Tanemasa Asano

In situ observation of nickel metal-induced lateral crystallization of amorphous silicon thin films

The lateral crystallization of amorphous silicon thin films induced by nickel was studied in detail, performing in situ annealing experiments with a transmission electron microscope. The nickel-induced crystallization starts with the fast growth of thin needle-like crystallites of [110] orientation, which advance along the 〈111〉 directions within the film plane. The fast growth rate and the small probability of the crystallite exhibiting the [110] orientation result in large crystalline grains. These grains are, however, composed of many small misorientated subgrains. It is thought that this is because the needle-like crystallite does not grow continuously but grows by successive jumps. Our model is that after the nickel disilicide precipitate grows a thin crystalline slice epitaxially at the leading edge of the needle-like crystallite, the nickel moves to the new leading edge and forms the new nickel disilicide precipitates to maintain the needle-like crystalline growth.

Heteroepitaxial Growth of Group-IIa-Fluoride Films on Si Substrates

Growth conditions and structures of vacuum-evaporated heteroepitaxial CaF2, SrF2 and BaF2 films on (111) and (100) oriented Si substrates have been investigated. Single crystal CaF2 films are grown on both Si(111) and (100) substrates at temperatures of 600–800°C and 500–600°C, respectively. CaF2 films on Si(111) have crystal orientations rotated 180° about the normal to the substrate surface. SrF2 and BaF2 films of good crystalline quality are grown on Si(111) at temperatures around 600°C, but are composed of two types of crystallites which have orientations either idential to those of the substrate or rotated 180° on the substrate surface about the surface normal. SrF2 and BaF2 films grown on Si(100) contain (111) oriented crystallites, and, in an extreme case, completely (111) oriented BaF2 films were grown on Si(100).

Effect of oxygen plasma exposure of porous spin-on-glass films

Hydrogen-methyl-siloxane-based porous spin-on-glass films were exposed to an oxidative plasma. The plasma exposure resulted in the loss of hydrophobic groups such as Si–H and Si–CH3. The formation of silanole groups, the decrease in film thickness, and moisture uptake were also observed. When the substrate was biased during exposure, these tendencies were found to be suppressed.

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.

Ni-imprint induced solid-phase crystallization in Si1−xGex (x: 0–1) on insulator

Position control of solid-phase crystallization in the amorphous Si1−xGex (x: 0–1) films on insulating substrates was investigated by using Ni-imprint technique. Crystal nucleation at the imprinted positions proceeded approximately 2–20 times, depending on Ge fraction, faster than the conventional solid-phase crystallization, which was due to the catalytic effect of Ni. As a result, large SiGe crystal regions (∼2μm) were obtained at controlled positions. On the other hand, the growth velocity did not changed, which suggested that grown regions contained few residual Ni atoms.

Enhanced nucleation in solid-phase crystallization of amorphous Si by imprint technology

A method to enhance crystal nucleation at controlled sites in solid-phase crystallization of amorphous Si is demonstrated. The method uses imprint with Ni-coated Si tips prior to conventional furnace annealing of amorphous Si films deposited on SiO2 substrates. The incubation time for crystallization is found to be greatly reduced at sites imprinted with the tips. This enhanced nucleation can be used to form large crystal grains up to about 7 μm in diameter at controlled sites. Results obtained from imprint with SiO2-covered Si tips suggest that the enhanced nucleation results not from physical effects of indentation but from a chemical effect of metal transfered from the tip to the film surface.

Field emission from ion‐milled diamond films on Si

Diamond grains were grown on Si substrates by plasma‐enhanced chemical vapor deposition. Ar ion milling was applied to the diamond/Si structures. It has been found that sharp diamond cones can be formed by ion milling if diamonds are in the form of isolated grains. It has also been found that the field emission current from diamond/Si samples is drastically increased by Ar ion milling and subsequent heat treatment in vacuum.

Schottky Source/Drain SOI MOSFET with Shallow Doped Extension

Silicon-on-insulator metal-oxide-semiconductor field-effect-transistor (SOI MOSFET) whose source and drain are composed of deep Schottky contact and shallow-doped extension is investigated. This new structure aims at reducing the floating body effect of a partially depleted SOI MOSFET while keeping its current drive at the same level as that of the conventional pn junction SOI MOSFET. The shallow doping was performed by implanting Sb to form n-channel devices. Incorporation of the shallow extensions into the Schottky source and drain SOI MOSFET can increase the current drive by about 2 orders of magnitude owing to the reduction of the effective Schottky barrier. It can also decrease the leakage current owing to the reduced field at the drain Schottky contact. The effect of the new source and drain structure on the floating body effect is investigated by fabricating devices with body contact. The body current in MOSFET operation and tests in lateral bipolar operation show that the proposed source/drain structure is effective in reducing the floating body effect and therefore suppressing the early drain breakdown of the SOI MOSFET.

Electron-beam exposure (EBE) and epitaxy of GaAs films on CaF2/Si structures

A novel heteroepitaxial method (electron-beam exposure and epitaxy: EBE-epitaxy) has been developed for growing GaAs films on top of CaF2/Si(111) structures. In this method, the surface of CaF2 films is modified by an electron beam (e-beam) under arsenic impingement prior to the growth of GaAs films. It has been found that this EBE-epitaxy is very effective in improving the quality of the GaAs films such as surface morphology, crystallinity and crystallographic orientation. The principal effects in the EBE-epitaxy to improve the crystalline quality are considered based on these experimental results to derive a model of the growth mechanism. Other effects, such as electron energy dependence, substrate temperature dependence during e-beam exposure and GaAs growth temperature dependence, are also investigated systematically. Subsequently, the growth condition for an ideal EBE-epitaxy is discussed.

Formation of GaAs-on-Insulator Structures on Si Substrates by Heteroepitaxial Growth of CaF2 and GaAs

Epitaxial GaAs layers have been grown on (100) and (111) oriented CaF2/Si structures by molecular beam epitaxy, and characterized mainly by ion channeling and cross-sectional transmission electron microscopy. GaAs films were found to grow epitaxially at conventional growth temperatures (≤600°C). GaAs films having better crystalline quality could be grown on (111) substrates, though the surface of these GaAs films was not flat. Planar defects were peculiarly observed in GaAs films grown on (100) substrates.