Depth Distribution Of Damage Research Articles

Non-Destructive Quantification of In-Plane Depth Distribution of Sub-Surface Damage on 4H-SiC Wafers Using Laser Light Scattering

The development of non-destructive quantitative evaluation techniques for the in-plane depth distribution of sub-surface damage (SSD) layer induced by mechanical processing of chemical mechanical polishing (CMP) finished SiC wafers is essential to reduce the occurrence of crystal defects during epitaxial growth. Until now, no wafer inspection method has been able to nondestructively and quantitatively assess the in-plane depth distribution of the SSD. This study investigates the correlation between the scattered light intensity measured nondestructively by the Laser light scattering (LLS) method and the SSD depth estimated by destructive inspection using the Dynamic AGE-ing® method, a sublimation-controlled etching and growth process, to develop a novel non-destructive SSD inspection method. As a result, it was found that there is an exponential relationship between the scattered light intensity by the LLS method on the bare wafer surface and the depth of the SSD layer that contributes to the formation of in-grown stacking faults (IGSF) during subsequent epitaxial growth. The results show that SiC wafer inspection using the novel LLS method, which introduces this relational equation, enables non-destructive and quantitative evaluation of SSD depth and in-plane distribution.

Temperature effect on irradiation damage in equiatomic multi-component alloys

Multiprincipally designed concentrated solid solution alloys, such as high entropy alloys (HEA) and equiatomic multi-component alloys (EAMC-alloys) have shown much promise for use as structural components in future nuclear energy production concepts. The irradiation tolerance in these novel alloys has been shown to be superior to that in more conventional metals used in current nuclear reactors. However, studies involving irradiation of HEAs and EAMC-alloys have usually been performed at room temperature. Hence, in this study the irradiation damage is investigated computationally in two different Ni-based EAMC-alloys and pure Ni at four different temperatures, ranging from 138 K to 800 K. The irradiation damage was studied by analyzing point defects, defect cluster sizes and dislocation networks in the materials. Dislocation loop mobility calculations were performed to help understanding the formation of different dislocation networks in the irradiated materials. Utilizing the knowledge of the depth distribution of damage, and using simulations of Rutherford backscattering in channeling conditions (RBS/c), we can relate our results to experimental data. The main findings are that the alloys have superior irradiation tolerance at all temperatures as compared to pure Ni, and that the damage is reduced in all materials with an increase in temperature.

Damage formation and recovery in Nd:CNGG crystal by carbon ion implantation

The formation of damage in neodymium doped calcium niobate gallium garnet was investigated after irradiation with 100 keV and 6 MeV C ions at room temperature. The damage was quantified by means of Rutherford backscattering spectrometry in channelling configuration (RBS/C). In order to cope with the superposition of the signal from Nb, Ga and Ca atoms, a special procedure was developed to reconstruct RBS/C spectra yielding the depth distribution of damage. For 6 MeV C ions, the high electronic energy loss of the ions significantly contributes to damage formation. In the nuclear regime, at low ion fluences, point defects are produced. Nucleation and growth of a second type of damage finally results in an amorphous layer. The final damage state is stable up to 600 °C. At 700 °C part of the implanted layer recrystallizes. Annealing at 800 °C decreases the remaining damage concentration from 100% to about 70%.

Effect of an increase in the density of collision cascades on the efficiency of the generation of primary displacements during the ion bombardment of Si

The depth distributions of structural damage induced in Si at room temperature by the implantation of P and PF4 with energies from 0.6 to 3.2 keV/amu are experimentally studied in a wide range of doses. It is found that, in all cases, the implantation of molecular PF4 ions forms practically single-mode defect distributions, with maximum at the target surface. This effect is caused by an increase in the generation of primary defects at the surface of the target. Individual cascades formed by atoms comprising molecule effectively overlap in the surface vicinity; this overlap gives rise to nonlinear processes in combined cascades due to a high density of displacements in such cascades. Quantitative estimation of increase of effectiveness of point defect generation by PF4 ions in respect to P ions is done on the base of experimental data.

Mechanical and microstructural changes in tungsten due to irradiation damage

Stress-relieved pure tungsten received three damage levels (0.10, 0.25 and 0.50 dpa) by self-tungsten ion beam irradiation at room temperature. Positron annihilation spectroscopy showed the formation of mono-vacancies and vacancy clusters after ion beam exposure. In the first irradiation step (0–0.10 dpa) some splitting up of large vacancy clusters occurred which became more numerous. For increasing dose to 0.25 dpa, growth of the vacancy clusters was seen. At 0.50 dpa a change in the defect formation seems to occur leading to a saturation in the lifetime signal obtained from the positrons. Nano-indentation on the cross-sections showed a flat damage depth distribution profile. The nano-indentation hardness increased for increasing damage dose without any saturation up to 0.50 dpa. This means that other defects such as dislocation loops and large sized voids seem to contribute.

