Thio- and seleno-ether complexes with Group 4 tetrahalides and tin tetrachloride: preparation and use in CVD for metal chalcogenide films

Reaction of TiCl4 or ZrI4 with the soft, neutral o-C6H4(CH2EMe)(2) (E = S or Se) in anhydrous CH2Cl2 (or toluene) yields the distorted octahedral chelate complexes [MX4{o-C6H4(CH2EMe)(2)}]. Using Et2Se gives [MX4(Et2Se)(2)] (M = Zr, X = Cl or I; M = Hf, X = I). The Sn(IV) analogues, [SnCl4{o-C6H4(CH2EMe)(2)}] and [SnCl4(Et2Se)(2)] were obtained similarly. These complexes have been characterised spectroscopically and analytically, and crystal structures of trans-[SnCl4(Et2Se)(2)] and some selenonium salts derived as minor by-products from the parent Group 4 complexes are described. The neutral chalcogenoether complexes have been evaluated as single source precursors to ME2/ME thin films via LPCVD. [TiCl4{o-C6H4(CH2EMe)(2)}] leads to the deposition of air and moisture stable TiE2 films (with no residual Cl). Coverage of the substrate is uniform with platelet growth perpendicular to the surface. The heavier Zr(IV) species do not lead to significant ZrE2 deposition. On the other hand, LPCVD of [SnCl4{o-C6H4(CH2SMe)(2)}] leads to deposition of SnS2 at lower temperatures and SnS at higher temperatures, while [SnCl4{o-C6H4(CH2SeMe)(2)}] gives rather uneven coatings of SnSe2. The Et2Se derivative, [SnCl4(Et2Se)(2)] leads to uniform deposition of SnSe2 with growth perpendicular to the substrate surface. The SnE2/SnE films are stable indefinitely to air and moisture. The generation of TiS2, SnS2 and SnS in this way are very rare examples of metal sulfide deposition from C-S bond fission within a thioether complex.