Rate-Limiting Reactions of Growth and Decomposition Kinetics of Very Thin Oxides on Si(001) Surfaces Studied by Reflection High-Energy Electron Diffraction Combined with Auger Electron Spectroscopy

Abstract

The growth and decomposition kinetics of very thin oxides on Si(001) surfaces were investigated by reflection high-energy electron diffraction combined with Auger electron spectroscopy (RHEED-AES) to monitor the reaction rates of oxide growth and decomposition in real time, and changes in surface structure and interface morphology simultaneously. The oxides prepared by stopping the second oxide layer growth at various coverages following the first oxide layer growth by Langmuirtype adsorption at 500 C under an O 2 pressure of 2:6 Â 10 À4 Pa were isothermally annealed by increasing temperature from 500 to 666 C at the same time that O 2 gas was quickly evacuated. It was observed that (1) oxide thickness continued to decrease significantly as measured on the basis of changes in O KLL Auger electron intensity ÁI O-KLL before voids appeared at a nucleation time t N as recognized by the appearance of half-order spots in RHEED patterns, (2) the SiO 2 /Si interface morphology was considerably roughened corresponding to ÁI O-KLL during void nucleation as observed by the evolution of the RHEED intensity of bulk diffraction spots ÁI bulk , (3) the ratio of ÁI bulk to ÁI O-KLL was almost constant, and (4) oxide decomposition rate during void nucleation, which was approximately given by ÁI O-KLL =t N , showed a good linear correlation with the second oxide layer growth rate immediately before starting the decomposition reaction. The good correlation between ÁI O-KLL =t N and clearly indicates that the rate-limiting reaction of the second oxide layer growth is closely related to that of the oxide decomposition during void nucleation. All the above-mentioned observations can be comprehensively interpreted using a reaction model proposed for the rate-limiting reactions of oxide growth and decomposition, in which the point defect generation (emitted Si atoms + vacancies) caused by the strain due to the volume expansion of oxidation plays a crucial role because of the high reactivity of the emitted Si atoms and vacancies with dangling bonds. Under an O 2 atmosphere, both emitted Si atoms and vacancies are the preferential adsorption sites of O 2 molecules in the oxide and at the SiO 2 /Si interface, respectively. The oxide can be decomposed by the emitted Si atoms to produce SiO molecules, which desorb from the surface, leading to oxide removal in vacuum with SiO 2 /Si interface morphology roughening, but may be oxidized within the oxide under an O 2 atmosphere.

Experimental estimation of oxidation-induced Si atoms emission on Si(001) surfaces

“…Small discrepancies after 2400 s were ascribed to gradual interfacial oxidation. 8,9 The RHEED intensities of the (1/2 0) and (0 1/2) spots, I (1/2 0) and I (0 1/2) , disappeared at 2400 s as seen in Fig. 2(b).…”

“…(1), which is constructed based on an oxidation reaction model of Langmuir-type adsorption. 8,9,12,14 …”

“…The details of the experimental apparatus and the measurement procedures and conditions are described elsewhere. 8 The base pressure of the reaction chamber was 7 × 10 −9 Pa. RHEED-AES enabled us to simultaneously measure the structural and morphological changes of the surface, as well as the extent of oxide coverage during the oxidation process. 19 In the RHEED-AES measurement, a primary electron beam of 10 keV for RHEED measurements was incident with a grazing angle of 1 • along the [100] azimuth to observe the (0 1/2) and (1/2 0) spot intensities resulting from the Si(001) 1 × 2 and 2 × 1 structures under the same diffraction conditions.…”

“…However, due to the high chemical activity of the emitted Si atoms, they can be expected to influence the growth and electrical properties of the oxide. 8,9 In addition, emission of Si atoms through a high-k dielectric has been observed during the formation of the high-k gate stack. 10 In order to clarify the influence of the emitted Si atoms on the oxide growth, it is necessary to determine the quantity of Si atoms emitted into the oxide.…”

Thermal instability of silicon-on-insulator thin films measured by low-energy electron microscopy

“…1(b)), forming an assembly of three dimensional Si nanocrystals. Previous works [1,2,3,4,5] have explored the thermal decomposition of ultrathin Si-oxide, and the subsequent dewetting of the Si (SOI) layer [6,7]. Here, we report two results which, to our knowledge, have not been reported previously.…”