A back-illuminated photodetector test system

Abstract

The application discloses a back-illuminated photoelectric detector testing system, which is used for realizing various optical characterization tests on a BSI type photodiode chip (including an array type or a single chip) in a bare chip state, and directly measuring responsivity uniformity, linearity uniformity and crosstalk levels between pixels without additional packaging to a PCB board. The back-illuminated photoelectric detector testing system is simple in structure, convenient to operate, reduces test equipment construction cost, and reduces time and cost of pre-test processing. Further, through cooperation of the positioning pin and the punched reference chip, the application has significant advantages in pixel-level local light irradiation and alignment accuracy, guarantees accuracy and repeatability of test results, and is particularly suitable for rapid performance evaluation and quality control in a research and development and mass production stage.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of photoelectric detection technology, and in particular to a back-illuminated photoelectric detector testing system. Background Technology

[0002] With the widespread application of image sensors and photodetectors in medical imaging, industrial inspection, and smart devices, the demand for optical testing of their performance is increasing. Traditional testing systems are mostly developed based on front-side illumination (FSI) photodetectors, where the light source and probe are located on the same side. A sliding mirror mechanism switches between uniform and modulated light, and a collimator guides the light source to the device surface. While this type of system simplifies the structure and enables multi-mode switching, its design is not suitable for back-side illumination (BSI) photodetectors. This is because the light incident surface and electrode surface of a BSI chip are on opposite sides of the device, making it difficult for traditional testing systems to simultaneously achieve both light illumination and electrode contact. Utility Model Content

[0003] This application provides a back-illuminated photodetector testing system that can meet the requirements for effective optical testing of BSI type photodiode chips.

[0004] This application provides a back-illuminated photodetector testing system, including: a light source module 10, a power supply module, and a probe station 14; wherein, The light source module 10 is used to provide uniform illumination to the back of the back-illuminated photodetector 17 under test. The light source module 10 includes a light source array for generating illumination, a PCB board 11, and a light-diffusing plate 13. The light source array is soldered onto the PCB board 11, and the light-diffusing plate 13 is disposed on the top of the light source module 10 to achieve uniform in-plane illumination. The bottom of the light source module 10 is fixed on the support platform. The power supply module is used to provide an adjustable voltage to the light source array in order to control the luminous intensity of the light source array; The probe station 14 is used to measure the photocurrent output of the back-illuminated photodetector 17 under test. The back-illuminated photodetector 17 under test is located below the probe station 14, with its back side in close contact with the light-diffusing plate 13 to receive light, and its front side facing the probe station 14 so that the probe of the probe station 14 can establish a conductive contact with its pixel electrode.

[0005] In one exemplary instance, it further includes: a reference module, used to read a value reflecting the actual output light intensity of the light source module 10, so as to perform real-time measurement and calibration of the output of the light source module 10.

[0006] In one exemplary instance, the reference module is a standard optical power meter or a reference photodiode.

[0007] In one exemplary instance, it also includes: a punch reference chip, used to physically confine the uniform light intensity output from the large area of ​​the light source module 10 to a specific small area, so as to provide precise and targeted light illumination to a specified pixel on the back-illuminated photodetector 17 under test. The front side of the punched reference chip faces the light-diffusing plate 13, and the back side of the punched reference chip is tightly overlapped with the back side of the back-illuminated photodetector 17 under test.

[0008] In one exemplary instance, it further includes a positioning pin 15 for ensuring that the back-illuminated photodetector 17 under test is strictly aligned with the punched reference chip in a two-dimensional direction.

[0009] In one exemplary instance, the locating pin 15 includes one or more.

[0010] In one exemplary instance, the punched reference chip and the back-illuminated photodetector 17 under test come from the same wafer and have the exact same structural layout and size.

[0011] In one exemplary instance, the light source array consists of LED beads 12 with uniform divergence angles.

[0012] In one exemplary instance, the probe station 14 is a manual probe station or an automated probe board.

[0013] In one exemplary instance, the light source module 10 is provided with an outer frame 16 around its perimeter to provide support.

[0014] The back-illuminated photodetector testing system provided in this application enables various optical characterization tests on BSI photodiode chips (including array-type or single-chip types) in their bare die state. It allows for direct measurement of responsivity uniformity, linearity uniformity, and inter-pixel crosstalk levels without additional packaging onto a PCB board. This back-illuminated photodetector testing system features a simple structure and convenient operation, reducing both the construction cost of testing equipment and the time and expense of pre-test processing.

