Low-temperature diffusion assisted by femtosecond laser-induced modifications at Ni/SiC interface

Abstract

We investigated low-temperature diffusion at the Ni/SiC interface with the assistance of femtosecond laser-induced modifications. Cross sections of the laser-irradiated lines of two different pulse energies -0.84 and 0.60 J/cm 2 in laser fluencewere compared before and after annealing at 673 K. At the laser fluence of 0.60 J/cm 2 , a single flat Ni-based particle was formed at the interface after annealing. The SiC crystal under the particle was defect-free. The present results suggest the potential application of femtosecond laser-induced modifications to the low-temperature fabrication of contacts at the interface without introducing crystal defects, e.g., dislocations and stacking faults, in SiC.

Femtosecond-laser-induced modifications on a 4H-SiC surface and their application to low-temperature diffusion at the Ni/SiC interface

“…In other words, although the average composition of the alloy layer was found to be Ni-10-12 mass % Si, the layer was thought to contain several types of Ni-silicide. In an earlier paper, 21) we reported the formation of a single Ni-Si alloy particle at the Ni=SiC interface irradiated with femtosecond laser pulses of 25 nJ at a fluence of 0.60 J=cm 2 . The chemical composition of the particle, Ni-10-12 mass % Si, was exactly the same as that found in this study.…”

“…Recently, we have irradiated the surface of a 4H-SiC crystal using a femtosecond laser at two different pulse energies of 35 and 25 nJ, followed by the deposition of a 100-nm-thick Ni film. 21) The irradiation was carried out along lines, and cross sections of laser-irradiated lines were observed by transmission electron microscopy (TEM) before and after low-temperature annealing at 673 K for 600 s. In the cross section of the line irradiated with 35 nJ laser pulses at a fluence of 0.84 J=cm 2 , we observed a surface concavity associated with a semispherical modification containing an amorphized region. In contrast, the crystallinity of SiC was maintained in the cross section of the line irradiated with 25 nJ laser pulses at a fluence of 0.60 J=cm 2 .…”

“…1, after annealing at 673 K for 600 s, a Ni-Si alloy particle with a convex-lens shape having a width of 600 nm (0.6 µm) was formed at the cross section of the laser-irradiated line with the fluence of 0.60 J=cm 2 . 21) The intensity at both edges of the alloy particle, x = ±0.3 µm, is calculated to be 0.873I 0 . Hence, we assume that this value is the critical intensity for inducing modifications to form a Ni-Si alloy particle at the Ni=SiC interface after annealing.…”

“…Recently, we explored the idea that the annealing temperature can be lowered by enhancing the reaction of Ni with SiC and the diffusion of Ni and Si atoms via the introduction of femtosecond-laserinduced modifications at the Ni=SiC interface. [19][20][21] A femtosecond laser produces intense and extremely small width pulses, typically about 100 fs. Since a femtosecondlaser pulse finishes before the relaxation of photoexcited electron energy into lattice vibration, the intense electric field of laser light athermally breaks the chemical bonds in the target.…”

“…Another important issue is the identification of Ni-silicide formed after low-temperature annealing, which was not carried out in an earlier study. 21) In addition, we have to visualize the distribution of C after annealing, owing to its potential importance in determining the electrical properties of contacts at the Ni=SiC interface. De Silva et al 22) reported on the control of C agglomeration by introducing amorphous regions on the SiC surface by Si ion implantation, followed by the Ni film deposition and the subsequent annealing at 1273 K.…”