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Optical, non-contact TSV evaluation
Keywords: non-contact, TSV evaluation, multipurpose wafer measurement
As a part of the 3D system are TSVs (Through Silicon Vias) the core technology for the integra-tion of multiple or heterogeneous chips in a 3D package. It allows using the shortest interconnection by using in 3rd dimension. The goal of further optimization is for the TSV formation on active chips to reserve a large portion of the wafer chip for the functional devices. TSV with aspect ratios 15/1 and more are tar-geted and require careful metrology control during process. ISIS sentronics provides SemDex systems for multi-purpose semi- and fully automated wafer measurements, equipped with several optical sensors for different tasks. The point StraDex f sensors evaluate thickness of silicon and other substrates, bow/ warp by scanning the wafer contactless. One in particular has been tailored to evaluate depth of unfilled TSVs and Remaining Silicon Thickness (RST). The area StraDex a sensor covers on the other hand a small area of about (0.4 mm)2 simultane-ously while being able to cover 3D structures at sub-µm lateral resolution of more than 100 µm in height or – to some extend – in depth. For large aspect ratios, we evaluate the diameter with the area sensor while obtaining the depth with the aforementioned point sensor. Also the etched “copper nails” can be directly evaluated with the area sensor at sub-µm level in lateral direction and nm-level in height. In addition, surface roughness can be inspected down to nm level for the indirect risk assessment of included micro-cracks being a potential consequence of grinding procedures. All sensors are based on “White-Light Interferometry”. The point sensors for silicon thickness eval-uation are operated with near infrared light and are extremely fast in data acquisition (4000 measurements/ sec). The area sensor runs at visible light with about 500 nm wavelength to permit highest possible lateral and axial resolution.
Dr. Alexander Knüttel, President
ISIS sentronics GmbH
Mannheim, Deutschland (DEU)

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