SIMS Depth Profiling Research Articles

Novel Zirconium Precursors for Atomic Layer Deposition of ZrO2 films

Five novel zirconium precursors - bis(N,N'-diisopropyl-1,3-propanediamide) zirconium (TCZR 1), tris(ethylmethylamide)(N,N,N'-trimethyl-1,2-ethaneamide-amine zirconium (TCZR 3), tris(dimethylamide)(N-ethyl-N',N'-dimethyl-1,2-ethaneamide-amine) zirconium (TCZR 4), mono-(N,N'-dimethyl-1,2-ethanediamide)-bis(cyclopentadienyl) zirconium (TCZR 5) and tris(ethylmethylamide)(N-ethyl-N',N'-dimethyl-1,2-ethaneamide-amine) zirconium (TCZR 6) have been synthesized and characterized by NMR, TGA, DSC and EA. The volatility of three precursors was measured by a Knudsen cell technique. The deposition behavior of these materials was evaluated in an ASM EmerAldTM ALD reactor or an ASM F-120 cross­flow reactor. Self-limiting deposition of ZrO2 films was observed with temperatures up to 300 {degree sign}C when used with oxygen plasma or ozone as the oxidant, as compared to more CVD-like behavior using bis(N, N'-di-tert-butyl-1,2-ethanediamide) zirconium (TCZR 2) and tetrakis(ethylmethylamide) zirconium (TEMAZ) under the same conditions. The resulting ZrO2 films from these novel precursors showed good step coverage (> 80%) on high aspect ratio structures, low carbon incorporation (< 2 atom%), high permittivity cubic/tetragonal phase, and growth rates comparable to TEMAZ based on analysis using X-ray diffraction, SIMS, and sputter depth profile AES. These results make the novel precursors promising candidates for ALD of high-k materials as storage capacitors in DRAM applications.

Focused ion beam implantation of Ga in Si and Ge: fluence‐dependent retention and surface morphology

AbstractFocused ion beam implantation of 30‐keV Ga+ ions in single‐crystalline Si and Ge was investigated by SIMS, using Cs+ primary ions for sputtering. Nine different implantation fluences ranging from 1 × 1013 to 1 × 1017 Ga+‐ions/cm2 were used, with implanted areas of 40 × 40 µm2. The Ga concentration distributions of these implants were determined by SIMS depth profiling. Such 30‐keV Ga implantations were also simulated by a dynamic Monte‐Carlo code that takes into account the gradual change of the near‐surface composition due to the Ga incorporation. In both approaches, an essentially linear increase of the Ga peak concentrations with fluence is found up to ∼1 × 1016cm−2; for higher fluences, the Ga content approaches a saturation level which is reached at about (1–2) × 1017cm−2. The measured and simulated peak concentrations of the Ga distributions are in good agreement. The most probable ranges obtained from the experiments correspond closely with the respective values from the simulations. The surface morphology caused by Ga+ implantation was investigated by atomic force microscopy (AFM). The AFM data indicate that for low fluences (&lt;3 × 1015cm−2) the surface within the implanted areas is growing outward (i.e. is swelling). For increasingly higher fluences, sputter‐induced erosion of the surface becomes dominant and distinct craters are formed for fluences above ∼1 × 1016cm−2. At the boundary of the implanted region a wall‐like structure is found to form upon Ga implantation; its height is growing with increasing fluence, reaching a value of ∼15 nm at 1 × 1017 Ga+‐ions/cm2. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Importance of water content in formation of porous anodic niobium oxide films in hot phosphate–glycerol electrolyte

Niobium has been anodized at a constant current density to 10 V with a current decay in 0.8 mol dm −3 K 2HPO 4–glycerol electrolyte containing 0.08–0.65 mass% water at 433 K to develop porous anodic oxide films. The film growth rate is markedly increased when the water content is reduced to 0.08 mass%; a 28 μm-thick porous film is developed in this electrolyte by anodizing for 3.6 ks, while the thickness is 4.6 and 2.6 μm in the electrolytes containing 0.16 and 0.65 mass% water respectively. For all the electrolytes, the film thickness changes approximately linearly with the charge passed during anodizing, indicating that chemical dissolution of the developing oxide is negligible. SIMS depth profiling analysis was carried for anodic films formed in electrolyte containing ∼0.4 mass% water with and without enrichment of H 2 18O. Findings disclose that water in the electrolyte is a predominant source of oxygen in the anodic oxide films. The anodic films formed in the electrolyte containing 0.65 mass% water are practically free from phosphorus species. Reduction in water content increased the incorporation of phosphorus species.

