Rutherford Backscattering Channeling Analysis Research Articles

Development and test of 2.45 GHz microwave ion source based intense ion beam experimental facility

An intense low energy ion beam facility has been designed, developed at Inter University Accelerator Centre (IUAC), New Delhi. This facility comprises of a 2.45 GHz microwave ion source, multi-electrode extraction system and an experimental chamber. The facility was designed to perform experiments using intense ion beams having energy in range of a few keV to a few tens of keV. The plasma chamber was designed keeping two additional ports for plasma diagnostics. In order to deliver intense ion beams on the target with low electric field, a four-electrode extraction system has been developed. This facility has been used for 10 keV N+ & O+ ion implantation in silicon at varying doses. The implanted samples have been characterized by using Rutherford Back Scattering (RBS), RBS Channeling (RBS-C) and Nuclear Resonance Analysis (NRA).

A geometric procedure for improved Rutherford backscattering channeling analysis of materials

Solving geometric and sample alignment issues is a major part of multi-axial Rutherford backscattering channeling (RBS-C) analysis of materials, especially involving complicated samples. However, a geometric standard does not exist for RBS-C, which complicates experimental procedures and makes experimental methods and data presentation inconsistent among different experiments. Our approach to solving RBS-C geometric issues, discussed here, is to introduce a geometric adjustment and sample manipulation procedure which defines the orientation and rotation of the sample with respect to a fixed coordinate system. This method makes rotational, alignment and sample manipulation operations involved in RBS-C more flexible and simpler. As a test case, we present multi-axial RBS-C maps of Si obtained via this methodology. Distortions arising in such RBS-C maps due to geometric effects, how they can affect alignment procedure and data extraction, and how our approach treats these issues are discussed.

Groups III and V impurity solubilities in silicon due to laser, flash, and solid-phase-epitaxial-regrowth anneals

In this work the authors studied impurity solubilities of groups III and V elements in silicon resulting from laser anneal, flash anneal, and solid-phase-epitaxial regrowth. Rutherford backscattering channeling analysis was used to determine substitutional impurity depth profiles generated from the difference between the random and aligned spectra. Despite the large difference in peak temperatures and times, the anneals produce similar results with maximum solubilities beating the maximum equilibrium values by one to two orders of magnitude depending on the impurity. The correlation between the metastable solubility and the equilibrium distribution coefficient allows a prediction of values for other impurities not extracted experimentally.

Investigation of heavily damaged ion implanted Si by atomistic simulation of Rutherford backscattering channeling spectra

Rutherford backscattering channeling (RBS-C) spectra of ion-implanted Si are simulated according to an atomistic model of radiation damage which consists of a distribution of point defects (split-〈110〉 interstitials and vacancies) structurally relaxed by empirical potentials. This model, successfully used to reproduce multiaxial spectra of lightly damaged Si, is applied here to the case of a heavily damaged sample. As a consequence of the increasing strain generated by lattice relaxation, simulations predict a superlinear trend of RBS-C disorder versus defect concentration in the range of intermediate damage density. This contrasts with the linear trend obtained by the usual description of defects as atoms randomly displaced in a rigid lattice. The new approach represents an improvement in the physical description of ion irradiation disorder within RBS-C analysis; however simulation results are found to be in less satisfactory agreement with spectra of a heavily damaged sample than with spectra of lightly damaged material. The description of damage as the result of the accumulation of simple point defects and the use of a static relaxation procedure instead of finite temperature molecular dynamics, are two possible reasons to explain the present limitations in describing the structural properties of heavily damaged, yet not completely amorphized, ion implanted Si.

Cathodoluminescence and solid phase epitaxy in Ba-irradiated α-quartz

The luminescent properties of quartz and silica doped with photoactive ions depend on the structural and chemical properties of the matrix and doping elements. The dynamic solid phase epitaxy of α-quartz during Ba+-ion implantation at 300–1170K and its relationship to cathodoluminescence emission are investigated in this work. Rutherford backscattering channeling analysis revealed that the amorphous layer created by 1×1015 175keVBaions∕cm2 at 300K almost disappeared when the implantation temperature was raised to 1120K. Between 770 and 1100K the cathodoluminescence spectra taken at room temperature exhibit dramatic changes with the implantation temperature and allow to distinguish between color centers related to quartz, ion-irradiated silica, and implanted Ba ions. After achieving almost complete epitaxial recovery, only a violet band at 3.4eV remained, which we attribute to Ba-related luminescence centers. Samples first implanted with Ba ions and then postannealed in air or O218 atmosphere up to 1320K did not show full epitaxy of the amorphized layer.

