Thermal imaging method for crack and hole detection in semiconductor devices

Abstract

The present disclosure relates to a system comprising: a first laser light source configured to emit laser light; a first focusing lens configured to direct the laser light from the first laser light source onto a first face of a workpiece; a thermal camera configured to capture a thermal image of a second face of the workpiece orthogonal to the first face; and a processor configured to identify a crack in the workpiece based on the thermal image.

Description

[0001] Cross-reference of related applications

[0002] This application claims priority to provisional patent application No. 63 / 547,147, filed November 3, 2023, the disclosure of which is hereby incorporated by reference. Technical Field

[0003] This disclosure relates to semiconductor manufacturing, and more specifically to inspection processes for detecting defects in semiconductor and solid-state battery manufacturing. Background Technology

[0004] The evolution of the electronics manufacturing industry places increasingly higher demands on yield management, and specifically on metrology and inspection systems. Critical dimensions continue to shrink, and the industry needs to reduce the time spent achieving high-yield, high-value production. Minimizing the total time from detecting a yield problem to resolving it maximizes the return on investment for electronics manufacturers.

[0005] Semiconductor devices, such as logic and memory devices, typically involve processing semiconductor wafers using numerous manufacturing processes to form the various features and multiple layers of the semiconductor device. For example, photolithography is a semiconductor manufacturing process involving transferring a pattern from a photomask to a photoresist disposed on a semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. The arrangement of multiple semiconductor devices manufactured on a single semiconductor wafer can be divided into individual semiconductor devices.

[0006] Inspection processes are used at various stages of electronics manufacturing to detect defects in wafers, electronic devices, or circuits, thereby promoting higher yields and, consequently, higher profits in the manufacturing process. Inspection has always been a crucial part of manufacturing electronic devices, such as integrated circuits (ICs) and printed circuit boards (PCBs), including assembled PCBs. However, as emerging markets (e.g., electric vehicles and others) strive for higher reliability requirements, the detection of structural defects in smaller packaged semiconductor devices has become necessary, as even relatively small defects can cause unintended failures of the device throughout its entire lifecycle.

[0007] During the dicing process of separating individual semiconductor devices from a single wafer, cracks may form along the edges surrounding the perimeter of the semiconductor device. To identify these cracks, a single sidewall of a near-infrared (NIR) or short-wave infrared (SWIR) illumination device is used, and a camera captures an image on the opposite sidewall. The NIR or SWIR light is transmitted through the semi-transparent semiconductor device, and the crack casts a shadow that can be detected in the image captured by the camera on the opposite side. However, this detection method is limited to semi-transparent semiconductor devices and is not applicable to opaque semiconductor devices.

[0008] Therefore, a method is needed to detect defects in opaque semiconductor devices. Summary of the Invention

[0009] Embodiments of this disclosure provide a system comprising: a first laser source configured to emit a laser; a first focusing lens configured to direct the laser from the first laser source onto a first surface of a workpiece; a thermal camera configured to capture a thermal image of a second surface of the workpiece, wherein the second surface is orthogonal to the first surface; and a processor configured to identify cracks in the workpiece based on the thermal image.

[0010] In some embodiments, the system further includes a first scanning mirror configured to guide the laser from the first laser source to scan across the first surface of the workpiece.

[0011] In some embodiments, the system further includes a stage. The workpiece can be placed on the stage, and the stage is movable to allow the laser from the first laser source to scan across the first surface of the workpiece.

[0012] In some embodiments, the first surface has a smaller cross-sectional area than the second surface. The laser may have a diameter less than or equal to the thickness of the first surface of the workpiece.

[0013] In some embodiments, the first surface has a larger cross-sectional area than the second surface. The first focusing lens may be configured to direct the laser onto the first surface of the workpiece near the edge adjacent to both the first and second surfaces.

[0014] In some embodiments, the system further includes: a second laser source configured to emit a laser; and a second focusing lens configured to direct the laser from the second laser source to a position on the first surface of the workpiece offset from the laser from the first laser source.

[0015] In some embodiments, the system further includes: a third laser source configured to emit laser light; and a third focusing lens configured to direct the laser light from the third laser source onto a third surface of the workpiece. The third surface may be orthogonal to the second surface and parallel to the first surface.

[0016] In some embodiments, the system further includes: a fourth laser source configured to emit laser light; and a fourth focusing lens configured to direct the laser light from the fourth laser source onto a fourth surface of the workpiece. The fourth surface may be orthogonal to the second surface and the first surface.

[0017] In some embodiments, the system further includes: a fifth laser source configured to emit laser light; and a fifth focusing lens configured to direct the laser light from the fifth laser source onto a fifth surface of the workpiece. The fifth surface may be orthogonal to the second surface and parallel to the fourth surface.

[0018] In some embodiments, the thermal camera is a forward-looking infrared (FLIR) camera.

[0019] In some embodiments, the processor is configured to identify the crack in the workpiece based on the thermal image by: obtaining the intensity of each pixel of the thermal image along the edges of the workpiece adjacent to the first and second surfaces; deriving a gradient map using the intensity of each pixel of the thermal image, the gradient map representing the spatial derivative of the temperature distribution along the edges of the workpiece adjacent to the first and second surfaces; and determining that the crack in the workpiece exists where there is a peak in the gradient map.

[0020] Another embodiment of this disclosure provides a method comprising: emitting a laser from a first laser source; using a first focusing lens to guide the laser from the first laser source onto a first surface of a workpiece; using a thermal camera to capture a thermal image of a second surface of the workpiece, wherein the second surface is orthogonal to the first surface; and using a processor to identify cracks in the workpiece based on the thermal image.

