High-Density Layer at the SiO₂/Si Interface Observed by Difference X-Ray Reflectivity

Abstract

We have developed a high-accuracy difference X-ray reflectivity (DXR) method using intense synchrotron radiation for the evaluation of ultrathin thermal oxides on Si(100). By carefully analyzing DXR data for gate oxides with thicknesses of 40 Å and 70 Å grown at 800° C to 1000° C, the existence of a dense ( ∼2.4 g/cm3), thin (∼10 Å) layer at the S i O 2/S i interface has been revealed. The thickness of the interfacial layer decreases with increasing oxidation temperature. Oxides grown in O3 or HCl/O2 have a thinner interfacial layer compared to those grown in O2.

Tunnel oxide passivated carrier-selective contacts based on ultra-thin SiO 2 layers

“…As described in literature [4][5][6][7] ozone-grown oxides are found to exhibit improved interface (less strain, transition layer is reduced, high density and less defects due to more saturated Si-O bonds) and electrical properties due to the occurring damage-free oxidation of the silicon surface. In addition, it is assumed that atomic oxygen is the main driving force of the oxidation because it is the species that has the feature to be particularly diffusion active in the SiO x layer and saturate silicon dangling bonds [8].…”

Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review

“…Models that introduce such a modified a-SiO 2 layer with slow O 2 diffusion explain the actual growth kinetics well [44,45]. On the other hand, X-ray reflectivity observations have evidenced the presence of compressed a-SiO 2 layer with density $2.4 g cm À3 ($2.2 g cm À3 for normal aSiO 2 ) [46,47]. Theoretical calculations as well support the slow diffusion of interstitial O 2 in the compressed a-SiO 2 layer [48-50].…”

Ultrathin gate dielectrics for silicon nanodevices

“…The periodic reversal of the SREM contrast during oxidation directly showed the layer-by-layer oxidation while interfacial step structure was maintained [6]. The existence of a dense (∼2.4 gm cm −3 ), thin (∼1 nm) layer at the SiO 2 /Si(100) interface has been demonstrated by a highaccuracy difference X-ray reflectively method [4]. Note that the oxide density near the interface is higher than that of bulk SiO 2 (2.35-2.36 gm cm −3 ) as well as bulk Si(2.33 gm cm −3 ).…”

“…The energy bandgap of 1.7-5.2 nm thick SiO 2 is maintained at 9.85 eV [3], indicating that the intrinsic nature of ultrathin SiO 2 is basically identical to that of bulk oxide although the density of the oxide layer near the SiO 2 /Si interface is higher than that of the bulk SiO 2 [4,5]. The thickness uniformity for 1-5 nm oxides on Si wafers is extremely good because the thermal oxidation of silicon proceeds through a layer-by-layer process on an atomic scale as directly demonstrated by scanning reflection electron microscopy [6].…”