High Resolution SIMS Research Articles

Mapping of intracellular halogenous molecules by low and high resolution SIMS microscopy

The subcellular distribution of halogenous molecules has been studied by SIMS microscopy in cultured cells of a human breast carcinoma (MCF-7 cell line). Two instruments of microanalysis were used. A low lateral resolution ion microscope (SMI 300 CAMECA) and a prototype scanning ion microscope equipped with a cesium gun that gives high lateral resolution images. This apparatus has been developed by G Slodzian, in Onera Laboratories (Office National d'Etudes et de Recherches Aérospatiales). Molecules studied by low lateral resolution ion microscope were halogenous steroids: fluorometholone, triamcinolone, bromocriptine and bromoandrosterone. Analytical images show that the first two compounds are mainly localized in the nuclear structure of MCF-7 cells whereas the last two molecules are localized in cytoplasm of these cells. Images were obtained with a resolution of 1 μm. With the scanning ion microscope, it is now possible to obtain images at the ultrastructural level. Four analytical images can be simultaneously obtained by a single scan of the imaged area, corresponding to a depth of erosion of the section of ten nm. The intranuclear distributions of three pyrimidine analogs, 5-bromo-2′-deoxyuridine, 5-iodo-2′-deoxyuridine and 5-fluorouracil have been studied in phase S and M of MCF-7 cells and these images have been compared to the distribution of sulfur, nitrogen and phosphorus. All these images have been obtained with a lateral resolution better that 100 nm.

Integrated Rib Waveguide-Photodetector Using Si/Si1−xGex Multiple Quantum Wells for Long Wavelenghts

ABSTRACTWe have investigated the structural, electrical, and optical quality of epitaxial Si and Si1−xGex films grown by MBE on SIMOX (Separation by IMplanted OXygen) silicon substrates. Epitaxial films grown on these SOI substrates have been characterized using planar and cross-sectional TEM, high resolution X-ray diffraction, SIMS, and Seeco chemical etching to delineate defects. We have fabricated Si/SiGe P-i-N photodetectors integrated with Si waveguides on SOI for long wavelength applications. Low reverse leakage current densities were seen in these device structures. The photodetector exhibited an internal quantum efficiency of 50% at 1.1 μm with a frequency response bandwidth of 2 GHz.

SUBMICRON SECONDARY ION MASS SPECTROMETER FOR THREE-DIMENSIONAL ANALYSIS OF MICROSTRUCTURE

A gallium focused ion beam (Ga-FIB) has characteristics of sharpness and high current density, which enables both high spatial resolution SIMS analysis and precise micromachining of materials. In situ combination of micromachining and high spatial resolution analysis brings a new field of microbeam analysis on materials: three-dimensional analysis of microstructure under microscopic observation. By utilizing a Ga-FIB SIMS, analysis of bureid fine particles in a thin film multilayer device and observation of cross-section of an inorganic microcapsule were made

Influence of Si segregation on the two-dimensional electron gas mobility of inverted HEMT structures

SIMS depth profiles of Si and Al as well as Hall mobility data are reported for inverted high electron mobility transistor (I-HEMT) structures grown by MBE at different substrate temperatures, T s , between 350 and 750°C. To obtain both high electron mobility μ(cm 2 (Vs) −1) and high electron density of the two-dimensional electron gas, the doped AlGaAs barrier was separated from the undoped GaAs layer by a 5 nm undoped AlGaAs spacer. By high resolution SIMS depth profiling this spacer was indeed found to be free of Si (detection limit 1×10 17 atoms cm −3) for structures grown at T s ⪕ 650°C . For T s = 700° C, however, the space contains more than 10 17 atoms cm −3. For T s = 750° C the heterojunction appears broadened and the spacer is doped with Si up to 1×10 18 atoms cm −3. The low temperature Hall data are in accordance with these observations. The highest mobility ( μ = 61,000 at T = 18 K) was recorded for T s = 500° C, and was found to decrease slowly to μ = 14,000 at T s = 700° C, then dropping abruptly to μ = 2300 for T s = 750° C. It is concluded that charge carrier scattering by ionized Si, which has migrated into the nominally undoped spacer, degrades the electrical performance of I-HEMTs grown at T s ⪖ 500° C. A control experiment demonstrated that the mechanism of Si migration is not diffusion, but segregation. At T s = 750° C a deterioration of the heterojunction and/ or a migration induced doping of the active channel is indicated.

