Camera focusing control system, method and device

Abstract

The invention discloses a camera focusing control system, method and device, and relates to the technical field of wafer detection. In the camera focusing control system, the position of a camera is adjusted, according to an optical signal which is collected by a photoelectric detector and can represent the distance between a wafer and a transverse beam splitter prism, the optical signal is converted into a voltage value and sent to a controller, and the controller determines the position of the camera corresponding to the maximum voltage value in all the voltage values as a target position; wherein when the voltage value is maximum, the distance between the wafer and the transverse beam splitter prism is equal to the distance between the reflecting mirror surface and the midpoint of the transverse beam splitter prism, and at the moment, the distance between the wafer and the camera is the target focal length of the camera. The optical signal is used for camera focusing, the camera can be adjusted to the optimal shooting focal length, and therefore the definition of the collected wafer image is improved, and the precision and accuracy of wafer detection are further improved.

Description

Technical Field

[0001] The present application relates to the field of wafer detection technology, and more specifically, to a camera focus control system, method and device. Background Art

[0002] In the semiconductor manufacturing process, the chips on the wafer need to be inspected and tested for quality. The chips on the wafer can be photographed by a camera, and the images obtained can be used to analyze whether the circuit manufacturing on the chip meets the quality requirements. However, since the chip size and the length of the circuit on the chip are approximately in the order of nanometers, the focal length between the camera and the chip needs to be adjusted to the nanometer level. If the camera is not focused accurately, it will affect the clarity of the captured chip image, resulting in measurement errors, thereby affecting the inspection quality of the chip. Therefore, camera focusing becomes one of the more difficult steps for photo inspection.

[0003] Therefore, there is an urgent need for a camera focus control method to improve the accuracy of focal length adjustment between the camera and the wafer. Summary of the invention

[0004] In view of the above problems, the present application provides a camera focus control system, method and device to achieve the purpose of improving the focus adjustment accuracy between the camera and the chip. The specific solution is as follows:

[0005] The first aspect of the present application provides a camera focus control system, which is applied to a wafer inspection device, comprising:

[0006] A camera focus module and a controller, the camera focus module comprising: a camera, a driving motor, a photodetector, a longitudinal beam splitter prism and a transverse beam splitter prism of a preset longitudinal length, and a reflective mirror surface arranged perpendicular to the transverse beam splitter prism, the distance between the reflective mirror surface and the midpoint of the transverse beam splitter prism being a preset transverse length, and the sum of the preset transverse length and the preset longitudinal length being the target focal length of the camera;

[0007] Wherein, one end of the longitudinal beam splitter prism is vertically installed at the midpoint of the transverse beam splitter prism, the other end of the longitudinal beam splitter prism is installed with the camera, the driving motor and the photoelectric detector are installed on the side of the longitudinal beam splitter prism, the driving motor is used to drive the longitudinal beam splitter prism to move, so that the camera focus module moves, the camera focus module is installed directly above the wafer placement platform, and the transverse beam splitter prism is parallel to the wafer placement platform;

[0008] The transverse beam splitter is used to reflect the wafer reflected light signal and the mirror reflected light signal to the longitudinal beam splitter, and the longitudinal beam splitter reflects the interference signal after the wafer reflected light signal and the mirror reflected light signal interfere with each other to the photodetector, and the photodetector converts the interference signal into a voltage value and sends the voltage value to the controller, the wafer reflected light signal is a signal obtained by the wafer to be tested reflecting the first light signal, and the mirror reflected light signal is a signal obtained by the reflector reflecting the second light signal, and the first light signal and the second light signal are both light signals with the same light phase emitted from the midpoint of the transverse beam splitter;

[0009] The controller is used to control the drive motor to drive the camera focus module with a preset fine-adjustment step distance, so that the camera moves from a fine-adjustment focus starting position to a fine-adjustment focus ending position, and obtain the camera position of the camera and the voltage value collected by the photoelectric detector during each movement; and determine the camera position corresponding to the maximum voltage value among all the voltage values ​​as the target position of the camera.

[0010] In a possible implementation, the lateral beam splitter prism includes: a beam splitter film lens arranged at the midpoint of the lateral beam splitter prism, used to split the light source signal incident from the end of the lateral beam splitter prism where the reflective mirror surface is not arranged into a first light signal and a second light signal, the first light signal and the second light signal have the same light phase and are perpendicular to each other, and are respectively emitted to the wafer to be tested and the reflective mirror surface.

[0011] In a possible implementation, the controller includes at least: a position information receiving socket, a drive instruction output socket, a voltage signal receiving socket, and a camera control instruction output socket;

[0012] The drive motor at least includes: a position information output socket and a drive instruction receiving socket;

[0013] The position information receiving socket is connected to the position information output socket;

[0014] The drive instruction output socket is connected to the drive instruction receiving socket;

[0015] The voltage signal receiving socket is connected to the voltage output socket of the photoelectric detector;

[0016] The camera control instruction output socket is connected to the camera control instruction receiving socket of the camera.

[0017] A second aspect of the present application provides a camera focus control method, which is applied to a controller in a camera focus control system of the first aspect or any implementation of the first aspect, and the camera focus control method includes:

[0018] In response to a wafer detection instruction, a driving motor is controlled to drive a camera focus module, so that the camera moves from a fine-adjustment focus starting position to a fine-adjustment focus end position at a preset fine-adjustment step distance, and the camera position of the camera and the voltage value collected by the photodetector are respectively obtained during each movement, wherein the voltage value is a voltage value obtained by the photodetector converting an interference signal, and the interference signal is an optical signal after interference between two reflection signals obtained by the wafer to be tested and the reflection mirror respectively reflecting optical signals with the same optical phase;

[0019] The camera position corresponding to the maximum voltage value among all the voltage values ​​is determined as the target position of the camera.

[0020] In a possible implementation, the process of determining the fine-adjustment focus starting position and the fine-adjustment focus ending position includes:

[0021] Controlling the driving motor to drive the camera focus module, so that the camera moves from a preset focus starting position to a preset focus ending position with a preset coarse adjustment step distance, and respectively obtaining the camera position corresponding to each movement and the wafer image taken by the camera;

[0022] The two camera positions corresponding to the two clearest wafer images among all the wafer images are respectively determined as the fine-adjustment focus starting position and the fine-adjustment focus ending position.

