Chemical Vapor Deposition and Characterization of Zirconia Films For High-k Dielectric Applications

Abstract

Due to the aggressive dimensional scaling of metal-oxide-semiconductor-field-effect-transistors (MOSFETs), direct tunneling current across the SiO2 gate dielectric layer has become a significant problem. High-k dielectric materials, such as ZrO2, HfO2, are expected to replace SiO2 as the gate dielectric layers to minimize direct tunneling currents. Development of the deposition processes and the characterization of high-k films have become significant challenges for the semiconductor industry. Based on multi-sample variable-angle spectroscopic ellipsometery (MS-VASE), we first developed a methodology to characterize ZrO2 films deposited on silicon. Results showed that proper modeling the optical properties of the interfacial layer is the key to accurate characterization. Using a stack model, consisting of an effective medium approximation (EMA) surface-roughness layer, a Tauc-Lorentz (TL) layer to represent the ZrO2 layer, and a second TL layer to represent the interfacial layer, we accurately extracted both thicknesses and optical constants of layers. The extracted surface-roughness and thickness values were confirmed by atomic force microscopy (AFM) and transmission electron microscopy (TEM) results. The following chapters cover studies of the initial-stage deposition of ZrO2 films from zirconium t-butoxide (ZTB) on both native silicon oxide and H-terminated silicon (H-Si) surfaces. In-situ SE was used to study the deposition process in real time. AFM, TEM, time of flight medium back scattering (ToF MEBS), and angle resolved X-ray photoelectron spectroscopy (ARXPS) were used to investigate the properties of deposited films. We discovered that film properties are affected by the nucleation and coalescence processes on different surfaces. A 3-dimensional nucleation process is predominant on H-Si surfaces due to the lack of reactive surface hydroxyl groups and high surface diffusivity of ZTB molecules. At temperatures about 350 °C, a layer-by-layer deposition process on native oxide surfaces leads to smooth, uniform ZrO2 films. An interfacial layer between the silicon substrate and ZrO2 is formed through two independent mechanisms: reaction between the starting surfaces and ZTB or its decomposition intermediates, and the diffusion of reactive oxidants through the forming ZrO2 interfacial stack layer and their reaction with the substrate.