Influence of Cr<Superscript>+</Superscript> ion implantation and pulsed ion-beam annealing on the formation and optical properties of Si/CrSi<Subscript>2</Subscript>/Si(111) heterostructures

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 10¹⁵ to 6 × 10¹⁶ cm⁻² and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi₂) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 10¹⁶ cm⁻². At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi₂ precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.     

Processing for optically active erbium in silicon by film co-deposition and ion-beam mixing

Techniques of film deposition by co-evaporation, ion-beam assisted mixing, oxygen ion implantation, and thermal annealing were been combined in a novel way to study processing of erbium-in-silicon thin-film materials for optoelectronics applications. Structures with erbium concentrations above atomic solubility in silicon and below that of silicide compounds were prepared by vacuum co-evaporation from two elemental sources to deposit 200-270 nm films on crystalline silicon substrates. Ar⁺ ions were implanted at 300 keV. Oxygen was incorporated by O⁺-ion implantation at 130 keV. Samples were annealed at 600 °C in vacuum. Concentration profiles of the constituent elements were obtained by Rutherford backscattering spectrometry. Results show that diffusion induced by ion-beam mixing and activated by thermal annealing depends on the deposited Si-Er profile and reaction with implanted oxygen. Room temperature photoluminescence spectra show Er³⁺ transitions in a 1480-1550 nm band and integrated intensities that increase with the oxygen-to-erbium ratio.     

TEM characterization of yttrium silicide layers synthesized by ion implantation

The structure of Si implanted with high doses of yttrium has been investigated by varying implantation doses and energies. As implantation doses increase into the low 10¹⁷ cm^–2 range, silicide precipitates form. The precipitates are thin and long and lie parallel to {111} planes in the Si matrix. As dopant concentrations increase, the precipitates themselves become more equiaxed, aspect ratios decrease, and precipitates densities increase until the precipitates coalesce to form a continuous buried layer of yttrium silicide within the Si matrix. The layer thickness is relatively uneven. As implant doses increase to 4×10¹⁷ cm^–2, the layer thicknesses become more uniform although there are still defects present. As the implant doses increase further, the precipitate bands on either side of the continuous layer decrease due to gettering of yttrium to the layer. As the energy of the implant is increased, the appearance of the sample is similar to that of the lower energy implants except that the layer is buried deeper in the Si matrix. Observations of the silicide are consistent with its having the AlB₂ structure with ordered vacancies on the Si sublattice.Address from July 1, 1992: Arizona State University, Tempe, AZ     

XRD and RBS study of annealing effects in titanium implanted a-silicon films

We have used ion implantation of 30 keV⁴⁸Ti⁺ ions into a-Si films at nominal doses of 10²⁰-10²¹ ions/m² to fabricate coherent silicide layers. Characterization of these layers and study of their annealing behaviour were carried out using XRD and RBS techniques. We find that the layers are a mixture of Ti₅Si₄, TiSi, TiSi₂ and Si. On annealing at relatively lower temperatures (up to ～ 300° C), predominant silicide phases present in the layer are Ti-rich, such as Ti₅Si₄ and TiSi. At higher temperatures, the Ti-rich layer has a tendency to consume unreacted Si from the film and to form a predominantly Si-rich silicide layer. A structure of silicon different from the diamond cubic structure is noticed in these implanted layers.     

A pulsed synthesis of β-FeSi2 layers on silicon implanted with Fe ions

Continuous layers and fine-grained films of β-FeSi₂ were synthesized using the implantation of Fe⁺ ions into Si (1 0 0) with subsequent pulsed nanosecond ion-beam treatment of the implanted layers. The X-ray diffraction studies showed that the pulsed ion-beam treatment brings about the formation of a mixture of two phases: FeSi and β-FeSi₂ with strained crystal lattices. Subsequent rapid thermal annealing led to the complete transformation of the FeSi phase into the β-FeSi₂ phase with the formation of a textured layer. The data obtained using Raman spectroscopy corroborate the formation of the β-FeSi₂ phase with a high degree of silicon crystallinity.The results of measuring the optical absorption point to the formation of β-FeSi₂ layers and precipitates with a direct-gap structure, an optical gap of E_g≈0.83 eV. The photoluminescence band peaked at λ≈1.56 μm and caused by direct band-to-band transitions in β-FeSi₂ was observed at temperatures lower than 210 K.     