[0023] In a possible implementation, controlling the driving motor to drive the camera focus module so that the camera moves from a preset focus starting position to a preset focus ending position with a preset coarse adjustment step distance, and respectively obtaining the camera position corresponding to each movement and the wafer image taken by the camera, includes:

[0024] Determine whether the current position information of the camera is within a preset focus range, where the preset focus range is a range defined by a preset focus starting position and a preset focus ending position;

[0025] When the current position information of the camera is within the preset focus range, controlling the driving motor to drive the camera focus module to move the camera once with a preset coarse adjustment step distance;

[0026] In response to receiving the current position information of the camera sent by the driving motor, a control instruction is sent to the camera, wherein the control instruction is a basis for the camera to photograph the wafer to be tested;

[0027] In response to receiving a wafer image captured by the camera, the position information and the wafer image are stored.

[0028] In a possible implementation, the process of determining the preset focus starting position and the preset focus ending position includes:

[0029] Controlling the driving motor to drive the camera focus module to move the camera within a preset range in the vertical direction, and obtaining camera position information and wafer images for each movement;

[0030] Identifying the clarity of the wafer image corresponding to each movement;

[0031] Based on the camera position information and the clarity corresponding to each of the wafer images, the camera position information at which the clarity reaches a preset clarity threshold during the process of the camera moving from bottom to top in the vertical direction is determined as the preset focus starting position; the camera position information at which the clarity reaches the preset clarity threshold during the process of the camera moving from bottom to top in the vertical direction is determined as the preset focus end position.

[0032] A third aspect of the present application provides a camera focus control device, which is applied to a controller in a camera focus control system according to the first aspect or any implementation of the first aspect, and the camera focus control device includes:

[0033] A control driving unit is used to control a driving motor to drive a camera focus module in response to a wafer detection instruction, so that the camera moves from a fine-adjustment focus starting position to a fine-adjustment focus end position at a preset fine-adjustment step distance, and obtains the camera position of the camera and a voltage value collected by a photodetector during each movement, wherein the voltage value is a voltage value obtained by the photodetector converting an interference signal, and the interference signal is an optical signal after interference between two reflection signals obtained by the wafer to be tested and the reflection mirror respectively reflecting optical signals with the same optical phase;

[0034] The target position determination unit is used to determine the camera position corresponding to the maximum voltage value among all the voltage values ​​as the target position of the camera.

[0035] The camera focus control system provided in the embodiment of the present application has a reflective mirror surface at one end of the transverse beam splitter prism, and the sum of the horizontal distance from the reflective mirror surface to the midpoint of the transverse beam splitter prism and the length of the longitudinal beam splitter prism is the target focal length of the camera. When the length of the longitudinal beam splitter prism remains unchanged, the end of the longitudinal beam splitter prism where the camera is not installed is adjusted, that is, the distance from the midpoint of the transverse beam splitter prism to the wafer to be measured is the same as the distance from the reflective mirror surface to the midpoint of the transverse beam splitter prism, so that the camera can reach the target focal length and can capture a clear wafer image.

[0036] The present application utilizes the principle that the optical phases of two optical signals that undergo constructive interference are the same, and the same optical phase can be understood as the same distance traveled by the two light waves. Two optical signals with the same optical phases are emitted to the wafer to be tested and the reflective mirror surface at the center position of the transverse beam splitter prism, respectively. If the vertical distance from the wafer to be tested to the center position is equal to the horizontal distance from the reflective mirror surface to the center position, then the optical phases of the reflected light signals of the wafer to be tested and the reflective mirror surface to the optical signal are also the same. In this case, constructive interference occurs after the two reflected light signals are reflected to the longitudinal beam splitter prism. Constructive interference is the superposition of optical signals, and the voltage value corresponding to the interference signal is the largest.

[0037] Based on this, when the controller controls the camera to automatically adjust to the position corresponding to the maximum voltage value, the distance from the wafer to be tested to the center position is equal to the distance from the reflector to the center position, and the vertical distance between the wafer to be tested and the camera is the target focal length of the camera. Therefore, the embodiment of the present application can automatically adjust the camera to the position of the target focal length according to the voltage value transmitted back each time it moves, so that the camera can capture clear wafer images and improve the camera focusing efficiency. And compared to the artificial millimeter-level focusing accuracy, the optical signal can achieve nanometer-level accuracy. Therefore, the present application uses optical signals to focus the camera, which can enable the camera to adjust to the optimal shooting focal length, thereby improving the clarity of the collected wafer image and further improving the precision and accuracy of wafer detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0039] Figure 1 A system architecture diagram of a camera focus control system provided in an embodiment of the present application;

[0040] Figure 2 A schematic diagram of the optical path of a camera focus control system provided in an embodiment of the present application;

[0041] Figure 3 A schematic diagram of a flow chart of a method for implementing camera focus control provided in an embodiment of the present application;

[0042] Figure 4 A circuit connection diagram of a drive motor provided in an embodiment of the present application;

[0043] Figure 5 A circuit connection diagram of a photoelectric detector provided in an embodiment of the present application;

[0044] Figure 6 A circuit connection diagram of a camera provided in an embodiment of the present application;

[0045] Figure 7 A schematic structural diagram of a camera focus control device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0047] In the process of detecting and testing wafers, it is necessary to analyze whether the circuits of the chips on the wafer meet the requirements based on the wafer pictures taken by the camera. However, since the length of the circuits on the wafer is approximately on the order of a few nanometers, the focal length between the camera and the chip needs to be adjusted to the nanometer level. If the camera is not focused accurately, it will affect the clarity of the captured chip image and cause measurement errors, thereby affecting the inspection quality of the chip. In addition, the circuit image on the wafer chip is 3D stereoscopic, and the heights of different test points of the chip are different. Therefore, the camera needs to adjust the focal length accordingly when testing different points. Therefore, camera focusing becomes one of the more difficult steps for photo detection. In the prior art, focusing technologies include camera autofocus, manual focus, and software algorithm focus light technology, but these technologies still have shortcomings such as insufficient focusing accuracy and automation.

