Abstract
In this work, the ohmic contact mechanism of Ni electrodes on C-faced 4H-n-SiC was investigated by evaluating the electrical and microstructural properties in the contact interface as a function of annealing temperatures ranging from 950 to 1100°C. We determined that Ni-silicide, especially the NiSi phase, plays a key role in the formation of ohmic contacts rather than an increase in carbon vacancies in the C-faced SiC substrate. A vertically oriented NiSi phase was observed in the thermally annealed sample at the optimized temperature that behaves as a current path. A further increase in annealing temperature leads to the degradation of ohmic behavior due to the formation of horizontal-type NiSi in the Ni-rich Ni-silicide/NiSi/SiC structure.
Highlights
Many technical challenges need to be overcome to improve the performance of 4H-SiC-based power devices, such as Schottky barrier diodes (SBDs) and metal-oxidesemiconductor field-effect transistors (MOSFETs)
With N = 3:28 × 1018 cm−3 and T = 300 K, the calculation shows that E00/kT was as low as 0.695 which lies in the thermionic field emission (TFE) regime [11]. ρsc was calculated using ρsc coth1/2ðE00À/qkAT∗Þ∗/cko2sÁh ðE00 /kT Þ
The ohmic contact mechanism of Ni contact to C-face and n-type 4H-SiC can be characterized as follows: (1) The carrier concentrations extracted from Hall-effect and I – V – T measurements for the sample annealed at optimized conditions (1050°C) are nearly constant
Summary
Many technical challenges need to be overcome to improve the performance of 4H-SiC-based power devices, such as Schottky barrier diodes (SBDs) and metal-oxidesemiconductor field-effect transistors (MOSFETs). Ρsc on Ni contacts to Si-faced 4H-nSiC epitaxial layer is between 2:8 × 10‐3 and 1:1 × 10‐6 Ω·cm under the high temperature annealing at ~1000°C, depending on the process technique and doping concentration [2, 6,7,8]. The thermal annealing at high temperature, can damage the oxide and SiC/SiO2 interface, which is undesirable for device fabrication. Ni-based metal structures have been studied in order to form the low resistance ohmic contact even under the low temperature annealing process. With low annealing temperature at 750°C or 950°C, the ohmic contacts have low ρsc values, respectively, of 8 × 10‐4 and 4:2 × 10‐5 Ω·cm and were achieved by using Ni/Ti/Al and Ni/Ti/Al/W metal schemes [9, 10]
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