Electrical and Optical Properties of PECVD SiC Thin Films for Surface Micromachined Devices

In this paper, the electrical and optical properties of undoped and in-situ doped amorphous SiC films are presented. The films are prepared by using mixture of methane (CH4) and silane (SiH4) as C and Si sources, phosphine (PH3) and diborane (B2H6) as doping gases. The bandgap, optical constant and absorption coefficient of the films are measured and a strong dependence on the layer composition and doping gas level is observed. The current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics of a-SixC1-x films are measured on Al/SixC1x/Al and Al/a-SixC(1-x/Si/Al capacitors. At high field, the Frenkel-Poole effect is more likely to be the conduction mechanism for Si-rich films, while the Schottky effect for C-rich films. For the p-type doped, the Frenkel-Poole effect is the only conduction mechanism, while for the n-type doped films the effect is less clear. An increase in dielectric constant is observed when the Si/C ratio increases. Using the conductance method the interface trapped density (Dit) is calculated and about 1.61x10eVcm. The flatband voltage (VFB) and the threshold voltage (VT) are determined as well. The obtained results show VFB = 8.1V and it slightly decreases with increasing silane flow rate, VT is about 10.8V and increases with decreasing silane flow rate.