D. Fathy

Formation of epitaxial layers of Ge on Si substrates by Ge implantation and oxidation

Thin epitaxial layers of Ge‐Si alloys have been formed on Si(100) substrates by steam oxidation of Ge‐implanted samples. During the oxidation, the Ge is totally piled up ahead of the SiO2/Si interface. This segregation of Ge leads to the formation of a distinct, Ge‐rich layer which is epitaxial with the underlying Si. The thickness of the Ge layer is dependent on the implantation dose. This layer and its two bounding interfaces with the oxide and Si are characterized as a function of the implantation dose and energy, using Rutherford backscattering and high‐resolution transmission electron microscopy.

Novel oxidation process in Ge+‐implanted Si and its effect on oxidation kinetics

Thermal oxidation of Si is shown to be substantially affected by the implantation of Ge+ ions. A unique morphology develops during steam oxidation due to the rejection of Ge from the oxide at the growth interface. The Ge pile‐up leads to the formation of a distinct layer of almost pure Ge between the oxide and the underlying Si. Oxidation rates are enhanced due to the presence of this film which is shown to increase the interfacial reaction rate. This increase is attributed to a decrease in the binding energy of Si atoms at the interface as a result of alloying with the Ge film. A model is proposed to account for the enhanced oxidation kinetics and is shown to be in good agreement with experimental data.

Atomic structure of ion implantation damage and process of amorphization in semiconductors

Atomic structure of ion implantation damage and the process of amorphization in silicon have been investigated using high‐resolution electron microscopy techniques. The specific damage energy density for crystalline to amorphous transition has been determined to be 6.0×1023 eV/cm3 or 12 eV/atom at 4 K with no annealing. The amorphous regions are produced when the damage energy deposited by the ions exceeds this critical value. Since the damage energy deposited by the ions is a strong function of ion implantation and substrate variables, the formation of amorphous regions and the process of amorphization are strong functions of these variables. The details of atomic structures of amorphous silicon containing microcrystallites and that of amorphous‐crystalline interfaces are presented. The calculations of the mean‐free path between collisions and the energy deposited per atom are found to be consistent with experimental observations on amorphization of silicon. Some results on the projected ranges of low‐en...

Influence of substrate temperature on the formation of buried oxide and surface crystallinity during high dose oxygen implantation into Si

The dependence of the implantation‐induced morphology on substrate heating during high dose O+ irradiation of Si was investigated. For high dose oxygen implantation, a continuous buried oxide layer forms during implantation. It is shown that the damage morphology in the crystalline region ahead of the buried oxide is extremely sensitive to variations in the temperature of the substrate about 475 °C. Both backscattering/channeling spectroscopy and transmission electron microscopy were used in determining the microstructure of the implanted samples.

Morphological instabilities and ion beam mixing in Ge

Abstract In light of the recent discovery [11,12] that heavy ion irradiation initiates a morphological instability in the amorphous phase of Ge which erupts to form surface craters, previous studies of ion beam mixing in the metal/Ge system [2,4] are re-examined. Correlated ion scattering/channeling and cross-section electron microscopy are utilized to study the Au/Ge and Al/Ge systems under a variety of mixing conditions. Implications for both the crater formation and ion beam mixing mechanisms are discussed.

Ion‐beam and laser mixing of nickel overlayers on silicon carbide

We have investigated ion‐beam and laser mixing of Ni overlayers on silicon carbide substrates using cross‐section and analytical techniques of electron microscopy, and ion scattering and channeling techniques. The thickness of the overlayers was varied from 200 to 500 A on both crystalline and polycrystalline substrates of silicon carbide. The thickness of the ion‐beam mixed region was found to increase with increasing dose of the implanted ions. The laser mixing was obtained only within a critical window of the pulse energy density (1.15±1.25 J cm−2) of a ruby laser (wavelength 0.693 μm, and pulse duration 28×10−9 s). The structure of the mixed region was found to be amorphous, with occasional presence of crystalline nickel silicide (Ni2Si) islands. The laser‐mixed SiC specimens showed a considerable improvement (>35%) in their fracture strength.

Ion beam processes in Si

Abstract Observation of the effects of implants of energetic ions at high dose rates into-Si have produced some exciting and interesting results. The mechanism whereby displacement damage produced by ions self-anneals during high dose rate implantation will be discussed. It will be shown that ion beam annealing (IBA) offers in certain situations unique possibilities for damage annealing. Annealing results of the near surface in Si with a buried oxide layer, formed by high dose implantation, will be presented in order to illustrate the advantages offered by IBA. It will be also shown that ion irradiation can stimulate the epitaxial recrystallization of amorphous overlayers in Si. The nonequilibrium alloying which results from such epitaxial processes will be discussed as well as mechanisms which limit the solid solubility during irradiation. Finally, a dose rate dependency for the production of stable damage by ion irradiation at a constant fluence has been observed. For low fluence implants, the amount of damage is substantially greater in the case of high flux rather than low flux implantation.

Explosive recrystallization during pulsed laser irradiation

The phenomenon of explosive recrystallization has been studied in Si+ and Cu+ implanted amorphous silicon layers by electron microscopy and Rutherford backscattering techniques (RBS). Cross‐section and plan‐view electron microscopy techniques (TEM) have been used to obtain a detailed characterization of microstructures associated with the explosive mode of recrystallization. RBS and analytical TEM studies on segregation of copper provided information on the mechanism of explosive recrystallization involving a thin liquid film interposed between crystallized and uncrystallized regions.

TEM study of ion beam mixed nickel silicides formed on SiC at different implant temperatures

Abstract High resolution and diffraction contrast transmission electron microscopy (TEM), together with Rutherford backscattering spectrometry (RBS), have been used to study intermixing between thin metal films of Ni ( ∼ 50 nm) on single crystals of (100) SiC substrates. As a result of inert-gas ion bombardment at different substrate temperatures it has been found that it is possible to form a uniform layer of nickel silicide with a sharp transition at the (100) planar interface. For a fixed dose of Xe+ ions at 350 keV the thickness of the silicide layer was found to be dependent on the substrate temperature. However, at all substrate temperatures a dominant phase of Ni2Si was detected. For implantations at room temperature, the mixed layer mainly consisted of small oriented islands at the original metal-semiconductor interface. Ion mixing at 300°C resulted in a intermixed layer with the thickness increased by a factor of 10; however, the layer was not uniform in structure. At an implantation temperature of 500°C and over, a uniform polycrystalline silicide layer was formed.

Optimized conditions for the formation of buried insulating layers in Si by high dose implantation of oxygen

Results are presented detailing the dependence of the residual damage on substrate temperature and dose for high dose implantation of oxygen in Si. It has been previously demonstrated that a buried oxide layer can be formed by this method. However, the usefulness of this silicon on insulator (SOI) structure has been limited by the considerable damage which accumulates in the crystal overlayer during irradiation. Much of the damage remains even after high temperature annealing. It is shown that the quality of the crystalline layer depends critically on the implant conditions. The preservation of the crystal quality of this layer by implanting at high temperatures to prevent defect clustering competes with the adverse effects caused by rapid diffusion of oxygen into this region. This leads to a rather narrow range of temperature over which optimization occurs. Rutherford backscattering/channeling spectroscopy and cross-sectional, transmission electron microscopy were used for analyzing the samples and for understanding the phenomena of formation of buried insulating layers.