Properties of fluorinated amorphous silicon-nitrogen-oxygen alloy (a-SiN xO y:H) deposited by plasma-enhanced chemical vapor deposition

Abstract

The properties of fluorinated amorphous silicon-nitrogen-oxygen (a-SiN x O y :H:F) alloys deposited in a plasma-enhanced chemical vapor deposition reactor using a mixture of monosilane (SiH 4) and nitrogen trifluoride (NF 3) were investigated. The deposition rate of the a-SiN x O y :H:F alloys was found to increase with increasing NF 3 flow rate. Auger electron spectroscopy revealed a uniform chemical composition in these alloys. An abrupt increase in the bulk conductivity of the a-SiN x O y :H:F alloys was observed when the NF 3 flow rate was increased from 4 sccm to 7 sccm, whereas the bulk conductivity decreased as the NF 3 flow rate was increased from 7 sccm to 24 sccm. This phenomenon is attributable to a structural transformation in the alloys deposited with 7 sccm of NF 3. Carrier conduction in bulk alloys exhibited three activation energies with transition temperatures at 373 and 240 K. Carrier conduction above 373 K is by thermionic emission of carriers from silicon grains. Between 240 and 373 K, conduction is by thermionic field emission of carriers. Below 240 K, carrier tunneling is the predominant conduction mechanism. Undoped a-SiN x O y :H:F alloys formed rectifying heterojunctions on crystalline p-type silicon. The electrical characteristics of these heterostructures are dominated by the silicon/alloy interface.