Ion Beam Induced Epitaxial Crystallization Process Research Articles

The RBS analysis for a thin amorphous Si layer formed on clean and H-terminated Si(0 0 1) surfaces followed by medium-energy IBIEC treatments

We have investigated the crystallization process of an amorphous Si layer grown on a clean and hydrogen-terminated Si(0 0 1) surfaces by ion beam induced epitaxial crystallization (IBIEC). It is widely known that the amorphous/crystalline (a/c) interface should be atomically controlled to achieve the high-quality Si epitaxy. In this study, we quantitatively clarify the influence of interfacial H amount to the IBIEC rate of the deposited amorphous Si layer. We initially prepared a typical H-free pristine Si(0 0 1)-(2 × 1) surface and two kinds of chemically H-terminated surfaces of as-treated and sequentially annealed at 350 °C in ultrahigh vacuum, corresponding to high (dihydride) and low (monohydride) hydrogen coverage, respectively. An amorphous Si layer was then in-situ deposited on these three types of surfaces by an electron bombardment evaporator at room temperature. The samples were irradiated by 180-keV Ar+ ions with an ion fluence of 5 × 1015 ions cm−2 at 300–500 °C. The Rutherford backscattering (RBS) analysis showed that the deposited Si on the dihydride surface is not crystallized at these temperatures; whereas, that on the monohydride surface is crystallized by Ar+ irradiation at 500 °C. The crystallization on the MH surface was found at significantly higher temperature than that on the H-free clean surface. The behavior of the interfacial H atoms during IBIEC process is discussed by means of RBS analysis.

Synchrotron x-ray multiple diffraction in the study of Fe+ ion implantation in Si(0 0 1)

In this work, x-ray multiple diffraction has been used as a three-dimensional high-resolution probe to study the Fe+ ion implantation process in Si(0 0 1). The semiconducting β-FeSi2 crystallographic phase has been synthesized by Fe ion co-implantation in Si(0 0 1) followed by ion-beam-induced epitaxial crystallization (IBIEC) and thermal treatment. This phase was clearly detected by the conventional techniques, micro-Raman scattering spectroscopy, transmission electron microscopy (TEM) and grazing incidence x-ray diffraction. Synchrotron radiation rocking curves (ω-scans) and mapping of the Bragg surface diffraction (BSD) of the Si matrix, as-implanted, after the IBIEC process and thermally treated, have enabled the detection of co-implanted regions formation that present distinct lattices in comparison with the matrix one clearly observed by TEM. Also, the compressive strain of both regions in depth by rocking curve and in-plane has been determined by using BSD, which is one order of magnitude smaller.

Ion-beam-induced epitaxial crystallization (IBIEC) and solid phase epitaxial growth (SPEG) of Si 1− xC x layers in Si fabricated by C ion implantation

Amorphous Si 1− x C x layers in Si(100) (0.013 ≤ x ≤ 0.032 at peak concentration) formed by 35 keV 12C implantation were crystallized by solid phase epitaxial growth (SPEG) up to 850°C and by ion-beam-induced epitaxial crystallization (IBIEC) with 400 keV Ar or Ge ions at 300–400°C. SPEG process has induced the epitaxial growth up to the surface for samples with x ≤ 0.019 and IBIEC process has induced that for samples with x ≤ 0.025. Rutherford backscattering spectrometry (RBS) measurements have revealed a direct scattering peak due to extended defects around the depth of peak C concentration both in SPEG-grown samples ( x = 0.019) and IBIEC-grown sample ( x = 0.025). X-ray diffraction (XRD) has shown a growth with smaller tensile strain in both SPEG- and IBIEC-grown samples than in fully strained layers. Photoluminescence (PL) measurements at 2 K have shown a strong I 1 line emission in IBIEC-grown samples, which can be attributed to vacancy clustering. The local configuration of defects around C atoms in the IBIEC-grown samples is thought to be an origin of the smaller tensile strain.

Ion beam modification of Si/SiC/Si layer systems

Buried, homogeneous silicon carbide (SiC) layers were formed in (100) and (111) silicon by ion beam synthesis (IBS). In order to study the ion beam induced epitaxial crystallization (IBIEC) of buried SiC layers, the carbide layers were amorphized by irradiation with 2 MeV Si 2+ ions at 300 K, followed by solid-phase epitaxial regrowth of surrounding amorphized silicon layers. IBIEC experiments were performed at 320° and 600°C using a 800 keV Si + beam. It is shown by transmission electron microscopy and electron diffraction that IBIEC works well on buried SiC layers and results in epitaxial recrystallization at considerably lower target temperatures than necessary for thermal annealing. The IBIEC process starts from both SiC/Si interfaces and may be accompanied by heterogeneous nucleation of poly-SiC as well as interfacial layer-by-layer amorphization, depending on irradiation conditions. The structure of the recrystallized regions in dependence of dose, dose rate, temperature and crystal orientation is described in detail.

