Dislocation-related luminescence in single-crystal silicon subjected to silicon ion implantation and subsequent annealing

Implantation of silicon ions with an energy of 100 keV at a dose of 1 × 10¹⁷ cm^?2 into n-type floatzone Si does not lead to the formation of an amorphous layer. Subsequent annealing in a chlorine-containing atmosphere at 1100°C gives rise to dislocation-related luminescence. The intensity of the dominant D1 line peaked at a wavelength of ～1.54 μm grows as the annealing time is increased from 15 to 60 min.     

Redistribution of ytterbium and oxygen in annealing of silicon layers amorphized by implantation

The redistribution of ytterbium and oxygen was studied in silicon layers that were implanted with 1-MeV Yb⁺ ions at a dose of 1×10¹⁴ cm^?2, which exceeds the amorphization threshold, and 135-keV O⁺ ions at a dose of 1×10¹⁵ cm^?2 and that were subsequently annealed at 620 and 900°C. The redistribution of Yb is due to segregation at the interface between the amorphous and single-crystal layers in solid-phase recrystallization of the buried amorphized layer. The redistribution of oxygen and its accumulation in regions with the highest concentration of Yb is associated with oxygen diffusion and the formation of YbO_n complexes with n varying from 1 to 6. The parameters characterizing the dependence of the Yb segregation coefficient on the thickness of the recrystallized layer and the formation of YbO_n complexes were determined.     

Negative annealing in silicon after the implantation of high-energy sodium ions

The implantation of sodium ions with an energy of 300 keV is carried out into high-resistivity p-Si. The annealing of defects at T _ann = 350–450°C and related activation of atoms (the latter occurs at the “tail” of atom distribution) are described by a first-order reaction. At T _ann = 450–525°C and irrespective of the ion dose, negative annealing is observed; this annealing is accompanied by an appreciable increase in the surface resistance ρ _s . According to estimations, the activation energy of this process amounts to ~2 eV. It is our opinion that the annealing is related to the precipitation of sodium donor atoms, which occurs at a depth exceeding by two–three times the projected range R _p of ions. The annealing of defects at T _ann = 525–700°C, which leads to a further decrease in ρ _s , features an activation energy of ~2.1 eV. The hypothesis that the “tail” in the profiles of sodium atoms measured by secondary-ion mass spectroscopy is due to the diffusion of these atoms from the walls of the crater to its center is verified. It is shown that this process is not implemented since the profiles of sodium atoms measured at room temperature do not differ from those measured at–140°C.     

Formation of buried oxide layers by high dose implantation of oxygen ions in silicon

Buried implanted oxide layers have been formed by high dose implantation of oxygen ions of the order of 1 × l0¹⁸−2 in silicon. The effects of dose at a given energy, and energy for a given peak concentration, on the distribution profile of oxygen have been studied. An approximately Gaussian distribution is observed at doses contributing less than the stoichiometric requirement of oxygen for the formation of silicon dioxide. A saturation in the oxygen peak concentration is reached when the stoichiometric requirement is exceeded. The excess implanted oxygen results in a broadening of the stoichiometric implanted oxide layer. A consequent reduction in the interface damage is observed. Other parameters being equal, at higher substrate temperatures the interface damage is decreased. For a given peak concentration, the implanted oxide is buried more deeply with increasing ion energy. Infra-red absorption characteristics of the implanted oxide are almost identical to those of thermal oxide layers grown in a dry oxygen ambient. The implanted oxide layer exhibits also an extremely high resistivity compared to the substrate material. Department of Electronics, University of Kent,Canterbury,Kent,U.K.     

Electric-field-shielding layers formed by oxygen implantation into silicon

The electric-field-shielding effect was found in a layer consisting of a mixture of polycrystalline silicon and silicon oxide formed by oxygen ion implanatation. The layer was formed between the buried SiO2 and the upper Si layer, which improved characteristics for MOSFETs fabricated using SIMOX (separation by implanted oxygen) technology. By forming this layer, the threshold voltages for the MOSFETs were almost independent of substrate bias. Drain-to-source breakdown voltages for the p-MOSFETs and n-MOSFETs were raised to 250 V and 180 V, respectively.     

Study of porous silicon obtained by krypton ion implantation and laser annealing

An ellipsometric technique is used to study the formation of a finely porous layer saturated with atoms of an inert gas in a crystalline silicon lattice that has been doped by high doses of krypton and then irradiated by nanosecond laser pulses. The changes in the complex refractive index of this layer induced by laser pulses at different powers are studied. A scanning field ion microscope is used to follow the transformation of the pores, as the energy per unit area of the annealing laser light is varied, and to estimate their sizes. Fiz. Tekh. Poluprovodn. 31, 1130–1134 (September 1997)     

High-voltage buried-channel MOS fabricated by oxygen implantation into silicon

A high-voltage offset-gate buried-channel MOS made on a SOS-like substrate is described. An isolation layer is formed by an oxygen implantation process called SIMOX. A 410 V buried SiO2 breakdown voltage and a 180 V drain breakdown voltage are obtained.     

