Multilayer thin-film coatings based on chromium nitride and aluminum nitride: Comparative depth profiling by secondary ion mass spectrometry and glow-discharge optical emission spectrometry

Round-robin characterization is reported on the sputter depth profiling of CrN/AlN multilayer thin-film coatings on nickel alloy by secondary ion mass spectrometry (SIMS) and glow-discharge optical emission spectrometry (GD-OES). It is demonstrated that a CAMECA SIMS 4550 Depth Profiler operated with 3 keV O ₂ ⁺ primary ions provides the best depth resolution and sensitivity. The key factor is sample rotation, which suppresses the negative influence of the surface topography (initial and ion-induced) on the depth profile characteristics.     

Quantification of antimony depth profiles in Sb-doped tin dioxide thin films

Sb-doped SnO₂ thin films, deposited by atomic layer epitaxy (ALE) for gas sensor applications, have been characterized by secondary ion mass spectrometry (SIMS). Quantification of the depth profile data has been carried out by preparing a series of ion implanted standards. Average concentrations determined by SIMS have been compared with Sb/Sn ratios obtained by X-ray fluorescence (XRF) spectrometry and proton induced X-ray emission (PIXE) spectrometry and have been found to be in good agreement. However, a detection limit of 5×10¹⁸ at cm^-3 could only be obtained because of mass interferences. SIMS data show that the ALE technique can be used to produce a controllable growth and doping of thin films.     

Ultrashallow depth profiling using SIMS and ion scattering spectroscopy

The accuracy of ultrashallow depth profiling was studied by secondary ion mass spectrometry (SIMS) and high‐resolution Rutherford backscattering spectroscopy (HRBS) to obtain reliable depth profiles of ultrathin gate dielectrics and ultrashallow dopant profiles, and to provide important information for the modeling and process control of advanced complimentary metal‐oxide semiconductor (CMOS) design. An ultrathin Si₃N₄/SiO₂ stacked layer (2.5 nm) and ultrashallow arsenic implantation distributions (3 keV, 1 × 10¹⁵ cm^?2) were used to explore the accuracy of near‐surface depth profiles measured by low‐energy O₂⁺ and Cs⁺ bombardment (0.25 and 0.5 keV) at oblique incidence. The SIMS depth profiles were compared with those by HRBS. Comparison between HRBS and SIMS nitrogen profiles in the stacked layer suggested that SIMS depth profiling with O₂⁺ at low energy (0.25 keV) and an impact angle of 78° provides accurate profiles. For the As⁺‐implanted Si, the HRBS depth profiles clearly showed redistribution in the near‐surface region. In contrast, those by the conventional SIMS measurement using Cs⁺ primary ions at oblique incidence were distorted at depths less than 5 nm. The distortion resulted from a long transient caused by the native oxide. To reduce the transient behavior and to obtain more accurate depth profiles in the near‐surface region, the use of O₂⁺ primary ions was found to be effective, and 0.25 keV O₂⁺ at normal incidence provided a more reliable result than Cs⁺ in the near‐surface region. Copyright © 2007 John Wiley & Sons, Ltd.     

Degradation of poly(acrylates) under SF5+ primary ion bombardment studied using time‐of‐flight secondary ion mass spectrometry. 1. Effect of main chain and pendant methyl groups

Polyatomic primary ions have been applied recently to the depth profiling of organic materials by secondary ion mass spectrometry (SIMS). Polyatomic primary ions offer low penetration depth and high damage removal rates in some polymers, but the relationship between polymer chemistry and degradation under polyatomic primary ion bombardment has not been studied systematically. In this study, positive and negative ion time‐of‐flight SIMS (ToF‐SIMS) was used to measure the damage of ～100 nm thick spin‐cast poly(methyl methacrylate) (PMMA), poly(methyl acrylate) (PMA) and poly(methacrylic acid) (PMAA), films under extended (～2 × 10¹⁴ ions cm^?2) 5 keV SF₅⁺ bombardment. These polymers were compared to determine the effect of the main chain and pendant methyl groups on their degradation under SF₅⁺ bombardment. The sputter rate of PMMA was approximately twice that of PMA or PMAA and the rate of damage accumulation was higher for PMA and PMAA than PMMA, suggesting that the main chain and pendant methyl groups played an important role in the degradation of these polymers under SF₅⁺ bombardment. These results are consistent with the literature on the thermal and radiation‐induced degradation of these polymers, which show that removal of the main chain or pendant methyl groups reduces the rate of depolymerization and increases the rate of intra‐ or intermolecular cross‐linking. Copyright © 2004 John Wiley & Sons, Ltd.     

