Characterization of buried SiO2 layers formed by ion implantation of oxygen

Oxygen has been ion implanted (200 keV) into silicon at doses ranging from 2E17/cm² to 2E18/cm². The peak oxygen concentration occurs at a depth of 0.5 μm. These doses produce peak oxygen concentrations which are below and above the concentrations necessary to form stoichiometric SiO₂. If the oxygen concentration exceeds stoichiometry, a buried SiO₂ layer is formed with a thin superficial silicon layer on the surface. This superficial silicon layer has been used as a seed for growing single crystal silicon epi. The resulting Silicon on Insulator (SOI) structure has been characterized by Rutherford backscattering, cross-sectional TEM, AES, optical microscopy, spreading resistance probe, Hall effect and infrared transmission measurements. The effects of dose, substrate temperature during the implant, and subsequent anneal conditions have been examined.     

C.M.O.S. devices fabricated on buried SiO2 layers formed by oxygen implantation into silicon

Buried SiO2, layers were formed by oxygen-ion (14O+) implantation into silicon. The impurity distribution of the oxygen-implanted silicon substrate was analysed by auger spectroscopy. The epitaxially-grown silicon layer on this substrate showed a good monocrystalline structure, and a 19-stage c.m.o.s. ring oscillator exhibited high performance in operation.     

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.     

Influence of oxygen on the ion-beam synthesis of silicon carbide buried layers in silicon

The properties of silicon structures with silicon carbide (SiC) buried layers produced by high-dose carbon implantation followed by a high-temperature anneal are investigated by Raman and infrared spectroscopy. The influence of the coimplantation of oxygen on the features of SiC buried layer formation is also studied. It is shown that in identical implantation and post-implantation annealing regimes a SiC buried layer forms more efficiently in CZ Si wafers or in Si (CZ or FZ) subjected to the coimplantation of oxygen. Thus, oxygen promotes SiC layer formation as a result of the formation of SiO_x precipitates and accommodation of the volume change in the region where the SiC phase forms. Carbon segregation and the formation of an amorphous carbon film on the SiC grain boundaries are also discovered. Fiz. Tekh. Poluprovodn. 32, 1414–1419 (December 1998)     

Vertical bipolar transistors on buried silicon nitride layers

The letter reports on the integration of vertically operating n-p-n-bipolar transistors with base widths of about 1 µm in silicon-on-insulator (SOI) structures. Nitrogen ion implantation at substrate temperatures of 550°C and subsequent SiCl4epitaxy provide SOI films with excellent crystalline quality. Conventional bipolar diffusion processes have been applied in order to fabricate diodes and vertical bipolar transistor arrays on thus isolated epitaxial layers. The leakage current of SOI diodes exceeds the value for bulk devices only by a factor of 2. The transistors exhibit emitter current gains of up to 100 and emitter-collector breakdown voltages of up to 35 V.     

Properties of buried SiC layers produced by carbon ion implantation in (100) bulk silicon and silicon-on-sapphire

Buried layers of SiC were formed in (100) single-crystal bulk silicon and silicon-on-sapphire by ion implantation of 125–180 keV, (0.56-1.00) × 10¹⁸ C/cm² at 30–40 μA/ cm² into samples held at 450-650° C. The as-implanted and 950° C annealed samples were characterized by differential infra-red absorbance and reflectance, Rutherford backscattering and channeling spectrometry, x-ray diffraction, four-point probe measurements, Dektak profilometry, I-V measurements, spreading resistance measurements and secondary ion mass spectrometry. Work done while affiliated with Rockwell International Corporation, Microelectronics Research & Development Center, 3370 Miraloma Avenue, Anaheim, CA 92803 and a Visiting Associate at the California Institute of Technology, Department of Applied Physics, Mail Code 116-81, Pasadena, CA 91125.     

