Fast scanning acoustic microscopy for subsurface imaging and inspection

Abstract

Embodiments of the present disclosure relate to fast scanning acoustic microscopy for subsurface imaging and inspection. For example, a system may include at least one processing device configured to perform operations including initiating imaging of a sample using an acoustic microscope, and causing the sample to be scanned at a radial distance relative to a center position of the sample to perform the imaging of the sample. The sample is located on a stage, and the stage rotates at a rotational speed determined based on the radial distance.

Description

Atorney Docket No.: 36119.2932 (L2283PCT)FAST SCANNING ACOUSTIC MICROSCOPY FOR SUBSURFACE IMAGING AND INSPECTIONTECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to microscopy, and more specifically relate to fast scanning acoustic microscopy for subsurface imaging and inspection.BACKGROUND

[0002] Microscopy generally refers to the use of microscopes to view objects that are too small to see with the naked eye. For example, microscopy may be used to view objects, such as features, formed on substrates of electronic devices (e.g., semiconductor substrates). One example of microscopy is optical (light) microscopy, which uses a system of visible light and lenses to magnify objects. Another example of microscopy is electron microscopy, which uses electron beams instead of visible light to image objects. Yet another example of microscopy is confocal microscopy, which uses a laser beam to scan across an object in a manner that eliminates out-of-focus light.SUMMARY

[0003] The following is a simplified summary of the disclosure in order to provide a basic understanding of some aspects of the disclosure. This summary is not an extensive overview of the disclosure. It is intended to neither identify key or critical elements of the disclosure, nor delineate any scope of the particular implementations of the disclosure or any scope of the claims. Its sole purpose is to present some concepts of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.

[0004] In some embodiments, a system includes at least one processing device configured to perform operations including initiating imaging of a sample using an acoustic microscope, and causing the sample to be scanned at a radial distance relative to a center position of the sample to perform the imaging of the sample. The sample is located on a stage, and the stage rotates at a rotational speed determined based on the radial distance.

[0005] In some embodiments, a method includes initiating, by at least one processing device, imaging of a sample using an acoustic microscope, and causing, by the at least one processing device, the sample to be scanned at a radial distance relative to a center position of the sample to perform the imaging of the sample. The sample is located on a stage, and the stage rotates at a rotational speed determined based on the radial distance.Attorney Docket No.: 36119.2932 (L2283PCT)

[0006] In some embodiments, a system includes a translational motion stage to receive a sample, and at least one group of scan heads located above the translational motion stage to generate an image of the sample by using acoustic microscopy. The at least one group of scan heads includes a plurality of scan heads arranged in a staggered formation.

[0007] Numerous other features are provided in accordance with these and other aspects of the disclosure. Other features and aspects of the present disclosure will become more fully apparent from the following detailed description, the claims, and the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that different references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.

[0009] FIG. 1 is a diagram of an example acoustic microscopy system, according to some embodiments.

[0010] FIGS. 2A-2B are graphs of an example implementation of an acoustic microscopy system using a rotational motion scanning method for subsurface imaging and inspection, according to some embodiments.

[0011] FIG. 3 is a diagram of an example acoustic microscopy system using a rotational motion scanning method for subsurface imaging and inspection, according to some embodiments.

[0012] FIG. 4 is a flowchart of an example method for implementing an acoustic microscopy system using a rotational motion scanning method for subsurface imaging and inspection, according to some embodiments.

[0013] FIGS. 5A-6 are diagrams of example implementations of acoustic microscopy¬ systems using translation motion scanning methods for subsurface imaging and inspection, according to some embodiments.

[0014] FIG. 7 is a flowchart of a method for implementing an acoustic microscopy system using a translational motion scanning method for subsurface imaging and inspection, according to some embodiments.

[0015] FIG. 8 depicts a diagrammatic representation of a machine in the example f orm of a computing device within which a set of instructions, for causing the machine to perform anyone or more of the methodologies discussed herein, may be executed.Attorney Docket No.: 36119.2932 (L2283PCT)DETAILED DESCRIPTION OF EMBODIMENTS

[0016] Embodiments of the present disclosure are directed to fast scanning acoustic microscopy for subsurface imaging and inspection. Advanced packaging generally refers to a collection of techniques and technologies used to integrate and connect multiple components, such as chips and / or dies, within a single package to improve performance, reduce size, and enhance functionality. Traditional packaginginvolves placing a single componentin a package that provides electrical connections to the outside world. However, advanced packaging moves beyond this by combiningmultiple components, oftenfrom differentprocessesortechnologies, into one compact, high-performance module. Advanced packaging may enable intercomponent communication higher speeds and lower latency as compared to traditional packaging by reducing the distance between them. By integrating multiple components in a smaller package, advanced packaging may enable more compact devices, which may be beneficial for advancements in consumer electronics, mobile devices, and wearables. Advanced packaging may enable heterogeneous integration of different types of components (central processingunits (CPUs), graphics processingunits (GPUs), memory, etc.) into a single package, even if each individual component is created using a different processing technology, which may allow for improved design flexibility and faster production. Moreover, by assembling individual components into a package, advanced packaging may be used to improve yield by reducing defects (e.g., smaller components have fewer defects).

