Seijiro Furukawa

Theoretical Considerations on Lateral Spread of Implanted Ions

This paper presents a theoretical analysis on the lateral spread of the distribution for implanted ions in amorphous targets. First, it is shown that the solutions of the second order differential equations concerning moments of the ranges are necessary and sufficient to estimate the lateral distribution, if the Gaussian distribution is assumed. The calculated results of , and the lateral spread are presented. Next, it is shown that the actual distribution function along the lateral direction is approximately expressed by the complementary error function at the window edge, in case when ions are implanted through the mask-window. The variation of the lateral spread with incident ion mass is also calculated. From these calculations, it is concluded that the lateral spread can not be neglected in the case of light ions such as B+ incident to Si.

Double heteroepitaxy in the Si (111)/CoSi2/Si structure

Epitaxial growth of CoSi2 films on Si substrates and the growth of Si films on the Si(111)/CoSi2 structure are investigated. Solid phase epitaxy is used to grow both CoSi2 and Si films. Molecular beam epitaxy is also used to grow the top Si films in the double heteroepitaxy. It has been found that two dominant factors required to obtain good epitaxial films are substrate cleaning by lamp heating before the film deposition and annealing of the deposited films without exposure to air. Excellent crystalline quality of the CoSi2 films on (111) Si substrates and good quality of the Si films on the Si(111)/CoSi2 structure have been demonstrated by ion channeling and backscattering techniques and reflection electron diffraction analysis. Uniformity of the grown films has also been examined by scanning electron microscopy.

Lateral solid phase epitaxy of amorphous Si films on Si substrates with SiO2 patterns

Lateral solid phase epitaxy of amorphous Si films vacuum evaporated on Si substrates with SiO2 patterns has been investigated, in which the films first grow vertically in the region directly contacted to the Si substrates and then grow laterally onto SiO2 patterns. It was found from transmission electron microscopy and Nomarski optical microscopy that the lateral growth occurred in dense amorphous Si films formed by evaporation on heated substrates and subsequent amorphization by Si+ ion implantation, but it hardly occurred in porous films deposited at room temperature. The maximum length of the epitaxial film on SiO2 was about 6 μm after 10‐h annealing at 600 °C.

Formation of uniform solid-phase epitaxial CoSi2 films by patterning method

This paper reports that uniform solid-phase epitaxial CoSi2 films without any holes can be fabricated by patterning the Si(111) substrate in the form of squares or stripes before the CoSi2 epitaxial growth. The surface energies of the CoSi2 and Si are considered theoretically. Since the surface energy of the Si(111) surface is smaller than that of the CoSi2(111) surface, the film tends to expose the Si substrate, forming holes in the films. The total surface energy on the patterned area is calculated numerically, showing that the film will be uniform if the pattern size is smaller than a certain critical dimension. The numerical calculations agree qualitatively with the experimental results.

Backscattering study on lateral spread of implanted ions

Without ambiguities due to the cutting angle of a mask edge and the annealing process, the lateral spread of implanted Kr ions into Si substrates has been directly measured by the He+ backscattering technique. The experimental results show good agreement with theoretical predictions.

Single Crystalline Silicide Formation

Formation conditions of single crystalline silicide films on Si substrates by solid phase reactions were investigated using MeV He+ Rutherford backscattering and channeling techniques and transmission electron microscopy. It was shown that single crystalline silicide films (NiSi2, CoSi2 and Pd2Si) can be formed on (111)Si when metals are deposited onto clean surfaces and they are annealed without exposure to air. Channeling minimum yields in the backscattering analysis were 0.03–0.04 in NiSi2 and CoSi2 films thinner than 150 nm and 0.06 in Pd2Si films thinner than 100 nm. In the transmission electron microscopy measurement, grain boundaries were not observed at least in an area of 100×100 µm2, but several defects like twins and dislocations were observed in some silicide films. The resistivity of silicide films was also measured by the four-point probe method, and the resistivities of CoSi2, Pd2Si and NiSi2 were about 15 µΩ-cm, 25 µΩ-cm and 35 µΩ-cm, respectively.

A heat‐resisting new amorphous silicon

By using the sputtering method in a mixture of Ar and SiF4 gases, a purely fluorinated amorphous‐silicon (a‐Si : F) has been deposited, which does not contain hydrogen, and whose dangling bonds are terminated only by fluorine. Fluorine content, infrared absorption, and temperature dependence of conductivity, and also their variation due to the annealing process, are experimentally studied for this a‐Si : F. It is found that all these are kept unchanged even after an annealing process at 600 °C, and that this new a‐Si : F is heat resistant.

Optimum Growth Conditions of GaAs(111)B Layers for Good Electrical Properties by Molecular Beam Epitaxy

Growth conditions of GaAs layers grown by molecular beam epitaxy (MBE) on (111)B-oriented GaAs substrates were optimized by surface morphology observation and Hall measurement. Good surface morphology was obtained by use of 1.5° off-oriented (111)B substrates. This paper reports for the first time that electron mobilities as high as those on (100) substrates can be obtained even at growth temperature as low as 530°C if the off-oriented (111)B substrates are used, whereas one higher than 600°C is necessary to obtain the same electron mobility on exactly (111)B-oriented substrates. MESFETs and Schottky diodes fabricated on the layer grown at the optimized condition show high electron mobility and suggest low concentration of defects.

Separate estimate of crystalline orientations and scattering centers in polycrystals by backscattering technique

A novel method using backscattering and channeling techniques is presented to estimate separately two dominant dechanneling factors in polycrystals, that is, spread of crystallite orientations and existence of scattering centers. It is theoretically shown that both factors can independently be estimated by measuring angular dependences of backscattering yield around the channeling axis. The angular dips on Pd2Si layers formed on single‐crystalline Si substrates are measured by using 1–2‐MeV protons, He+, and N+ ions. The channeling measurements using N+ ions are shown to be a useful tool for analysis of polycrystalline layers. By using the above method, crystalline perfection of these layers is also discussed.

Channeling and backscattering studies of the crystalline perfection and the thermal stability of epitaxial PtSi films on Si

Ion‐channeling and backscattering techniques, with some addition of reflection electron‐diffraction analysis, have been employed to study the crystalline perfection and thermal stability of epitaxial PtSi films on (111)Si substrates. It was found that a preferred orientation of crystallites in the films strongly depends on film thicknesses above 300 A. It was also found that the annealing temperature affects the spread in preferred orientation. The angular and energy‐dependence measurements of backscattering yields have shown that the angular spreads in crystallite orientations in the PtSi films are larger than 0.5° for annealing times of 0.5–8 h, temperatures of 400–750 °C, and film thicknesses of 100–1600 A. Epitaxial PtSi films on (111)Si are more stable than nonepitaxial ones on (100)Si up to temperatures 100 °C greater. It was concluded that the stability of the epitaxial films originates in the preferred orientation of crystallites in the films.