[0021] In some embodiments, the method may further include using a first scanning mirror to scan the laser from the first laser source across the first surface of the workpiece.

[0022] In some embodiments, the method may further include moving a stage relative to the laser to scan the laser from the first laser source across the first surface of the workpiece. The workpiece may be placed on the stage.

[0023] In some embodiments, the method may further include rotating the stage about an axis perpendicular to the laser light from the first laser source, such that the laser light from the first laser source is guided by the first focusing lens onto a fourth surface of the workpiece. The fourth surface may be orthogonal to both the second surface and the first surface.

[0024] In some embodiments, the method may further include: emitting a laser from a second laser source; and using a second focusing lens to guide the laser from the second laser source to a position on the first surface of the workpiece that is offset from the laser from the first laser source.

[0025] In some embodiments, the method may further include: emitting laser light from a third laser source; and using a third focusing lens to guide the laser light from the third laser source onto a third surface of the workpiece. The third surface may be orthogonal to the second surface and parallel to the first surface.

[0026] In some embodiments, the method may further include: emitting laser light from a fourth laser source; and using a fourth focusing lens to guide the laser light from the fourth laser source onto a fourth surface of the workpiece. The fourth surface may be orthogonal to the second surface and the first surface.

[0027] In some embodiments, the method may further include: emitting laser light from a fifth laser source; and using a fifth focusing lens to guide the laser light from the fifth laser source onto a fifth surface of the workpiece. The fifth surface may be orthogonal to the second surface and parallel to the fourth surface.

[0028] In some embodiments, using the processor to identify the crack in the workpiece based on the thermal image includes: obtaining the intensity of each pixel of the thermal image along the edges of the workpiece adjacent to the first and second surfaces; deriving a gradient map using the intensity of each pixel of the thermal image, the gradient map representing the spatial derivative of the temperature distribution along the edges of the workpiece adjacent to the first and second surfaces; and determining that the crack in the workpiece exists at the location of a peak in the gradient map. Attached Figure Description

[0029] For a more complete understanding of the nature and purpose of this disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0030] Figure 1 This is a side view of a system according to an embodiment of the present disclosure;

[0031] Figure 2A This is a top perspective view of an exemplary workpiece according to an embodiment of this disclosure;

[0032] Figure 2B yes Figure 2A A bottom-view perspective view of an exemplary workpiece;

[0033] Figure 3 This is a top view of a system according to an embodiment of the present disclosure;

[0034] Figure 4A This is a side view of a system according to another embodiment of the present disclosure;

[0035] Figure 4B yes Figure 4A A top view of the system;

[0036] Figure 5 This is a top view of a system according to an embodiment of the present disclosure;

[0037] Figure 6 This is a top view of a system according to another embodiment of the present disclosure;

[0038] Figure 7 This is a flowchart of a method according to an embodiment of the present disclosure;

[0039] Figure 8 This is a flowchart of a method according to another embodiment of the present disclosure;

[0040] Figure 9 This is a flowchart of a method according to another embodiment of the present disclosure;

[0041] Figure 10 This is a flowchart of a method according to another embodiment of the present disclosure; and

[0042] Figure 11 This is a flowchart of a method according to another embodiment of the present disclosure. Detailed Implementation

[0043] Although the claimed object will be described with reference to specific embodiments, other embodiments (including those that do not provide all the benefits and features set forth herein) are also within the scope of this disclosure. Various structural, logical, procedural, and electronic changes may be made without departing from the scope of this disclosure. Therefore, the scope of this disclosure is defined only by reference to the appended claims.

[0044] Embodiments of this disclosure provide a system 100, such as Figure 1 The system 100 may be an inspection or measurement system for processing or picking workpiece 110. Workpiece 110 may be one or more layers of a semiconductor wafer, die, substrate, IC, PCB, flat panel display (FPD), or solid-state battery or other type of device. Workpiece 110 may be opaque or may contain one or more opaque layers. Alternatively, workpiece 110 may be optically transparent, but may at least partially absorb laser light. As mentioned herein, workpiece 110 may have a six-sided structure, including a first side 111, a second side 112, a third side 113, a fourth side 114, a fifth side 115, and a sixth side 116, as shown below. Figure 2A and Figure 2BThe image is shown in the image. Alternatively, the workpiece 110 may be a cylindrical structure, wherein the first surface 111 is a continuous annular surface. The workpiece 110 may be mounted on a stage 105. For example, a sixth surface 116 may be mounted on the stage 105. The stage 105 may be configured to translate (i.e., move in the X, Y, and / or Z directions) and / or rotate (e.g., along the Z-axis) to change the orientation of the workpiece 110 relative to other elements of the system 100.

[0045] System 100 may include a first laser source 121. The first laser source 121 may be a laser diode or other laser source configured to emit laser light. The laser may be a pulsed laser or a continuous laser beam. The first laser source 121 may be coupled to a first optical fiber 131. The first optical fiber 131 may guide the laser emitted by the first laser source 121 to a first collimator 141 to generate a first laser beam 151. The first laser source 121 may be configured to generate a first laser beam 151 having a wavelength that can be efficiently absorbed by the workpiece 110 and having sufficient power to heat the material of the workpiece 110 to one or more °C. For example, the first laser beam 151 may have a wavelength in the visible or near-IR spectrum and have a power of several watts. In the example, when the workpiece 110 of the silicon wafer is transparent to SWIR imaging at wavelengths of about 1100 nm to about 1300 nm, the first laser source 121 may be configured to generate a first laser beam 151 having a wavelength of about 400 nm to 950 nm to be absorbed by the workpiece 110 and heat the workpiece 110.

