Ni-Silicide Ohmic Contacts on 4H-SiC Formed by Multi Pulse Excimer Laser Annealing

The formation of ohmic contacts by laser annealing approach is of great importance forSiC power devices, since it allows their fabrication on thin substrates, that is of crucial significanceto reduce power dissipation. Ni silicide reaction under UV laser irradiation has been studied in detailwith particular focus on single pulse approach, in order to describe the early stage of reaction process.The use of a multi pulse approach, for the formation of Ni silicide-based ohmic contacts by means ofexcimer laser annealing, has been investigated in this work. The reaction process has beencharacterized, as a function of number of pulses, by means of X-Ray Diffraction (XRD) andTransmission Electron Microscopy (TEM) analysis. Laser process simulations, formulated in theframework of phase-field theory, have been performed in order to predict the evolution of materialduring reaction under annealing. Simulations show that reaction moves to Si-rich phases withincreasing number of pulses, with a co-existence of Ni2Si and Ni3Si2 phases for the three pulsesprocess. Moreover, simulations show critical differences, in terms of the uniformity of the distributionof the silicide phases along the film, between the single pulse and the multi pulses cases and theincreasing of thickness of silicide phases with the pulse sequence. These predictions are in goodagreement with the findings of XRD and TEM analyses. The electrical properties of the reacted layerhave been evaluated on Schottky Barrier Diodes (SBD) devices, confirming the ohmic behaviour ofmulti pulse annealed samples.