Yasushi Hoshino

Characterization of Hot-Implanted Fe near the SiO2/Si Interface

We have investigated nanoparticles formed in the vicinity of a SiO2/Si interface by Fe implantation at substrate temperatures of 300, 600, and 800 °C. The implantation energies are selected to assign peak positions of the implanted Fe profiles at the SiO2/Si interface. The size and crystal orientation of the nanoparticles are confirmed by cross-sectional transmission electron microscopy (TEM) and transmission electron diffraction (TED) analysis. The depth profile of implanted Fe was analyzed by Rutherford backscattering spectroscopy (RBS). It is found in the TEM image of the 300 °C-implanted sample that tiny clusters with a mean diameter of 2.4 nm are grown in the SiO2 layer. In addition, some Fe clusters are precipitated in the vicinity of the SiO2/Si interface. On the other hand, we observe nanoclusters with a mean diameter of 3.2 nm at a certain depth in the SiO2 layer for the 600 °C-implanted sample. Some of the clusters in the SiO2 layer have a crystalline structure of α-Fe. Furthermore, β-FeSi2 with comparatively larger diameters of 5–10 nm is found to precipitate at the SiO2/Si interface from the analysis of TEM and TED images. Most of the implanted Fe atoms are segregated either just on the SiO2 surface or at the SiO2/Si interface in the 800 °C-implantation case. The anomalous diffusion of Fe in the SiO2 layer seems to be explained by the ion-beam-irradiation effect at high temperatures.

Interdiffusion Analysis of Au/Ti and Au/Pt/Ti Electrode Structures Grown on Diamond (001) Surface by Rutherford Backscattering Spectroscopy

We have directly studied the elemental depth profiles of Au/Ti and Au/Pt/Ti multiple-layers, which are candidates as ohmic materials for a p-type diamond substrate, grown on diamond (001) surfaces at room temperature (RT) and 550 °C using Rutherford backscattering method. Significant interlayer diffusion between Au and Ti is observed for the samples without a sandwiched Pt layer, resulting in diffusion of some Ti atoms to the surface. On the other hand, the trilayer structure of Au/Pt/Ti forms a thermally stable electrode up to 1000 °C. It is also found that the interfacial TiCx layer grown at 550 °C is thicker than that deposited at RT followed by post-deposition annealing at 550 °C. The effective thickness of the Pt layer is estimated to be more than 20 nm to prevent Ti segregation to the surface.

A novel mechanism of ultrathin SOI synthesis by extremely low-energy hot O+ implantation

Extremely low-energy oxygen implantations at 10 keV in silicon were challengingly performed to directly synthesize ultrathin silicon-on-insulator (SOI) structure separated by a buried oxide (BOX) layer. We quantitatively investigated the optimum condition and the formation mechanism of homogeneous and continuous stoichiometric SOI/BOX structure. In this study, oxygen ions were implanted into Si(0 0 1) substrates with keeping the temperatures at 500, 800, and 1000 °C with ion-fluences from 0.5 to ions cm−2. These samples were then postannealed at high temperatures from 950 to 1150 °C in Ar ambient for several hours. We found that ultrathin stoichiometric SOI/BOX structure with less than 20 nm thick was synthesized by oxygen implantation with an ion dose of ions cm−2 from 500 °C to 800 °C followed by annealing at a significantly low temperature of 1050 °C for 5 h. According to the RBS-channeling analysis, the crystallinity was excellent as quality as that of the SOI structure formed by a wafer-bonding method. We found that the BOX layer was finally formed around the deeper end of the oxygen distribution in the as-implanted sample, though the depth of the BOX formation was much deeper than the projected range of oxygen and the damage peak of silicon. The formation process of the SOI/BOX structure proposed so far could not be applicable to the present conditions for ultrathin SOI/BOX synthesis by extremely low-energy implantation followed by low-temperature annealing. We thus suggested a novel mechanism of the ultrathin SOI/BOX synthesis as follows. The mechanism during the thermal treatment was demonstrated that the recrystallization of the damaged Si layers induced by ion irradiation took place from the very surface with relatively less irradiation-damages toward deeper layers with sweeping interstitial oxygen atoms, and the condensed oxygen atoms finally synthesized the stoichiometric BOX layer.

Direct synthesis of ultrathin SOI structure by extremely low-energy oxygen implantation

We performed extremely low-energy 16O+ implantation at 10 keV (Rp ∼ 25 nm) followed by annealing aiming at directly synthesizing an ultrathin Si layer separated by a buried SiO2 layer in Si(001) substrates, and then investigated feasible condition of recrystallization and stabilization of the superficial Si and the buried oxide layer by significantly low temperature annealing. The elemental compositions were analyzed by Rutherford backscattering (RBS) and secondary ion mass spectroscopy (SIMS). The crystallinity of the superficial Si layer was quantitatively confirmed by ananlyzing RBS-channeling spectra. Cross-sectional morphologies and atomic configurations were observed by transmission electron microscope (TEM). As a result, we succeeded in directly synthesizing an ultrathin single-crystalline silicon layer with ≤20 nm thick separated by a thin buried stoichiometric SiO2 layer with ≤20 nm thick formed by extremely low-energy 16O+ implantation followed by surprisingly low temperature annealing at 1050∘u2009C.