Annealing temperature dependent properties for Ni/Ti/W Ohmic contacts simultaneously formed on n- and p-type 4H-SiC

Abstract

The paper investigated the annealing temperature dependence of electrical and structural properties for Ni (50 nm)/Ti (60 nm)/W (60 nm) Ohmic contacts simultaneously formed on n- and p-type 4H-SiC by in-depth electrical and physical characterization. With the annealing temperature rising in the range of 900 °C–1050 °C, the specific contact resistances (SCRs) of both n- and p-type Ohmic contacts monotonously decreased with a similar trend in the range of 1 × 10−4–1 × 10−6 Ω cm2, which was favorable for the simultaneous formation of n- and p-type Ohmic contacts with lower SCRs in the active region. For n-type Ohmic contacts, the variation of SCRs with annealing temperatures was correlated to the relative proportion of the total contact area occupied by the (220) plane compared to the other planes for the polycrystalline and textured δ-Ni2Si film at the contact interface characterized by x-ray diffraction. Furthermore, the surface morphology of Ohmic contacts under different annealing temperatures was highly similar with almost identical root mean square roughness of about 6.2 nm measured by atomic force microscopy (AFM), which was thought to be smooth enough for the wire bonding process from the perspective of device applications. The distinct W layer with no evidence of obvious intermixing and the great distance of released free carbon away from the contact surface makes the surface morphology smooth and uniform.