Redistribution of erbium during the crystallization of buried amorphous silicon layers

The redistribution of Er during its implantation in silicon at doses close to the amorphization threshold and its subsequent solid-phase epitaxial (SPE) crystallization is investigated. The formation of a buried amorphous (a) layer is discovered at Er doses equal to 5×10¹³ and 1×10¹⁴ cm⁻² using Rutherford backscattering. The segregation of Er in this case takes place inwardly from the two directions corresponding to the upper and lower boundaries of the buried αlayer and leads to the formation of a concentration peak at the meeting place of the two crystallization fronts. A method for calculating the coordinate dependence of the segregation coefficient k from the distribution profiles of the erbium impurity before and after annealing is proposed. The k(x) curve exhibits a drop, whose width increases with decreasing Er implantation dose. Its appearance is attributed to the nonequilibrium nature of the segregation process at the beginning of SPE crystallization. Fiz. Tekh. Poluprovodn. 33, 652–655 (June 1999)     

Modeling Si nanoprecipitate formation in SiO2 layers with excess Si atoms

Computer simulations based on the Monte Carlo method are used to analyze processes leading to the formation of luminescence centers in SiO₂ implanted with Si ions. The simulations, which take place in a two-dimensional space, mimic the growth of silicon nanoprecipitates in layers containing several at.% of excess silicon. It is assumed that percolation clusters made up of neighboring Si atoms form first. As the annealing temperature increases, these clusters grow and compactify into nano-sized inclusions of a well-defined phase. It is shown that a dose dependence arises from an abrupt enhancement of the probability of forming direct Si-Si bonds when the concentration of silicon exceeds ∼1 at. %. Under these conditions, percolation chains and clusters form even before annealing begins. The effect of the temperature of subsequent anneals up to 900 °C is modeled via the well-known temperature dependence of Si diffusion in SiO₂. It is assumed that annealing at moderate temperatures increases the mobility of Si atoms, thereby facilitating percolation and development of clusters due to an increase in the interaction radius. Intrinsic diffusion processes that occur at high temperatures transform branching clusters into nanoprecipitates with well-defined phase boundaries. The dose and temperature intervals for the formation of precipitates obtained from these simulations are in agreement with the experimental intervals of dose and temperatures corresponding to the appearance of and changes in luminescence. Fiz. Tekh. Poluprovodn. 33, 389–394 (April 1999)     

The role of nitrogen in the formation of luminescent silicon nanoprecipitates during heat treatment of SiO2 layers implanted with Si+ ions

Twenty-five kiloelectronvolt Si⁺ ions with doses of (1–4)×10¹⁶ cm^?2 and 13-keV N⁺ ions with doses of (0.2–2)×10¹⁶ cm^?2 were implanted into SiO₂ layers, which were then annealed at 900–1100°C to form luminescent silicon nanoprecipitates. The effect of nitrogen on this process was deduced from the behavior of the photoluminescence spectra. It was found, for a certain ratio between the concentrations of implanted silicon and nitrogen, that the photoluminescence intensity increases significantly, and its peak shifts to shorter wavelengths. It is concluded that the number of precipitation nuclei increases owing to the interaction of nitrogen with excess silicon. Eventually, this results in an increase in the number of nanocrystals and in a decrease in their average sizes. In spite of introducing additional precipitation nuclei, the minimal concentrations of excess Si on the order of 10²¹ cm^?3 and heat treatments at temperatures higher than 1000°C were still required for the formation of nanocrystals.     

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.     

Formation and control of boron buried layers in silicon using anexcimer laser

Buried layers have been shown to enhance performance of Si MOSFETs in the deep submicrometer regime. Epitaxial growth methods such as atomic layer doping or ion implantation are currently used for the formation of such doping profiles. In this work, we propose an alternative approach, using a XeCl (λ=308 mn) pulsed excimer laser, for the fabrication of pulse-shaped B profiles in Si. This process affords simplicity, versatility, and independent control over the depth, width, and the height of the B buried layer     

Composition analysis of oxidized buried SiC layers in silicon from EFTEM images

Energy filter transmission election microscopy (EFTEM) is used to investigate the composition of a Si/SiO_x/SiC multilayer structure formed by ion-beam synthesis. The implanted dose is used as a standard for the quantification of the elemental maps. The carbon redistribution upon the oxidation of SiC is monitored.     

Silicon ion implantation for growing structurally perfect silicon layers on sapphire

The paper presents the results of studying a method for improving the crystal structure of ô silicon epitaxial layer on a sapphire substrate by its preliminary amorphization with high-energy silicon ions followed by its recovery (solid-phase recrystallization) to a structurally perfect single-crystal state. The structural and electrical parameters of silicon-on-sapphire compositions are comparatively analyzed before and after solid-phase recrystallization.     

