Ohmic Contacts on p-Type Al-Implanted 4H-SiC Layers after Different Post-Implantation Annealings.

Monia Spera,Domenico Corso,Andrea Severino,Salvatore Di Franco,Angelo Alberto Messina,Filippo Giannazzo,Giuseppe Greco,Fabrizio Roccaforte

doi:10.3390/ma12213468

Abstract

This paper reports on the electrical activation and Ohmic contact properties on p-type Al-implanted silicon carbide (4H-SiC). In particular, the contacts were formed on 4H-SiC-implanted layers, subjected to three different post-implantation annealing processes, at 1675 °C, 1175 °C, and 1825 °C. Under these post-implantation annealing conditions, the electrical activation of the Al dopant species increased from 39% to 56%. The Ti/Al/Ni contacts showed an Ohmic behavior after annealing at 950 °C. The specific contact resistance ρc could be lowered by a factor of 2.6 with the increase of the post-implantation annealing temperature. The result can be useful for application in device fabrication. Moreover, the dependence of ρc on the active acceptor concentration followed the thermionic field emission model, with a barrier height of 0.63 eV.

Highlights

Silicon carbide (4H-SiC) is an outstanding semiconductor material that offers enormous advantages with respect to silicon, in terms of energy efficiency in high-temperature, high-power and high-frequency applications [1,2,3].One of the peculiarities of 4H-SiC is the low diffusivity of the dopant species even at high temperatures, making ion implantation an obligatory route for selective area doping in device fabrication [1,4]
Aluminum (Al) ion-implantation is used for the p-type doping of 4H-SiC, and the implant is typically followed by high-temperature post-implantation annealings (>1600 ◦ C) for the electrical activation of the dopant [5,6,7]
4H-SiC layers activated under different post-implantation annealings (1675 ◦ C, 1175 ◦ C, and 1825 ◦ C)

Summary

Introduction

Silicon carbide (4H-SiC) is an outstanding semiconductor material that offers enormous advantages with respect to silicon, in terms of energy efficiency in high-temperature, high-power and high-frequency applications [1,2,3].One of the peculiarities of 4H-SiC is the low diffusivity of the dopant species even at high temperatures, making ion implantation an obligatory route for selective area doping in device fabrication [1,4]. The major 4H-SiC devices, e.g., Schottky diodes, Junction Barrier Schottky (JBS) diodes, and metal oxide semiconductor field effect transistors (MOSFETs), are fabricated using ion-implantation doping [1]. The p-type doped regions are very important in both JBS and MOSFETs, as their electrical properties have a significant impact on the device’s performance. In this context, the Ohmic contacts formation on p-type 4H-SiC is inherently a challenging task, due to the wide band gap of the material (leading to high metal/semiconductor barrier heights) and to the high ionization energy of the Al acceptors [8]. Since the properties of Al-implanted 4H-SiC layers critically depend on the large variety of reported experimental doping and annealing conditions [9,10,11,12], Materials 2019, 12, 3468; doi:10.3390/ma12213468 www.mdpi.com/journal/materials

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