Cathodoluminescence versus dynamical epitaxy of Ba-ion irradiated α-quartz

Doping α-quartz with photoactive ions without destroying its crystalline structure appears to be a promising way to tune its luminescent and structural properties. We have achieved dynamic solid phase epitaxial regrowth and cathodoluminescence of 175keV Ba-ion irradiated α-quartz in the temperature range from 300 to 1170K. Rutherford Backscattering Channeling analysis showed that the amorphous layer produced by 1×1015 Baions∕cm2 at 300K had almost disappeared at an implantation temperature of 1123K. Room temperature cathodoluminescence exhibited dramatic changes in the optical spectra as a function of the implantation temperature and allowed to distinguish between color centers related to quartz, ion-irradiated silica and implanted Ba. Between 770 and 1100K, room-temperature cathodoluminescence showed a predominant blue and other weak bands connected to various known defects in the Si-O-Si network. However, after achieving almost complete solid phase epitaxial recovery, only a violet band at 3.4eV remained, which we attribute to Ba-related luminescence centers.

Stable violet cathodoluminescence of α-quartz after Ge+ implantation at elevated temperature

Doping single-crystalline α-quartz with 120keV Ge+-ion implantation under the conditions of dynamic solid phase epitaxial regrowth has been studied as function of ion fluence and substrate temperature. In particular, the light emitting properties possibly suitable for optoelectronic devices have been investigated by measuring cathodoluminescence spectra for implantation temperatures from 300 to 1223K and for analyzing temperatures from 10−300K. Rutherford backscattering channeling analysis showed that the Ge implantation produced amorphous layers varying in depth with temperature. At a fluence of 7×1014Ge-ions∕cm2 and an implantation temperature of 1073K, Ge implantation is accompanied by a strong increase in the luminescence intensity of a violet band, which we associate with Ge-related defects or Ge clusters. This violet band is very stable and has a long lifetime of 6μs. All the other bands observed are connected to known oxygen defect centers in the SiO2 network.

Interpretation of ion-channeling spectra in ion-implanted Si with models of structurally relaxed point defects and clusters

We investigate the application of atomistic models of self-interstitial defects to the simulation of Rutherford backscattering-channeling (RBS-C) spectra in ion irradiated Si. By the comparison of simulated and experimental measurements, we verify the ability of different models, either of elementary interstitials or of small clusters, to reproduce experimental spectra measured under different alignment conditions in Si lightly damaged by ${\mathrm{Si}}^{+}$ ion implantation. A model system for RBS-C simulation is built by inserting a distribution of defects in a supercell with size of $\ensuremath{\sim}{10}^{6}$ atoms. The system is then structurally relaxed by the application of the classical environment-dependent interatomic potential (EDIP). After adjusting the defect distribution in order to fit the $〈100〉$ RBS-C spectrum, simulations are performed under the other alignment conditions investigated. The scattering factors of defects are then extracted from both experimental and simulated RBS-C spectra and compared. It is shown that the anisotropy of experimental damage is not compatible with a significant presence of random (incoherent) disorder, but can be reproduced by some of the defect models under consideration: the split-$〈110〉$ interstitial, the diinterstitial formed by the addition of an interstitial to the split-$〈110〉$ interstitial, and two different configurations of the four-interstitial aggregate; one formed by two close diinterstitials and the other by the aggregation of four split-$〈100〉$ interstitials. Due to the different $〈100〉$ scattering factors of the four defect configurations which are found to reproduce experimental spectra, there is an inherent uncertainty of a factor of 2 in the estimate of the amount of interstitials by $〈100〉$ RBS-C analysis. The agreement between simulations and experiments is remarkable, considering that the method makes use of physical, although empirical, models of defects, where the only adjustable parameter is the absolute concentration of interstitials.

Wet Etching of Al2 O 3 for Selective Patterning of Microstructures Using Ar + Ion Implantation and H 3 PO 4

A new etching method for single‐crystal is proposed using implantation and chemical etching. Photolitographically defined patterns are transferred into sharp structures on the wafer surface by selectively removing the damaged material. A double implantation of at 50 keV followed by 180 keV was performed on all samples, using a dose of for the low‐energy implant. Doses of , and were used for the 180 keV implant. Scanning electron microscopy and atomic force microscopy were used to characterize the pattern obtained, while transmission electron microscopy and Rutherford backscattering channeling analysis were employed to study the implanted layer. Under the conditions investigated, both the etchable range (90 to 160 nm) and the etching rate (1 to 7 nm/min) were found to be strongly correlated with the implanted dose. Sharp and uniform interfaces between etched and unetched regions were obtained, forming steps with an average slope of 30 to 45°. The proposed method offers high selectivity, lack of contamination of the substrate, and compatibility with standard processing.