[0015] Furthermore, through the cooperation of the positioning pin and the punched reference chip, this invention has significant advantages in pixel-level local light illumination and alignment accuracy, ensuring the accuracy and repeatability of test results, and is particularly suitable for rapid performance evaluation and quality control in the R&D and mass production stages.

[0016] Other features and advantages of this invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of this invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0017] The accompanying drawings are used to provide a further understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0018] Figure 1 This is a schematic diagram of the composition and structure of the back-illuminated photodetector test system in an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

[0020] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0022] It is understood that the terms "first" and "second" used in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0023] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0024] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0025] The steps illustrated in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases the steps shown or described may be performed in a different order than that presented here.

[0026] Traditional testing systems are primarily used for FSI (Flat Sensor Injection) structure chips. These systems require a dual-segment collimator to direct light to the chip surface and a mirror to switch the light source mode. While structurally simple, they suffer from the following drawbacks: complex and bulky light source and detector structures; lack of support for testing BSI (Block Surface Injection) chips with asymmetrical structures (light incident and electrode surfaces on different sides); inability to effectively perform low-light local illumination and pixel crosstalk testing, especially in the bare die stage where packaging is not required; and limited light source adjustment and positioning accuracy, making it difficult to cover the entire array or micro-pixel area.

[0027] To address the issue of insufficient optical testing capabilities for BSI-type photodiode chips, this application provides a back-illuminated photodetector testing system, comprising at least: a light source module 10, a power supply module, and a probe station 14; wherein... The light source module 10 is used to provide uniform illumination to the back of the back-illuminated photodetector 17 under test. The light source module 10 includes a light source array for generating illumination, a PCB board 11, and a light-diffusing plate 13. The light source array is soldered onto the PCB board 11, and the light-diffusing plate 13 is disposed on the top of the light source module 10 to achieve uniform in-plane illumination. The bottom of the light source module 10 is fixed on the support platform. Power supply module: Used to provide adjustable voltage to the light source array in order to control the luminous intensity of the light source array; The probe station 14 is used to measure the photocurrent output of the back-illuminated photodetector 17 under test. The back-illuminated photodetector 17 under test is located below the probe station 14, with its back side in close contact with the light-diffusing plate 13 to receive light, and its front side facing the probe station 14 so that the probe of the probe station 14 can establish a conductive contact with its pixel electrode.

[0028] This invention primarily addresses the optical characterization requirements of BSI-type photodetectors. It employs an inverted light source-detector structure, placing the light source below the detector so that its light illuminates the back of the device. The front of the device allows for easy movement of a probe to detect different pixels, obtaining a photocurrent uniformity mapping map of the entire pixel array. Furthermore, by adjusting the light intensity of the light source and testing the photocurrent values ​​of the pixels under different light intensities, a mapping map of the linearity characteristics of the entire pixel array can be obtained. Further, by designing a special aperture, specific pixels can be illuminated with low light to obtain the photocurrent values ​​of neighboring pixels, thus revealing the crosstalk level between the excited pixel and its neighbors.

[0029] In one exemplary instance, such as Figure 1 As shown, the light source array in the light source module 10 is formed by soldering regularly arranged LED beads 12 with uniform divergence angles onto a PCB board 11 (also called a light source board). The bottom of the light source module 10 is kept flat to facilitate secure fixation to the support platform. In one embodiment, the bottom of the light source module 10 can be fixed to the support platform using a vacuum adsorption method. An outer frame 16 can be provided around the light source module 10 to provide support. In one embodiment, the outer frame 16 can be made of, but is not limited to, aluminum or rigid plastic. The top of the light source module 10 is covered with a light-diffusing plate 13 to scatter and homogenize the light emitted by the light source array (LED array) under the light-diffusing plate 13, making the light intensity of the entire light source board more uniform within the planar range.

[0030] In one exemplary embodiment, the power supply module that powers the LED light source in the light source module 10 is capable of accurately measuring and adjusting the supply current and voltage to the LED light source array, thereby achieving controllable light intensity. More preferably, the power supply module can also display the voltage supplied to the LED light source and the real-time current flowing through the LED light source.

[0031] In one exemplary instance, the back-illuminated photodetector testing system provided in this application embodiment may further include: a reference module, used to read the value reflecting the actual output light intensity of the light source module 10, so as to perform real-time measurement and calibration of the output of the light source module 10, thereby ensuring that the light intensity change is known and accurate, making the linearity test results reliable, and thus realizing accurate linearity testing.

