Ion Beam Induced Epitaxial Crystallization Research Articles

Dose rate dependence of the ion-beam-induced epitaxial crystallization in silicon

The dose rate dependence of 300 keV Si + ion-beam-induced epitaxial crystallization (IBIEC) of a 200 nm thick amorphous silicon surface layer at 400°C is investigated in the range from 3 × 10 10 up to 3 × 10 13 cm −2 s −1. The amorphous silicon layer thicknesses have been measured by RBS/C. In order to obtain very precise results and to rule out depth dependent effects the ion doses were chosen so that for any dose rate the regrown thickness is about half the original layer thickness. It has been found that the regrowth rate (regrown thickness/ion dose) is indirectly proportional to the fourth root of the dose rate. This is in excellent agreement with theoretical predictions from a point defect diffusion model of IBIEC considering pairwise defect annihilation.

Ion Beam Induced Epitaxial Crystallization of Single Crystalline 6H-SiC

ABSTRACTFor the first time, ion beam induced epitaxial crystallization (IBIEC) has been found in SiC. The effect of 300 keV Si+ irradiation through an amorphous surface layer in single crystalline 6H-SiC at 477±5°C has been investigated by RBS/C and XTEM. A shrinkage of the amorphous layer was found after ion irradiation at this temperature which is caused by both an ion dose independent thermal regrowth of about 20 nm and an additional ion beam induced epitaxial crystallization with a rate of about 1.5 nm/ 1016 cm-2.

Ion beam induced epitaxial crystallization of sapphire

The epitaxial recrystallization of an amorphous Al 2O 3 layer, formed by In ion implantation, on a crystalline substrate has been induced by high energy Si ion irradiation at a temperature as low as 400°C. At such a temperature, the rate of thermally induced recrystallization is negligible. The extent of crystallization of an amorphous layer and the redistribution of In atoms during ion beam induced epitaxial crystallization (IBIEC) have been compared with thermal annealing behaviour at 700°C. The most striking difference between the two annealing regimes are that IBIEC at low temperatures results in (1) more extensive epitaxy which is insensitive to the presence of In, and (2) negligible In redistribution.

Ion Beam Induced Epitaxial Crystallization of Single Crystalline 6H-SiC

ABSTRACTFor the first time, ion beam induced epitaxial crystallization (IBIEC) has been found in SiC. The effect of 300 keV Si+ irradiation through an amorphous surface layer in single crystalline 6H-SiC at 477+5°C has been investigated by RBS/C and XTEM. A shrinkage of the amorphous layer was found after ion irradiation at this temperature which is caused by both an ion dose independent thermal regrowth of about 20 nm and an additional ion beam induced epitaxial crystallization with a rate of about 1.5 nm/ 1016 cm−2.

Comparison Between Ion-Beam and Thermal-Annealing Induced Solid Phase Epitaxy in Fe-Implanted Si

Rutherford backscattering spectrometry and transmission electron microscopy were used to compare thermally induced solid phase epitaxy (SPE) with ion-beam induced epitaxial crystallization (IBIEC) of Fe-implanted Si (001). It was found that thermal annealing leads to both Si SPE and β-FeSi2 precipitation at 520°C, but has no visible effect at 320°C. In contrast, Si SPE and FeSi2 precipitation occur at both 320 and 520°C, when ion irradiation is introduced. The precipitates grow epitaxially as γ-FeSi2 at 320°C, but consist of both β-FeSi2 and γ-FeSi2 at 520°C. It was also found that thermal annealing at 520°C results in Fe segregation toward the surface, while IBIEC basically retains the as-implanted Fe profile.