[0017] One advanced packaging technique is 2.5 dimensional (2.5D) packaging. In 2.5D packaging, multiple components may be placed side-by-side on an interposer, which is a layer of silicon or other suitable material with through vias (e.g., through silicon vias (TSVs)) that functions as a high-density wiring platform. The interposer may enable high -bandwidth communication between components without integrating them into a single chip. 2.5D packaging allows for heterogeneous integration of different chips, such as logic, memory, and specialized processors, each potentially fabricated using different process technologies. This approach may improve system performance and power efficiency by reducing interconnect lengths and enabling wider data buses between chips. Additionally, 2.5D packaging may facilitate easier testing and replacement of individual components, enhancing yield and reliability.

[0018] Another advanced packaging technique is three-dimensional (3 D) packaging. In 3D packaging, multiple components are stacked on each other (e.g., vertically on top of each other) to form a package. Connections between the stacked components may be made using through-vias, which may allow signals to pass through the layers. 3D packaging may enable evenAttorney Docket No.: 36119.2932 (L2283PCT)greater integration density than 2.5D by stacking dies directly, which may significantly reduce the overall footprint of the package and improve signal speed due to shorter vertical interconnects. This technique is particularly advantageous for memory devices, such as high-bandwidth memory (HBM), where multiple memory dies are stacked to achieve higher capacity and bandwidth. 3D packaging may also facilitate integration of different types of devices, such as logic and memory', in a single vertical stack, but it introduces additional challenges in thermal management and manufacturing complexity7.

[0019] A substrate of an electronic device (e.g., wafer), such as an advanced package, may include one or more subsurface features, such as delaminations, voids, inclusions, etc., that reside underneath an exposed surface of the electronic device. Subsurface inspection of semiconductor substrates has recently gained much greater significance in the context of advanced packaging, where there is interest in establishing the health of various bonds to ensure that there are no subsurface features (e.g., delaminations, voids and / or inclusions).

[0020] However, given that subsurface features may be located underneath an exposed surface of an electronic device (e.g., advanced package), they may notbe visible using optical microscopy imaging techniques. One issue in the inspection of subsurface features is generating sufficient signal strength and contrast due at least in part to the complete or partial obscuration of the subsurface features caused to the presence of an impenetrable layer in between the interrogation beam and the features of interest. In applications in which there on direct method exists of optically interacting with a subsurface feature, the use of well- established optical inspection tools is not possible.

[0021] One type of system that may be used for subsurface imaging and inspection of subsurface features is an acoustic microscopy system, which may include an acoustic microscope. In some embodiments, the acoustic microscope is a scanning acoustic microscope (SAM). For example, FIG. 1 is a diagram of an acoustic microscopy system (“system”) 100 for subsurface imaging and inspection, accordingto some embodiments. The system 100 may include several components. An acoustic pulse generator 110 may be provided to generate electronic pulses for acoustic excitation. A switching network 120 may be included to manage the routing of signals within the system. A detection system 130, such as detection electronics, may be used to process received signals. The acoustic microscope may include an acoustic lens 140, which may focus acoustic pulses, and an ultrasonic transducer 150, which may be formed on a first side of the lens and may be implemented using a piezoelectric material. The system 100 may further include a system controller 160, which may coordinate the operation of the various components, and a stage 170, which mayAttorney Docket No.: 36119.2932 (L2283PCT)support and position samples for inspection. In some embodiments, the ultrasonic transducer 150 may be implemented using a piezoelectric material.

[0022] As further shown, the system 100 may further include a sample 180. In some embodiments, the sample 180 is a substrate of an electronic device (e.g., a wafer). In some embodiments, and as shown in FIG. 1, the sample 180 may include multiple layers including a layer 182 and a layer 184 formed on the layer 182. As further shown in FIG. 1, the sample 180 may include at least one feature 186. In this example, the at least one feature 186 is a subsurface feature, since it is underneath the surface of the layer 184 of the sample 180. In other embodiments, the at least one feature 186 may be a surface feature formed on the surface of the sample 180 (e.g., on the surface of the layer 184).

[0023] The system 100 may further include a fluid 190 on the sample 180. The acoustic lens 140 may have a concave curvature 142 formed within a second side of the acoustic lens 140 opposite the first side, which is in contact with the fluid 190. The fluid 190 may enable propagation of high frequency sound waves generated by the ultrasonic transducer 150. In some embodiments, the fluid 190 is water. However, the fluid 190 may be any fluid suitable for propagating high frequency sound waves.