Investigation of silicon doped by zinc ions with a large dose

The formation of nanoparticles in СZn-Si(100) implanted with ⁶⁴Zn⁺ ions using a dose of 5 × 10¹⁶ cm^–2 and an energy of 50 keV at room temperature with subsequent thermal processing in oxygen at temperatures ranging from 400 to 900°C is studied. The surface topology is investigated with scanning electron (in the secondary emission mode) and atomic force microscopes. The structure and composition of the near-surface silicon layer are examined using a high-resolution transmission electronic microscope fitted with a device for energy dispersive microanalysis. An amorphized near-surface Si layer up to 130 nm thick forms when zinc is implanted. Amorphous zinc nanoparticles with an average size of 4 nm are observed in this layer. A damaged silicon layer 50 nm thick also forms due to radiation defects. The metallic zinc phase is found in the sample after low-temperature annealing in the range of 400–600°C. When the annealing temperature is raised to 700°C, zinc oxide ZnO phase can form in the near-surface layer. The complex ZnO · Zn₂SiO₄ phase presumably emerges at temperatures of 800°C or higher, and zinc-containing nanoparticles with lateral sizes of 20–50 nm form on the sample’s surface.     

Evolution of CoSi2 buried structures created by high temperature Co+ ion implantation into Si(1 0 0) during post-implantation annealing

The evolution of buried structures of cobalt disilicide, which are formed in a Si(1 0 0) matrix by 400 keV Co⁺ ion implantation at 875 K substrate temperature with subsequent rapid thermal annealing at 1275 K was studied by cross-sectional transmission electron microscopy (X-TEM). The analysis of identical samples with successive variations of the implanted doses and annealing times allows a detailed observation of the role of defects, created by the ion flux, on the process of ripening and growth of CoSi₂ precipitates. We found that transport of the implanted material along diffusive links leads to the formation of a secondary CoSi₂ distribution between the main layer and the surface. Post-implantation annealing results in the evolution of defects into dislocations, which affects the mobility and therefore the growth of CoSi₂ precipitates. Increasing the annealing time leads to the separate growth of precipitates in each layer. The result is not the formation of a single uniform buried layer because the distance between the individual layers is too large due to a screening effect, which operates during the ripening stage.     

TEM analysis of the influence of dose on damage behavior in MeV Au2+-implanted silicon

Extended lattice damage created by implantation of 3.6 MeV Au²⁺ ions has been investigated using transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). Systematic observations of damage for Au²⁺ ions implanted with varying doses into silicon are explained in terms of a model. The origin of two distinct bands of extended defects is explained in terms of annealing of the central region of implant-damage, during the course of the implantation. Two distinct bands of Au precipitates are observed in high-dose implanted samples. This observation is explained as being the result, in part, of segregation of gold in front of a recrystallizing front, and in part, of gettering of dopant-atoms to nodes in a dislocation network. The network arises as a result of dynamic annealing of damaged crystalline silicon.     

Ion beam modification of silicide-silicon interfaces

We have modified the contact interface between Pd₂Si and n-Si by ion implantation and investigated the effect of the implantation on Schottky barrier height and rate of silicide formation by electrical current-voltage measurements and Rutherford backscattering spectroscopy. Various ions, As. P, B. O and Si at 50 keV and up to a dose of 5 × 10¹⁴ ions/cm² were implanted into Si wafers before the Pd-deposition to form Pd₂Si. In the case of As and P, the implantation showed a large erect on the subsequent Pd₂Si formation; the formation is enhanced in the as-implanted samples, but it is retarded if an annealing at 600°C precedes the Pd-deposition. Silicide formation was found generally to help reduce the implantation damage (with or without the 600°C annealing) and showed improvements on the electrical characteristics of the contact interface. Consumption of the entire implanted region by silicide formation is found necessary for obtaining a good diode performance. In the case of As implantation, a lowering of the Schottky barrier height of Pd₂Si has been observed.     

Silicon nanocrystals in SiO2 matrix obtained by ion implantation under cyclic dose accumulation

Silicon ions were implanted into the films of silicon oxide obtained by thermal oxidation of silicon wafers in a damp oxygen. Accumulation of the implantation dose was performed either in one step or cyclically in step-by-step mode, and after each stage of implantation the samples were annealed in a dry nitrogen. The second series of the samples differed from the first one by the formation of SiO₂ matrix that included additional annealing in the air at 1100 °C for 3 h before ion implantation. X-ray absorption near edge structure (XANES) was obtained with the use of synchrotron radiation. Two absorption edges were observed in all of Si L_2,3-spectra. One of them is related to elementary silicon while the other one-to silicon in SiO₂. The fine structure of the first one indicates the formation of nanocrystalline silicon nc-Si in SiO₂ matrix. Its atomic and electron structure depends on the technology of formation. For both series of samples, a cyclical accumulation of the total dose Φ=10¹⁷ cm⁻² (for the total time of annealing—2 h) resulted in the appearance of more distinct structure in the range of absorption edge for the elementary silicon as compared with the case of single-step accumulation dose. In the more “dense” oxide of the samples from the second series, the probability of formation of silicon nanocrystals in a thin near-surface region of the implanted layer was reduced. These results can be interpreted with the account of the previously obtained photoluminescence, Raman scattering and electron microscopy data for these samples.     

