RBS Measurements Research Articles

Surface related degradation of InP-based HEMTs during thermal stress

Degradation of unpassivated InP HEMTs related to the surface of InAlAs was studied. In ungated HEMTs, the drain current decreased after annealing at temperatures as low as 250°C. RBS measurements revealed that lattice disorder was induced on the surface on InAlAs during thermal treatment, which was considered to be due to either the introduction of vacancies or In segregation. Surface-related degradation was effectively suppressed by passivating devices with SiN layers.

Influence of arsenic ion implantation on the formation of Ti-silicides

The effects of arsenic ion implantation on the formation of Ti-silicides from TiN/Ti bilayer contacts on silicon were investigated. The TiN/Ti layers were sputter deposited in a single run, 90 nm of Ti and 80 nm of TiN (by reactive sputtering) on (111) Si wafers. The TiN/Ti/c-Si structures were then implanted with As + ions at 400–500 keV, to the doses from 1 × 10 15to 1 sx 10 16ions/cm 2, with the projected ion range near the Ti/Si interface. After implantation the samples were thermally treated in a vacuum, from 2 to 20 min at 650 °C and 2–10 min at 900 °C. Characterization of samples included RBS, XRD, SEM and electrical measurements. We have observed initial ion beam mixing at the Ti/Si interface, depending on the As + ion range. Annealing at 650 °C induces the Ti-Si reaction, formation of silicides, which strongly depends on the implanted arsenic dose. At 900 °C and for low implanted doses the Ti-Si reaction is completed, consuming the whole Ti layer to form the C54 TiSi 2 phase, while at high doses the Ti-Si reaction is retarded, causing segregation of arsenic near the TiN/Ti interface. The top TiN layer remains stable during implantation and thermal processing.

High depth resolution Rutherford scattering using forward angles

Rutherford scattering of MeV 4He ions at forward angles has been used to determine the thickness and composition of single Si 1 − x Ge x layers in Si. With scattering angles of about 20° the obtained depth resolution is up to 25% better than with standard RBS at glancing backward angles. The large scattering cross section at forward angles allows for the use of a small solid angle while maintaining good count rates and short acquisition times. Geometrical broadening of the energy spectra, due to the finite acceptance angle of the detector, is thus negligible. The kinematic factor is close to 1 for almost all elements in this geometry. Layers with different composition are therefore only distinguishable by the differences in spectrum height. The best accuracy for the stoichiometry is obtained by combining the measured energy loss in a layer with the areal density of the heavier element in that layer, which can be determined by standard RBS. The results are compared to RBS and X-ray diffraction measurements. The influence of multiple scattering is illustrated and a comparison to depth resolution calculations with the DEPTH code is made.

A study of gas-sensing properties of sputtered α-SnWO 4 thin films

Thin films of stannous tungstate have been grown by reactive co-sputtering in an 11% O 2/Ar atmosphere where a tungsten target is operated in the r.f. mode and a tin target in the d.c. mode. The deposited amorphous films are annealed for 4 h at 400 or 600 °C in order to crystallize the films. XRD together with RBS, EDS and CEMS measurements are used for the characterization of the films. The films sputtered with 150 W power for both modes are found to have crystalline α-SnWO 4 structure after annealing at 400 °C. CEMS results show that tin is in a divalent form (Sn 2+) in α-SnWO 4 films. The electrical resistivity together with the gas-response properties to different gases of the α-SnWO 4 films have been measured at different temperatures between room temperature and 400 °C. In the case of response to CO and NO in air, an unusual dual-conductance behaviour is found. For comparison, measurements have also been made with a pure WO 3 film and with some Sn x WO y films having lower tin concentrations ( x<1).

Near-threshold ablation of target material irradiated with pulsed ion beams

The process of target ablation induced by pulsed ion beams is investigated. The beam power density of 0.01–0.1 GW/cm2 is around the sublimation energy of the target material. The thickness of the layer to be removed from the target is estimated from the temperature distribution calculated numerically with a diffusion equation. The emitted particles are collected with C collectors, which are later subjected to RBS and SEM/EPMA analyses. It is found that ablated particles forming a film on the collector amount to only 10% of the target atoms within the maximum range of the ions, while a significant amount of the ablated material is observed as macroscopic particles with equivalent diameters up to several tens of micrometers. TOF measurements of the ablation plume together with RBS measurements of thin-film targets after irradiation suggest that the formation of the film is predominated by vaporization from the surface of the ablated mass, which is recondensed on the collector before completing the vaporization.