Epitaxial KNbO3 thin films on KTaO3, MgAl2O4, and MgO substrates

Epitaxial potassium niobate (KNbO3) thin films have been deposited on KTaO3 (100), MgAl2O4 (100), and MgO (100) substrates using ion-beam sputter deposition. X-ray-diffraction results show that KNbO3 films have orthorhombic (110) orientation on all three substrates. Rutherford backscattering channeling analysis of KNbO3 films on KTaO3, MgAl2O4, and MgO exhibits minimum scattering yields (χmin) of 7%, 9%, and 18% for the Nb peak, respectively. This illustrates how the quality of epitaxy improves as the lattice mismatch decreases. Prism-coupling measurements reveal near-bulk refractive indices of about 2.27 for TE modes and 2.22 for TM modes for films on each substrate.

Preparation of Si 1−xGe x thin crystalline films by pulsed excimer laser annealing of heavily Ge implanted Si

Thin crystalline Si 1−xGe x layers were obtained by irradiating heavily Ge implanted (10 17 atoms cm −2) 〈100〉 oriented Si substrates with a pulsed excimer (ArF) laser. The respective influences of the implantation conditions, laser energy density or number of successive laser pulses were investigated using Rutherford backscattering channeling analysis and Raman spectroscopy. In particular, it is shown that layers of good crystalline quality can be readily obtained, the width almost constant Ge concentration being controlled by the irradiation conditions. Optimizing these conditions leads to 200 nm thick alloy layers with a constant Ge content x = 0.14. These results were interpreted using a computer simulation based on the melting-resolidification process which occur during the pulsed laser irradiations.

Adsorption of atomic hydrogen on Si(100) surface.

The interaction of atomic hydrogen (deuterium) was studied by nuclear reaction analysis and Rutherford backscattering-channeling analysis. The hydrogen coverage as a function of exposure is found to exhibit a plateau at about 2.0 monolayers. The coverage continues to increase with further exposures of atomic hydrogen (deuterium), a consequence of localized etching of the silicon surface. The channeling data show that the Si(100)-2\ifmmode\times\else\texttimes\fi{}1 surface is highly strained. The strains parallel to the (100) surface are mostly removed on the ``saturated'' bulklike Si(100)-1\ifmmode\times\else\texttimes\fi{}1-H surface.

Crystallinity of a-axis oriented YBa2Cu3O7−δ thin film epitaxially grown on NdGaO3 (110) by 95 MHz magnetron sputtering

An a-axis oriented 400 Å YBa2Cu3O7−δ film has been epitaxially deposited on a NdGaO3 (110) substrate by rf magnetron sputtering using a single YBa2Cu5Ox target. An excitation frequency of 94.92 MHz, seven times as high as the conventionally used 13.56 MHz, results in a lower self-bias voltage which reduces degradation of films caused by resputtering due to negatively charged oxygen. Sharp streaks corresponding to the c-axis lattice parameter of YBa2Cu3O7−δ have been observed by reflection high-energy electron diffraction, showing that the c-axis is parallel to the surface of the NdGaO3 substrate and the film surface is smooth on an atomic scale. The crystallinity has been characterized by Rutherford backscattering channeling analysis. A minimum yield, χmin of 3.2%, has confirmed excellent crystallinity of the a-axis oriented film.

Partial epitaxial growth of Ni 2Ge and NiGe on Ge(111)

Transmission electron microscopy (TEM), scanning electron microscopy (SEM), Rutherford backscattering (RBS) channeling and Read camera glancing X-ray diffraction analysis have been applied to study the interfacial reactions of nickel thin films on Ge(111) with particular emphasis on the epitaxial growth of Ni 2Ge and NiGe at this surface. Ni 2Ge and NiGe were found to grow epitaxially at 160°C and 250°C respectively. Epitaxial Ni 2Ge regions, 30 nm in average size, were observed to cover about 100% of the surface area. The orientation relationships were analyzed to be Ni 2Ge[0001]Ge[111] and Ni 2Ge( 10 ̄ 10) Ge ̄ 220). The best NiGe epitaxy was obtained in samples annealed at 500°C for 1 h. The orientation relationships were determined to be NiGe[010]Ge[111] and NiGe(002) Ge ̄ 220). The average size of epitaxial regions was measured to be about 4.5 μm. The areal fraction of epitaxial regions for NiGe was found to be about 70%. NiGe was found to agglomerate to form islands after 600°C annealing. The results obtained from Read camera glancing-angle X-ray diffraction and RBS channeling analysis were found to agree with those from TEM and SEM examinations.

