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shifting to methods of non-destructive testing like Scanning Acoustic Microscopy. SAM is a non-invasive and non-


destructive ultrasonic testing method that is quickly becoming the preferred technique for testing and failure analysis involving stacked dies or wafers. The equipment utilises ultrasound


waves to non-destructively examine internal structures, interfaces and surfaces of opaque substrates. The resulting acoustic signatures can be constructed into 3-dimensional images that are analysed to detect and characterise device flaws such as cracks, delamination, inclusions and voids in bonding interfaces, as well as to evaluate soldering and other interface connections. SAM is already the industry


standard for 100 per cent inspection of semiconductor components to identify defects such as voids, cracks and delamination within microelectronic devices. Now the technology has been adapted


to facilitate 100 per cent inspection of hybrid bonded packages. Innovations in the design of wafer chucks, array transducers and AI-based analysis of inspection data are converging to provide a more robust SAM solution for fabs involved in hybrid bonding.


Solving the Hybrid Bonding Inspection Challenge With hybrid bonding, various steps must be reliably performed to ensure quality, with any failures resulting in unacceptable defects. The stakes are higher than ever considering that even one bad wafer, die or interconnection could cause the entire package to be discarded down the line. Sub 10-micron defect detection is the new normal. The process begins by manufacturing


the wafers or dies in a semiconductor fab before the chips are bonded together. Typically, the key process steps include the preparation and creation of the pre-bonding layers, the bonding process itself, the post-bond anneal and the associated inspection and metrology at


each of the steps. With conventional SAM techniques,


wafers were held horizontally in a chuck and processed in a water medium, and this occasionally could lead to water ingress, trapping water, which could cause significant issues in the next step of assembly. By re-designing the chuck in a


vertical orientation, PVA TePla OKOS, a Virginia-based manufacturer of SAM and industrial ultrasonic non- destructive (NDT) systems, can use gravity to eliminate any concern over water ingress, along with other water management technologies. Scanning acoustic microscopy works


by directing focused sound from a transducer at a small point on a target object. The sound hitting the object is either scattered, absorbed, reflected or transmitted. By detecting the direction of scattered pulses as well as the ‘time of flight,’ the presence of a boundary or object can be determined as well as its distance. To produce an image, samples are


scanned point by point and line by line. 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. The images are then analysed to detect and characterise flaws such as cracks, delamination and voids. Advancements in AI-based analysis of


the data collected from SAM inspection of wafer-to-wafer hybrid bonding will further automate quality assurance and increase fab production. When fabs take advantage of the


higher level of failure detection and analysis, the production yield and overall reliability of high-performance chips improve significantly. Every fab will eventually move towards this level of failure analysis because of the level of detection and precision required for hybrid bonding. Hybrid bonding represents a significant advancement in chip


packaging technology, offering numerous benefits that enhance performance, efficiency and scalability of semiconductor devices. SAM stands ready to deliver 100


per cent non-destructive inspection of vertically stacked and bonded die-to- wafer (D2W) or wafer-to-wafer (W2W) packages at extremely high speeds to help facilitate the adoption of this technology.


For more information, contact PVA TePla OKOS at info@okos.com or visit www.okos.com.


www.electronicsworld.co.uk Dec 2024/Jan 2025 17


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