In situ and tomographic characterization of damage and dislocation processes in irradiated metallic alloys by transmission electron microscopy

Abstract

Damage processes in MgO irradiated with medium-energy heavy ions

The micro-structural modifications produced in MgO single crystals exposed to medium-energy heavy ions (1.2-MeV Au) were investigated using Rutherford backscattering spectrometry in channeling geometry coupled to Monte-Carlo analyses, secondary ion mass spectrometry, X-ray diffraction and transmission electron microscopy. The damage accumulation and the elastic strain variation were interpreted in the framework of the multi-step damage accumulation (MSDA) model. Both build-ups follow a multi-step process similar to that recently observed for ion-irradiated yttria-stabilized zirconia (YSZ) single crystals. However, in MgO, an unexpectedly high disorder level occurs far beyond the theoretical damage distribution. These results strongly suggest that the migration of defects created in the near-surface layer is most likely at the origin of the broadening of the damage depth distribution in MgO.

Low-temperature damage formation in ion implanted InP

Damage formation in ion implanted InP is studied by quasi–in situ Rutherford backscattering spectrometry (RBS) in channelling configuration. Subsequent implantation steps are performed at 15K each followed by immediate RBS analysis without changing the environment or the temperature of the sample. 30keV He, 150keV N and 350keV Ca ions were applied. The depth distribution of damage is in good agreement with that calculated with the SRIM code. The evolution of damage at the maximum of the distribution as a function of the ion fluence is described assuming damage formation within single ion impacts and stimulated growth of damage when the collision cascades start to overlap with cross sections σd and σg, respectively. These cross sections are found to depend on the primary energies deposited in the displacement of lattice atoms and in electronic interactions calculated with the SRIM code. The obtained empirical formulas are capable to represent the experimental results for different III–V compounds implanted at 15K with various ion species.

Ion‐induced damage evaluation with Ar cluster ion beams

Ion‐induced damage on organic materials has been evaluated with secondary ion mass spectrometry. However, conventional sputtering beams such as SF5+ and C60+ cannot etch organic materials without inducing damage, and evaluating the damage depth distribution in these materials is difficult. Large gas cluster ions can etch organic materials without damage, and in this study, the damaged layer thickness was evaluated by molecular depth profiling with Ar cluster ion beam. The characteristic molecular ions were not detected in the spectra after etching with Ar monomer beam, indicating that the chemical structures of phenyl‐C61‐butyric acid methyl ester (PCBM) and polystyrene (PS) were seriously damaged. The intensity of the fullerene molecular ion reached a peak at the depth of about 35 nm. For PS, the peak intensity of m/z 91 increased with sputtering depth and saturated at about 45 nm. These values agreed with the projection range of Ar+ in PCBM and PS, respectively. These results indicate that the ion‐induced damage depth was the same as the projection range of its ion. Copyright © 2012 John Wiley & Sons, Ltd.

Stabilization of organic thin film transistors by ion implantation

We report on the effects of low energy ion implantation (N and Ne) in the reduction and control of the degradation of pentacene organic thin film transistors (OTFTs) due to the exposure to atmosphere (i.e. oxygen and water). We have observed that a controlled damage depth distribution preserves the functionality of the devices, even if ion implantation induces significant molecular structure modifications, in particular a combination of dehydrogenation and carbonification effects. No relevant changes in the pentacene thin film thickness have been observed. The two major transport parameters that characterize OTFT performance are the carrier mobility and the threshold voltage. We have monitored the effectiveness of this process in stabilizing the device by monitoring the carrier mobility and the threshold voltage over a long time (over 2000h). Finally, we have assessed by depth resolved X-ray Photoemission Spectroscopy analyses that, by selectively implanting with ions that can react with the hydrocarbon matrix (e.g. N+), it is possible to locally modify the charge distribution within the organic layer.

