Low-energy Secondary Ion Mass Spectrometry Research Articles

Improvement of extra low impact energy SIMS data reduction algorithm for process control

This work explores quantitative boron depth profiling in the top first nanometer using dynamic secondary ion mass spectrometry (SIMS). Dynamic SIMS measurements were performed with a magnetic sector CAMECA IMS Wf/SC Ultra, using extremely low impact energy O2+ (below 250 eV) sputtering. It was concluded that the modification of quantification protocol by the creation of a surface transient curve can provide a tool for the accurate characterization of low energy implantation wafers, including boron, under extremely low energy sputtering conditions with an oxygen beam.

Silver Diffusion in Organic Optoelectronic Devices: Deposition-Related Processes versus Secondary Ion Mass Spectrometry Analysis Artifacts

The development of organic optoelectronic devices relies on controlling interfaces during thin-film deposition and requires an accurate characterization of the film composition at these interfaces. Dynamic secondary ion mass spectrometry (SIMS) is widely used to investigate multilayer thin-film structures. Routine analysis protocols are well established for classical semiconductor samples, but for organic or mixed metallic–organic samples the limitations of the technique are less well established. In the current work, low-energy dynamic SIMS is used on metal–organic multilayered model structures similar to those in organic optoelectronic devices to study the origin of diffusion of metal into the organic layer (e.g., irradiation-induced diffusion during SIMS analysis or during the deposition process). Samples contain silver and organic compounds sequentially deposited by thermal evaporation in vacuum onto a Si substrate. They are analyzed using a 250 eV to 1 keV Cs+ primary ion beam. It is found that the m...

Low energy SIMS characterization of passive oxide films formed on a low-nickel stainless steel in alkaline media

Low-energy secondary ion mass spectrometry (SIMS) was used to study the oxide films formed on a low-nickel austenitic stainless steel (SS), potential replacement to conventional AISI 304 SS in reinforced concrete structures (RCS) that are subjected to aggressive environments. The effect of carbonation and the presence of chloride ions were studied. The oxide films formed a chemically gradated bi-layer structure with an outer layer predominately constituted by iron oxides and an inner layer enriched in chromium oxides. Chloride ions were not found in the oxide film but did have an effect on film structure and thickness.

Ag-Organic Layered Samples for Optoelectronic Applications: Interface Width and Roughening Using a 500 eV Cs+ Probe in Dynamic Secondary Ion Mass Spectrometry

The performance of organic optoelectronic devices depends a lot on interface structure and width. Dynamic secondary ion mass spectrometry (SIMS) has been widely used to investigate interfaces in classical semiconductor devices and limitations are quite well understood. For low-energy dynamic SIMS on organic optoelectronic devices, sputter-induced diffusion processes and roughness formation have only been investigated sparsely. In this work we use low-energy dynamic SIMS depth profiling on metal-organic multilayered model samples with compositions similar to organic optoelectronic devices to investigate limitations in the calculation of interface widths due to sputter-induced roughness formation. The samples consist of silver and organic compounds (e.g., tris(8-hydroxyquinolinato) aluminum (Alq(3)) and metal phthalocyanines) sequentially deposited by thermal evaporation in vacuum onto a Si substrate. They are analyzed by a 500 eV Cs(+) primary ion beam. Surface roughness at the SIMS crater bottoms is characterized by AFM as a function of crater depth. We find that the roughness in SIMS craters is limited to approximately 1.5 nm, which is much smaller than the interface width of the as-deposited interfaces. Thus, for the studied organic-inorganic interfaces, low-energy dynamic SIMS can yield accurate information about interface morphology, allowing the study of its dependence on sample preparation conditions and its implication on device properties.

Calibration correction of ultra low energy SIMS profiles based on MEIS analysis of shallow arsenic implants in silicon

Secondary ion mass spectrometry (SIMS) and medium energy ion scattering (MEIS) have been applied to the characterization of ultra‐shallow distributions of arsenic in silicon obtained by ion implantation. A previously developed quantitative model for the correction of results obtained by ultra low energy SIMS was tested on different types of samples. The model deals with the different sputtering regimes in SiO2 and Si and corrects the analysis behaviour at the SiO2/Si interface. Model results were compared with MEIS which yields depth profiles that are more accurate and can be quantified from first principles. The obtained model was tested on samples with or without a pre‐amorphization implant step prior to As implantation and subsequently annealed at 550 °C in a partially oxidizing atmosphere. Results show excellent agreement on As peak position and shape; however, MEIS detects differences between profiles of preamorphised and non‐preamorphised samples whereas SIMS profiles of these samples are almost identical. Copyright © 2012 John Wiley & Sons, Ltd.

