Segregation and diffusion of impurities in amorphous Si during furnace and ion-beam-induced epitaxy will be discussed. The use of ion beams to enhance the crystal growth process has resulted in novel behavior for fast diffusers such as Au. Diffusion is enhanced in the temperature range 300–700 K with activation energies ∼0.3 eV. Segregation and trapping are analogous to behavior at liquid-solid interfaces

The segregation of Ag and Cu impurities in amorphous Si during both thermal and ion beam induced epitaxial crystallization has been studied. During thermal regrowth at 550°C, both Ag and Cu are initially trapped at increasing concentration in the shrinking a-Si layer. At a critical concentration, though, regrowth becomes non-planar and the impurities are no longer entirely trapped in the a-Si. Above 0.08 at% and 0.15 at% respectively, the excess impurity is lost to the crystal region and diffuses rapidly away from the interface. Under low temperature (200 - 400°C) epitaxy induced by a 2.5 MeV Ar+ beam, segregation and trapping are initially observed. As regrowth proceeds, however, the segregation no longer follows the simple model

In this work we measured the functional dependence of the solid phase epitaxial (SPE) regrowth of amorphous silicon on the implanted phosphorous concentration, Np. The growth rates of self-ion amorphized layers in silicon wafers with (100) substrate orientation were measured by in situ, high precision, isothermal cw laser interferometry for temperatures from 460°C to 590°C, and concentrations in the range 2x1017 cm-3<Np<4x1020 cm-3. For low impurity concentrations, the fractional increase in the intrinsic SPE growth velocity ΔV/Vi depended linearly on Np as previously established for boron. For a given impurity concentration, the relative change V/Vi decreased with increasing annealing temperature.

Buried amorphous layers are produced in Si(100) by implantation of 100 keV P+ and Si+ ions under channeling condition along the <100>-direction. Rutherford Backscattering Spectrometry in combination with channeling shows that a continuous buried amorphous. layer with a thickness of 1300 Å results under a crystalline toplayer with a thickness of 600 Å. After Solid Phase Epitaxy a highly concentrated defect layer remains for all implants at the depth where the two amorphous/crystalline interfaces of the buried amorphous layer meet. Planar channeling along (100)-direction shows that dislocation loops are present after SPE regrowth at the ‘interface’ of the two crystalline regions for all implants. The size of the dislocation loops becomes smaller in the presence of phosphorus. Moreover, channeling analysis shows that in case of Rapid Thermal Annealing treatment in addition to the SPE regrowth process the defect structures present after full recrystallization can be more easily dissolved in case of the phosphorus implants as compared to the silicon self implant

Ion-assisted regrowth of chemical vapor deposited amorphous Si layers was investigated for different cleaning procedures. The process was directly monitored by transient reflectivity measurements. The c-a interface stops at the deposited layer/substrate interface for doses depending on the effectiveness of the cleaning procedure in removing the native oxide. Small concentrations of twins are found in the regrown layer. Their amount is also correlated to the cleaning procedure. In oxygen implanted bare Si samples the ion-induced growth rate is reduced to 0.3 of the normal value at a peak O concentration of 1 X 1021/cm3. The results on the ion-induced regrowth of deposited layers are explained in terms of oxygen profile broadening during irradiation and retardation of the growth for the presence of dissolved O.

Residual lattice disorder in lμm-thick silicon films as a function of the dose rate of 120 keV Ar+ ion implantations has been investigated. At a fluence of l×1 014 ions/cm2, low dose rates produced a highly damaged surface layer as expected; however, at a dose rate sufficient to locally heat the implanted film to a temperature of approximately 700°K, essentially complete annealing of the lattice disorder was observed. This temperature is significantly less than that normally required for post-implant thermal annealing. Measurements of lattice disorder were based on medium energy Rutherford backscattering and channeling analyses.

Damage formation during hot implants of 600 keV As or Ge ions into Si was investigated by changing the target temperature (>150 °C) and the ion fluence. The defect distributions, as obtained by channeling analysis, are characterized by a gaussian shape whose maximum coincide with the peak of the energy density deposition and with a width of 200 nm. The amount of damage is a factor of two higher for Ge than for As ion implants, and a similar result was found for the damage created by Ge implants into bare Si or Si doped with a near constant As concentration of 2×10 20/cm3. The transition to amorphous formation is quite sharp for As (around 120 °C) and quite broad for Ge implants. The different amount and kind of extended defects is probably due to an interaction of the mobile point defects, vacancies and interstitials, with As. The interaction probably increases the defects annihilation rate.

