Several recent experiments assessing the role of impurities (C, O), dopants (P, B) and clustering on defect evolution in ion implanted Si are reviewed. Deep level transient spectroscopy measurements were used to analyze the defect structure in a wide range of ion implantation fluences (1×108–5×1013 cm−2) and annealing temperatures (100–800 °C). By using substrates with a different impurity content and comparing ion implanted and electron irradiated Si samples, many interesting features of defect evolution in Si have been elucidated. It is found that only a small percentage, 4–16 % depending on ion mass, of the Frenkel pairs generated by the beam escape direct recombination and is stored into an equal number of room temperature stable vacancy- (V-) and interstitial-type (I-) defect complexes. Identical defect structures and annealing behavior have been measured in ion implanted (1.2 MeV Si, 1×108–1×1010/cm2) and electron irradiated (9.2 MeV to fluences between 1 and 3×1015/cm2) samples in spite of the fact that denser collision cascades are produced by the ions. The O and C content of the substrate plays a major role in determining the point defect migration, the room temperature stable defect structures and their annealing behavior. Annealing at temperatures up to 300 °C produces a concomitant reduction of the I- and V-type defect complexes concentration, demonstrating that defect annihilation occurs preferentially in the bulk. At temperatures above 300 °C, when all V-type complexes have been annealed out, ion implanted samples present a residual I-type damage, storing 2–3 I per implanted ion. This unbalance is not observed in electron irradiated samples and it is a direct consequence of the extra implanted ion. The simple point defect structures produced at low ion fluence (1×108–1×1011 /cm2) anneal at ∼ 550 °C. At higher fluences (∼ 1012–1013/cm2) and for annealing temperatures above 500 °C the deep level spectrum is dominated by two signatures at Ev+0.33 eV and at Ev+0.52 eV that we have associated to Si interstitial clusters. Impurities (C, O and B) play a role in determining nucleation kinetics of these defects, but they are not their main constituents. The dissolution temperature of these clusters indicates that they might store the interstitials that drive transient enhanced diffusion phenomena occurring in the absence of extended defects. Finally, at higher implantation fluence, a signature of extended defects is observed and associated to the presence of {311} defects detected by transmission electron microscopy analyses.

Deep centers related to proton-induced defects and impurities in n-Si were investigated using an in-situ DLTS system. The measurement system was installed in the beamline of NRIM cyclotron. Floating zone (FZ) or Czochralski (CZ) Si was irradiated at a flux of about 30 nA/cm2. The total dose was varied between 1.0 ∼ 7.2 × 1013 ions/cm2. Samples were irradiated at 200 K or 300 K. Their defect concentrations were determined by in-situ DLTS. Quantitative relationship between oxygen and phosphorus concentration and defect creation rates were presented. Isothermal annealing at 250 K was conducted for a CZ-Si sample and the resuflt indicated the meta-stable nature of the carbon defect complex.

Structural changes in thin amorphous SiO2 (a-SiO2) films induced by ion bombardment were examined with FT-IR and ESR techniques. 10MeV H+, 15MeV He+, 2MeV Li+, 4MeV C+ and 30MeV Si6+ ions, which traverse the 200nm thick of SiO2 layer without chemical reaction with SiO2, were used as ion beams with dosage of 1012−1016cm−2. A decrease in the frequency of one peak in the infrared absorption spectrum from 1078cm−1 to 1041cm−1 and an increase of a second peak from 805cm−1 to 830cm−1 were simultaneously observed with cumulative ion dose. The concentration of E' centers has a maximum as a function of dosage in the region of 1–5×1019cm−3. We propose that a reduction of the Si-O-Si bond angle followed by displacement of oxygen is induced with ion bombardment.

This study has investigated the microstructure of ultra high dose (∼ 1018 cm−2) self implantation into Si. Implants have been carried out into both (100) Si and pre-amorphised Si as a function of implant temperature between liquid nitrogen temperature and 350°C. Results show that high dose implantation into completely amorphous Si (a-Si) produces layers which regrow quite well during subsequent solid phase epitaxy. In contrast, implantation into crystalline Si (c-Si) or part amorphous/part crystalline Si can lead to rich and varied microstructures at elevated temperatures, even extending to porous-like structures in some cases. Strong dynamic annealing and agglomeration of points defects in c-Si is thought to be responsible for such behaviour.