Calibration correction of ultra low energy SIMS profiles based on MEIS analyses for arsenic shallow implants in silicon

Secondary ion mass spectrometry (SIMS) and medium energy ion scattering (MEIS) have been applied to the characterization of ultra shallow distribution of arsenic in silicon obtained by ion implantation at 0.5–5 keV. MEIS offers the advantage of accurate quantification and ultimate depth resolution <1 nm but the detection limit achievable is always poorer than the one obtained by SIMS. The comparison of the results obtained by the two techniques allows to discriminate among different SIMS quantification processes in order to individuate the best in terms of accuracy in the initial transient width and at the SiO 2–silicon interface and develop quantitative model for SIMS profiles to align them to the curves as determined by MEIS. This model relies on different sputtering condition in SiO 2 (such as sputtering rate and ion yield) and additionally compensates analysis behavior in SiO 2/Si interface.

Analysis and fragmentation of organic samples by (low‐energy) dynamic SIMS

AbstractUp to now, the analysis of organic or biological samples was mainly investigated using static SIMS, while dynamic SIMS was generally limited to the analysis of inorganic samples. The increasing sophistication of organic optoelectronic devices (e.g. organic light emitting diodes and organic photovoltaic cells, etc.) requires molecular‐level dimensional control in the fabrication of multilayered structures with specifically engineered interfaces. However, analytical tools for monitoring such fabrication precision are scarce. In a current project, we address this challenge by advancing the development of low‐energy Secondary Ion Mass Spectrometry (LE‐SIMS) for the analysis of organic‐based optoelectronic materials systems.In the present work, we investigate the fragmentation as well as the ionization mechanisms for several molecules used in such devices: fullerene, copper phthalocyanine and tris(8‐hydroxyquinolinato) aluminium have been deposited onto silicon wafers. The study has been carried out on a Cameca SC‐Ultra instrument under Cs+ bombardment for various impact energies in the M− mode. Constant M− secondary ion intensities have been observed throughout the organic layers for some characteristic fragments of the organic molecules. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Thin epitaxial Si films as a passivation method for Ge(1 0 0): Influence of deposition temperature on Ge surface segregation and the high-k/Ge interface quality

Epitaxial fully strained Si films are known to form an effective passivation of the Ge(1 0 0) surface. However, we show using low-energy secondary ion mass spectrometry (SIMS) that considerable Ge surface segregation occurs for Si films grown from SiH 4 at 500 °C. In this study, we develop an alternative deposition process at 350 °C using Si 3H 8 which significantly decreases the Ge peak at the Si surface. We attribute this strong reduction mainly to the fact that growth at 350 °C from trisilane proceeds below the Si–H desorption temperature. Charge pumping measurements on n-type Ge devices show a reduction by approximately a factor three in the high-k/substrate interface trap density for the samples with 350 °C Si passivation, compared to those using a Si passivation deposited at 500 °C.

Surface roughening and erosion rate change at low energy SIMS depth profiling of silicon during oblique [formula omitted] bombardment

Surface roughening of boron δ -doped Si samples under low energy (0.5 keV/ O 2 + , 44 ° and 54 ° , and 1.0 keV/ O 2 + , 48 ° ) O 2 + bombardment at oblique incidence with and without oxygen flooding was studied with atomic force microscopy (AFM) and secondary ion mass spectrometry (SIMS). The erosion rate, the surface topography and the depth resolution as a function of depth have been measured. Changes in secondary ion yields have been correlated with changes in surface topography. It is found that the surface roughness depends on impact energy and incidence angle without flooding. The roughness decreases with decreasing impact energy. For the same energy (0.5 keV/ O 2 + ), the wavelength increases slightly with increasing angle of incidence and the roughness increases with increasing angle of incidence. With flooding, the roughness can be efficiently avoided. The best conditions to avoid roughness when analysing ultra shallow profiles with our magnetic sector instrument is 0.5 keV/ O 2 + , 44 ° with flooding. A procedure for the depth calibration of the profiles revealed that surface roughness causes an erosion rate change as measured using the shift of the position of the measured B peaks with and without flooding. The consequences of the roughness in terms of depth resolution of the profiles are analysed with and without flooding. Moreover, we show that the value of the Gaussian broadening parameter of the depth resolution function is closely related to the final dispersion of the heights in the crater bottom.

The analysis of a thin SiO2/Si3N4/SiO2 stack: A comparative study of low-energy heavy ion elastic recoil detection, high-resolution Rutherford backscattering and secondary ion mass spectrometry

The analysis of thin films in the range of 10nm and less has become very important in microelectronics. The goal of this article is an evaluation of low-energy TOF-ERDA (time-of-flight elastic recoil detection analysis) in comparison with low-energy SIMS (secondary ion mass spectrometry) and HRBS (high-resolution Rutherford backscattering spectrometry), using a thin SiO2/Si3N4/SiO2 stack as a test vehicle. Comparisons are made on the depth resolution, its loss as a function of depth and the quantification accuracy.