[0032] In one embodiment, the reference module can be a standard optical power meter capable of calibrating the light intensity emitted by an LED. A standard optical power meter is a device specifically designed to accurately measure the light power (light intensity) emitted by a light source.

[0033] In one embodiment, the reference module can be a calibrated reference photodiode of the same type. The reference photodiode is a rigorously calibrated photodiode whose output current under different light intensities is known, so the light intensity illuminating it can be deduced.

[0034] In one embodiment, the probe station 14 can be a manual probe station, suitable for small-batch or R&D scenarios, relying on manual adjustment. In another embodiment, the probe station 14 can be an automated probe board, which integrates an array of pins, capable of contacting multiple pixels at once, suitable for rapid batch testing.

[0035] In one embodiment, the probe station 14 is mounted on a programmable translation stage and moves precisely in two dimensions to achieve contact positioning of the selected pixel and obtain the photocurrent value of the contact pixel.

[0036] In one exemplary embodiment, when performing high-precision crosstalk characteristic testing, the back-illuminated photodetector testing system provided in this application embodiment may further include: a punched reference chip, used to physically confine the uniform light intensity output from the large-area LED uniform light source of the light source module 10 to a specific micro-area, thereby providing precise, targeted illumination to a specified pixel on the back-illuminated photodetector under test. Through high-precision alignment with the back-illuminated photodetector 17 under test, accurate single-pixel illumination is achieved. This method in this application embodiment avoids the errors caused by traditional reliance on packaging or XY translation stage positioning, making the test simpler and the results more reliable. In this application embodiment, the punched reference chip is used as an auxiliary structure to achieve localized low-light illumination, and is particularly suitable for crosstalk testing of back-illuminated photodiode array chips (BSI chips).

[0037] In one embodiment, the reference chip with a hole (chip B) and the back-illuminated photodetector under test (chip A) come from the same wafer and have identical structural layout and dimensions. During fabrication, a location on chip B corresponding to the target pixel is selected, and a hole is drilled in its central area using high-precision laser technology. This drilling area is typically 5% to 10% of the target pixel size; for example, for a 1mm × 1mm pixel, the diameter of the micro-hole is generally 50μm to 100μm. After drilling, chip B becomes a micro-aperture with localized light transmission, capable of blocking most light and allowing only a small amount of light to pass through the designated area and be projected onto the target pixel on chip A.

[0038] In one embodiment, during actual testing, the front of chip B faces the light-diffusing plate 13 of the light source module 10, and the back of chip B is tightly stacked with the back of chip A; the front of chip A (i.e., the electrode surface) faces upward and contacts the probe station 14 to realize the acquisition of electrical signals.

[0039] To ensure strict alignment of chip A and chip B in the X and Y directions, this embodiment may further include positioning pins 15, which may include one or more. In one embodiment, an X-direction positioning pin and a Y-direction positioning pin may be provided on the light source module 10 carrier platform. When chip A and chip B are stacked, they simultaneously abut against these two positioning pins, thus ensuring pixel-level alignment in the planar direction. This alignment accuracy depends on the chip cutting process, and the error is generally controlled within ±10μm, which is sufficient to meet the requirements of pixel-level crosstalk testing.

[0040] Through the above structural and process design, the back-illuminated photodetector testing system provided by this invention achieves photoelectric response acquisition of the target pixel and its neighboring pixels under local illumination without the need for packaging or high-precision translation alignment, thereby accurately calculating the optical crosstalk level between pixels. This significantly reduces testing costs and operational complexity, and improves the efficiency and data reliability of die-level BSI chip testing.

[0041] In one exemplary instance, combined with Figure 1 Taking a back-illuminated photodetector 17 as an example of a photodiode array, the uniformity of the responsivity of the photodiode array 17 can be tested using a light source module 10, a power supply module, and a probe station 14. The specific test principle may include: The light source module 10 is fixed to the carrier stage by vacuum adsorption, and the carrier stage is then mounted and fixed on a two-dimensional translation stage. The back side of the photodiode chip 17 is placed tightly against the light-diffusing plate 13 of the light source module 10 and mechanically fixed to ensure stable light reception. The front side of the photodiode chip 17 (i.e., the plane containing the anode and cathode) faces the probe station 14, and multiple probes of the probe station 14 contact the anode and cathode of multiple pixels of the photodiode array 17, thereby allowing simultaneous testing of the photocurrent values ​​of multiple pixels. By moving the carrier stage, the photodiode chip 17 is tested in sections for each pixel area, ultimately obtaining a two-dimensional mapping of the photocurrent of all pixels in the entire photodiode chip 17. By calculating the degree to which the photocurrent of each pixel deviates from the overall mean, the responsivity uniformity information of the photodiode array 17 can be obtained.

