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(CF3)(2))(4)(HNMe(2))(2), a volatile solid (subl 70-75 degrees C at 0.06 Torr), was synthesized in high yield by reacting Sn(NMe(2))(4) with (CF3)(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(CF3)(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 degrees C. The films are highly transparent in the visible region (>85%) and have resistivities as low as 2.1 x 10(-3) Omega cm. In contrast to the results obtained for the tin(IV) precursor, the tin(II) compound Sn(OCH(CF3)(2))(2)(HNMe(2)) in combination with air or water vapor gave nonconductive transparent films at substrate temperatures of 180-250 degrees C having composition SnO0.9-1.3F0.1-0.4. These film stoichiometries suggest that hydrolysis was the primary film-forming reaction and that the tin was not oxidized in the deposition process.