Pulsed ion beam treatment of materials provides an attractive alternative to pulsed laser processing for near surface modification of semiconductors, metals and polymers. The transfer of energy to the sample occurs by electronic and nuclear stopping over depths extending to several microns depending on ion species and voltage. A numerical code for modeling the melt and solidification behavior of materials under ion beam processing has been developed. The code and parameter extraction procedures were validated experimentally by comparing simulations with experimental measurements of the melt duration in silicon. The sensitivity of the melt behavior to variations in the beam properties was also investigated. The quiescent nature of the melt was confirmed by measurements of the diffusion of arsenic in the melt. These results demonstrate that simulations of the ion beam treatment can quantitatively match experimental results with no adjustable parameters.

Many crystalline ceramics can be amorphized within high-energy collision cascades whose overlap leads to global structural amorphization. Because the structural rearrangements amount to topological disordering, we have chosen to model these rearrangements using a topological modeling tool as an alternative to molecular dynamics simulations. We focus on the tetrahedral network compounds SiO2, Si3N4, and SiC, each compound comprising corner-sharing tetrahedral units, because they represent increasingly topologically constrained structures. SiO2 and SiC are easily amorphized experimentally, whereas Si 3N4 proves very difficult to amorphize. In this model, we consider the tetrahedron as the base unit, whose identity is largely retained throughout. In a collision cascade, all bonds in the neighborhood of a designated tetrahedron are broken, and we reform bonds in this region according to a set of local rules appropriate to crystalline assembly, each tetrahedron coordinating with available neighboring tetrahedra (insofar as is possible) in accordance with these rules. We generate fairly well connected amorphized structures for SiO2, but run into underconnected networks for Si3N4 and SiC which are irreparable without rebreaking and reforming primary tetrahedral bonds. The resulting structures are analyzed for ring content and bond angle distributions for comparison to the crystalline precursors.

The process of defect formation and the threshold energies for Si and C displacements along various crystallographic directions in cubic silicon carbide (β-SiC) have been examined using molecular dynamics simulations. A combination of Tersoff and first-principles potentials was used to model the inter-atomic interactions. The lowest threshold energies for C and Si displacements were found to be 28 and 36 eV, respectively. These displacement threshold energies show excellent agreement with the results of recent first-principles calculations in SiC and with experimental observations. Simulation of a 10 keV Si cascade yielded values of about 0.1 ps for the cascade lifetime and about 3.5 for the ratio of the number of surviving C defects to Si defects. Anti-site defects were found on both Si and C sublattices. These defects may play an important role in the amorphization of SiC by energetic particle irradiation.

Low energy argon-ion assisted growth of thin molybdenum films (∼ 60 Å) has been studied by molecular dynamics simulations. The effects of a single ion impact are discussed, but more particularly we consider film growth from a manufacturing viewpoint and examine the properties of the completed films. Results for ion-beam assisted deposition are compared with those for unassisted growth (i.e. physical vapor deposition). Surface morphology, defect generation, argon incorporation, and the various responsible atomic mechanisms are discussed.

Argon incorporation and defect creation were studied experimentally. Direct desorption measurements have been used to establish the argon implantation profile. A projected range and range straggle of 0.8 and 3.5 Å were found. Argon is incorporated at substitutional positions. The creation rate of defects by argon was studied by helium desorption spectrometry. A net creation rate of (0.7 ± 0.4) × 10−3 vacancy/argon atom was found. Ion assisted deposition at elevated substrate temperatures shows that all incorporated argon acts as helium trap. Argon fluence variations show an effective cross-section for self sputtering of 31 Å2, a trapping probability of 6.5%, and a maximum achievable argon concentration of 4 × 10−3

