D.H. Zhu

C54‐TiSi2 formed by direct high current Ti‐ion implantation

We report, in this letter, the formation of TiSi2 by direct Ti‐ion implantation into silicon wafers using a metal vapor vacuum arc ion source. Implantation was conducted by 80 KeV Ti ions to a dose of 5×1017/cm2 with various ion current densities. When the ion current density exceeded 100 μA/cm2, the equilibrium TiSi2 of the C54 structure was uniquely formed. Additional evidence of the formation of C54‐TiSi2 was given by the resistivity measurements, i.e., the sheet resistivity was below 3.0 Ω/⧠. The formation mechanism is also discussed in terms of the beam heating effect during implantation.

Formation of a CoSi2 layer by Co ion implantation using a metal vapor vacuum arc ion source

Abstract CoSi 2 was formed by metal vapor vacuum arc ion implantation in both crystalline silicon and crystalline silicon deposited with a thin Co film. When the Si(111) wafers were implanted by Co ions at an extracted voltage of 40 kV with a current density of 100 and 152 μA/cm 2 to a fixed nominal dose of 2 × 10 17 /cm 2 , a continuous CoSi 2 layer was formed and the resistivities were in the range of 14–20 μΩ cm. When the Si wafers deposited with a Co film were implanted by Co ions at an extracted voltage of 20 kV with a current density of 100 μA/cm 2 to a dose ranging from 2 × 10 17 /cm 2 to 6 × 10 17 /cm 2 , several Co-silicides were observed. Increasing the implanted dose or post-implantation annealing facilitated Co consumption and the transition from Co-rich silicide to CoSi 2 .

A preliminary study of the formation of WSi2 by high-current W ion implantation

Two differently structured WSi2 phases were formed by direct W ion implantation, for the first time, into silicon wafers using a metal vapour vacuum arc ion source. Implantation of W ions was conducted with an extract voltage of 40 kV, various beam densities from 50 to 115 mu A cm-2 and a fixed dose of 5*1017 cm-2. It was found that the formation of WSi2 with either a hexagonal or a tetragonal structure depended on the ion current density. The temperature rise caused by beam heating and the beam-striking time related to the dose were calculated, and they were responsible for the formation and evolution related to the differently structured WSi2 phases.

CRYSTALLIZATION OF SISN AND SISNC LAYERS IN SI BY SOLID PHASE EPITAXY AND ION-BEAM-INDUCED EPITAXY

Abstract For the synthesis of novel group-IV semiconductors, crystalline growth of amorphous Si1−xSnx and Si1−x−ySnxCy layers in Si formed by Sn and C ion implantation has been investigated with solid phase epitaxial growth (SPEG) and ion-beam-induced epitaxial crystallization (IBIEC). Si(100) wafers were implanted at RT with 110 keV or 270 keV 120Sn ions to a dose up to x = 0.03 at peak concentration and 17 keV or 35 keV 12C ions up to y = 0.025 at peak concentration. SPEG experiments at 750°C have shown epitaxial crystallization of the strained alloy layer in the Si 1−x Sn x Si sampl (x = 0.03) and strain-compensated layer in the Si 1−x−y Sn x C y Si sample with medium C concentration (x = 0.03 and y = 0.019). IBIEC experiments performed with 400 keV Ar ions at 350°C have also induced epitaxial crystallization for the Si 1−x Sn x Si sample (x = 0.025), whereas those of Si1−x−ySnxCy (x = 0.025 and y = 0.014) have shown a collapse of epitaxial growth. Photoluminescence (PL) from SPEG-grown Si1−xSnx and Si1−x−ySnxCy samples has shown neither prominent I1 nor G peaks. Present results have revealed features in crystalline growth properties, in both techniques, for the non-thermal equilibrium fabrication of these new alloy semiconductors.

