High Dose Oxygen Implantation Research Articles

Oxide formation during ion bombardment of small silicon structures

The kinetics of high dose oxygen implantation and of surface sputtering in silicon are investigated by atomic force microscopy, transmission electron microscopy, transmission electron holography, and electron energy-loss spectroscopy. The implantation was performed into accurately defined submicrometer areas. The behavior of the erosion rate as a function of the implantation dose proved to be nonmonotonic. After native oxide sputtering, a period dominated by (i) implantation of oxygen and (ii) induced oxide formation with volume increase takes place, causing a maximum surface step around the bombarded area of about 1.1 to 1.3 nm at bombardment doses below 2×1016 O+ cm−2. Subsequently, higher doses cause a sputtering of the surface with a sputter yield of about 0.32 Si atoms/O+. Electron holography revealed the double layer character of the implanted region, and electron energy-loss spectroscopy, especially near the relevant Si-L23 ionization edge, identified these two layers which are (i) amorphous silicon oxide and (ii) amorphized silicon. Electron energy-loss line scans show the oxygen distribution inside the implanted areas with a lateral resolution of about 1–2 nm. It was found that the interface between the oxidized layer and the amorphized silicon sharpens with increasing implantation dose.

Influence of high dose and high energy oxygen implantation on the mechanical surface properties of aluminium

The increase in hardness and wear of aluminium was studied as a function of the oxygen ion implantation dose and energy. The ion energy was varied from 100 keV to 2 MeV. The maximum oxygen concentration within the implanted layer was varied in the range 20–55 at.%. The relative hardness increase due to implantation as a function of depth was studied using dynamic microhardness measurements. The maximum hardness increase varied between 1.8 and 3.5 depending on the implantation energy and fluence. The wear behaviour was investigated using a steel ball sliding on an implanted aluminium disc with ethanol as lubricant. By implantation at 100 keV, it was possible to avoid adhesive wear and cladding using a load of 200 mN. At higher implantation energies, a clear wear track was observed for this load, as for the non-implanted sample. However, the cross-sectional area of the wear track was remarkably reduced, e.g. by a factor of ten after 20 min sliding for 1 × 10 18 O + cm −2 implanted at 200 keV. The optimum wear improvement was obtained by a three-step implantation process using energies of 100 keV, 1 MeV and 2 MeV.

Improvement of the mechanical surface properties of aluminium by high dose oxygen implantation

In commercial semi-hard aluminium substrates layers with a high concentration of very small Al 2O 3 precipitates were formed by oxygen implantation in the energy range from 100 keV to 2 MeV. The depth distribution of the implanted oxygen has been determined by computer simulation and Auger depth profiling. The maximum oxygen concentration within the implanted layer covers the range from about 20 to 55 at.%. Auger electron spectroscopy is also used in order to prove the oxide formation. The depth dependence of the relative hardness increase due to the implantation has been studied using depth resolving measurements of the dynamic microhardness. The observed maximum hardness increase varies between 1.8 and 3.5 depending on implantation energy and fluence. The wear behaviour has been investigated using a steel ball sliding on the implanted aluminium disc with ethanol as lubricant. By an implantation at 100 keV it was possible to avoid adhesive wear and cladding for a load of 200 mN. Only for a load of 1.6 N the wear becomes comparable to the non-implanted state. At higher implantation energies a clear wear track is observed like for the non-implanted sample. However, the cross-section area of the wear track is remarkably reduced, e.g. by a factor 10 after 20 min sliding with a load of 200 mN for 1 × 10 18O +/cm 2 implanted at 200 keV. The optimum wear improvement has been obtained by a three step implantation using the energies 100 keV, 1 MeV and 2 MeV.

Structural defects in SIMOX

The sources of the defects in the Si-overlayer and the SiO 2 buried layer which are produced during high dose oxygen implantation and annealing treatment are discussed. These defects are related with the significant differences in the formation of thermally grown oxide and the buried oxide (BOX) in SIMOX. Trapping of Si in the BOX results in the formation of Si-islands and strained SiSi bonds. Stacking fault (SF) complexes are formed during the high temperature annealing at the back side of the Si-overlayer due to the dissolution of the SiO 2 precipitates.