[0046] System 100 may further include a first focusing lens 161. In some embodiments, the first focusing lens 161 may be a flat-field focusing (f-theta) lens or other types of lens. The first focusing lens 161 may be configured to guide a first laser beam 151 onto a first surface 111 of workpiece 110. For example, the first laser beam 151 may be guided along an edge of workpiece 110 adjacent to the first surface 111 and the second surface 112. The edge of workpiece 110 may include the edge itself adjacent to the first surface 111 and the second surface 112 and / or a peripheral region along the edge, the peripheral region being, for example, less than 1 mm wide. The first focusing lens 161 may guide a laser spot from the first laser beam 151 onto the first surface 111 of workpiece 110. In some embodiments, the diameter of the laser spot may be less than or equal to the thickness of the first surface 111. For example, the diameter of the laser spot may be from 24 µm to 750 µm. By directing the first laser beam 151 onto the first surface 111 of the workpiece 110, heat can be generated from the laser spot into the workpiece 110 in a non-uniform temperature distribution. For example, the temperature distribution can indicate one or more temperature variations (e.g., 10°C or more or 100°C) in the workpiece 110 based on the first laser beam 151.

[0047] System 100 may further include a thermal camera 170. The thermal camera 170 may be a forward-looking infrared (FLIR) camera or other type of camera. The thermal camera 170 may be sensitive to thermal radiation emitted by the workpiece. For example, the thermal camera 170 may have a wavelength sensitivity range covering a portion of the MWIR to LWIR range (which may be 3 µm to 15 µm). The thermal camera 170 may be directed toward a second surface 112 of the workpiece 110. For example, the field of view of the thermal camera 170 may cover the second surface 112 of the workpiece 110 or a portion of the second surface of the workpiece 110. The second surface 112 may be orthogonal to the first surface 111 of the workpiece 110. In other words, the first surface 111 and the second surface 112 may be adjacent surfaces of the workpiece 110 connected at their edges. The thermal camera 170 may be configured to capture a thermal image 171 of the second surface 112 of the workpiece 110. Specifically, the heat generated on the first surface 111 by the laser spot from the first laser beam 151 may have a non-uniform temperature distribution that extends into the workpiece 110. Therefore, the thermal image 171 may reflect a non-uniform temperature distribution on the second surface 112 of the workpiece 110 (e.g., the highest temperature is found at the location of the laser spot on the edge of the second surface 112, and the temperature decreases away from the edge adjacent to the first surface 111 and along said edge).

[0048] System 100 may further include processor 175. Processor 175 may include a microprocessor, microcontroller, or other device.

[0049] Processor 175 may be coupled to components of system 100 in any suitable manner (e.g., via one or more transmission media, which may include wired and / or wireless transmission media) such that processor 175 can receive output. Processor 175 may be configured to perform certain functions using the output. Inspection tools may receive instructions or other information from processor 175. Processor 175 may optionally communicate electronically with another inspection tool, metrology tool, repair tool, or re-inspection tool (not specified) to receive additional information or send instructions.

[0050] Processor 175 may be part of various systems, including personal computer systems, graphics computers, mainframe computer systems, workstations, network appliances, Internet appliances, or other devices. A subsystem or system may also include any suitable processor known in the art, such as a parallel processor. Additionally, the subsystem or system may include a platform with high-speed processing and software as a standalone or network-linked tool. Processor 175 may be located in system 100 or another device or otherwise become part of system 100 or another device. In an example, processor 175 may be part of a standalone control unit or in a centralized quality control unit. Multiple processors 175 may be used to define multiple subsystems of system 100.

[0051] In practice, processor 175 can be implemented by any combination of hardware, software, and firmware. Furthermore, its functions as described herein can be performed by a single unit or divided among different components, each of which can in turn be implemented by any combination of hardware, software, and firmware. Program code or instructions that enable processor 175 to perform various methods and functions can be stored in a readable storage medium (e.g., memory).

[0052] If system 100 comprises more than one subsystem, then different processors 175 can be coupled to each other to enable the transmission of images, data, information, instructions, etc., between the subsystems. For example, a subsystem can be coupled to an additional subsystem via any suitable transmission medium that can contain any suitable wired and / or wireless transmission medium known in this art. Two or more such subsystems can also be effectively coupled by sharing a computer-readable storage medium (not shown).

[0053] Processor 175 may be configured to perform certain functions using the outputs of system 100 or other outputs. For example, processor 175 may be configured to send outputs to an electronic data storage unit or another storage medium. Processor 175 may be further configured as described herein.

[0054] Processor 175 may be configured according to any of the embodiments described herein. Processor 175 may also be configured to perform other functions or additional steps using the output of system 100 or using images or data from other sources.

