Jyoji Nakata

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 ∼300u2009°C substrate temperature (much lower than the ordinary solid phase epitaxial growth temperature of ∼600u2009°C). The temperature just under the beam spot is estimated to be at most ∼20°u2009C 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.

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.

Direct evidence of Er atoms occupying an interstitial site in metalorganic chemical vapor deposition‐grown GaAs:Er

Er doped GaAs grown by metalorganic chemical vapor deposition is studied by the Rutherford backscattering channeling method. We directly confirmed, for the first time, that Er ions occupy a somewhat displaced tetrahedral interstitial site, rather than a substitutional site, in the GaAs host. This is concluded from the observation of a remarkable peak of the doped Er ions caused by the flux peaking effect in the 〈110〉 channeling direction. Also leading to this conclusion is the fact that the ratios of the 〈111〉 and 〈100〉 channeling yields to the random yields for Er ions were larger than those for the GaAs host. Moreover, we observe peak shifts towards the higher energy region in the 〈110〉 spectra compared to the random spectra. This is due to the lower stopping power of He ions in the GaAs host in the channeling direction than in the random direction. We deduce the strikingly small stopping power ratio of the 〈110〉 to the random incidence is also discussed.

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.

A Rutherford Backscattering Spectroscopic Study of the Aluminum Antimonide Oxidation Process in Air

The oxidation process of aluminum antimonide (AlSb) in air is investigated in detail using Rutherford backscattering spectroscopy (RBS). It is verified that AlSb is extremely liable to be oxidized by slight exposure to air. The oxidation is found to be a two-step process: an initial fast step and a subsequent slower one. In the initial step, a surface oxide with a thickness of about 150 A is formed after AlSb is exposed to air for only a matter of minutes. This oxide gradually thickens in the subsequent step, reaching the AlSb/GaSb interface after exposure for about eighty hours. It is also clarified that the oxidized AlSb layer is amorphous and that a partly oxidized region is formed under the amorphous oxidized AlSb layer in a precursory state.

High Energy As+ Ion Implantation into Si–Arsenic Profiles and Electrical Activation Characteristics–

High energy (a few MeV) As+ was uniformly implanted into 2 Si (111) wafers at doses of 1013–1016 cm-2. Implanted As profiles were precisely measured by the Rutherford backscattering method (RBS) over a wide energy range (0.5–2.5 MeV). Experimental values for Rp and ΔRp were larger than the LSS calculation values by about 15% and 30%, respectively. After annealing, carrier profiles were measured by the differential sheet resistance and C-V methods. They agreed well with a Gaussian distribution, defined by Rp and ΔRp measured by RBS, from peak to surface over 4 figures of concentration. Implanted As is easily activated by 700°C annealing with low doses (~1014 cm-2). Activation ratio depends mainly on peak arsenic concentration and not on implantation energy.

Suppression of AlSb oxidation with hydrocarbon passivation layer induced by MeV‐He+ irradiation

A very thin hydrocarbon coating layer of at most a few monolayers induced by the electronic scattering of MeV‐He+ ion‐beam irradiation effectively and completely suppresses oxidation of the compound semiconductor AlSb, which is liable to be oxidized by mere exposure to air, because of the coating layer’s hydrophobic property. Of the many kinds of hydrocarbons, alkyl and phenyl groups are particularly effective for oxidation suppression. The AlSb oxidation mechanism and oxidation suppression mechanism are discussed.

Novel Low Temperature (\lesssim300°C) Annealing of Amorphous Si by Scanned High Energy (∼2.5 MeV) Heavy Ion Beam

Novel ion beam annealing (HIBA, High energy heavy Ion Beam Annealing) with high energy (~2.5 MeV) heavy ion beam is presented. By HIBA, an amorphous Si layer is recrystallized below (~300°C of substrate temperature (much lower than oridinary solid phase epitaxial growth temperature ~600°C). Also, the temperature just under the beam spot is estimated to be ~20°C higher at most than that of surrounding region, because of large beam spot size (~10 mm) and rapid scan speed (~104 cm/s). This low temperature feature is quite different from the conventional furnace, laser, electron or low energy ion beam annealing. After HIBA, impurity As atoms are located at substitutional site with no tetrahedral interstitial component and are scarcely redistributed.

The anomalous refractive index in the ellipsometric evaluation of an inhomogeneous film

Abstract When the refractive index of a surface film is a function n(x) of x, where x is the coordinate normal to the film surface, the values of the film thickness d and the film index n determined ellipsometrically by assuming that the film is homogeneous can be significantly different from the real thickness d and the mean index 〈n〉 = 1 d ∫ 0 d n(x) d x respectively. In this work the relative differences e d = ( d −d) d and e n = ( n −〈n〉) 〈n〉 were computed as functions of the film thickness d for SiO2 films on silicon substrates. Three types of refractive index profile n(x) were assumed. It is shown that ed and en can become quite large when the optical path length difference between the light reflected at the air-film interface and that reflected at the film-substrate interface approaches mλ(m = 1, 2, 3, …). A method is proposed by which a better estimate of film thickness can be obtained from a single observation of Δ and Ψ. This method is useful when en is small.

Source/Drain Ion Implantation into Ultra-Thin-Single-Crystalline-Silicon-Layer of Separation by IMplanted OXygen (SIMOX) Wafers

Problems associated with ion implantation into ultra-thin-film SIMOX (Separation by IMplanted OXygen) of SOI (silicon on insulator) structures are discussed. We realized n-type source/drain region with lower resistance by P+ ion implantation. To decrease the resistance of the implanted layer, the amorphized high-dose layer must be recrystallized by annealing. We show that the possibility of recrystallization can be predicted by TRIM simulation. Moreover, it was found that excess phosphorus above the solid solubility segregates in the Si/SiO2 interface.