Photoluminescence studies of epitaxial Si 1− xGe x and Si 1− x−yGe xC y layers on Si formed by ion beam synthesis

Low temperature (2 K) photoluminescence (PL) properties of epitaxial Si 1− x Ge x and Si 1− x−y Ge x C y layers on Si ( x = 0.13 and y = 0.014 at peak concentration) formed by ion beam synthesis (IBS) have been investigated. Samples were prepared by a high-dose Ge with/without C ion implantation (I 2) at room temperature and by subsequent three different crystallization techniques: (i) furnace annealing (FA) process up to 840°C, (ii) ion beam-induced epitaxial crystallization (IBIEC) process with 400 keV Ge or Ar ions at 300–350°C, and (iii) IBIEC process followed by FA process up to 640°C (IBIEC + FA). Although FA-grown Si 1− x−y Ge x C y samples showed G-line (C sSi iC s complex) emission at 0.969 eV, IBIEC-grown samples presented a sharp I 1 non-phonon emission at 1.0193 eV. This indicates that C atoms agglomeration is dominant for FA-grown samples, while a creation of trigonal tetravacancy cluster is dominant for IBIEC-grown samples. On the other hand, (IBIEC with Ge ions + FA)-grown Si 1− x−y Ge x C y samples showed neither G-line nor I 1-related emissions, which indicates that good crystalline Si 1− x−y Ge x C y layers without C agglomeration were formed by this process. In contrast, (IBIEC with Ar ions + FA)-grown samples exhibited novel successive PL vibronic sidebands at 0.98–1.03 eV. From their excitation power dependence measurements, they were found to be associated with exciton bound to defects levels created by Ar + bombardment.

Ion beam induced amorphization and recrystallization of Si/SiC/Si layer systems

Epitaxial, buried silicon carbide (SiC) layers have been fabricated in (100) and (111) silicon by ion beam synthesis (IBS). In order to study the ion beam induced epitaxial crystallization (IBIEC) of buried SiC layers, the resulting Si/SiC/Si layer systems were amorphized using 2 MeV Si 2+ ion irradiation at 300 K. An unexpected high critical dose for the amorphization of the buried layers is observed. Buried, amorphous SiC layers were irradiated with 800 keV Si + ions at 320 and 600°C, respectively, in order to achieve ion beam induced epitaxial crystallisation. It is demonstrated that IBIEC works well on buried layers and results in epitaxial recrystallization at considerably lower target temperatures than necessary for thermal annealing. The IBIEC process starts from both SiC/Si interfaces and may be accompanied by heterogenous nucleation of poly-SiC as well as interfacial layer-by-layer amorphization, depending on irradiation conditions. The structure of the recrystallized regions in dependence of dose, dose rate, temperature and crystal orientation is presented by means of TEM investigations.

Epitaxial crystallization and nucleation during MeV-ion beam processing of amorphous GaAs surface layers

〈100〉-GaAs wafers were preamorphized in a thin surface layer using 50 keV 14N +-ions. Ion beam induced epitaxial crystallization (IBIEC) and interfacial amorphization (IBIIA) were studied as a function of the target temperature using MeV Ar +- or Kr +-ions. Backscattering experiments and electron microscopy show that the IBIEC process is stopped above a critical irradiation temperature due to enhanced ion beam induced nucleation and growth of crystallites. At a fixed dose an optimum irradiation temperature for IBIEC was found, at which the recrystallized layer thickness has a maximum and crystallite formation is negligible. This offers the possibility to crystallize much larger thicknesses than ≈65 nm which stands for the maximum value reported up to now.

