Temperature effects on the ruggedness of SiC Schottky diodes under surge current J. León a,⇑ , X. Perpiñà a , V. Banu a , J. Montserrat a , M. Berthou b , M. Vellvehi a , P. Godignon a , X. Jordà a a Systems Integration Department, IMB-CNM (CSIC), Campus Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Barcelona, Spain b Department of Methods for Systems Engineering, Ampere Laboratory, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, F 69134 Ecully Cedex, France article info Article history: Received 25 June 2014 Accepted 8 July 2014 Available online xxxx Keywords: Wide-bandgap Ruggedness Failure analysis Silicon carbide Schottky barrier diodes Infrared lock-in thermography abstract This work analyzes the effects of temperature on the destruction of 1.2 kV–10 A silicon carbide (SiC) tungsten-based Schottky barrier diodes (W-SBD’s) under surge current tests. First, W-SBD’s were aged and tested up to failure under surge current pulses, showing no ageing at 40 A amplitudes and a surge current capability of 64 A and 59 A when they are tested at room temperature (RT) and 200 °C, respec- tively. Then, they were inspected by IR lock-in thermography and Small sIgnal Modulation for Thermal Analysis (SIMTA) technique, all they showing physical failure signatures at the active area periphery. Scanning Electron Microscope inspections after Focused Ion Beam millings at these locations revealed that metal degradation due to field stopper bipolar activation was the failure mechanism. At RT, the sam- ples showed lighter degradation (electromigration and thermomigration, contact reconstruction), while at 200 °C, the metal contact was also sputtered off at the periphery. This correlates with the peripheral bipolar current density enhancement (bipolar activation voltage reduction) with temperature. These results are extensible to junction barrier Schottky diodes, as they present the same structure leading them to fail: Schottky and bipolar diodes parallel connected. Considering this, new solutions were pro- posed to enhance the W-SBD’s ruggedness under overloading conditions. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction In the last years, junction barrier Schottky (JBS) structures have been proposed as the best solution to increase the blocking capa- bility of silicon carbide (SiC) Schottky barrier diodes (SBD’s) [1– 3], using a distributed P–N junction along the active area instead of only at the device periphery (field stopper). However, this not only affects the reverse characteristics, but also modifies the device thermal behavior at forward bias [4]. In contrast with SBD’s, whose positive temperature coefficient is dictated by the series resistance [5], JBS thermal behavior is predominated by the bipolar junction, which turns the overall temperature coefficient to negative [4]. Notice that both structures present Schottky and bipolar contacts parallel connected, whose current density balance is dictated by the device temperature [4], which could cause destructive local self-heating effects, especially in high temperature applications [6,7]. To observe how this affects the ruggedness of such devices under electrical overloading conditions, this work analyzes the structural weak spots that caused the failure (i.e., physical failure signatures) of several 1.2 kV 10 A SiC tungsten-based SBD’s (W- SBD’s) under destructive surge current pulses (surge current capa- bility test) [8–12]. Such test was submitted to two groups of 5 W- SBD’s, the first one at room temperature (RT, 25 °C), and the second one at 200 °C. Since the aspect ratio between Schottky and bipolar contact is larger in SBD’s [13], the effect of temperature on the cur- rent density balance can be better studied, while the results can be extensible to JBS structures at different current scales [14]. To per- form such analysis, the infrared (IR) emission of the weak spots, acting as hot spots, was modulated and detected by using the Small sIgnal Modulation for Thermal Analysis (SIMTA) technique. This is performed by biasing the device at a fixed operating point of its static electrical output, and then superposing a small voltage ripple at a fixed frequency, which is performed by specific circuitry. This generates a thermal field in the frequency domain that is the detected by lock-in thermography (LIT) [15], which allows locating such weak spots. Then, Focused Ion Beam (FIB) millings at these locations, gathered with Scanning Electron Microscope (SEM) inspections, were carried out to reveal whether any structural modification occurred at the hot spots. In addition, Energy Disper- sive X-ray spectroscopy (EDX) measurements were performed to determine the materials involved in the failure (compositional information). http://dx.doi.org/10.1016/j.microrel.2014.07.020 0026-2714/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +34 93 594 77 00x2441; fax: +34 93 580 14 96. E-mail address: javier.leon@imb-cnm.csic.es (J. León). Microelectronics Reliability xxx (2014) xxx–xxx Contents lists available at ScienceDirect Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel Please cite this article in press as: León J et al. Temperature effects on the ruggedness of SiC Schottky diodes under surge current. Microelectron Reliab (2014), http://dx.doi.org/10.1016/j.microrel.2014.07.020