4H-SiC MOSFETs with a Stable Protective Coating for Harsh Environment Applications

Abstract

In this work we present 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with a stable protective coating for harsh environment applications. Both inversion channel (IC) and buried channel (BC) MOSFETs were realized on n-4H-SiC substrates with a p-epilayer. Stacked ONO gate dielectric and Ti/TiN/Pt/Ti interconnect were used. Ni and Ti ohmic contacts in combination with a-SiOx/a-SiNy and a-SiOx/a-SiC protective coatings were compared. The MOSFETs showed excellent transistor characteristics up to 600 °C and exceptional stability during long-term aging at 600 °C in air and during accelerated aging at 700 °C including temperature cycling and air/moisture environment.

Long-term stability of nickel-based ohmic contacts with n-type and p-type 4H-SiC in a high-temperature environment

“…To address the oxidation issue, a conductive diffusion barrier that can prevent diffusion of oxygen into the contact metal has been suggested [34][35][36][37][38][39] . A conductive diffusion barrier, such as TaRuN 36,37) and TiN 38,39) , is formed between the contact metal and the capping layer to slow the diffusion of oxygen and/or the reaction of oxygen with the contact metal and capping layer.…”

“…33) To address the oxidation issue, a conductive diffusion barrier that can prevent diffusion of oxygen into the contact metal has been suggested. [34][35][36][37][38][39] A conductive diffusion barrier, such as TaRuN 36,37) and TiN, 38,39) is formed between the contact metal and the capping layer to slow the diffusion of oxygen and/or the reaction of oxygen with the contact metal and capping layer. The experimentally demonstrated performance of conductive diffusion barrier with TaRuN changed contact resistance only slightly from 2 × 10 −5 Ω cm 2 to 3 × 10 −5 Ω cm 2 for 2000 h in air over 300 °C.…”

Structural and Reliability Analysis of Ohmic Contacts to SiC with a Stable Protective Coating for Harsh Environment Applications

“…9,10 We have recently developed stable protective coatings based on PECVD amorphous silicon oxide (a-SiO x ) and amorphous hydrogenated silicon carbide (a-SiC) and studied their suitability for harsh environment applications up to 700 • C. 11,12 In following work, the developed protective coatings were successfully implemented to enhance the stability of Ni and Ti ohmic contacts to n-SiC 13 and achieve thus excellent SiC-MISFET stability benchmarks. 14 In this work we present a comprehensive structural and reliability analysis on Ni and Ti-based contact metallizations with an a-SiO x /a-SiC protective coating. Extensive reliability testing was employed along with detailed material analysis to identify the dominant reactions and the main degradation mechanisms of the complex multilayer contact metallizations during aging up to 700 • C. The electrical properties of the contact metallizations were studied by means of transmission line measurement (TLM) and circular transmission line measurement (cTLM) test structures.…”