Resistivity changes of heavily-boron-doped CVD-prepared polycrystalline silicon caused by thermal annealing

Heavily-boron-doped polycrystalline Si films were deposited at 600°C on thermally grown SiO₂ by the thermal decomposition of SiH₄-BCl₃-H₂ mixture. Resistivity changes with isochronal or sequential annealing were systematically examined. Temperature dependence of equilibrium saturation carrier concentration was determined at 800 ～ 1100°C. Since as-deposited polycrystalline Si is in the super-saturated state, carrier concentration decreases from the super-saturated to equilibrium saturation value by annealings over 700°C for poly Si doped with over 2 × 10²⁰ cm^?3 resulting in anomalous resistivity change. Carrier concentration changes reversibly between saturation values with sequential annealing and is determined by the last annealing temperature when the annealing time is long enough. Mobility increases with annealing temperature, however, less increase is found for heavily doped poly Si, which is attributed to the suppression of grain growth caused by electrically inactive Si-B compounds.     

Defect engineering in implantation technology of silicon light-emitting structures with dislocation-related luminescence

Results obtained in development of physical foundations of ion implantation technology for fabrication of silicon light-emitting structures (LESs) based on dislocation-related luminescence and intended for operation at wavelengths close to ∼1.6 μm are summarized. The development of the concept of defect engineering in the technology of semiconductor devices makes it possible to determine the fundamental aspects of the process of defect formation; reveal specific features of the emission spectra related to changes in the implantation conditions of Er, Dy, Ho, O, and Si ions and the subsequent annealing; and design light-emitting structures with a desirable spectrum of luminescent centers and extended structural defects. The technological conditions in which only a single type of extended structural defect (Frank loops, perfect prismatic loops, or pure edge dislocations) is introduced into the light-emitting layer are found, which enables analysis of the correlation between the concentration of extended defects of a certain type and the intensity of lines of the dislocation-related luminescence. The key role of intrinsic point lattice defects in the origination and transformation of extended structural defects and luminescent centers responsible for the dislocation-related luminescence is revealed. It is found that the efficiency of luminescence excitation from the so-called D1 centers, which are of particular interest for practical applications, varies by more than two orders of magnitude between structures fabricated using different technological procedures. High-efficiency silicon light-emitting diodes with room-temperature dislocation-related luminescence have been fabricated.     

Study of silicon doped with zinc ions and annealed in oxygen

The results of studies of the surface layer of silicon and the formation of precipitates in Czochralski n-Si (100) samples implanted with ⁶⁴Zn⁺ ions with an energy of 50 keV and a dose of 5 × 10¹⁶ cm^–2 at room temperature and then oxidized at temperatures from 400 to 900°C are reported. The surface is visualized using an electron microscope, while visualization of the surface layer is conducted via profiling in depth by elemental mapping using Auger electron spectroscopy. The distribution of impurity ions in silicon is analyzed using a time-of-flight secondary-ion mass spectrometer. Using X-ray photoelectron spectroscopy, the chemical state of atoms of the silicon matrix and zinc and oxygen impurity atoms is studied, and the phase composition of the implanted and annealed samples is refined. After the implantation of zinc, two maxima of the zinc concentration, one at the wafer surface and the other at a depth of 70 nm, are observed. In this case, nanoparticles of the Zn metal phase and ZnO phase, about 10 nm in dimensions, are formed at the surface and in the surface layer. After annealing in oxygen, the ZnO · Zn₂SiO₄ and Zn · ZnO phases are detected near the surface and at a depth of 50 nm, respectively.     

Effect of annealing in oxygen radicals on luminescence and electrical conductivity of ZnO:N films

It is shown that the introduction of a nitrogen acceptor impurity when growing zinc oxide films can result in the formation of hole conduction only after annealing in atomic oxygen vapor. Annealing affects not only electrical properties but also the luminescence of ZnO:N. The bands in the photoluminescence spectrum, which are related to nitrogen, appear in the ultraviolet and visible regions.     

Characterization of strained silicon on relaxed SiGe layer made by H ion implantation and annealing in ultra-high vacuum ambient

Twenty-nanometer-thick Si cap layer/74-nm-thick Si_0.72Ge_0.28 epilayer/Si heterostructural sample was implanted by 25 keV H⁺ ion to a dose of 1 × 10¹⁶ cm⁻² and subsequently annealed in ultra-high vacuum ambient at the temperature of 800 °C for 30 min. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristic of Si/SiGe/Si heterostructure. Investigations by RBS/C demonstrate that the Si_0.72Ge_0.28 layer show good crystal quality (21.1% of channel minimum yield). The relaxation degree of partially relaxed Si_0.72Ge_0.28 layer was around 74%, which was obtained by HRXRD. The computation process of the relaxation degree of strain in SiGe layer according to HRXRD rocking curve was also thoroughly introduced. Raman analysis revealed that stress, σ and strain, ε in the thin strained-Si layer were around 1.2 Gpa and 0.52%, respectively. In addition, the small surface roughness in the formed strained-Si/relaxed Si_0.72Ge_0.28 layer/Si heterostructural sample was observed via AFM image.     

