X-ray reflectivity study of hydrogen implanted silicon

The X-ray reflectivity (XRR) technique was used to study monocrystalline silicon samples implanted with H₂ ions at an energy of 31 keV and to the dose of 2 × 10¹⁶ hydrogen atoms/cm². All samples were subsequently isochronally annealed in vacuum at different temperatures in the range from 100 to 900 °C. Although the hydrogen depth distribution was expected to be smooth initially, fringes in the XRR spectra were observed already in the implanted but not annealed sample, revealing the presence of a well-defined film-like structure. Annealing enhances the film top to bottom interface correlation due to structural relaxation, resulting in the appearance of fringes in the larger angular range, already at low annealing temperatures. The thickness of the film decreases slowly up to 350 °C where substantial changes in the roughness are observed, probably due to the onset of larger clusters formation. Further annealing at higher temperatures restores the high correlation of the film interfaces, while the thickness decreases with the temperature more rapidly.     

Modifications of He implantation induced cavities in silicon by MeV silicon implantation

Doppler broadening spectroscopy (DBS) coupled to a slow positron beam has been used to investigate the formation of He-cavities in the presence of high vacancy concentrations in Cz-Si (1 1 1). Si samples were first implanted with MeV Si ions in order to create a damaged Si layer. DBS measurements show the presence of divacancy (SV₂/SSi lattice=1.052,WV₂/WSi lattice=0.83) from the surface up to 4.2 μm depth with a concentration higher than 10¹⁸ cm⁻³. The thickness of this damaged layer was confirmed by spreading resistance measurements. In the second step, samples were implanted with 50 keV ³He with fluence of 10¹⁶ cm⁻². DBS results show that the apparent divancancy concentration decreases at ³He implantation depth ∼435 nm due to ³He passivation of vacancies that occurs during the implantation process. After 900 °C annealing, large defects are detected at depth up to 2 μm and (S, W) values suggest the detection of cavities at the implantation depth. We also report the possible presence of impurity complexes. The formation of these complexes is attributed to the gettering of metallic impurities present in the Si sample.     

Effect of oxygen implantation on ionoluminescence of porous silicon

We report on ionoluminescence investigations of porous Si prepared from the p⁺-type Si, which exhibited, after prolonged ambient air exposure, moderate photon emission with a maximum in the red–orange region. In an attempt to activate a shorter wavelength emission, the samples were implanted with 225 keV O⁺ ions at the dose of 1×10¹⁷ cm⁻². The strong blue band at 2.7 eV, well known in silica, has emerged in the ionoluminescence spectra following the oxygen implantation. The results of the comparative ionoluminescence experiments, performed on both porous Si and two forms of silica, show the important role of SiO₂ defect-related states in ion-induced optical emission from porous Si.     

Controlled gold doping of silicon by using ion implantation

A new technology is suggested to dope silicon devices with gold for carrier life time adjustment with high accuracy and reproducibility. Ion implantation is used to dope the sample with a well defined total amount of gold. This gold dose is redistributed by high temperature anneal. A computer simulation of gold diffusion and experimental radio tracer results show that highly accurate gold doping can be obtained in bulk material when temperatures around 1000 C are applied during the redistribution anneal. Damage free surfaces must be used to reduce the gold content gettered in surfaces.     

XPS study of silicon surface after ultra-low-energy ion implantation

Ultra-low-energy ion implantation of silicon with a hydrogen-terminated (0 0 1) surface was carried out using a mass-separated ³¹P⁺ ion beam. The ion energy was 30 eV, the displacement energy of silicon, and the ion doses were 6 × 10¹³ ions/cm². Annealing after the implantation was not carried out. The effects of ion implantation on the surface electrical state of silicon were investigated using X-ray photoelectron spectroscopy (XPS). The Si 2p peak position using XPS depends on the doping conditions because the Fermi level of the hydrogen-terminated silicon surface is unpinned. The Si 2p peak position of the specimen after ion implantation at a vacuum pressure of 3 × 10⁻⁷ Pa was shifted to the higher energy region. It suggested the possibility of phosphorus doping in silicon without annealing. In the case of ion implantation at 5 × 10⁻⁵ Pa, the Si 2p peak position was not shifted, and the peak was broadened because of the damage by the fast neutrals. Ultra-low-energy ion doping can be achieved at ultra-high-vacuum conditions.     

