Universal mechanisms of Al metallization ageing in power MOSFET devices |
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| Institution: | 1. CEMES-CNRS, 29 rue Jeanne Marvig, 31055 Toulouse Cedex 4, France;2. Freescale Semiconductor Inc., 134 Avenue du Général Eisenhower, 31100 Toulouse, France;1. Texas Instruments, Haggertystr. 1, 85356 Freising, Germany;2. Infineon Technologies AG, Am Campeon 1-12, 85579 Neubiberg, Germany;1. Purdue University, School of Materials Engineering, West Lafayette, IN 47907, United States;2. Purdue University, School of Mechanical Engineering, West Lafayette, IN 47907, United States;1. Universidade Federal do Rio Grande do Sul—UFRGS, Porto Alegre 90035-190, Brazil;2. IMEC, Leuven B-3001, Belgium;3. TU Wien, Vienna A-1040, Austria;1. IBM T.J. Watson Research Center, Route 134, Yorktown Heights, NY 10598, USA;2. IBM Systems and Technology Group, IBM Deutschland Research and Development, Boeblingen, Germany |
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| Abstract: | Power MOSFET devices are extensively used in the automotive industry, but their modes of ageing are still poorly understood. Here we focus on the physical degradation mechanisms that occur in the upper Al-based metallization layer (source). This layer undergoes thermo-mechanical structural modifications due to the combination of electrical pulses and differences between the various coefficients of thermal expansion. Using electronic and ionic microscopy, we show that ageing can be divided in 2 phases where dislocation-based plasticity and then grain boundary diffusion become predominant. As a result, grain boundary grooving and surface roughening follows a partial division of the later in disconnected Al grains. Such a degradation of the metallization has been widely observed in various devices. It may lead to the observed augmentation of resistivity and also to the focusing of the various current paths, promoting hot spots and subsequent failure. |
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| Keywords: | Al metallization Plastic deformation Grain boundary diffusion TEM FIB |
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