G. Scilla

Boron, phosphorus, and arsenic diffusion in TiSi2

The diffusivities of B, P, and As implanted in TiSi2 are analyzed between 500 and 900 °C by secondary ion mass spectroscopy. It is shown that P and As have high (and almost equal) diffusivities compared with B which appears immobile. This difference is presumed to be related to the very high stability of TiB2 (as compared with TiSi2) and the probable precipitation of B in the form of a titanium boride. The lattice diffusion coefficients for As and P are deduced from the diffusion profiles; they range from 10−17 to 10−14 cm2/s between 550 and 800 ° C. The activation energies are found to be, respectively, 1.8 and 2.0 eV; values close to the activation energy for the self‐diffusion of Si in TiSi2, 1.8 eV. The diffusion profiles also show a high grain boundary diffusivity and an accumulation of dopant at the TiSi2–Si interface.

Experimental evidence of both interstitial‐ and vacancy‐assisted diffusion of Ge in Si

We present the first experimental identification of the diffusion mechanisms of Ge in Si. Using thermal nitridation reactions to create either excess self‐interstitials or vacancies, it is established that under equilibrium conditions at 1050 °C Ge diffusion takes place by both substitutional‐interstitial interchange and vacancy mechanisms, with comparable contributions from each. If previous conjectures that Ge diffusion in Si is similar to Si self‐diffusion are correct, our findings support the idea that Si self‐diffusion takes place by both interstitial and vacancy mechanisms.

Hydrogen plasma induced defects in silicon

The nature of extended defects in silicon introduced by hydrogen containing plasmas has been studied by transmission electron microscopy for a variety of technological processes. Depending on the doping level of the substrate, the substrate temperature and the presence/absence of simultaneous energetic ion bombardment, {111} planar defects, gas bubbles, and a heavily damaged near‐surface region have been observed.

Processing of La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films by dual‐ion‐beam sputtering

High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual‐ion‐beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd‐YAP, MgO, SrF2, Si, CaF2, ZrO2‐9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x‐ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to ...

Reaction of titanium with germanium and silicon-germanium alloys

The reaction of Ti with pure Ge and several Ge‐Si alloys has been investigated with the double aim of understanding the reaction with Ge and of throwing some light on the still vexing problem of the Ti‐Si reaction. With pure Ge one observes first of all the formation of Ti6Ge5 until complete consumption of the Ti is present. This is followed by the clearly identifiable nucleation of TiGe2, initially forming islands that grow laterally. With a 50‐50 (at. %) alloy of Si and Ge, one still observes distinct growth steps, but there is overlap between the growth of the initial phase, and the nucleation and growth of Ti(Ge,Si)2.

Diffusion of Sb, Ga, Ge, and (As) in TiSi2

Gallium, Sb, and Ge were implanted into thick (about 400 nm) layers of TiSi2 prepared by metal‐silicon reaction. The diffusion of the implanted atoms was analyzed by means of secondary ion mass spectrometry. Gallium was introduced because a former study had shown that the usual p‐type dopant B does not diffuse in TiSi2. Germanium was used in lieu of a Si tracer. Its diffusion characteristics are compared to those of P and As (as well as Si) which had been investigated previously. Germanium and Ga diffuse readily above 600 °C, but Sb does not. Its diffusion appears to be limited to grain‐boundary effects. Accumulations of the diffusing atoms are observed (except for Sb) at the silicide‐silicon interface. These are due to kinetic effects, namely fast diffusion at grain boundaries and interfaces, rather than to real adsorption which is an equilibrium condition. Because diffusion in intermetallic compounds has been shown to be significantly affected by variations in stoichiometry, experiments were conducted w...

Quantitative oxygen measurements in OMPVE Al x Ga 1- x as grown by methyl precursors

Oxygen has always been considered to be a major contaminant in the organo-metallic vapor phase epitaxy (OMVPE) of AlxGa1−xAs. Oxygen incorporation has been invoked as a contributor to low luminescence efficiency, dopant compensation and degradation of surface morphology among other deleterious effects. This study presents quantitative measurements of oxygen concentration in nominally high purity AlxGa1−xAs. The oxygen concentration was measured as a function of alloy composition, growth temperature, andV/III ratio. Quantitative secondary ion mass spectroscopy (SIMS) measurements were used to determine the oxygen content as well as the carbon concentration in the film. The oxygen concentration increases with decreased growth temperature and V/III ratio while increasing superlinearly with Al content in the epitaxial layer.

High carbon doping efficiency of bromomethanes in gas source molecular beam epitaxial growth of GaAs

Carbon tetrabromide (CBr4) and bromoform (CHBr3) have been studied as carbon doping sources for GaAs grown by gas source molecular beam epitaxy (GSMBE) with elemental Ga and thermally cracked AsH3. Hole concentrations in excess of 1×1020 cm−3 have been measured by Hall effect in both CBr4‐ and CHBr3‐doped GaAs, which agrees closely with the atomic C concentration from secondary‐ion mass spectrometry, indicating complete electrical activity of the incorporated carbon. The GaAs growth rate is unaffected by the CBr4 and CHBr3 fluxes over the range of dopant flow investigated. The efficiencies of carbon incorporation from CBr4 and CHBr3 are, respectively, 750 and 25 times that of trimethylgallium (TMG), which is commonly employed as a carbon doping source in metalorganic MBE (MOMBE). The sensitivity of carbon incorporation to varying substrate temperature and V/III ratio has been observed to be significantly reduced with CBr4 and CHBr3 from that obtained under similar growth conditions with TMG in MOMBE.

Processing of La/sub 1. 8/Sr/sub 0. 2/CuO/sub 4/ and YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting thin films by dual-ion-beam sputtering

High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual‐ion‐beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd‐YAP, MgO, SrF2, Si, CaF2, ZrO2‐9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x‐ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to ...

The diffusion of elements implanted in films of cobalt disilicide

The diffusion of several elements implanted into layers of CoSi2 with a nominal thickness of 800 nm, grown by metal‐silicon reaction, has been studied by secondary ion mass spectroscopy. Boron has by far the highest mobility. It is totally homogenized by heat treatment for 0.5 h at 800 °C; it displays evidence of grain‐boundary diffusion at 400 °C and of lattice diffusion at 450 °C. The next group of elements, gallium, phosphorus, and germanium (used as a tracer in lieu of a silicon isotope) diffuse distinctly less rapidly, and remain nonhomogenized after annealing at 800 °C. The lattice diffusion of arsenic and antimony is not detectable (by the means presently used), even after heat treatment at the same relatively high temperature. Low‐temperature effects, and effects far away from the implanted region, are dominated by grain‐boundary diffusion. The lattice diffusion increases from boron to phosphorus and germanium, with activation energies determined to be 2.0 and 2.7 eV for boron and phosphorus, resp...