An 17O NMR study on oxygen exchange in YBa 2Cu 3O 7− x

This study evaluated the effect of reaction conditions on the extent and uniformity of 17O-labeled YBa 2Cu 3O 7− x . It was shown by 17O NMR spectroscopy and high-resolution SIMS that statistical 17O-enrichment is achieved at high temperatures by synthesis from oxides under an 17O 2 atmosphere, or by direct 17O 2 exchange of preformed YBa 2Cu 3O 7− x . Nonuniform enrichment can be achieved at low temperatures and with the use of short reaction times. An 17O 2 circulator is described which proved useful for handling, purifying, and recovering the labeled oxygen.

Ion microprobe analysis of laser-deposited Y–Ba–Cu thin film: Effects of anneal temperature

We have employed high spatial resolution (<50 nm) SIMS to study thin film deposited on SrTiO3, produced by pulsed laser evaporation of bulk stoichiometric YBa2Cu3Ox pellets derived from either BaCO3 or Ba3N2. The grain growth, film-substrate interaction, and carbon contamination of the films were examined as a function of post-deposition anneal temperature ranging between 700 °C and 900 °C. On the surface of both types of film, we found overgrowth crystals, which are enriched in copper, that increased in size from a few tenths of a micron to several microns with increasing anneal temperature. Above 800 °C, the film forms a polycrystalline structure with grain size of ∼1 micron. With increasing anneal temperature, more strontium was observed on the surface of the film. Films prepared from YBa2Cu3Ox targets derived from BaCO3 and Ba3N2 were both contaminated with carbon: however, only the former showed segregated carbon along the grain boundaries of the polycrystalline film annealed at 900 °C.

Rapid thermal nitridation of thin SiO2 films

An alternative to SiO2 for gate dielectric applications in MIS devices is nitrided silicon dioxide. A study of this material is presented in this paper. Thin SiO2 layers (10 nm minimum thickness) were grown on silicon substrates and subsequently nitrided in ammonia at 1 atm using a rapid thermal processing system. Nitridation times ranged from 3 sec to 60 sec at temperatures from 900 to 1200‡ C. The resulting films were then characterized using a variety of techniques including high resolution TEM, XPS, AES, SIMS, and electrical measurements (C-V). Higher temperatures and longer processing times resulted in the accumulation of nitrogen at the film surface and at the Si/SiO2 interface. As expected, the electrical characteristics of the nitrided films were strongly influenced by the processing conditions. The morphology of the interface, as revealed by high-resolution TEM, was also altered by the nitridation process, especially for high processing temperatures (>1000° C).

Low temperature MBE growth of high quality modulation doped AlGaAs/GaAs MQWs for ultra-high-speed laser diodes

Highly Be-modulation-doped ( p=2×10 19 cm -3) AlGaAs/ GaAs MQWs without interface disorder for ultra-high-speed laser diodes have been grown by molecular beam epitaxy (MBE). The MQWs were grown at low substrate temperatures below 600°C to avoid diffusion of highly doped Be during growth. Structures of the modulation doped MQW were analyzed by high resolution SIMS and TEM analysis, which showed that no disordering took place at the MQW region. Photoluminescent peak wavelength of the modulation doped MQW was shifted to 13 meV lower energy side from that of an undoped MQW at 77 K as a result of energy band bending. The modulation doped MQW laser, though grown at such low growth temperatures, showed stable room temperature operation with extremely high relaxation oscillation frequency up to 30 GHz, which is about twice as high as previous top data.

High spatial resolution SIMS investigation of oxides formed on stainless steel under PWR conditions

High spatial resolution SIMS has been used to measure the variation in cobalt concentrations in oxide layers of stainless steel. Mass spectra from micron-sized crystals formed on the oxidised surface were recorded and depth profiles were taken through the inner oxide layer extending into the base metal. These measurements, used in conjuction with results from other more quantifiable techniques, allowed estimates to be made of the variation in cobalt concentration within the surface layers of the sample.

Microfocused ion beam applications in microelectronics

Finely focused ion beams with current densities on the order of one A/cm2 with beam diameters as small as 0.1 μm are used in a wide variety of surface processing applications in microelectronic research. Some of the techniques include scanning ion microscopy and high spatial resolution SIMS, micromachining by physical sputtering, ion beam induced surface chemistry for etching and deposition, maskless implantations, and lithography. The primary commercial application to date has been defect repair for photomasks although integrated circuit modification for diagnostic purposes is emerging as important. Focused ion beams have also been applied to III–V materials for in situ processing, lithography, and fabrication of integrated optics devices by micromachining. Several focused ion beam techniques and applications will be reviewed. Particular emphasis will be placed on micromachining, deposition, and SIMS techniques.