[0048] To solve the above problems, an embodiment of the present application provides a camera focus control system, which is used to achieve high-precision focusing between the camera and the wafer.

[0049] Reference Figure 1 , a system architecture diagram of a camera focus control system provided in an embodiment of the present application, wherein the camera focus control system includes: a camera focus module and a controller. The camera focus module includes: a camera 10, a drive motor 20, a photodetector 30, a longitudinal beam splitter prism 40 and a transverse beam splitter prism 50 of a preset longitudinal length, and a reflective mirror 60 arranged perpendicular to the transverse beam splitter prism 50, the distance between the reflective mirror 60 and the midpoint of the transverse beam splitter prism 50 is a preset transverse length, and the sum of the preset transverse length and the preset longitudinal length is the target focal length of the camera 10.

[0050] Among them, one end of the longitudinal beam splitter prism 40 is vertically installed at the midpoint of the transverse beam splitter prism 50, and the camera 10 is installed at the other end of the longitudinal beam splitter prism 40. The driving motor 20 and the photodetector 30 are installed on the side of the longitudinal beam splitter prism 40. The driving motor 20 is used to drive the longitudinal beam splitter prism 40 to move, so that the camera focus module moves. The camera focus module is installed directly above the wafer placement platform 90, and the transverse beam splitter prism 50 is parallel to the wafer placement platform 90.

[0051] The controller has certain data processing capabilities, and the ability to control and coordinate various devices, circuits or processes inside or outside the system according to predetermined programs or instructions to achieve the focus of the camera. The controller can be a hardware circuit (such as an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a general processor, a digital signal processor (DSP), a microprocessor or a microcontroller, etc.), or a combination of these hardware circuits. For example, the controller can be a hardware system with an instruction execution function, such as a CPU, DSP, etc., or a hardware system without an instruction execution function, such as an ASIC, FPGA, etc., or a combination of the above hardware systems without an instruction execution function and hardware systems with an instruction execution function.

[0052] In the embodiments of this application, refer to Figure 1 The controller at least includes: a position information receiving socket 01, a drive instruction output socket 02, a voltage signal receiving socket 03 and a camera control instruction output socket 04; the drive motor 20 at least includes: a position information output socket 05 and a drive instruction receiving socket 06; the position information receiving socket 01 is connected to the position information output socket 05; the drive instruction output socket 02 is connected to the drive instruction receiving socket 06; the voltage signal receiving socket 03 is connected to the voltage output socket 07 of the photodetector 30; the camera control instruction output socket 04 is connected to the camera control instruction receiving socket 08 of the camera 10.

[0053] The controller receives the camera position output by the position information output socket 05 of the drive motor 20 and the wafer image captured by the camera through the position information receiving socket 01; outputs the driving instruction to the driving instruction receiving socket 06 of the drive motor 20 through the driving instruction output socket 02, and controls the drive motor 20 to drive the camera focus module to move; receives the voltage value converted from the light signal input by the voltage output socket 07 of the photodetector 30 through the voltage signal receiving socket 03; inputs the camera shooting instruction to the camera control instruction receiving socket 08 of the camera 10 through the camera control instruction output socket 04, and controls the camera 10 to capture the wafer image at the current position. Based on this, the controller controls the camera focus module to achieve focusing according to the received image information and voltage value. For details, please refer to the description of the camera focus control method below.

[0054] In the camera focus module, the camera 10, the transverse beam splitter prism 50, and the drive motor 20 are connected as a whole through the longitudinal beam splitter prism 40. When the drive motor drives the longitudinal beam splitter prism to move up and down in the Z direction, the camera 10, the transverse beam splitter prism 50, and the drive motor 20 are also moved together, thereby achieving the purpose of adjusting the camera focus. Figure 1 In the figure, it is not possible to directly see the structural connection between the photodetector 30 and the reflective mirror 60 and the longitudinal beam splitter prism. In actual application, the photodetector 30 and the reflective mirror 60 can be fixed at corresponding positions by fixing components such as connecting rods, so that they can move with the movement of the longitudinal beam splitter prism 40.

[0055] Among them, the camera 10 is a camera, which is a device that forms an image using the principle of optical imaging and uses film to record the image. In the embodiment of the present application, Cam can refer to a camera, which is used to shoot the wafer 70 placed directly below the camera. The drive motor 20 is a device that converts electrical energy into kinetic energy, which is used to drive the longitudinal beam splitter prism to move up and down in the Z direction. In the embodiment of the present application, the drive motor can be a piezoelectric ceramic motor (PZT), also known as an ultrasonic motor, which is a driving mechanism that uses the inverse piezoelectric effect of piezoelectric materials to convert the high-frequency electrical energy applied to the piezoelectric ceramic into the vibration energy of the elastic vibrator, and obtains power by means of the friction between the stator and the rotor. Since the drive motor drives the camera focus module in the Z direction, "Z-PZT" can be used to specifically refer to the drive motor below. The photodetector 30 is used to convert the received light signal into an electrical signal. In the embodiment of the present application, the photodetector can be a photodiode (PD), also known as a photosensitive diode, which is a light detector that can convert a light signal into a current or voltage signal. The PD below also specifically refers to a photodiode or a photodetector. BeamSplitters are optical components that can split a beam of light into two beams according to a certain reflection and transmission ratio.

[0056] The distance between the reflective mirror surface 60 and the midpoint of the transverse beam splitter prism 50 is a preset transverse length, and the sum of the preset transverse length and the preset longitudinal length is the target focal length of the camera 10. It can be understood that in the embodiment of the present application, when the best shooting focal length of the camera is known, the focus of the camera is adjusted to the distance between the camera and the upper surface of the wafer to be measured, that is, L1+L3, so that the distance between the focused camera and the upper surface of the wafer to be measured is the best focal length, that is, "L1+L3=target focal length". The target focal length is the best shooting focal length. When L3 is fixed, the target focal length is achieved by adjusting the length of L1. Therefore, the embodiment of the present application sets L2 to "target focal length-L3", and the camera only needs to adjust the camera focus module to a position where L1 is equal to L2, and the camera reaches the target focal length.