Molecular statics and molecular dynamics (MD) simulations based on the embedded atom method (EAM) are used to model the energetics and mobility of tightly bound clusters of selfinterstitial atoms (SIA) in bcc iron. Single and clusters of SIA are directly produced in displacement cascades generated in neutron and high energy charged particle beam irradiations. The clusters are composed of <111> split dumbbells and crowdions with binding energies in excess of 1 eV. Clusters containing specified ‘magic’ numbers of SIA can be described as perfect prismatic dislocation loops with Burgers vector b=a/2<111>; however, the core region is extended compared to an isolated edge dislocation and the loops are intrinsically kinked. As the loops grow, SIA occupy successive edge rows, with minimum energy cusps found at the magic numbers corresponding to filled hexagonal shells. The SIA clusters are highly mobile, undergoing rapid one-dimensional diffusion on their glide prism. The activation energy for glide diffusion is less than 0.3 eV and the corresponding mechanism is related to easy motion of the intrinsic kinks. The kinks, which are preferentially observed on the hexagonal corners, propagate around the loop periphery, resulting in stochastic increments of glide. Image drift forces bias cluster motion near free surfaces and the consequential annihilation of clusters at the surface produces islands bounded by hexagonal ledges. The potential effect of islands modifying surface topology is also discussed. While these simulations are specific to iron, similar behavior is expected for other cubic alloys.

This paper reviews recent R&D activity in advanced beam technologies funded by MITI and JST. A large-scale national project known as AMMTRA (Advanced Material-Processing and Machining Technology Research Association) funded by MITI has made a significant contribution to industrial applications of beam processing by developing high density ion and laser beam equipment. A subsequent program, the ACTA (Advanced Chemical Processing Technology Research Association) project involves development of multi-beam deposition systems for metal and dielectric materials formation including several systems which combine ion and laser beams, ion beams and CVD and plasma, and laser beams with sputtering. NEDO Proposal Based Project and JST (The Japan Science and Technology Corporation)-Exploitation and Application Study Project are fundamentally aimed to transfer technology from university to industry. Research in gas cluster ion beam technology is currently being conducted in the following areas: (i) shallow ion implantation for 0.1 μ m PMOS junction formation, (ii) high rate etching and smoothing for Si, diamond, SiC and metal oxide films and (iii) thin film depositions for optical filter and transparent conductive film. The gas cluster ion beam processes are discussed in comparison with traditional ion beam processing methods which are presently limited by available atomic and molecular ion beams.

In order to interpret the projection range and to reveal the mechanism of damage formation by cluster ion impact, molecular dynamics simulations of a fullerene carbon cluster (C60) impacting on diamond (001) surfaces were performed. When the kinetic energy of C60 is as low as 200eV/atom, C60 implants into the substrate deeper than a monomer ion with the same energy per atom because of the clearing-way effect. The kinetic energy of the cluster disperses isotropically because of the multiple-collision effect, and then a large hemispherical damage region is formed. When the energy of the cluster is as high as 2keV/atom, the cluster dissociates in the substrate, and then cascade damage is formed like in a case of a monomer ion impact. The projection range of incident atoms becomes similar to that of the monomer with the same energy per atom. However, the number of displacements of C60 is larger than the summation of 60 monomer carbons. The displacement yield of fullerene is 4 to 7 times higher than that of monomer carbon. This result agrees with the measurement of the displacements made on sapphire substrates with C60 and C2 irradiation.

A new oxide film formation technique using gas-cluster ion beams has been developed. 02 cluster ions were used to irradiate during the evaporation of metal atoms, and PbOx and In203 films were grown. At the acceleration voltages above 5 kV, polycrystalline PbOx films preferentially oriented to (111) were obtained. A significant smoothing effect was observed with an acceleration voltage as low as 1 kV. An average surface roughness of 0.9 nm was obtained at 7 kV. Oxygen cluster ion beams are also utilized to grow In203 films, which are widely used as conductive-transparent films in flat panel display. In203 was deposited on glass or silicon substrates with simultaneous irradiation with an oxygen cluster ion beam. Highly transparent (80%) and low resistivity (<4×10−4 Ωcm) films were obtained with 7keV oxygen cluster ion beams. Kinetic energy of above 3keV is necessary to obtain low resistivity films. These results clearly indicate that the kinetic energy of the cluster is effectively used to enhance oxidation on the surface without radiation damage, in spite of the high acceleration voltages.

Cluster ion beam processes provide new surface modification techniques, such as surface smoothing, high rate sputtering and very shallow implantation, because of the unique interactions between cluster and surface atoms. To understand interactions with cluster and surface, Scanning Tunneling Microscope (STM) observations have been done for single impact traces.

Highly Oriented Pyrolitic Graphite (HOPG) surfaces were bombarded by carbon cluster ions (Va≤300kV), and large ridges and craters have been observed as a result of single cluster ion impact. The impact site diameters are proportional to the cluster size up to 10 atoms, and increase drastically for cluster sizes above 10. This indicates that non-linear multiple collisions occur only when a local area is bombarded by more than 10 atoms at the same time.