Ion beam-induced interfacial growth in Si and silicides

We review the mechanisms and consequences of ion beam-induced epitaxial crystallization (IBIEC) in the transition metal- or rare earth-implanted aSi cSi systems, as determined from in situ transmission electron microscopy (TEM) during irradiation, combined with channeling, high resolution TEM and optical measurements. IBIEC experiments on nm-size crystals confirm previously measured low values of interface roughness in IBIEC. We have performed interfacial growth simulations which indicate that the IBIEC process is, in fact, interface roughness-limited. They also suggest that interfacial growth processes are similar in several respects to surface growth processes, and that they largely determine (i) the growth habit of silicide precipitation, which is dominated by the interfacial energy, (ii) the possibility of trapping a large fraction of the impurities in non-equilibrium sites, leading to significant supersaturation. A consequence of this effect is to allow incorporation of large (over 300-fold supersaturation) Er concentrations in the substitutional sites of the Si lattice, leading to room-temperature photoluminescence (without any oxygen co-implantation). Evidence of a new, thermally induced instability in interfacial growth is presented: it displays both intermittency and very high growth rates, and is strongly affected by ion irradiation.

Structural characterization of ion-beam-induced epitaxially crystallized thin layers of III–V and IV–IV semiconductors

Structural properties of ion-beam-induced epitaxial crystallization (IBIEC) for amorphous layers of GaAs on GaAs(100), BP on BP(100) and Si 1− x Ge x and Si 1− x− y Ge x C y on Si(100) have been investigated. Crystallization was induced by ion bombardment with 400 keV Ne, Ar or Kr at 150 °C for GaAs and at 350 °C for BP. Epitaxial crystallization up to the surface was observed both in GaAs and BP at temperatures much below those required for the solid phase epitaxial growth (SPEG). The growth rate per nuclear energy deposition density has shown a larger dependence on ion dose rate in cases of heavier ion bombardments both for GaAs and BP. Crystallization of a-GaAs with ions whose projected ranges are within the amorphous layer thickness was also observed at 150 °C. Epitaxial crystallization of Si 1− x Ge x and Si 1− x− y Ge x C y layers ( x = 0.13 and y = 0.014 at peak concentration) on Si(100) formed by high-dose implantation of 80 keV Ge and 17 keV C ions has been observed in the IBIEC process with 400 keV Ar ion bombardments at 300–400 °C. Crystalline growth by IBIEC has shown a larger growth rate in Si 1−x−yGe xC y Si} than in Si 1−xGe x Si} with the same Ge concentration for all bombardments under investigation. X-ray rocking-curve measurements have shown a strain-compensated growth in Si 1−x−yGe xC y Si} , whereas Si 1−xGe x Si} samples have shown a growth with strain accommodation.

Amorphization and recrystallization of 6H-SiC by ion-beam irradiation

Amorphization of 6H-SiC with 200 keV Ge+ ions at room temperature and subsequent ion-beam-induced epitaxial crystallization (IBIEC) with 300 keV Si+ ions at 480 °C have been studied by Rutherford backscattering spectrometry/channeling and transmission electron microscopy analysis. Experimental results on amorphous layer thicknesses have been compared with trim calculations in association with the critical energy density model. Density changes during amorphization have been observed by step height measurements. Particular attention has been directed to the crystal quality and a possible polytype transformation during the IBIEC regrowth. The IBIEC process consists of two stages and results in a multilayer structure. In the initial phase an epitaxial growth of 6H-SiC has been obtained. With increasing IBIEC dose the epitaxial growth changes to columnar growth and is stopped by polycrystallization of 3C polytype in the near-surface region.

Ion-Beam-Induced Epitaxy and Solid Phase Epitaxy of Sigec on Si Formed by Ge and C Ion Implantation and their Structural and Optical Properties

AbstractEpitaxial layers of Si1-x-yGexCy on Si(100) (x=0.13 and y=0.014 at peak concentration) were formed by ion implantation of Ge ions and C ions at room temperature (RT) and by subsequent IBIEC (ion-beam-induced epitaxial crystallization) process with 400keV Ge and ar ions at 300-400°C and SPEG (solid phase epitaxial growth) process up to 840°C. Crystallization up to the surface both by IBIEC and SPEG processes has been confirmed with RBS-channeling analysis. X-ray diffraction experiments have demonstrated strain compensation by incorporation of C atoms for IBIEC-grown Si1-x-yGexCy/Si samples, whereas strain accommodation due to C precipitation has been observed for SPEG-grown Si1-x-yGexCy/Si samples. Photoluminescence (PL) observed at 2K from IBIEC-grown samples has shown intense I1 peak with/without I1 related (Ar) peak and that from SPEG-grown samples has shown G line emission. these optical properties could suggest that small vacancy agglomeration is dominant in IBIEC-grown samples and C agglomeration is dominant in SPEG-grown samples, respectively.