Shigenari Shida

Orientation selective epitaxial growth of CeO2(100) and CeO2(110) layers on Si(100) substrates

It is found that epitaxial CeO2 layers with (100) or (110) orientation can be selectively grown on Si(100) substrates by controlling substrate bias in reactive dc magnetron sputtering. Adopting a two step growth method; ultrathin metallic Ce layer deposition at room temperature followed by a silicidation process at 800 °C, and subsequent reactive sputtering in an Ar/O2 mixture environment, the CeO2(100) layer is grown on practical Si(100) surfaces prepared by the usual wet cleaning method.

Origin of crystalline quality deterioration in epitaxial growth of CeO2 layers on Si substrates

CeO2 layers with various degrees of crystallinity are characterized to get insight into the origin of the deterioration of epitaxial layers on Si substrates. The surface morphology of CeO2 layers is studied using atomic force microscopy and is correlated with the crystallinity of the layer determined by reflection high-energy electron diffraction. It is clearly observed that the surface morphology changes according to the crystallinity of the CeO2 layers. Single crystalline CeO2(110) layers with good crystallinity have a nanometer-scale periodically corrugated surface structure, which consists of (111) facets. As the crystalline quality of the CeO2 layers becomes worse, the number of irregularly shaped hillocks and tetrahedral hillocks increases and corresponds to distorted (110) grains and (111)-oriented polycrystalline grains, respectively. It is found that the crystalline quality is not uniform; different regions of crystallinity are distributed from place to place and the ratio of their population cha...

Optimization of Growth Parameters in Electron-Beam-Induced Orientation Selective Epitaxy of CeO2 ( 100 ) ∕ Si ( 100 ) Structures

Based on orientation selective epitaxy (OSE) of CeO 2 (100) and CeO 2 (110) layers on Si(100) substrates by substrate bias control in reactive magnetron sputtering, we have found the OSE growth of CeO 2 (100) layers induced by electron-beam irradiation, instead of substrate bias. In order to improve crystalline quality and interfacial properties, growth parameters of incident electron energy and an oxygen flow rate are analyzed, including the effect of oxygen radical beams. The electron-beam-induced OSE method gives a way to two-dimensionally spatially varied OSE.

Characterization of orientation-selective-epitaxial CeO2 layers on Si(100) substrates by x-ray diffraction and cross-sectional transmission electron microscopy

Orientation-selective-epitaxially grown CeO2 layers on Si(100) substrates are characterized by x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). XRD analyses prove how diffraction intensities of CeO2 (200) and (220) peaks vary depending on substrate bias under which the layers grew. It is confirmed that (200) and (220) peaks reach maxima at ±15 and 0V biases, respectively, where they are pure single crystalline of respective orientations. Samples grown at other bias have both (200) and (220) peaks, whose peak intensity ratio varies as the bias voltage departs from above three values. These results agree well with the reported results by reflection high energy electron diffraction analyses. XTEM observations are carried out utilizing focused ion beam technology in sample fabrication. In CeO2(110)∕Si(100) samples, interfacial amorphous layers are seen, which are similar with commonly reported results. XTEM lattice images clarify the nonexistence of interfacial amorphous la...

A method to determine long-range order parameters from electron diffraction intensities detected by a CCD camera

To determine long-range order parameters from electron diffraction intensities, the authors have developed a CCD camera system to detect precisely electron diffraction intensities, a method for quickly and precisely measuring specimen thickness, and a computer programming to calculate long-range order parameters from the ratio of superlattice and fundamental diffraction intensities. Thickness variation over a diffraction area is taken into consideration in the calculation of electron diffraction intensities on the basis of the multi-slice method, and long-range order parameters are calculated by the successive approximation method. The absorptive form factors are also calculated from experimental data of diffraction intensities by parameter fitting, and the effect of absorption on the calculation of long-range order parameters is examined. The values of Cu(3)Au alloys aged at 523 and 653 K that were obtained by averaging long-range order parameters determined for several diffraction areas with the developed method are close to the reported data obtained by the X-ray diffraction method. The main causes for the deviation of long-range order parameters determined for several diffraction areas are also discussed.

Electron beam induced orientation selective epitaxial growth of CeO2(100) layers on Si(100) substrates by dc reactive sputtering

From studies on the epitaxial growth of CeO2 layers on Si(100) substrates using reactive dc magnetron sputtering, it has been found that the epitaxial CeO2 layer with (100) or (110) orientation is selectively grown by controlling substrate bias and the growth rate. In order to develop this technology into two dimensional orientation selectivity, we attempt to grow CeO2(100) by low energy electron irradiation, as an alternative way to substrate bias application. It proved that electron beams in two energy regions of 30 ~ 40 and 80 ~ 100 eV are effective on preferential growth of CeO2(100) layers. Interfacial structures of CeO2(100)/Si(100) are studied using cross-sectional transmission electron microscopy.

Highly separated hybrid orientation structure of CeO2(100) and (110) on Si(100) substrates by electron beam-induced orientation-selective epitaxy

The hybrid orientation structure of the CeO2(100) and (110) regions on Si(100) substrates is studied using electron beam-induced orientation-selective epitaxial (OSE) growth by reactive magnetron sputtering. Two separate areas of growth are seen, with CeO2(100) layers found to grow in areas irradiated by electrons during the growth process, and the CeO2(110) layers growing in the areas not irradiated by the beam. The lateral orientation mapping obtained by x-ray diffraction measurements reveals the existence of transition regions between these two orientation areas. The width of the transition region is found to decrease proportionally as the logarithm of the underlying Si substrate resistivity. The OSE growth experiments using silicon-on-insulator substrates with lithographically formed trenches show that perfect isolation of the two areas becomes possible by optimizing the geometry of the trenches.