Image acquisition system and method using area-array camera flying shooting mode

Abstract

The invention discloses an image acquisition system and method using an area-array camera flying shooting mode. In the system, a pulse type laser provides a laser light source and is used for irradiating the surface of a wafer; the collection optical lens group is used for collecting optical signals such as scattering and reflection of laser beams caused by wafer surface defects and pattern structures, and imaging the wafer surface to the CMOS area-array camera; the wafer carrier drives the wafer to move, so that the CMOS area-array camera can collect and image all areas of the whole wafer; the CMOS area-array camera receives the optical signal, converts the optical signal into a voltage signal, and finally outputs corresponding data to the image acquisition card; the image acquisition card is used for receiving image data from the CMOS area-array camera and carrying out image preprocessing; and finally image processing is completed on the computer. According to the invention, instant high-intensity illumination is realized, motion blur is reduced, equipment power consumption is reduced, and a jelly effect of shooting a moving object image by an area-array camera is eliminated.

Description

Technical Field

[0001] The present invention relates to the field of image acquisition technology, and in particular to an image acquisition system and method using a flying shooting mode of an area array camera. Background Art

[0002] The current image sensors are mainly CCD and CMOS. The basic structure of CCD is a series of MOS capacitors connected in series. The voltage pulse timing on the capacitor controls the generation and change of the semiconductor surface well, thereby realizing the storage and transfer readout of the photogenerated charge signal. Due to the characteristics of signal transfer, the charge transfer speed is very limited, so the imaging speed is not high. In addition, since the capacitors are connected in series, a problem with one capacitor will affect the transmission of the entire row of signals, so the process requirements are high, the yield is low, and the cost is high. Each pixel of CMOS is composed of diodes and transistors. Each pixel is independent of each other. There is no need to move the charge serially during the entire signal transmission process. A problem with a pixel does not affect the performance of other pixels. Therefore, the shortcomings of CCD in signal transmission are overcome, so the process requirements are not very harsh.

[0003] CMOS image sensors can use a rolling shutter for exposure. During operation, the pixel array in the sensor is discharged and exposed row by row from top to bottom, and the image data is output from the sensor after the exposure. Therefore, there is an exposure time difference between pixels in different rows on the sensor. Due to the existence of the exposure time difference, when shooting moving objects, the image will be distorted, forming the so-called "jello effect".

[0004] In the field of semiconductor back-end packaging and testing, the detection accuracy and sensitivity are generally low, usually in the micron level. In the corresponding back-end defect detection, the CMOS / CCD area array camera is used with a low-magnification optical imaging system, and its detection FOV (field of view) will also be large enough. Using the "go-stop-shoot" acquisition method, whether using a global shutter or a rolling shutter, the acquisition of the entire wafer can be completed quickly.

[0005] In the field of semiconductor front-end production, very high detection accuracy and sensitivity are required. At the sub-micron level, even defects of tens of nanometers need to be detected. In the corresponding defect detection, the CMOS area array camera is used with a high-magnification objective lens, and its detection FOV will be very small. If the "go-stop-shoot" image acquisition method is still used, it will take a lot of time to complete the acquisition of the entire wafer, and the detection efficiency is extremely low, which seriously affects the production capacity. At the same time, in the front-end defect detection, the light source power is also a bottleneck. The light energy per unit area is weak and requires a long exposure time. If continuous light illumination is used, the light source is in a waiting state when the wafer moves, and the energy utilization rate of the light source is greatly reduced. Therefore, area array cameras are usually not used to acquire images of the entire wafer, but only for defect re-inspection.

[0006] Patent CN115348394A, exposure device, exposure control method and shooting terminal, adds a liquid crystal light valve between the CMOS image sensor and the lens to solve the problem of uneven exposure caused by the untimely response of the mechanical shutter. However, the light transmittance of the liquid crystal light valve is poor and is not suitable for semiconductor detection. Summary of the invention

[0007] The present invention provides an image acquisition system and method using a flying shooting mode of an area array camera. A pulsed laser beam is used in conjunction with a galvanometer to sequentially expose areas, thereby achieving instantaneous strong light illumination, reducing motion blur, and reducing equipment power consumption. The "jello effect" of images of moving objects captured by an area array camera is eliminated by matching a wafer stage, a laser beam, and a CMOS image sensor through motion control.

