Structural Analyses of Thin SiO₂Films Formed by Thermal Oxidation of Atomically Flat Si Surface by Using Synchrotron Radiation X-Ray Characterization

Abstract

Partially crystalline structures in thin SiO 2 films formed by thermal oxidation of atomically flat Si surface were investigated by performing X-ray reflectometry and grazing incidence X-ray diffraction measurements. The densities of the SiO 2 films were higher than those of amorphous SiO 2 films, especially at the SiO 2 /Si interface. The structure of thermally grown SiO 2 has been expected to be amorphous, but sharp diffraction peaks were observed in GIXRD measurements. The diffraction peaks tended to reflect a cristobalite-like structure with preferential orientations to the Si substrate. In addition, the lattice spacing of the cristobalite-like structure was estimated from the GIXRD measurement and found to be isotropically distorted. Silicon dioxide (SiO 2 ) thin films of less than 10 nm are among the important dielectric materials for semiconductor devices, and many research studies on this material are actively being performed. [1][2][3][4][5][6] It is necessary to understand the formation process of the oxidation film to get high quality insulation characteristic. Thin SiO 2 films provide excellent electrical insulation and interface state densities, and they can readily be obtained using thermal oxidation. Generally, thermally grown SiO 2 film has an amorphous structure based on six-membered rings consisting of Si-O triangular pyramids. However, it was also reported that relatively thick SiO 2 film has a residual ordered structure reflecting the crystalline structure of the Si substrate.7-11 However, the detailed structure of the SiO 2 film has not been sufficiently revealed by these studies yet. In particular, the evaluation of thin SiO 2 films of less than 10 nm is very difficult because of the small scattering volume and the probably low degree of order in the structure. In this study, X-ray reflectometry (XRR) and grazing incident-angle X-ray diffraction (GIXRD) using synchrotron radiation were performed to evaluate the structures of thin SiO 2 films on the atomically flat surface. ExperimentalThin SiO 2 films were fabricated on the Si (001) substrate after the atomic-order planarization process consisting of thermal annealing at 1200• C for 30 min in a pure Ar atmosphere. 12-14 The Si surface thus had monoatomic steps with a height of 0.136 nm and atomically flat terraces with a width of approximately 150 nm. The surface roughness in each terrace was 0.03 nm; it was less than the detection limit of atomic force microscopy. Then, thermal oxidation was carried out in a pure oxygen atmosphere with three different temperatures. We prepared a SiO 2 sample grown with an 800• C process for 82 min, with a 900• C process for 13 min and with an 1100• C process for 30 sec. These thicknesses of SiO 2 films were approximately 7 nm. The purities of used oxygen gas were 99.9995%. GIXRD measurements were performed at SPring-8 BL46XU (2012A1597) using synchrotron radiation with a photon energy of 10 keV. The penetration depth of the X-rays into the sample varied rapidly near the critical angle. 15,16 The grazing an...

ITO/SiO2/ITO Structure on a Sapphire Substrate Using the Oxidation of Ultra-Thin Si Films as an Insulating Layer for One-Glass-Solution Capacitive Touch-Screen Panels

“…In contrast, several studies were reported that certain thermally grown SiO2 films consist of crystalline domains [16,17], so the polycrystalline SiO2 phase can be plausibly expected along with the amorphous phase in the annealed films. Nagta et al reported that the thermally grown crystalline SiO2 by means of thermal oxidation possess high density which is about 4.4 g/cm 3 , while the amorphous phase density was about 2.2 g/cm 3 [18]. The cross-sectional TEM image of the Si/sapphire film oxidized at 823 K is presented in Figure 1b.…”