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3C-SiC devices are hampered by a high crystal defect density due to the hetero-epitaxial growth of these films, which results in the presence of stacking faults (SF). In this paper high growth rate CVD processes have been used to try to reduce the SF density in 3C-SiC films. In a first step a high growth rate (30 μm/h) has been used to grow 50 μm thick 3C-SiC layer on (100) Si. Then the silicon substrate was removed via etching and a further 3C-SiC growth was performed with a higher growth rate (90 μm/h) at a higher temperature (1600 °C) to obtain a final thickness of 150 μm. The SF presence and density were evaluated by TEM analysis performed on as-grown samples and SEM analysis on KOH etched samples with various thicknesses. A decrease of SF density was observed with an increase of 3C-SiC film thickness, with the best results (500/cm) obtained for the thickest sample. The 3C-SiC film quality and orientation was evaluated by XRD are correlated with film thickness and SF density.
In this paper the defects generated by ion implantation in 4H-SiC DIMOSFET (Double Implanted MOSFETs), and their evolution after annealing process, have been studied in detail. The point defects generated by the source or body implantation process have been detected by micro-photoluminescence (µPL) and the effect of these defects on the electrical characteristics of the DIMOSFET has been studied. The role of the annealing process has been carefully investigated by using different temperatures. It appears fundamental for the restoring of the crystal damage. The effect of the ion implantation dose has been investigated as well. By reducing the source ion implanted dose a large decrease of point defects has been detected and a considerable improvement of the electrical characteristic of the DIMOSFET has been observed.
Silicon carbide (SiC) detectors were used to analyze the multi-MeV ions of the plasma produced by irradiation of various targets with a 300-ps laser at intensity of 1016 W/cm2. The SiC detectors were realized by fabricating Schottky diodes on 80 μm epitaxial layer. The low dopant concentration and defect density of the epilayer allowed the realization of good performance detectors. The use of SiC detectors ensures the cutting of the visible and soft ultraviolet radiation emitted from plasma enhancing the sensitivity to very fast ions. The time-of-flight spectra obtained by irradiating different targets show a peak associated to protons and various peaks relative to different charge states of ions. Processing of the experimental data allows to estimate the energies of the protons and of the different ions emitted from laser-induced plasma. The SiC detector results are compared with the ones obtained by Ion Collector and a Thomson Parabola spectrometer.
When a Ta layer is deposited at the Si/Ti interface a new phase has been detected, i.e. theTiSi2C40. The C40-C54 transformation kinetics and the film morphology are consistent with an increase of the nucleation density with respect to the C49-C54 transition. The activation energies for the nucleation rate (4.2±0.3 eV) and the growth velocity (4.0±0.4 eV) have been obtained from the in situ sheet resistance and the Transmission Electron Microscopy results. These results show that the process with a Ta layer at the Ti/Si interface has a greater scalability with respect to the standard TiSi2 process.
The interfacial reaction and phase formation as a function of the annealing temperature (600÷1000°C) and times were investigated on nickel thin films evaporated on n type 6H-SiC (0001) substrate. The study was carried out employing a combination of Rutherford Backscattering Spectrometry, X-Ray Diffraction, Transmission Electron Microscopy and sheet resistance measurements. Also several TLM structures and Schottky diodes were fabricated with the same processes and a correlation has been found between the annealing process and the electrical measurements. The only nickel silicide phase that has been observed between 600 and 950 °C was the Ni2Si. The carbon of the consumed silicon carbide layer has been dissolved in the silicide film, during the reaction, forming carbon precipitates. The Ni2Si/SiC Schottky diodes show an almost ideal characteristics (n=1.07) and a barrier height of about 1.3 eV. From the electrical characterisation a non uniform Schottky barrier height seems to be formed.
The effect of a thin Ta layer at the Ti/Si interface on the kinetic of the C49-C54 transition will be shown in detail. The transformation kinetic has been monitored by in situ sheet resistance measurements that, coupled to structural characterisation, allowed to evidence the presence of an intermediate phase before the C54 formation. The temperature of the C54 phase formation decreases with a Ta concentration of 4.5·1015 cm−2 and μ-Raman images of partially transformed samples indicates that the density of C54 grains in presence of Ta is about one order of magnitude higher with respect to pure Ti/Si samples.
We discuss the rather scattered measurements of the lattice parameters for C49 TiSi2, which are reported in literature, along with new and accurate X-ray diffraction measurements and ab-initio calculations. Both agree in indicating that the density of the metastable C49 structure cannot be much smaller than the one for the polymorphic C54 phase, as it is commonly reported. We conclude by demonstrating that only in the case of such a smaller difference in density between the two phases, the elastic strain contribution to the nucleation energy of the C54 structure in the C49 matrix can be neglected. The estimation of the critical radius strongly depends on this issue.
The kinetics of the C49-C54 polymorphic transformation in titanium disilicides thin films grown on amorphous Si substrate has been followed by sheet resistance and Infrared Spectroscopy measurements on both blanket samples and submicron lines. The transformation of a fine grained C49 films (davg=30 nm) into the C54 phase was complete after annealing for ∼300 s at a temperature of 700 °C in blanket samples and of 730 °C in submicron lines. The Avrami exponent decreases from n=3 in blanket films to n=l in stripes. The transformation time at a given temperature increases with decreasing linewidth in agreement with the nucleation density model. Infrared Spectroscopy shows no shift of the peaks of the C49 phonons going from blanket to patterned films, suggesting the lack of strain on TiSi2 patterned films. The different behavior between blanket and laterally limited samples has been explained in terms of the different surface energies.
The thermal stability of patterned cobalt silicide layers grown on amorphous silicon has been studied in the temperature range between 850 and 1000 °C. The degradation of patterned CoSi2, detected by resistance measurements, occurs via grain agglomeration at a temperature ∼100 °C lower than in blanket film. The reduction of the stability window in patterned samples is due to geometric constraints,. which results in a greater growth rate of the median grains with respect to lateral grains.
Ultra-Shallow p+/n and n+/p junctions were fabricated using a Silicide-As-Diffusion-Source (SADS) process and a low thermal budget (800÷900 °C). A thin layer (50 nm) of CoSi2 was implanted with As and BF2 and subsequently diffused at different temperatures and times to form two Ultra-Shallow junctions with a junction depth of 14 and 20 nm. These diodes were extensively investigated by I-V and C-V measurements in the range of temperature between 80 and 500 K. TEM delineation was used to controll the junction uniformity.
The secondary defect annihilation by one- and two-step titanium silicidation in SiGe layers, formed by high dose Ge implantation, has been studied systematically as a function of the Ge fluence, implantation energy, silicide thickness, and silicide process conditions. In all cases the Ti thickness was kept below 20 nm, resulting in very thin Ti silicide layers typically less than 40 nm. The silicide phase was inspected by x-ray diffraction and transmission electron diffraction. Channelling Rutherford backscattering spectrometry and transmission electron microscopy were used to follow the end of range dislocation loop annihilation as a function of the silicide process conditions. The end of range loop annealing and the influence of silicidation is presented in this paper for Ge fluences above 3×1015 cm−2 and energies ranging from 70 keV to 140 keV. A model based on loop coarsening is presented which describes the observed loop annihilation behaviour.
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