C. Clerc

Progress report on Aramis, the 2 MV tandem at Orsay

Abstract Aramis is a home built multipurpose 2 MV electrostatic tandem accelerator. A large variety of ions are available for high energy implantation. Characterization possibilities are also quite large in the Van de Graaff mode owing to the Penning positive ion source in the terminal. A second beam line is now available that sends the beam into the target chamber of the 200 kV medium current implanter. We will provide a progress report on the machine and present some results regarding in situ studies of multilayer mixing and implanted silicide layers

MeV gold irradiation induced damage in α-quartz: Competition between nuclear and electronic stopping

Abstract Damage creation in crystalline α-quartz by irradiation is studied using gold ions of energies between 0.5 and 10 MeV. For all ions, the total stopping power (d E /d x ) tot has a value of about 4.5 keV/nm, whereas the contribution of the electronic stopping power ranges from 0.93 keV/nm at 0.5 MeV to 3.6 keV/nm at 10 MeV. This variation allows us to test which role the nuclear and the electronic collisions plays for the damage processes. The kinetic of the ion induced damage was determined by channeling RBS and the volume increase by profilometry. Single ion impacts create damage when electronic stopping dominates, while several impacts are necessary to achieve damage in the nuclear stopping regime. A detailed analysis allows us to deduce the damage cross-sections of the two processes. The electronic stopping power of damage creation appears above an electronic d E /d x threshold of 1.4±0.3 keV/nm.

Damage kinetics in MeV gold ion – Irradiated crystalline quartz

Abstract Damage creation in crystalline α -quartz under gold irradiation was studied at 1.0 and 5.5 MeV using the ARAMIS accelerator at CSNSM (Orsay). Although at these energies the total stopping powers are nearly equal (respectively, 4.20 and 4.46 keV nm −1 ), the electronic stopping power is only 1.23 keV nm −1 (25% of the total) at 1 MeV while it reaches 2.75 keV nm −1 (62% of the total) at 5.5 MeV. The electronic stopping power threshold for damage creation in α -quartz is about 1.8 keV/nm [1] . The experiment thus allows us to follow the damage production kinetics due to nuclear collisions (at 1 MeV) versus electronic collisions (at 5.5 MeV). The damage was determined by channeling Rutherford backscattering (RBS-C) using the 2 MV Van de Graaff at DPM (Villeurbanne). Single ion impacts create damage when electronic stopping dominates, while several impacts are necessary to achieve complete damage when nuclear stopping dominates. Differences in damage efficiencies will be discussed.

THE 3-D PROFILING OF B IONS IMPLANTED INTO SI

Abstract Recently the lateral (2-D) profiling of B ions implanted into crystalline Si has been measured using various tomography techniques. By the aid of Monte Carlo simulations the 3-D distribution is examined for the case of 80 keV B ions implanted into (100) Si. We present an asymmetric function expressing the lateral straggling versus depth. This is an exponential function whose component is a third order polynomial. The parameters involved bear the dependence of the incident angle on the 2-D profiles, including the cases of aligned and random incidence.

Implantation-induced disorder in amorphous Ge: Production and relaxation

Abstract Extended X-ray absorption fine structure and Raman spectroscopy have been utilised to measure implantation-induced micro-structural modifications in amorphous Ge including increases in bond length, broadening of the bond-angle distribution, and non-Gaussian static disorder as functions of ion dose. The resulting evolution of the inter-atomic distance distribution, over an ion dose range extending two orders of magnitude beyond that required for amorphisation, demonstrates the influence of implant conditions on amorphous phase structure. Results are attributed to increased fractions of three- and fivefold coordinated atoms as a means of accommodating implantation-induced point defects in the amorphous phase. In contrast, a common, ion-dose-independent structure is apparent following low-temperature, thermally-induced relaxation as consistent with the annealing of point defects in the amorphous phase. Structural relaxation is manifested by reductions in both bond-length and bond-angle distortion and the relaxation enthalpy for each component has been calculated separately.

THE TWO-DIMENSIONAL PROFILING OF LIGHT IONS INTO CRYSTAL

Abstract Using a computer simulation we examine the dependence of the incident tilt angle θ and the incident energy E0 on two-dimensional concentration profiles of implanted ions into crystalline targets. For each profile, the quantity called the ‘microscopic lateral straggling’ ΔRL(z) is evaluated as a function of depth z. The values ΔRL(z) produced in the case of aligned incidence definitely differ from those of random incidence, in the peak height, the peak depth, and the peak width. When implanted into random direction, the depth at the maximum of ΔRL(z) and the FWHM (full width at half maximum) are very close to the mean projected range Rp and its straggling ΔRp, respectively. In the case of aligned incidence, however, such a correlation is not seen. In addition, the detailed behavior of ΔRL(z) is shown by an exponential function whose exponent is the third-order polynomial of z. It expresses the whole profile of ΔRL(z), including asymmetry due to either channeling- or random-tail, without connecting the two functions. Our expression is available for B ions into (100) Si with energies up to 500 keV. Four coefficients involved in the equation carres the dependence of both θ and E0.

Structure and low-temperature thermal relaxation of ion-implanted germanium

The structure of implantation-induced damage in Ge has been investigated using high resolution extended X-ray absorption fine structure spectroscopy (EXAFS). EXAFS data analysis was performed with the Cumulant Method. For the crystalline-to-amorphous transformation, a progressive increase in bond-length was observed without the presence of an asymmetry in interatomic distance distribution (RDF). Beyond the amorphization threshold the RDF was dose dependent and asymmetric, where the bond-length and asymmetry increased as functions of ion dose. Such an effect was attributed to the formation of three- and five-fold coordinated atoms within the amorphous phase. Low-temperature thermal annealing resulted in structural relaxation of the amorphous phase as evidenced by a reduction in the centroid, asymmetry and width of the RDF, as consistent with a reduction in the fraction of non four-fold coordinated atoms. The results have been compared to other EXAFS studies of amorphous Ge, and it is suggested that the range of bond-lengths reported therein is related to the sample preparation method and state of relaxation.

The impact parameter dependence of the energy straggling of protons into GaAs

Abstract The present work examines the impact parameter dependence of the electronic straggling, Q e , for protons implanted into GaAs, by comparing the two cases of aligned and random implantations. A Monte-Carlo simulation program based on the ACOCT code is used, and the results are compared to ion profile measurements obtained by SIMS and ERDA. The simulation yields electronic stopping power, S e , and electronic straggling, Q e values for ions inside the crystal all along their slowing-down process. The energy dependence of Q e is also derived. The calculations reveal the impact parameter dependence of Q e qualitatively well.

Range straggling of 1 H and 2 H in crystalline matrices

The present work deals with the energy dependence of the range straggling, ΔR p , of 1 H and 2 H ions implanted into GaAs in random direction. Computer simulations using the ACOCT code are compared to results obtained by SIMS and ERDA. Simulations reproduce reasonably well experimental data at ion energies less than 200keV. They reveal that both the electronic stopping power, S e , and energy straggling, Q e , are much larger than the corresponding nuclear ones, respectively S n and Q n . Thus Q e can be evaluated by means of the incident energy dependence of AR P , taking advantage of the use of two isotopes of hydrogen: 1 H and 2 H.