[0024] At a given instant, the acoustic pulse generator 110 may impart an electronic pulse (which may be in pure tone or chirp format) to the ultrasonic transducer 150, which may cause the ultrasonic transducer 150 to generate an acoustic pulse. The acoustic pulse is directed through the acoustic lens 140, and towards the concave curvature 142, to focus the acoustic pulse onto a spot with respect to the at least one feature 186. The position of the acoustic lens 140 with respect to the sample 180 may be noted with high accuracy. As the focused acoustic pulse interacts with the sample 180 (e.g., the at least one feature 186), some amount of energy is reflected back toward the acoustic lens 140 as a reflected acoustic pulse. The reflected acoustic pulse travels back through the acoustic lens 140 to the ultrasonic transducer 150, which in turn may convert the reflected acoustic pulse into an electrical signal. Thus, the system controller 160 may record position and the reflected signal level. In the fast scanning axis, the focal spot may be made to move past the sample 180 (either by scanning the acoustic lens, or the sample) by 1 pixel between any two adjacent pulses. The process may be repeated for each pixel on the sample in order to generate a complete image of the sample 180. Accordingly, the ultrasonic transducer 150 may act as a transmitter of an acoustic pulse toward the sample 180, and a receiver of a reflected acoustic pulse reflected off the sample 180 (e.g., a sound wave or acoustic pulse transceiver). Given the relatively slow speed of sound (e.g., as compared with the speed of light), the time taken for an acousticAtorney Docket No.: 36119.2932 (L2283PCT)pulse transmited by an ultrasonic transducer 150 to travel to the at least one feature 186 and to return back to the ultrasonic transducer 150 is not negligible. Accordingly, a time delay may be experienced that corresponds to a separation in time between the transmission of an acoustic pulse by the ultrasonic transducer 150 toward the at least one feature 186, and the receipt of the reflected acoustic pulse from the at least one feature 186 by the ultrasonic transducer 150.

[0025] The switching network 120, which separates outgoing and incoming signals, may direct the electrical signal towards the detection system 130. The detection system 130 may¬ be used to detect the at least one feature 186 from the electrical signal and generate an image of the sample 180 for inspection.

[0026] The system controller 160 (e.g., computing device, processing device, etc.) may be communicatively coupled to one or more of the acoustic pulse generator 110, the switching network and / or the detection system 130. The system controller 160 may be and / or include a computing device such as a personal computer, a server computer, a programmable logic controller (PLC), a microcontroller, system on a chip (SoC), and so on. The system controller 160 may include one or more processing devices, which may be general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processing device may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets or processors implementing a combination of instruction sets. The processing device may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. System controller 160 may include a data storage device (e.g., one or more disk drives and / or solid-state drives), a main memory, a static memory, a network interface, and / or other components. The system controller 160 may execute instructions to perform any one or more of the methodologies and / or embodiments described herein. The instructions may be stored on a computer readable storage medium, which may include the main memory, static memory, secondary storage and / or processing device (during execution of the instructions). The system controller 160 may also be configured to permit entry and display of data, operating commands, and the like by a human operator.

[0027] In some implementations, the system 100 uses a translational motion scanning method (e.g., rectilinear scanning method) to generate an image of the sample 180 (e.g., theAttorney Docket No.: 36119.2932 (L2283PCT)at least one feature 186). More specifically, the translational motion scanning method may implement translational motion of the sample 180 (e.g., approximately straight-line motion) to generate the image of the sample. For example, the translational motion scanning method may implement bidirectional or two-dimensional (2D) translational motion to generate a 2D image of the sample 180 at a given plane. More specifically, using bidirectional translational motion, a spot on the sample 180 may be scanned along a first direction (e.g., a horizontal direction along the x-axis, or x-direction) and a second direction perpendicular to the first direction (e.g., a vertical direction along the y-axis, ory-direction), and the signal received at each point may be recorded as a function of the spot position. The scanning function m y be performed by either moving the acoustic lens 140 or the sample 180 in a raster mode. For example, the stage 170 may be a translation motion stage that may cause the sample 180 to move translation ally in one or more directions (e g., bidirectional motion).

[0028] One limitation to scanning throughput of the system 100 using a translational motion scanning method is the finite time needed between any two successive acoustic pulses due to the sound speed limitations in the body of the acoustic lens 140. For example, the body of the acoustic lens 140 maybe formedfrom sapphire havingan acoustic velocity of 11,300 meters per second (m / sec) and a thickness of 2 millimeters (mm). In this case, the travel time for an acoustic pulse to reach the at least one feature 186 and return may be on the order of 0.4 microseconds (ps). The pulse-to-pulse timing (i.e., pixel time), which may define the limit of speed in data acquisition using the system 100, may be set to, for example, 1 ps.

[0029] Another limitation to scanning throughput of the system 100 using a translational motion scanning method may arise from the scanning parameters. For example, assume a 5 micrometer (pm) pixel size for an image to be generated by a scan. To complete a 300 mm scan of a sample 180, the system 100 may visit about2.9 gigapixels. Assumingthe 1 ps pixel time, this may correspond to about 2900 s of data acquisition time. Although this time duration is very long, in itself it may not be completely unacceptable. The issue, more precisely, is how to scan the sample 180 to comply with such a limit. For example, implementing bidirectional, translational motion scanning as described above may be very slow (e.g., the sample 180 sampled at 5-pm pixels may translate into 30,000 swaths across the substrate). Thus, even if the stage 170, as a translational motion stage, may be capable of translation motion at a speed of at least 1 m / sec, the total turn-around time alone may translate into hours of time needed to inspect the sample 180.