[0055] Processor 175 can be communicatively coupled to any of the various components or subsystems of system 100 in any manner known in the art. Furthermore, processor 175 can be configured to receive and / or acquire data or information (e.g., inspection results from an inspection system (e.g., a re-inspection tool), a remote database containing design data, and the like) from other systems via a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium can serve as a data link between processor 175 and other subsystems of system 100 or systems external to system 100. The various steps, functions, and / or operations of system 100, as well as the methods disclosed herein, are implemented by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controls / switches, microcontrollers, or computing systems. Program instructions implementing the methods (e.g., the methods described herein) can be transmitted via a carrier medium or stored on a carrier medium. The carrier medium may include storage media such as read-only memory, random access memory, magnetic disk or optical disk, non-volatile memory, solid-state memory, magnetic tape, and the like. The carrier medium may include transmission media, such as wires, cables, or wireless transmission links. For example, the various steps described throughout this disclosure may be implemented by a single processor 175 (or computer subsystem), or alternatively by multiple processors 175 (or multiple computer subsystems). Furthermore, different subsystems of system 100 may comprise one or more computing or logic systems. Therefore, the foregoing description should not be construed as a limitation of this disclosure but is merely illustrative.

[0056] The processor 175 can communicate electronically with the first laser source 121. For example, the processor 175 can be configured to send instructions to the first laser source 121 to emit a laser, which generates a first laser beam 151 guided by a first focusing lens 161 onto a first surface 111 of the workpiece 110.

[0057] The processor 175 can communicate electronically with the stage 105. For example, the processor 175 can be configured to send instructions to the motors or actuators of the stage 105 to cause the stage 105 to translate or rotate (e.g., in...). Figure 1 and Figure 3 (In the direction shown in the image), this causes the first laser beam 151 to scan across the first surface 111 of the workpiece 110.

[0058] In some embodiments, system 100 may further include a first scanning mirror 181. The first scanning mirror 181 may be disposed between the first collimator 141 and the first focusing lens 161. The first scanning mirror 181 may be configured to move or rotate (e.g., as shown in the image). Figure 3(As shown in the image) to change the direction of the first laser beam 151 passing through the first focusing lens 161. The processor 175 can be configured to send instructions to move the first scanning mirror 181. By moving the first scanning mirror 181, the laser spot from the first laser beam 151 can scan across the first surface 111 of the workpiece 110.

[0059] Processor 175 can communicate electronically with thermal camera 170. For example, processor 175 can be configured to send instructions to thermal camera 170 to capture one or more thermal images 171 of the second surface 112 of workpiece 110. Thermal camera 170 can be configured to capture one or more thermal images 171 of the second surface 112 of workpiece 110 synchronously with a first laser beam 151 directed at the first surface 111 of workpiece 110. For example, thermal camera 170 can capture one or more thermal images 171 of the second surface 112 of workpiece 110 within a fraction of a second after the first laser source 121 is turned off. The specific timing of capturing one or more thermal images 171 may depend on the nature of the first laser source 121 and the thermal conductivity of workpiece 110.

[0060] Processor 175 can be configured to determine the presence of crack 117 in workpiece 110 based on thermal image 171. Crack 117 may extend from first surface 111 into workpiece 110 (e.g., across second surface 112 or below second surface 112 near the edge adjacent to first surface 111 and second surface 112), such as... Figure 3 The processor 175 can be configured to obtain the intensity of each pixel of a thermal image along the edges of the workpiece 110 adjacent to the first surface 111 and the second surface 112, the edges of which may include the edge itself and the peripheral surface of the second surface 112 adjacent to the edge (e.g., an area of ​​1 mm or less). Based on the heat generated on the first surface 111 by the laser spot from the first laser beam 151, the intensity of the pixel may correspond to the temperature of the region of the second surface 112 of the workpiece 110. The processor 175 can be configured to derive a gradient map using the intensity of each pixel of the thermal image 171, the gradient map representing the spatial derivative of the temperature distribution along the edges of the workpiece 110 adjacent to the first surface 111 and the second surface 112. For example, the intensity of each pixel along the edges of the workpiece 110 may be normalized based on the temperature distribution. Based on the proximity to the laser spot, defect-free portions of the workpiece 110 may have a smooth transition in the temperature distribution or gradient map. Cracks 117 or defects in the workpiece 110 may exhibit spikes or peaks compared to the gradients of neighboring pixels. Processor 175 can be configured to determine that a crack 117 in workpiece 110 exists at a peak in the gradient map. Processor 175 can use edge detection algorithms or other algorithms to identify the peak in the gradient map. Therefore, crack 117 and other defects in workpiece 110 can be identified.

[0061] The size of the identifiable crack 117 may depend on the resolution of the thermal camera 170. For example, a thermal camera 170 with 50 µm pixels may be used to detect cracks 117 with a thickness of less than 1 µm. In some embodiments, a thermal camera 170 with a pixel resolution of 5 to 200 µm may be used to detect cracks 117 as thin as 100 nm.

[0062] Although crack 117 is described in workpiece 110, system 100 can also be used to detect other types of defects in other types of workpieces. For example, system 100 can be used to detect air gaps in wafer-to-wafer and die-to-wafer bonding, open circuits in metal lines of PCBs or FPDs, cracks in different layers constituting solid-state batteries or embedded semiconductor dies, delamination on PCBs, or other application scenarios, and is not limited herein.

[0063] In some embodiments, the first surface 111 may have a smaller cross-sectional area than the second surface 112. For example, as Figure 1 As shown, the first surface 111 can correspond to the side wall of the workpiece 110, and the second surface 112 can correspond to the top surface of the workpiece 110. For example... Figure 3 As shown, the first focusing lens 161 can be configured to guide the first laser beam 151 onto the first surface 111 of the workpiece 110 with a laser spot having a diameter less than or equal to the thickness of the first surface 111. Therefore, the laser spot from the first laser beam 151 can illuminate a large portion of the thickness of the first surface 111. By moving the stage 105 or the first scanning mirror 181, the first laser beam 151 can be scanned across the first surface 111 of the workpiece 110 to generate heat along the thickness of the first surface 111.

