Determination of the crystalline volume fraction by Raman scattering in amorphous germanium layers formed by implantation of indium ions

Swift heavy-ion (SHI) irradiation of amorphous germanium (a-Ge) layers leads to a strong volume expansion accompanied by a nonsaturating irreversible plastic deformation (ion hammering), which are consequences of the high local electronic energy deposition within the region of the a-Ge layer. We present a detailed study of the influence of SHI irradiation parameters on the effect of plastic deformation and structural modification. Specially prepared a-Ge layers were irradiated using two SHI energies and different angles of incidence, thus resulting in a variation of the electronic energy deposition per depth ${\ensuremath{\epsilon}}_{e}$ between 14.0 and 38.6 keV nm${}^{\ensuremath{-}1}$. For all irradiation parameters used a strong swelling of the irradiated material was observed, which is caused by the formation and growth of randomly distributed voids, leading to a gradual transformation of the amorphous layer into a sponge-like porous structure as established by cross-section scanning electron microscopy investigations. The swelling depends linearly on the ion fluence and on the value of ${\ensuremath{\epsilon}}_{e}$, thus clearly demonstrating that the structural changes are determined solely by the electronic energy deposited within the amorphous layer. Plastic deformation shows a superlinear dependence on the ion fluence due to the simultaneous volume expansion. This influence of structural modification on plastic deformation is described by a simple approach, thus allowing estimation of the deformation yield. With these results the threshold values of the electronic energy deposition for the onset of both structural modification and plastic deformation due to SHI irradiation are determined. Furthermore, based on these results, the longstanding question concerning the reason for the structural modification observed in SHI-irradiated crystalline Ge is answered.

We have applied spectroscopic ellipsometry (SE) to measure amorphized layer thickness after implantation and solid phase re-growth at low annealing temperatures as a non-destructive, in line implant monitoring technique. The SE measurement treats the heavily damaged layer as a part of the amorphized layer. And it is an area very sensitive to the temperature. Therefore, this sensitivity of detecting the heavily damaged layer can be used for monitoring the performance and conditions of individual implanters. In this paper, we examine the thickness of amorphous and heavily-damaged interface layers formed by cluster ion implantation (B10Hx, B16Hy, B36Hz, C5Ha, C7Hb, C16Hc), by helium ions in a plasma doping tool, and single ion implantation. In addition, we report on behavior in the amorphous layer formed by As ion implantation with a heat-treatment of 100-600 degree C.

Epitaxial crystallization of a-Si and a-GaAs induced by low-energy ion bombardments

Porous Ge layers consisting of nanowires were formed by low‐energy high‐dose implantation of monocrystalline c‐Ge substrate with Ag+ and Cu+ ions. The obtained layers were studied by Raman spectroscopy using solid‐state and He‐Ne exciting lasers with wavelength of 532 and 633 nm, respectively. The crystalline volume fraction and local temperature of porous layers at the surface sites of laser probing were determined. To interpret the change in the shape of the spectra under the action of laser radiation, deconvolution into amorphous and nanocrystalline components was carried out. Analysis of the spectral line shape made it possible to estimate the crystalline and amorphous volume fractions. The quantum confinement model for Ge nanocrystallites was taken into account for accurate estimations of volume fractions. These estimates showed that the implanted amorphous layers of all samples were locally crystallized with a solid‐state laser. He‐Ne laser excitation resulted in partial crystallization only for layers obtained by Cu+ ion implantation. The measured ratio of the Stokes to anti‐Stokes components demonstrated that the porous layers obtained by implanting Ag+ ion were not heated by a He‐Ne laser and according to the analysis of spectral lines, the crystalline volume fraction did not appear in these layers during probing. The results obtained are explained by the difference in the penetration depth for various samples of the exciting radiation.

ABSTRACTWe demonstrate the possibilities of plasma enhanced chemical vapor deposition (PECVD) and solid phase epitaxy to obtain germanium on silicon with excellent crystalline properties, even for very thin layers (< 100 nm). Amorphous germanium layers are deposited by PECVD on silicon substrates. Deposition of an amorphous layer, without the presence of crystalline seeds, is critical. Crystalline inclusions must be avoided to obtain high crystal quality and a smooth surface after crystallization. PECVD is well suited for deposition of amorphous layers because low temperature deposition and high growth rates are possible. Additional experiments with molecular beam epitaxy show that it is not mandatory to have hydrogen present inside the germanium layer to obtain highly crystalline germanium. Atomic hydrogen plays, however, an important role during deposition by lowering the surface adatom mobility and consequently increasing the disorder of the deposited layer. Synchrotron X-ray diffraction shows no germanium diffraction, indicating that the layer does not contain crystalline seeds. Crystallization can be performed at limited temperatures: Raman measurements show crystallization between 400 and 425 °C. Another important advantage of the proposed method is the scalability: germanium layers of larger diameter can be obtained by simply using larger silicon substrates.

