A. La Ferla

Ion‐induced epitaxial growth of chemical vapor deposited Si layers

Thin layers of Si were chemical vapor deposited onto as‐received 〈100〉 p‐type Si wafers. The samples were subsequently implanted with 1×1015/cm2, 80 keV As. The native oxide film impedes the growth even at 800 °C, 1 h; instead irradiation with 600 keV Kr++ at 450 °C causes the epitaxial growth of the entire deposited and amorphized Si layer. The sheet resistance of these As‐doped layers (130 Ω/⧠) coincides with that of samples in which the amorphous layer was obtained by As ion implantation only. The value is at least ten times lower than that of the polycrystalline layer doped with the same amount of As.

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.

Influence of a thin interfacial oxide layer on the ion beam assisted epitaxial crystallization of deposited Si

The epitaxial crystallization of chemical vapor deposited Si layers on 〈100〉 Si substrates with a thin interfacial oxide layer was induced by a 600 keV Kr beam in the temperature range 350–500 °C. During irradiation the single crystal‐amorphous interface velocity was measured in situ by monitoring the reflectivity of He‐Ne laser light. We show that a critical irradiation dose is needed before the interfacial oxide breaks down and epitaxial regrowth can take place. This critical dose depends exponentially on the reciprocal temperature with an activation energy of 0.44 eV.

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.

Implants of 15–50 MeV Boron ions into silicon☆

Boron ions were implanted in floating-zone Si〈100〉 wafers of 2 × 103 Ω cm resistivity at energies in the range 15–50 MeV and for doses between 1013 and 1015 cm−2. The implanted samples were furnance annealed in the temperature range 800–1250 °C. The samples were analysed by spreading resistance profilometry and boron concentrations as low as 1013 cm−3 were measured owing to the low value of the bulk doping. The range distribution for the different implant energies is compared with a numerical analysis based on Bethe electronic energy loss, electronic straggling and single large-angle Rutherford backscattering Good agreements are found for the projected range and the straggling; some discrepancies are evidence, however, in the tail of the dopant distribution. The boron diffusion was measured at 1250 °C for several hours, either in nitrogen or in an oxidant ambient. The diffusion during oxidation is enhanced by about 60%, indicating that interstitials at these temperatures migrate over distances of at least 100 μm.

Al‐O complex formation in ion implanted Czochralski and floating‐zone Si substrates

Aluminum ions at 100 MeV were implanted into floating‐zone (FZ) and Czochralski (CZ) grown Si substrates. At this energy the influence of the surface on the subsequent thermal treatment is negligible. In FZ samples the electrical active dose, as measured by spreading resistance profilometry, is independent of the annealing time at 1200 °C. In the CZ samples instead it considerably decreases with time. Secondary ion mass spectrometry analysis in CZ samples have revealed the presence of a multipeak structure around the projected range region for both Al and O signals. In FZ the structure is just detectable. The results imply that the Al‐O complex formation is enhanced by the presence of oxygen but that it is catalyzed by the damage created during the implant. The carrier profiles coincide in both CZ and FZ diffused substrates by predeposition of Al from a solid source, i.e., in damage‐free samples.

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.

Ion beam annealing during high current density implants of phosphorus into silicon

The damage left by high current density∼10 μA/cm2 implants of 120‐keV P+ into 4‐in. (500‐μm‐thick) and 5‐in. (600‐μm‐thick) Si wafers of 〈100〉 orientation has been measured by 2.0‐MeV He backscattering in combination with the channeling effect technique. The fluences ranged between 1 and 7.5×1015/cm2. The amount of disorder is highest at 1×1015/cm2 and then decreases with fluence. The annealing of the amorphous layer takes place by the movement of two and one amorphous–single crystal interfaces for the 500‐ and 600‐μm‐thick wafers, respectively. The experimental data are compared with a beam annealing model based on the temperature‐rise profile, the amount of point defects generated by the ion in the collision cascade volume, and the assumption of a regrowth process governed by an activation energy of 0.25 eV.

Implants of aluminum in the 50–120 MeV energy range into silicon

Abstract Al ions in the 50–120 MeV energy range were implanted in Si substrates for fluences varying between 1 × 10 14 and 3.5 × 10 15 /cm 2 . The electrical and chemical Al distributions were obtained by spreading resistance profilometry and secondary ion mass spectroscopy and the two principal moments, R p and ΔR p , were measured. On low resistivity samples, τ = 0.01 Ω cm , the disorder profile induced by the 100 MeV Al implant was determined from the electrical measurement of the inactivated bulk dopant (boron) distribution. The diffusion coefficient of Al implanted into floating-zone silicon was extracted from the electrical profiles after thermal treatments in the 1000–1290°C temperature range with the result D = 7.4 exp [ −3.42( eV ) kT ] ( cm 2 s ) .

Channeling effects in high energy implantation of N+ in silicon

Abstract Nitrogen implantation in Si single crystals in the 600 keV to 1.4 MeV energy range in random, 〈100〉 and 〈110〉 alignment conditions on 〈100〉 cut silicon wafers was performed. The 6 × 10 13 –2 × 10 16 cm −2 fluence range was investigated. The beam alignment along the various axial directions was precisely checked by monitoring the backscattered nitrogen signal. RBS-channeling analysis was performed in order to measure the damage profiles. The nitrogen concentration profiles were analyzed by SIMS in all the implanted samples. The behaviour of the channeled component and the amorphization process was studied as a function of the dose for all the implantation orientations. The energy loss of the channeled ions was also estimated.