Feature: T&M


of SiC devices, it is highly important to identify potential defects through advanced metrology systems like scanning acoustic microscopy, or SAM. Tis is a non-invasive, non-destructive, ultrasonic testing method capable of high speed 100% testing, and an industry standard for the inspection of semiconductor components inside microelectronic devices. Its recent advances also allow it to detect much smaller defects than previously possible. In the past, detecting a 500-micron defect was an achievement, now the benchmark is 50 microns. With this type of testing, we can inspect materials and discover flaws that were previously undetected. In fact, SAM seems to address at least


one of the goals identified by the National Institute of Standards and Techn ology (NIST) in its report “Strategic Opportunities for US Semiconductor Manufacturing identifies 7 Grand Challenges” as necessary for the US to lead the global semiconductor manufacturing industry once again. Te report identifies 32 “path forward elements” that describe potential strategies, one of which is advanced metrology for future microelectronics manufacturing. SAM can address the “rapid, high-resolution, non- destructive techniques for characterising defects and impurities and correlating them with performance and reliability”.


SAM SAM functions by directing focused sound from a transducer at a small point on a target object. Te sound hitting the object is either scattered, absorbed, reflected or transmitted. By detecting the direction of scattered pulses and their time of flight, the presence of a boundary or an object can be determined, as well as its distance. Samples are then scanned point by point


or line by line to produce an image. Scanning modes range from single layer views to tray scans and cross-sections. Multi-layer scans can include up to 50 independent layers. Depth-specific information can be extracted and applied to create two- and three- dimensional images that can be analysed to detect and characterise flaws such as cracks, inclusions and voids. Smaller manufacturers and independent testing labs are likely to have a tabletop SAM


instrument that provides a scan envelope of over 300mm, with a maximum scan velocity of 500mm/s and accuracy and repeatability of ±5 microns. Soſtware allows using saved data to virtually re-scan, view and analyse data for simultaneous real-time analysis or post-collection review. Oſten, such tabletop units are used to analyse data for failure analysis, product inspection, quality control, R&D and process validation, as well as to determine product reliability in process quality control and vendor qualification. As requirements rise to accommodate


testing for higher levels of production, SiC crystal growers, wafer manufacturers and semiconductor fabs will typically use a larger system for high-speed inspection. Te challenge here is to perform the inspection at extremely high throughput, with 100% flaw identification, and remove those SiC crystals or sliced wafers that don’t meet the quality requirements. Tis requires more advanced equipment that can simultaneously inspect several layers, oſten on multiple channels, scanning multiple samples in handling trays in an automated fashion to accelerate the process. SAM can also be custom designed


to be fully integrated into high-volume manufacturing systems. Advanced inspection technologies detect minute flaws in SiC boules and semiconductor wafers for 100% inspection of all materials. Recent advancements in SAM technology


have also significantly improved throughput speeds and defect detectability. When high throughput is required for 100% inspection, ultra-fast single or dual-gantry scanning systems are used along with multi-head transducers, to simultaneously scan for higher throughput.


The software As important as the physical and mechanical aspects of scanning is the soſtware, which improves scan resolution and analyses the information. Multi-axis options enable A, B and C scans, contour following, off-line analysis, and virtual rescanning of chips, resulting in highly-accurate internal and external inspection of defects and thickness measurement via the inspection soſtware. An off-line analysis mode is also available for virtual scanning. A soſtware-driven model can reduce costs


of SAM testing whilst delivering the same quality of inspection results, making this type of equipment within reach of smaller SiC testing labs. Every SiC crystal grower and semicon-


ductor wafer producer will eventually move towards a higher level of failure analysis because of today’s stringent detection and precision requirements. Te cost advantages and time savings of SAM equipment make this possible. In fact, advanced SAM systems are now considered essential tools in SiC production facilities, R&D and quality assurance labs.


Cutting-edge metrology is essential for efficient electronics


www.electronicsworld.co.uk June 2024 29


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