[0008] The present invention provides an image acquisition system using a flying shooting method of an area array camera, comprising: a pulsed laser, a collection optical lens group, a wafer stage, a CMOS area array camera, an image acquisition card, a reflector, a reflection light lens group, and a laser scanning galvanometer, wherein:

[0009] A pulsed laser provides a laser light source for irradiating the wafer surface;

[0010] The collection optical lens group is used to collect the scattered laser beam caused by the wafer surface defects and pattern structures, reflect the light signal, and image it to the CMOS area array camera;

[0011] The wafer stage drives the wafer to move, allowing the CMOS area array camera to collect and image all areas of the entire wafer;

[0012] CMOS area array camera receives light signals and converts them into voltage signals, and finally outputs the corresponding data to the image acquisition card;

[0013] Image acquisition card, used to receive image data from CMOS area array camera and perform image preprocessing; finally, image processing is completed on the computer;

[0014] Among them, the image acquisition system includes bright field light path and dark field light path:

[0015] The bright field optical path is that the pulsed laser emits incident light to the reflector, and the light is irradiated to the wafer surface in a near normal line through the reflector and reflected; the reflected light on the wafer surface is then gathered by the reflective light lens group, and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through the cable;

[0016] The dark field optical path uses a pulsed laser to emit incident light at a low angle to illuminate the wafer surface. If there are no protrusions or depressions on the wafer surface, the incident light will be reflected; if there are protrusions or depressions on the wafer surface or wafer pattern structures, part of the incident light will be scattered to form scattered light; the scattered light is collected by the collection optical lens group and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through a cable.

[0017] Furthermore, in the bright field light path and the dark field light path, there are one or more CMOS area array cameras and image acquisition cards, and the CMOS area array cameras and image acquisition cards are arranged correspondingly.

[0018] Furthermore, a galvanometer is provided in the optical path of the pulsed laser, and the galvanometer is used to control the deflection of the laser beam to be incident on the wafer.

[0019] The present invention also provides an image acquisition method using a flying shooting method of an area array camera, comprising the following steps, wherein the image acquisition system comprises a bright field light path and a dark field light path, wherein:

[0020] The bright field optical path is that the pulsed laser emits incident light to the reflector, and the light is irradiated to the wafer surface in a near normal line through the reflector and reflected; the reflected light on the wafer surface is then gathered by the reflective light lens group, and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through the cable;

[0021] The dark field optical path uses a pulsed laser to emit incident light at a low angle to illuminate the wafer surface. If there are no protrusions or depressions on the wafer surface, the incident light will be reflected; if there are protrusions or depressions on the wafer surface or wafer pattern structures, part of the incident light will be scattered to form scattered light; the scattered light is collected by the collection optical lens group and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through the cable;

[0022] Define a×b as the target size of the CMOS area array camera, where:

[0023] Define the length a direction as the X direction of the coordinate system and there are m columns of pixels. The pixel arrangement along the direction of increasing positive horizontal coordinate from the origin of the coordinate system is defined as a1, a2, a3...am in sequence;

[0024] Define the width b direction as the y direction of the coordinate system and there are n rows of pixels. The pixel arrangement along the direction of increasing positive ordinate from the origin of the coordinate system is defined as bn, bn-1, bn-2...b1 in sequence;

[0025] The x-direction of the coordinate system is the wafer moving direction, and the y-direction of the coordinate system is the rolling shutter exposure direction of the CMOS area array camera:

[0026] When the wafer moves in the direction from a1 to am, the CMOS area array camera rolling shutter exposure direction is forward exposure from b1 to bn;

[0027] When the wafer moves in the direction from am to a1 in sequence, the rolling shutter exposure direction of the CMOS area array camera is reverse exposure from bn to b1.

[0028] Furthermore, the moving speed of the wafer stage satisfies:

[0029]

[0030] Among them, L is the length of a frame image, and L is expressed as:

[0031]

[0032] c is the chip pixel size of the CMOS area array camera, m is the number of pixels in the X direction of the CMOS area array camera, q is the number of CMOS area array cameras, p is the magnification of the microscope objective, f is the frame rate of the CMOS area array camera, and t is the time of one frame.

[0033] Furthermore, the pulsed laser frequency S satisfies

[0034] S≥f×n

[0035] Where n is the number of pixels in the Y direction of the CMOS area array camera, and f is the frame rate of the CMOS area array camera.

[0036] Furthermore, a galvanometer is provided in the optical path of the pulsed laser, and the galvanometer is used to control the deflection of the laser beam to be incident on the wafer.

[0037] Furthermore, in the bright field light path and the dark field light path, there are one or more CMOS area array cameras and image acquisition cards, and the CMOS area array cameras and image acquisition cards are arranged correspondingly.