Degradation of poly(acrylates) under SF5+ primary ion bombardment studied using time‐of‐flight secondary ion mass spectrometry. 2. Poly(n‐alkyl methacrylates)

Polyatomic primary ions offer low penetration depth and high damage removal rates in some polymers, facilitating their use in the molecular depth profiling of these polymers by secondary ion mass spectrometry (SIMS). This study is the second in a series of systematic characterizations of the effect of polymer chemistry on degradation under polyatomic primary ion bombardment. In this study, time‐of‐flight SIMS (ToF‐SIMS) was used to measure the damage of ～90 nm thick spin‐cast poly(methyl methacrylate), poly(n‐butyl methacrylate), poly(n‐octyl methacrylate) and poly(n‐dodecyl methacrylate) films under extended (～2 × 10¹⁴ ions cm^?2) 5 keV SF₅⁺ bombardment. The degradation of the poly(n‐alkyl methacrylates) were compared to determine the effect of the length of the alkyl pendant group on their degradation under SF₅⁺ bombardment. The sputter rate and stability of the characteristic secondary ion intensities of these polymers decreased linearly with alkyl pendant group length, suggesting that lengthening the n‐alkyl pendant group resulted in increased loss of the alkyl pendant groups and intra‐ or intermolecular cross‐linking under SF₅⁺ bombardment. These results are partially at variance with the literature on the thermal degradation of these polymers, which suggested that these polymers degrade primarily via depolymerization with minimal intra‐ or intermolecular cross‐linking. Copyright © 2004 John Wiley & Sons, Ltd.     

Time‐of‐flight secondary ion mass spectroscopic characterization of the nitrogen profile of shallow gate oxynitride thermally grown on a silicon substrate

Silicon oxynitride has been used as a shallow gate oxide material for microelectronics and its thickness has been reduced over the years to only a few tens of angstroms due to device size scaling. The nitride distribution and density characteristic in the gate oxide thus becomes imperative for the devices. The shallow depth profiling capability using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) has huge potential for the nitrogen characterization of the shallow gate oxide film. In this article, both positive and negative spectra of TOF‐SIMS on silicon oxynitride have been extensively studied and it was found that the silicon nitride clusters Si_xN^? (x = 1–4) are able to represent the nitrogen profiles because their ion yields are high enough, especially for the low‐level nitride doping in the oxide, which is formed by the annealing of nitric oxide on SiO₂/Si. The gate oxide thickness measured by the TOF‐SIMS profiling method using ¹⁸O or CsO profile calibration was found to correlate very well with transmission electron microscope measurement. The nitrogen concentration in the gate oxide measured using the TOF‐SIMS method was consistent with the results obtained using the dynamic SIMS method, which is currently applied to relatively thicker oxynitride films. Copyright © 2012 John Wiley & Sons, Ltd.     

Are cluster ion analysis beams good choices for hydrogen depth profiling using time‐of‐flight secondary ion mass spectrometry?

For more than three decades, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used for elemental depth profiling. In recent years, cluster primary ion sources (principally, C₆₀⁺, Bi_n⁺, and Au_n⁺) have become widely available, and they can greatly enhance the signal intensity of molecular ions (10–1000 times). Understanding the performance of cluster ion analysis beams used in elemental depth profiling can greatly assist normal ToF‐SIMS users in choosing the optimal analysis beam for depth profiling work. Presently, however, the experimental data are lacking, and such choices are difficult to make. In this paper, hydrogen and deuterium depth profiling were studied using six different analysis beams—25 keV Bi⁺, Bi₃⁺, Bi₅⁺, 50 keV Bi₃²⁺, 10 keV C₆₀⁺, and 20 keV C₆₀²⁺. The effort shows that cluster primary ions do enhance H^? and D^? yields, but the enhancement is only about 1.5–4.0 times when compared to atomic Bi⁺ ions. Because the currents of atomic ion analysis beams are much stronger than the currents of cluster ion analysis beams for most commercial ToF‐SIMS instruments, the atomic ion analysis beams can provide the strongest H^? and D^? signal intensities, and may be the best choices for hydrogen and deuterium depth profiling. In addition, two representative nuclides, ³⁰Si and ¹⁸O, were also studied and yielded results similar to those of H^? and D^?. Copyright © 2011 John Wiley & Sons, Ltd.     