Silicon nanocrystal formation upon annealing of SiO2 layers implanted with Si ions

The formation of silicon nanocrystals in SiO₂ layers implanted with Si ions was investigated by Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence. The excess Si concentration was varied between 3 and 14 at. %. It was found that Si clusters are formed immediately after implantation. As the temperature of the subsequent annealing was raised, the segregation of Si accompanied by the formation of Si-Si₄ bonds was enhanced but the scattering by clusters was reduced. This effect is attributed to the transformation of loosely packed clusters into compact, separate-phase nanoscale Si precipitates, with the Raman peak observed at 490 cm^?1 being related to surface scattering. The process of Si segregation was completed at 1000°C. Nevertheless, characteristic nanocrystal photoluminescence was observed only after annealing at 1100°C. Simultaneously, scattering in the range 495–520 cm^?1, typical of nanocrystals, appeared; however, the “surface-related” peak at 490 cm^?1 persisted. It is argued that nanocrystals are composed of an inside region and a surface layer, which is responsible for their increased formation temperature.     

C-V and C-t analysis of buried oxide layers formed by high-dose oxygen implantation

For silicon-on-insulator devices with very thin active layers, the quality of the buried oxide layer and its interface with the top silicon layer can significantly affect device performance. This study focuses on the characterization of buried oxide layers formed by high-dose oxygen implantation into Si wafers. Capacitance-voltage (C-V) and capac-itance-time (C-t) measurements were performed on the epilayer/buried oxide/substrate capacitors. From high frequency C-V measurements, data on fixed oxide charge, inter-face traps, and donor densities were obtained for both buried oxide interfaces, as well as the thickness of the buried oxide layer. From C-t measurements, minority carrier generation lifetimes were calculated for thin depletion regions on both sides of the buried oxide. The data is correlated to changes in implanted dose, anneal temperature, and anneal time.     

The formation of silicon nanocrystals in SiO<Subscript>2</Subscript> layers by the implantation of Si ions with intermediate heat treatments

The effect of heat treatments at 1100°C on an ion-beam synthesis of Si nanocrystals in SiO₂ layers is studied. The ion-implanted samples are subjected either to a single heat treatment after the total ion dose (10¹⁷ cm^?2 has been implanted, two heat treatments (a heat treatment after the ion implantation of each half of the total dose), or three heat treatments (a heat treatment after each third of the dose). The total duration of the heat treatments is maintained at 2 h. It is found that the intermediate heat treatments lead to a shift of the Raman spectrum of the nanocrystals to longer wavelengths and to a shift of the photoluminescence spectrum to shorter wavelengths. Study using electron microscopy shows that the size of the nanoprecipitates decreases, which is accompanied by the disappearance of the characteristic features of crystallinity; however, the features of photoluminescence remain characteristic of the nanocrystals. The experimental data obtained are accounted for by a preferential drain of Si atoms to newly formed clusters, which is consistent with the results of a corresponding numerical simulation. It is believed that small nanocrystals make the main contribution to photoluminescence, whereas the Raman scattering and electron microscopy are more sensitive to larger nanocrystals.     

Improvement of crystalline quality of the surface layer in buried implanted oxide structures by silicon implantation

An improvement of the crystalline quality of the surface layer in buried implanted oxide structures in silicon has been achieved by silicon in implantation and subsequent 570°C anneal treatment.     

Optimisation in resolving the buried line potential of VLSI circuits

During inspection or failure analysis of integrated circuits using an electron beam tester, an additional uncertainty linked to the operating conditions and structures under test must be considered to determine the potential of buried lines, apart from the systematic errors generally expected.<>     

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.     

The manufacture and performance of diodes made in dielectricallyisolated silicon substrates containing buried metallic layers

Results are reported on the performance of diffused p⁺n diode structures manufactured on a novel silicon-on-metal-on-insulator (SMI) substrate. This substrate consists of a thin single crystal silicon layer on top of a tungsten disilicide covered oxidized silicon wafer. The diodes show excellent characteristics with an exponential current-voltage (I-V) relationship over nine orders of magnitude and an ideality factor of 1.005, under forward bias conditions. The reverse leakage current is low with a minority carrier lifetime of typically 500 μs. The diodes show no evidence of stress induced defects or degraded performance due to W migration during processing. The SMI substrate is therefore shown to be compatible with standard manufacturing processes