Interatomic potential in solids and its applications to range calculations

The phenomenon of dopants migrating towards the surface against the concentration gradient may be useful to control junction depth for ultra-shallow profiles. We apply high-resolution SIMS—in combination with channelling Rutherford backscattering spectroscopy (RBS)—to reveal these subtle, yet highly significant changes in dopant profiles during or after solid phase epitaxial regrowth (SPER) in germanium-preamorphized silicon. We observe redistribution for shallow implantations of arsenic in preamorphized Si towards the surface during SPER. This is caused by segregation of As in front of the amorphous/crystalline (a/c) Si interface. Also for boron anomalous behavior has recently been reported, showing preferential migration towards the surface after crystalline regrowth at high concentrations for shallow implantation of BF2+ in crystalline Si or B+ in Ge-preamorphized Si. Here, we investigate the time- and temperature-dependence of this phenomenon to clear up the mechanism for redistribution during crystalline regrowth. Redistribution of B is shown to occur only partly during SPER, most likely caused by segregation. Still, significant changes take place after completion of SPER during prolonged annealing. We propose that this is provoked by the locally steep concentration gradient of interstitials close to the surface after restoration of the crystalline structure.

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A new method of spectra acquisition and exact mass determination of resolved peaks in high mass resolution ion microscopy

AbstractA major problem in high resolution mass spectrometry of solid materials has been the difficulty or even the impossibility associated with identifying the resolved peaks, i.e. the determination of their exact mass. A method of exact mass determination (relative precision in the range of 10−5) of resolved peaks is presented which requires no foreknowledge of the specimen. The method is derived from mass spectrometry techniques commonly employed for the analysis of liquid or gaseous organic samples, and is based on three steps: (1) the use of an external reference sample; (2) sequential analysis of the reference and unknown sample; and (3) superposition of the two spectra. The technique is illustrated using a standard CAMECA IMS 3f ion microscope.A further advance has been the development of single ion sensitive mass spectrography, where the entire spectrum within a narrow mass range is simultaneously viewed in real time. Spectra acquisition times are reduced by a factor of up to ten. Mass spectrography allows the detection of transient peaks or peaks of rapidly varying intensity, e.g. thin surface films or oxides. Using an image processor the spectra may be integrated or averaged in real time before storing in memory. Real time spectra acquisition and interpretation make high mass resolution SIMS (indispensable in material science) a routine operation providing information otherwise difficult or impossible to obtain.

Electromigration of silicon and phosphorus in tantalum polycide interconnections

TaSi 2 /n+-poly-Si interconnections of integrated circuits were investigated after high direct current density stress at elevated temperatures. The current density was increased up to values that caused failures of the interconnections due to electromigration. We found in our experiments that material migrated from the anode to the cathode causing open-circuit failure at the anode region. At the cathode, the material piled up forming hillocks. Material depletion and accumulation are caused by positive or negative mass flow divergences due to temperature gradients near the pads. The accumulated material at the cathode was analyzed by high-resolution Auger and SIMS spectroscopy. The obtained spectra show only silicon and phosphorus peaks with an increased phosphorus concentration at the cathode area. Hence, it can be concluded that in TaSi 2 /n+-poly-Si interconnection mainly material of the polysilicon layer including the dopant phosphorus is moved by electromigration. In contrast to these results of dc experiments, no electromigration occurred during equivalent ac stress.

6236. High resolution SIMS and neutron depth profiling of boron through oxide-silicon interfaces

6236. High resolution SIMS and neutron depth profiling of boron through oxide-silicon interfaces

Characterization of shallow (R p <20 nm) As- and B-implanted and electron-beam annealed silicon

