Nanostructure and nanochemistry of gate dielectrics and processing of tunable dielectrics by chemical vapor deposition.

摘要

PbTiO₃-SrTiO₃ (PST) thin films that are voltage tunable were developed for high-frequency application by a metal-organic chemical vapor deposition technique at rates of 10–15 nm/min. PST films (90–150nm) were deposited on Pt/TiO₂/SiO₂/Si and Sapphire (0001) substrates and characterized by various techniques to control the composition and structure. The tunability and dielectric loss (tanδ) of a 90nm PST film were 37% and 0.02, respectively, at 1MHz and 3V in a parallel plates capacitor (Pt/PST/Pt) configuration. PST films on (0001) Sapphire were epitaxial with an orientation relationship of PST [1 1 1]// Sapphire [0 0 0 1], and in-plane alignment of PST [1 ı 0]// Sapphire [2 ı ı 0] and PST [ı ı 2]// Sapphire [0 1 ı 0]. A coplanar waveguide structure was used to determine the tunability (31.3%) and figure of merit (13 degrees/dB) of an epitaxial 100nm PST film on Sapphire at 12 GHz. The tanδ, derived from transmission-type resonator, is explained in terms of composition inhomogeneities and in-plane biaxial stress due to lattice mismatch between PST and Sapphire.; A 4nm-ZrOx/1.2nm-SiOx layer structure was formed on 200mm Si wafers by a manufacturable atomic layer chemical vapor deposition (ALCVD) technique for advanced metal oxide semiconductor gate dielectrics. The nanostructure and nanochemistry of this gate stack were investigated by various techniques, before and after oxygen annealing (700°C). The results showed that a multiphase and heterogeneous structure evolved, defined as Zr-O/interlayer(IL)/Si stack. The critical parameters that control the nanostructural and nanochemical evolution are discussed using some simple mechanistic explanations and literature data. The stacks were characterized for their dielectric and electrical properties using a Pt/Zr-O/IL/Si capacitor configuration. The flat band shift (ΔV _FB), capacitance voltage hysteresis, and leakage current density were correlated with defects and roughness of the interface, thickness of IL, and asymmetry of the band structure. The calculated (using a bi-layer model of ZrO₂ and SiO₂) and measured equivalent oxide thicknesses were inconsistent and the capacitances in accumulation were frequency dispersive. These results are explained in light of the nanostructure and nanochemistry that evolved.