Effect of High Temperature—Pressure on Buried Silicon Dioxide in Simox and Soi Structures

The effect of annealing at 1520–1570 K under high pressure (HP, up to 1.2GPa) on the structure of SiO₂ in oxygen implanted silicon (Si:O) and in silicon with buried SiO₂ layer (SOI) was investigated by TEM, X-Ray and FTIR methods. Depending on the implantation and treatment parameters, SiO₂ precipitates or continuous SiO₂ layers, sometimes with defects at the SiO₂/Si boundary, are created. A stress dependent shift of asymmetric stretching vibration mode associated with Si-O bonds towards lower frequencies is detected for SiO₂ in the HT—HP treated Si:O and SOI samples.     

Ground state magnetic properties of ultrathin fcc Fe and Co films on Cu(001) surfaces

The oxidation characteristics of silicon implanted with a low dose of nitrogen (1–3×10¹⁵cm^–2) have been studied for dry oxidation conditions at 1020°C. The wafers were subjected to a pre-oxidation annealing. Complete inhibition of the oxide growth occurs in the initial stage of oxidation, while the oxidation rate for prolonged oxidation is identical to that for pure silicon. The oxidation resistance increases with the implantation dose. The resistance is attributed to the formation of a nitrogen-rich surface film during annealing. This layer, which consists of only a few monolayers, is presumably composed of oxynitride. The electrical characteristics of MOS capacitors formed on implanted wafers show that the interface state density is not significantly increased by the low-dose N implantation.     

Formation of oriented rodlike nickel silicide precipitates during magnetron deposition of carbon and nickel on silicon

Formation of rodlike structures elongated in the 〈100〉 and 〈010〉 directions of silicon crystal was observed during magnetron codeposition of carbon and nickel on (100) silicon substrate with a natural oxide layer. Rodlike structures did not form during deposition in similar conditions on (111) silicon substrate. It has been revealed that the rodlike structures represent epitaxial nickel silicide precipitates. The results of experimental study of the composition, structure, and shape of forming silicide clusters as a function of the silicon substrate orientation and the codeposited layer thickness are presented.     

Changes of structure and composition of a zinc ion-implanted silicon surface during nanoparticle formation upon thermal treatment

Data from investigating the formation of nanoparticles (NPs) on a surface of silicon wafers after zinc ion implantation and thermal annealing are presented. The investigation is conducted by means of trans-mission electron microscopy, electron diffraction analysis, energy dispersive microanalysis, scanning tunneling microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. It is found that on their surfaces, the implanted samples have only films of amorphous silicon containing implanted zinc, oxygen, and carbon contamination. Thermal treatment in the range of 400–800°C leads to the formation NP with 20–50 nm wide and 10 nm tall on a wafer’s surface, plus a silicon oxide layer about 20 nm thick. NPs are composed of zinc compounds of the ZnO, ZnSiO₃, or Zn₂SiO₄ types. These NPs disappear after annealing at 1000°C.     

Chemical and phase compositions of silicon oxide films with nanocrystals prepared by carbon ion implantation

The chemical and phase compositions of silicon oxide films with self-assembled nanoclusters prepared by ion implantation of carbon into SiO _x (x < 2) suboxide films with subsequent annealing in a nitrogen atmosphere have been investigated using X-ray photoelectron spectroscopy in combination with depth profiling by ion sputtering. It has been found that the relative concentration of oxygen in the maximum of the distribution of implanted carbon atoms is decreased, whereas the relative concentration of silicon remains almost identical over the depth in the layer containing the implanted carbon. The in-depth distributions of carbon and silicon in different chemical states have been determined. In the regions adjacent to the layer with a maximum carbon content, the annealing results in the formation of silicon oxide layers, which are close in composition to SiO₂ and contain silicon nanocrystals, whereas the implanted layer, in addition to the SiO₂ phase, contains silicon oxide species Si²⁺ and Si³⁺ with stoichiometric formulas SiO and Si₂O₃, respectively. The film contains carbon in the form of SiC and elemental carbon phases. The lower limit of the average size of silicon nanoclusters has been estimated as ∼2 nm. The photoluminescence spectra of the films have been interpreted using the obtained results.     

