The electrical characteristics of 4H-SiC schottky diodes after inductively coupled plasma etching
The electrical characteristics of metal contacts fabricated on 4H-SiC have been investigated. Sputtered nickel ohmic contacts have been successfully produced on untreated 4H-SiC substrates and 4H-SiC surfaces cleaned with aggressive chemicals and ion sputtering. The current-voltage (I–V) characteristics of asdeposited contacts are observed to be nonohmic on all surfaces. After annealing at 1,000°C in a N2 atmosphere, the contacts are seen to become ohmic with considerably less annealing time being required for the samples exposed to aggressive cleaning stages. Schottky diodes were then produced on the silicon carbide (SiC) surface after etching in an SF6/O2 inductively coupled plasma (ICP) for 3 min at varying substrate bias voltages and also on an untreated surface used as a control sample. The ideality factors of all diodes formed on the etched surfaces increased in comparison to the control sample. The highest ideality factor was observed for the diodes produced after etching at −0-V and −245-V bias voltage. A two-diode and resistor model was applied to the results that successfully accounted for the excess leakage paths. The defect density of each SiC surface was calculated using both the measured and the simulated ideality factors. An annealing stage was successful at reducing the ideality factors of all the diodes formed. The defect density calculated using the measured ideality factors of the annealed diodes was seen to have been reduced by an order of magnitude.