[0038] The beneficial effects of the present invention are:

[0039] 1. The present invention utilizes the rolling shutter exposure of the CMOS sensor camera and adopts a pulsed laser beam in conjunction with a galvanometer to expose areas in sequence, which can achieve instantaneous strong light illumination and reduce equipment power consumption; at the same time, the strong laser pulse output and the rolling shutter camera exposure frequency are synchronized to achieve effective utilization of laser energy and ultra-short exposure time, thereby reducing motion blur.

[0040] 2. The moving speed of the wafer stage of the present invention matches the exposure row and column of the CMOS image sensor, which is convenient for subsequent image processing.

[0041] 3. The present invention matches the wafer stage, laser beam, and CMOS image sensor through motion control, so that the direction of each row of the CMOS image sensor is the same as the movement direction of the wafer. When using the CMOS sensor camera, the spatial arrangement makes the exposure direction parallel to the movement direction of the stage, eliminating the "jelly effect" of the area array camera in taking images of moving objects.

[0042] 4. Multiple CMOS area array cameras can be used for field of view stitching on the optical path to solve the image distortion problem by optimizing the layout direction of the CMOS image sensor. When capturing images of the wafer, the wafer does not need to stop when moving, and continuous image capture can be achieved in a flying manner, thereby improving detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0044] Figure 1 The figure is a schematic diagram of a single image acquisition by the CMOS area array camera of the present invention.

[0045] Figure 2 It is a pixel row and column diagram of the image of the present invention.

[0046] Figure 3 It is a schematic diagram of the positive exposure of the present invention.

[0047] Figure 4 It is a schematic diagram of reverse exposure of the present invention.

[0048] Figure 5 Schematic diagram of the dark field light path of the present invention.

[0049] Figure 6 It is a schematic diagram of the bright field light path of the present invention.

[0050] Figure 7 Schematic diagram of the dark field multi-camera optical path of the present invention.

[0051] Figure 8 It is a schematic diagram of the bright field multi-camera optical path of the present invention. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0053] The technical solutions provided by various embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0054] like Figure 5 , 6 As shown, the present invention provides an image acquisition system using a flying shooting method of an area array camera, comprising: a pulsed laser, a collection optical lens group, a wafer stage, a CMOS area array camera, an image acquisition card, a reflector, a reflective light lens group, and a laser scanning galvanometer, wherein:

[0055] A pulsed laser provides a laser light source for irradiating the wafer surface;

[0056] The collection optical lens group is used to collect the scattered and reflected light signals of the laser beam caused by the wafer surface defects and pattern structures, and image them to the CMOS area array camera. When there are no defects on the wafer surface, the incident laser beam will be reflected and the collection optical lens group will not collect the scattered light.

[0057] The wafer stage drives the wafer to move, allowing the CMOS area array camera to collect scattered light conditions of the entire wafer;

[0058] CMOS area array camera receives light signals and converts them into voltage signals, and finally outputs the corresponding data to the image acquisition card;

[0059] Image acquisition card, used to receive image data from CMOS area array camera and perform image preprocessing; finally, image processing is completed on the computer;

[0060] Among them, the image acquisition system includes bright field light path and dark field light path:

[0061] The bright field light route uses a pulsed laser to emit incident light to a reflector, which then irradiates the wafer surface in a near-normal direction and reflects it. The reflected light from the wafer surface is then gathered by a reflective light lens group and finally imaged to a CMOS area array camera, and the data is transmitted to an image acquisition card via a cable.

[0062] Dark field optical routing uses a pulsed laser to emit incident light at a low angle to illuminate the wafer surface. If there are no protrusions or depressions on the wafer surface, the incident light will be reflected; if there are protrusions or depressions or wafer pattern structures on the wafer surface, part of the incident light will be scattered to form scattered light; the scattered light is collected by the collection optical lens group and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card via cables.

[0063] like Figure 7 , 8 As shown, in the bright field light path and the dark field light path, there are one or more CMOS area array cameras and image acquisition cards, and the CMOS area array cameras and image acquisition cards are set accordingly.

[0064] In this embodiment, a pulsed laser is provided with a galvanometer in its optical path, and the galvanometer is used to control the deflection of the laser beam to achieve rapid sequential exposure, instantaneous strong light illumination, and reduce motion blur.

[0065] The present invention also provides an image acquisition method using a flying shooting method of an area array camera, comprising the following steps, wherein the image acquisition system comprises a bright field light path and a dark field light path, wherein:

[0066] The bright field light route uses a pulsed laser to emit incident light to a reflector, which then irradiates the wafer surface in a near-normal direction and reflects it. The reflected light from the wafer surface is then gathered by a reflective light lens group and finally imaged to a CMOS area array camera, and the data is transmitted to an image acquisition card via a cable.