Optical Properties of Epitaxial Plt Thin Films

AbstractMetalorganic chemical vapor deposition (MOCVD) was used to prepare epitaxial or highly oriented PLT (Pb1-xLaxTiO3) thin films with x in the range of 0.21 to 0.34. The growth of PLT films resulted in three-dimensional epitaxial heterostructures on (100) surface of the MgO and the KTaO3 substrates. The PLT film grown on the KTaO3 (100) substrate has a significantly lower minimum channeling yield compared to that on the MgO (100) substrate because of the smaller lattice mismatch. The thickness and the refractive indices in the wavelength range of 435 to 1,523 nm were measured by the prism coupling method. The measured film thickness of 570 nm was in good agreement with that from RBS measurements. The refractive index of PLT film is smaller than that of PbTiO3, its difference at 632.8 nm is about 2.5 %. The dispersion of the refractive index was well fitted to a Sellmeier dispersion formula.

Tungsten Silicide Films Based on Dichlorosilane Chemistry for sub 0.5 Micron Applications

AbstractCVD WSix, films have found widespread use as ultra thin gate, wordline and bitline interconnects due to the lower resistance that polycide offers. For submicron technologies, WSix films based on the monosilane chemistry shows limitations due to the incorporation of high concentrations of Fluorine ions and poor step coverage. Recent work has shown that, WSix films based on the dichlorosilane (DCS) chemistry minimizes these problems. One of the major issues in DCS WSix films is the in-depth compositional non uniformity, especially those deposited on poly-Si substrates. The formation of a W-rich region at the WSix/poly-Si interface can cause localized stresses which can result in cracking and adhesion problems. In this paper, we report the composition and structure of DCS WSix, films deposited on undoped, doped and in situ doped poly-Si and oxide substrates. We have investigated the effect of different processing conditions on Si/W uniformity and the formation of W-rich and Si-rich interfaces, and the role of the nucleation step in modulating the Si/W ratio at the WSix/poly-Si interface. The impact of a Si-rich region at the WSix/poly-Si interface on silicide film properties has also been explored. RBS measurements were used to determine the composition profile through the depth of the film and Si/W uniformity in terms of Si-rich and W-rich interfaces. SIMS measurements were used to determine the impurity content in the silicide film and at the film/substrate interface.

Thermal Stability in Pd-Based Contacts to p-Type In0.53Ga0.47as Characterized by Rbs

AbstractThe resistivity and interfacial characteristics of Pd/Zn/Pd/Au and Pd/Zn/Au/LaBd6/Au contacts to p-In0.53Ga0.47As have been investigated. Annealing of the contacts at 375–425°C yielded a minimum in specific contact resistance, p,, of 2 × 10-7 Δ cm2 for the Pd/Zn/Pd/Au contacts and 1 Δ cm2 for the Pd/Zn/Au/LaB6/Au configuration. This is the lowest reported measurement of pc for an ohmic contact to p-In0.53Ga0.47As doped to ≤1 × 1019 cm−3. In the Pd/Zn/Au/LaB6/Au scheme, the minimum in pc was the same irrespective of whether the Zn was incorporated as a structural layer or as Zn ions implanted into the interfacial Pd prior to metallization. The effect of thickness of the Zn layer on pc has been determined for the Pd/Zn/Au/LaB6/Au scheme. RBS measurements have shown that during annealing, the LaB6 layer acted as a barrier to the indiffusion of Au and to the degradation of the In0.53Ga0.47As substrate.

Silver Cluster Formation in Implanted A12O3 Single Crystals

AbstractSingle crystals of sapphire were implanted at room temperature with 300 keV-Ag+. The metal precipitate was characterized by a multitechnique approach including RBS, optical absorption and Raman spectroscopy. RBS measurements were used to determine the depth-profiles of the implanted ions. Ag depth profiles, derived from RBS are in good agreement with the results predicted by Monte Carlo simulations. Linear absorption spectroscopy has been used to characterize the effects of the ion fluence on the optical properties of the metal colloids in the UV-Vis region. The broad absorption band due to the surface plasmon resonance shows an appreciable red-shift when the fluence of bombarding ions increases. Raman scattering from acoustic vibrations of the silver clusters progressively shifts toward the laser frequency with increasing implantation dose. From low-frequency Raman spectra an evaluation of the average size of metal aggregates was derived.

