M. Bianconi

Effect of low dose high energy O3+ implantation on refractive index and linear electro-optic properties in X-cut LiNbO3: Planar optical waveguide formation and characterization

X-cut LiNbO3 crystals were implanted at room temperature by 5.0 MeV O3+ ions with doses ranging from 1.0×1014 to 6.0×1014 O/cm2. Secondary ion mass spectrometry profiles of atomic species migration as well as damage profiles by the Rutherford backscattering channeling technique and refractive index variation were investigated as a function of dose and subsequent annealing conditions. Two different kinds of damage produced by oxygen implantation were seen: near-surface damage correlated to electronic stopping, which causes an increase of the extraordinary refractive index, and end-of-ion range damage generated by collision cascades, which decreases the extraordinary refractive index values. The different nature of the two kinds of damage is also seen by the different temperature conditions needed for recovery. Low loss planar optical waveguides were obtained and characterized by the prism coupling technique.

Damage effects produced in the near-surface region of x-cut LiNbO3 by low dose, high energy implantation of nitrogen, oxygen, and fluorine ions

The damage effects produced in the near-surface region of x-cut LiNbO3 by low dose, high energy implantation of carbon, nitrogen, oxygen, and fluorine ions are investigated as a function of the dose and substrate temperature during the implant process. The damage profiles were obtained by the Rutherford backscattering RBS-channeling technique, whereas the compositional profiles were performed by secondary ion mass spectrometry. The experimental results showed that the mechanisms governing the damage formation at the surface are strongly connected to the interaction of defects produced when the electronic energy loss exceeds a given threshold close to 220 eV/A. In particular, we observed a damage pileup compatible with a growth of three-dimensional defect clusters.

Different methods for the determination of damage profiles in Si from RBS-channeling spectra: a comparison

Abstract RBS-channeling spectra of deep ion implants in silicon were analyzed to extract the displaced atoms depth profiles by different methods. In all cases it was assumed that defects in as-implanted samples can be described as atoms randomly displaced from the lattice sites. In the first method, based on the two beam model, the dechanneling induced by defects was calculated either linearly or following a recently developed semi-empirical formula. In the second method the analyzing beam was divided into a greater number of components to follow the transverse energy distribution of the ions. Finally a three-dimensional Monte Carlo code containing a detailed description of each ion path was used to identify the limits of the previous approaches. It is shown that when high amounts of damage are considered all the methods produce essentially the same profiles. On the contrary they considerably disagree in other cases. Moreover, Monte Carlo calculations indicate that to obtain reliable results it is necessary to take into account a correct description of the channeling energy loss process during ion penetration into a disordered crystal.

Ion implantation induced swelling in 6H-SiC

Ion implantation induced surface expansion (swelling) of 6H-SiC was investigated through the measurement of the step height between implanted and unimplanted areas. The samples were irradiated at room temperature with 500 keV Al+ ions in the dose range 1.25×1014–3×1015 ions cm−2. Swelling was related to dose and the area density of ion-induced damage measured by Rutherford backscattering channeling technique. The observed trend is consistent with the hypothesis that the volume expansion of the ion damaged crystal is proportional to the area density of displaced atoms, plus an additional relaxation occurring at the onset of the crystalline to amorphous transition.

Determination of He electronic energy loss in crystalline Si by Monte-Carlo simulation of Rutherford backscattering–channeling spectra

Spectra of He ions backscattered from thin (001) Si membranes and bulk Si/SiO2 wafers are analyzed with the aid of simulation based on the binary collision approximation. Due to precise control of experimental parameters and detailed fitting of random spectra in thin specimens, the curve of random electronic energy loss per unit length in the energy interval 1.5–3 MeV can be given with an estimated accuracy better than 2%. The electronic energy loss in 〈001〉 alignment is determined through the fit of channeling spectra measured in bulk Si/SiO2 samples. This is performed by the adjustment of the parameters of the semi-empirical model used in the calculation to describe the dependence of He electronic energy loss on the impact parameter of nuclear collisions. The model reproduces data reported in the literature for the 〈001〉 direction, but overestimates 〈011〉 electronic energy loss at energies below 1.5 MeV. The different ability to simulate energy loss in the two orientations is attributed to the limitations of the model to account for the non-uniform distribution of valence electrons in the Si lattice.