Ohmic contacts formed on single- and poly-crystalline silicon using ion implantation and low-temperature annealing

The evolution in integrated-circuit technology is towards lower process temperatures and a consequential decrease in layer junction depths, a step that may not be compatible with ohmic contact formation and low sheet resistance layers using present technology. In this letter, we present a method whereby ohmic contacts are made to antimony ion-implanted layers of both single and polycrystalline silicon that are annealed at temperatures less than 700°C. Experimental results suggest that these contacts and the shallow relatively low sheet resistance layers produced offer considerable promise for future generation integrated-circuit technology.     

Precipitates caused by prolonged high-temperature annealing in floating zone silicon wafer grown from Czochralski single-crystal rod

The behavior of precipitates in a floating zone silicon crystal produced from a Czochralski single-crystal ingot has been studied. Large precipitates of α-Si₃N₄ crystal, having a dimension of about 2 μm, were formed at the mid-depth in the wafer by annealing at a high temperature in an ambient N₂ (70%)+O₂ (30%) atmosphere. The number of precipitates detected by cross-sectional X-ray topography increased with increasing annealing time. Because preannealing accompanying silicon oxidation in an ambient Ar+O₂ atmosphere prevented the precipitates formation, interstitial silicon is considered to eliminate the origin of precipitate.     

Mixing of nickel and silicon by incoherent-light-pulse annealing

Mixed layers of Ni and Si were formed by pulsed incoherent-light annealing of Ni thin films evaporated on Si substrates. Incoherent light pulse of 36 μs produced in an arc-discharge plasma system was used as the energy source for annealings. A thin layer (300 Å) of amorphous silicon (a-Si) deposited on 800–1000 Å thick Ni films was found to increase light absorption significantly. The light energy needed to form uniform mixing was measured to be about 23 J/cm². Rutherford backscattering and Auger electron spectroscopy techniques were used for qualitative analysis of a-Si/Ni/Si samples. Optimum operating conditions of the light source was determined.     

Thermally stimulated current measurements on silicon junctions produced by implantation of low energy boron ions

Thermally stimulated current (TSC) measurements have been performed directly on junctions realized by implantation of low energy (15 keV) boron ions into N-type silicon after annealing treatments at different temperatures between 180 and 500°C. The TSC curves have been analysed by a new method based on the measurement of the mean time before re-emission of the trapped carriers and compared with that of Grossweiner. Both methods indicate that the dominant level is a hole trap located at >Ev + 0·25 eV. This defect anneals at 260°C and is believed to be correlated with the vacancy-vacancy association.     

Charge state of luminescence centers in the Si-SiO<Subscript>2</Subscript> structures subjected to sequential implantation with silicon and carbon ions

Electroluminescence of Si-SiO₂ structures subjected to sequential implantation of silicon and carbon ions and to postimplantation annealing is studied. It is shown that two bands appear in the electroluminescence spectrum with energies of 2.7 and 4.3 eV as a result of ion implantation. After annealing, the band peaked at the energy of 3.2 eV appears in the spectrum; this band can be related to the formation silicon-carbide clusters. Charge characteristics of the structures under study are obtained. It is shown that the luminescence centers responsible for all bands are not charged.     

Effects of predoping and implantation conditions on diffusion of silicon in gallium arsenide subjected to electron-beam annealing

Measurements of capacitance-voltage characteristics and Rutherford backscattering were used to study the parameters of silicon diffusion from preliminarily formed n-type layers into semi-insulating GaAs under electron-beam annealing and conventional heat treatment. The layers were doped with either sulfur or silicon. The degree of ²⁸Si electrical activation and ²⁸Si diffusion coefficient are found to depend on the dopant used to form the n-type layer and on the implantation conditions (continuous or pulsed-repetitive, with a pulse width of 1.3×10^?2 s and duty factor of 100).     

The effect of oxygen on segregation-induced redistribution of rare-earth elements in silicon layers amorphized by ion implantation

A model of segregation-induced redistribution of impurities of rare-earth elements during solid-phase epitaxial crystallization of silicon layers amorphized by ion implantation is developed. This model is based on the assumption that a transition layer with a high mobility of atoms is formed at the interphase boundary on the side of a-Si; the thickness of this layer is governed by the diffusion length of vacancies in a-Si. The Er concentration profiles in Si implanted with both erbium and oxygen ions are analyzed in the context of the model. It shown that, in the case of high doses of implantation of rare-earth ions, it is necessary to take into account the formation of R_m clusters (m = 4), where R denotes the atom of a rare-earth element, whereas, if oxygen ions are also implanted, formation of the complexes RO_n (n = 3–6) should be taken into account; these complexes affect the transition-layer thickness and segregation coefficient.