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

Abstract

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.