[0030] Some techniques to increase the scan speed of the system 100 using translational motion scanning methods may include mounting the lens on a fast-moving flexural sinusoidalAttorney Docket No.: 36119.2932 (L2283PCT)or voice-coil scanner. However, these techniques may also suffer from scanning throughput issues. For example, a flexural sinusoidal scanner may operate at 50 hertz (Hz) over a 2 mm stroke (i.e., 400 pixels at 5 pm / pixel), which may correspond to a data pixel time of 1 / (400*2*50) gs = 25 ps (for a one-sided scan). Accordingly, these implementations may result in a multi-hour scan time.

[0031] Aspects and implementations of the instant disclosure address the above-described and other shortcomings by enabling fast scanning acoustic microscopy for subsurface imaging and inspection of subsurface features (e.g., delaminations, voids and / or inclusions). Embodiments described herein may be used to detect subsurface features of electronic devices, such as advanced packages, with increased throughput as compared to other techniques.

[0032] In some embodiments, the system 100 uses a rotational motion scanning method to generate an image of the sample 180 for subsurface imaging and inspection. For example, the stage 170 may be a rotational motion stage that rotates the sample. The rotational motion of the sample 180 may be defined using a polar coordinate system, particularly an (R, 9) coordinate system, in which the R coordinate of a spot on the sample 180 defines the radius or radial distance of the position of the spot on the sample 180 from a reference point, and the 0 coordinate of the spot on the sample 180 defines the angular location of the spot (e.g., relative to the horizontal). In some embodiments, the acoustic lens 140 is kept stationary, and the stage 170 moves the sample 180 along both the R and 0 dimensions. In alternative embodiments, the sample 180 rotates (e.g., moves only along the 0 dimension) and the acoustic lens 140 (slowly) moves along the R dimension to cover the entire sample.Illustratively, the 1 ps pixel time limitation may correspond to the motion of the acoustic lens 140 or the sample 180 past each other ata speed of 5 m / sec (e.g., for 5 pm pixels), and such motion may be realized with a rotational speed of about 5 rotation s / second (rot / s).

[0033] In some embodiments, the rotational speed of the sample 180 is approximately con slant for all radial positions of spots on the sample 180 relative to the center of the sample 180. In some embodiments, the rotational speed of the sample 180 is modified based on the radial position of the spot on the sample 180 relative to the center of the sample 180. For example, as the radial distance of the position of the spot on the sample 180 approaches the center of the sample 180, the rotational speed of the sample 180 may be increased inversely proportional to the radial position of the spot on the sample 180 (and vice versa). This also allows an increase in the radial scan speed. Accordingly, modifying rotational speed based on the radial position of the spot on the sample 180 may increase scanning throughput of theAttorney Docket No.: 36119.2932 (L2283PCT)system 100, as compared to maintaining an approximately constant rotational speed that is agnostic to the radial position of the spot on the sample 180. Illustrations of these embodiments will now be described with reference to FIGS. 2A-2B.

[0034] For example, FIG. 2A depicts a graph 200A of a rotational speed or rate profile (e.g., rotations per minute (RPM)) having an x-axis 210 corresponding to the radial position of a spot on a sample, and a y-axis 220 corresponding to the rotational speed of the sample as a function of the radial position of the spot.?\s may be seen in FIG. 2A, there may be a maximum rotational speed (e.g., rotational speed ceiling or limit) to maintain a data rate, which may correspond to the total scan time. Once the maximum rotational speed is reached, it may be maintained as the rotational speed for the remainder of the substrate scan. FIG. 2B is an associated graph 200B of the time taken per rotation (with the rotational speed ceiling) having an x-axis 230 corresponding to rotation count, and a y-axis 240 corresponding to the time taken per rotation as a function of the rotation count. The total scan time for the substrate may be determined as the area underneath the curve shown in FIG. 2B (e.g., the integral of the function defining the curve shown in FIG. 2B from the initial rotation count to the final rotation count). In some embodiments, multiple scan heads (“heads”) are distributed along respective radii to reduce the total scan time.

[0035] For example, FIG. 3 is a diagram of a top-down view of an acoustic microscopy system (“system”) 300 using a rotational motion scanning method, in accordance with some embodiments. As shown, the system 300 may include the sample 180, which may be located on the stage 170 (not shown in FIG. 3), as described above with reference to FIG. 1. The sample 180 may be configured to rotate in a given direction. In this illustrative example, the sample 180 may rotate in a counter-clockwise direction. However, the direction should not be considered limiting.

[0036] The system 300 may further include a bridge 305, located above the sample 180, on which multiple heads may be attached. In this example, three heads 310-1, 310-2, and 310-3 may be attached to the bridge 305. However, the number of heads should not be considered limiting. More specifically, the three heads 310-1, 310-2, and 310-3 may be positioned at three respective radii relative to the center of the sample 180, corresponding to respective circles 320-1, 320-2, and 320-3. Each of the individual heads 310-1 through 310-3 may perform a continuous or near-continuous spiral scan of the sample 180 with reduced scan time as compared to translational motion scans that may require sample turnaround. The use of multiple heads may further reduce the total scan time as compared to a single head. Illustratively, if the radius of the circle 320-1 is 50 mm, the radius of the circle 320-2 is 100Atorney Docket No.: 36119.2932 (L2283PCT)mm, and the radius of the circle 320-3 is 150 mm, then the total scan time for the sample 180 may be reduced by, e.g., about 66%.

