity information of the second harmonic generated at the third target position.
[0066] refer to Figure 7 The diagram illustrates another testing process according to an embodiment of this application. The rectangular dashed box indicates the location in the core material layer 133 where the shell layer 132 will form. That is, after doping of the core material layer, detecting the core material layer 133 yields third intensity information. The third target location is located within the region where the shell layer 132 will form. Thus, after the shell layer 132 is formed, the first target location can be detected to obtain first intensity information, as shown in the reference diagram. Figure 8 The diagram shown is a schematic of another test process according to an embodiment of this application, with the first target location located in the shell 132.
[0067] In practice, an additional reference film layer can be set on the buried oxide layer. The reference film layer and the core material layer are formed simultaneously and have the same parameters. That is, the reference film layer is also heavily doped. When the upper surface of the core material layer is etched to obtain the groove, the reference film layer will not be processed, so that the reference film layer is left as is. In this way, the detection of the third target position can be performed before or after the detection of the first target position.
[0068] Since the core and shell layers are made of the same material but have different doping conditions, they form an interface. Lattice mismatch at the interface also leads to the generation of second harmonics (HHMs). Therefore, the interface also contributes to HHMs, the principle being the contribution of the interface electric field to the HHM signal. In this embodiment, a test laser can be focused onto a preset position at the interface between the core and shell layers and continuously irradiated for a fourth preset time period to obtain the fourth intensity information of the HHM generated at the preset position. The defect density information at the preset position is determined based on the initial intensity value in the fourth intensity information (i.e., the intensity value at the initial moment in the fourth preset time period). The defect type at the preset position is determined based on the intensity change information in the fourth intensity information. Accordingly, the detection of the interface between the core and shell layers can be achieved.
[0069] In this embodiment, a second harmonic generation method using laser light is employed for optical characterization of the film under test. This method does not damage the interface and allows for rapid detection of the film. Furthermore, due to its non-destructive nature, relevant testing steps can be inserted during device fabrication, offering greater flexibility. Specifically, a non-destructive optical second harmonic method is used to perform rapid and flexible analysis of the doping and interface conditions of refilled, low-doped regions in Core-Shell devices. Preliminary characterization results can be obtained without waiting for device fabrication to complete. The second harmonic signal allows for rapid analysis of doping and interfaces during the device fabrication process, offering greater flexibility and non-destructive analysis advantages compared to traditional electrical methods.
[0070] This application provides a film layer detection method. A test laser is provided to a first target position within the film layer and continuously irradiated for a first preset time period. First intensity information of the second harmonic generated at the first target position is obtained. The doping concentration information at the first target position is determined based on the initial intensity value in the first intensity information. The doping type at the first target position is determined based on the intensity change information in the first intensity information. This allows for the determination of the doping type and concentration within the film layer based on the intensity information of the second harmonic, enabling monitoring of the film layer. The monitoring timing and methods are flexible, do not cause physical damage to the film layer, and do not require the fabrication of a complete device structure including electrodes. Therefore, rapid analysis and online monitoring of the film layer can be achieved.
[0071] The above description is merely a preferred embodiment of this application. Although this application has disclosed preferred embodiments above, it is not intended to limit this application. Any person skilled in the art can make many possible variations and modifications to the technical solutions of this application using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of this application. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this application without departing from the content of the technical solutions of this application shall still fall within the protection scope of the technical solutions of this application.
Claims
1. A method for detecting film layers, characterized in that, The method includes: Provide the film layer to be tested; The test laser is focused onto a first target position within the film layer to be tested and continuously irradiated for a first preset time period to obtain the first intensity information of the second harmonic generated at the first target position. The doping concentration information of the first target location is determined based on the initial intensity value in the first intensity information; the doping type of the first target location is determined based on the intensity change information in the first intensity information.
2. The method according to claim 1, characterized in that, The method further includes: The test laser is focused onto the second target position within the film layer to be tested and continuously irradiated for a second preset time period to obtain the second intensity information of the second harmonic generated at the second target position; The doping concentration information of the second target location is determined based on the initial intensity value in the second intensity information; the doping type of the second target location is determined based on the intensity change information in the second intensity information. The doping uniformity of the film under test is determined based on the doping concentration information at the first target location and the doping concentration information at the second target location.
3. The method according to claim 1, characterized in that, The device under test includes a substrate, a buried oxide layer and a channel layer stacked sequentially on the substrate, wherein the film layer under test is the channel layer.
4. The method according to claim 3, characterized in that, The channel layer includes a core layer and a shell layer. The upper surface of the core layer has a groove, and the shell layer is located in the groove. The doping concentration of the shell layer is less than that of the core layer.
5. The method according to claim 4, characterized in that, The method further includes: The test laser is focused onto the third target position in the reference film layer on the buried oxide layer and continuously irradiated for a third preset time period to obtain the third intensity information of the second harmonic generated at the third target position. The position of the third target position in the reference film layer is consistent with the position of the first target position in the film layer under test. The structure of the reference film layer is the same as that of the channel layer, and the material of the reference film layer is the same as that of the core layer. The first intensity information is calibrated using the third intensity information.
6. The method according to claim 5, characterized in that, The step of focusing the test laser onto a third target position within a reference film layer on the buried oxide layer and continuously irradiating it for a third preset time period to obtain the third intensity information of the second harmonic generated at the third target position includes: A core material layer is formed on the buried oxide layer. Before etching a groove on the upper surface of the core material layer, the core material layer is used as a reference film layer on the buried oxide layer. A laser is focused on a third target position within the reference film layer on the buried oxide layer for a third preset time period to obtain the third intensity information of the second harmonic generated by the third target position during the third preset time period.
7. The method according to claim 3, characterized in that, The method further includes: The test laser is focused at a preset position at the interface between the core layer and the shell layer, and continuously irradiated for a fourth preset time period to obtain the fourth intensity information of the second harmonic generated at the preset position. The defect density information at the preset location is determined based on the initial intensity value in the fourth intensity information; the defect type at the preset location is determined based on the intensity change information in the fourth intensity information.
8. The method according to any one of claims 1-7, characterized in that, The pulse width of the test laser is on the order of hundreds of femtoseconds, the wavelength range of the test laser is 700-850nm, and the wavelength of the second harmonic is half the wavelength of the test laser.
9. The method according to claim 8, characterized in that, The step of focusing the test laser onto a first target position within the film layer under test and continuously irradiating it for a first preset time period to obtain the first intensity information of the second harmonic generated at the first target position includes: The test laser is focused onto a first target position within the film layer to be tested and continuously irradiated for a first preset time period to obtain the emitted signal generated at the first target position. The emitted signal is filtered and detected to obtain the first intensity information of the second harmonic.
10. The method according to claim 9, characterized in that, The method further includes: The test laser is adjusted to a preset polarization state before being focused; The outgoing signal is adjusted to a preset polarization state before filtering.