Formation of SiGe and SiGeC Layers on Si by Ge and C Ion Implantation and Subsequent Ion-Beam-Induced Epitaxial Crystallization

ABSTRACTFabrication of Si1-xGex and Si-1-x-yGexCy layers on Si(100) by high-dose ion implantation of 72Ge ions without and with 12C ions and subsequent high-energy and low-energy ion-beam-induced epitaxial crystallization (IBIEC) has been investigated. Structural properties of the surface layers were observed by RBS-channeling technique. Si(100) wafers were implanted with 150keV and 80keV Ge ions at room temperature so as to produce a peak concentration of Ge amounting to approximately 2 and 14 at.%, respectively. C ions were additionally implanted to a fluence of 10% of Ge concentration for the SiGeC samples. IBΓEC experiments performed with 400keV 18Ar ion bombardments have induced crystallization of the amorphous layers of SiGe and SiGeC on Si up to the surface at 400°C for both samples with low Ge concentration (2%) and high Ge concentration (14%). IBIEC using 72Ge ions with energies whose projected ranges are within the amorphous layer was alternatively performed for SiGe layer on Si. Bombardments of 140keV and 40keV Ge ions at 400°C have induced crystallization up to the surface with a slight disorder in the grown layer. Present experimental results suggest a novel ion beam synthesis method of fabrication of SiGe (SiGeC) on Si at low temperatures.

Low-energy ion-beam-induced epitaxial crystallization of GaAs

Properties of the ion-beam-induced epitaxial crystallization (IBIEC) of thin layers of amorphous GaAs with a thickness of about 110 nm formed by As ion implantation have been investigated by using low-energy Ar and Kr ions with their projected ranges within the amorphous layer thickness. Recrystallization of the amorphous layer due to bombardments of Ar ions with energies higher than 60 keV and Kr ions with those higher than 110 keV was observed to proceed up to the sample surface in a layer-by-layer growth manner with residual defects remaining in the recrystallized layer. After eliminating the sputtering effect, regrowth rates per ion fluence were observed to have pseudo-linear dependence on incident ion energy whereas regrowth rates per nuclear energy deposition density showed to vary strongly as a function of incident ion energy. Present results suggest a crucial role of defect formation and its migration in the amorphous layer in the IBIEC.

Solid-Phase Epitaxial Crystallisation of GexSi1-x Alloy Layers

ABSTRACTThermally-induced solid-phase epitaxial crystallisation (SPEC) and ion-beam-induced epitaxial crystallisation (IBIEC) of amorphous GexSi1-x alloy layers is examined for three different starting structures: a) strain-relaxed alloy layers of uniform composition, b) strained alloy layers of uniform composition, and c) Ge implanted Si layers. Thermal annealing experiments show that the activation energy for strain-relaxed alloys is higher than that expected from a simple extrapolation between the activation energies of Si and Ge, and exceeds that of Si for x ≤ 0.3. Experiments on thin strained layers show that MBE grown strained layers which are stable during annealing at 1100°C for 60 s are also fully strained after SPEC, whereas layers which relax during annealing at 1100°C also relax during SPEC. Experiments on ion-implanted GeχSiι_x structures show that fully strained Si/GexSi1-x /Si heterostructures can be fabricated for ion fluences below a critical fluence, and as for uniform alloy layers that this critical fluence is accurately predicted by equilibrium theory. Strain relaxation during SPEC of uniform alloys and implanted structures is shown to be correlated with a sudden reduction in crystallisation velocity which is believed to be caused by stress-induced roughening or faceting of the crystalline/amorphous interface. IBIEC of thick (800 nm) implanted layers is shown to be limited by competition from ion-beam induced random crystallisation, while thin (120 nm) uniform alloys and implanted structures are shown to crystallise ephaxially and to exhibit similar behaviour to thermally annealed samples under certain conditions.

Ion-beam-induced epitaxy in B-implanted silicon preamorphized with Ge ions

The ion-beam-induced epitaxial crystallization (IBIEC) of B +-implanted Si(100) layers, which are preamorphized by Ge + ion implantation, has been studied by a 400 keV Ar +-ion irradiation at temperature ranges from 300 to 475°C. A minimum Rutherford backscattering yield of the regrowth layer is improved to 7.8% for an Ar + ion dose of 1.3×10 16/cm 2 at a substrate temperature of 400°C. The activation energy for IBIEC is estimated to be 0.22 eV. A peak of the depth B profile evaluated by secondary ion mass spectroscopy is shifted to about 35 nm toward the surface after Ar + ion irradiation. However, the electrical activation of the implanted B atoms is restricted within about 10%. It is also demonstrated that the lateral crystallinity of the amorphous layer can be recovered selectively by the IBIEC technique.

