Precursor Oxidation State Control of Film Stoichiometry in the Metal−Organic Chemical Vapor Deposition of Tin Oxide Thin Films

A new tin(IV) hexafluoroisopropoxide complex and a related tin(II) compound were used as low-pressure chemical vapor deposition precursors to tin oxide thin films. The films were characterized by backscattering and elastic recoil spectrometries, Auger and UV−vis spectroscopies, and nuclear reaction analysis. Sn(OCH(CF 3 ) 2 ) 4 (HNMe 2 ) 2, a volatile solid (subl 70−75 °C at 0.06 Torr), was synthesized in high yield by reacting Sn(NMe 2 ) 4 with (CF 3 ) 2 CHOH. A crystal structure determination shows that it has an octahedral structure with trans -amine ligands. Low-pressure chemical vapor deposition using Sn(OCH(CF 3 ) 2 ) 4 (HNMe 2 ) 2 and air as precursors gave fluorine-doped tin oxide films (O/Sn = 1.8−2.4; F/Sn = 0.005−0.026) at substrate temperatures of 200−450 °C. The films are highly transparent in the visible region (>85%) and have resistivities as low as 2.1 × 10 - 3 Ω cm. In contrast to the results obtained for the tin(IV) precursor, the tin(II) compound Sn(OCH(CF 3 ) 2 ) 2 (HNMe 2 ) in combination with air or water vapor gave nonconductive transparent films at substrate temperatures of 180−250 °C having composition SnO 0.9 - 1.3 F 0.1 - 0.4 . These film stoichiometries suggest that hydrolysis was the primary film-forming reaction and that the tin was not oxidized in the deposition process.