Indium implantation at 77°K into a–axis sapphire to peak concentrations of 6–45 mol % In produces amorphous surface layers. Isothermal annealing in Ar at temperatures between 600–900°C shows effects strongly dependent on ion dose. At lower doses <2×1016 In/cm2, the amorphous layer undergoes epitaxial regrowth as the amorphous to crystalline interface advances out towards the surface. Regrowth velocity is high in about the first half hour of the anneal. Regrowth obeys Arrhenius behaviour with an activation energy of 0.7eV for initial faster growth and 1.28eV for further anneal times. The amorphous phase transforms directly to ⊥-A12O3 without any evidence of an intermediary γ-phase. At higher doses, epitaxial regrowth is substantially retarded and rapid diffusion of In within the amorphous phase dominates.

Damage produced by 1.0-2.5 MeV self-ion and O-ion implantation into Si and Ge single crystals has been characterized by cross-sectional electron microscopy and ion channeling. In Si, it is observed that the damage morphology varies substantially along the ion's track. Near the end-of-range of the ion, damage accumulation is very similar to that which occurs during medium- to low-energy implantation (i.e., damage increases monotonically with dose until the lattice is made completely amorphous). In front of this end-of-range region, however, damage saturates at a very low level for moderate implantation fluences. A model based on homogeneous damage nucleation in Si is discussed. For Ge, damage accumulation is very different; a monotonic increase of damage with dose is observed over the entire range of the ion. Possible mechanisms responsible for the differences between Si and Ge are discussed.

The combination of electrical, Transmission Electron Microscopy and Triple Crystal X-ray Diffraction measurements allow us to separate the existence of a local impurity activation process from the amorphous- crystal transformation. The local process occurs in the highly damaged surface layer induced by the arsenic implantation and is efficient well below the Solid Phase Epitaxy transition temperature. It is suggested that point defect migration should play an important role in the electrical impurity activation at low annealing temperatures.

To clarify the generation mechanism of radiation damage induced in SiO2/Si by plasma processes, effects of three different beams, i.e., ions, neutrals and vacuum ultraviolet (VUV) photons have been evaluated independently. The radiation damage caused by these energetic bombardments has been measured by capacitance-voltage (C-V) measurements. These reveal that bombardments with a 250 eV Neo neutral beam generate + far less flat-band voltage shifts ( ΔVFB) than those with a Ne+ ion beam of equal kinetic energy. This c n be interpreted in terms of the differences in charge build-up and in hole production upon the incidence of these particles. VUV photons produced in the plasma are also responsible for large ΔVFB.

Low energy (6 keV) BF2 implantation was carried out using single crystal, Ge-preamorphized, and Si-preamorphized silicon substrates. Implanted substrates were rapid thermal annealed at temperatures from 600°C to 1050'C and boron channeling, diffusion, and activation were studied. Ge and Si preamorphization energies were chosen to produce nearly identical amorphous layer depths as determined by TEM micrographs (approximately 40 nm in both cases). Boron segregation to the end-of-range damage region was observed for 6 keV BF2 implantation into crystalline silicon, although none was detected in preamorphized substrates. Junction depths as shallow as 50 nm were obtained. In this ultra-low energy regime for ion implantation, boron diffusion was found to be as important as boron channeling in determining the junction depth, and thus, preamorphization does not result in a significant reduction in junction depth. However, the formation of junctions shallower than 100 rmu appears to require RTA temperatures below 1000°C which can lead to incomplete activation unless the substrate has been preamorphized. In the case of preamorphized samples, Hall measurements revealed that nearly complete electrical activation can be obtained for preamorphized samples after a 10 second rapid thermal anneal at temperatures as low as 600°C.

Implantations of annealed SIMOX and Si wafers have been done using P and Ga to investigate the effect of excess oxygen and oxygen precipitates on amorphous layer regrowth and category II (end-of-range) dislocation loop elimination. Solid phase epitaxial regrowth of the amorphous silicon in both SIMOX and Si control wafers occurred at 550°C without the formation of category III defects and annealing at 900°C 16 hours resulted in complete removal of the category II defects. In an oxidizing ambient, the implanted SIMOX wafer again exhibited complete defect elimination whereas the Si control wafer showed growth and development of extrinsic stacking faults. It is speculated that the buried oxide may act as a sink for the Si. SIMS results indicate the dopant getters to the Si/SiO2 interfaces and that redistribution can be modelled reasonably well with SUPREME III.

This work addresses the formation of Separation by IMplantation of OXygen (SIMOX) structures by multiple oxygen implantation into silicon and high temperature annealing. We observed no threading dislocation defects in the several plane view TEM and XTEM micro graphs of each of the samples implanted with a single dose of up to 8 × 1017 0+/cm2. We also demonstrated that with a multiple low-dose (3 to 4 × 1017 0+/cm2) oxygen implantation and high temperature annealing process, we are able to produce continuous and uniform buried SiO2 layers with a total dose of 1.1 × 1018 0+/cm2 (about 60% of the total dose for standard SIMOX). The density of defects is about 105/cm2. There are no silicon islands in the buried layer, no SiO2 precipitates in the silicon top layer, and the Si-SiO2 interfaces are sharp and smooth. SIMOX material with a high-quality Si top layer and a continuous buried layer has been produced with a total dose of 7 × 1017 0+/cm2 (40% of the total dose for standard SIMOX) and a two-step process. However, in this case there are a few Si islands present in the buried SiO2 layer.