Defect formation in oxygen-multiply implanted silicon-on-insulator material

High dose oxygen implantation (SIMOX) has been a successful fabrication technology of silicon-on-insulator (SOI) material for CMOS circuits with reduced power consumption and higher operating speed. However, high density (~108 cm-2) of the through-thickness defects (TTD) in the top Si layer of SIMOX is one of the most serious problems. Hill et al. reported multiple implant/anneal method to remarkably reduce defect densities to <104 cm-2. In the multiple implant/anneal material, however, ~106 cm2 of the final dominant defects, including stacking fault pyramids (SFP) and the precipitate-dislocation complexes (PDC), still remained after high temperature annealing. In this work, the microstructures and formation mechanism of the final defects were studied by various TEM techniques.Silicon (100) wafers were sequentially triple implanted to doses of 6/6/6×l017 at 200kev and 620°C. After each implantation the wafers were held at 1000°C for 2 hours and annealed at 1325°C for 4 hours in argon ambient plus 5% oxygen. Cross-section (XTEM) and plan-view (PTEM) transmission electron microscopy specimens were examined by using a weak beam dark field (WBDF) and high resolution electron microscopy (HREM) techniques in JEM 2000FX and Topcon 002B operating at 200kev.

Silicon on Insulator Obtained by High Dose Oxygen Implantation, Microstructure, and Formation Mechanism

The significant difference in the formation of thermally grown oxide and the buried oxide (BOX) produced by high dose oxygen implantation in silicon (SIMOX) is described. The different sources of the defects in the Si overlayer and the buried layer produced during implantation and annealing treatment are discussed. The trapping of Si in the BOX results in the formation of Si islands and strained Si—Si bonds. Stacking fault (SF) complexes are formed during the high temperature annealing at the interface between the Si overlayer and the buried oxide due to the dissolution of the precipitates. The morphology and density of the SF complexes under different implantation conditions are studied. The role of the sacrificial oxidation of the Si overlayer in the defect generation before and after high temperature annealing is discussed.

Behavior of contact-silicided TFSOI gate structures

As semiconductor device dimensions shrink and packing-densities rise, issues of parasitic capacitance and circuit speed become increasingly important. The use of thin-film silicon-on-insulator (TFSOI) substrates for device fabrication is being explored in order to increase switching speeds. One version of TFSOI being explored for device fabrication is SIMOX (Silicon-separation by Implanted OXygen).A buried oxide layer is created by highdose oxygen implantation into silicon wafers followed by annealing to cause coalescence of oxide regions into a continuous layer. A thin silicon layer remains above the buried oxide (~220 nm Si after additional thinning). Device structures can now be fabricated upon this thin silicon layer.Current fabrication of metal-oxidesemiconductor field-effect transistors (MOSFETs) requires formation of a polysilicon/oxide gate between source and drain regions. Contact to the source/drain and gate regions is typically made by use of TiSi2 layers followedby Al(Cu) metal lines. TiSi2 has a relatively low contact resistance and reduces the series resistance of both source/drain as well as gate regions

Origin of the defect structures in oxygen-implanted silicon-on-insulator material

Silicon-on-insulator material fabricated by high-dose oxygen implantation (known as SIMOX) has been used for high speed and radiation hard devices and is under consideration for use in low power applications. However, a continuing problem has been crystalline defects in the top silicon layer. SIMOX is fabricated by two distinct methods: a single oxygen implant to a dose of 1.8×l018 cm-2 followed by a high-temperature anneal (≥1300°C, 4-6 hr) or by multiple lower dose implants (∼6×l017 cm-2) with high-temperature anneals after each implant. To date, there has been no systematic comparison of the defect structures produced by these two fabrication methods. Therefore, we have compared the defect structure and densities in multiple vs. single implant wafers. In this paper we describe the origin and characteristics of the defect structures in SIMOX and show how their densities are controlled by the processing method and conditions.Silicon (100) wafers were implanted in a high current implanter at ∼620°C to doses of 1.8×l018 or 0.6/0.6/0.6×l018 cm-2 and annealed at 1325°C, 4 hr in 0.5% or 5% O2 in Ar. Cross-section (XTEM) and plan-view (PTEM) samples were studied with bright field and weak beam dark field techniques in a transmission electron microscope operating at 200 keV.

Thermally stable oxygen implant isolation of p-type Al0.2Ga0.8As

High dose oxygen implantation was used to form high resistivity regions in p-type Al0.2Ga0.8As. By achieving oxygen concentrations 30 times the grown-in beryllium concentration we created Al0.2Ga0.8As layers with a sheet resistance of over 1010 Ω/⧠ that were stable to 900 °C. Samples implanted with a base dose of 2×1014 cm−2 showed an apparent activation energy for conduction of 0.67 eV after annealing at 800 °C.

