Influence of Ni and Nb thickness on low specific contact resistance and high-temperature reliability of ohmic contacts to 4H-SiC

Abstract

The influence of Ni and Nb thickness on the electrical properties and high-temperature reliability of Ni(x)/Nb(100 – x)/n-type 4H-SiC ohmic contacts, where x = 25, 50 or 75 nm, was investigated. Two-dimensional X-ray diffraction, hard X-ray photoelectron spectroscopy and transmission electron microscopy analyses indicated that a relatively high Ni concentration had a strong influence on low specific contact resistance due to the greater formation of Ni2Si at the contact interface, whereas a higher density of Nb improved the ability to collect excess carbon atoms by the formation of Nb6C5 at the interface, ensuring high-temperature reliability of the contacts. The experimental results showed that the Ni(50)/Nb(50)/4H-SiC ohmic contact is a potential candidate for high-temperature and harsh environment applications.

500 °C high-temperature reliability of Ni/Nb ohmic contact on n-type 4H-SiC

“…Whereas, as reported in Ref. 23, though the Ni (75 nm)/Nb(25 nm)/4H-SiC without applying the surface treatment had a low specific contact resistance after the fabrication process, it lost the ohmic behavior just at a temperature of 150 °C. It was supposed that without applying the CF 4 :O 2 surface treatment, the concentration of carbon atoms at the contact interface is too large for the thin Nb layer.…”

“…As reported in Ref. 23, the Ni(50 nm)/Nb(50 nm)/4H-SiC contact remained a stable ohmic behavior when being aged at 400 °C, therefore, at first, the reliability of this sample at 500 °C ambient temperature was investigated. Figure 3 shows the I-V characteristics of the Ni(50 nm)/Nb(50 nm)/4H-SiC without applying the CF 4 :O 2 surface etching as fabricated [Fig.…”

“…Though the results reported in Ref. 23 indicated that the Ni(50)/ Nb(50)/4H-SiC had the ability to eliminate the excess carbon atoms at the interface of the contact and thus enhanced the hightemperature reliability when operating at 400 °C ambient temperature, the degradation of this contact after just 25 h of aging at 500 °C suggests that there was a chemical reaction and/ or chemical redistribution at the interface of the contact when operating in this environmental condition.…”

“…The fabrication process of Ni/Nb/4H-SiC ohmic contact with and without the surface etching has been reported somewhere. 21,23,24) A 336 μm thick n-type 4H-SiC (0001) bulk substrate with a doping concentration of 1.0 × 10 18 cm −3 was used in this research. The resistivity of the SiC substrate was 14.2 mΩ.cm.…”

“…Recently, the dependence of Ni and Nb thickness on low specific contact resistance and high-temperature reliability has been investigated. 23) The results indicated that to obtain both low specific contact resistance and high-temperature reliability, the Ni(50 nm)/Nb(50 nm) was the optimal choice. Recently, the Ni/Nb ohmic contact to 4H-SiC with CF 4 :O 2 surface etching has been studied.…”