Investigation of the kinetics of crystallisation of Al/a-Ge bilayer by electrical conductivity measurement

Ion implantation has become the most common method of doping in the semiconductor industry. Precise concentration profiles with exact spatial locations are achievable. However, direct implantation of the desired dopant does not always meet the stringent size requirements of ultra large scale integration (ULSI). Implantation of light ions, such as boron, tend to channel down open crystallographic orientations in crystalline substrates resulting in enhanced ion penetration and an extended doping tail. Channeling can be prevented by creation of an amorphous surface layer prior to the dopant implant. The amorphous layer can be created by implanting heavy isoelectronic ions, such as Ge+, or by implanting molecular dopant ions like BF2. Solid phase epitaxial (SPE) regrowth restores the crystallinity of the amorphous layer and activates the dopant. However, the ion implantation process damages the crystalline material adjacent to the amorphous- crystalline (a/c) interface.

This study was directed toward exploring the relationship between the implant conditions and the depth and nature of the amorphous layers generated in silicon. Interest in amorphous layer morphology stems from its role in affecting crystal defects remaining after amorphous-to-crystalline transformation. High-dose implants of As, P, and B were used to generate buried and surface amorphous layers at slightly higher than room temperature. The amorphous layer depths were measured and the depth-fluence and depth-energy relationships were compared with Brice’s analysis. It was found that good fits were obtained for a threshold damage density of 2.5×1020 keV cm−3 for As and 1.0×1021 keV cm−3 for P. For B, the results could be described by a threshold damage density of 5.0×1021 keV cm−3 or greater. Lower weight ion implantations exhibit a greater tendency to generate buried amorphous layers as well as to generate amorphous layers which include a smaller fraction of the total implanted fluence than is found for heavier ion implantations. These two factors make it more likely for residual crystal defects to be associated with lower weight ion implant distributions.

Channeling and transmission electron microscopy have been used to investigate the parameters that govern the extent of damage in ion-implanted GaAs and the crystal quality following capless furnace annealing at low temperature (∼400 °C). The implantation-induced disorder showed a strong dependence on the implanted ion mass and on the substrate temperature during implantation. When the implantation produced a fully amorphous surface layer the main parameter governing the regrowth was the amorphous thickness. Formation of microtwins after annealing was observed when the initial amorphous layer was thicker than 400 Å. Also, the number of extended residual defects after annealing increased linearly with the initial amorphous thickness and extrapolation of that curve predicts good regrowth of very thin (<400 Å) GaAs amorphous layers produced by ion implantation. A model is presented to explain the observed features of the low-temperature annealing of GaAs.

Characterization of carbon ion implantation induced graded microstructure and phase transformation in stainless steel

Reordering of ion implanted amorphous Si layers with rapid thermal annealing (RTA) was investigated with spectroscopic ellipsometry. The reordering rates in the temperature range of 450-550/spl deg/C by RTA agree well with earlier studies using conventional furnace annealing. The reordering rate for a lower dose (As 3/spl times/10/sup 14/ cm/sup -2/) was found to be faster than that for a higher dose (As 4/spl times/10/sup 15/ cm/sup -2/), perhaps because of higher concentrations of knock-on implanted oxygen. The amorphous layer thickness for Ge ion implantation was same as that for equivalent energy and dose As ion implantation. However the reordering rate for Ge implanted layers was much slower than that of As implantation, almost same as that for Si ion implantation. In the case of 3/spl times/10/sup 14/ cm/sup -2/ As dose high reordering rate was observed for a thin (7 nm) layer as well as reordering at temperature, lower than 450/spl deg/C. It was due to the roughness of a wide transient layer and did not occur in case of high dose As implantation; 4/spl times/10/sup 15/ cm/sup -2/ because of a narrow transient layer.

High temperature oxidation resistance of an amorphous layer induced by ion implantation on the surface of Ni-based superalloy GH202

Enhancing the wear resistance of polycrystalline diamond tools in Cf/SiC machining via ion implantation

Damage-free machining of monocrystalline silicon carbide

Ion implantation, employing Si, Ar, and Cu ions in the energy range from 275 to 600 keV, was used to form amorphous silicon layers buried in a crystalline matrix. Different layer geometries were produced, with 150–620-nm-thick amorphous layers, separated from the surface by 120–350-nm-thick crystalline layers. Crystallization of the amorphous layers was induced by 32-ns pulsed ruby laser irradiation. Real-time reflectivity and conductivity measurements indicate that internal melting can be initiated at the amorphous-crystalline interface, immediately followed by explosive crystallization of the buried layer. Channeling and cross-section transmission electron microscopy reveal that in both Si(100) and Si(111) samples explosive crystallization proceeds epitaxially with twin formation, the twin density being higher in Si(111) than in Si(100). The measured crystal growth velocities range from 15 to 16 m/s, close to the fundamental limit for crystalline ordering at a Si liquid-crystalline interface. Computer modeling of heat flow and phase transformations supports the experimental data.