[0057] Based on this, the embodiments of this application are based on Figure 1 Build the system structure, adjust the camera height, and use optical principles to verify the relationship between L1 and L2. According to the relationship between L1 and L2, adjust the camera height so that L1=L2 to achieve the best shooting focal length. Figure 2 , a schematic diagram of the optical path of a camera focus control system provided in an embodiment of the present application, wherein a transverse beam splitter prism is used to reflect a wafer reflected light signal and a mirror reflected light signal to a longitudinal beam splitter prism, and the longitudinal beam splitter prism reflects an interference signal after interference between the wafer reflected light signal and the mirror reflected light signal to a photodetector, and the photodetector converts the interference signal into a voltage value and sends the voltage value to a controller, the wafer reflected light signal is a signal obtained by the wafer to be tested reflecting the first light signal, and the mirror reflected light signal is a signal obtained by the reflective mirror reflecting the second light signal, and the first light signal and the second light signal are both light signals with the same light phase emitted from the midpoint of the transverse beam splitter prism.

[0058] Figure 2 The dotted line in the figure represents the light signal, wherein the light source is taken in from the left side of the lateral beam splitter prism 50, that is, the side where the reflective mirror 60 is not provided, referring to Figure 1 The beam splitter lens 80, which is arranged at the midpoint of the transverse beam splitter prism, splits the light source signal incident from the end of the transverse beam splitter prism without the reflector into a first light signal and a second light signal. The first light signal and the second light signal have the same light phase and are perpendicular to each other, and are respectively directed to the wafer to be tested and the reflector. The first light signal is directed to the reflector 60 along the incident direction of the light source, and the second light signal is perpendicular to the incident direction of the light source and is directed to the wafer to be tested.

[0059] The first light signal is reflected after hitting the wafer to be tested, and the reflected light is recorded as the wafer reflected light signal, which enters the transverse beam splitter prism; the second light signal hits the reflective mirror 60, undergoes total reflection and returns to the transverse beam splitter prism, and the reflected light is recorded as the mirror reflected light signal. The two beams of light reflected on the transverse beam splitter prism continue to propagate in the Z direction through the transverse beam splitter prism, and then the two beams of reflected light are transmitted to the photodetector PD through the longitudinal beam splitter prism.

[0060] The wafer reflected light signal and the mirror reflected light signal interfere with each other on the photodetector PD. When two coherent light beams meet at a certain point in space, constructive interference or destructive interference will occur. If the peaks or troughs of the two light beams meet and overlap, constructive interference will occur, and the light intensity detected at the meeting point will increase. If the peak of one light beam meets and overlaps the trough of another light beam, destructive interference will occur, and the light intensity detected at the meeting point will decrease.

[0061] It can be seen that constructive interference will occur between two beams of light with the same optical phase. Since the optical phases of the first optical signal and the second optical signal are the same, only when the reflected light corresponding to the first optical signal and the second optical signal travels the same distance, the optical phases of the wafer reflected light signal and the mirror reflected light signal corresponding to the two optical signals can be the same. That is, only when L2=L3, the optical phases of the wafer reflected light signal and the mirror reflected light signal are the same, and the wafer reflected light signal and the mirror reflected light signal will constructively interfere in PD, and the light intensity detected by the photodetector PD is the largest. On the contrary, if the reflected light corresponding to the first optical signal and the second optical signal travels different distances, that is, L2≠L3, the optical phases of the wafer reflected light signal and the mirror reflected light signal are different, and at this time, the wafer reflected light signal and the mirror reflected light signal will destructively interfere in PD, and the light intensity detected by the photodetector PD is small.

[0062] The present application embodiment is based on Figure 1 Build the system structure, adjust the camera height, and use optical principles to verify the relationship between L1 and L2. According to the relationship between L1 and L2, adjust the camera height so that L1=L2 to achieve the best shooting focal length. For details, refer to Figure 3 , a flowchart of a camera focus control method provided in an embodiment of the present application is provided, and the camera focus control method of the controller of the camera focus control system is described, which specifically includes the following steps:

[0063] Step S110 , in response to the wafer inspection instruction, controlling the driving motor to drive the camera focus module, so that the camera moves from the fine adjustment focus starting position to the fine adjustment focus ending position with a preset fine adjustment step distance.

[0064] Step S120, respectively obtaining the camera position of the camera and the voltage value collected by the photoelectric detector during each movement.

[0065] Step S130: The camera position corresponding to the maximum voltage value among all the voltage values ​​is determined as the target position of the camera.

[0066] The controller controls the camera focus module to move in the Z direction. Each time it moves, the photodetector PD transmits the voltage value converted from the collected light signal corresponding to this movement to the controller. As can be seen from the above, the voltage value is the voltage value obtained by the photodetector converting the interference signal. The interference signal is the light signal after the two reflected signals obtained by the wafer to be tested and the reflective mirror respectively reflecting the light signal of the same light phase interfere with each other, that is, the voltage value obtained by converting the light signal after the wafer reflected light signal and the mirror reflected light signal interfere with each other at PD.

[0067] After collecting the voltage values ​​corresponding to multiple focusing positions, the controller compares all the voltage values, determines the maximum voltage value, and uses the camera position corresponding to the maximum voltage value as the target position of the camera. It can be understood that the larger the voltage value, the stronger the light intensity received by the photodetector, and when L2=L1, the wafer reflected light signal and the mirror reflected light signal will constructively interfere, and the superposition of the two beams of light received by the photodetector PD is the strongest, so the converted voltage value is the largest. Therefore, when the voltage value is the largest, the corresponding L1 and L2 are equal, and at this position, the distance between the camera and the wafer to be tested is the target focal length.

[0068] In addition, during the focusing process, the controller does not perform focusing randomly, but focuses between the fine focus starting position and the fine focus end position, where the fine focus starting position and the fine focus end position can be determined based on the measurable height of the wafer to be measured. For example, if the target focal length of the camera is 10cm and the wafer height can be measured to be 0.5cm, the camera position can be 9.5cm. However, due to the limited measurable magnitude and the inability to achieve nanometer-level accuracy, 9.4~9.6cm is used as the fine focus position range, and the light signal is used for focusing. Generally, the visible light wavelength range is from 380 nanometers (nm) to 740 nanometers (nm), so the focal length can be adjusted within the range of 380-740nm to achieve high-precision focal length adjustment.

