Highly Selective Chemical Vapor Deposition of Tin Diselenide Thin Films onto Patterned Substrates via Single Source Diselenoether Precursors

The distorted octahedral complexes [SnCl4{nBuSe­(CH2)nSenBu}] (n = 2
or 3),
(1) and (2), obtained from reaction of SnCl4 with the neutral bidentate ligands and characterized by IR/Raman
and multinuclear (1H, 77Se­{1H} and 119Sn) NMR spectroscopy and X-ray crystallography, serve as
very effective single source precursors for low pressure chemical
vapor deposition (LPCVD) of microcrystalline, single phase tin diselenide
films onto SiO2, Si and TiN substrates. Scanning Electron
Microscopy (SEM) and Atomic Force Microscopy (AFM) imaging show hexagonal
plate crystallites which grow perpendicular to the substrate surface
in the thicker films, but align mostly parallel to the surface when
the quantity of reagent is reduced to limit the film thickness. X-ray
diffraction (XRD) and Raman spectroscopy on the deposited films are
consistent with hexagonal SnSe2 (P3̅m1; a = b = 3.81 Å; c = 6.13 Å), with strong evidence for preferred orientation
of the crystallites in thinner (0.5–2 μm) samples, consistent
with crystal plate growth parallel to the substrate surface. Hall
measurements show the deposited SnSe2 is a n-type semiconductor.
The resistivity of the crystalline films is 210 (±10) mΩ
cm and carrier density is 5.0 × 1018 cm–3. Very highly selective film growth from these reagents onto photolithographically
patterned substrates is observed, with deposition strongly preferred
onto the (conducting) TiN surfaces of SiO2/TiN patterned
substrates, and onto the SiO2 surfaces of Si/SiO2 patterned substrates. A correlation between the high selectivity
and high contact angle of a water droplet on the substrate surfaces
is observed.