Electrochemical corrosion behaviour of Pb-free Sn–8.5Zn–0.05Al–XGa and Sn–3Ag–0.5Cu alloys in chloride containing aqueous solution

The electrochemical corrosion behaviour of Pb-free Sn–8.5Zn–0.05Al–XGa and Sn–3Ag–0.5Cu alloys was investigated in 3.5% NaCl solution by using potentiodynamic polarization techniques. The results obtained from polarization studies revealed that there was a negative shift in the corrosion potential with increase in Ga content from 0.02 to 0.2 wt% in the Sn–8.5Zn–0.05Al–XGa alloy. These changes were also reflected in the corrosion current density ( I corr) value, corrosion rate and linear polarization resistance (LPR) of the four element alloy. However, for Sn–3Ag–0.5Cu alloy a significant increase in the corrosion rate and corrosion current density was observed as compared to the four element alloys. SIMS depth profile results established that ZnO present on the outer surface of Sn–8.5Zn–0.05Al–0.05Ga alloy played a major role in the formation of the oxide film. Oxides of Sn, Al and Ga contributed a little towards the formation of film on the outer surface of the alloy. On the other hand, Ag 2O was primarily responsible for the formation of the oxide film on the outer surface of Sn–3Ag–0.5Cu alloy.

SIMS depth profiling analysis of halogens in CdTe/CdS/TSO solar cells using Cs 2M + cluster ions

SIMS depth profiling analysis of Au(Cu)/CdTe/CdS/SnO 2 solar cell structures were done. We analyzed these structures in the so-called CsM + mode and found an extremely high yield of Cs 2Hn + cluster ions, where Hn is halogen, in comparison with CsHn + ion yield and in comparison with yields of other Cs 2M + clusters, where M is another metal or non-metal element. There was no any interference for Cs 2Hn + cluster ions (for F and Cl) with other clusters in the concentration range of interest. This makes it possible to perform analysis of all elements of interest in noticed solar cells (halogens, metals and non-metals) during only one SIMS analysis. Possible explanation of the found anomalous yield is discussed.

Quantification of SiGe layer composition using MCs + and MCs 2+ secondary ions in ToF-SIMS and magnetic SIMS

The interest in using semiconducting layers of SiGe in microelectronics means it is important to be able to characterise the composition of such layers as a function of depth. SIMS is an essential technique for characterising such layers but quantification of the Ge concentration in SIMS depth profiles of SiGe requires knowledge of the secondary ion generation efficiency as a function of Ge concentration. We have studied the secondary ion emission of MCs + and MCs 2 + ions for SiGe layers with Ge concentrations ranging from 0 to 85 at.% Ge. A CAMECA IMS-5F and an ION-TOF ToF-SIMS V both with a 2 keV Cs primary beam were used. We find a good linear correlation between the ratio of SIMS secondary ion intensities I(GeCs n +)/ I(SiCs n +) (where n = 1 and 2) and the composition ratio [Ge]/[Si]. The same linear correlation is observed for results obtained using the ToF-SIMS, but the RSF deviates slightly from a linear relationship with the Ge concentration. If a sample with several known Ge concentrations is used as a standard to determine the factor of proportionality between the ratio of secondary ion intensities and the composition ratio then the Ge concentration in an unknown sample can be determined from the point by point GeCs n +/SiCs n + ratio, where n = 1 and 2.

