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

The electrical characteristics of TiSix contacts to nitrogen implanted 6H-S iC are investigated using linear transmission line method structures at tem peratures up to 673 K. Nitrogen is implanted into a p-type (N-A approximate to 1 x 10(16) cm(-3)) 6H-SiC epilayer at 500 degrees C and activated at 17 00 degrees C, resulting in an activated donor concentration of N-D 5 x 10(1 9) cm(-3) to a depth of 300 nm with a reduced electrically active surface c oncentration of about N-D = 5 x 10(18) cm(-3). Sputtered titanium silicide is used as contact metallization. Five different contact formation temperat ures T-A ranging from 900 to 1150 degrees C are applied to the samples in o rder to investigate the specific contact resistance rho(c). Whereas an anne al of at least 950 degrees C is necessary to achieve an ohmic contact behav ior, samples annealed at 1150 degrees C show specific contact resistance of 7 x 10(-6) Ohm cm(2) at room temperature, which decreases monotonically to 4 x 10(-6) Ohm cm(2) at 673 K. The sheet resistance R-s (resistivity rho(s )) of the n(+)-implanted layer is 521 Ohm/square (15.6 x 10(-3) Ohm cm) at 303 K. Up to 573 K, R-s declines to 354 Ohm/square (10.6 x 10(-3) Ohm cm) a s the incomplete ionization of the nitrogen dopants dominates the temperatu re behavior. Above 573 K, the reduction of the electron mobility via phonon scattering dominates, and R s increases to 363 Ohm/square (10.9 x 10(-3) O hm cm) at 673 K. From the resistivity as a function of temperature, the low field mobility mu(0) is 149 cm(2)/V s at 300 K, and the temperature expone nt alpha = 1.62 of the power law dependence can be deduced. (C) 1999 Americ an Institute of Physics. [S0021-8979(99)00805-1].