Nucleation, Hydroxylation, and Crystallization Effects in ALD SrO

• Published in: Journal of physical chemistry. C Vol. 117; no. 22; pp. 11578 - 11583
• Main Authors: Wang, Han, Jiang, Xiaoqiang, Fu, Kan, Willis, Brian. G
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 06.06.2013
• Subjects: Composition and phase identification; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Optical instruments, equipment and techniques; Physics; Polarimeters and ellipsometers; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Theory and models of film growth; Thin film structure and morphology; Vapor phase epitaxy; growth from vapor phase; Crystalline phase; Stoichiometry; Atomic layer method; Nucleation; Phase composition; Spectroscopic ellipsometry; Grazing incidence; Crystallization; Polycrystals; Crystal growth from vapors; XRD; Silicates; Real time; Texture; Transients; Thin films; Growth mechanism; X-ray photoelectron spectra
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp3126472

The atomic layer deposition (ALD) of SrO thin films from strontium bis(tri(isopropyl)cyclopentadienyl) (Sr(C5 i Pr3H2)2) and H2O was studied by using in situ real-time spectroscopic ellipsometry (RTSE), ex situ X-ray photoelectron spectroscopy (XPS), and grazing-incidence X-ray diffraction (GI-XRD). It is found that with H2O as the oxidant, deposition temperature strongly affects film composition. At 250 °C films consist of polycrystalline Sr(OH)2 while at 350 °C polycrystalline SrO is observed. The growth per cycle (GPC) is found to be sensitive not only to the crystalline phase (Sr(OH)2 vs SrO) but also the crystalline orientation. For films prepared at high temperatures and subsequently cooled for continued growth at lower temperatures, an unusual transient growth per cycle (GPC) enhancement of over 160% for more than 100 cycles is observed. The enhancement is found to be related to the orientation of the Sr(OH)2 phase, which is influenced by the underlying crystal texture of the substrate. Substrate nucleation effects were also observed for growth on SiO2/Si substrates. A Sr silicate layer with stoichiometry close to Sr2SiO4 forms spontaneously during ALD growth and transiently enhances the GPC.