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The effect of oxygen flooding during ultralow energy SIMS depth profiling of silicon with Cs+ primary ions is presented. New experimental data show the effective sputtering yield of silicon in the presence of oxygen, as well as the energy distribution of the secondary Si- ions. It is found that the component sputtering yield of Si is very sensitive to minute amounts of oxygen in the proximity of the sputtered surface. At these very low flooding pressures (in the 10-9–10-8 mbar range), one cannot account for a full oxidation in the time frame of a typical measurement; it is concluded that in this particular case, which is technologically very relevant, small traces of oxygen will change the desorption characteristics of cesium as well as silicon. It shows that oxygen that is adsorbed to the silicon surface provides an attachment site for impinging cesium ions and thereby increases the retention capacity of cesium tremendously. Also, oxygen changes the secondary ion yield and can even promote the desorption of Si from the analysis surface. [ABSTRACT FROM AUTHOR]

Secondary ion mass spectrometry has become the preferred tool for impurity profiling primarily due to its excellent depth resolution and high detection sensitivity. Prerequisite in obtaining high detection sensitivity for positive secondary ions is the use of oxygen as primary ions. This leads to a high degree of oxidation of the sample surface, which is essential for a high secondary ion ionization efficiency. Unfortunately, this oxygen bombardment not only leads to the transformation of the original target surface into an oxidized layer but, as the latter requires a certain fluence before stationary state is reached, inherently causes some nonlinearities and transients in the secondary ion signal and the fluence-eroded depth relation. In this work a computer code implantation, sputtering, replacement/relocation, and diffusion (ISRD) has been optimized to predict the compositional changes of the sample surface (or altered layer formation), the sputter yields and the surface regression as a result of the interaction of oxygen beams with Si-targets. This article describes a careful reevaluation of the previously used version of ISRD (and the parameters contained in the program) in order to obtain a systematic agreement with experimental data on sputter yields, altered layer formation, and surface recession, and with other theoretical predictions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract Rutherford backscattering spectrometry (RBS) is an analysis method to quantify reference free the atomic areal density of a thin film, in particular sensitive to those cases where the elements of the film are heavier than the substrate. The ultimate sensitivity is determined by the ratio between the signal intensity from the thin film and the background signal originating from e.g. pulse pile-up events related to the scattering from the substrate atoms or dark noise intrinsic to the detector. We demonstrate that the sensitivity of RBS can be improved by reducing the pulse pile-up and dark noise background through the implementation of a magnet sector and a silicon strip detector as combined double energy dispersive analyzer. A limit-of-detection of 3∙1011 Ru/cm2 on Si is achieved. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the oxidation of GaAs and Al[subx]Ga[1-x]As targets by oxygen irradiation. Background on secondary ion mass spectrometry; Experimental procedures; Results.

Presents a study that examined the influence of oxygen on the analysis of a platinum/silicon structure with secondary ion mass spectrometry. Experimental details; Results of the study; Conclusions.

A time of flight-energy (TOF-E) telescope is often used to detect the scattered and recoiled atoms in elastic recoil detection analysis. The experimental two-dimensional TOF-E histogram may be numerically transformed into a time of flight-mass (TOF-M) histogram. The limited mass resolution in the TOF-M histogram, which results from the limited energy resolution of the energy detector, makes it sometimes difficult to discriminate elements with a small difference in atomic mass. We describe a mass discrimination procedure to numerically discriminate the elements in the TOF-M histogram. The procedure is illustrated on a sample consisting of an Al and a Si layer deposited on a MgO substrate. Besides, we apply the procedure to discriminate Al and Si in a sample consisting of Al 2 O 3 deposited on MoS 2 /SiO 2 /Si. [ABSTRACT FROM AUTHOR]

We describe the ion beam analysis activities at imec. Rutherford backscattering spectrometry and time of flight-energy (TOF-E) elastic recoil detection analysis are pursued to support the nano-electronics research and development. We outline the experimental set-up and we introduce a new data acquisition software platform. Finally, we illustrate the use of Rutherford backscattering spectrometry to map the thickness of a metallic thin film on a 300 mm Si wafer. [ABSTRACT FROM AUTHOR]

