Contact formation in SiC devices

Enhancement of the Stability of Ti and Ni Ohmic Contacts to 4H-SiC with a Stable Protective Coating for Harsh Environment Applications

“…Here, a rough SiC/Ni contact interface as well as voids and an additional layer below the Ti/ TiN/Pt interconnect are evident. These observations are consistent with detailed transmission electron microscopy (TEM) studies on as-processed Ni contacts to n-SiC, 20,24 where formation of Kirkendall voids at the SiC-contact interface and segregation of excess carbon to the top region of the contact layer were reported. The Ni contacts appear thus to be less stable than Ti contacts from the morphological point of view.…”

“…It is known that the morphological stability of Ni contacts is limited by the segregation of C atoms and the void formation at the SiC/contact interface that occur during the silicidation reaction. [18][19][20][21] Incidentally, no adhesion failure was visible for either Ni contacts without the Ti/TaSi x /Pt stack (wafer D) or Ti contacts with the Ti/TaSi x /Pt stack (wafer A) after the processing. The magnitude of adhesion failure because of stress build-up in the Ti/TaSi x /Pt stack in wafer A is believed to be limited by the strong adhesion of Ti on SiC.…”

Kinetic study of interfacial solid state reactions in the Ni/4H–SiC contact

“…Many transition metals and metal combinations, such as Al, Fe, Cr, Ti, Co, Pt, Ni, Ti/Al, Ta/Pt, Ti/Pt/Au, Ta/Ni/Ta and Ti/Ni/Ti/Au, have been studied to form excellent contacts to n-or p-type SiC [2,3,[5][6][7][8][9][10][11][12][13]. Most of work is mainly focused on the interface reactions between different metals and SiC from a view point of material science [3][4][5][6][7][8][9][10][11][12]. It is well known that there are two kinds of the chemical reaction pathways between SiC and metals, of which silicides and free carbon, silicides and carbides or ternary phases are produced respectively [6].…”

Current-Induced Degradation of Nickel Ohmic Contacts to SiC

“…The presence of voids is similar to that reported in other studies, where Kirkendall voids were observed in the Ni/SiC reaction region after annealing. [14][15][16] The large change in surface morphology can be attributed to the growth of voids, likely due to stresses from the high current density and Joule heating. Large void growth would reduce the active area of the contact, requiring an increase in applied voltage to sustain a constant current through the device.…”

“…12,13 Although Ni has shown the ability to provide a low specific contact resistance to SiC, the reaction products of the necessary high-temperature anneal, including carbon segregation during nickel silicide formation, have the potential to cause reliability problems. [14][15][16] This paper will examine the stability of Ni ohmic contacts to SiC under high current density. The aforementioned reliability studies of contacts to Si were performed by stressing two contacts laterally through an implanted layer, typically using a crossbridge Kelvin resistor structure to measure the specific contact resistance.…”