SnO 2 transparent conductor films produced by filtered vacuum arc deposition

Abstract

Thin films of SnO 2 were prepared using an Sn cathode vacuum arc deposition system, operated with a low pressure O 2 atmosphere. The plasma flux emerging through an annular anode passed into a magnetized quarter torus, which bent the plasma beam, separating it from macroparticle contaminants. Within a time of 5–15s after arc ignition, the initial background pressure P i in the system was rapidly pumped by the plasma jet to a working pressure P w that was two orders of magnitude lower. For 4 < P w<8 mTorr (1 Torr = 133 Pa), transparent conductive coatings could be obtained on unbiased glass substrates at room temperature, with the following characteristics: sheet resistivities of 50 ohms/□; resistivity, about 0.003 ohmscm; optical transmission, greater than 85%, deposition rate, 10 nm s −1. At P w<3 mTorr, an optically reflective, low conductivity film was obtained. At P w > 12 mTorr, the arc pump-down time was very long and the deposition rate was very low. The films were analyzed by X-ray diffraction, transmission and scanning electron microscopy (TEM, SEM), Auger electron spectroscopy (AES), and resistivity and transparency measurements. The changes in the films under thermal treatment in vacuo and in Ar were also examined. According to the X-ray and TEM diffraction data, as-deposited films on non-heated substrates and substrates heated to 200°C consist of an amorphous phase. Crystallization of the amorphous phase prepared at P w=6 mTorr to tetragonal SnO 2 occurs at 450°C. At P w<3 mTorr, however, the films deposited crystallize to SnO after annealing. The AES results show that the films consist of only Sn and O, and that the shape of the Sn spectra changes with the Sn oxidation states. Ar annealing and rapid thermal annealing at a temperature of 300°C decreased the resistivity of the films deposited at P w=6 mTorr to 8 × 10 −4ohms cm, while the film structure remained amorphous. These films have resistivities equivalent to the best values obtained by any method for undoped SnO 2, while the deposition time is less for the same film thickness.