Kenji Kajiyama

Schottky barrier height of n‐InxGa1−xAs diodes

The barrier heights φB of Au/n‐InxGa1−xAs diodes are measured by the capacitance‐voltage and saturation current methods. The composition dependence of the barrier height is φB (eV) = 0.95 − 1.90x + 0.90x2. A low barrier height with a relatively wide band gap is obtained in this system.

Novel low‐temperature recrystallization of amorphous silicon by high‐energy ion beam

An entirely new beam annealing method that employs a high‐energy (∼2.5 MeV) heavy ion (As75, Kr84) beam is presented. With this technology, an amorphous Si layer is recrystallized at below ∼300 °C substrate temperature (much lower than the ordinary solid phase epitaxial growth temperature of ∼600 °C). The temperature just under the beam spot is estimated to be at most ∼20° C higher than that in the surrounding region, because of the large beam spot size (∼10 mmφ) and rapid scan speed (∼104 cm/s). This low‐temperature annealing feature is quite different from the case for conventional furnace, laser, electron, and low‐energy ion beam annealing. After recrystallization, impurity As atoms are located at substitutional sites with no tetrahedral interstitial components, and are scarcely redistributed.

Surface Silicon Crystallinity and Anomalous Composition Profiles of Buried SiO2 and Si3N4 Layers Fabricated by Oxygen and Nitrogen Implantation in Silicon

Buried SiO2 and Si3N4 with residual crystalline surface silicon were fabricated by implantation of O+, O2+, N+ and N2+ into single-crystal silicon with 0.6–3.0×1018 atom/cm2 dose at an energy of 70–150 keV/atom. The implanted silicon wafers were annealed at 1150°C to recover the surface silicon crystallinity and to ensure good Si–O and Si–N bonds. After this, high-quality crystalline silicon layers were grown epitaxially on the implanted surface. The surface silicon damage and the buried layer composition profiles were measured reliably by the Rutherford backscattering method together with the channeling technique. In the buried layers, the O/Si ratio did not exceed the stoichiometric ratio of 2.0 for SiO2 even before annealing. However, the N/Si ratio exceeded the stoichiometric ratio of 4/3 for Si3N4.

Solid‐phase lateral epitaxy of chemical‐vapor‐deposited amorphous silicon by furnace annealing

A single‐crystalline silicon‐on‐insulator structure has been fabricated with solid‐phase lateral epitaxy. Chemical‐vapor‐deposited amorphous silicon (CVD a‐Si) deposited on a SiO2 stripe is crystallized by furnace annealing. A new CVD technique (clean CVD) has met the conditions required for solid‐phase epitaxy; clean interface and reduction of impurities and microcrystallites in the a‐Si film. In the case of a 4‐μm‐wide SiO2 stripe parallel to the 〈100〉 direction, the entire deposited layer grows epitaxially by low‐temperature furnace annealing (550∼650 °C). In the case of a 10‐μm‐wide SiO2 stripe, the whole surface region also grows epitaxially, although the deep region partially becomes polycrystalline in areas distant from the open substrate surface. The grown‐layer crystallinity is improved by subsequent high‐temperature annealing.

Amorphous‐Si/crystalline‐Si facet formation during Si solid‐phase epitaxy near Si/SiO2 boundary

Amorphous‐Si (a‐Si)/crystalline‐Si (c‐Si) interface facet formation was found during Si solid‐phase epitaxy (SPE) near the Si/SiO2 boundary. A (110) facet is formed during (010)b‐[100]SPE (SPE growth in the [100] direction and near the (010) boundary between a‐Si and SiO2). A (111) facet is formed during (011)b‐[100]SPE. The facet formation is explained with an atomistic model wherein an a‐Si atom must complete at least two undistorted bonds to attain SPE growth, and the boundary condition wherein an a‐Si atom cannot form undistorted bond to Si/SiO2 boundary.

