Resolution Secondary Ion Mass Spectrometry Research Articles

High mass resolution secondary ion mass spectrometry via simultaneous detection with a charge-coupled device

High mass resolution secondary ion mass spectrometry via simultaneous detection with a charge-coupled device

High resolution secondary ion mass spectrometry depth profiling using continuous sample rotation and its application to superlattice and delta-doped sample analysis

We report the development of secondary ion mass spectrometry (SIMS) with continuous sample rotation to achieve high resolution that is independent of depth during compositional and dopant sputter depth profiling. Sample rotation reduces the ion beam-induced surface roughness that often limits the depth resolution in SIMS. To illustrate the effects of sample rotation on SIMS analysis, measurements both with and without rotation were performed on a molecular beam epitaxy grown AlGaAs/GaAs superlattice with 100 periods and 5-nm-thick layers, and a boron delta-doped (atomically planar) Si sample, with dopant concentrations from 1016–1021 atoms/cm3 at depths of 0.5–2.0 μm.

Modulation-Doped Multi-Quantum Well (MD-MQW) Lasers. II. Experiment

Detailed experimental results on p-type modulation-doped multi-quantum well (MD-MQW) lasers are discussed. The GaAs/GaAlAs MD-MQW laser was grown by low temperature (600°C) molecular beam epitaxy using Be as the p-type dopant. The realization of the p-type MD-MQW structure was fully confirmed by high resolution secondary ion mass spectroscopy, transmission electron microscopy, and photoluminescence measurement. An ultrahigh relaxation oscillation frequency of up to 30 GHz was realized, which is 2.5 times that of undoped MQW lasers and also 5 times that of double heterostructure lasers. In addition, the spectral chirping width of p-type MD-MQW lasers was experimentally confirmed to be 1/5 that of undoped MQW lasers. These improvements result from the enhancement of the differential gain due to the modulation doping effect in addition to the quantum size effect. These results are in good agreement with the theoretical analyis.

Effect of Residual Phosphorus on Amorphous Silicon Thin Film Transistors

ABSTRACTEffects of residual phosphorus in the channel region of amorphous silicon thin film transistors(a-Si TFTs) on the TFT characteristics were quantitatively investigated. Concentration and the depth profile of the residual phosphorus were measured by high resolution secondary ion mass spectroscopy(SIMS). The OFF characteristics of a-Si TFTs were also measured.The SIMS data showed that the phosphorus exists about 100nm deep into intrinsic a-Si(i-a-Si), but the OFF characteristics showed that the activity of the residual phosphorus is 4 order of magnitude lower than that of heavily phosphorus doped a-Si(+-a-Si). The residual phosphorus is found to be inactive and stable, and has little effect on a-Si TFT characteristics.These results enabled us to fabricate inverted staggered a-Si TFTs by the simplest process using only 2 photo-mask steps and 1 self-aligned exposure.

Simultaneous quantitative determination of the distribution of dopants in silicon by high mass resolution secondary ion mass spectrometry

Simultaneous quantitative determination of the distribution of dopants in silicon by high mass resolution secondary ion mass spectrometry

Quantitative analysis by submicron secondary ion mass spectrometry

In order to apply secondary ion mass spectrometry (SIMS) to quantitative analysis of submicron areas, we made a high-spatial resolution SIMS (submicron SIMS) by combining a focused metal ion beam, a plane-focusing mass spectrometer, and a multichannel parallel detection system. A 35 kV, 100 pA beam with diameter on the sample of <0.1 μm was used. During measurements, this high-current density ion beam can destroy the sample with a large sputtering rate when slowly rastered. This causes rapid changes in both absolute and relative intensities of secondary ions. In our system, a 120-channel parallel detector covers the 1:2 mass range of m/e dispersion. By using this submicron SIMS, quantitative factors in the analysis of microstructures on the surface were investigated. Sputtering yield and, consequently, secondary ion intensity depend largely upon the angle between the primary beam and the sample surface just under the beam irradiation; such topographic effects distort the quantitative results. In order to avoid such distortions, it was found to be advantageous to shave off the analyzed feature from one edge to the other. By using such a sputtering method, the incident angle of the primary beam to the surface being sputtered is held constant. Accordingly, the quantitative power of submicron SIMS was greatly improved.

High spatial resolution secondary ion imaging and secondary ion mass spectrometry of aluminium‐lithium alloys

SUMMARYSamples of aluminium‐lithium alloys have been observed by scanning ion microscopy and analysed by secondary ion mass spectrometry. The high signal‐to‐noise ratio of the positive secondary lithium ion opens up the possibility of both high resolution imaging and microanalysis of lithium distributions in aluminium and other materials. Some of the problems encountered due to sample preparation are discussed and ion images of both the artefacts and the true lithium distribution are shown.

High spatial resolution secondary ion mass spectrometry with parallel detection system

High-resolution secondary ion mass spectrometry is constructed by combining focused liquid metal ion beam and simultaneous detection mass spectrometer. A beam diameter on the sample is estimated to be less than 0.1 μm with the current of 100 pA, when the accelerating voltage is 35 kV. The detector is composed of a microchannel plate, and a multianode–multiamplifier–multicounter system controlled by a personal computer. The prototype multichannel detector covers the 1:2 mass range of m/e dispersion with a 120-channel parallel counting system. By using a multichannel parallel detection scheme, a spectral data acquisition rate several tens of times larger than that of the single-channel scheme was achieved. An ion-induced secondary electron image, a total secondary ion image, and mass-analyzed ion images (element maps) were obtained. In the individual analysis of a small particle, rapid and distinctive intensity changes for multiple elements were observed. This indicates that our detecting system is suitable for the accurate analysis of small-volume samples.