[0067] Dark field optical routing uses a pulsed laser to emit incident light at a low angle to illuminate the wafer surface. If there are no protrusions or depressions on the wafer surface, the incident light will be reflected; if there are protrusions or depressions on the wafer surface or wafer pattern structures, part of the incident light will be scattered to form scattered light; the scattered light is collected by the collection optical lens group and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through cables;

[0068] like Figure 1 , 2 As shown, Figure 1 There are 3 stripes with different gray values ​​in the feature. The actual image is composed of Figure 2 The pixel rows and columns shown in the figure are composed of a×b, and the target size of the CMOS area array camera is defined as:

[0069] Define the length a direction as the X direction of the coordinate system and there are m columns of pixels. The pixel arrangement along the direction of increasing positive horizontal coordinate from the origin of the coordinate system is defined as a1, a2, a3...am in sequence;

[0070] Define the width b direction as the y direction of the coordinate system and there are n rows of pixels. The pixel arrangement along the direction of increasing positive ordinate from the origin of the coordinate system is defined as bn, bn-1, bn-2...b1 in sequence;

[0071] The x-direction of the coordinate system is the wafer moving direction, and the y-direction of the coordinate system is the rolling shutter exposure direction of the CMOS area array camera:

[0072] like Figure 3 As shown, when the wafer moves in the direction from a1 to am, the rolling shutter exposure direction of the CMOS area array camera is in the positive exposure direction from b1 to bn;

[0073] like Figure 4 As shown, when the wafer moves in the direction from am to a1 in sequence, the rolling shutter exposure direction of the CMOS area array camera is reverse exposure from bn to b1.

[0074] The CMOS area array camera with rolling shutter exposure exposes and collects images row by row in sequence. The exposure and collection time of each row is very short. During the collection, there is a relative displacement between the wafer and the camera. By controlling the movement speed of the wafer, the "jelly effect" of the image can be eliminated, forming a Figure 2 Schematic normal image.

[0075] In this embodiment, the moving speed of the wafer stage satisfies:

[0076]

[0077] Among them, L is the length of a frame image, and L is expressed as:

[0078]

[0079] c is the pixel size of the CMOS area array camera chip, m is the number of pixels in the X direction of the CMOS area array camera, q is the number of CMOS area array cameras, p is the magnification of the microscope objective lens, f is the frame rate of the CMOS area array camera, and t is the time of 1 frame

[0080] At the same time, the pulsed laser frequency S satisfies

[0081] S≥f×n

[0082] Where n represents the number of pixels in the Y direction of the CMOS area array camera, and f represents the frame rate of the CMOS area array camera. The relationship and definition of the above parameters are shown in Table 1.

[0083] Table 1

[0084]

[0085] For example, a camera with a resolution of 2448x 2048, a frame rate of 150fps, a camera chip pixel size of 5μm*5μm, and a microscope objective lens of 30x; when the number of cameras is 1, the calculation results are shown in Table 2:

[0086] Table 2

[0087]

[0088] When the number of cameras is 2, the calculation results are shown in Table 3:

[0089] Table 3

[0090]

[0091] It can be seen that when the number of cameras increases, the movement speed of the stage will also increase, which means that the image acquisition efficiency and equipment detection efficiency can be improved.

[0092] In addition, in the bright field optical path and the dark field optical path, there is one or more CMOS area array cameras and image acquisition cards, and the CMOS area array cameras and image acquisition cards are set accordingly. Figure 7 As shown in the figure, it is a schematic diagram of the dark field multi-camera optical path. Figure 8 The figure shows a schematic diagram of the bright field multi-camera optical path.

[0093] In summary, the present invention uses a pulsed laser beam in conjunction with a galvanometer to expose areas in sequence, which can achieve instantaneous strong light illumination and reduce equipment power consumption; at the same time, the strong laser pulse output and the rolling shutter camera row exposure frequency are synchronized to achieve effective use of laser energy and ultra-short exposure time, reducing motion blur. The movement speed of the wafer stage matches the exposure rows and columns of the CMOS image sensor to facilitate subsequent image processing. By matching the wafer stage, laser beam, and CMOS image sensor through motion control, the direction of each row of the CMOS image sensor is the same as the direction of wafer movement, eliminating the "jelly effect" of the array camera taking images of moving objects. Multiple CMOS array cameras can be used for field of view splicing on the optical path, and the image distortion problem can be solved by optimizing the layout direction of the CMOS image sensor; when capturing images of the wafer, the wafer movement does not need to stop, and continuous image capture in a flying manner is achieved to improve detection efficiency.