Behavior of implanted hydrogen in thermally stimulated blistering in silicon

The processes of accumulation of ion implanted hydrogen in blisters in silicon and its release during the thermal treatment from 350 to 1020?°C have been studied by optical techniques. It was established that accumulation of gaseous hydrogen inside blisters takes place at temperatures lower than ～450–500?°C and is accompanied by the growth of blister thickness and deformation of their caps. At higher temperatures the gaseous hydrogen goes out of the cavities dissolving in silicon. Due to the internal pressure dropping the elastically deformed top layer partially relaxes and the blister thickness decreases. Etching of the surface layer reveals the agglomerations of small voids (<0.3?mm) located in the place of blisters approximately at their depth. Proceeding from the fact that the processes in blistering are similar to those in ion cut, the following conclusions with respect to the latter were drawn. The exfoliation processes themselves occur at temperatures lower than ～500?°C. The exfoliation efficiency particularly at the higher temperatures is essentially dependent on the heating rate.     

Excess Si concentration dependence of the photoluminescence of Si nanoclusters in SiO2 fabricated by ion implantation

A method for the fabrication of luminescent Si nanoclusters in an amorphous SiO₂ matrix by ion implantation and annealing, and the detailed mechanisms for the photoluminescence are reported. We have measured the implanted ion dose, annealing time and excitation energy dependence of the photoluminescence from implanted layers. The samples were fabricated by Si ion implantation into SiO₂ and subsequent high-temperature annealing. After annealing, a photoluminescence band below 1.7 eV has been observed. The peak energy of the photoluminescence is found to be independent of annealing time and excitation energy, while the intensity of the luminescence increases as the annealing time and excitation energy increase. Moreover, we found that the peak energy of the luminescence is strongly affected by the dose of implanted Si ions especially in the high dose range. These results indicate that the photons are absorbed by Si nanoclusters, for which the band-gap energy is modified by the quantum confinement effects, and the emission is not simply due to direct electron–hole recombination inside Si nanoclusters, but is related to defects probably at the interface between Si nanoclusters and SiO₂, for which the energy state is affected by Si cluster–cluster interactions. It seems that Si nanoclusters react via a thin oxide interface and the local concentrations of Si nanoclusters play an important role in the peak energy of the photoluminescence.     

Light emitting diode structure based on Si nanocrystals formed by implantation into thermal oxide

Light emitting diodes (LED), continuously operable at room temperature, have been fabricated by Si⁺ ion implantation into SiO₂ and subsequent annealing in order to form Si nanocrystals. A highly doped poly-Si layer was used to enhance injection into nanocrystals. Visible electroluminescence (EL) was observed from the LEDs with oxide thickness 180 Å for bias voltages above 8 V. The EL decay transient was similar to stretched-exponential decays observed for photoluminescence (PL) from Si nanocrystals.     

Enhancement of saturation magnetization in Cr-ion implanted silicon by high temperature annealing

Magnetic properties and microstructure of Cr-implanted Si have been investigated by alternating gradient magnetometer (AGM), superconducting quantum interference device (SQUID) magnetometer, and transmission electron microscopy (TEM). p-Type (1 0 0) Si wafers were implanted at 200 keV at room temperature with a dosage of 1 × 10¹⁶ cm⁻² Cr ions and then annealed at 600-900 °C for 5 min. The effect of annealing on the structure and magnetic properties of Cr-implanted Si is studied. The as-implanted sample shows a square M-H loop at low temperature. Magnetic signal becomes weaker after short time annealing of the as-implanted sample at 600 °C, 700 °C, and 800 °C. However, the 900 °C annealed sample exhibits large saturation magnetization at room temperature. TEM images reveal that the implanting process caused amorphization of Si, while annealing at 900 °C led to partial recovery of the crystal. The enhancement of saturation magnetization can be explained by the redistribution and accumulation of Cr atoms in the vacancy-rich region of Si during annealing.     