RF-plasma source qualification and compositional characterisation of GaNAs superlattices using SIMS

The potential of GaAs-based dilute nitride alloys, such as GaNAs and GaInNAs, for use in long-wavelength telecommunication applications has led to intensive research into their growth and physical properties. In order to produce high quality GaNAs-based devices it is essential that the material and growth source is fully characterised. In this paper, we present a study of MBE grown dilute GaN x As 1− x ( x ≈ 0.01) structures grown using two different nitrogen RF-plasma sources. The samples have been characterised using low energy secondary ion mass spectrometry (SIMS), whilst the attributes of the RF-plasma sources have also been fully assessed with this analytical technique. The study shows that low energy SIMS is essential in order to fully characterise the structure and purity of the GaNAs superlattices grown and can also assist in qualification of the RF-plasma source used for growth.

Quantitative analysis of the Ge concentration in a SiGe quantum well: comparison of low-energy RBS and SIMS measurements

The germanium concentration and the position and thickness of the quantum well in molecular beam epitaxy (MBE)-grown SiGe were quantitatively analyzed via low-energy Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). In these samples, the concentrations of Si and Ge were assumed to be constant, except for the quantum well, where the germanium concentration was lower. The thickness of the analyzed quantum well was about 12 nm and it was situated at a depth of about 60 nm below the surface. A dip showed up in the RBS spectra due to the lower germanium concentration in the quantum well, and this was evaluated. Good depth resolution was required in order to obtain quantitative results, and this was obtained by choosing a primary energy of 500 keV and a tilt angle of 51 degrees with respect to the surface normal. Quantitative information was deduced from the raw data by comparing it with SIMNRA simulated spectra. The SIMS measurements were performed with oxygen primary ions. Given the response function of the SIMS instrument (the SIMS depth profile of the germanium delta (delta) layer), and using the forward convolution (point-to-point convolution) model, it is possible to determine the germanium concentration and the thickness of the analyzed quantum well from the raw SIMS data. The aim of this work was to compare the results obtained via RBS and SIMS and to show their potential for use in the semiconductor and microelectronics industry. The detection of trace elements (here the doping element antimony) that could not be evaluated with RBS in low-energy mode is also demonstrated using SIMS instead.

Characterization of nitrogen distribution in HfO2 with low energy secondary ion mass spectrometry

Accurate characterization of the nitrogen distribution in a thin HfO2 film is important for process development on the nitridation of HfO2. Low energy secondary ion mass spectrometry (LESIMS) is potentially the technique of choice, thanks to the combined strength of high depth resolution and high detection sensitivity. By using a 250 eV, 60° O2+ primary beam and detecting NO−30 and O2−32 secondary ions, SIMS analysis was capable of profiling nitrogen in HfO2 with very short surface transient and minimal matrix effect across the HfO2–Si interface. This particular condition also exhibited desirable low yield of Si− secondary ions, i.e., minimal contribution of Si−30 to NO−30 through mass interference. Applications of this technique revealed incorporation of nitrogen at high levels in the top part of a HfO2 film by the modified magnetic type (MMT) plasma nitridation. The data also suggested loss of nitrogen near the top of an HfO2 film but no depletion across the interface between HfO2 and the interfacial as a result of the post nitridation anneal in O2.

Low energy RBS and SIMS analysis of the SiGe quantum well

The Ge concentration in a MBE grown SiGe and the depth of the quantum well has been quantitatively analysed by means of low energy Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). The concentrations of Si and Ge were supposed to be constant, except for the quantum well, where the nominal germanium concentration was at 5%. Quantitative information was deduced out of raw data by comparison to SIMNRA simulated spectra. With the knowledge of the response function of the SIMS instrument (germanium delta (δ) layer) and using the model of forward convolution (point to point convolution) it is possible to determine the germanium concentration and the thickness of the analysed quantum well out of raw SIMS data.

A new secondary ion mass spectrometry (SIMS) system with high-intensity cluster ion source

Secondary ion mass spectrometry (SIMS) with gas cluster ion beams (GCIB) was investigated with experiments and molecular dynamics (MD) simulations. A new cluster SIMS system with high-intensity cluster ion source has been developed. Ar cluster ion beam with the average size of 2000 was utilized as a primary ion beam. The beam diameter is less than 1 mm at the target position, and a current density of 10 μA/cm 2 is obtained. The etch rate of Si with this current density is more than 20 nm/min, which is far beyond the etch rate in recent low energy SIMS system. The secondary ion intensity linearly increases with the acceleration voltage. A threshold voltage of a few keV for secondary ion emission was found. These results are consistent with previous sputtering experiments.

