Yoshiaki Matsushita

Thermally Induced Microdefects in Czochralski-Grown Silicon: Nucleation and Growth Behavior

The current understanding of thermally induced microdefects in Czochralski-grown silicon crystals is briefly reviewed and our investigations of the defects are described. The microdefects originate in oxygen precipitation occurring during thermal treatments after crystal growth. Both homogeneous and heterogeneous nucleation models have been proposed for the oxygen precipitation. The homogeneous nucleation model is contradicted because a low density of microdefects are induced in recent high-quality crystals even at high oxygen concentrations. A heterogeneous nucleation model is proposed, based on detailed investigations of the thermal behaviors of microdefects. It is demonstrated that the oxygen precipitation is governed by nucleation sites (carbon atoms) and the thermal history of wafers after crystal growth besides the oxygen concentration of the wafer.

A study on thermally induced microdefects in czochralski-grown silicon crystals: Dependence on annealing temperature and starting materials.

Thermally induced microdefects in Czochralski-grown (CZ) silicon crystals have been investigated by both TEM and IR absorption techniques. Dependence of the defect behavior on both the annealing temperature and the starting materials was studied. It was found that the defect nature varies with the temperature, and that the defect density increases exponentially with the decrease of the annealing temperature. The increase in density also has a strong correlation with the initial carbon concentration in the wafer. It is concluded that the oxygen precipitates are heterogeneously formed at sites which have certain correlation with carbon atoms.

Solid-Phase Lateral Epitaxial Growth onto Adjacent SiO2 Film from Amorphous Silicon Deposited on Single-Crystal Silicon Substrate

Single-crystal silicon films (200 nm thick) have been grown laterally by thermal annealing from amorphous silicon evaporated on a single-crystal (100) silicon substrate and implanted with ~1016/cm2 Si, onto an adjacent SiO2 film by solid-phase epitaxy. The key requirements for this kind of lateral epitaxy appear to be a high-dose Si ion implanatation and low temperature (575°C) annealing for a long period in order to suppress the nucleation of randomly-oriented crystals on the SiO2 film.

Growth Mode Discrimination of Thin Films by Auger Electron Spectroscopy

The growth mode of thin films is studied by Auger electron spectroscopy (AES) in comparison with the observations by electron microscope (EM). The simple criteria to discriminate by AES between the nucleation and growth (NG) and the monolayer overgrowth (MO) modes, which take account of the different trends of coverage of substrate surface by overgrown film, are shown to give consistent results with EM: Pd/MoS2, PbTe/MgO are NG and Pd/Au, Au/Pd, Ag/Au, Pd/Ag, GeTe/PbSe are MO. The case of GeTe/PbTe, which gives antinomic features in EM, is decided by AES to be MO. The values of escape depth for several Auger electrons are determined and compared with previous data. The problems of interdiffusion across the interface in MO are discussed.

Effect of Hydrogen Termination on Surface Roughness Variation of Si(110) by Reflow Oxidation during High-Temperature Ar Annealing

It is well known that a smooth surface can be realized for silicon (Si) wafers by Si surface reconstruction using high-temperature annealing. We previously reported that it is crucial to maintain a smooth reconstructed surface to restrict accidental oxidation during the unloading process (i.e., reflow oxidation) in high-temperature annealing. The surface roughnesses of both Si(100) and Si(110) were proved by suppressing the reflow oxidation. Furthermore, for suppressing the reflow oxidation, we evaluated the thickness of the reflow oxidation layer and the surface structure of the Si(110) wafer by replacing the injected Ar gas with H2 in the cooling process during high-temperature Ar annealing. The H2 atmosphere condition induced a change by etching the reconstructed surface, and the H-terminated surface on Si(110) formed SiH2, which effectively suppressed the reflow and characteristic line oxidations, resulting in a smooth terrace-and-step structure.

Effect of Reflow Oxidation on Si Surface Roughness during High-Temperature Annealing

It is well known that a smooth surface of silicon (Si) wafers can be obtained by Si surface reconstruction using high-temperature annealing. However, there is a possibility that smooth Si surfaces are deteriorated by oxidation (called reflow oxidation) during unloading after the high-temperature annealing. Therefore, it is important to investigate the effect of oxidation on the surface steps and terraces on Si wafers at the atomic level during unloading. We have examined the effect of unloading temperature after Ar annealing on oxide formation on the surfaces of Si(100) and Si(110) substrates. The change in the surface roughness was also measured. Our results indicate a significant improvement with rms values of 0.01 nm for both Si(100) and Si(110) wafer surfaces upon low-temperature unloading. A very flat surface with an rms value of 0.046 nm was achieved for a Si(100) wafer.

Heteroepitaxy of chalcogenide compounds II. Monolayer overgrowth process accompanied by lattice transformation

Abstract The growth processes of orthorhombic SnSe and rhombohedral GeTe on NaCl-type PbSe, PbTe and SnTe have been studied by still and in situ electron microscopy, with the following results. (i) Growth proceeds in the monolayer overgrowth mode, as for the substrate-deposit combinations of chalcogenides of the same NaCl-type structure reported in Part I. (ii) Lattice recovery of the overgrown films from the initial pseudomorphic structure to the natural structure proceeds by the development of sets of differently spaced misfit dislocations in appropriate directions, with the formation of doubly positioned regions. (iii) The growth of GeTe on PbTe shows a different aspect from that observed for all other cases in Parts I and II, which exhibit straightforward monolayer overgrowth. Initially, bundles of closely spaced short-segmented misfit dislocations are formed into many island-like patches, suggesting that overgrowth proceeds in the nucleation and growth mode. At a later stage, however, generation and extension of the patches takes place, piloted by a singly extending misfit dislocation; this suggests the monolayer overgrowth mode, which is confirmed by Auger electron spectroscopy. (iv) Climb plays a primary role in the formation of misfit dislocations. For SnSe growth on (001) PbSe, PbTe and SnTe, however, misfit dislocations are glissile along the interface and their rearrangement by slip during growth leads to a well-defined configuration of doubly positioned regions in the later stages, with the overgrown lattices in the two regions in coherent twin contact with each other at the boundaries.

Monolayer overgrowth in heteroepitaxy of chalcogenide compounds with NaCl- and distorted NaCl-structures

Abstract Monolayer overgrowth of thin is found to take place in a characteristic way during heteroepitaxy of chalcogenide compounds in the case of deposit-substrate combination of different symmetry. The lattice transformation of the film from the initially pseudomorphic structure to the natural structure proceeds by the formation of sets of appropriately-oriented misfit dislocations (MDs) of different density. The method of identification of the growth mode, coherency between the overgrowth and substrate lattices and configuration and formation mechanism of MDs are discussed in comparison with the case of simple monolayer overgrowth without lattice transformation and the case involving nucleation and growth.

Quantum Chemical Analysis of Metal Adsorption Mechanism onto Silicon Surface in Cleaning Solution

Fe3+ and Al3+ complex ion structures in aqueous solution were estimated by ab initio molecular orbital theory. The reactivity between the metal complex ions and Si surface depends on the pH of the solution, which was well explained by the frontier orbital theory. Based on the result of theoretical estimation, the addition of a chelating agent to basic solution to prevent the OH- ion from coordinating with metal ions is demonstrated to be effective in suppressing metal adsorption to the silicon surface.