Effect of primary oxygen ion implantation on SIMS depth profiling in glasses

The influence of the primary oxygen ion implantation on SIMS in-depth profiles in halide and chalcogenide glasses was examined. Various behaviours of particular profiles were generally explained in terms of the chemical affinity of analysed reactants and modifications of the glass structure induced by primary ions.     

Effect of hydrogen dilution on the silicon cluster volume fraction of a hydrogenated amorphous silicon film prepared using plasma-enhanced chemical vapor deposition

We investigated the effect of hydrogen dilution on the Si cluster volume fraction of hydrogenated amorphous films by varying the hydrogen dilution ratio at 0.5 Torr and compared it to that obtained at pure silane discharge at 0.3, 0.4, and 0.5 Torr. The correlation between the plasma emission characteristic, deposition rate, and cluster volume fraction in the hydrogen dilution plasma was described. The cluster volume fractions of films under hydrogen dilution conditions were similar to those of the pure silane but showed a higher deposition rate. The results suggest that under hydrogen dilution conditions, it is possible to maintain a higher deposition rate with a lower cluster incorporation rate.     

A technique for positron spectroscopy of monovacancies formed by low-temperature ion implantation of silicon

A system for positron beam-based Doppler broadening spectroscopy of the formation and evolution of monovacancy defects in silicon is described. The apparatus allows in situ ion implantation at low temperatures (∼50 K) followed by positron beam assay. First measurements for 6 keV He implantation, at post-implant temperatures between 60 and 300 K are presented. Benefits and drawbacks of this system are discussed.     

Structural and photoluminescence properties of Si nanoclusters obtained by ion implantation into Si3N4 films

In the present paper we report structural and photoluminescence (PL) results from samples obtained by Si implantation into stoichiometric silicon nitride (Si₃N₄) films. The Si excess was introduced in the matrix by 170 keV Si implantation performed at different temperatures with a fluence of Φ=1×10¹⁷ Si/cm². The annealing temperature was varied between 350 and 900 °C in order to form the Si precipitates. PL measurements, with a 488 nm Ar laser as an excitation source, show two superimposed broad PL bands centered around 760 and 900 nm. The maximum PL yield is achieved for the samples annealed at 475 °C. Transmission electron microscopy (TEM) measurements show the formation of amorphous nanoclusters and their evolution with the annealing temperature.     

Implications of ion implantation technology on ion implanted active devices in silicon

The use of ion implantation to make integrated devices in silicon implies a good knowledge of the behavior of various parts of the device. This paper deals with three main topics: First the electrical characteristics of implanted diodes are described and their variations as a function of annealing temperature lead to a physical model taking into account the anisotropy of impurity concentration gradients. Second, experimental conditions before, during and after implantation are shown to have a strong influence on the quality of the final device, particularly on the value of the reverse leakage current. Third, effects of bombardment on silicon dioxide layers are studied. It is found that recovery of the layers is generally complete after a 300°C annealing.

Contributions of these various parameters to the overall electrical characteristics of ion implanted self-aligned MOS transistors are finally considered. Substantial increase in the maximum oscillation frequency and reduction of the active surface areas of the device are the most evident advantages of using ion implantation technology.     