[0069] For details, please refer to Figure 2 , Figure 4 , Figure 5The connection between the controller and the Z-PZT and PD in the camera focus module shown in the figure realizes the control of the drive motor and the photodetector. The drive motor Z-PZT is connected to the DAC analog-to-digital output of the controller through an aerospace plug. The ARM processor of the controller transmits the signal that controls the movement of the PZT to the drive motor Z-PZT through the connection line of "DAC analog-to-digital output-signal conditioning circuit-aviation plug", thereby driving the camera focus module. Figure 2 In the circuit connection diagram of the controller shown, when the ARM processor determines that the current camera position has not reached the fine focus end position, it transmits the instruction M1 for the drive motor to the drive motor Z-PZT through the connection line of "waveform file-processor-digital analog converter DAC". It can be understood that the controller transmits the waveform file corresponding to the maximum voltage value to the processor, and the processor responds to the waveform file of the maximum voltage value to generate the control instruction M1 for controlling the piezoelectric ceramic motor or the drive motor, and the digital analog converter DAC converts the instruction M1 into an analog signal suitable for the drive motor and transmits it to the drive motor.

[0070] During the process of being driven, the driving motor Z-PZT outputs the position signal of the camera every time it moves, and transmits the position signal M2 to the "ADC sampling" module in the controller through the connection between the "aviation plug" and the controller. The ADC sampling module converts the position signal into an analog signal commonly used by the controller, and transmits it to the ARM processor of the controller through the transmission circuit in the controller, namely "filter-trigonometrics-data processing-memory" and "filter-data processing-memory", so as to achieve the caching of the camera position and the subsequent selection and output of the best focus position. It can be understood that first, the interference signals such as noise in the camera position signal collected by the ADC sampling module are filtered out through a filter to obtain a non-interference position signal. Further, the non-interference position signal is analyzed by using functional modules with signal processing capabilities such as trigonometry and data processing to obtain the accurate camera position, and the camera position is stored in the memory, so as to facilitate the subsequent acquisition of the camera position corresponding to the maximum voltage value from the memory.

[0071] During the fine-tuning process, as the camera position changes, the light signal collected by the photodetector PD also changes, and the converted voltage value also changes accordingly. Therefore, the photodetector PD also needs to re-upload the voltage value corresponding to the current camera position to the controller after each movement of the camera. Therefore, the photodetector PD is physically connected to the controller through an aviation plug, and the aviation plug transmits the light intensity signal M3 output by the photodetector to the ADC sampling module in the controller, where the light intensity signal M3 is a voltage value signal converted from the light signal, and the magnitude of the voltage value can characterize the intensity of the corresponding light signal. Furthermore, the ADC sampling module transmits the light intensity signal M3 to the ARM processor through the "filter-trigonometry-data processing-memory" and "filter-data processing-memory" lines, so that the ARM processor compares the light intensity signals corresponding to each camera position and determines the camera position with the strongest light intensity as the target focusing position for the wafer to be tested. It can be understood that the interference signal in the light intensity signal M3 received by the ADC sampling module is first filtered out through a filter to obtain an interference-free light intensity signal. Furthermore, the interference-free position signal is processed in terms of waveform, period, data analysis, etc. using functional modules with signal processing capabilities such as trigonometry and data processing to obtain the voltage value corresponding to the current camera position, and the voltage value is stored in the memory to facilitate subsequent comparison with voltage values ​​corresponding to multiple different camera positions.

[0072] In summary, the camera focus control system provided by the embodiment of the present application is provided with a reflective mirror at one end of the transverse beam splitter prism, and the sum of the horizontal distance from the reflective mirror to the midpoint of the transverse beam splitter prism and the length of the longitudinal beam splitter prism is the target focal length of the camera. When the length of the longitudinal beam splitter prism remains unchanged, the end of the longitudinal beam splitter prism where the camera is not installed is adjusted, that is, the distance from the midpoint of the transverse beam splitter prism to the wafer to be measured is the same as the distance from the reflective mirror to the midpoint of the transverse beam splitter prism, so that the camera can reach the target focal length and can capture a clear wafer image.

[0073] The present application utilizes the principle that the optical phases of two optical signals that undergo constructive interference are the same, and the same optical phase can be understood as the same distance traveled by the two light waves. Two optical signals with the same optical phases are emitted to the wafer to be tested and the reflective mirror surface at the center position of the transverse beam splitter prism, respectively. If the vertical distance from the wafer to be tested to the center position is equal to the horizontal distance from the reflective mirror surface to the center position, then the optical phases of the reflected light signals of the wafer to be tested and the reflective mirror surface to the optical signal are also the same. In this case, constructive interference occurs after the two reflected light signals are reflected to the longitudinal beam splitter prism. Constructive interference is the superposition of optical signals, and the voltage value corresponding to the interference signal is the largest.

[0074] Based on this, when the controller controls the camera to automatically adjust to the position corresponding to the maximum voltage value, the distance from the wafer to be tested to the center position is equal to the distance from the reflector to the center position, and the vertical distance between the wafer to be tested and the camera is the target focal length of the camera. Therefore, the embodiment of the present application can automatically adjust the camera to the position of the target focal length according to the voltage value transmitted back each time it moves, so that the camera can capture clear wafer images and improve the camera focusing efficiency. And compared to the artificial millimeter-level focusing accuracy, the optical signal can achieve nanometer-level accuracy. Therefore, the present application uses optical signals to focus the camera, which can enable the camera to adjust to the optimal shooting focal length, thereby improving the clarity of the collected wafer image and further improving the precision and accuracy of wafer detection.

[0075] Next, other possible implementations of the camera focus control system and the camera focus control method provided in the embodiments of the present application are described.

