Epitaxial strontium titanate films grown by atomic layer deposition on SrTiO3-buffered Si(001) substrates

Abstract

Epitaxial strontium titanate (STO) films have been grown by atomic layer deposition (ALD) on Si(001) substrates with a thin STO buffer layer grown by molecular beam epitaxy (MBE). Four unit cells of STO grown by MBE serve as the surface template for ALD growth. The STO films grown by ALD are crystalline as-deposited with minimal, if any, amorphous SiOx layer at the STO-Si interface. The growth of STO was achieved using bis(triisopropylcyclopentadienyl)-strontium, titanium tetraisopropoxide, and water as the coreactants at a substrate temperature of 250 °C. In situ x-ray photoelectron spectroscopy (XPS) analysis revealed that the ALD process did not induce additional Si–O bonding at the STO-Si interface. Postdeposition XPS analysis also revealed sporadic carbon incorporation in the as-deposited films. However, annealing at a temperature of 250 °C for 30 min in moderate to high vacuum (10−6–10−9 Torr) removed the carbon species. Higher annealing temperatures (>275 °C) gave rise to a small increase in Si–O bonding, as indicated by XPS, but no reduced Ti species were observed. X-ray diffraction revealed that the as-deposited STO films were c-axis oriented and fully crystalline. A rocking curve around the STO(002) reflection gave a full width at half maximum of 0.30° ± 0.06° for film thicknesses ranging from 5 to 25 nm. Cross-sectional transmission electron microscopy revealed that the STO films were continuous with conformal growth to the substrate and smooth interfaces between the ALD- and MBE-grown STO. Overall, the results indicate that thick, crystalline STO can be grown on Si(001) substrates by ALD with minimal formation of an amorphous SiOx layer using a four-unit-cell STO buffer layer grown by MBE to serve as the surface template.

Oxide Materials at the Two-Dimensional Limit

“…Observing a variation of film density, crystallinity, surface roughness, texture (grain orientation and size), and tetragonality among differently fabricated samples is consistent with observations that film microstructure varies with deposition method, [231] temperature and growth rate [232][233][234], post-deposition treatments [235], strain [236], and stoichiometry . [237] The variation in the BTO films discussed here cannot be used to generally evaluate the different deposition techniques, as none of the deposition has been thoroughly optimized.…”

Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates

“…35,36 A four-unit-cell STO buffer layer grown on Si (001) by MBE provided a stable template for the growth of several crystalline oxides, including anatase TiO 2 , STO, BTO, and LAO. [35][36][37][38] Crystalline BTO grown by this method was c-axis oriented, indicating an out-of-plane polarization, with negligible amorphous layer and a sharp STO-Si interface. 38 In this work, we validate the growth of crystalline La:STO films on Si (001) substrates using a combined MBE-ALD growth method.…”

Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications

“…Both the Sr and Hf metalorganic precursors are commercially available, reactive with water, and have been previously used for ALD. [38][39][40][41][42][43][44][45][46][47][48] Alternating subcycles of Sr and Hf are used to deposit stoichiometric to slightly Sr-rich (56%) films. During each subcycle the metalorganic is dosed for 2 s to ensure complete saturation of the surface, and subsequently purged for 15 s with ultrahigh purity Ar.…”

“…Previous work from our group has shown that Sr-rich STO films maintain the perovskite structure, while Ti-rich STO films are more likely to be amorphous. 46 The samples grown for this study varied slightly in cation stoichiometry from 52% to 56% Sr.…”