Superconducting and structural properties of epitaxial Bi 2Sr 2CaCu 2O 8−δ/Bi 2Sr 2YCu 2O 8−δ/Bi 2Sr 2CaCu 2O 8−δ heterostructures

We have prepared Bi 2Sr 2CaCu 2O 8−δ/Bi 2Sr 2YCu 2O 8−δ/Bi 2Sr 2CaCu 2O 8−δ trilayer structures, using a “in situ” DC-sputtering process at high oxygen pressures on (001) SrTiO 3 substrates. Bi 2Sr 2CaCu 2O 8−δ films were used for superconducting electrodes and semiconductor-like Bi 2Sr 2YCu 2O 8−δ films with thickness down 5 nm were used as barrier layers. Both materials have the same crystalline structures and allowed the epitaxial growth of the heterstructure as shown by X-ray, RBS measurements and cross section TEM analysis. The superconducting properties were examined by resistance, AC-susceptibility and current-voltage characteristics as function of the temperature. For junctions with areas of 120×120μm 2 defined by photolitography a RSJ behavior was found at temperatures below T c.

Study of multilayer substrate surface roughness using RBS with improved depth resolution

In magnetic superlattices the thickness of the layers and their interface structure are determinant for the magnetic properties. However, the 5 nm depth resolution normally achieved with the RBS technique is not enough to allow the study of these systems. In this paper, depth resolutions down to 1.2 nm, recently achieved in RBS measurements of Co/Re superlattices using grazing angle of incidence, are compared to computer simulations, and good agreement is found. The effect of the substrate surface roughness is taken into account using a simple phenomenological model. A way to further improve the depth resolution is also discussed.

The growth of crossover structures of laser ablated YBCO or BSCCO thin films with different insulating materials

Trilayers of YBCO or BSCCO (2212) on SrTiO3 substrates were fabricated by laser ablation with different insulating materials like SrTiO3, CeO2 and MgO as intermediate layers. The growth of trilayer systems was investigated by SEM, RBS, XRD and electrical measurements for both in situ and ex situ ablation processes. For trilayers YBCO-SrTiO3-YBCO we found, at optimal conditions for the SrTiO3 growth chi min of 5% for in situ and 9% for ex situ fabricated samples. The TCO of both YBCO layers was higher than 89 K. The trilayers based on BSCCO showed a chi min of 45% and a TCO approximately=35 K. For crossover structures all three layers were patterned by ion beam etching. To solve the problem of growth of a top YBCO layer on a patterned bottom bilayer of YBCO and SrTiO3, the etching angles of the bottom system were modified by special choice of the parameters of the ion beam etching process. So we found TCO values of more than 89 K and a critical current density of jc (77 K)>105 A cm-2 for the top YBCO layer. The resistances of the SrTiO3 and CeO2 insulating films showed semiconducting behaviour and reached 107 Omega cm and 106 Omega cm, respectively. With the described technology the first YBCO thin film coils were fabricated.

RBS, AES and XPS analysis of ion beam induced nitridation of Si and SiGe alloys

Nitridation of Si and SiGe alloys under normal incidence 12 keV N + 2 bombardment has been studied by in situ 1 MeV 4He RBS and by ex situ XPS and AES analysis. The in situ RBS measurements, which alternate with the sputtering/bombardment cycles, show the build-up of the nitrogen content in the silicon and Si .86Ge .14 sample with increasing N + 2 dose. For the silicon a stoichiometric ratio close to that of Si 3N 4 is found. In the case of the SiGe alloy a depletion of the Ge from the surface is noticed. Ex situ XPS measurements on the same samples indicate that nitrogen is bonded with silicon and germanium according to the Si 3N 4 and Ge 3N 4 phase. AES analysis of the steady state composition gives a depth profile with qualitative information on the chemical binding. Nitridation of a silicon sample with a buried Ge layer demonstrates that during the nitrogen build-up a large densification and even some swelling of the surface layer occurs. The transient region of nitridation before steady state is reached is explained by a two-phase model.

RBS analysis of thin MoSix films: Correlation between stoichiometry and some features of sputtering

The well separated peaks in the RBS spectrum of thin MoSix films permit the determination of the atomic area densities of both components with fairly good accuracy to obtain the film composition x within error limits of ± 3%. Taking advantage of this fact we studied the substrate radial distributions of the composition of MoSix films deposited by planar dc magnetron sputtering from a circular compound target. The RBS measurements were confirmed by cross-checks with AES profilings. The distributions indicate a remarkable asymmetry in the sputtering characteristics of Si and Mo, respectively, which is interpreted to be due mainly to differences in the angular function of the target emission. By a simulation procedure the shape of these angular functions can be calculated. It results that in the sputtering of Mo atoms, by contrast to Si, there is a higher amount of emission events into directions far from the target normal.

