Discharge diagnosis and controlled deposition of SnO_x:F films by DC-reactive sputtering from a metallic tin target

Fluorine-doped tin oxide (SnO_x:F) films on glass substrates have been prepared by reactive magnetron DC-sputtering in Ar-O₂-Freon plasma from a metallic tin target. We studied the relationship between the discharge characteristics and film properties and found the discharge conditions in which the films belong to the SnO₂ or to the SnO stoichiometry, by proposing a phase diagram for this system. We showed that the film stoichiometry is closely related to the tin valence changes at the target. We found that there is a narrow voltage band and a limit value in the oxygen content where the films have SnO₂ stoichiometry; outside this region SnO films are obtained. We studied the crystallinity and the optical properties of the SnO₂ films. The results show that crystalline films have cassiterite-like diffraction patterns with preferred orientation in the (110) planes. The crystallinity of the films is improved when the discharge voltage and oxygen content increase. A thermal annealing of the amorphous films at 500°C leaves them in the crystalline cassiterite-like form. The films have a transmittance of ~80% in the visible region of the spectrum and a uniform thickness.