[0037] One aspect of this approach is that, for the same rotation speed and sampling size (e.g., pixel size), the data rate may drop as the position of a given head becomes closer to the center of the sample 180. Alternatively, the pixel size may drop for a uniform data rate. However, these considerations maybe addressedby altering sampling times to accommodate any such variations.

[0038] The radial speed at which the sample 180 and / or the acoustic lens (e.g., the acoustic lens 140 of FIG. 1) may move maybe related to the pixel size. For example, to maintain the pixel size, there may be an inverse relationship between the rotation speed of the sample 180 and the radial distance away from the center of the sample 180. Illustratively, for a 5 pm pixel, the radial position of the focal spot on the sample 180 may move by about 5 pm per rotation. This may help to ensure that a given 2D feature on which the spot on the sample 180 has passed in the previous rotation is again sampled by the spot on the sample 180 in the present rotation. Thus, data may be generated in both the tangential and radial directions for a given feature, from which the shape of the feature may be reconstructed. Monitoring of the instantaneous position of the spot on the sample 180 may be a factor for the successful reconstruction of an image of a feature. Since any two adjacent circles of a spiral scan may be separated by a pixel in the radial direction, the two circles may differ in length by the pixel length multiplied by 2TC. In the illustrative example of a 5 pm pixel, the length difference is about 31 pm. The sampling timing of the sample 180 may be continuously adjusted to account for this difference.

[0039] Another aspect is maintaining focus during the scan of the sample 180, which may be due at least in part to changes in the distance between the sample 180 and the acoustic lens. To address this, in some embodiments, each of the heads 310-1 through 310-3 may be associated with a height adjusting mechanism, such as a piezoelectric translator or positioner. The local z-position of the sample 180 with respect to the focal spot of each of the heads 310-1 through 310-3 may be sensed (e.g., using an interferometric sensor), and fed back to the piezoelectric translator so as to maintain focus. One cause of a periodic shift in the z-position of the sample 180 is atilt or deformation in the stage or pedestal, whichmay be manifested as periodic z-motion of the sample 180 with respect to the focal spot. Although the rotational speed of the sample 180 may increase as the radial position gets closer to the center of the sample 180, the amplitude of this z-modulation may be reduced, and thus the piezoelectric translator may handle this phenomenon. If more heads are deployed, then the rotational speedAtorney Docket No.: 36119.2932 (L2283PCT)of the sample 180 may be further reduced without eroding the throughput to facilitate the z-positioning process. Alternatively, the total scan time may be reduced to improve the throughput.

[0040] FIG. 4 is a flowchart of a method 400 for implementing an acoustic microscopy system using a translational motion scanning method for subsurface imaging and inspection, according to some embodiments. The method 400 is performed by a system that may include hardware (circuitry, dedicated logic, optical measuring tools as described herein, etc.), software (such as is run on a general-purpose computer system or a dedicated machine), firmware, or some combination thereof. In some embodiments, the method 400 is performed by a system controller of an acoustic microscopy system, such the system controller 160 of FIG. 1. In other or similar implementations, one or more operations of the method 400 may be performed by one or more other machines not depicted in the figures,

[0041] At operation 410, processing logic initiates imaging of a sample using an acoustic microscopy. More specifically, the acoustic microscope may direct acoustic pulses toward the sample. For example, initiating imaging of the sample may include causing an acoustic pulse generator to generate an acoustic pulse. In some embodiments, the imaging is subsurface imaging of a subsurface feature of the sample. In some embodiments, the imaging is surface imaging of a surface feature of the sample. In some embodiments, the sample is a substrate associated with an electronic device (e.g., wafer). The acoustic microscopy system may include at least one scan head located above the sample. In some embodiments, multiple scan heads are located above the sample at respective radial distances relative to the center position.

[0042] At operation 420, processing logic causes the sample to be scanned at a radial distance relative to a center position of the sample. More specifically, processing logic may cause the sample to rotate (e.g., a stage on which the sample is located on) at a rotational speed determined based on the radial distance (e.g., inversely proportional to the distance). The spiral scan resulting from the scanning at operation 420 may correspond to a pixel having a pixel size.

[0043] At operation 430, processing logic determines whether imaging is complete. If so, then the process ends. If not, processing logic may revert back to operation 420 to cause the sample to be scanned at a different radial distance relative to the center position of the sample. For example, if the different radial distance is less than the previous radial distance, then the rotational speed may be increased to maintain the pixel size. Further details regarding operations 410-430 are described above with reference to FIGS. 1-3.Attorney Docket No.: 36119.2932 (L2283PCT)