Depth profile analysis of thin film solar cells using SNMS and SIMS

SNMS (sputtered neutrals mass spectrometry) and SIMS (secondary ion mass spectrometry) are used for the depth profile analysis of thin film solar cells based on amorphous silicon. In order to enhance depth resolution, model systems are analyzed only representing parts of the layered system. Results concerning the TCO (transparent conducting oxide)/p interface and the n/i interface are presented. To minimize matrix effects, SNMS is used when the sample consists of layers with different matrices. Examples are the TCO/p interface (where the transition lengths of the depth profiles are found to be sharper when ZnO is used as TCO compared to SnO₂) and SnO₂/ZnO interfaces in coated TCO layers (where a Sn contamination inside the ZnO layer is found depending on the plasma pressure during the ZnO deposition). SIMS is used when the limits of detection reached by SNMS are not sufficient. Examples are H depth profiles in ZnO layers or P depth profiles near the n/i-interface.     

Degradation of poly(acrylates) under SF5+ primary ion bombardment studied using time‐of‐flight secondary ion mass spectrometry. 3. Poly(hydroxyethyl methacrylate) with chemical derivatization

Molecular depth profiling of polymers by secondary ion mass spectrometry (SIMS) has focused on the use of polyatomic primary ions due to their low penetration depth and high damage removal rates in some polymers. This study is the third in a series of systematic characterizations of the effect of polymer chemistry on degradation under polyatomic primary ion bombardment. In this study, time‐of‐flight SIMS (ToF‐SIMS) was used to assess 5 keV SF₅⁺‐induced damage of ～90 nm thick spin‐cast poly(2‐hydroxyethyl methacrylate) (PHEMA) and ～130 nm thick trifluoroacetic anhydride‐derivatized PHEMA (TFAA‐PHEMA) films. The degradation of these polymers under extended SF₅⁺ bombardment (～2 × 10¹⁴ ions cm^?2) was compared to determine the effect of the pendant group chemistry on their degradation. The sputter rate and ion‐induced damage accumulation rate of PHEMA were similar to a poly(n‐alkyl methacrylate) of similar pendant group length, suggesting that the addition of a terminal hydroxyl group to the alkyl pendant group does not markedly change the stability of poly(n‐alkyl methacrylates) under SF₅⁺ bombardment. The sputter rate and ion‐induced damage accumulation rate of TFAA‐PHEMA were much higher than a poly(n‐alkyl methacrylate) of similar pendant group length, suggesting that derivatization of the terminal hydroxyl group can significantly reduce degradation of the polymer under SF₅⁺ bombardment. This result is in good agreement with the literature on the thermal and radiation‐induced degradation of fluorinated poly(alkyl methacrylates), which suggests that the electron‐withdrawing fluorinated pendant group increases the probability of depolymerization. Copyright © 2004 John Wiley & Sons, Ltd.     

AIB induced chemical reactions at surfaces detected by SIMS

Secondary ion mass spectrometry (SIMS) has been used to detect the reactions induced by active ion bombardment (AIB) of N⁺₂ on surfaces of pyrolytic graphite and a (100) Si crystal. The SIMS spectra exhibit ions of CN^?, HCN^?, H_nC₂N^?(n = 2, 3, 4), HN^?, and SiN^?, indicating that reactions take place with the graphite and silicon as well as adsorbed hydrogen on the surfaces.     

SIMS depth profiling of vertical p-channel Si-MOS transistor structures

SIMS depth profiling during O₂ ⁺ bombardment has been performed to analyse epitaxially grown Si p-n-p layers, which define the p-channel region in vertical Si-p MOS transistors, as well as to establish “on-chip” depth profiling of the functional vertical device. The SIMS detection limit of ³¹P in Si, phosphorus used as n-type dopant in the transistor, has been optimised as a function of the residual gas pressure in the SIMS analysis chamber and of the sputter erosion rate. We demonstrate that good vacuum during SIMS analysis combined with high erosion rates allows the simultaneous quantitative SIMS depth profiling of n- and p-type dopant concentrations in the vertical transistor. Small area “on-chip” SIMS depth profiling through the layered structure of Al-contact/TiSi₂/Si(p-n-p)/Si-substrate has been performed. Factors influencing the depth resolution during “on-chip” analysis of the transistor are discussed especially in terms of sputtering induced ripple formation at the erosion crater bottom, which has been imaged with atomic force microscopy. Received: 15 August 1996 / Revised: 17 January 1997 / Accepted: 21 January 1997     

Investigation of metallic interdiffusion in Al x Ga1−x N/GaN/sapphire heterostructures used for microelectronic devices by SEM/EDX and SIMS depth profiling

Secondary ion mass spectrometry (SIMS) depth profiling has been applied to the study of the thermal annealing of ohmic contacts for high electron mobility transistors. The metallic stacks (Ti/Al/Ni/Au) were deposited over the Al_0.28Ga_0.72N/GaN/sapphire heterostructures and subjected to a rapid thermal annealing (850 °C for 30 s under N₂ atmosphere) to improve the contact performance. The surface morphology and the in-depth chemical distribution of the layered contacts were severely modified due to the treatment. These modifications have been analyzed by SIMS depth profiling and scanning electron microscopy–energy-dispersive X-ray microanalysis. The SIMS analysis conditions have been optimized to achieve simultaneously good sensitivity and to avoid ion-induced mixing effects produced by the primary beam sputtering.     

