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NDT.net Issue - 2019-11 - NEWS
NDT.net Issue: 2019-11
Publication: e-Journal of Nondestructive Testing (NDT) ISSN 1435-4934 (NDT.net Journal)

X-RAY Inspection of Micro-Electro Mechanical Systems (MEMS)

TWI Ltd (The Welding Institute)193, Great Abington, Cambridge, United Kingdom

TWI is a consortium member of a Horizon 2020 funded project, called CITCOM. The project aims to create a near-line production inspection and measurement system capable of identifying defects introduced in the fabrication stage of micro-electro-mechanical systems (MEMS). The system uses a combination of non-destructive testing (NDT) techniques, including optical imaging and 2D x-ray imaging.

The components of the system, including an x-ray source, x-ray detector, and manipulator, were specifically selected and integrated for the purpose of inspecting MEMS, which are inherently challenging to inspect. MEMS are typically manufactured using a variety of processes such as deposition, lithography, and etching, producing thicknesses between 1 to 100µm, as well as using materials such as silicon, due to its inexpensiveness, availability, and ability to incorporate electronic functionality. This combination of small thicknesses and materials with low atomic numbers, such as silicon, make x-ray radiography difficult.

Current x-ray system set up
Current x-ray system set up.

Therefore, micron resolution is required to detect the smallest of defects within MEMS. The new system achieves this through the combination of a Nano-focused X-ray source, paired with a sensitive, small pitch X-ray detector. TWI conducted some initial tests on some MEMS samples, which proved the successful functionality of the system, as well as the control software developed in LabView.

The below images are an example of the systems functionality for metrology inspection, these six, independent images were captured as the manipulator rasters the sample across the beam-line between the source and detector to capture the full area of the sample.

High resolution X-ray inspection of MEMS samples. Samples provided by Phillips Research
High resolution X-ray inspection of MEMS samples. Samples provided by Phillips Research.

Future development plans, before the final delivery in October 2020, include installing a large substrate manipulator on the system, making it capable of inspecting MEMS wafers with up to 8” diameter. Also, the team plan to give the system a radiation shielding and safety system, allowing the system to be a standalone unit for laboratory use.

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