Partial epitaxial growth of cobalt germanides on (111)Ge

Localized epitaxial Co5Ge7 and CoGe2 have been grown in cobalt thin films on (111)Ge in the solid phase epitaxy regime. The orientation relationships between epitaxial germanides and the substrates as well as the configuration of the interfacial dislocations were analyzed by transmission electron microscopy (TEM) in detail. Surface morphology was examined by scanning electron microscopy. The results obtained from Read camera glancing angle x-ray diffraction and Rutherford backscattering channeling analysis were found to corroborate with those from TEM examinations.

Melting and misalignment of solid crystalline krypton inclusions in aluminum.

Ion-implantation--induced crystalline krypton inclusions in aluminum, epitaxially aligned with the matrix, have been investigated with x-ray diffraction and Rutherford-backscattering channeling analysis. The data show a dual size distribution of the krypton bubbles. In samples annealed up to 620 K and subsequently cooled, the larger bubbles melt in a pressure-broadened transition at 114--118 K. The smaller bubbles remain solid upon heating but, as a result of a roughening transition on the aluminum facets of the cavities, the Kr crystallites gradually lose their epitaxial alignment.

Oxygen Ion Implantation into Germanium

AbstractSingle crystal (111) and (100) Ge wafers were implanted with 16O (180 keV, 2.0 x 1018/cm2, 14–28 ¼A/cm2 ) at substrate temperatures of 250, 330, and 500°C. Implanted samples were annealed at 350, 450, 550, and 650°C for 30–90 minutes in an Ar ambient. Rutherford backscattering channeling analysis and cross-sectional transmission electron microscopy indicate that an amorphous buried layer is formed by implantation and that the overlayer contains a dense network of precipitates. Electron spin resonance measurements indicate that the layer does not contain GeO2, but rather oxygen deficient GeO2. Annealing of samples up to 550°C showed no change in the morphology, however, after annealing at 650°C the buried layer was gone and all that remained was a damaged Ge substrate with little or no oxygen. Further annealing for 60 min left nearly virgin Ge.

Synthesis of dilute magnetic semiconductors by ion implantation

We have synthesized layers of CdMnTe by implantation of Mn into CdTe. Samples of CdTe have been implanted with Mn ions of 60 keV energy to fluences in the range 1 × 10 3 cm −2 to 2 × 10 16 cm −2 resulting in local concentrations of up to 10% at the maximum of the Mn distribution. Rutherford backscattering-channeling analysis has been used to study the radiation damage after implantation and after subsequent rapid thermal annealing (RTA). These experiments reveal that RTA for 15 s at a temperature T ≥ 700°C results in the complete recovery of the lattice order. Photoluminescence (PL) measurements of a sample showing complete annealing reveal an increase in the band gap corresponding to the synthesis of very dilute ( x = 0.004) Cd 1− x Mn x Te. A shift of the excitonic PL peak to lower energies is observed when a magnetic field H ≤ 1 T is applied. These measurements provide clear evidence for the synthesis of a DMS by ion implantation.

Synthesis of the Dilute Magnetic Semiconductor CdMnTe by Ion Implantation of Mn into CdTe

AbstractThe dilute magnetic semiconductor CdMnTe has been synthesized by ion implantation of Mn into CdTe. Samples of CdTe have been implanted with Mn ions of 60 keV energy to fluences in the range 1 × 1013 cm−2 to 2×1016 cm−2 and subsequently annealed, using rapid thermal annealing, for 10–15 sec at temperatures 300 ≤ TA ≤ 730°C. The successful formation of a near surface layer of CdMnTe is demonstrated by studies of the structural, electronic and magnetic properties of the ion implanted and annealed sampies; Rutherford backscattering-channeling analysis of the radiation-induced damage indicates complete recovery of lattice order after annealing at 700°C. Photoluminescence measurements, performed at 2K, reveal an increase in the energy band gap of the ion implanted alloy with respect to CdTe. Application of magnetic fields, up to 8T, produce both the characteristic energy shift of the excitonic recombination peak and polarization of the emitted radiation (in the Faraday configuration) previously observed in bulk–grown CdMnTe material.