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Contactless visible light probing for nanoscale ICs through 10 μm bulk silicon

Boit, Christian; Lohrke, Heiko; Scholz, Philipp; Beyreuther, Anne; Kerst, Uwe; Iwaki, Y.

This paper explains why only optical techniques will be able to provide debug and diagnosis of bulk silicon FinFET technologies. In order to apply optical techniques through a convenient thickness of silicon on the one hand, light is limited to NIR to minimize absorption. To match resolution requirements on the other hand, it becomes mandatory to use shorter wavelengths. Two key issues have to be addressed: First, the penetration depth of visible light is only a few μm. This challenges device preparation and integrity. Our approach makes use of confocal microscopy suppressing back surface reflection and thus relaxing the preparation requirements to around 10 μm. Second, only solid immersion lenses (SIL) enable nanoscale resolution. But instead of silicon, materials transparent to visible light and providing a high refractive index are necessary. Our concept is based on 658 nm/633 nm laser and supports GaP as SIL material. We demonstrate the power of confocal imaging and prove contactless probing through a device thickness of 10 μm. We discuss how confocal optics relax the thickness requirements for visible light imaging and probing and we layout the concept for a GaP SIL. This concept opens the path to the design of nanoscale visible light debug and diagnosis.
Published in: Proceedings of the 35th Annual NANO Testing Symposium (NANOTS2015), Institute of NANO Testing