SIMS depth profiling and TEM imaging of the SIMS altered layer

A reduction in the scale of semiconducting devices has created many challenges in SIMS depth profiling. With fewer and shallower dopant atoms, depth resolutions have had to improve significantly especially in the first few nanometres. It is widely accepted that by using lower primary ion beam energies to minimise transient widths and beam induced mixing that the depth resolution can be optimized. The development of the Floating Low-energy Ion Gun (FLIG) has enabled SIMS to operate with beam energies in sub-keV regions enabling depth profiling of shallow features. Accurate depth profiling also relies on accurate depth calibration. Typically depth calibration is performed by measuring SIMS crater depths and assuming a constant sputter rate thus incurring an error. TEM analysis in conjunction with SIMS has successfully been used to depth calibrate a test structure with an error <0.5 nm. The top 5 nm of a surface is a problematic region for SIMS depth profiling due to depth calibrations issues. The current work is to obtain an accurate depth profile of a 5 nm thick altered layer using TEM to assist depth calibration. With the depth resolution being dependent on the altered layer, the analysis of sub-keV altered layers will give an insight into the ultimate depth resolution attainable.

Angular distribution of sputtered matter under Cs + bombardment with oblique incidence

Silicon, germanium and indium phosphide targets are sputtered with a cesium ion beam. The energy of impact is changed from 2 keV to 10 keV and the incidence angle of bombardment is modified from 30° to 60°. Emitted matter is collected on a semi-cylindrical copper foil. Subsequently, spatially resolved thicknesses and elemental compositions of the deposit are determined by means of SIMS depth profiles. These distributions across the deposit allow us to deduce the angular distribution of emitted matter. Our experimental data show that the preferential direction as well as the spreading around this direction can be altered, with more or less efficiency, by the variation of the bombardment parameters. For the indium phosphide, we also study the elemental composition of the deposit in function of the emission angle. It shows an increasing deviation from stoichiometry with increasing emission angle.

Superhydrophilicity and XPS study of boron-doped TiO 2

This study examines the superhydrophilicity and chemical state of boron-doped TiO 2 prepared by the ion implantation method and explores the effect of annealing on them. XRD measurements show that the implanted sample forms a polycrystalline structure of anatase with no trace of rutile. Their water-contact angles are significantly reduced upon irradiation with ultraviolet light. The Ti 2p XPS spectra of the oxide exhibit a shoulder peak at the lower binding energy side of the main peak, whereas no shoulder is observed in single-crystal and annealed TiO 2. This suggests that the titanium ions with lower valences are produced by boron doping and they disappear on subsequent annealing. The SIMS depth profile of boron in the as-implanted TiO 2 exhibits a peak at a depth of 15–20 nm, whereas this peak disappears upon annealing. The water-contact angles increased on annealing under ultraviolet light illumination. It is concluded that the improvement in the superhydrophilicity by boron doping is due to the reduction of titanium, and the deterioration of superhydrophilicity with the subsequent annealing is due to the oxidation of reduced titanium and the inward diffusion of boron.

The effect of C 60 cluster ion beam bombardment in sputter depth profiling of organic–inorganic hybrid multiple thin films

The effects of C 60 cluster ion beam bombardment in sputter depth profiling of inorganic–organic hybrid multiple nm thin films were studied. The dependence of SIMS depth profiles on sputter ion species such as 500 eV Cs +, 10 keV C 60 +, 20 keV C 60 2+ and 30 keV C 60 3+ was investigated to study the effect of cluster ion bombardment on depth resolution, sputtering yield, damage accumulation, and sampling depth.

SIMS characterization of segregation in InAs/GaAs heterostructures

We performed a detailed study of in situ indium segregation in InAs/GaAs heterostructures during conventional MBE growth process. A set of heterostructures grown under different substrate temperatures was tested. We used in the study a recently developed equation for SIMS's Depth Resolution Function (DRF), which included Recoil Implantation, Cascade Mixing and Sputtering Induced Roughness phenomena (RMR model). Segregation process was included in this DRF as an exponentially increasing function. Then we found from experimental SIMS depth profiles segregation parameters for different growth temperatures and the energy activation for the segregation process. It was found equal to 0.27 eV that is close to values published in literature. A segregation free regime of the growth process was developed experimentally.