In Situ Self Ion Beam Annealing of Damage in Si during High Energy (0.53 MeV–2.56 MeV) As + Ion Implantation

High energy As+ ions have been implanted by a 2.5 MeV Van-de-Graaff accelerator. Implantation induced damage in silicon crystal is anomalously smaller than that estimated from the calculation for nuclear deposited energy density. The logarithm for observed damage degree depends linearly on the inverse absolute temperature of the wafer during implantation. The 0.18 eV activation energy coincides with the 0.18 eV migration energy for the doubly negative vacancy. The anomalously small damage is attributed to in situ recrystallization of damage assisted by migration of the doubly negative vacancy (V-) which is formed by high energy heavy ion implantation. As the wafer temperature is below 300°C, and activation energy is small, ordinary solid phase epitaxial regrowth does not occur.

Kinetics of Antimony Doping in Silicon Molecular Beam Epitaxy

A new kinetic model for Sb doping into the Si MBE layer is proposed. In this model, Sb doping steps are assumed as follows: a fraction of impinging Sb4 molecules adsorbs on the growing Si surface (adlayer) and monoatomic Sb desorbs from the adlayer into vapor; a fraction of monoatomic Sb in the adlayer is incorporated into the bulk, so that surface-concentration of Sb atoms may be in equilibrium with bulk-concentration of Sb. According to this model, calculated results successfully represent the present experimental data on relations between incident Sb4 flux, Sb concentration in the adlayer and that in bulk. As a result, it is indicated that doping levels in MBE layers are uniquely determined by Sb concentration in the adlayer, and not by Sb4 flux/Si flux ratio, when Si growth rate is lower than 1 A/s.

Silicon avalanche photodiodes with low multiplication noise and high-speed response

Low-noise and high-speed silicon avalanche photodiodes with low breakdown voltage are reported. The diode structure with a low-high-low impurity density profile is proposed to have low-noise characteristics. Multiplication noise and depletion layer width of several structures are compared theoretically, and effects of impurity density profile of the avalanche region are discussed. Built-in field is also provided to realize high-speed response without increasing operating voltage. Silicon avalanche photodiodes with the above mentioned structure have been fabricated with long time substrate annealing, ion implantation, and epitaxial growth. Attained performances are as follows: noise parameter k = 0.027 - 0.040, output pulse half width τ = 260 ps for a mode-locked Nd:YAG laser pulse, gain-bandwidth product up to 300 GHz at M = 400, quantum efficiency 0.55 - 0.66 at the 0.81- to 0.83-µm wavelength, and breakdown voltage about 100 V.

Solid-Phase Epitaxy of CVD Amorphous Si Film on Crystalline Si

The authors demonstrate that CVD amorphous Si crystallizes epitaxially on a (100)Si substrate with furnace annealing at temperatures of 600°C or below. Cleaning the substrate surface and depositing amorphous film at a low temperature with a high deposition rate are essential to this procedure. After loading the substrate into a CVD reactor, the substrate surface is first etched with H2 to remove native oxide at 1100°C, and then with HCl to prevent foreign atom adsorption up to a low deposition temperature of 550°C. The low temperature prevents microcrystallite formation, and the high deposition rate hinders foreign atom inclusion during deposition. With the appropriate cleaning and deposition conditions, the resultant epitaxial layer crystallinity has been proven to be good through Rutherford backscattering and reflection electron diffraction measurement.

Precise Profiles for Arsenic Implanted in Si and SiO2 over a Wide Implantation Energy Range (10 keV–2.56 MeV)

Arsenic ions were implanted into Si and SiO2 over a wide energy range (10 keV–2.56 MeV). Implantation profiles were precisely measured by the normal and glancing angle Rutherford backscattering method. They are closely approximated by joined half-Gaussian distributions. For Si, the experimental Rp and ΔRp values are systematically ~15% and ~30% larger than the LSS calculation values over the present full implantation energy range of 10 keV–2.56 MeV. For SiO2 the experimental Rp and ΔRp values are systematically 20–30% and 40–50% larger over the same implantation energy range. The experimental third-moment, µp, is positive below ~500 keV, and is negative above ~500 keV implantation energy, for both Si and SiO2.