Measurement and Control of In-Plane Surface Chemistry During Oxidation of H-Terminated (111)Si

Abstract

In-plane directional control of surface chemistry during interface formation can lead to new opportunities regarding device structures and applications. Control of this type requires techniques that can probe and hence provide feedback on the chemical reactivity of bonds not only in specific directions but also in real time. Here, we demonstrate both control and measurement of the oxidation of H-terminated (111) Si. Control is achieved by externally applying uniaxial strain, and measurement by second-harmonic generation (SHG) together with the anisotropic-bond model of nonlinear optics. In this system anisotropy results because bonds in the strain direction oxidize faster than those perpendicular to it, leading in addition to transient structural changes that can also be detected at the bond level by SHG.silicon | hyperpolarizability | ellipsometry | metrology | optical T he oxidation of silicon is one of the most technologically important chemical reactions. Because dangling bonds trap and/ or scatter carriers, well-organized bonding at Si∕SiO 2 interfaces is critical to device performance. Therefore, although Si oxidation has been studied for many years, the formation dynamics of Si∕SiO 2 interfaces continues to be of interest. The information provided to date regarding oxidation kinetics has been obtained primarily by standard spectroscopic and microscopic structuralanalysis techniques. For example, scanning tunneling microscopy and atomic force microscopy (AFM) studies have revealed the role of surface morphology during oxidation (1, 2). IR absorption experiments have probed the changes in vibrational modes during oxidation and have provided information about the chemical reactions involved in the process (3). Spectroscopic ellipsometry has provided data about growth rates (4). At the same time, considerable effort has been invested in manipulating Si oxidation kinetics. For example, uni-and biaxial strains have been used in manufacturing Si-based devices, taking advantage of the fact that tensile stress increases the overall oxidation rate of thermally grown oxides (5).The effect of strain on the morphology of clean vicinal and on-axis Si surfaces has been well studied by microscopic methods (6, 7). However, an atomic-level understanding of the specific effects of strain on surface chemistry is presently unknown. Here, we investigate oxidation of strained and unstrained H-terminated (111) Si in real time using second-harmonic generation (SHG), and we analyze these data with the anisotropic-bond model (ABM) of nonlinear optics. The bond-specific information that we obtain reveals two important aspects of the relevant chemical dynamics. First, strain changes the oxidation rates of Si─Si back bonds that are oriented in different directions, and second, the average back-bond directions themselves change as a result of this anisotropic oxidation. Fig. 1 provides an atomic-level view of the configuration, showing the bonding of the outermost bilayer of a (111) Si surface. Each outer-layer Si atom has one "up" bon...

Improving ALD-Al2O3 Surface Passivation of Si Utilizing Pre-Existing SiOx

“…Most of the Si-CH 3 species can eventually become hydrolyzed by neighboring Al-OH species once the coverage of Al-OH is large enough [48], and the H-terminated Si may eventually also become oxidized during the H 2 O and O 3 pulses. The oxidation of H-terminated Si by H 2 O has been studied in detail previously, and it is believed that Si-OH and H 2 are formed initially, and that the OH-group then inserts into a Si-Si back bond, creating Si-O-Si and regenerates a Si-H bond at the surface, which then reacts with more H 2 O [49], [50]. The low growth rates are thus likely to result in an AlO x layer with a different structure and density than an AlO x layer growing at steady-state growth conditions after the first cycle.…”