Hydrogen-Induced Defects in Silicon by CF4/x% H2 (0≤x≤ 100) RIE and H2 Plasma

ABSTRACTThe extended defects induced by hydrogen diffusion in silicon during the process of (1) CF4/x% H2(0≤x≤100) reactive ion etching, or (2) hydrogenation in H2 plasma, or (3) passivation of boron acceptors in H2 plasma, are studied by high resolution electron microscopy and secondary ion mass spectrometry. In reactive ion etched Si, a higher density of {111} planar defects are produced as the concentration of H2 in the etching gas and/or the overetch time is increased. The Si surface appears rough after reactive ion etching. Similar {111} planar defects are also found in Si after a H2 plasma treatment at 200°C for 3 hours, while the Si surface remains smooth. Boron im-plantation (30keV, 1015 at/cm2) and furnace annealing (1000°C, 30 min) processes are found to introduce stacking faults and perfect dislocation loops into silicon wafers. After subsequent exposure of boron implanted Si to a H2 plasma (200°C, 3 hours), microprecipitates associated with dislocation loops are observed.These results indicate that the apparent surface roughness (top 30 Å layer) in reac-tive ion etched Si is caused by energetic ion bombardment (∼500 eV). However, the {111} planar defects in CF4/x% H2(x>40%) reactive ion etched Si and the {111} planar defects and microprecipitates in H2 plasma treated Si are induced by the super-saturation of hydrogen diffused into Si during the plasma treatment process.

Applications of microfocussed ion beams in surface and thin film analysis

The use of microfocussed ion beams from liquid metal ion sources has allowed new standards of spatial resolution to be obtained in secondary ion mass spectrometry (SIMS). The combination of high spatial resolution with high sensitivity makes SIMS imaging a powerful technique for materials characterization and production problem-solving. In this paper a SIMS instrument is described which provides 500 Å spatial resolution using a gallium liquid metal ion source. This is used in combination with a high transmission quadrupole mass filter to produce chemical maps with both positive and negative secondary ions up to 1200 amu. Physical images containing topographical information are also possible by detection of secondary electrons or the total ion signal. A computer framestore facility allows ion and electron images to be stored digitally and subsequently overlaid in different colours. Images may be analysed retrospectively and processing facilities available include the addition, subtraction and ratioing of images, retrospective line-scan analysis, image rotation and zoom. In particular, the acquisition of a set of mass-selected images may be stored sequentially as a multi-element three-dimensional array. These data may be software-reconstructed to form an image of any plane through the original matrix. Examples of high resolution SIMS and the new techniques of data processing are given on a variety of samples including thin films and semiconductors.

Residual sulphur and silicon doping in InP and GaInAs

The samples studied here are either InP single crystals grown by the liquid encapsulation Czochralski technique or GaInAs epilayers grown on InP by molecular beam epitaxy or liquid phase epitaxy. They were characterized by secondary ion mass spectrometry (SIMS), Hall effect measurements, spark source mass spectrography (SSMS), and scanning electron microscopy (SEM). Quantitative high resolution SIMS analyses identify sulphur and silicon as background residual donors in these materials, but, it is found that the concentration of sulphur ranging from 4 × 10 15 to 8 × 10 16 cm −3 is about one order of magnitude higher than that of silicon. The donor concentrations determined either from electrical measurements or from SIMS analyses agree to within a factor of two over almost two orders of magnitude. Nevertheless, the behaviour of silicon in InP is still unclear. In homogeneous regions of the crystals, silicon is found by SIMS, at a low concentration, in the 3 × 10 14 –6 × 10 15 cm −3 range. But, sometimes, in regions where microtopographies are visible, perhaps precipitates or inclusions, the silicon concentration grows up to anomalously high levels. This fact is confirmed by bulk SSMS analyses.

The growth of ultra-thin layer superlattices by metalorganic chemical vapor deposition

The growth of very thin, abrupt-interface, uniform epitaxial heterostructures of AlGaAsGaAs and GaAsPGaAs by metalorganic chemical vapor deposition (MOCVD) is described. A brief description of the growth process as it applies to thin layers grown uniformly over large area is given. High resolution transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) data on lattice matched ultra-thin superlattices of AlGaAsGaAs and on strained layer superlattices (SLS) of GaAsPGaAs are presented. Convergent beam electron diffraction techniques are used to obtain higher order Laue zone line patterns from which the strain in these SLS structures can be determined.

Excitation of molecules formed by ion bombardment of surfaces

We report the observation of optical emission from molecular species AB ∗ formed when a solid A is bombarded by energetic heavy ions B +. The vibrational spectra of CN, SiN, and A1N were observed during N 2 + bombardment of C, Si and Al. To confirm our identification of the observed spectra, we performed high resolution secondary ion mass spectrometry experiments. The possibility of formation of these molecules by recombination is examined and we propose a mechanism whereby the emitting species is ejected as an intact molecule in a vibrationally excited state.