Influence of the absorption layer on the pulsed laser (355 nm) annealing thermal budget during formation of Ni-based ohmic contacts on 4H-SiC substrate

Abstract

Laser annealing has attracted significant attention for ohmic contacts of the 4H-SiC substrate, especially Ni-based ohmic contact. In this study, a metallic capping layer (Ti, Nb, Mo, W, or Ag) was placed on the top of Ni as the absorption layer for a 355 nm laser, and the effect of the absorption layer on the laser annealing thermal budget was investigated. The temperature fields of the layer (30 nm)/Ni (70 nm)/4H-SiC (100 μm) contacts were simulated numerically using the finite element method. The results demonstrated that the thermal budget can be affected by the main properties of the layer, including the laser absorptivity, thermal conduction coefficient, specific heat capacity, and density. In thermal budget recipes, the energy density required for ohmic contact at each pulse width can be reduced when the product of the latter three parameters is low. However, the optical absorptivity of the layer is critical to reducing the thermal budget. Ti, which has high absorptivity, a small product, and a high melting point, is an excellent absorption layer for Ni-based ohmic contacts that connect to the 4H-SiC substrate.