[0076] In one possible implementation, the process of determining the fine-tuning focus starting position and the fine-tuning focus ending position includes: controlling the drive motor to drive the camera focus module to move the camera from a preset focus starting position to a preset focus ending position with a preset coarse adjustment step distance, and obtaining the camera position corresponding to each movement and the wafer image taken by the camera respectively; and determining the two camera positions corresponding to the two clearest wafer images among all wafer images as the fine-tuning focus starting position and the fine-tuning focus ending position respectively.

[0077] It is understandable that the purpose of setting the fine-adjustment focus starting position and the fine-adjustment focus end position is to obtain the best focus position for fine focusing within the focal length range where the image is relatively clear, thereby improving the focusing efficiency of fine focusing. Therefore, before using the optical signal for fine focusing, the embodiment of the present application first determines a focus range where the image is relatively clear and close to the best focus position based on the clarity of the image captured by the camera. The embodiment of the present application may refer to this process as coarse focusing, which reduces the adjustment process of fine focusing, thereby improving the focusing efficiency.

[0078] In the process of coarse focusing, no light source may be provided, and focusing may be performed only according to the wafer image captured by the camera. The driving motor is controlled to drive the camera focus module, so that the camera moves from the preset focus starting position to the preset focus end position with a preset coarse adjustment step distance, and the camera position information corresponding to each movement and the wafer image captured by the camera are respectively obtained, including: judging whether the current camera position information is within the preset focus range, the preset focus range is the range defined by the preset focus starting position and the preset focus end position; when the current camera position information is within the preset focus range, the driving motor is controlled to drive the camera focus module, so that the camera moves once with the preset coarse adjustment step distance; in response to receiving the current camera position information sent by the driving motor, a control instruction is sent to the camera, and the control instruction is the basis for the camera to capture the wafer to be tested; in response to receiving the wafer image captured by the camera, the position information and the wafer image are stored.

[0079] Specifically, according to the preset coarse adjustment step distance, the controller controls the driving motor to drive the camera to move from the preset coarse adjustment step distance to the preset focus starting position. Each time it moves, the controller sends an image acquisition instruction to the camera, and the camera responds to the instruction to capture an image of the wafer to be tested, and the driving motor transmits the wafer image captured by the camera and the camera position back to the controller. Among them, the coarse adjustment step distance is much larger than the fine adjustment step distance. The controller analyzes the clarity, focusing effect, etc. of each wafer image transmitted back, and compares the analysis results of the wafer image corresponding to each camera position, and determines the focusing range defined by the camera position corresponding to the two clearest and best focusing wafer images as the range containing the best focusing position, and then determines them as the fine adjustment focus starting position and fine adjustment focus end position respectively.

[0080] Among them, the process of determining the preset focus starting position and the preset focus ending position includes: controlling the driving motor to drive the camera focus module to move the camera within a preset range in the vertical direction, and obtaining the camera position information and wafer image of each movement; identifying the clarity of the wafer image corresponding to each movement; based on the camera position information and clarity corresponding to each wafer image, determining the camera position information whose clarity reaches a preset clarity threshold in the process of the camera moving from bottom to top in the vertical direction as the preset focus starting position; determining the camera position information whose clarity reaches a preset clarity threshold in the process of the camera moving from bottom to top in the vertical direction as the preset focus ending position.

[0081] Optionally, the focus range defined by the preset focus starting position and the preset focus end position can be the area range where the camera is allowed to move. In the embodiment of the present application, the preset focus starting position and the preset focus end position are the critical focal length values ​​for the camera to collect the wafer image from the module to become clear. It can be understood that the relationship between the focal length and clarity of the camera can be parabolic, such as taking the best focal length as the midpoint, adjusting the focal length between the camera and the wafer in the Z direction, as the focal length of the camera and the wafer increases, the clarity of the image collected by the camera gradually decreases, but at a certain critical value, the image begins to blur; similarly, taking the best focal length as the midpoint, as the focal length of the camera and the wafer decreases, the clarity of the image collected by the camera gradually decreases, but at a certain critical value, the image begins to blur. Therefore, the camera has two critical values, between which the image has a certain clarity and can find the best focal length position from it. Therefore, before the rough adjustment, the embodiment of the present application first scans and focuses within the range of the camera's allowed focal length adjustment to find the two critical values, and further performs rough adjustment between the ranges defined by the two critical values.

[0082] As can be seen from the above, in the embodiment of the present application, except for steps S110-S130, the coarse adjustment of the focal length requires the camera to capture images, so the controller is required to control the camera to capture images. Specifically, referring to the figure, the controller is connected to the camera Cam through a unidirectional output line, and the controller sends a control instruction for controlling the camera to shoot to the camera Cam.

[0083] Reference Figure 6 , a circuit connection diagram of a camera provided in an embodiment of the present application, the connection relationship between the camera and components such as resistors (R120, R130, R125, R126, R127, R111), transistors (BC846BW), and power supplies in the camera focus module enables the camera to operate normally, and receives the control instructions of the controller to the camera Cam through the "Cam control input". The camera responds to the received control instructions and captures the image of the wafer to be tested located directly below the camera, and the captured image can be sent to the controller together with the camera position through the drive motor Z-PZT to avoid confusion in the correspondence between the camera position and the wafer image. Optionally, the controller and the camera Cam can also be connected through a bidirectional transmission line, that is, the wafer image captured by the camera is transmitted to the controller by the camera itself.

[0084] In summary, the embodiment of the present application uses DAC to control the camera to move from the maximum deviation of the focal length to the minimum deviation, that is, to move from the preset focus starting position of the coarse adjustment to the preset focus end position. Each time it moves to a certain position coordinate, the trigger circuit controls the camera to take a photo. The camera will take a series of photos continuously during the process of moving from the maximum deviation to the minimum deviation. The controller analyzes and processes the clarity of this series of images through a preset algorithm, finds the two clearest photos, and thus locates the position of the focal length deviation, realizes the coarse adjustment of the focal length, and finds the fine adjustment position range.