[0042] In one exemplary instance, combined with Figure 1 Taking a back-illuminated photodetector 17 as an example of a photodiode array, the linearity and uniformity of the photodiode array 17 can be tested using a light source module 10, a power supply module, a reference module, and a probe station 14. The specific test principle can include: The light source module 10 is fixed to the carrier stage using vacuum adsorption, and the carrier stage is then mounted and fixed on a two-dimensional translation stage. The back of the photodiode array 17 is placed against the light-diffusing plate 13 of the light source module 10 and mechanically fixed to ensure stable light reception. The front of the photodiode array 17 (i.e., the plane containing the anode and cathode electrodes) faces the probe station 14, and multiple probes of the probe station 14 contact multiple pixel electrodes of the photodiode array 17. During testing, the output voltage of the light source module 10 is adjusted to change the output light power (or light intensity), and the actual light intensity value is read through a reference module. When the light intensity reaches a first predetermined value, the carrier stage is moved to sequentially collect the photocurrent of each pixel in the entire array, obtaining a photocurrent mapping map corresponding to the first light intensity level. Then, the light intensity is adjusted to a second predetermined value, and the above test process is repeated to obtain a photocurrent mapping map corresponding to the second light intensity level. The ratio of the two light intensity values ​​is calculated. The ratio of the photocurrent of each pixel under two different light intensities is... By comparing the deviation of the S value of each pixel from the R value, the linearity uniformity information of each pixel in the photodiode array 17 can be obtained.

[0043] In one exemplary instance, combined with Figure 1 Taking a back-illuminated photodetector 17 as an example of a photodiode array, the crosstalk characteristics of the photodiode array 17 can be tested using a light source module 10, a power supply module, a reference module, a probe station 14, a punched reference chip, and positioning pins 15. The specific test principle can include: The light source module 10 is fixed to the carrier stage by vacuum adsorption, and the carrier stage is then mounted and fixed on a two-dimensional translation stage. The front side of the punched reference chip B (i.e., the chip serving as the micro-aperture) is placed tightly against the light-diffusing plate 13, and the back side of the chip to be tested, A (i.e., the photodiode array 17), is placed tightly against the back side of chip B. By simultaneously pressing chip A and chip B against the positioning pin 15, high-precision alignment in the X and Y directions is ensured. The aligned and stacked chips A and B are mechanically fixed as a whole, with the front side (electrode surface) of chip A facing the probe stage 14. The probe contacts the electrode, and the photocurrent of the target pixel of chip A corresponding to the micro-aperture of chip B is measured. ) and the photocurrent of its adjacent pixels ( ).according to The optical crosstalk level of the target pixel can be calculated by multiplying by 100%.

[0044] Compared to optical test structures designed for FSI photodiode array detectors, this utility model is specifically designed for the testing needs of BSI photodiode array detectors. Since the light incident surface and the electrode surface in contact with the probe are located on opposite sides of the BSI device, the traditional FSI structure's co-planar arrangement of the light source and probe is unsuitable. This utility model employs a bottom-up light source structure, coupled with a light-diffusing plate, ensuring that the light incident surface of the chip under test faces downwards and the electronic electrode surface faces upwards, thus simultaneously satisfying the requirement that the probe contact electrodes and light illumination are on opposite sides.

[0045] In some embodiments, for single-pixel crosstalk testing of BSI chips, traditional methods are limited by the lack of graphic markings on the back of the chip, requiring a high-precision two-dimensional translation stage to locate the pixel position by coordinates. Since the light source must be positioned with the back of the chip facing upwards, it cannot simultaneously contact the front electrodes, necessitating the chip to be packaged onto a PCB board and the electrical signals exported via pins or gold fingers. This not only increases packaging costs and process complexity but also prolongs the testing cycle. This invention utilizes another chip from the same wafer, with identical size and layout, as a reference chip B for drilling holes. Micro-hole laser processing is performed at the target pixel location to form a light-transmitting hole serving as a micro-aperture. During testing, chip B is simply stacked on the back of the chip under test (A), and precise alignment in the X / Y directions is achieved using positioning pins. This allows for localized low-light illumination and crosstalk testing of the target pixel and its neighboring pixels without the need for packaging or coordinate calculations.