[0064] The first laser source 121 may operate in continuous wave (CW) mode in conjunction with continuous scanning of the first scanning mirror 181 or the stage 105, or it may operate in pulse mode or quasi-continuous wave (QCW) mode, wherein the first scanning mirror 181 or the stage 105 performs discrete steps between pulses to illuminate discrete points on the workpiece 110.

[0065] In some embodiments, the first surface 111 may have a larger cross-sectional area than the second surface 112. For example, as Figure 4A As shown, the first surface 111 may correspond to the top surface of the workpiece 110, and the second surface 112 may correspond to the side wall of the workpiece 110. Alternatively, the first surface 111 may correspond to the bottom surface of the workpiece 110. Figure 4BAs shown, a first focusing lens 161 can be configured to guide a first laser beam 151 onto a first surface 111 of a workpiece 110 near the edges adjacent to the first surface 111 and the second surface 112. By moving the stage 105 or the first scanning mirror 181, the first laser beam 151 can scan across the first surface 111 of the workpiece 110 to generate heat near the edges adjacent to the first surface 111 and the second surface 112. In some embodiments, a thermal camera 170 can be guided at the first surface 111 or the second surface 112 to capture one or more thermal images 171. Alternatively, the thermal camera 170 can be arranged at an angle, wherein at least a portion of both the first surface 111 and the second surface 112 of the workpiece 110 is within the field of view of the thermal camera 170, such that one or more thermal images 171 include the edges of the workpiece 110 adjacent to the first surface 111 and the second surface 112.

[0066] In some embodiments, system 100 may further include an additional laser source. For example, system 100 may further include a second laser source 122, such as... Figure 5 The second laser source 122 can be configured to emit laser light and can be similar to the first laser source 121. For example, the second laser source 122 can be coupled to a second optical fiber 132, which can be configured to guide the laser light from the second laser source 122 to a second collimator 142 to generate a second laser beam 152. Alternatively, a beam splitter, fiber splitter, diffractive optics, or other optical elements can be used to separate the second laser beam 152 from the first laser beam 151 to use a single laser source. The second focusing lens 162 can be configured to guide the second laser beam 152 to a position on the first surface 111 of the workpiece 110 that is offset from the second laser beam 152. For example, the first laser beam 151 can be guided at one end of the first surface 111 and the second laser beam 152 can be guided at the midpoint of the first surface 111. By moving the stage 105 or the first scanning mirror 181 and the corresponding second scanning mirror 182 (or a single scanning mirror), the first laser beam 151 and the second laser beam 152 can scan across the first surface 111 of the workpiece 110. The detection efficiency can be improved by using both the first laser source 121 and the second laser source 122, because the scanning distance is reduced due to the portion of the first surface 111 illuminated by the laser spot from each laser source. An additional laser source can be used to illuminate the first surface 111 of the workpiece with an additional laser spot, which can further improve the detection efficiency.

[0067] In some embodiments, after the system 100 detects a crack 117 on the first surface 111 of the workpiece 110, the other sides of the workpiece 110 can be processed. For example, the processor 175 can be configured to send instructions to the stage 105 to (e.g., from) Figure 3 or Figure 5The position shown in the image is rotated 90 degrees (clockwise or counterclockwise) by 180 degrees, such that the first laser beam 151 is guided to each of the third surface 113, the fourth surface 114, and the fifth surface 115 of the workpiece, and the thermal camera 170 captures the corresponding thermal image 171 in each orientation to detect cracks 117 in each orientation of the workpiece 110.

[0068] In some embodiments, the system 100 may be configured to simultaneously detect cracks 117 on multiple sides of the workpiece 110. For example, the system 100 may further include a third laser source 123, a fourth laser source 124, and a fifth laser source 125, such as... Figure 6 As shown in the diagram. Similar to the first laser source 121, the third laser source 123, the fourth laser source 124, and the fifth laser source 125 can be configured to emit lasers. For example, each of the third laser source 123, the fourth laser source 124, and the fifth laser source 125 can be coupled to a third optical fiber 133, a fourth optical fiber 134, and a fifth optical fiber 135, respectively. The third optical fiber 133, the fourth optical fiber 134, and the fifth optical fiber 135 can be configured to guide the laser from each source to a corresponding third collimator 143, a fourth collimator 144, or a fifth collimator 145 to generate a third laser beam 153, a fourth laser beam 154, and a fifth laser beam 155. Alternatively, beam splitters, fiber splitters, diffractive optics, or other optical elements can be used to separate the third laser beam 153, the fourth laser beam 154, and / or the fifth laser beam 155 from the first laser beam 151 to use fewer laser sources. A third focusing lens 163 may be configured to guide a third laser beam 153 onto a third surface 113 of a workpiece 110. The third surface 113 may be orthogonal to the second surface 112 and parallel to the first surface 111. A fourth focusing lens 164 may be configured to guide a fourth laser beam 154 onto a fourth surface 114 of a workpiece 110. The fourth surface 114 may be orthogonal to both the second surface 112 and the first surface 111. A fifth focusing lens 165 may be configured to guide a fifth laser beam 155 onto a fifth surface 115 of a workpiece 110. The fifth surface 115 may be orthogonal to the second surface 112 and parallel to the fourth surface 114. A third scanning mirror 183, a fourth scanning mirror 184, and a fifth scanning mirror 185 may be used to scan the corresponding laser spots from the third laser beam 153, the fourth laser beam 154, and the fifth laser beam 155 across the corresponding surfaces 113, 114, and 115 of the workpiece 110. By using the first laser source 121, the third laser source 123, the fourth laser source 124, and the fifth laser source 125, the detection efficiency can be improved because the stage 105 can remain stationary while each of the first surface 111, the third surface 113, the fourth surface 114, and the fifth surface 115 of the workpiece 110 is irradiated by a laser spot from each laser source, and a single thermal image 171 can be processed to detect defects along each surface.