Computer simulation of SIMOX and SIMNI formed by low-energy ion implantation

The computer program IRIS (Implantation of Reactive Ions into Silicon) has been modified and used to simulate low energy (< 100 keV), high dose oxygen and nitrogen implantation into silicon before and after annealing. There are some differences between high dose O + and N + implantation used to form buried insulating layers for SOI structures (SIMOX and SIMNI). Both ion species cause crystal swelling and surface sputtering and change the thickness of the layers. However the O/Si ratio in oxide layers saturates at the stoichiometric value of SiO 2, whilst the N/Si ratio can exceed that of Si 3N 4. Nitrogen will accumulate in the silicon nitride layer, eventually being trapped as nitrogen bubbles. It is found that the method of sequential implantation and annealing will reduce the thickness of the top silicon layer in SIMOX samples, but has an opposite effect during nitrogen implantation.

Electric field dependent paramagnetic defect creation in single-step high dose oxygen implanted SIMOX films

The creation of X-ray induced oxygen-vacancy defects was studied in high dose oxygen implantation (SIMOX) wafers produced by single-step implantation and annealing. It is shown that SIMOX is substantially more radiation sensitive (for these defects) than thermal or bulk oxide. Irradiation in the presence of an electric field of approximately 0.5–1 MV cm −1 is found to enhance the rate of defect creation by more than twice. Further enhanced defect creation is observed in SIMOX samples whose substrate has been chemically thinned prior to irradiation. This enhancement is attributed to modification of the network induced by hydrogen introduced during the thinning process.

Development of second generation oxygen implanter

Separation by implantation of oxygen (SIMOX) is the most advanced technique for achieving silicon-on-insulator material. The buried oxide layer is formed through a very high dose oxygen implantation process. Until recently, the only available practical equipment for implantation was a research-oriented machine based on a five year old design. The maturation of the technology has necessitated the development of a true manufacturing implanter and Ibis Technology has undertaken such a design. It will have four times the throughput capability of the previous design, coupled with advanced controls and automation capabilities. The details of the new design, comparisons with the existing equipment, and preliminary results are reported.

鉄表層の電気化学的性質に及ぼす酸素イオン注入効果

A study has been made of the electrochemical properties and of the microscopic characteristics such as surface composition and structure for oxygen-implanted iron surface layers. Oxygen implantation into pure iron was performed at fluences ranging from 1.4×10-2 to 2.2×10-1C·cm-2 and an accelelation voltage of 80kV, using non-massseparated ions. Electrochemical reaction was measured by multi-sweep cyclic voltammetry in an acetate buffer solution of pH=5.0. AES, RBS, XPS and XRD were used to analyze the depth dependence of atomic fractions and chemical bonding states, and the crystal structure of implanted layers. The atomic fraction of oxygen saturated at approximately 60% to form a trapezoidal distribution at high doses, and oxygen atoms combined with iron to form crystalline oxides. The peak anodic dissolution current density for iron subjected to high-dose oxygen implantation was approximately 1/20 that for pure iron, owing to the formation of surface layers with a trapezoidal oxygen distribution consisting of iron oxides.

Nuclear microprobe ion-channelling analysis of total dielectric isolation structures in silicon

The production of isolated device islands by high dose oxygen implantation into silicon followed by high temperature annealing has been termed total dielectric isolation (TDI). Higher packing densities, higher frequency performance and radiation hardness are the three potential advantages of fabricating very large scale integrated circuits by this method. Because of the microscopic size of the silicon islands, they cannot be analysed using conventional ion-channelling apparatus. However, some nuclear microprobes are now available which produce small diameter, low convergence MeV ion beams suitable for microscopic ion-channelling analysis. Thus, a technique which has proved very useful in analysing the near surface region in bulk semiconductor samples can now be applied to semiconductor device structures. The authors report on a preliminary study of TDI structures using the Surrey scanning microprobe. Measurements of crystalline quality, silicon thickness and buried oxide thickness were obtained from isolated islands. Secondary electron and optical microscopy were used to assess beam damage, and the feasibility of nuclear microprobe analysis of TDI structures is discussed.