Depth profiling of organic materials using improved ion beam conditions

We used the so-called dual beam mode of depth profiling to start a systematic investigation of organic depth profiling with a time of flight secondary ion mass spectrometer (TOF-SIMS) instrument. Similar to inorganic profiling, we found the dual beam mode beneficial because sample erosion and sample analysis are decoupled and can be optimised independently. We applied different primary projectiles such as C 60, O 2 and Cs for sputtering to a variety of organic specimens, using a wide range of impact energies. Results are discussed with respect to the feasibility of the different approaches to organic depth profiling in SIMS.

Cesium near-surface concentration in low energy, negative mode dynamic SIMS

Reducing the energy of the primary ions will improve the depth resolution in SIMS depth profiling. At ultra low energies (<150 eV) the sputtering yield is drastically reduced. In this report we will focus on Cs + ions, which are commonly used for their enhancement of negative secondary ion formation, and discuss the impact of these extreme conditions on the steady state surface concentration of cesium. In contrary to what is found from sputtering-based retention models, the steady state surface concentration of (retained) cesium on silicon reaches a maximum value in the order of 15 at%.

RF magnetron sputtered La 3+-modified PZT thin films: Perovskite phase stabilization and properties

In this work, we report the preparation of lanthanum-modified lead zirconate titanate (PLZT) thin films in pure perovskite phase by RF magnetron sputtering. Various deposition parameters such as target-to-substrate spacing, sputtering gas composition, deposition temperature, post-deposition annealing temperature and time have been optimized to obtain PLZT films in pure perovskite phase. The films prepared in pure argon at 100 W RF power without external substrate heating exhibit pure perovskite phase after rapid thermal annealing (RTA) at 700 °C for 5 min. The film prepared at 225 °C substrate temperature also exhibits pure perovskite phase after RTA at 700 °C for 2 min. SIMS depth profile performed on one of the pure perovskite films (RTA at 700 °C for 5 min) shows very good stoichiometric uniformity of all elements of PLZT. The surface morphology of the films was examined using SEM and AFM. The dielectric, ferroelectric and electrical properties of the pure perovskite films were also investigated in detail. The remanent polarization for the films annealed at 700 °C for 5 and 2 min were found to be 15 and 13.5 μC cm −2, respectively. Both the films have high DC resistivity of the order of 10 11 Ω cm at the electric field of ∼80 kV cm −1.

SIMS artifacts in the near surface depth profiling of oxygen conducting ceramics

Using ultra low energy SIMS ion beams of oxygen and nitrogen, the very near surface region of an 16O annealed La 0.8Sr 0.2MnO 3 pellet has been depth profiled in order to investigate the surface layer composition and to determine any perturbing ion beam–target interactions. By ratioing the measured cation species, the results indicate that only Sr segregation at the near surface can be clearly identified, and no separate oxide layer was present on the top surface. By monitoring the build up of the altered layer associated with SIMS depth profiling, it was observed that the depth at which the altered layer was fully formed was deeper than the expected projected range, R p , of the ion beam. These results confirm Sr excess in the near surface, which will have an effect on the vacancy concentration and therefore the surface exchange coefficient, k.

High depth resolution SIMS analysis using metal cluster complex ion bombardment

SIMS depth profiles were measured using metal cluster complex ions of Ir4(CO)7+ as a primary ion beam in order to obtain high depth resolution. Depth resolution was evaluated as a function of primary ion species, energy and incident angle using a multiple boron delta-doped silicon sample. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same bombardment condition due to reduction of atomic mixing in the depth. The best depth resolution was 0.9 nm under the bombardment condition of 5 keV, 45° with oxygen flooding, which approaches the value measured with state of the art SIMS analyses. However, depth resolution was not improved by decreasing the cluster ion energy (less than 5 keV), even though the roughness of the sputtered surface was suppressed. The limit of depth resolution improvement may be caused by a carbon cover-layer that prevents the formation of surface oxide that buffers atomic mixing. To overcome this issue, it will be necessary to eliminate carbon from the cluster ion.

