Direct observation of the layer-by-layer growth of initial oxide layers on Si(100) surface during thermal oxidation

Abstract

We present the results of an x-ray photoelectron spectroscopy investigation in the real-time regime of the kinetics of high-temperature oxidation of the Si(100) surface. The dependence of the net concentration of silicon atoms in all oxidation states (i.e., Si ,+ , Si 2+ , Si 3+ , Si 4+ ) on oxygen exposure is found to exhibit a "step"-like behavior, each "step" corresponding to one oxide layer. The results obtained suggest a mechanism of layer-by-layer growth of initial oxide layers, with oxide-phase formation taking place at the Si-SiC>2 interface. PACS numbers: 81.60.Cp, 82.65.Jv, 82.80.PvIt was proposed recently [1,2] that the unique electrophysical characteristics of the Si-SiC>2 interface are likely determined by the formation kinetics of the transition region in thermal oxidation. However, the mechanism of formation of this transition region between silicon crystal and bulk S1O2 has yet been revealed, despite extensive study [2,3]. The reason for an atomically abrupt Si-SiC>2 interface is not understood either. The composition and structure of the transition region have been investigated previously. In particular, Grunthaner et ai [4], and subsequently others [5-11], found in Si 2/7 photoelectron spectra peaks attributed [4,5] to silicon atoms in different oxidation states, i.e., Si 14 ", Si 24 ", Si 34 ", and Si 44 ". The role of these states in oxide formation is still under discussion. In this Letter we report results which demonstrate for the first time that the growth of initial oxide monolayers proceeds by a layer-by-layer growth mechanism. Initially, there is accumulation of silicon atoms in Si 1 * and Si 24 " states at the interface, which is then followed by their transition into Si 3+ and Si 44 " at a constant quantity of silicon atoms in all Si w+ states. This quantity stands for one oxide layer.The experiments were carried out on the XSAM-800 spectrometer (the energy resolution is 0.9 eV). The x-ray photoemission spectrometry method was used (Mg Ka source). The electron binding energy was measured with 0.1 -eV reproducibility. The oxidation kinetics was investigated directly in the analyzer chamber in a real-time regime [12], contrary to the usually used [6,13] point-bypoint regime after a certain exposure. Admitting oxygen into the chamber (/? = 10~~6 Torr), we registered Si 2/7 and O Is spectra one by one every 3 min. The sample temperature of 1135 K was chosen in accordance with the conventional silicon-oxidation regime [1-3]. The spectrum of Si 2p recorded after oxidation, along with the result of its decomposition into components by leastsquares fitting after background subtraction, is depicted in Fig. 1. The peaks corresponding to Si 14 ", Si 24 ", Si 34 ", and Si 4+ states are shifted by 1.0, 1.7, 2.6, and 3.8 eV, respectively, towards higher binding energies relative to the substrate Si 2p peak (99 eV). These shifts are consistent with the results of previous studies: 0.6, 1.5, 2.8, and 4.5 eV (Ref. [4]); 1.0, 1.8, 2.7, and 3.5 eV (Ref. [5]); 1.0, 1.7, 2.6, and 3.6 eV (Ref. [6]); 0.95, ...

Atomic layer chemical vapor deposition of ZrO2-based dielectric films: Nanostructure and nanochemistry

“…Since the calculated resolution for this low loss region is ϳ1 nm, this low oxidation state of Si 1.32ϩ implies that the rate of oxidation at the Si/SiO x interface is limited by the diffusion of oxidizing species through the Zr-O layer. 63,64 A schematic of the nanostructure and nanochemistry that has evolved in the annealed Zr-O/IL/Si stack is illustrated in Fig. 12.…”

Monolayer oxidation onSi(001)−(2×1)studied by means of reflectance difference spectroscopy

“…8 The passive oxidation modes have been recently identified by real-time measurement with photoemission spectroscopic methods. [5][6][7] The passive oxidation can be subdivided into Langmuir-type adsorption and the two-dimensional island growth. 5,6 At an oxygen pressure of 2.7ϫ 10 −5 Pa and a temperature between 853 and 913 K, the uptake curve of O͑2p͒ intensity exhibits an exponential curve for Langmuir-type adsorption, while it follows a sigmoid curve for two-dimensional island growth.…”

“…The initial growth modes have recently been identified by real-time measurement with Auger electron spectroscopy ͑AES͒, 5 ultraviolet photoemission spectroscopy ͑UPS͒, 6 and x-ray photoemission spectroscopy. 7 Oxidation modes on Si͑001͒ can be classified into two regimes. Over a wide range of pressure-temperature conditions, there is a critical curve which separates the oxidation modes for which etching is the dominant process ͑active oxidation regime͒ from those which produce SiO 2 growth ͑pas-sive oxidation regime͒.…”

Direct observation of two-dimensional growth at SiO2/Si(111) interface

“…However, at the atomic level, the oxidation mechanism is not yet completely understood. Recently, the layer-by-layer process model, where oxidation is modeled as a layer-by-layer process at the SiO 2 /Si interface, was proposed from the measurements of high-resolution transmission electron microscopy (TEM), scanning reflection electron microscopy (SREM), reflection high-energy electron diffraction, and X-ray photoelectron spectroscopy (XPS) [6][7][8][9][10][11][12][13][14][15][16]. In this study, we directly observed the morphology change of the SiO 2 /Si(111) interfaces of oxide films grown at different temperatures, 1050 and 900°C, with various thickness from 4 to 14 nm under near normal conditions where metal-oxidesemiconductor devices are fabricated.…”