Peculiarities of the electron structure of nanosized ion-implanted layers in silicon

The effect of implantation of Ba, P, B, and alkali element ions with a low energy (E ₀ < 5 keV) on the electron structure of a thin surface region of p- and n-type Si(111) single crystals is investigated by photoelectron and secondary electron-electron spectroscopy. It is shown that irrespective of the ion species, high-dose ion implantation leads to a sharp narrowing of the band gap in silicon, which can be explained by overlapping of the wavefunctions of electrons of impurity atoms and the formation of the impurity subband overlapping with the allowed band. After implantation thermal annealing, SiP, BaSi, and SiB3 films of nano-sized thickness are obtained for the first time. Optimal regimes of ion implantation and subsequent annealing for the formation of silicide films are determined, and their electron structure is investigated.     

Boron implantations in silicon: A comparison of charge carrier and boron concentration profiles

The concentration profiles of boron implanted in silicon were measured using secondary ion mass spectrometry. The accompanying charge carrier profiles were determined by Hall-effect sheet-resistivity measurements combined with layer removal by anodic oxidation and etching. From a mutual comparison of these profiles an electrically inactive boron fraction was found to exist in the region of maximum boron concentration. This fraction can be correlated with boron precipitates. In high dose implantations the precipitates still exist after annealing at 1000°C. In the tail of the profile a small electrically inactive boron fraction was observed. This fraction was correlated with fast diffusing non-substitutional boron. Near the surface a charge carrier peak was found that can be correlated with the damage caused by implantation. The interpretation of the observed electrical effects was facilitated by investigations on boron concentration profiles of layers implanted with different doses and annealed in accordance with different time-temperature schedules.     

Effects of Helium and Oxygen Common Implantation in Silicon Wafer

Defect engineering for SiO2 precipitation is investigated using He-ion implantation as the first stage of separation by implanted oxygen （SIMOX）. Cavities axe created in Si by implantation with helium ions. After thermal annealing at different temperatures, the sample is implanted with 120 keV 8.0 ×1016 cm 2 0 ions. The Q ion energy is chosen such that the peak of the concentration distribution is centred at the cavity band. For comparison, another sample is implanted with O ions alone. Cross-sectionM transmission electron microscopy （XTEM）, Fourier transform infrared absorbance spectrometry （FTIR） and atomic force microscopy （AFM） measurements are used to investigate the samples. The results show that a narrow nano-cavity layer is found to be excellent nucleation sites that effectively assisted SiO2 formation and released crystal lattice strain associated with silicon oxidation.     

Effects of magnesium film thickness and annealing temperature on formation of Mg2Si films on silicon (1 1 1) substrate deposited by magnetron sputtering

Magnesium films of various thicknesses were first deposited on silicon (1 1 1) substrates by magnetron sputtering method and then annealed in annealing furnace filled with argon gas. The effects of the magnesium film thickness and the annealing temperature on the formation of Mg₂Si films were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The Mg₂Si thin films thus obtained were found to be polycrystalline and the Mg₂Si (2 2 0) orientation is preferred regardless of the magnesium film thickness and annealing temperature. XRD results indicate that high quality magnesium silicide films are produced if the magnesium/silicon samples are annealed at 400 °C for 5 h. Otherwise, the synthesized films annealed at annealing temperatures lower than 350 °C or higher than 450 °C contain magnesium crystallites or magnesium oxide. SEM images have revealed that microstructure grains in the polycrystalline films are about 1-5 μm in dimensions, and the texture of the Mg₂Si films becomes denser and more homogeneous as the thickness of the magnesium film increases.     

The fabrication of nickel silicide ohmic contacts to n-type 6H-silicon carbide

This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi硅化镍;欧姆触点;n型碳化硅;制造;能带;带隙Project supported by the National Basic Research Program of China (Grant No~2002CB311904), the National Defense Basic Research Program of China (Grant No~51327010101) and the National Natural Science Foundation of China (Grant No~60376001).2006-09-192006-10-30This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi2/SiC structure axe formed on N-wells created by N^＋ ion implantation into Si-faced p-type 6H-SiC epilayer respectively. NiSi and NiSi2 films are prepared by annealing the Ni and Si films separately deposited. A two-step annealing technology is performed for decreasing of oxidation problems occurred during high temperature processes. The specific contact resistance Pc of NiSi contact to n-type 6H-SiC as low as 1.78× 10^-6Ωcm^2 is achieved after a two-step annealing at 350 ℃for 20 min and 950℃ for 3 min in N2. And 3.84×10-6Ωcm^2 for NiSi2 contact is achieved. The result for sheet resistance Rsh of the N＋ implanted layers is about 1210Ω/□. X-ray diffraction analysis shows the formation of nickel silicide phases at the metal/n-SiC interface after thermal annealing. The surfaces of the nickel silicide after thermal annealing are analysed by scanning electron microscope.