G. Mezey

Ion beam mixing in amorphous silicon I. Experimental investigation

Atomic mixing in amorphous Si has been investigated by measuring the irradiation-induced spreading of very thin impurity layers embedded in vacuum-deposited Si as a function of ion species, dose, implantation temperature and impurity species. Samples consisting of ∼10 A layers of Ni, Ge, Pd, Sn, Sb, Pt and Au at depths of 200–600 A were irradiated at temperatures from 77 to 523 K with 50–300 keV Ne+, Ar+, Kr+ and Xe+ ions to doses of about 1014−1017 ions cm−2 and analyzed by 1.5 MeV He+ ion backscattering spectrometry. The morphologies of the samples before and after irradiation were examined by transmission and scanning electron microscopy. The effective diffusion lengths squared, Dt, were deduced from the increases in the variances of the backscattering signals from the impurity species. This quantity was found to vary linearly with the ion dose φ for Kr+ doses ranging from 6.3 × 1014 to 2.0 × 1016 ions cm−2 for the markersthat were investigated (Ge, Sb and Pt). This suggests that Dtφ is a pertinent parameter to characterize the interaction of ion beams with amorphous Si. Dtφ was found to be independent of the temperature during irradiation from ∼80K to ∼300 K for Ni, Ge, Sn, Sb, Pt and Au markers. Mixing of Pd is strongly temperature-dependent over the entire range investigated. Our data are consistent with a linear dependence of Dtφ on νRp, the total nuclear energy loss divided by the projected range.

Hydrogen and deuterium measurements by elastic recoil detection using alpha particles

Abstract This paper presents recoil cross sections for both H and D for alpha particle bombardment in the energy range of 1.6 to 3.4 MeV. For hydrogen and deuterium, a non-Rutherford cross-section was found. For deuterium, a resonance at 2.15 MeV with fwhm of 75 keV was obtained. Calculations were carried out to find the geometrical arrangement where the maximum information concerning the probing depth can be obtained in the energy range of 1–10 MeV. In contrast to the generally accepted 30° scattering angle, another configuration is suggested.

Comparative study on Fe32Ni36Cr14P12B6 metallic glass and its polycrystalline modification bombarded by 2000 keV helium ions with high fluence

Abstract Surface deformations on both amorphous and polycrystalline alloys of METGLASS 2826A caused by high dose bombardment of helium ions of energy 2 and 3.52 MeV were examined by RBS analysis and SEM. Both observations confirm that the resistance of the amorphous form against flaking is 70% higher. The morphology of the metallic glass surface after flaking is characterized by a wave-like structure. For higher energy bombardment and higher current density the surface deformations are characterized by competition of two processes, i.e. exfoliation and flaking presumably due to temperature effects.

Formation of GdSi2 under UHV evaporation and in situ annealing

GdSi2 was prepared under ultrahigh vacuum conditions. Prior to processing, a clean interface was produced using diluted HF dipping. It is pointed out that the ‘‘critical temperature’’ for formation published earlier is probably an artifact and correlation between the interface native oxide and the critical temperature is established.

An investigation of ion-bombarded silicon by ellipsometry and channeling effect

Abstract Both ellipsometry and channeling measurements were applied to investigate how the surface layer of single crystal silicon becomes amorphous when subjected to implantation of different doses. The characteristic behaviour of ellipsometric parameters is reported in correlation with the increasing amount of buried disorder. The transition between the partially disordered and the fully amorphous phase is a breaking point on the ψ-Δ-plot. The ellipsometric parameters of the highest dose implants, where only the thickness of the amorphous layer increases, follow the theoretical spiral curve. Besides in the case of fully amorphous layers, the ellipsometry is a fast and non-destructive method with which to estimate the thickness of these films.

High-dose Ge implantation into 〈100〉 Si☆

Abstract Annealing behavior of radiation damage formed by the implantation of 75 Ge + ions into silicon was measured by channelling, with concentrations of germanium up to 14 at.% in 〈100〉 Si. At higher concentrations after annealing residual damage was located both at the interface of the damaged and undamaged crystal and at the surface. The interface defect was attributed to lattice mismatch. As for the surface defects, despite reasonable implantation conditions, the effect of recoiled oxygen or carbon cannot be ruled out. The kinetics of regrowth was not affected by the presence of Ge atoms. Apart from atoms is stable damaged regions, the Ge atoms showed highly substitutional character.

