Surface Metallization of Silicon Carbide By Electroless Deposition
Authors: Yamada Naoki , Sadakane Daisuke , Fukuda Kenji , Sakamoto Susumu , Fukumuro Naoki , Yae Shinji 
Published: February 2020

Silicon carbide (SiC) is one of the most promising semiconductor materials for a next generation of power devices. Its physical properties such as breakdown electric field and thermal conductivity are higher and more suitable for efficient power devices than those of silicon, which is common semiconductor material for the present devices. The metallization of SiC surfaces is a key technology to use SiC for power devices. The autocatalytic electroless deposition, which is a conventional method to metallize non-conductive substrates, has several advantages, however, cannot produce adhesive metal films directly on SiC. We recently developed a new surface-activation process for the direct electroless deposition of adhesive metal films on silicon substrates (1, 2). This process uses gold (Au) nanoparticles epitacially grown on silicon by an electroless displacement deposition (3, 4). In this study, this process is applied for formation of adhesive metal films on SiC.
The single crystalline n-type 4H-SiC (0001) wafers were used as the substrates. Au nanoparticles were deposited on SiC substrates using a HAuCl4 solution containing HF or KOH under photoillumination using a Hg-Xe short arc lamp. Then, nickel-phosphorus alloy (Ni-P) films were electrolessly formed on the SiC substrates by using NiSO4 solution containing NaPH2O2as a reducing agent. The adhesion of the electrolessly deposited Ni-P films on SiC substrates was examined by a tape test based on Japanese Industrial Standard JIS H8504 corresponding to ISO 2819.
Figure 1 shows SEM images of Au-nanoparticle-deposited SiC substrates. The size and particle density of Au deposited using the solution containing KOH (Fig. 1 (b)) were larger than that using HF (Fig.1 (a)). The surface of SiC substrates was roughened by the electroless deposition of Au nanoparticles. No photoillumination significantly attenuated the Au deposition. These results indicate that this Au nanoparticle deposition is a photoelectrochemical displacement reaction.
The autocatalytic electroless deposition of Ni-P films was initiated on the Au-nanoparticle-deposited SiC substrate. No deposition occurred on a bare SiC substrate. The adhesion of metal films formed on the SiC substrates depended on the deposition time of Au nanoparticles. Immersion of SiC substrates in the Au-deposition solution containing KOH for 15 min obtained high adhesion. No peeling occurred up to 1.3 μm in thickness of Ni-P films by the tape test. This result is similar to that in the case of single crystalline silicon substrates (1 - 4).
In conclusion, we successfully formed adhesive metal films directly on single crystalline SiC substrates by using wet processes that are electroless displacement deposition of Au nanoparticles and common autocatalytic electroless deposition of Ni-P alloy films.
Acknowledgements
The present work was partly supported by KAKENHI (26289276) from JSPS and A-STEP from JST.
References
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4) N. Yamada, S. Sakamoto, N. Fukumuro, and S. Yae., Symposium Z01 in this meeting (2016).

Figure 1