Takao Yonehara

Epitaxial layer transfer by bond and etch back of porous Si

We demonstrate a novel method for bond and etch back silicon on insulator in which an epitaxial Si layer over porous Si is transferred onto a dissimilar substrate by bonding and etch back of porous Si. The highest etching selectivity (100 000:1) between the porous Si and the epitaxial layer is achieved by the alkali free solution of HF, H2O2, and H2O which is essential for this single etch‐stop method to produce a submicron‐thick active layer with superior thickness uniformity (473±14 nm) across a 5 in. silicon‐on‐insulator wafer.

Control of Grain Boundary Location By Selective Nucleation Over Amorphous Substrates

A selective nucleation based crystal-growth-technique over amorphous substrates is originated. The method manipulates nucleation sites and periods and hence, controls the grain boundary location by modifing the substrate surface. In Si, small Si 3 N 4 nucleation sites are formed, 1–2 pm in diameter, 100 μm in period, over Sio 2 . One Si nucleus is formed exclusively in the small area of Si 3 N 4 by CVD. The highly faceted and periodically located nuclei grow over SiO 2 up to 100 μm in diameter before impingement. A MOS-FET fabricated inside the island operates comparably to the bulk Si control

Effects of hydrogen annealing on heteroepitaxial-Ge layers on Si: Surface roughness and electrical quality

We have studied the effect of hydrogen annealing on the surface roughness of germanium (Ge) layers grown by chemical vapor deposition on silicon using atomic force microscopy and cross-sectional high resolution scanning electron microscopy (HR-SEM). Our results indicate a strong reduction of roughness that approaches 90% at 825°C. The smoother Ge surface allowed for the fabrication of metal-oxide-semiconductor capacitors using germanium oxynitride (GeOxNy) as the gate dielectric. Electrical quality was studied using high frequency capacitance–voltage characteristic of epi-Ge showing negligible hysteresis. We discuss the results in terms of Ge–H cluster formation, which lowers the diffusion barrier, allowing for higher diffusivity and surface mobility. The temperature dependence shows tapering off for temperatures exceeding 800°C, indicating a barrier reduction of ∼92meV.

Epitaxial growth on porous Si for a new bond and etchback silicon-on-insulator

A new bond and etchback silicon-on-insulator (SOI) has been proposed and demonstrated, in which epitaxial layers on porous Si are transferred by bonding and etching back porous Si. The key processes are epitaxial growth on porous Si and selective removal of porous Si. In the epitaxial layers over porous Si, the major defects are stacking faults, which can be reduced to 10 3 to 10 4 /cm 2 by raising the H 2 prebake temperature and lengthening the immersion time in diluted HF prior to the prebake. Bondable smooth surfaces were formed at growth temperatures below 900°C. A highly selective etchant of HF-H 2 O 2 was discovered and enabled us to etch off porous Si with a selectivity of 10 5 , leaving behind epitaxial layers on the oxidized handle wafers. The rough as-etched SOI surface was smooth comparable to that of the commercially available bulk-polished wafer, and boron concentration in the SOI-Si layer was simultaneously decreased to ∼1 x 10 16 /cm 3 , by H 2 annealing. Finally, a uniform SOI layer of 507 nm ±3% across a 5 in. wafer was achieved by this method.

Hydrogen annealed silicon‐on‐insulator

Hydrogen annealing effects on silicon‐on‐insulator (SOI) materials are reported. High boron concentration of ∼2×1018/cm3 in 0.1‐μm‐thick SOI layer produced by bond and etch‐back SOI (BESOI) method is reduced to ∼ 5×1015/cm3 by annealing at 1150 °C for 1 h. The BESOI surface became very smooth comparable to commercially available polished wafer simultaneously. Separation‐by‐implantation‐of‐oxygen wafer was also smoothed by the hydrogen anneal. This is due to surface migration of Si atoms driven by surface energy minimization after removing native oxide.

Fabrication of high-quality p-MOSFET in Ge grown heteroepitaxially on Si

We have successfully demonstrated high-performance p-MOSFETs in germanium grown directly on Si using a novel heteroepitaxial growth technique, which uses multisteps of hydrogen annealing and growth to confine misfit dislocations near the Ge-Si interface, thus not threading to the surface as expected in this 4.2% lattice-mismatched system. We used a low thermal budget process with silicon dioxide on germanium oxynitride (GeO/sub x/N/sub y/) gate dielectric and Si/sub 0.75/Ge/sub 0.25/ gate electrode. Characterization of the device using cross-sectional transmission electron microscopy and atomic force microscopy at different stages of the fabrication illustrates device-quality interfaces that yielded hole effective mobility as high as 250 cm/sup 2//Vs.

High-efficiency metal-semiconductor-metal photodetectors on heteroepitaxially grown Ge on Si

We demonstrate extremely efficient germanium-on-silicon metal-semiconductor-metal photodetectors with responsivities (R) as high as 0.85 A/W at 1.55 microm and 2V reverse bias. Ge was directly grown on Si by using a novel heteroepitaxial growth technique, which uses multisteps of growth and hydrogen annealing to reduce surface roughness and threading dislocations that form due to the 4.2% lattice mismatch. Photodiodes on such layers exhibit reverse dark currents of 100 mA/cm2 and external quantum efficiency up to 68%. This technology is promising to realize monolithically integrated optoelectronics.

Manipulation of nucleation sites and periods over amorphous substrates

A selective nucleation based crystal growth technique over amorphous substrates is originated. The method manipulates nucleation sites and periods, and hence, controls the grain boundary location by modifying the substrate surface. In Si, Si3 N4 provides artificial nucleation sites, 1–2 μm in diameter, 100 μ m in period, which is surrounded by SiO2 . One Si nucleus is formed exclusively in a small portion of Si3 N4 . The highly faceted and periodically located nuclei grow over SiO2 up to 100 μm in diameter before impingement. A field‐effect transistor fabricated inside the island operates comparably to the bulk Si control.

Transient nucleation and manipulation of nucleation sites in solid‐state crystallization of a‐Si films

Solid‐state nucleation of Si crystals in a‐Si films is controlled by Si ion implantation prior to the isothermal annealing. The process of the nucleation includes a long transient period that causes the diminishing shape of the grain size distribution (GSD). The parameters appearing in the kinetic theory of transient nucleation are estimated from the GSD in a‐Si. It is found that the ion implantation reduces the steady‐state nucleation rate and elongates the time lag, while the growth rate is almost constant. The dependence of the above parameters is simulated based on the model of heterogeneous nucleation. It is qualitatively suggested that the suppression of the nucleation can be attributed to the modification of the interface to the SiO2 underlayer such as the changes in the self‐diffusion or in the interfacial energy. When the nucleation rate is spatially controlled in the plane of the film, a small portion provides the artificial nucleation site. If the sites are periodically placed, the GSD shrinks ...

Crystal forms by solid‐state recrystallization of amorphous Si films on SiO2

The recrystallization behavior of amorphous silicon films formed by Si+ ion bombardment onto polycrystalline silicon films has been studied. Two crystal forms have been identified by transmission electron microscopy and electron diffraction for the first time. Disk‐shaped crystals are formed as a result of the presence of {111} twin planes parallel to the film surface. Threefold symmetric crystals are formed by the presence of the three {111} twin planes that are not parallel to the film surface. Their feature looks less dendritic due to restricted space of film thickness in which crystal branches may grow. These two crystal forms have 〈111〉 direction normal to the film surface. A model for the formation of these crystals is proprosed in the process of solid‐state recrystallization.