[0044] Referring back to FIG. 1, in alternative embodiments, the system 100 may use a translational motion scanning method for subsurface imaging and inspection of the sample 180. For example, the stage 170 may be a translational motion stage (e.g., x-y motion stage). To address the drawbacks of typical translational motion scanning methods as described above, the system 100 may include multiple heads divided into multiple groups of heads. Illustratively, if the system 100 includes 20 heads, the 20 heads may be grouped into 5 scanner groups of 4 heads each, 4 scanner groups of 5 heads each, or any suitable combination of groups of heads. However, the number of heads and / or groups of heads should not be considered limiting. Each group of heads may have its own height controller to ensure that proper focus is maintained as the sample is scanned. The individual lenses in each group of heads may be aligned in the z-direction, so that a single focus tracking mechanism may keep the entire scanner group in focus. Each group of heads may be implemented within a translational motion scanner (e.g., bidirectional motion scanner), such as a flexural scanner or voice coil scanner. For example, each group of heads may be placed onto a bridge structure over the sample 180 (e.g., staggered over the sample 180). Fast action of the translational motion scanner may cause each head of a group of heads to perform a line scan per cycle (e.g., the horizontal orx-direction). The continuously moving translational motion stage may advance by one pixel in the perpendicular direction during each fast line scan time (e.g., the y-direction). As a result, each of the heads may define a lane on the sample 180, similar to a swim lane. The edges of any two adjacent lanes may overlap by a small amount (e.g., about 10 pixels), which may allow for alignment of the data in adjacent lanes. The number of swaths during a scan (e.g., unidirectional scan) may be equal to the number of groups of heads, with each swath including a set of partially overlapping lanes (e.g., 4 lanes in a 4-head per scanner group embodiment). At this point, the stage 180, in the other direction (e.g., x-direction), may advance by an amount equal to the total width of a swath (e.g., the total width of the lanes in each swath). For example, if each lane extends about 2 mm, for the 4-head per scanner group example described above, then the stage 170 may advance by 8 mm (i.e., 4 heads multiplied by 2 mm). Then, the stage 170 may begin moving in a second direction perpendicular to the first direction (e.g., the y-direction). In this manner, each group of heads may define lanes as before, but in the second direction. At the end of this scan, the sample 180 may be scanned by 10 swaths, with each swath including 4 lanes. The process may then resume as follows: the stage 170 may move in the first direction (e.g., the x-direction) by the equivalent of a single swath width, and then the stage 170 may move in the second direction (e.g., the y-direction). This process may repeat until the entire sample 180 isAttorney Docket No.: 36119.2932 (L2283PCT)scanned. Further details regarding implementing the system 100 using a translational motion scanning method for subsurface imaging and inspection of the sample 180 will now be described below with reference to FIGS, 5A-7.

[0045] FIG. 5 is a diagram 500 A of an example implementation of an acoustic microscopy system using a translation motion scanning method for subsurface imaging and inspection, according to some embodiments. The diagram 500A shows a group of heads 510A, which may include head 512A. In this illustrative example, the heads of the group of heads 510A may be arranged in a zigzag or zipper formation. Although the group of heads 510A in this example may include four heads (e.g., 4-head per scanner group), the number of heads in a scanner group should not be considered limiting.

[0046] The diagram 500A further shows multiple swaths 520A through 526A, and each head of the group of heads 510A may scan a respective swath of the multiple swaths 520 A through 526A. For example, the head 512 A may scan the swath 526 A. During the scan, each head of the group of heads 510A may move rapidly in a first direction (e.g., the horizontal direction) within the width of its respective swath (as indicated by the horizontal arrow shown in diagram 500A) as each head of the group of heads 510A may proceed across the sample in a second direction perpendicular to the first direction (e.g., the vertical direction). For example, the motion in the first direction may have a frequency defined by a sinusoidal wave function. There may be overlap regions between adjacent swaths, such as an overlap region 530A between the swath 524A and the swath 526A, to help ensure continuity in pixel stitching. Accordingly, instead of a single head scanning a single swath, multiple heads may be arranged to scan multiple swaths in the same direction.

[0047] FIG. 5B is a diagram 500B of an example implementation of an acoustic microscopy system using a translation motion scanning method for subsurface imaging and inspection, according to some embodiments. The diagram 500B shows a group of heads 510B, including head 512B. In this illustrative example, the heads of the group of heads 510B may be arranged in a diagonal formation. Although the group of heads 510B in this example may include four heads (e.g., 4-head per scanner group), the number of heads in a scanner group should not be considered limiting. The diagram 500B further shows multiple swaths 520B through 526B, and each head of the group of heads 510B may scan a respective swath of the multiple swaths 520B through 526B. For example, the head 512B may scan the swath 526B. During the scan, each head of the group of heads 510B may move rapidly in a first direction (e.g., the horizontal direction) within the width of its respective swath (as indicated by the horizontal arrow shown in the diagram 500B) as each head of the group of heads 510BAttorney Docket No.: 36119.2932 (L2283PCT)may proceed across the sample in a second direction perpendicular to the first direction (e.g., the vertical direction). For example, the motion in the first direction may have a frequency defined by a sinusoidal wave function. There may be overlap regions between adjacent swaths, such as an overlap region 530B between the swath 524B and the swath 526B, to help ensure continuity in pixel stitching. Accordingly, instead of a single head scanning a single swath, multiple heads may be arranged to scan multiple swaths in the same direction.

