Temperature behavior of specific contact resistance and resistivity on nitrogen implanted 6H-SiC with titanium silicide ohmic contacts

Abstract

The electrical characteristics of TiSix contacts to nitrogen implanted 6H-SiC are investigated using linear transmission line method structures at temperatures up to 673 K. Nitrogen is implanted into a p-type (NA≈1×1016 cm−3) 6H-SiC epilayer at 500 °C and activated at 1700 °C, resulting in an activated donor concentration of ND=5×1019 cm−3 to a depth of 300 nm with a reduced electrically active surface concentration of about ND≈5×1018 cm−3. Sputtered titanium silicide is used as contact metallization. Five different contact formation temperatures TA ranging from 900 to 1150 °C are applied to the samples in order to investigate the specific contact resistance ρc. Whereas an anneal of at least 950 °C is necessary to achieve an ohmic contact behavior, samples annealed at 1150 °C show specific contact resistance of 7×10−6 Ω cm2 at room temperature, which decreases monotonically to 4×10−6 Ω cm2 at 673 K. The sheet resistance Rs (resistivity ρs) of the n+-implanted layer is 521 Ω/□ (15.6×10−3 Ω cm) at 303 K. Up to 573 K, Rs declines to 354 Ω/□ (10.6×10−3 Ω cm) as the incomplete ionization of the nitrogen dopants dominates the temperature behavior. Above 573 K, the reduction of the electron mobility via phonon scattering dominates, and Rs increases to 363 Ω/□ (10.9×10−3 Ω cm) at 673 K. From the resistivity as a function of temperature, the low field mobility μ0 is 149 cm2/V s at 300 K, and the temperature exponent α=1.62 of the power law dependence can be deduced.