Stopping and damage parameters for Monte Carlo simulation of MeV implants in crystalline Si

Semiempirical models of electronic energy loss and damage formation for MeV ions (B, P, As) implanted in silicon at room temperature were investigated through the comparison of measurements with Monte Carlo simulations of both impurity and damage depth distributions. Accurate prediction of dopant profiles in an amorphous target and in a low-dose implanted crystal is achieved by a proper parametrization of well known analytic stopping models. Moreover, to accurately describe the dynamic effects of damage accumulation in medium dose implants, a dependence on ion energy of the efficiency parameter used in the Kinchin–Pease (KP) model must be introduced in the simulation. Such a factor, determined by the fit of the measured integral of defect profiles, is found to decrease for P and As ions with increasing the nuclear energy released to primary recoil atoms, apparently reaching a saturation value of about 0.25. Full cascade simulations show that the increasing fraction of the primary recoils energy spent in e...

On the dynamics of the damage growth in 5 MeV oxygen-implanted lithium niobate

The damage induced by 5 MeV oxygen ion implantation in x-cut congruent LiNbO3 has been investigated by Rutherford backscattering spectrometry channeling technique. The dynamics of the damage growth has been described by an analytical formula considering the separate contributions of nuclear and electronic energy deposition. It has been hypothesized that the nuclear damage provides the localization of the energy released to the electronic subsystem necessary for the conversion into atomic displacements. The strong influence of the preexisting defects on the damage pileup, foreseen by the analytical formula, has been experimentally verified by pre-implanting the samples with 500 keV oxygen ions. It has been shown that a subsequent 5 MeV oxygen implantation step gives rise to an impressive damage accumulation, eventually leading to the total amorphization of the surface, even at moderate fluences.

The Si surface yield as a calibration standard for RBS

Abstract The Rutherford backscattering spectroscopy (RBS) surface height of a pure bulk material can be used as an absolute standard value to calibrate the detector solid angle. This work presents the results of an international collaboration started at the beginning of 1998 to define the surface height of the RBS spectrum ( H 0 ) of Si, amorphized by ion implantation to avoid channeling. The analyses were performed with 1–3 MeV He beams and 170° scattering angle. The detector solid angle was estimated in the different laboratories either by geometrical measurement or by a calibrated standard. The agreement of the experimental H 0 values is of the order ±2%, the claimed accuracy for RBS. The results are also consistent at 2% level with both the stopping power measurements of Konac et al. (1998), and the measurements of Lennard et al. (1999).

Step-index optical waveguide produced by multi-step ion implantation in LiNbO3.

The refractive indexes, material attenuation and damage fractions of a multi-step ion implanted Lithium Niobate (LiNbO3) waveguide were analyzed as functions of the annealing temperatures. An almost flat damage depth profile was designed to reduce the uncertainties related to the indexes profile shape, thus providing a better test-case for the characterizations. The measurements performed on the fabricated optical waveguides confirmed the predicted step-index profiles showing that the light is confined inside the damaged layer. The low measured attenuation (less than 0.8 dB/cm @ 632.8 nm) makes the obtained waveguide attractive for device fabrication.

Vacancy effects in transient diffusion of Sb induced by ion implantation of Si+ and As+ ions

The influence of defects injected by room temperature, high-energy implantation of Si and As ions on the diffusion of Sb marker in Si is investigated. MeV ions induce transient enhanced diffusion (TED) of ion implanted Sb, which increases with increasing the vacancy supersaturation generated in the Sb-doped region by the knock-on recoil mechanism. TED lasts a few minutes for annealing at 800 and 900 °C. The results indicate that at these temperatures the buildup and decay of vacancy supersaturation in the near-surface region occurs on a shorter time scale than the release of interstitials from the buried damage layer. The dominant role of vacancies is also indicated by the very low TED observed in B-doped samples processed under similar conditions. For 1000 °C annealing some effect of the retardation induced on Sb diffusion by interstitials flowing from the deep region is found after 15 min annealing. Preliminary results of defect injection by nonamorphizing medium-energy implants indicate that a smaller,...