Inspecting semiconductor assemblies for damage and defects
For semiconductor assemblies, the requirement of a precise, thorough inspection for damage and defects is especially high. With the help of infrared light, active components and/or structures on any surface or depth within the wafer may be checked for defects and for damage incurred during production. This can be done on the wafer level and also after dicing. Inspection tasks include:
- Inspection for surface defects as well as defects in volume material (inclusions, etc.) in bare wafers.
- Alignment tasks mean checking that two fiducial structures are properly oriented to each other. This is always important when multiple wafers are stacked; in such a case the fiducials can only be seen with the help of infrared light.
- Inspection of bonded wafers for bonding defects, particles and contamination, and frit measurement.
- Investigation of the underfill beneath a FlipChip: here, we inspect for voids in the underfill and for correct positioning of the FlipChip.
Another special application is the inspection of MEMS (Micro Electro-Mechanical Systems). MEMS are composed of many mechanical elements, sensors and electrical circuits on a single substrate or chip. MEMS can, among other things, be employed as acceleration sensors for airbags. Just as it is in quality assurance of unstructured raw wafer material, it is essential to recognize defects in the silicon bulk material after the cap wafer is bonded. With infrared illumination, an optical structural analysis and investigation for contaminants is possible within minutes per wafer.
