Role of the bias voltage during the deposition of thin tin oxide films by plasma assisted chemical vapor deposition

Nonstoichiometric thin tin oxide films have been deposited from an Ar-tetramethyltin-O-2 mixture in an rf glow discharge diode reactor at low pressure (15 Pa) and at low temperature (25-100 degrees C). These films are amorphous and present a high transmittance (95%) in the visible region. The conductivity of the films have been increased considerably (10(-2) to 10(2) Omega(-1) cm(-1)) in a triode system (substrate electrode biased by another rf generator), for treatment times as short as 10 min with a deposition rate of 30 nm/min. This increase of the conductivity leads to a decrease of the gap energy from 3.5 to 2.5 eV accompanied with a slight decrease of the transmittance (from 95% to 89% +/- 2%) and of the grain size (95 to 43 nm). The tin oxide-substrate interface analyzed by Rutherford backscattering has shown to be an abrupt one. (C) 1998 American Vacuum Society. [S0734-2101(98)10804-7].