Laser Processing of Ti Contacts for Ohmic Behavior on P‑Type 4H-SiC

Abstract

This work explores a key challenge in power device fabrication: the formation of ohmic contacts on p-type 4H-silicon carbide (SiC). We demonstrate a selective, low thermal budget approach using single titanium (Ti) metallization combined with pulsed laser annealing (PLA), as an alternative to both metallic multilayer stacks and conventional high-temperature annealing. By applying PLA with fluences above 3.6 J/cm², Ti contacts exhibit linear current-voltage (I-V) behavior, indicating effective ohmic contact formation, with over 50% improvement in conduction observed at 3.8 J/cm². Cross-sectional transmission electron microscopy (TEM) and elemental mapping reveal that higher fluences promote deeper SiC consumption, and the formation of a continuous, epitaxially regrown SiC layer, bonded to a uniform titanium carbide (TiC) layer extended deeper into the p-doped region. This structure supports efficient charge transfer and strong interfacial bonding. Furthermore, increasing fluence drives the transient liquid phase composition from Ti-rich toward a more balanced Ti-Si-C composition, promoting the formation of ternary phases enriched in Si and C that enhance interfacial stability and electrical performance. This work demonstrates that PLA offers precise control over interfacial reactions and contact microstructures, offering a scalable, selective, and thermally efficient approach for ohmic contacts on p-type 4H-SiC, advancing the development of high-performance, next-generation SiC-based power electronics.

Keywords: merged PiN Schoktty; ohmic contact; phase composition; pulsed laser annealing; silicon carbide.

1

I–V characteristics, acquired between adjacent TLM pads, at three different distances of 10, 30, and 50 μm, fabricated by depositing on p⁺ 4H-SiC 100 nm of Ni and 20 nm of Ti followed by RTA at 1000 and 1100 °C, respectively. The inset shows R_T values for the 100 nm Ni sample annealed at 1000 °C.

2

Schematic illustration (a) of Ni contacts on p-type implanted 4H-SiC in a MPS structure and the corresponding plan view scanning electron microscopy (SEM) (b) after RTA above 900 °C, revealing the formation of NiSi protrusion extending beyond the p⁺ 4H-SiC region.

3

I–V characteristics, acquired between adjacent TLM pads, made with 20 nm of Ti, at distance of 10 μm, after two laser pulses at 3.4, 3.6, and 3.8 J/cm² region. The inset shows R _T values for the samples irradiated at 3.6 and 3.8 J/cm².

4

Cross-sectional Dark Field Scanning Transmission Electron Microscopy (DF-STEM) images of 20 nm of Ti deposited on p⁺ 4H-SiC layer irradiated with two distinct laser pulse fluences at (a) 3.4 J/cm² and (f) 3.8 J/cm². The electron energy loss spectroscopy (EELS) elemental maps reveal the distribution of key elements within the irradiated region: Ti (b, g), Si (c, h), C (d, i), and O (e, l), respectively. These maps highlight the changes in elemental composition and diffusion behavior induced by varying laser fluences.

5

Cross-sectional STEM images of Ti contacts on p+ 4H-SiC layer irradiated with two laser pulses at (a) 3.4 J/cm² and (b) 3.8 J/cm². The images highlight the variation in thickness of the modified region, from the SiO₂ top layer to the SiC substrate, and the formation of distinct compound layers.

6

High-resolution TEM images of the sample irradiated with two laser pulses at 3.8 J/cm², with the relative FFT revealing the coexistence of well-defined crystalline regions, including 3C-TiC and 3C-SiC, epitaxially grown on the 4H-SiC epi-layer.