The annealing characteristics of shallow (Rp <20 nm) arsenic- and boron-implanted layers were found to be a complex function of the thermal cycle which the sample experienced. Arsenic at 10 keV and boron at 4.5 keV (derived from 20 keV BF+2 ) were implanted in the dose range 1014–1016 cm−2 into (100) Si. The optimal implant doses to maximize conductivity with essentially undiffused layers of device quality material were 2 × 1015 and 1015 cm−2 for As and B, respectively. A comparison of rapid isothermal annealing using the multiple-scan electron-beam annealing method and conventional furnace annealing was made. For arsenic minimum resistivities of about 2 × 10−4 Ω cm were obtained after furnace annealing at 550 °C for 15 min or electron-beam annealing with a peak temperature between about 700 and 1100 °C during a 100 ms (or 1 s) anneal. For boron, electron-beam annealing for 100 ms (or 1 s) with a peak temperature of between ∼700 and 1000 °C produced a resistivity of 7 × 10−4 Ω cm which compared with 1.2 × 10−3 Ω cm following conventional furnace annealing. High-resolution SIMS showed that peak temperatures of up to about 1000 and 1100 °C for B and As layers, respectively, may be reached with essentially no diffusion. An extension of diffusion theory applicable to conventional furnace annealing of deeper implant gave results in accord with SIMS profiles.

High resolution SIMS and neutron depth profiling of boron through oxide–silicon interfaces

SIMS and neutron depth profiling (NDP) have been used to study the distribution 10B+ implanted into silicon through thermal oxide, and its segregation at the oxide–silicon interface on annealing. Using the reaction 10B (n,∝)7 Li, and a grazing exit geometry, the depth resolution in the ∝- particle spectrum in NDP is ∼10 nm. Better depth resolution is obtained in the calibrated SIMS profiles. For a wafer implanted with 70 keV 10B+ through 194 nm SiO2 to a dose of 1×1016 cm−2, the segregation coefficient after annealing at 1000 °C for 30 min was ∼3 from NDP. The segregated B was resolved better by SIMS and segregation coefficient of 10 was indicated from the SIMS depth profile. Analysis of the B profile in the Si surface after chemically stripping the SiO2 indicated a value ≥50. Higher depth resolution with NDP should be achievable by using a more grazing exit geometry, but higher flux neutron sources are required to maintain reasonable counting times.

Focussed Ion Beams from Liquid Metal Ion Sources Theory and Applications

ABSTRACTA theoretical model of liquid metal ion source (LMIS) operation has been developed by Kingham and Swanson. In this paper we consider beams from LMIS on the basis of this model. In particular we consider properties such as angular intensity, energy spread and relative abundance of differently charged species of the ion beam, and the dependence of these properties on source current and elemental composition. The conclusion is that the brightest focussed beam for a given probe size is attainable at the lowest possible source current as previously stated by Swanson. LMIS sources have an onset current of typically 1-2[A and will not operate stably below this current, thus limiting the maximum focussed ion beam brightness. The physical reason for this is discussed. The relevance of these properties to fine focussed ion beam applications, particularly semiconductor processing, is discussed. Useful, and in some cases unique, device manufacturing techniques can be postulated using one or more of the momentum, energy or atomic addition properties inherant tothis type of system. Advanced research tools are discussed, together with some examples of the use of microfocussed ion beams with probe sizes down to less than 50nm. Immediate applications include: high resolution ion imaging and SIMS microanalysis; ion beam machining and microfabrication; ion beam resist exposure and ion beam mask repair.

Artifacts in high resolution SIMS: the contribution of the ion source

Liquid metal ion sources (LMIS) used as fine focused beam probes release, in addition to the desired elemental ion, other charged particles and energetic neutral atoms of low intensity. We have analysed the charged particle beam components from a Ga + LMIS used in a commercial ion probe with a simple mass spectrometer. For comparison, results are shown for the beam from a liquid Cs + ion source which was analysed by a similar method. For both metals we detected charged micro-droplets of nanometer dimensions accompanying the primary ion beam. In addition a range of molecular ions, Cs n +, was observed from the caesium source. The kinetics of these satellite particles are investigated leading to a brief discussion of the implication for SIMS surface analysis.

Properties of interfaces in (CdZn)S/CuInSe2 heterojunctions

The efficiency and operational characteristics of the (CdZn)S/CuInSe2 heterojunction solar cell are significantly improved as a result of a postfabrication heat treatment in an oxygen containing environment. The effects of this critical annealing process on the microchemical and microelectrical properties of the various cell layers and interfaces are investigated. Time-resolved EBIC and laser scanning techniques are correlated with cell performance data to identify two separate mechanisms that affect cell response. High resolution SIMS is used to evaluate compositional changes and interdiffusion effects, showing that penetration of the Cu-ternary layer by the oxygen is minimal. Light and dark current–voltage characteristics and diagnostic spectral response data are used to explain changes in cell operation.