Effect of Cr implantation on structural and optical properties of AlN thin films

Molecular beam epitaxy (MBE) grown AlN thin layer on sapphire substrates have been implanted with Cr⁺ ions for various dose from 10¹³ to 10¹⁵ cm⁻². The analyses were carried out by an X-ray diffractometer (XRD), Raman spectroscopy, a spectrophotometer and spectroscopic ellipsometry (SE) for structural and optical analyses. E₂(high) and A₁(LO) Raman modes of AlN layer have been observed and analyzed. The behavior of Raman shift and the variation in intensity and in peak width of Raman modes as a function of ions flux are explained on the basis of chromium substituting aluminum atom and implantation-induced lattice damage. Both Raman and X-ray analyses reveal that the incorporation of chromium atoms increases in the host lattice with the increasing of Cr ions fluence. The band gap energy was determined by using transmission spectra. It was found that the band gap energy decreases as the ion dose increases. The band gap of the unimplanted AlN is 6.02 eV and it decreases down to 5.92 eV for the Cr⁺-implanted AlN with a ion dose of 1×10¹⁵ cm⁻². Optical properties such as optical constants of the samples were examined by using a spectroscopic ellipsometer. It was observed that the refractive index (n) decreases with the increasing of ion dose.     

直拉硅单晶中原生氧沉淀的透射电镜研究

利用透射电镜对掺氮(NCZ) 和普通 (CZ) 直拉硅单晶中的原生氧沉淀进行研究. 研究表明，在NCZ样品中，有高密度的粒径为5nm的氧沉淀生成，而在CZ样品中，没有观察到这种氧沉淀. 初步认为，这种细小的氧沉淀是以650℃低温下形成的N-O复合体为核心在随后的冷却过程中形成. 关键词： 直拉硅 透射电镜 氧沉淀     

Correlating Raman peak shifts with phase transformation and defect densities: a comprehensive TEM and Raman study on silicon

Silicon is the most often used material in micro electromechanical systems (MEMS). Detailed understanding of its mechanical properties as well as the microstructure is crucial for the reliability of MEMS devices. In this paper, we investigate the microstructure changes upon indentation of single crystalline (100) oriented silicon by transmission electron microscopy (TEM) and Raman microscopy. TEM cross sections were prepared by focused ion beam (FIB) at the location of the indent. Raman microscopy and TEM revealed the occurrence of phase transformations and residual stresses upon deformation. Raman microscopy was also used directly on the cross‐sectional TEM lamella and thus microstructural details could be correlated to peak shape and peak position. The results show, however, that due to the implanted Ga⁺ ions in the lamella the silicon Raman peak is shifted significantly to lower wavenumbers. This hinders a quantitative analysis of residual stresses in the lamella. Furthermore, Raman microscopy also possesses the ability to map deformation structures with a lateral resolution in the submicron range. Copyright © 2009 John Wiley & Sons, Ltd.     

High-temperature pretreatment of Ni nanoparticles enhances the growth of high-density carbon fiber bundles during microwave plasma chemical vapor deposition

This paper presents an experimental study on the effect of the pretreatment procedure of Ni nanoparticles (NPs) on the growth of multiwalled carbon fiber (CNF) bundles by means of microwave plasma chemical vapor deposition (MPCVD). We used atomic force microscopy to investigate a series of pretreated Ni films. The structures and compositions of the CNFs on the via were investigated using scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy.The geometric shape of the Ni NPs was identified in terms of their roughness, which decreased upon increasing the pretreatment temperature, resulting subsequently in the synthesis of high-density CNFs. The diameter and shape of the Ni NPs were the dominant factors affecting the size and density of the CNFs bundles. We obtained CNFs that fully filled the via effectively; they might serve as potential interconnects in future nanodevices.     

A comparative study of donor formation in dysprosium, holmium, and erbium implanted silicon

Formation of donor centers in Czochralski grown silicon doped with dysprosium, holmium, and erbium is discussed. Donor states of three kinds are introduced in the implanted layers after annealing at T=700°C. Shallow donor states with ionization energies between 20 and 40 meV are attributed to oxygen -related thermal donors. Other donor centers in the energy range of E_C−(60…70) meV and E_C−(100…120) meV appear to be dependent on dopants. After a 900°C anneal strong changes in the donor formation are observed only in silicon doped with erbium. Instead of donors at E_C−(118±5) meV, new donor centres at E_C−(145±5) meV are formed. Reportedly, the latter ones are involved in the excitation process of the Er³⁺ ions with a characteristic luminescence line at ≈1.54 μm.