Ion-beam-induced simultaneous epitaxial growth of α- and cubic FeSi 2 in Si (100) at 320°C

By combining room temperature Fe ion implantation in Si (100) at concentrations of 2–18 at.% with 500 keV Si ion beam-induced epitaxial crystallization at 330°C, we have simultaneously synthesized the cubic and the tetragonal FeSi 2 phases. Structural characterization was performed by cross-sectional transmission electron microscopy, Rutherford backscattering spectroscopy and ion channeling. The epitaxial relations to the Si matrix were determined. The results indicate the importance of the interfacial energy for the formation of the α-phase whose equilibrium formation temperature is above 950°C.

Dose Rate Dependence of the Ion Beam Induced Epitaxial Crystallization in Silicon

ABSTRACTThe dose rate dependence of 300 keV Si+ ion beam induced epitaxial crystallization (IBIEC) of a 200 nm thick amorphous silicon surface layer at 400°C is investigated in the ion dose rate range from 3 · 1010 up to 3 · 1013cm2s−1. The experimental results are compared with theoretical predictions from several models. Special emphasis is given to the influence of the depth distribution of the nuclear energy deposition on the growth process during both the experiment and the theoretical analysis. According to our experimental results the IBIEC rate is indirectly proportional to the fourth root of the dose rate. This is in excellent agreement with a point defect diffusion model of IBIEC considering pairwise defect annihilation.

Ion Beam Induced Crystallization of Amorphous Si from NiSi2 Precipitates: An In Situ Study

ABSTRACTBy first growing NiSi2 precipitates in a-Si and then irradiating with a 150 keV Si beam, we have studied ion beam induced epitaxial crystallization (IBIEC) of Si initiated at a-Si/NiSi2 precipitate interfaces. The growth shape and its temperature dependence are studied in-beam via in situ transmission electron microscopy. Interface roughening is evidenced. Preliminary results for the Co-Si system are also reported.

Ion-beam-induced epitaxial crystallization and amorphization in silicon

The ion-beam-induced epitaxial crystallization (IBIEC) and planar amorphization of amorphous Si (a-Si) layers onto single-crystal Si substrates is reviewed. In particular, the dependence of the process on substrate temperature, on substrate orientation and on the energy deposited by the impinging ions into electronic and elastic collisions is treated in detail and discussed. Emphasis is also given to the influence of impurities on IBIEC, where a variety of different phenomena are observed. For instance, fast diffusers, such as Au, are seen to be swept by the moving c-a boundary and present intriguing segregation profiles. Slow diffusers such as As or O, on the other hand, have not enough mobility to move over long-range distances even in the presence of irradiation, but they can strongly modify the kinetics of IBIEC. Dopants such as B, P and As, for example, enhance the ion-induced growth rate by a factor of 2–3, while O retards it. It is also shown that by decreasing the substrate temperature (or by increasing the ion flux) IBIEC can be reversed resulting in a planar layer-by-layer amorphization. This phenomenon evidences the unique non-equilibrium features of ion-assisted phase transitions in silicon which are the result of a dynamic balance between defect production rate and defect annihilation rate. These data are discussed, mainly in comparison with the purely thermally activated growth of a-Si and a possible explanation of the observed phenomena is presented in terms of a simple model. Finally, new possible applications of the phenomenon, such as the ion-induced regrowth of deposited Si layers and of deposited GeSi heterostructures, are illustrated, demonstrating the high potentialities of ion-beam processing in producing epitaxial layers in a non-conventional manner.

Phenomenological description of ion-beam-induced epitaxial crystallization of amorphous silicon.

In this paper we report detailed experimental measurements on the dependence of the ion-beam-induced epitaxial crystallization (IBIEC) of amorphous silicon on dopant concentration. The results show that the presence of B, P, and As dopants enhances IBIEC. In particular a logarithmic relationship between the ion-induced growth rate and dopant concentration is found for all of the impurities. In order to explain this behavior a phenomenological model of IBIEC will also be presented. The model postulates that the same defect is responsible for both thermal and ion-beam annealing. It combines the structural and electronic features of the description proposed by Williams and Elliman for conventional thermal epitaxial growth, with the intracascade approach of Jackson to the ion-assisted regrowth. Defects responsible for IBIEC are identified in kinklike steps formed onto [110] ledges at the crystalline-amorphous interface. These kinks are assumed to be generated thermally within the thermal-spike regime of each collision cascade. After defect generation, then, our approach follows Jackson's as far as the temporal evolution of defects is concerned. The model can account for all of the experimental results previously explained by the Jackson model and, moreover, can account for the doping and orientation dependences of IBIEC. This description is discussed and quantitatively compared with the experimental data.