[0046] Furthermore, in some embodiments, this invention integrates various components such as the light source module 10, power supply module, reference module, probe station 14, punched reference chip, and positioning pin 15 into an integrated optical testing system. This system simultaneously characterizes various optical properties, including response uniformity, linearity uniformity, and crosstalk level, making it particularly suitable for applications such as CT imaging that demand high performance from photodiode arrays. This integrated system design in the embodiments of this application significantly improves the applicability and flexibility of the testing.

[0047] This invention enables various optical characterization tests on BSI-type photodiode chips (including array-type or single-chip types) in their bare die state, allowing direct measurement of responsivity uniformity, linearity uniformity, and inter-pixel crosstalk levels without additional packaging onto a PCB board. The back-illuminated photodetector testing system provided by this invention features a simple structure and convenient operation, reducing both the construction cost of testing equipment and the time and expense of pre-test processing. Furthermore, through the cooperation of positioning pins and a punched reference chip, this invention offers significant advantages in pixel-level local illumination and alignment accuracy, ensuring the accuracy and repeatability of test results, making it particularly suitable for rapid performance evaluation and quality control during the R&D and mass production stages.

[0048] Although the embodiments disclosed in this application are as described above, the content described is merely for the purpose of understanding this application and is not intended to limit this application. Any person skilled in the art to which this application pertains may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in this application; however, the scope of patent protection of this application shall still be determined by the scope defined in the appended claims.

Claims

1. A back-illuminated photodetector testing system, characterized in that, include: The light source module (10), power supply module, and probe station (14) are included. The light source module (10) is used to provide uniform illumination to the back of the back-illuminated photodetector (17) under test. The light source module (10) includes a light source array for generating illumination, a PCB board (11), and a light-diffusing plate (13). The light source array is soldered onto the PCB board (11), and the light-diffusing plate (13) is disposed on the top of the light source module (10) to achieve uniform in-plane illumination. The bottom of the light source module (10) is fixed on the support platform. The power supply module is used to provide an adjustable voltage to the light source array in order to control the luminous intensity of the light source array; The probe station (14) is used to measure the photocurrent output of the back-illuminated photodetector (17) under test. The back-illuminated photodetector (17) under test is located below the probe station (14), with its back side in close contact with the light-diffusing plate (13) to receive light, and its front side facing the probe station (14) so ​​that the probe of the probe station (14) can establish a conductive contact with its pixel electrode.

2. The back-illuminated photodetector testing system according to claim 1, characterized in that, it further... include: The reference module is used to read the value reflecting the actual output light intensity of the light source module (10) so as to perform real-time measurement and calibration of the output of the light source module (10).

3. The back-illuminated photodetector testing system according to claim 2, wherein, The reference module is a standard optical power meter or a reference photodiode.

4. The back-illuminated photodetector testing system according to claim 1, characterized in that, it also... include: The punch reference chip is used to physically limit the uniform light intensity output from the large area of ​​the light source module (10) to a specific small area so as to provide precise and targeted light illumination to a specified pixel on the back-illuminated photodetector (17) under test. The front side of the punched reference chip faces the light-diffusing plate (13), and the back side of the punched reference chip is tightly overlapped with the back side of the back-illuminated photodetector (17) under test.

5. The back-illuminated photodetector testing system according to claim 4, characterized in that, it further... include: Positioning pins (15) are used to ensure that the back-illuminated photodetector under test (17) and the punched reference chip are strictly aligned in two dimensions.

6. The back-illuminated photodetector testing system according to claim 5, wherein, The locating pin (15) may include one or more.

7. The back-illuminated photodetector testing system according to claim 4 or 5, wherein, The punched reference chip and the back-illuminated photodetector under test (17) come from the same wafer and have the same structural layout and size.

8. The back-illuminated photodetector testing system according to claim 1, 2, 4 or 5, wherein, The light source array consists of LED beads with a uniform divergence angle (12).

9. The back-illuminated photodetector testing system according to claim 1, 2, 4 or 5, wherein, The probe station (14) is a manual probe station or an automated probe board.

10. The back-illuminated photodetector testing system according to claim 1, 2, 4 or 5, wherein, The light source module (10) is surrounded by an outer frame (16) that provides support.

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