Exfoliation on stainless steel and inconel produced by 0.8-4 MeV helium ion bombardment

Abstract In order to try and outline the energy dependence of surface deformations such as exfoliation and flaking on candidate CTR first-wall materials, stainless steel and two types of inconels were bombarded by 0.8, 1 and 4 MeV helium ions. All the bombarded spots could be characterized by large exfoliations covering almost the total implanted area. No spontaneous rupture was observed except on one type of inconel where flaking took place right after reaching the critical dose. After mechanical opening of the formations, similar inner morphology was found as in our previous studies on gold [5,6].

Surface deformations and gas escape process studied by quasi-simultaneous multiple-energy He irradiation

Abstract Single crystal silicon wafer covered by Al foil of thickness 5 μm was irradiated quasi-simultaneously by multiple-energy He ions up to the fluence level of 3.3 × 10 19 ions/cm 2 . The implantation was performed by 3.5 MeV 4 He + through a moving Al absorber foil in such a way that a nearly uniform He distribution was obtained extending in both Si and Al to depth intervals of 1.9 × 10 19 Si/cm 2 and of 1.5 × 10 19 Al/cm 2 , respectively. During irradiation the evolution of the He concentration-depth profile was studied in situ by 3 MeV proton RBS analysis. It was found that the He concentration in the Al cover foil, after reaching a maximum value of 30 at.% began to decrease. This accelerated re-emission process was initiated near the inter-boundary surface and extended inward gradually. No significant He escape was observed from the Si up to the applied dose, so at the end of the implantation a He concentraton of 80 at.% has been reached. Exposing both inter-boundary surfaces to SEM, flaking from numerous spots was observed on the Al but not on the Si where only one crater was found. After mechanically breaking the implanted Si wafer and Al cover foil it could be seen on the fracture surfaces that regions containing a large amount of He acquire a sponge-like structure. Channels and large cavities were also observed in this region of the broken Si produced as cracks of interconnected He bubbles. The appearance of the flaking processes clearly demonstrates that even with such a depth distribution the He implanted in the materials in spite of re-emission may reach the critical value for blistering or flaking. The critical concentrations required for the observed surface deformation together with the thickness of the flaked layers evaluated from RBS and SEM observations are discussed.

Flaking and wave-like structure on MeV energy high-dose 4He + bombarded silicon

Abstract In previous work different types of metallic glasses were irradiated under the same experimental conditions by 1 or 2 MeV 4 He + ions up to a fluence of 10 18 ions/cm 2 . It was found that, at a critical dose, flaking occurred and on the flaked surface a wave pattern consisting of periodical elevations was observed. The appearance of this pattern was independent of the material composition and the manufacturing technology of the target as well as on the applied He + energy provided the current was kept low to avoid beam heating effects. Surprisingly a similar pattern was also observed in the present work on the flaked surface of single crystal silicon after irradiation with MeV energy He + ions up to the same fluence. Consequently it is suggested that this pattern is not related to amorphous structure, as was previously thought to be the most probable, but rather seems to be a more general phenomenon. Possible mechanisms of the formation are discussed.

Investigation of solid phase epitaxial regrowth on ion-implanted silicon by backscattering spectrometry and ellipsometry

Abstract During solid phase epitaxial regrowth (SPEG) of ion-implanted silicon the thickness of the remaining amorphous layer decreases with increasing annealing time. This amorphous layer is optically different from the as-implanted one in the wavelength region of 1–10 μm. We have investigated the thermally stabilized state by ellipsometry at a wavelength of 632.8 nm. To establish an appropriate optical model and to check the thickness data obtained from ellipsometry. we used high depth resolution backscattering spectrometry combined with channeling (BS). Using special arrangements in backscattering spectrometry such as glancing detection and 16O(α, α)16 elastic nuclear scattering, we were able to construct realistic optical models both for amorphization and recrystallization experiments. The complex refractive index for as-implanted amorphous silicon is 4.63-0.76i and for thermally stabilized silicon is 4.55-0.35i. The thickness data of amorphous layers obtained by ellipsometry are in good agreement with values deduced from BS.