[0048] FIG. 6 is a diagram 600 of a top-down view of an example implementation of an acoustic microscopy system using a translation motion scanning method for subsurface imaging and inspection, according to some embodiments. The diagram 600 shows multiple groups of heads 610-1 through 610-5 attached above a sample 620 (e.g., wafer). Each group of heads 610-1 through 610-5 may include multiple heads arranged in a staggered formation above the sample 620 to scan multiple swaths in the same direction. For example, each group of heads 610-1 through 610-5 may be similar to at least one of the group of heads 510A of FIG. 5A and / or the group of heads 510B of FIG. 5B. The multiple groups of heads 610-1 through 610-5 may scan respective regions of the sample 620 simultaneously. For example, during the scan, the group of heads 610-1 may start from a first end of the sample 620 (e.g., corresponding to the top of the diagram 600) and proceed, without loss of generality, toward a second end of the sample 620 opposite the first end (e.g., corresponding to the bottom of the diagram 600). The group of heads 610-1 may then complete its swath by proceeding back toward the first end of the sample 620. Upon returning to the first end of the sample 620, the group of heads 610-1 may move in the perpendicular direction by an amount equal to the total width of the swaths scanned by the group of heads 610-1 (e.g., the width of the swaths 520 A through 526 A of FIG. 5 A or the width of the swaths 520B through 526B of FIG. 5B). Although five groups of heads are shown in the diagram 600, the number of groups of heads should not be considered limiting. For example, in some embodiments, the acoustic microscopy system includes a single group of heads. Increasing the number of groups of heads may increase throughput, at the expense of implementation complexity. Accordingly, the number of groups of heads used to scan the sample 620 may be selected to achieve an appropriate balance between throughput and complexity.

[0049] FIG. 7 is a flowchart of a method 700 for implementing an acoustic microscopy system using a translational motion scanning method for subsurface imaging and inspection, according to some embodiments. The method 700 is performed by a system that may include hardware (circuitry, dedicated logic, optical measuring tools as described herein, etc.), software (such as is run on a general-purpose computer system or a dedicated machine).Attorney Docket No.: 36119.2932 (L2283PCT)firmware, or some combination thereof. In some embodiments, the method 700 is performed by a system controller of an acoustic microscopy system, such the system controller 160 of FIG. 1. In other or similar implementations, one or more operations of the method 700 may be performed by one or more other machines not depicted in the figures.

[0050] At operation 710, processing logic initiates imaging of a sample using an acoustic microscopy. More specifically, the acoustic microscope directs acoustic pulses toward the sample. For example, initiating imaging of the sample may include causing an acoustic pulse generator to generate an acoustic pulse. In some embodiments, the imaging is subsurface imaging of a subsurface feature of the sample. In some embodiments, the imaging is surface imaging of a surface feature of the sample. In some embodiments, the sample is a substrate associated with an electronic device (e.g., wafer). The acoustic microscopy system may include multiple scan groups of heads located above the sample. Each scan group of heads may include multiple scan heads, where each scan head of a scan group is configured to scan a respective swath of the sample.

[0051] At operation 720, processing logic causes the sample to be scanned using translational motion. For example, causing the sample to be scanned using translational motion may include causing a stage on which the sample is on to move translationally (e.g., rectilinearly). Further details regarding operations 710-720 are described above with reference to FIGS. 1 and 5A-6.

[0052] Embodiments of the present disclosure provide various technical advantages. For example, embodiments described herein may be used to perform subsurface imaging and inspection of samples with increased scanning throughput as compared to traditional imaging and inspection techniques.

[0053] FIG. 8 depicts a diagrammatic representation of a machine in the example form of a computing device 800 within which a set of instructions, for causing the machine to perform any one or more of the methodologies discussed herein, may be executed. In alternative embodiments, the machine may be connected (e.g., networked) to other machines in a Local Area Network (LAN), an intranet, an extranet, or the Internet. The machine may operate in tire capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC), a tablet computer, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch orbridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by th at machine. Further, while only a single machine is illustrated, the termAtorney Docket No.: 36119.2932 (L2283PCT)“machine” shall also be taken to include any collection of machines (e.g., computers) that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. In embodiments, computing device 800 may correspond to the system controller 160 of FIG. 1.

[0054] The computing device 800 includes a processing device 802, a main memory 804 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM), etc.), a static memory 806 (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory (e.g., a data storage device 818), which communicate with each other via a bus 808.

[0055] Processing device 802 may represent one or more general-purpose processors such as a microprocessor, central processing unit, or the like. More particularly, the processing device 802 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processing device 802 may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processing device 802 may also be or include a system on a chip (SoC), programmable logic controller (PLC), or other type of processing device. Processing device 802 is configured to execute the processing logic for performing operations discussed herein.

[0056] The computing device 800 may further include a network interface device 822 for communicating with a network 864. The computing device 800 also may include a video display unit 810 (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device 812 (e.g., a keyboard), a cursor control device 814 (e.g., a mouse), and a signal generation device 820 (e.g., a speaker).