[0069] In some embodiments, the system 100 may include a first laser source 121 and a third laser source 123, which illuminate the first laser beam 151 and the third laser beam 153 onto the parallel first surface 111 and the third surface 113 of the workpiece. Then, by rotating the stage 105 by 90 degrees, the first laser beam 151 and the third laser beam 153 can illuminate the parallel fourth surface 114 and the fifth surface 115, which improves detection efficiency without requiring a fourth laser source 124 and a fifth laser source 125.

[0070] In some embodiments, the system 100 may include a second laser source 122, which may illuminate each of the third surface 113, fourth surface 114, and fifth surface 115 of the workpiece 110 with an additional laser spot by means of each of the third laser source 123, fourth laser source 124, and fifth laser source 125 parallel to each of them, which may further improve detection efficiency.

[0071] Using system 100, the first laser source 121 generates heat along the first surface 111 of workpiece 110 using a first laser beam 151, while the thermal camera 170 captures a thermal image 171 of the second surface 112 of workpiece 110. This thermal image 171 can be used to detect cracks 117 and other defects at the interface between the first surface 111 and the second surface 112 of workpiece 110. System 100 can quickly scan opaque workpieces 110 for rapid inspection.

[0072] Another embodiment of this disclosure provides method 200. For example... Figure 7 As shown in the figure, method 200 may include the following steps.

[0073] In step 210, laser light is emitted from a first laser source. The first laser source may be a laser diode or other laser source configured to emit laser light. The laser light may be a pulsed laser or a continuous laser beam. The first laser source may be coupled to a first optical fiber. The first optical fiber may guide the laser light emitted by the first laser source to a first collimator to generate a first laser beam.

[0074] In step 220, a first focusing lens is used to guide the laser beam from the first laser source onto the first surface of the workpiece. For example, the first focusing lens can guide a laser spot from the first laser beam onto the first surface of the workpiece. In some embodiments, the diameter of the laser spot may be less than or equal to the thickness of the first surface. For example, the diameter of the laser spot may be 25 to 750 µm. By guiding the first laser beam onto the first surface of the workpiece, heat can be generated from the laser spot into the workpiece in a non-uniform temperature distribution.

[0075] In step 230, a thermal image of the second surface of the workpiece is captured using a thermal camera. The thermal camera may be a forward-looking infrared (FLIR) camera or other types of non-contact temperature measurement sensors or sensor arrays. The thermal camera may be guided toward the second surface of the workpiece. The second surface may be orthogonal to the first surface. In other words, the first and second surfaces may be adjacent surfaces of the workpiece connected at their edges. The heat generated on the first surface by the laser spot from the first laser beam may have a non-uniform temperature distribution that extends throughout the workpiece. Therefore, the thermal image may reflect the non-uniform temperature distribution on the second surface of the workpiece (e.g., the highest temperature at the edge of the second surface, and the temperature decreasing away from the edge adjacent to the first surface).

[0076] In step 240, the processor identifies cracks in the workpiece based on the thermal image. The cracks may extend from the first surface into the workpiece (e.g., across the second surface near the edge adjacent to both the first and second surfaces, or below the second surface).

[0077] In some embodiments, step 240 may include, for example: Figure 8 The following steps are shown in the image.

[0078] In step 241, the intensity of each pixel of the thermal image along the edges adjacent to the first and second surfaces of the workpiece is obtained. Based on the heat generated on the first surface by the laser spot from the first laser beam, the pixel intensity corresponds to the temperature of a region on the second surface of the workpiece. In step 242, a gradient map is derived using the intensity of each pixel of the thermal image, the gradient map representing the spatial derivative of the temperature distribution along the edges adjacent to the first and second surfaces of the workpiece. Based on the proximity to the laser spot, defect-free portions of the workpiece can have a smooth transition in the temperature distribution. Cracks or defects in the workpiece can have intensity spikes or peaks compared to the gradients of neighboring pixels.

[0079] In step 243, it is determined that a crack exists in the workpiece at the location of a peak in the gradient map. For example, an edge detection algorithm or other types of algorithms can be used to identify the peak in the gradient map. Therefore, cracks and other defects in the workpiece can be identified. In some embodiments, the crack may have a sub-micron thickness.

[0080] Although describing cracks in a workpiece, method 200 can also be used to detect other types of defects in other types of workpieces. For example, method 200 can be used to detect air gaps in wafer-to-wafer and die-to-wafer bonding, open circuits in metal lines of PCBs or FPDs, cracks in different layers constituting solid-state batteries or embedded semiconductor dies, delamination on PCBs, or other application scenarios, and is not limited herein.

[0081] In some embodiments, method 200 may further include, for example, Figure 9 The steps 227a or 227b shown in the document.

[0082] In step 227a, a first scanning mirror is used to scan the laser beam from the first laser source across the first surface of the workpiece. The first scanning mirror may be positioned between the first collimator and the first focusing lens. The first scanning mirror may be configured to move or rotate to change the direction of the first laser beam passing through the first focusing lens. By moving the first scanning mirror, the laser spot from the first laser beam can be scanned across the first surface of the workpiece.