Structural, electrical and optical properties of ZnO/Si structures prepared by sputtering or pulsed laser deposition

The present paper is based on study of polycrystalline ZnO:Al films deposited by RF sputtering in Ar atmosphere and by pulsed laser deposition (PLD) on p and n-type Si. The structural, electrical and optical properties of processed devices were investigated before and after annealing in temperature range of 400–600°C. Films deposited by RF sputtering show conductive ZnO:Al n-type layer. After annealing in N2 atmosphere the conductivity of ZnO layer increased as ZnO/Si interface exhibits diffusion of Si into ZnO and O into Si. This effect was confirmed show promising photodetector properties in the spectral range of 380 ÷ 1050 nm by SIMS depth profile measurements. PLD deposited ZnO films under certain growth conditions (400°C) in O2 atmosphere show p-type layer formation. The investigated Si/ZnO heterostructures shows promising photodetector properties in the spectral range of 380 ÷ 1050 nm.

Applications of focused ion beam SIMS in materials science

Focused ion beam instruments (FIB) can be used both for materials processing and materials analysis, since the ion beam used in the FIB milling process generates several potentially useful analytical signals such as electrons, ions and photons. Thus, several different modes of FIB based analysis are possible, depending on the detectors placed within the instrument. In this paper we discuss some applications of focused ion beam instruments equipped with a secondary ion mass spectrometer (FIB SIMS) and a secondary electron detector (FIB SED). We describe the FIB SIMS instrumentation, and various aspects of instrumental design. Different modes of operation are discussed, including SIMS mass spectrometry, SIMS imaging and SIMS depth profiling. Applications of FIB SIMS analysis in materials science are given. Materials discussed include micrometeorites and micrometeorite impact sites on metal foils, an oxide ceramic for a solid oxide fuel cell (La0.9Sr0.1CoO3), glass, stainless steel, zeolite beads, superconducting and semiconducting multilayers and aerospace alloys.

Characterization of surface oxide layers formed on FeAl alloys by annealing under different atmospheres

AbstractXPS and SIMS were used for characterizing the surface oxide layers formed on FeAl alloys during annealing under atmospheres with different partial pressures of oxygen, which were controlled by H2O/H2 ratios in the gas. The XPS results showed that an aluminum oxide (Al2O3) layer was formed on the surfaces of samples annealed at a high temperature under a low partial pressure of oxygen, while such a layer was not formed on the surfaces of samples annealed under a high partial pressure of oxygen. SIMS depth profiles showed that the surfaces of samples annealed at high temperatures under a low partial pressure of oxygen were covered with a thin Al2O3 layer of approximately 50 nm thickness. It was also shown that oxygen penetrated the samples annealed under a high partial pressure of oxygen, and the depth profile of oxygen was correlated with that of aluminum. This indicates that internal oxidation of aluminum occurs in the samples annealed under a high partial pressure of oxygen. Grazing‐incidence X‐ray diffraction (GIXD) was also employed for analyzing the structure of the Al2O3 layer formed on the surface of samples annealed under a low partial pressure of oxygen. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Three-Dimensional Compositional Analysis of Drug Eluting Stent Coatings Using Cluster Secondary Ion Mass Spectrometry

Cluster secondary ion mass spectrometry (cluster SIMS) employing an SF5+ polyatomic primary ion sputter source in conjunction with a Bi3+ analysis source was used to obtain three-dimensional molecular information in polymeric-based drug-eluting stent coatings. The formulations of the coatings varied from 0% to 50% (w/w) sirolimus drug in poly(lactic-co-glycolic acid) and were prepared on both MP35N metal alloy coupons and bare metal stents. All cluster SIMS depth profiles obtained indicated a drug-enriched surface region, followed by a drug-depletion region, and finally a constant bulk composition region, similar to previous data obtained in polymeric blend systems. The drug overlayer thickness was determined to increase with increasing sirolimus content. Sample temperature was determined to play an important role in the resulting depth profiles, where it was shown that the best profiles were obtained at low temperatures (-100 degrees C). At these temperatures, molecular signals typically remained constant through the entire depth of the film (approximately 6.5 microm) in some cases, as opposed to the typical 1 microm-2 microm depth limit, which is achievable at room temperature. The 3-D imaging capabilities of cluster SIMS were successfully demonstrated and indicated a significant amount of subsurface domain formation in the 25% and 50% sirolimus samples, but not in the 5% sample, which was homogeneous. These results clearly illustrate the utility of cluster SIMS for probing the 3-D structure in polymeric-based drug delivery devices.