[0094] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. An image acquisition system using a flying camera, characterized in that: include: Pulsed laser, collection optical lens group, wafer stage, CMOS array camera, image acquisition card, reflector, reflected light lens group, laser scanning galvanometer, including: A pulsed laser provides a laser light source for irradiating the wafer surface; The collection optical lens group is used to collect the scattered laser beam caused by the wafer surface defects and pattern structures, reflect the light signal, and image it to the CMOS area array camera; The wafer stage drives the wafer to move, allowing the CMOS area array camera to collect scattered light conditions of the entire wafer; CMOS area array camera receives light signals and converts them into voltage signals, and finally outputs the corresponding data to the image acquisition card; Image acquisition card, used to receive image data from CMOS area array camera and perform image preprocessing; finally, image processing is completed on the computer; Among them, the image acquisition system includes bright field light path and dark field light path: The bright field optical path is that the pulsed laser emits incident light to the reflector, and the light is irradiated to the wafer surface in a near normal line through the reflector and reflected; the reflected light on the wafer surface is then gathered by the reflective light lens group, and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through the cable; The dark field optical path uses a pulsed laser to emit incident light at a low angle to illuminate the wafer surface. If there are no protrusions or depressions on the wafer surface, the incident light will be reflected; if there are protrusions or depressions on the wafer surface or wafer pattern structures, part of the incident light will be scattered to form scattered light; the scattered light is collected by the collection optical lens group and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through a cable.

2. The image acquisition system using a flying shooting method of an area array camera according to claim 1, characterized in that: In the bright field light path and the dark field light path, there are one or more CMOS area array cameras and image acquisition cards, and the CMOS area array cameras and image acquisition cards are arranged correspondingly.

3. The image acquisition system using a flying shooting method of an area array camera according to claim 1, characterized in that: A galvanometer is arranged in the optical path of the pulsed laser, and the laser beam is deflected and incident on the wafer by the galvanometer.

4. An image acquisition method using a flying camera, characterized in that: The method comprises the following steps, wherein the image acquisition system comprises a bright field light path and a dark field light path, wherein: The bright field optical path is that the pulsed laser emits incident light to the reflector, and the light is irradiated to the wafer surface in a near normal line through the reflector and reflected; the reflected light on the wafer surface is then gathered by the reflective light lens group, and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through the cable; The dark field optical path uses a pulsed laser to emit incident light at a low angle to illuminate the wafer surface. If there are no protrusions or depressions on the wafer surface, the incident light will be reflected; if there are protrusions or depressions on the wafer surface or wafer pattern structures, part of the incident light will be scattered to form scattered light; the scattered light is collected by the collection optical lens group and finally imaged to the CMOS area array camera, and the data is transmitted to the image acquisition card through the cable; Define a×b as the target size of the CMOS area array camera, where: Define the length a direction as the X direction of the coordinate system and there are m columns of pixels. The pixel arrangement along the direction of increasing positive horizontal coordinate from the origin of the coordinate system is defined as a1, a2, a3...am in sequence; Define the width b direction as the y direction of the coordinate system and there are n rows of pixels. The pixel arrangement along the direction of increasing positive ordinate from the origin of the coordinate system is defined as bn, bn-1, bn-2...b1 in sequence; The x-direction of the coordinate system is the wafer moving direction, and the y-direction of the coordinate system is the rolling shutter exposure direction of the CMOS area array camera: When the wafer moves in the direction from a1 to am, the CMOS area array camera rolling shutter exposure direction is forward exposure from b1 to bn; When the wafer moves in the direction from am to a1 in sequence, the rolling shutter exposure direction of the CMOS area array camera is reverse exposure from bn to b1.

5. The image acquisition method using a flying camera according to claim 4, characterized in that: The moving speed of the wafer stage meets the following requirements: Among them, L is the length of a frame image, and L is expressed as: c is the chip pixel size of the CMOS area array camera, m is the number of pixels in the X direction of the CMOS area array camera, q is the number of CMOS area array cameras, p is the magnification of the microscope objective, f is the frame rate of the CMOS area array camera, and t is the time of one frame.

6. The image acquisition method using a flying camera according to claim 4, characterized in that: The pulsed laser frequency S satisfies S≥f×n Where n is the number of pixels in the Y direction of the CMOS area array camera, and f is the frame rate of the CMOS area array camera.

7. The image acquisition method using a flying camera according to claim 4, characterized in that: A galvanometer is arranged in the optical path of the pulsed laser, and the laser beam is deflected and incident on the wafer by the galvanometer.

8. The image acquisition method using a flying camera according to claim 4, characterized in that: In the bright field light path and the dark field light path, there are one or more CMOS area array cameras and image acquisition cards, and the CMOS area array cameras and image acquisition cards are arranged correspondingly.

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