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Aluminum-germanium wafer bonding of (AlGaIn)N thin-film light-emitting diodes

: Goßler, C.; Kunzer, M.; Baum, M.; Wiemer, M.; Moser, R.; Passow, T.; Köhler, K.; Schwarz, U.T.; Wagner, J.


Microsystem Technologies 19 (2013), Nr.5, S.655-659
ISSN: 0946-7076
Fraunhofer IAF ()
Fraunhofer ENAS ()

Eutectic aluminum-germanium wafer bonding was used to fabricate (AlGaIn)N thin-film light-emitting diodes (LEDs). Wafer bonding was carried out on 2`' wafer level at a bond temperature of 470 (0)C using patterned Al bond pads on the GaN-on-sapphire LED epiwafer and plain Ge substrates. The microstructure of the joint formation was characterized via cross-section analysis using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Scanning acoustic microscopy was used to investigate the bond interface. The shear strength was determined to be 1-2 kN/cm(2). The formation of a liquid Al-Ge phase is evident from crosssection analysis and optical microscopy. During solidification, Al and Ge are separated into distinct phases again, which is revealed by EDX. The obtained bond is not free of micro-voids, yet it is mechanically stable and suited for the fabrication of thin-film LEDs by removing the sapphire substrate via laser lift-off, which is also demonstrated.