Ion-beam-induced epitaxial crystallization (IBIEC) and solid phase epitaxial growth (SPEG) of Si1−xCx layers in Si fabricated by C ion implantation

Amorphous Si1−xCx layers in Si(100) (0.013 ≤ x ≤ 0.032 at peak concentration) formed by 35 keV 12C implantation were crystallized by solid phase epitaxial growth (SPEG) up to 850°C and by ion-beam-induced epitaxial crystallization (IBIEC) with 400 keV Ar or Ge ions at 300–400°C. SPEG process has induced the epitaxial growth up to the surface for samples with x ≤ 0.019 and IBIEC process has induced that for samples with x ≤ 0.025. Rutherford backscattering spectrometry (RBS) measurements have revealed a direct scattering peak due to extended defects around the depth of peak C concentration both in SPEG-grown samples (x = 0.019) and IBIEC-grown sample (x = 0.025). X-ray diffraction (XRD) has shown a growth with smaller tensile strain in both SPEG- and IBIEC-grown samples than in fully strained layers. Photoluminescence (PL) measurements at 2 K have shown a strong I1 line emission in IBIEC-grown samples, which can be attributed to vacancy clustering. The local configuration of defects around C atoms in the IBIEC-grown samples is thought to be an origin of the smaller tensile strain.

Anodic and air oxidation of niobium studied by ion beam analysis with implanted Xe marker

Abstract Xe marker implantation and backscattering analysis were used to study the growth mechanism of anodic oxides on niobium. In 5 wt% aqueous ammonium citrate solution, analysis of the Xe marker movement demonstrated that the oxide was formed mainly within the existing oxide through the transport of both niobium cations and oxygen anions from each side when the anodic oxidation was carried out with a constant current density of 1.0 mA cm −2 and a limiting oxidation potential from 60 to 100 V. During anodization, the transport numbers of niobium increased with the elevation of potential. The air oxidation behavior of niobium and the profile of Xe ions at the temperature of 200–500°C were also studied. The growth law of niobium oxide was obtained and no movement of the peak position of Xe ions was observed when the temperature was below 350°C.

Electron emission from Pd-carbon compound film on carbon nanoislands

Electron emission from Pd-carbon compound thin film based on carbon nanoislands is reported. The carbon nanoislands, which are formed by etching uniform carbon film in oxygen plasma using Bi nanoislands as the mask, introduce local heating of Pd-carbon thin film on it and help in forming the electron emission area. Electron emission with good stability and uniformity is reproducibly obtained with the emission efficiency up to 0.9% when an anode voltage of 3 kV is applied with a distance of 2 mm.

A NEW SILICIDATION TECHNIQUE BY METAL VAPOR VACUUM ARC ION IMPLANTATION

Using Metal Vapor Vacuum Arc ion source, high current density metal ion implantation was conducted to synthesize metal-silicides. The stable phases of C54-TiSi 2 , CoSi 2 , β-FeSi 2 , NbSi 2 and TaSi 2 were formed directly by MEVVA implantation of respective metal ions into single crystalline Si wafers under appropriate parameters. By increasing the current density and the ion dose, the equilibrium α-FeSi 2 , tetragonal-MoSi 2 , and tetragonal-WSi 2 phases were also formed through phase transformation from their respective counterparts stabilized at lower temperatures. The temperature rise caused by implantation was calculated to compare with the experimental data. Both results confirmed that the simultaneous thermal annealing effect resulted from high current density implantation was responsible for the formation and evolution of the studied metal-silicides. Besides, the electrical properties of some metal-silicides were improved considerably by post thermal annealing.

Magnetic properties of iron/noble-metal nano-multilayers

The iron/noble metal nano-multilayers were prepared by vapor deposition. The microstructure and the magnetic hysteresis loops of the films were analyzed and measured by various instruments. It was found that the magnetic moment per Fe atom in iron/noble metal multilayers was considerably enhanced with decreasing Fe layer thickness with a fixed noble-metal thickness, and was up to 120% for Fe(5nm)/Au(8nm), 120% far Fe(1.2nm)/Ag(9nm) and 150% for Fe(1.5nm)/Cu(7.5nm) multilayers within an error of 6%, respectively. The possible mechanism of the magnetic moment enhancement is also discussed in connection with the current theories.