[0085] Furthermore, the camera is controlled to move from the fine adjustment starting position to the fine adjustment end position of the fine adjustment position range, and the position coordinates are determined each time the camera moves, and the voltage value collected by the photodetector is obtained at the same time. In the process of the camera moving from the fine adjustment starting position to the fine adjustment end position, the photodetector collects a series of voltage values. The controller determines the maximum voltage value by comparing each voltage value, thereby locating the camera position corresponding to the maximum voltage value as the optimal focus position, that is, the target position. The embodiment of the present application utilizes the coarse adjustment and fine adjustment methods to improve the camera focusing efficiency, and utilizes the precision of the light signal for focusing, thereby improving the focusing accuracy.

[0086] The following is a description of a camera focus control device provided in an embodiment of the present application. The camera focus control device described below and the camera focus control method described above can refer to each other.

[0087] First, combine Figure 7 , a camera focus control device of a controller in a camera focus control system is introduced, such as Figure 7 As shown, the camera focus control device may include:

[0088] The control driving unit 100 is used to control the driving motor to drive the camera focus module in response to the wafer detection instruction, so that the camera moves from the fine-adjustment focus starting position to the fine-adjustment focus end position with a preset fine-adjustment step distance, and obtains the camera position of the camera and the voltage value collected by the photodetector during each movement, wherein the voltage value is a voltage value obtained by the photodetector converting the interference signal, and the interference signal is a light signal after interference between two reflection signals obtained by the wafer to be tested and the reflection mirror respectively reflecting the light signal with the same light phase;

[0089] The target position determination unit 200 is used to determine the camera position corresponding to the maximum voltage value among all the voltage values ​​as the target position of the camera.

[0090] In a possible implementation, the functional unit for determining the fine-adjustment focus starting position and the fine-adjustment focus ending position includes:

[0091] A coarse adjustment subunit, used for controlling the driving motor to drive the camera focus module, so that the camera moves from a preset focus starting position to a preset focus ending position with a preset coarse adjustment step distance, and respectively obtaining the camera position corresponding to each movement and the wafer image taken by the camera;

[0092] The position determination subunit is used to determine the two camera positions corresponding to the two clearest wafer images among all the wafer images as the fine-adjustment focus starting position and the fine-adjustment focus ending position respectively.

[0093] In a possible implementation, the coarse tuning subunit includes:

[0094] A position determination subunit, used to determine whether the current position information of the camera is within a preset focus range, wherein the preset focus range is a range defined by a preset focus starting position and a preset focus end position;

[0095] A moving subunit, used for controlling the driving motor to drive the camera focusing module when the current position information of the camera is within the preset focusing range, so that the camera moves once with a preset coarse adjustment step distance;

[0096] A control shooting subunit, configured to send a control instruction to the camera in response to receiving the current position information of the camera sent by the driving motor, wherein the control instruction is a basis for the camera to shoot the wafer to be tested;

[0097] The image storage subunit is used to store the position information and the wafer image in response to receiving the wafer image taken by the camera.

[0098] In a possible implementation, the functional unit for determining the preset focus starting position and the preset focus ending position includes:

[0099] A focusing subunit, used for controlling the driving motor to drive the camera focusing module, so that the camera moves within a preset range in the vertical direction, and obtaining the camera position information and wafer image of each movement;

[0100] A clarity recognition unit, used to recognize the clarity of the wafer image corresponding to each movement;

[0101] A position range determination unit is used to determine, based on the camera position information and the clarity corresponding to each of the wafer images, the camera position information at which the clarity reaches a preset clarity threshold during the process of the camera moving from bottom to top in the vertical direction, as a preset focus starting position; and to determine the camera position information at which the clarity reaches the preset clarity threshold during the process of the camera moving from bottom to top in the vertical direction, as a preset focus end position.

[0102] In summary, the camera focus control system provided by the embodiment of the present application is provided with a reflective mirror at one end of the transverse beam splitter prism, and the sum of the horizontal distance from the reflective mirror to the midpoint of the transverse beam splitter prism and the length of the longitudinal beam splitter prism is the target focal length of the camera. When the length of the longitudinal beam splitter prism remains unchanged, the end of the longitudinal beam splitter prism where the camera is not installed is adjusted, that is, the distance from the midpoint of the transverse beam splitter prism to the wafer to be measured is the same as the distance from the reflective mirror to the midpoint of the transverse beam splitter prism, so that the camera can reach the target focal length and can capture a clear wafer image.

[0103] The present application utilizes the principle that the optical phases of two optical signals that undergo constructive interference are the same, and the same optical phase can be understood as the same distance traveled by the two light waves. Two optical signals with the same optical phases are emitted to the wafer to be tested and the reflective mirror surface at the center position of the transverse beam splitter prism, respectively. If the vertical distance from the wafer to be tested to the center position is equal to the horizontal distance from the reflective mirror surface to the center position, then the optical phases of the reflected light signals of the wafer to be tested and the reflective mirror surface to the optical signal are also the same. In this case, constructive interference occurs after the two reflected light signals are reflected to the longitudinal beam splitter prism. Constructive interference is the superposition of optical signals, and the voltage value corresponding to the interference signal is the largest.

[0104] Based on this, when the controller controls the camera to automatically adjust to the position corresponding to the maximum voltage value, the distance from the wafer to be tested to the center position is equal to the distance from the reflector to the center position, and the vertical distance between the wafer to be tested and the camera is the target focal length of the camera. Therefore, the embodiment of the present application can automatically adjust the camera to the position of the target focal length according to the voltage value transmitted back each time it moves, so that the camera can capture clear wafer images and improve the camera focusing efficiency. And compared to the artificial millimeter-level focusing accuracy, the optical signal can achieve nanometer-level accuracy. Therefore, the present application uses optical signals to focus the camera, which can enable the camera to adjust to the optimal shooting focal length, thereby improving the clarity of the collected wafer image and further improving the precision and accuracy of wafer detection.