The role of SIMS in cultural heritage studies

Secondary ion mass spectrometry (SIMS) is a highly sensitive chemical analysis technique available in variants, which are top monolayer specific (static SIMS) or which can extract micro-volume analyses or depth profiles (dynamic SIMS). The technique offers ppm or even ppb atomic sensitivity for the consumption of extremely small sample volumes. In the area of cultural heritage, SIMS has been applied to a diverse range of problems including technology and authenticity, origin and provenance, degradation processes, such as corrosion and weathering, and conservation. In this paper, the basic attributes and limitations of the technique are described. An outline is given of applications to glasses (obsidian dating, conservation of stained glass and Venetian glass), metals (simulated archaeological bronzes), pigments and human remains, focusing on conservation problems such as the assessment and suppression of corrosion, other degrading processes, identification of materials using speciation. The topic of ultra low energy SIMS, newly applied to cultural heritage materials, is briefly described.

Self-Assembled Monolayer of l-Cysteine on Au(111): Hydrogen Exchange between Zwitterionic l-Cysteine and Physisorbed Water

A self-assembled monolayer (SAM) of l-cysteine [HSCH2CH(NH2)COOH] was prepared on a Au(111) surface by vapor deposition in ultrahigh vacuum and was characterized by techniques of temperature-programmed desorption (TPD), Cs+ reactive ion scattering (Cs+ RIS), and low-energy secondary ion mass spectrometry (LESIMS). Analysis of the amino acid functional groups of SAM indicated that l-cysteine molecules exist in the zwitterionic form. Upon physisorption of the D2O overlayer on the SAM, the −NH3+ functional group of cysteine readily exchanges their H atoms with D2O in the temperature range 125−230 K. The H/D exchange of the −NH3+ group sequentially occurs with D2O molecules that are directly hydrogen-bonded to the SAM, and the long-range proton transfer to the upper layer water molecules does not occur. Temperature-programmed reaction study and kinetic analysis yielded an activation energy of 13 ± 1 kJ mol-1 for the H/D exchange reaction, which suggests proton tunneling as a mechanism.

Ge–Sn semiconductors for band-gap and lattice engineering

We describe a class of Si-based semiconductors in the Ge1−xSnx system. Deuterium-stabilized Sn hydrides provide a low-temperature route to a broad range of highly metastable compositions and structures. Perfectly epitaxial diamond-cubic Ge1−xSnx alloys are grown directly on Si(100) and exhibit high thermal stability, superior crystallinity, and crystallographic and optical properties, such as adjustable band gaps and lattice constants. These properties are completely characterized by Rutherford backscattering, low-energy secondary ion mass spectrometry, high-resolution transmission electron microscopy, x-ray diffraction (rocking curves), as well as infrared and Raman spectroscopies and spectroscopic ellipsometry. Ab initio density functional theory simulations are also used to elucidate the structural and spectroscopic behavior.

Process Control of Epi-Layers for SiGe:C Hetero-Structure Bipolar Transistors

ABSTRACTThe SiGe:C hetero-structure bipolar transistor (HBT) has turned into a key technology for wireless communication. This paper describes the metrology tools for SiGe epitaxy process control. Two types of analysis are critical, (1) routine control of SiGe base and Si cap thicknesses, location and thickness of the doping layer, doping dose, Ge composition profile, and their uniformity across the wafer; and (2) root-cause analysis on non-routine problems. This is achieved by developing a transmission electron microscopy (TEM) technique allowing a thickness measurement with a reproducibility better than 3 Å. Charge-compensated low-energy secondary ion mass spectrometry (SIMS) using an optical conductivity enhancement (OCE) allows a Ge composition measurement to a required precision of 0.5 at. %.

New Ge-Sn materials with adjustable bandgaps and lattice constants

ABSTRACTThe synthesis and optical properties of a new class of Si-based infrared semiconductors in the Ge1-x Snx system are described. Chemical methods based on deuterium-stabilized Sn hydrides and UHV-CVD were used to prepare a wide range of metastable compositions and structures directly on silicon. These materials exhibit high thermal stability, superior crystallinity, and unique crystallographic and optical properties, such as adjustable band gaps and lattice constants. These properties are characterized by Rutherford backscattering, low-energy secondary ion mass spectrometry, high-resolution transmission electron microscopy, x-ray diffraction as well as infrared and Raman spectroscopies and spectroscopic ellipsometry. The films grow essentially strain free and display a strong compositional dependence of the band structure.