Ion-beam-induced epitaxial crystallisation (IBIEC) of amorphous silicon layers produced by chemical vapour deposition

Amorphous silicon layers deposited by chemical vapour deposition on monocrystalline silicon substrates were epitaxially recrystallised by ion beam induced epitaxial crystallisation at 400°C after preamorphisation of the transition region layer/substrate. In this manner, a layer with a thickness of 400 nm was recrystallised by implanting silicon ions at 330 keV with a dose of about 1×1017cm−2.

Ion-beam induced crystallization and amorphization at a crystalline/amorphous interface in silicon

Previous investigations have shown that solid-phase epitaxial crystallization (SPEC) can be catalyzed by defects which are produced by ion bombardment [1–3]. This so-called ion-beam induced epitaxial crystallization (IBIEC) takes place at temperatures which are low compared to those required to induce equivalent thermal-only epitaxial crystallization. Using Rutherford backscattering/ion channeling, we have investigated the temperature dependence of the crystalline/amorphous (c/a) interface dynamics in self-amorphized silicon during irradiations with 1.5 MeV Xe ions. At temperatures above 260°C, the Xe-ion beam induced crystallization with an activation of ≈ 0.24 eV, as was previously reported for MeV Ne-ion irradiations [2]. However, at temperatures below a critical temperature of ≈ 220°C, the interface displacement is reversed and the amorphous phase grows at the expense of the crystalline phase. We choose to call this latter phenomenon ion-beam induced interface amorphization (IBIIA). At temperatures above and below ≈ 220°C, the c/a-interface displacement is linearly dependent on Xe-ion fluence. Transmission electron microscopy studies of these two regimes reveal that very similar interface structures are associated with both IBIEC and IBIIA, and these interfaces are remarkedly smoother than the c/a interfaces which are produced in the present studies either by preannealing self-amorphized silicon at 450°C for 15 min or by Xe ion end-of-range damage. The results of this work identify. IBIIA and IBIEC to be inverses of one another for the 1.5 MeV Xe-ion case and this reversibility is discussed in terms of a model which considers the relative contribution of defect complexes to the total free energy of the crystalline phase.

Defect Structures Generated by Buried Amorphous Layer Regrowth in <100> Arsenic Implanted Silicon

AbstractPlan-view and 90° cross-sectional TEM examination was used to investigate the correlation between the type of amorphous layer produced and the resulting defect structure observed upon annealing. Both <100> and <111> Si wafers were ion implanted with high energy (190 keV) arsenic over a range of doses(1 × 1015/cm2 to 5 × 1015/cm2). A Wayflow endstation was used allowing ion beam induced epitaxial crystallization (IBIEC)[8] or dynamic annealing of the sample to occur. Implanted <111> Si is shown to form a continuous amorphous layer up to the surface, while <100> implanted Si forms a buried amorphous layer. The regrowth of the buried x-layer by furnace annealing is shown to be responsible for the formation of shear type dislocation loops at the interface where the two x/c regrowth fronts meet (catagory IV defects).[7] However if the buried layer is regrown by dynamic annealing a different structure results.In addition to using <111> wafers, other parameter changes which resulted in the formation of surface amorphous layers included decreasing the implant energy from 190 keV to 100 keV, or implanting the wafer at 77K instead of using the Wayflow endstation. Regrowth of the surface amorphous layers produced by these changes did not result in the formation of shear type dislocation loops. Further annealing of the 100 keV Wayflow implant and the 190 keV 77K implant at 900°C for 30 minutes resulted in the formation of small prismatic extrinsic dislocation loops beneath the location of the original amorphous/crystalline interface (catagory II defects).[71]