ToF-secondary ion mass-spectrometric study of copper deposition and stripping on directly heated screen-printed gold electrodes

We report about a new kind of directly heated gold electrode. All electrodes including a directly heated gold loop electrode, a Ag pseudo reference, and a carbon counter electrode have been screen-printed on a ceramic alumina substrate. Thermal behaviour was studied by potentiometry using either an external or the integrated reference electrode. Stripping voltammetric copper signals were greatly improved at elevated deposition temperature. Secondary ion mass spectrometric studies (ToF-SIMS) revealed that different negative ionic species of copper complexes can be found on the gold electrode surface as a result of ion bombardment during SIMS analysis like Cu^?, CuCl^? and CuCl₂ ^?. SIMS surface imaging using a fine focussed ion beam over the surface allowed us to obtain ion images (chemical maps) of the analyzed sample. SIMS depth profile analysis of the gold loop electrode was performed after copper deposition at room temperature (23 °C) and at 60 °C. CuCl₂ ^? ion was used for the depth profile studies as it has shown the highest intensity among other observed species. Surface spectroscopic analysis, surface imaging and depth profile analysis have shown that the amount of deposited copper species on the gold loop electrode was increased upon increasing electrode temperature during the deposition step. Therefore, the presence of chloride in the solution will hinder underpotential deposition of Cu(0) and lead to badly defined and resolved stripping peaks.     

Static secondary ion mass spectrometry of organic plasma-deposited films created from stable isotope-labeled precursors. II. Mixtures of acetone and oxygen

A series of plasma-deposited films (PDFs), created by blending controlled ratios of acetone vapor and oxygen in the feed to the plasma reactor, were analyzed by static secondary ion mass spectrometry (SIMS). Examination of the quadrupole-based static SIMS fragmentation patterns of acetone–O₂ PDFs created from ¹³C-labeled acetone generally allowed the hydrocarbon secondary ions to be distinguished from oxygen-containing secondary ions. These results were compared with those obtained via high-mass resolution time-of-flight (TOF)-SIMS. The identified secondary ions were then assigned structural attributes, based on comparison of the static SIMS spectra of the acetone–O₂ PDFs with those of conventional hydrocarbon and oxygen-containing polymers. A preliminary investigation to unravel the mechanism of oxygen incorporation in the acetone–O₂ PDFs from the two plasma feed components was undertaken through the analysis of PDFs created from 1,2,3¹³C₃-acetone(¹⁶O) vapor and ¹⁸O₂ gas.     

Depth profiling in secondary ion mass spectrometry for ultra‐thin layer with nanometer order thickness by mesa‐structure fabrication

We attempted to make an accurate depth profiling in secondary ion mass spectrometry (SIMS) including backside SIMS for ultra‐thin nanometer order layer. The depth profiles for HfO₂ layers that were 3 and 5 nm thick in a‐Si/HfO₂/Si were measured using quadrupole and magnetic sector type SIMS instruments. The depth profiling for an ultra‐thin layer with a high depth resolution strongly depends on how the crater‐edge and knock‐on effects can be properly reduced. Therefore, it is important to control the analyzing conditions, such as the primary ion energy, the beam focusing size, the incidence angle, the rastered area, and detected area to reduce these effects. The crater‐edge effect was significantly reduced by fabricating the sample into a mesa‐shaped structure using a photolithography technique. The knock‐on effect will be serious when the depth of the layer of interest from the surface is located within the depth of the ion mixing region due to the penetration of the primary ions. Finally, we were able to separately assign the origin of the distortion to the crater‐edge effect and knock‐on effect. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel isotope analysis of oxygen in uranium oxides: comparison of secondary ion mass spectrometry,glow discharge mass spectrometry and thermal ionization mass spectrometry