Heavy ion irradiations in the electronic stopping power (Se.) regime have been performed in amorphous materials. Latent tracks have been observed in amorphous semiconductors (a-Ge, a-Si) and their radii have been deduced from a phenomenological analysis in an amorphous metallic alloy, in vitreous silica and “polymer” like amorphous carbon. A transient thermal model is developed describing the energy diffusion by the electron gas, by the atomic lattice and the energy exchange between the two subsystems. According to Fick's law, the classical equations of heat flow in the two subsystems (electrons and atoms) are numerically solved in a cylindrical geometry taking into account the temperature dependence of all the parameters. A simulation of annealing of nuclear collisions induced defects in crystalline iron allows to determine a local temperature. Electronic defect creation occurs when Se. increases and becomes larger than a threshold which is correlated with the appearance of a molten phase. Using such a criterion, the radii of latent tracks are reproduced in both a - Ge and a - Si with the same value of the electron-phonon coupling despite large differences in their lattice thermodynamic parameters. Such a model is applied to amorphous metallic alloy Fe85B15, vitreous silica and amorphous carbon.

The damage cross section velocity effect is studied in LiNbO3, Y3Fe5O12 and SiO2 α-quartz. The application of our thermal spike model reveals that the efficiency of track formation varies by a factor of two in the range of 2–4 MeV/nucleon. The effect is explained by the varying fraction of energy deposition to the lattice involving lattice ions.

The creep velocity of B203 glass fibers under irradiation with 2.5 MeV electrons at low flux ( around 5 1013 e-cm−2s−1) has been studied versus temperature. As under very high energy heavy ions irradiation (1.6 GeV argon), the viscosity is drastically reduced below 300°C. An important difference between the two kinds of irradiation is the occurrence of a compaction phenomenon at the beginning of electron irradiation experiments. The results can be understood by assuming two totally different mechanisms: a relaxation driven by melting of the glass along the path of the ions for very high energy heavy ion irradiations and a relaxation driven by individual radiation induced points defects for high energy electron irradiations.

A pronounced swelling effect occurs when irradiating SiO2 quartz with heavy ions (F, S, Cu, Kr, Xe, Ta, and Pb) in the electronic energy loss regime. Using a profilometer, the out-of-plane swelling was measured by scanning over the border line between an irradiated and a virgin area of the sample surface. The step height varied between 20 and 300 nm depending on the fluence, the electronic energy loss and the total range of the ions. From complementary Rutherford backscattering experiments under channelling condition (RBS-C), the damage fraction and corresponding track radii were extracted. Normalising the step height per incoming ion and by the projected range, a critical energy loss of 1.8 ± 0.5 keV/nm was found which is in good agreement with the threshold observed by RBS-C. Swelling can be explained by the amorphisation induced along the ion trajectories. The experimental results in quartz are compared to swelling data obtained under similar irradiation conditions in LiNbO3

The interactions of cascade remnants with freely migrating defects (FMDs) during dual light and heavy-ion irradiations in Cu-lat.%Au at 400°C were investigated using Rutherford backscattering spectrometry. Near-surface Au depletion driven by 1.5-MeV He ion irradiation was suppressed by concurrent bombardment with 1.2-MeV Ag ions. The dual irradiation effect suggests that shortlived cascade remnants created by heavy ions act as recombination centers for FMDs, reducing radiation-induced segregation (RIS). The effects of the total cascade volume generated by heavyion beams on the suppression of RIS were examined. The investigation revealed when 800-keV Cu and 1.2-MeV Ag ion beams produce nearly the same total cascade volume per second, their suppression effects on 1.5-MeV He-induced Au transport are also nearly equal even though the total cascade volume produced per ion for each are different. This result indicates that the suppression effect of cascade remnants produced by heavy ions depends on the total cascade volume induced per unit time and not on the total cascade volume per ion generated by individual ions of different mass and energy.

New examples of characterization of vacancy-type defects in ion implanted and annealed SiC by the established technique of slow positron implantation spectroscopy are presented. In particular, the estimation of the depths of damaged regions and their change (a) after post-irradiation annealing, or (b) due to variation of substrate temperature during implantation, is addressed.