[0105] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0106] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0107] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A camera focus control system, characterized in that: include: A camera focus module and a controller, the camera focus module comprising: a camera, a driving motor, a photodetector, a longitudinal beam splitter prism and a transverse beam splitter prism of a preset longitudinal length, and a reflective mirror surface arranged perpendicular to the transverse beam splitter prism, the distance between the reflective mirror surface and the midpoint of the transverse beam splitter prism being a preset transverse length, and the sum of the preset transverse length and the preset longitudinal length being the target focal length of the camera; Wherein, one end of the longitudinal beam splitter prism is vertically installed at the midpoint of the transverse beam splitter prism, the other end of the longitudinal beam splitter prism is installed with the camera, the driving motor and the photoelectric detector are installed on the side of the longitudinal beam splitter prism, the driving motor is used to drive the longitudinal beam splitter prism to move, so that the camera focus module moves, the camera focus module is installed directly above the wafer placement platform, and the transverse beam splitter prism is parallel to the wafer placement platform; The transverse beam splitter is used to reflect the wafer reflected light signal and the mirror reflected light signal to the longitudinal beam splitter, and the longitudinal beam splitter reflects the interference signal after the wafer reflected light signal and the mirror reflected light signal interfere with each other to the photodetector, and the photodetector converts the interference signal into a voltage value and sends the voltage value to the controller, the wafer reflected light signal is a signal obtained by the wafer to be tested reflecting the first light signal, and the mirror reflected light signal is a signal obtained by the reflector reflecting the second light signal, and the first light signal and the second light signal are both light signals with the same light phase emitted from the midpoint of the transverse beam splitter; The controller is used to control the drive motor to drive the camera focus module with a preset fine-adjustment step distance, so that the camera moves from a fine-adjustment focus starting position to a fine-adjustment focus ending position, and obtain the camera position of the camera and the voltage value collected by the photoelectric detector during each movement; and determine the camera position corresponding to the maximum voltage value among all the voltage values ​​as the target position of the camera.

2. The camera focus control system according to claim 1, characterized in that: The transverse beam splitter prism includes: a beam splitter film lens arranged at the midpoint of the transverse beam splitter prism, used for splitting a light source signal incident from the end of the transverse beam splitter prism where the reflective mirror surface is not arranged into a first light signal and a second light signal, wherein the first light signal and the second light signal have the same light phase and are perpendicular to each other, and are respectively emitted to the wafer to be tested and the reflective mirror surface.

3. The camera focus control system according to claim 1, characterized in that: The controller at least includes: a position information receiving socket, a drive instruction output socket, a voltage signal receiving socket and a camera control instruction output socket; The drive motor at least includes: a position information output socket and a drive instruction receiving socket; The position information receiving socket is connected to the position information output socket; The drive instruction output socket is connected to the drive instruction receiving socket; The voltage signal receiving socket is connected to the voltage output socket of the photoelectric detector; The camera control instruction output socket is connected to the camera control instruction receiving socket of the camera.

4. A camera focus control method, characterized in that: A controller used in a camera focus control system according to any one of claims 1 to 3, wherein the camera focus control method comprises: In response to a wafer detection instruction, a driving motor is controlled to drive a camera focus module, so that the camera moves from a fine-adjustment focus starting position to a fine-adjustment focus end position at a preset fine-adjustment step distance, and the camera position of the camera and the voltage value collected by the photodetector are respectively obtained during each movement, wherein the voltage value is a voltage value obtained by the photodetector converting an interference signal, and the interference signal is an optical signal after interference between two reflection signals obtained by the wafer to be tested and the reflection mirror respectively reflecting optical signals with the same optical phase; The camera position corresponding to the maximum voltage value among all the voltage values ​​is determined as the target position of the camera.

5. The camera focus control method according to claim 4, characterized in that: The process of determining the fine-adjustment focus starting position and the fine-adjustment focus ending position includes: Controlling the driving motor to drive the camera focus module, so that the camera moves from a preset focus starting position to a preset focus ending position with a preset coarse adjustment step distance, and respectively obtaining the camera position corresponding to each movement and the wafer image taken by the camera; The two camera positions corresponding to the two clearest wafer images among all the wafer images are respectively determined as the fine-adjustment focus starting position and the fine-adjustment focus ending position.

6. The camera focus control method according to claim 5, characterized in that: The controlling the driving motor to drive the camera focus module so that the camera moves from a preset focus starting position to a preset focus ending position with a preset coarse adjustment step distance, and respectively obtaining the camera position corresponding to each movement and the wafer image taken by the camera, comprises: Determine whether the current position information of the camera is within a preset focus range, where the preset focus range is a range defined by a preset focus starting position and a preset focus ending position; When the current position information of the camera is within the preset focus range, controlling the driving motor to drive the camera focus module to move the camera once with a preset coarse adjustment step distance; In response to receiving the current position information of the camera sent by the driving motor, a control instruction is sent to the camera, wherein the control instruction is a basis for the camera to photograph the wafer to be tested; In response to receiving a wafer image captured by the camera, the position information and the wafer image are stored.

7. The camera focus control method according to claim 5, characterized in that: The process of determining the preset focus starting position and the preset focus ending position includes: Controlling the driving motor to drive the camera focus module to move the camera within a preset range in the vertical direction, and obtaining camera position information and wafer images for each movement; Identifying the clarity of the wafer image corresponding to each movement; Based on the camera position information and the clarity corresponding to each of the wafer images, the camera position information at which the clarity reaches a preset clarity threshold during the process of the camera moving from bottom to top in the vertical direction is determined as the preset focus starting position; the camera position information at which the clarity reaches the preset clarity threshold during the process of the camera moving from bottom to top in the vertical direction is determined as the preset focus end position.

8. A camera focus control device, characterized in that: A controller used in a camera focus control system according to any one of claims 1 to 3, wherein the camera focus control device comprises: A control driving unit is used to control a driving motor to drive a camera focus module in response to a wafer detection instruction, so that the camera moves from a fine-adjustment focus starting position to a fine-adjustment focus end position at a preset fine-adjustment step distance, and obtains the camera position of the camera and a voltage value collected by a photodetector during each movement, wherein the voltage value is a voltage value obtained by the photodetector converting an interference signal, and the interference signal is an optical signal after interference between two reflection signals obtained by the wafer to be tested and the reflection mirror respectively reflecting optical signals with the same optical phase; The target position determination unit is used to determine the camera position corresponding to the maximum voltage value among all the voltage values ​​as the target position of the camera.

Images