Susumu Sakamoto

Displacement deposition of gold nanoparticles and electroless deposition of nickel films on silicon-carbide (4H-SiC) wafers

Metallisation of silicon carbide (SiC) wafers is a key technology for producing efficient power devices. Conventional autocatalytic electroless deposition cannot produce adherent metal films directly on SiC substrates. The authors applied their recently developed surface-activation process for electroless metal-film deposition on silicon wafers to SiC wafers. Gold nanoparticles were produced on 4H-SiC substrates by displacement deposition after immersing the substrates in a tetrachloroauric(III) acid solution that includes hydrofluoric acid or potassium hydroxide. The size and the particle density of the deposited gold are changed with deposition parameters such as the surface condition of the substrates, the solution composition, and the UV-light illumination. The gold nanoparticles work not only as catalysts to initiate autocatalytic electroless deposition but also as binding-points between the metal film and the SiC surface. Adherent and uniform nickel-phosphorus alloy films are produced on such SiC substrates by autocatalytic electroless deposition without any further treatments.

New Surface-Activation-Process for Electroless Deposition of Adhesive Metal (Ni, Cu) Films on Si Substrates

Adhesive metal film formation on Si is important for obtaining infallible electric contacts in various devices. Autocatalytic electroless deposition, which is a conventional method to metalize nonmetallic substrates, requires surface activation (catalyzation pretreatment) of substrates. For Si substrates, obtaining adhesive metal films with conventional surface activation process, such as two-step method consisting of sensitization and activation, is difficult. The new surface-activationprocess for producing adhesive films, which we recently reported for electroless Ni and Co deposition, electrolessly forms metal nanorods in Si (1, 2). These nanorods work as catalytic nanoanchors for electrolessly depositing adhesive metal films on Si. The process consists of the three electroless steps shown in Fig. 1: Step 1) displacement deposition of metal nanoparticles (3); Step 2) metal-particle-assisted HF etching for catalytic nanopore formation; and Step 3) autocatalytic electroless deposition for metal filling in Si nanopores and metal-film formation on the whole Si surface. In this study, this new surface-activation-process is applied not only to Ni but also to Cu deposition on Si substrates.