Ion-implantation induced amorphization has been used to modify the linearity of response of ultrafast photoconductive switches fabricated on SOS. The extent of amorphization was determined using various materials characterization techniques. TRIM-86 Monte Carlo calculations were used to model the defect densities produced by ion implantation. Linearity of response is critically dependent upon the nature of the semiconductor region under metallic contacts and the character of the response is opposite to that expected from reports in the literature.

Shallow P+ junctions have been fabricated using reverse-type dopant preamorphization by Sb. The junctions ∼100 nm in depth have leakage current below 10 nA/cm2, sheetresistance less than 200 Ω/□ and ideality factor in the range 1.01–1.03. This type of amorphization scheme provides electrical activation of B at low temperature, which is very promising for low temperature processing applications. The importance of process optimization was demonstrated. The electrical results were correlated with residual defect structure observed by cross-sectional TEM.

The combination of arsenic and boron implantation with rapid thermal annealing (RTA) has been investigated to form shallow p-n junctions under a titanium silicide (TiSi2) metallization. The use of TiSi2 as a connection material can lead to the destruction of the junction if the kinetics of silicidation and doping are not well controlled. The purpose of this study is to better understand and control these kinetics, using far-from equilibrium processing such as ion implantation and RTA. The structures were characterized by Rutherford Backscattering Spectometry (RBS) for arsenic and silicide profiling, Secondary Ion Mass Spectometry (SIMS) for boron profiling, Scanning Electron Microscopy (SEM), and electrical sheet resistance measurements. Two procedures were investigated. Both involved the thermal reaction of Ti thin films, sputter-deposited with thicknesses ranging between 40 and 80 nm. In the first experiment, the as-deposited films were implanted with either 115 keV arsenic or 28 keV boron to form the junction, disperse the native oxide, and ion beam mix the Ti and Si. The films were then subjected to an RTA at 750°C for 15 to 60 seconds, which leads to TiSi2 formation in unimplanted films. Implantation was found to actually prevent TiSi2 formation. Ion transport calculations indicated that dopant pile-up at the interface might inhibit silicidation while higher energies and larger implant doses can more effectively ion beam mix Ti and Si. A more attractive solution consists of first forming TiSi2 from the as-deposited Ti by RTA, and then implanting to form the junction. This resulted in better control of the junction thickness. A sharp increase in the TiSi2 resistivity was found after implantation but the original value could be restored by a second RTA. This RTA also electrically activated the dopants and recrystallized the junction. The material properties of Ti/Si and TiSi2/Si under ion bombardment, RTA, doping, and conventional furnace annealing will be discussed.

The effect of heat treatments on the microstructure, composition and I–V characteristics of Al/TiW/a-Si contacts was studied.

It was found that heat; treatments of the amorophized contacts at the temperature range of 450–520°C led to an interdiffusion of Si atoms into the Al film and of Al atoms into the a-Si region through the Ti:W layer and silicides formation.However, no such interdiffusion and silicides formation could be detected in the contacts made of the unamorphized Si substrate under identical heat treatments.

The I–V characteristics of the amorphized contacts are explained by a model of electrical conductivity in amorphous solids.

Further progress in IC dimension reduction, increase in integration degree and speed require development and use of new current-conducting materials. This is due to the fact that existing current-conducting systems based on aluminium are low temperature, characterized by low electromi gration stability and require use of complex barrier layersi[l]. Polycide currentconducting materials have quite high resistance, interact with aluminium and are sensitive to the formation conditions. From this point of view, borides and titanium borides in particular are very promising for making current-conducting systems since they are very much characterized by good barrier properties, high conductance, properties and electromigration stability [2].

Epitaxial silicide growth is of great interest to many researchers and process engineers working in the field of microelectronics. The interest towards epitaxial silicides is due, firstly to the fact that these structures are suitable for systematic investigation of physics of a metal-semiconductor interface, and secondly that epitaxial intermetallic structures on silicon allow development of new devices such as threedimensional ones. At present, however, one can successfully form layers with epitaxial structure with thickness of no more than 150 nm using solid-state reaction in the metal layersilicon substrate system. Such values satisfy researchers dealing with problems of epitaxial growth because main processes occur in the range of 10–20 Å [1]From a technological point of view, however, it is desirable to form layers with thickness up to 1 μm.