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Thermomechanical local stress in assembled GaN LEDs investigated by Raman optical spectroscopy
Author(s): Raffaella Signorini; Fosca Conti; Enrico Brugnolotto; Danilo Pedron; E. Liu; Sri Krishna Bhogaraju; Gordon Elger
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Paper Abstract

Integrated circuits constitute a complex mosaic, where materials with different characteristics, grown or deposited in different ways and at different temperatures, are linked together in various geometries. It is well known that during and after processing of these devices, mechanical stresses develop in the layers. These stresses may be due to thermal steps, intrinsic stresses, which are inherent in the formation process of the film, or due to the geometry of the material. For example, high stresses are present in the substrate at film edges. The presence of local residual stress has an important effect on the electrical properties of electronic devices, in particular on the reliability and the lifetime of the semiconductor components.

The present work focuses on the optical investigation of the thermomechanical stress of semiconductor materials used to realize new LED modules for front lighting application. Blue LEDs, based on gallium nitride (GaN) on sapphire, are bonded to a silicon carrier using gold silicon. Afterwards the sapphire is removed. The GaN on silicon devices are soldered by eutectic AuSn soldered on copper substrates, with different thicknesses. In the solder process different AuSn solder layer are achieved by varying the bond force. Raman spectroscopy is used to investigate the influence of the assembly process and assembly material on the local stress in the semiconductor. By that the physical, mechanical and chemical properties of the interconnect material can be analyzed. A model is developed to simulate the thermomechanical stress in the GaN LED assemblies. The Raman results validate the computational model. The phenomena are evaluated at room temperature, at -50°C and at 180°C.

Paper Details

Date Published: 26 April 2019
PDF: 10 pages
Proc. SPIE 11031, Integrated Optics: Design, Devices, Systems, and Applications V, 110310I (26 April 2019); doi: 10.1117/12.2520992
Show Author Affiliations
Raffaella Signorini, Univ. degli Studi di Padova (Italy)
Fosca Conti, Univ. degli Studi di Padova (Italy)
Enrico Brugnolotto, Univ. degli Studi di Padova (Italy)
Danilo Pedron, Univ. degli Studi di Padova (Italy)
E. Liu, Technische Hochschule Ingolstadt (Germany)
Sri Krishna Bhogaraju, Technische Hochschule Ingolstadt (Germany)
Gordon Elger, Technische Hochschule Ingolstadt (Germany)

Published in SPIE Proceedings Vol. 11031:
Integrated Optics: Design, Devices, Systems, and Applications V
Pavel Cheben; Jiří Čtyroký; Iñigo Molina-Fernández, Editor(s)

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