Correlation between implantation defects and dopants in Fe-implanted SiC

SiC single crystals were implanted with Fe ions and the effects of implantation temperature, Fe concentration, and subsequent swift heavy ion irradiation on both dopant and damage depth distributions were evaluated by using RBS and channelling techniques. It is found that an increase of the implantation temperature above the threshold temperature for amorphization can lead to the formation of a broad layer (∼50 nm) containing a large concentration of implanted Fe atoms (∼2 at.%) but almost free of implantation defects. This particular configuration is likely due to dynamic annealing during implantation combined with defect annihilation at the surface. It is only observed when the implanted species concentration does not exceed a critical value (which lies between 2 and 5 at.% in the present system). Post-implantation swift heavy ion irradiation leads to a further decrease of the damage level, while the Fe distribution is not affected. The Fe substitutional fraction has been evaluated in the different tested conditions. A maximum value of ∼50% is found when implantation is performed at the temperature above that required to prevent amorphization (470 K in the present system). Swift-heavy ion irradiation seems to induce Fe atoms relocation at substitutional positions.

Probabilistic Study on Corrosion Damage Distribution and Fatigue Lives of LY12CZ Aluminum Alloy Structure

A probabilistic neural network was developed to classify corrosion damage depth ranges based on the aluminum alloy failure mode. The results obtained indicate that corrosion damage depth for aluminum alloy can be classified into three groups. Statistical study on classified corrosion damage was carried out. The results show that pitting corrosion depth for aluminum alloy is in conforms to Gumbel distribution. The normal distribution fits well with intergranular corrosion depth and the exfoliation corrosion depth is consistent with Weibull distribution law. It may be necessary to use several distribution functions rather than a single distribution to represent corrosion damage characteristics due to the large distribution of corrosion depth in aircraft materials. According to corrosion damage depth distribution, corrosion depth was simulated by Monte Carlo method and used as the starting crack size. Fatigue lives were estimated by using a life prediction program AFGROW and the results are in good agreement with the experimental data. A probabilistic analysis shows that the distribution of fatigue lives is strongly correlated to the distribution of corrosion damage depth and should be classified into several groups to study.

Aging control of organic thin film transistors via ion-implantation

One of the open issues in organic electronics is the long-term stability of devices based on organic materials, as oxidation is believed to be a major reason for early device failure. The focus of our research is to investigate the effects of low energy ion implantation (N and Ne) in the reduction and control of the degradation of pentacene organic thin film transistors (OTFTs) due to the exposure to atmosphere (i.e. oxygen and water). Despite the strong molecular structure modifications induced by ion implantation, we have observed that a controlled damage depth distribution preserves the functionality of the device. The electrical properties of the pentacene layer and of the OTFT have been investigated by means of current–voltage and photocurrent spectroscopy analyses. We have characterized the structural modification induced by ion implantation and we have monitored the effectiveness of this process in stabilizing the device carrier mobility and threshold voltage over a long time (over 2000 h). In particular, we have assessed by depth resolved X-ray photoemission spectroscopy analyses that, by selectively implanting with ions that can react with the hydrocarbon matrix (e.g. N +), it is possible to locally modify the charge distribution within the organic layer.

Thermal behaviour of helium-implanted spinel single crystals

The study of the microstructural modifications induced in spinel implanted with 4He + at 4.7 at.% and subsequently annealed at 1075 K is addressed in this paper. The combination of three analysis techniques Rutherford backscattering spectrometry in channeling geometry (RBS/C), X-ray diffraction and transmission electron microscopy was used in order to gain information about the damage depth distribution, the nature of radiation defects, and the occurrence of microstructural modifications. In as-implanted crystals the disorder level is weak, and the damage principally consists of small helium-vacancy clusters. These defects induce a tensile strain in the direction normal to the implanted crystal surface. After annealing, a surprising increase of the disorder level is measured by RBS/C. This increased backscattering yield is due to the formation of a particular type of He-vacancy clusters, namely He platelets, which also induce a relaxation of the strain.

Damage induced by electronic excitation in ion-irradiated yttria-stabilized zirconia

This article presents a study of the damage production in yttria-stabilized cubic zirconia single crystals irradiated with swift heavy ions. The combination of techniques which probe the material at different spatial scales (Rutherford backscattering spectrometry in channeling geometry, x-ray diffraction, transmission electron microscopy, and atomic force microscopy) was used in order to gain information about the damage depth distribution, the disordering buildup, the nature of radiation defects, and the occurrence of microstructural modifications. The damage results from the formation of tracks, due to the huge electronic excitations induced in the wake of incident ions. The melting of the material in the core of tracks, via a thermal spike mechanism, leads to the creation of large hillocks at the surface of the crystals. The overlapping of ion tracks at high fluence (above ∼1012 cm−2) induces a severe transformation of the microstructure of the material. Nanodomains slightly disoriented from the main crystallographic direction are formed, with a size decreasing with increasing irradiation fluence. These results may be used to predict the damage evolution in other nonamorphizable ceramics irradiated with swift heavy ions.