Microanalysis of high-dose oxygen-implanted germanium

High-dose ion implantation is being increasingly used to produce buried oxide layers in silicon for high speed CMOS and VLSI applications. Ion implantation into germanium has been used to control optical properties. Germanium implanted with high dose oxygen is a promising material for photodetectors and solar energy converters. In the present study the structural changes in germanium caused by high dose oxygen implantation, giving low reflectivity in the far-UV and visible, were characterized by HREM and high spatial resolution AEM.The single crystal n-type germanium {111} wafers were implanted with O+ ions to doses of lx1017 to 1.5xl018 cm-2 at 45 keV. The implantation temperature was estimated to be about 400°C. The absorption behavior of the implanted samples was measured by Infrared (IR) spectroscopy. The compositional profiles of implanted layers were obtained by Rutherford Backscattering Spectrometry (RBS) and position-resolved EELS. Cross-sectional TEM samples for microstructural characterization were prepared by mechanical polishing and ion milling. A Philips 400ST/FEG analytical microscope was used for nanoprobe experiments, at 100 kV. Microstructural investigation was performed using ISI-002B and JEM-2000FX microscopes, at 200 kV.

Oxygen bubble formation and evolution during oxygen implantation and annealing of silicon-on-insulator material

Silicon-on-insulator (SOI) material fabricated by high dose oxygen implantation (SIMOX) is a material increasingly used for higher speed and radiation hard circuits. During implantation a variety of structural changes occur, including the formation of defects, bubbles, precipitates, and the buried oxide layer. The topic of bubble formation and evolution has received only limited study. Sjoreen et al. first reported the presence of spherical, randomly distributed precipitates near the top surface of the silicon layer. El-Ghor et al. further examined these precipitates and proposed that they were cavities filled with oxygen. Maszara confirmed the presence of spheroids filled with oxygen in the silicon top surface region in the 1mA cm-2 as-implanted samples. In this work, transmission electron microscopy (TEM) techniques were used to investigate the effect of implantation conditions on the bubble formation and the effect of subsequent annealing conditions on the evolution of bubbles.

High-dose oxygen implantation into silica

High doses of the stable oxygen-18 tracer isotope have been implanted at 200 keV into thick thermal oxide on silicon to study oxide sputtering in conditions similar to the formation of isolated silicon device islands by SIMOX. Final tracer distributions were obtained by secondary ion mass spectrometry confirming the high mobility of oxygen within the silica, diffusion coefficient 1.7 × 10 −12 cm 2 s −1, with rapid desorbtion of excess oxygen from the top silica surface after perfect isotopic exchange as the oxide layer remains at the stoichiometry of SiO 2.

High-dose oxygen implantation of multilayered thin films for the formation of high-temperature superconductors: A feasibility study

A high-dose ion implantation technique for the formation of high-temperature superconducting thin films on silicon substrates is investigated. This technique consists of three steps: (1) deposition of a multilayer sample of the appropriate composition, (2) implantation of oxygen to mix the layers and oxidize the resulting film simultaneously, (3) annealing in oxygen to form the superconductor (and to supplement the oxygen content, if necessary). Potential advantages of the technique are discussed. Thin films have been fabricated and implanted. Moderately homogeneous film of the composition Y 1Ba 2Cu 3O 6 were achieved. Initial annealing studies suggest that a mixture formed by this method does not crystallize below a temperature of 700°C for a 1 min rapid thermal anneal.

Evolution of Buried Oxide “Pipe” Defects Upon Implantation Through Particles in Simox Material

ABSTRACTWe have investigated the effect of the presence of oxide particles on the surface of silicon wafers during high energy, high dose implantation of oxygen into silicon. It was found that for single implants with doses of 1.5 × 1018/cm2 or 1.8 × 1018/cm2, such particles produce a non-continuous buried oxide layer in the as-implanted condition as well as after annealing. Etching results showed that no defects, which formed etchable paths through the buried oxide, were produced for particles with diameters 0.43 um or below for the lower dose and 0.53 um for the higher dose.

Redistribution and electrical activation of implanted arsenic in silicon on insulator substrates formed by oxygen ion implantation

The redistribution and electrical activity of implanted arsenic in separation by implanted oxygen (SIMOX) and bulk silicon substrates are compared. The SIMOX substrates were prepared by high dose oxygen implantation followed by high-temperature annealing. Subsequently doses of 5×1015 As+/cm−2 at 70 keV were implanted into the substrates and, also, bulk silicon. The samples were annealed to activate the arsenic. It was observed that (i) the same percentage activation was measured in both SIMOX samples and bulk silicon, (ii) no anomalous diffusion was seen in the SIMOX samples, and (iii) during further high-temperature annealing the buried oxide acts as a diffusion barrier. This data confirms the high quality of SIMOX material currently being prepared.