[0083] In step 227b, the stage is moved relative to the laser to allow the laser beam from the first laser source to scan across a first surface of the workpiece. For example, a motor or actuator of the stage may translate or rotate the stage, causing the first laser beam to scan across the first surface of the workpiece. In some embodiments where the workpiece is cylindrical, rotating the stage relative to the laser allows the laser to scan across annular surfaces of the workpiece.

[0084] In some embodiments, method 200 may further include Figure 9 Step 250 is shown in the diagram. In step 250, the stage is rotated about an axis perpendicular to the laser light from the first laser source, thereby guiding the laser light from the first laser source onto different surfaces of the workpiece. For example, by rotating the stage by 90 degrees, the laser light from the first laser source can be guided to the fourth or fifth surface of the workpiece, and by rotating the stage by 180 degrees, the laser light from the first laser source can be guided to the third surface of the workpiece. Therefore, by using successive 90-degree rotations, the laser light from the first laser source can scan across the first, third, fourth, and fifth surfaces of the workpiece. Step 230 can be repeated after each rotation to capture thermal images of the corresponding surfaces of the workpiece and identify cracks based on the images.

[0085] In some embodiments, method 200 may further include, for example, Figure 10 Steps 212 and 222 are shown in the diagram.

[0086] In step 212, laser light is emitted from a second laser source. The second laser source may be configured to emit laser light and may be similar to the first laser source. For example, the second laser source may be coupled to a second optical fiber, which may be configured to guide the laser light from the second laser source to a second collimator to generate a second laser beam. In some embodiments, instead of using a second laser source, the second laser beam may be generated by using a beam splitter, fiber splitter, diffractive optical element, or other optical element to separate the first laser beam.

[0087] In step 222, the laser beam from the second laser source is guided by the second focusing lens to a position on the first surface of the workpiece that is offset from the laser beam from the first laser source. For example, the first laser beam can be guided to one end of the first surface and the second laser beam can be guided to the midpoint of the first surface.

[0088] By moving the stage or the first scanning mirror and the corresponding second scanning mirror (or a single scanning mirror), the first and second laser beams can scan across the first surface of the workpiece. Using both the first and second laser sources improves detection efficiency because the scanning distance is reduced due to the portion of the first surface illuminated by the laser spot from each laser source. Additional laser sources can be used to illuminate the first surface of the workpiece with additional laser spots, which further improves detection efficiency.

[0089] although Figure 10 Steps 210 and 212 are described as being performed simultaneously, but these steps may be performed at different times and are not limited herein. Similarly, the sequence of steps 220 and 222 may depend on the sequence of previous steps 210 and 212 and is not limited herein.

[0090] In some embodiments, method 200 may further include, for example, Figure 11 Steps 213 and 223 are shown in the diagram.

[0091] In step 213, laser light is emitted from a third laser source. The third laser source may be configured to emit laser light and may be similar to the first laser source. For example, the third laser source may be coupled to a third optical fiber, which may be configured to guide the laser light from the third laser source to a third collimator to generate a third laser beam.

[0092] In step 223, a third focusing lens is used to guide the laser beam from the third laser source onto the third surface of the workpiece. For example, the third focusing lens can guide the third laser beam onto the third surface of the workpiece. The third surface can be orthogonal to the second surface and parallel to the first surface.

[0093] A third scanning mirror can be used to scan the third surface of the workpiece with a laser spot from a third laser beam. This improves inspection efficiency because both the first and third surfaces can be illuminated simultaneously with laser spots from each laser source. The stage can then be rotated to further illuminate the adjacent fourth and fifth surfaces of the workpiece.

[0094] In some embodiments, method 200 may further include the following steps.

[0095] In step 214, laser light is emitted from a fourth laser source. The fourth laser source may be configured to emit laser light and may be similar to the first laser source. For example, the fourth laser source may be coupled to a fourth optical fiber, which may be configured to guide the laser light from the fourth laser source to a fourth collimator to generate a fourth laser beam.

[0096] In step 215, laser light is emitted from a fifth laser source. The fifth laser source may be configured to emit laser light and may be similar to the first laser source. For example, the fifth laser source may be coupled to a fifth optical fiber, which may be configured to guide the laser light from the fifth laser source to a fifth collimator to generate a fifth laser beam.

[0097] In step 224, a fourth focusing lens is used to guide the laser beam from the fourth laser source onto the fourth surface of the workpiece. For example, the fourth focusing lens can guide the fourth laser beam onto the fourth surface of the workpiece. The fourth surface can be orthogonal to the second surface and the first surface.

[0098] In step 225, a fifth focusing lens is used to guide the laser beam from the fifth laser source onto the fifth surface of the workpiece. For example, the fifth focusing lens can guide the fifth laser beam onto the fifth surface of the workpiece. The fifth surface can be orthogonal to the second surface and parallel to the fourth surface.

[0099] The fourth and fifth scanning mirrors can be used to scan the fourth and fifth surfaces of the workpiece using laser spots from the fourth and fifth laser beams. Therefore, inspection efficiency can be improved because each of the first, third, fourth, and fifth surfaces can be illuminated with a laser spot from each laser source while the stage remains stationary, and a single thermal image can be processed to detect defects along each surface.

[0100] although Figure 11 Steps 210, 213, 214, and 215 are described as being performed simultaneously, but these steps may be performed at different times and are not restricted herein. Similarly, the sequence of steps 220, 223, 224, and 225 may depend on the sequence of previous steps 210, 213, 214, and 215 and is not restricted herein.

