G. Galvagno

Diffusion and outdiffusion of aluminium implanted into silicon

The diffusion of aluminium in single-crystal silicon has been studied in the temperature range 1000-1290 degrees C. A low implantation dose (1*1014 Al cm-2) was used to avoid dopant precipitation and a high energy (6.0 MeV) to reduce the influence, if any, of the surface. The experimental profiles, measured by spreading resistance, have been fitted taking into account the escape of Al from the Si surface into the ambient atmosphere. A pre-exponential value of 8.88 cm2 s-1 and an activation energy of 3.44 eV have been found in this experiment. When aluminium is implanted through a capping layer, a reduction of the residual amount has been observed at medium energy (300 keV), while no difference has been measured at high energy (6 MeV).

Axial channeling of boron ions into silicon

Abstract Channeling boron implants were performed into (100) and (110) silicon substrates in the energy range 80–700 keV. The dose ranged between 3.5 × 1011 and 1 × 1015 atoms/cm2. The axial channeling concentration profiles of implanted B+ were compared with that obtained for incidence along the random direction of the crystal and with that obtained by implantation in amorphous silicon. The electrical and chemical boron distributions were obtained by spreading resistance and secondary ion mass spectrometry measurements, respectively. The inelastic stopping power, Sc, was extracted from the experimental maximum ranges for the [100] and [110] axis. The energ dependence of the electronic stopping power is given by Sc = KEp with p[100] = 0.469±0.010 and p[110] = 0.554±0.004. Simulations obtained by the MARLOWE code, using the Oen-Robinson impact parameter dependent formula, for the electronic energy loss reproduce quite well the experimental depth profiles.

Al‐O interactions in ion‐implanted crystalline silicon

The formation and dissolution of Si‐O‐Al precipitates have been investigated in Czochralski silicon wafers implanted with 6 MeV Al ions and thermally processed. The data have been compared to the O precipitation in samples implanted with 6 MeV Si or P ions. The amount of precipitated O atoms is about one order of magnitude higher for Al than for Si or P implanted samples. Moreover, a strong gettering of the Al atoms by the silicon dioxide precipitates has been observed. The precipitate evolution has been studied for different annealing times and temperatures. The oxygen precipitation has been simulated by the classical theory of nucleation and growth, with the introduction of new factors that take into account the implant damage distribution, the agglomeration of point defects during the initial stages of the annealing and the oxygen outdiffusion from the sample surface.

Optical and electrical properties of 4H-SiC epitaxial layer grown with HCl addition

The introduction of hydrogen chloride (HCl) in the deposition chamber during the growth of 4H-SiC epitaxial layers allows very high growth rates to be achieved. The properties of the epilayers and the growth rate depend on many parameters such as the growth temperature and the C/Si, Cl/Si, and Si∕H2 ratios. We have used optical and electrical measurements to investigate the effect of the Cl/Si and Si∕H2 ratio and growth temperature on the epitaxial growth process. The growth rate increases with increasing Si∕H2 ratio and higher growth rates are obtained when HCl is added to the gas flow. Optical microscopy shows an improvement of the surface morphology, and luminescence measurements reveal a decrease in the concentration of complex defects with increasing Cl/Si ratio in the range of 0.05–2.0 and with increasing growth temperature from 1550 °C to 1650 °C. The electrical measurements on the diodes realized on these epitaxial layers show a decrease of the leakage current with increasing Cl/Si ratio and growt...

Al‐Based Precipitate Evolution during High Temperature Annealing of Al Implanted in Si

Al-based precipitate evolution for 80 keV Al ions implanted in Si has been investigated. Precipitates are formed during high temperature annealings of 1 [times] 10[sup 15]/cm[sup 2] implanted samples. They are located at two depths where Al concentration peaks are detected. Al atoms are gettered into the extended defects present in the crystal and/or precipitate when their concentration is higher than the solid solubility value at the annealing temperature. Increasing annealing time, precipitates dissolve out and only a small fraction of atoms diffuses into the sample, meanwhile the greater part evaporates from the sample. At 1 [times] 10[sup 13]/cm[sup 2] dose Al concentration is below the solid solubility limit. The secondary defects are not detected and the dopant profile does not display anomalous peaks. Moreover, all the implanted Al is electrically active and remains in the sample during the first instant of annealing. At higher annealing times it diffuses out of the sample reducing the residual dose.

Very High Growth Rate Epitaxy Processes with Chlorine Addition

The growth rate of 4H-SiC epi layers has been increased by a factor 19 (up to 112 μm/h) with respect to the standard process with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl have been characterized by electrical, optical and structural characterization methods. An optimized process without the addition of HCl is reported for comparison. The Schottky diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process with the advantage of an epitaxial growth rate three times higher.

Drift mobility in 4H-SiC Schottky diodes

In this work, the temperature dependence of the mobility along the c axis in 4H-SiC was determined from the current voltage (I‐V) characteristics of Schottky diodes in the temperature range 80–700 K. The procedure used series resistance measurements in Schottky diodes for extracting the mobility values in the epitaxial layer. For a dopant concentration of 1.2×1016cm−3, at room temperature, a mobility value of 724cm2∕(Vs) was found, which decreased to 48.6cm2∕(Vs) at 700 K. In the temperature range 200–700 K, a dependence of the mobility as T−3 was determined.

Channeling implants of B ions into silicon surfaces

Abstract The profiles of boron ions impinging along the axis of silicon single crystal at energies in the 80–700 keV range were measured by SIMS. By a simple subtraction procedure the distributions for aligned incidence of the beam were decomposed into a random and into a channeled profile. The corresponding mean ranges, Rr , for random and Rc for channeled particles, as well as the “maximum” range Rm for well-channeled particles were compared with values calculated by appropriate theoretical models. For well-channeled particles the reduced electronic stopping power in the center of the channel was calculated assuming an exponential dependence of the impact parameter. It turned out. that all measured values could be reproduced by this theoretical model.

Epitaxial Layers Grown with HCl Addition: A Comparison with the Standard Process

The growth rate of 4H-SiC epi layers has been increased by a factor 3 (up to 18μm/h) with respect to the standard process with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl have been characterized by electrical, optical and structural characterization methods. An optimized process without the addition of HCl is reported for comparison. The Schottky diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process with the advantage of an epitaxial growth rate three times higher.

Formation and annealing of defects during high-temperature processing of ion-implanted epitaxial silicon: the role of dopant implants

Abstract We have investigated the optical and structural characteristics of defect evolution during high-temperature annealing of keV-ion-implanted epitaxial silicon using optical microscopy (OM), photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Postimplantation annealing in oxygen ambient resulted in oxidation-induced stacking faults (OISFs) and dislocations. The PL spectrum of these samples is dominated primarily by a dislocation-related D1 line, which is particularly strong in Al-implanted samples as a consequence of the enhanced formation of dislocations with Al implantation. Comparative analysis of the PL signature and OM observations of defects for different implants suggests that D1 and D2 lines result from dislocations rather than in the OISFs. Indeed, it is found that OISFs act as a nonradiative recombination channel in the luminescence of Si. PL studies of N 2 -annealed samples indicate the formation of nonradiative defect centres. In the case of dopant implants, after rapid thermal annealing (RTA) for 2 min in N 2 ambient, the specific signature of extended defects was found from PL studies, while TEM analysis reveals the presence of precipitates located in a region with a high dislocation density. In comparison with other dopants, Al implants show an enhanced formation of extended defects, and they are found even at a depth beyond the end-of-ion range damage.