The natural variation of the oxygen isotopic composition is used among geologists to determine paleotemperatures and the origin of minerals. In recent studies, oxygen isotopic composition has been recognized as a possible tool for identification of the origin of seized uranium oxides in nuclear forensic science. In the last 10 years, great effort has been made to develop new direct and accurate n(¹⁸O)/n(¹⁶O) measurements methods. Traditionally, n(¹⁸O)/n(¹⁶O) analyses are performed by gas mass spectrometry. In this work, a novel oxygen isotope analysis by thermal ionization mass spectrometry (TIMS), using metal oxide ion species (UO⁺), is compared to the direct methods: glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS). Because of the possible application of the n(¹⁸O)/n(¹⁶O) ratio in nuclear forensics science, the samples were solid, pure UO₂ or U₃O₈ particles. The precision achieved using TIMS analysis was 0.04%, which is similar or even better than the one obtained using the SIMS technique (0.05%), and clearly better if compared to that of GDMS (0.5%). The samples used by TIMS are micrograms in size. The suitability of TIMS as a n(¹⁸O)/n(¹⁶O) measurement method is verified by SIMS measurements. In addition, TIMS results have been confirmed by characterizing the n(¹⁸O)/n(¹⁶O) ratio of UO₂ sample also by the traditional method of static vacuum mass spectrometry at the University of Chicago.     

Sputtering induced recombination of nitrogen isotopes on tungsten

Adsorbed isotopic mixtures of ¹⁴N₂ and ¹⁵N₂ at low coverages on polycrystalline tungsten have been used as model systems for studying sputtering induced recombination during secondary ion mass spectrometry (SIMS). Earlier studies have shown that N₂ is completely dissociated on a W surface at low coverage. Thermal desorption spectroscopy (TDS) has been employed here to confirm this fact; our results show that complete isotopic mixing occurs. Adsorbed nitrogen can be sputtered as both atoms and molecules and sputtering induced recombination of adsorbate atoms increases as primary ion energy increases. Sputtering induced recombination is detected through isotopic mixing in SIMS. The data show that the dominant mechanism for sputtering of dimers (N₂) is not direct emission from the surface but rather a sputtering induced recombination mechanism.     

Investigation of block depth distribution in PS‐b‐PMMA block copolymer using ultra‐low‐energy cesium sputtering in ToF‐SIMS

Directed self‐assembly of block copolymers (BCPs) is a promising candidate for next generation nanolithography. In order to validate a given pattern, the lateral and in‐depth distributions of the blocks should be well characterized; for the latter, time‐of‐flight (ToF) SIMS is a particularly well‐adapted technique. Here, we use an ION‐TOF ToF‐SIMS V in negative mode to provide qualitative information on the in‐depth organization of polystyrene‐b‐polymethylmethacrylate (PS‐b‐PMMA) BCP thin films. Using low‐energy Cs⁺ sputtering and Bi₃⁺ as the analysis ions, PS and PMMA homopolymer films are first analyzed in order to identify the characteristic secondary ions for each block. PS‐b‐PMMA BCPs are then characterized showing that self‐assembled nanodomains are clearly observed after annealing. We also demonstrate that the ToF‐SIMS technique is able to distinguish between the different morphologies of BCP investigated in this work (lamellae, spheres or cylinders). ToF‐SIMS characterization on BCP is in good agreement with XPS analysis performed on the same samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Organic secondary ion mass spectrometry: Signal enhancement by water vapor injection

The enhancement of the static secondary ion mass spectrometry (SIMS) signals resulting from the injection, closely to the sample surface, of H₂O vapor at relatively high-pressure, was investigated for a set of organic materials. While the ion signals are generally improved with increasing H₂O pressure upon 12 keV Ga⁺ bombardment, a specific enhancement of the protonated ion intensity is clearly demonstrated in each case. For instance, the presence of H₂O vapor induces an enhancement by one order of magnitude of the [M+ H]⁺ static SIMS intensity for the antioxidant Irgafos 168 and a ∼1.5-fold increase for polymers such as poly(vinyl pyrrolidone).     

Time of flight secondary ion mass spectrometric determination of molecular weight distributions of low polydispersity poly(dimethyl siloxane) with polyatomic primary ions

This work reports a comparison of oligomer and fragment ion intensities resulting from primary ion bombardment with several primary ion sources (Bi_n⁺, C₆₀⁺, and Cs⁺) at various energies in secondary ion mass spectrometry (SIMS). Although the use of polyatomic primary ions are of great interest due to increased secondary ion efficiency and yield, we demonstrate that monatomic primary ions result in increased oligomer ion yield for polymers prepared as submonolayer films on silver substrates. The enhancement of oligomer secondary ion yield with monatomic ions is evidence that monatomic primary ions have a shallower sampling depth than polyatomic ions, resulting from a collision cascade that is less energetic at the sample surface. The results are also consistent with a lower degree of fragmentation of the resultant secondary ions, which is observed when evaluating the fragmentation data and the spectral data.