Radiation effects in yttria-stabilized zirconia: Comparison between nuclear and electronic processes

Yttria-stabilized zirconia (YSZ) single crystals were irradiated with heavy ions at energies ranging from a few MeV to a few GeV in order to compare the effects of nuclear collisions and electronic excitations. The amount of damage created by irradiation was measured as a function of the ion fluence by Rutherford backscattering and channeling spectrometry (RBS/C). Monte-Carlo simulations of RBS/C data show that both the depth distributions of radiation damage and the damage build-up strongly depend on the type of irradiation. At low energy (4MeV Au ions) the damage exhibits a peak around the ion projected range (∼500nm) and it accumulates with a double-step process; at high energy (940MeV Pb ions) the damage profiles are rather flat up to several micrometers and the damage accumulation is monotonous (one-step). RBS/C and X-ray diffraction results show that the various irradiations never lead to total disordering of irradiated layers (amorphization), even at the highest fluences used in the experiments.

Ion Beam Analysis and Computer Simulation of Damage Accumulation in Nitrogen Implanted 6H-SiC: Effects of Channeling

500 keV nitrogen implantations at different tilt angles (0o, 0.5o, 1.2o, 1.6o, 4o) with respect to the c-axis of 6H-SiC were carried out. Radiation damage distributions have been investigated by Backscattering Spectrometry combined with channeling technique (BS/C) using 3550 keV 4He+ ion beam. A comparative simultaneous evaluation of the damage depth distributions in the Si and C sublattices of 6H-SiC led to a correction factor of 0.8 in the electronic stopping power of 4He+ ions along <0001> channel. Full-cascade Crystal-TRIM simulations with the same set of damage accumulation model parameters could reconstruct the measured shapes and heights of damage distributions for all implantation tilt angles. Secondary defect generation effects in addition to the primary point defect accumulation were assumed in the analysis.

Spatial separation of vacancy and interstitial defects formed in Si by oxygen-ion irradiation at elevated temperature

A study of damage depth distribution in Si by elevated temperature O+-ion implantation was performed using three structures: (i) bulk Si, (ii) Si∕SiO2∕bulk Si, and (iii) SiO2∕bulk Si. The samples were implanted at 250 °C with a dose of 5×1016cm−2 at an energy of 185 keV. By this approach, the damage depth profile distributes along the SiO2 and Si layers in a different manner according to the sample structure. A comparative analysis of the high-resolution x-ray diffraction spectra taken from the implanted samples permitted us to infer on the spatial separation between vacancy and interstitial-rich layers, which are associated with the presence of negative and positive strained layers, respectively.

Dose-dependence of ion implantation-caused damage in silicon measured by ellipsometry and backscattering spectrometry

100 keV Ar and Xe ions, as well as 40 and 60 keV Ge ions were implanted at room temperature into single-crystalline silicon. The used doses covered the range from slightly damaged to totally amorphized layers for the Xe, Ar and Ge ions, respectively. The relative damage was characterized using spectroscopic ellipsometry (SE) with the Bruggeman effective medium approximation combining the dielectric function of single-crystalline and ion implantation-amorphized silicon. The depth distribution of damage was described by the coupled half-Gaussian model and with an improved model, which describes the damage profile using sublayers with thicknesses inversely proportional to the slope of the profile. The SE results were cross-checked using Rutherford backscattering spectrometry (RBS). The damage peaks were determined from the SE and RBS measurements for different ions and different doses ranging from slight damage to total damage. Comparing the damage peaks (caused by the same doses) determined with SE and RBS, a systematic deviation can be observed: SE measures more damage than RBS for lower and less damage than RBS for higher doses.

Damage production in cubic zirconia irradiated with swift heavy ions

The damage produced in cubic zirconia single crystals irradiated with swift heavy ions is studied with the Rutherford backscattering and channeling (RBS/C) techniques. Damage depth distributions are extracted from the analysis of RBS/C data with a Monte-Carlo simulation code. Relatively flat damage profiles are obtained up to depths higher than 2 μm, with a defect-depleted zone in the vicinity of the crystal surface. The damage concentration increases strongly with the electronic energy loss with a threshold at 20–25 keV/nm. The production of damage at high (d E/d x) e likely results from the formation of non-amorphous tracks.