Bi-implanted silicon reference material revisited: uniformity of the remaining batch

A remaining batch of 65 samples of the Bi-implanted silicon reference material, issued earlier by our institution, has been investigated extensively with respect to the uniformity of the implanted Bi-layer. For this purpose long-time RBS measurements were performed in the multichannel scaling (MCS) mode. The determined non-uniformity expressed as the relative range of the bismuth fluence between its maximum and minimum values is 7%. The relative amount of the Bi fluence in individual chips as presented in this paper serves as basis to assign individual calibration values to each implanted chip. Furthermore, an estimate of the uniformity within each sample can be based upon the acquired MCS data.

Ion-beam induced CoSi 2 layers: formation and contact properties

In this study, the influence of Ge and As ion energy, respectively, on the mixing behavior and the contact properties of the CoSi system was investigated by Monte Carlo simulations, SIMS, RBS, TEM, and electrical measurements. To achieve silicided n + p junctions, 30 nm Co on Si was mixed with (1–5)×10 15 cm −2 Ge or As ions in the energy range from 50 to 200 keV. Silicidation was performed in a RTA system at 700 and 1000°C. In the case of Ge mixing, the n + p junction was formed by As implantation either before or after silicidation. It could be shown that ion-beam mixing with Ge and As ions followed by rapid thermal annealing lead to homogeneous silicidation for all mixing energies and ion species used. SIMS analysis of doping profiles as well as measurement of leakage currents revealed, however, that only Ge ion-beam mixing is an appropriate method for formation of low-resistivity, homogeneous silicide contacts either on previously or subsequently formed shallow n + p junctions.

Growth of epitaxial lithium tantalate on sapphire by chemical beam epitaxy from lithium hexaethoxy-tantalate

Abstract LiTaO3 films were grown on sapphire by chemical beam epitaxy from a double metal alkoxide, LiTa(OEt)6, using a Knudsen cell with a microchannel orifice plate designed specifically for moisture sensitive metallorganic precursors. Films were characterized by XRD, ICP, RBS, optical coupling and transmission measurements. Elemental analysis (ICP) found the films to be slightly lithium deficient (Li/Ta= .942±.058). Growth was epitaxial on (0001) sapphire above 625°C with (0001)//(0001), [112]//[112]. The dispersion of refractive index with wavelength was determined from the interference pattern in the transmission spectra and from measurements of coupling angles into the TEo and TMo modes, and fitted to an electron oscillator model.

Growth Kinetics and Materials Properties of Cu5Si

ABSTRACTThin copper films have been passivated by exposure to a dilute silane mixture (2% SiH4/Ar) at temperatures in the range of 225 - 375 °C. Previous XRD characterization indicates the surface layer to be Cu5Si[l]. Subsequently, the growth kinetics were examined by sheet resistance (Rs), RBS and step height measurements. Two distinct growth regimes are observed. The flow rate and time dependencies of the low temperature growth indicate parabolic solid state diffusion limited growth. The corresponding activation energy is 0.7 eV. A mass transport limitation is evidenced at higher temperatures. In addition, the biaxial stress and adhesion responses have been observed using the substrate curvature technique and scotch tape peel tests, respectively. A biaxial modulus (Eb) of 2.9x1011 Pa and coefficient of thermal expansion (CTE) of 8.6xl0-6 /°C have been determined from stress temperature cycling on Si and a-quartz substrates.

GeV heavy ion induced adhesion enhancement

The adhesion of metal films on polymers is important in microtechnology. In this work we combined the chemical and physical techniques and irradiated pretreated polymers. The irradiation of Cu deposited on etched Teflon surfaces with GeV Bi ions improved the adhesion by an order of magnitude. The correlation of adhesion enhancement with ion energy and fluence was investigated. XPS and RBS measurements on the interface surface exposed after peeling were performed and the point of fracture was observed.

Determination of cadmium in potassium-rich samples by combining PIXE and RBS measurements

The combination of PIXE and RBS measurements enables the deconvolution of the interference between the Cd-L- and the K-K α-line for the quantitative analysis of Cd-concentration in the ppm region. An evaluation of the experimental data using the results of these measurements is given. The scattering cross sections for protons on nitrogen, oxygen, silicon and potassium were determined in the energy range between 1.0 and 1.8 MeV by means of calibration standards formed by ion implantation in order to reduce the experimental error of the RBS investigation. A comparison with alternative methods confirms the accuracy and sensitivity of our measurements.