[0057] The data storage device 818 may include a machine-readable storage medium (or more specifically a non-transitory computer-readable storage medium) 824 on which is stored one or more sets of instructions 826 embodying any one or more of the methodologies or functions described herein. A non-transitory storage medium refers to a storage medium other than a carrier wave. The instructions 826 may also reside, completely or at least partially, within the main memory 804 and / or within the processing device 802 during execution thereof by the computer device 800, the main memory 804 and the processing device 802 also constituting computer-readable storage media.Attomey Docket No.: 36119.2932 (L2283PCT)

[0058] While the non-transitory computer-readable storage medium 824 is shown in an example embodiment to be a single medium, the term “computer-readable storage medium” should be taken to include a single medium or multiple media (e g., a centralized or distributed database, and / or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable storage medium” shall also be taken to include any medium that is capable of storing or encoding a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. The term “computer-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media.

[0059] The preceding description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth in order to provide a good understanding of several embodim ents of the present disclosure. It will be apparent to one skilled in the art, however, that at least some embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present disclosure. Thus, the specific details set forth are merely exemplary. Particular implementations may vary from these exemplary details and still be contemplated to be within the scope of the present disclosure.

[0060] Reference throughout this specification to “one embodiment” or “an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. In addition, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” When the term “about” or “approximately” is used herein, this is intended to mean that the nominal value presented is precise within ± 10%.

[0061] Although the operations of the methods herein are shown and described in a particular order, the order of operations of each method may be altered so that certain operations may be performed in an inverse order so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent and / or alternating manner.

[0062] It is understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. The scope of the disclosure should, therefore, beAtorney Docket No.: 36119.2932 (L2283PCT)determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

Attorney Docket No.: 36119.2932 (L2283PCT)CLAIMSWhat is claimed is:

1. A system comprising:at least one processing device configured to perform operations comprising:initiating imaging of a sample using an acoustic microscope, wherein the sample is located on a stage; andcausing the sample to be scanned at a radial distance relative to a center position of the sample to perform the imaging of the sample, wherein the stage rotates at a rotational speed determined based on the radial distance.

2. The system of claim 1, wherein the operations further comprise:determining whether the imaging of the sample is complete; andin response to determining that the imaging of the sample is incomplete, causing the sample to be scanned at a second radial distance relative to the center position of the sample different from the radial distance, wherein the stage rotates at a second rotational speed, different from the rotational speed, determined based on the radial distance.

3. The system of claim 1, wherein the rotational speed is determined to maintain a pixel size.

4. The system of claim 1, wherein the imaging of the sample comprises subsurface imaging of a subsurface feature of the sample.

5. The system of claim 1, further comprising an acoustic pulse generator, wherein initiating the imaging of the sample comprises causing the acoustic pulse generator to generate an acoustic pulse to be directed to the sample using the acoustic microscope.

6. The system of claim 1, further comprising:the acoustic microscope comprising an acoustic lens to direct an acoustic pulse toward the sample, and an ultrasonic transducer to convert a reflected acoustic pulse from the sample into an electrical signal; anda detection system to process the electrical signal for generating an image of the sample.Attorney Docket No.: 36119.2932 (L2283PCT)7. The system of claim 6, further comprising a switching network to receive the electrical signal from the ultrasonic transducer, and to send the electrical signal to the detection system.

8. A method comprising:initiating, by at least one processing device, imaging of a sample using an acoustic microscope, wherein the sample is located on a stage; andcausing, by the at least one processing device, the sample to be scanned at a radial distance relative to a center position of the sample to perform the imaging of the sample, wherein the stage rotates at a rotational speed determined based on the radial distance.

9. The method of claim 8, further comprising:determining, by the at least one processing device, whether the imaging of the sample is complete; andin response to determining that the imaging of the sample is incomplete, causing, by the at least one processing device, the sample to be scanned at a second radial distance relative to the center position of the sample different from the radial distance, wherein the stage rotates at a second rotational speed, different from the rotational speed, determined based on the radial distance.

10. The method of claim 8, wherein the rotational speed is determined to maintain a pixel size.

11. The method of claim 8, wherein the imaging of the sample comprises subsurface imaging of a subsurface feature of the sample.

12. The method of claim 8, wherein initiating the imaging of the sample comprises causing an acoustic pulse generator to generate an acoustic pulse to be directed to the sample using the acoustic microscope.

13. The method of claim 8, wherein the acoustic microscope comprises an acoustic lens to direct an acoustic pulse toward the sample, and an ultrasonic transducer to convert a reflected acoustic pulse from the sample into an electrical signal.Atorney Docket No.: 36119.2932 (L2283PCT)14. A system comprising:a translational motion stage to receive a sample; andat least one group of scan heads located above the translational motion stage to generate an image of the sample by using acoustic microscopy, wherein the at least one group of scan heads comprises a plurality of scan heads arranged in a staggered formation.

15. The system of claim 14, wherein the at least one group of scan heads comprises a plurality' of groups of scan heads.

16. The system of claim 14, wherein each scan head of the plurality of scan heads is configured to scan a respective swath of a plurality' of swaths.

17. The system of claim 16, wherein:the plurality of scan heads comprises a first scan head to scan a first swath of the plurality of swaths, and a second scan head adjacent to the first scan head to scan a second swath of the plurality of swaths; andthe first swath and the second swath define an overlap region.

18. The system of claim 14, wherein the staggered formation is a zigzag formation.

19. The system of claim 14, wherein the staggered formation is a diagonal formation.

20. The system of claim 14, wherein the image comprises a subsurface feature of the sample.

Images