[0101] Using method 200, a laser source generates heat along the first surface of the workpiece, while a thermal camera captures a thermal image of the second surface. This thermal image can be used to detect cracks and other defects at the interface between the first and second surfaces. Method 200 can be rapidly applied to opaque workpieces for quick inspection.

[0102] Although this disclosure has been described with respect to one or more specific embodiments, it should be understood that other embodiments of this disclosure may be made without departing from the scope of this disclosure. Therefore, this disclosure is to be considered limited only by the appended claims and their reasonable interpretation.

Claims

1. A system comprising: A first laser source, configured to emit laser light; A first focusing lens is configured to direct the laser light from the first laser source onto a first surface of the workpiece; A thermal camera configured to capture a thermal image of a second side of the workpiece, wherein the second side is orthogonal to the first side; and A processor configured to identify cracks in the workpiece based on the thermal image.

2. The system according to claim 1, further comprising: A first scanning mirror is configured to guide the laser from the first laser source to scan across the first surface of the workpiece.

3. The system according to claim 1, further comprising: A stage, wherein the workpiece is placed on the stage, and the stage is movable to allow the laser from the first laser source to scan across the first surface of the workpiece.

4. The system of claim 1, wherein the first surface has a smaller cross-sectional area than the second surface.

5. The system of claim 4, wherein the laser has a diameter less than or equal to the thickness of the first surface of the workpiece.

6. The system of claim 1, wherein the first surface has a cross-sectional area larger than that of the second surface.

7. The system of claim 6, wherein the first focusing lens is configured to direct the laser onto the first surface of the workpiece near the edge adjacent to the first surface and the second surface.

8. The system according to claim 1, further comprising: A second laser source, configured to emit laser light; and A second focusing lens is configured to direct the laser from the second laser source to a position on the first surface of the workpiece that is offset from the laser from the first laser source.

9. The system according to claim 1, further comprising: A third laser source, configured to emit laser light; and A third focusing lens is configured to guide the laser from the third laser source onto a third surface of the workpiece, wherein the third surface is orthogonal to the second surface and parallel to the first surface.

10. The system of claim 9, further comprising: A fourth laser source, configured to emit laser light; A fourth focusing lens is configured to guide the laser from the fourth laser source onto a fourth surface of the workpiece, wherein the fourth surface is orthogonal to the second surface and the first surface; A fifth laser source, configured to emit laser light; and A fifth focusing lens is configured to guide the laser from the fifth laser source onto a fifth surface of the workpiece, wherein the fifth surface is orthogonal to the second surface and parallel to the fourth surface.

11. The system of claim 1, wherein the thermal camera is a forward-looking infrared (FLIR) camera.

12. The system of claim 1, wherein the processor is configured to identify the crack in the workpiece based on the thermal image by: The intensity of each pixel of the thermal image along the edges adjacent to the first and second surfaces of the workpiece is obtained; A gradient map is derived using the intensity of each pixel of the thermal image, the gradient map representing the spatial derivative of the temperature distribution along the edges of the workpiece adjacent to the first and second surfaces; and The crack in the workpiece is determined to exist at the point where a peak is found in the gradient graph.

13. A method comprising: Laser light is emitted from the first laser source; The laser light from the first laser source is guided onto the first surface of the workpiece using a first focusing lens; A thermal image of a second side of the workpiece is captured using a thermal camera, wherein the second side is orthogonal to the first side; and The processor identifies cracks in the workpiece based on the thermal image.

14. The method of claim 13, further comprising: The laser from the first laser source is used to scan across the first surface of the workpiece using a first scanning mirror.

15. The method of claim 13, further comprising: The stage is moved relative to the laser so that the laser from the first laser source scans across the first surface of the workpiece, wherein the workpiece is placed on the stage.

16. The method of claim 13, further comprising: Emitting laser light from a second laser source; and The laser from the second laser source is guided by a second focusing lens to a position on the first surface of the workpiece that is offset from the laser from the first laser source.

17. The method of claim 13, further comprising: Laser light is emitted from a third laser source; and A third focusing lens is used to guide the laser from the third laser source onto a third surface of the workpiece, wherein the third surface is orthogonal to the second surface and parallel to the first surface.

18. The method of claim 17, further comprising: Laser light is emitted from the fourth laser source; A fourth focusing lens is used to guide the laser from the fourth laser source onto a fourth surface of the workpiece, wherein the fourth surface is orthogonal to the second surface and the first surface; Laser light is emitted from the fifth laser source; and A fifth focusing lens is used to guide the laser from the fifth laser source onto the fifth surface of the workpiece, wherein the fifth surface is orthogonal to the second surface and parallel to the fourth surface.

19. The method of claim 13, wherein the workpiece is placed on a stage, and the method further comprises: The stage is rotated about an axis perpendicular to the laser from the first laser source, such that the laser from the first laser source is guided by the first focusing lens onto a fourth surface of the workpiece, wherein the fourth surface is orthogonal to the second surface and the first surface.

20. The method of claim 13, wherein using the processor to identify the crack in the workpiece based on the thermal image comprises: The intensity of each pixel of the thermal image along the edges adjacent to the first and second surfaces of the workpiece is obtained; A gradient map is derived using the intensity of each pixel of the thermal image, the gradient map representing the spatial derivative of the temperature distribution along the edges of the workpiece adjacent to the first and second surfaces; and The crack in the workpiece is determined to exist at the point where a peak is found in the gradient graph.

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