With the transition from planar to three-dimensional device architectures, devices such as FinFETs, TFETs and nanowires etc. become omnipresent. This requires the dopant atom positioning relative to the gate edges and contacts with controlled 3D distribution, adequate conformality, appropriate concentrations and activation, all of which are important challenges which need to be resolved since they determine the device performance. Developing an appropriate doping technology for the next technology generation requires a concurrent effort in establishing adequate metrology such that appropriate feedback on process steps and the underlying physics can be generated in a timely manner and with sufficient resolution and accuracy. When assessing performance of such metrology tools and concepts for 3D devices and structures, one needs to address not only the ability to achieve 3D spatial resolution, but also the physical property which is probed, i.e. dopants versus carriers, as well as the complexity of the method used because this impacts on success rate, turn-around time, throughput, automation etc. An evaluation in terms of time to data is as important as the technical capabilities. Although techniques with inherently good 3D resolution (e.g. atom probe tomography) might appear to offer the ideal solution for these applications, routine application is still hampered by localization problems during sample preparation, reconstruction artefacts due to inhomogeneous evaporation and differential laser light absorption, limited sensitivity due to the reduced counting statistics, poor tip yield, small throughput, etc. Hence, complementary analysis using 1D methods like secondary ion mass spectrometry (SIMS) are being explored to provide dopant or composition analysis in 3D structures given its high degree of reproducibility, ease of application and industrial acceptance. Targeting carrier profiling in 3D structures and confined volumes as a complement to atom probe (or SIMS) dopant profiles, has led to the extension of scanning probe microscopy (SPM) methods (which are inherently 2D) toward 3D metrology by exploiting either dedicated test structures or through novel approaches such as Scalpel SPM. The application of these SPM methods for 3D structures and confined volumes has demonstrated that the changing surface/volume ratio in confined devices leads to various phenomena (e.g. dopant deactivation, enhanced diffusion,..) which are not observed in blanket sample experiments. More emphasis should therefore be placed on the analysis of devices and structures with the relevant dimensions relative to the exploration of blanket experiments. Thus, the metrology concepts addressed in this paper may be very useful for such investigations. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the peculiar light coupling and absorption properties of a dielectric particle with a varying nanoscale radius and a high aspect ratio. To build progressive understanding, different levels of geometrical refinement with increasing complexity are proposed and compared. This study concludes that, in an elongated dielectric particle with a varying radius, light is coupled and absorbed only at optically resonant positions, i.e. where the radius allows for the constructive interference between the multiple internal reflections occurring inside the particle. The position, extension and magnitude of these resonance maxima, which vary according to the refinement level of the model, are discussed. [Copyright &y& Elsevier]

Several studies have been reported on the quantification of Ge in Si1-xGex using SIMS with oxygen or cesium primary ions. Most of them were limited to lower Ge concentrations. In this paper, we discussed procedures to quantify Ge content in Si1-xGex with x ranging from 0.11 to 0.70 by using low-energy Cs+ and O2+ primary beams. The results showed that at impact energy of 250 eV, the Ge secondary ion yield changed dramatically against the SiGe matrix composition with a Cs+ primary beam, whereas the change was minimal with an O2+ primary beam. As a result, quantification by using the reference signal inside Si substrate became difficult as no linear correlation exists between the Ge intensity and the Ge concentration in the case of Cs+ primary ions. However, the correlation between the ratios of secondary intensities I(Ge)/I(Si) within the SiGe layers and the composition ratio [Ge]/[Si] is monotonic (although nonlinear). Hence, quantification based on the ratios of the secondary ion intensities versus the ratios of the corresponding contents worked for both Cs+ and O2+ primary beams to quantify the Ge content of an unknown SiGe sample. In addition to this, we reported the angular (incidence angles between 0° and 70°) dependence of the sputter yield of SiGe as a function of Cs+ primary ion energy (150-500 eV). Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The atom probe analysis of a full gate stack (metal gate/high-k dielectric) in a 3D finFET is reported. The measurement reliability in this kind of heterogeneous structure is discussed in the light of different artefacts, i.e. mass overlap and 3D reconstruction artefacts. [Copyright &y& Elsevier]

Abstract: Atom-probe (AP) analysis of silicon based samples frequently fail due to rupture of the tip. We have investigated the stability and failure mechanisms of silicon tips when prepared for AP analysis via Focused Ion Beam (FIB) milling. We observed four mechanisms that commonly lead to failure of the tips. These mechanisms are a deformation of the tips apex due to an interaction between the oxidized amorphous layer and induced mechanical vibrations, a rip off of an isolating oxide-layer, the rip off of a cap layer due to insufficient adhesion and a failure of the tip in the course of the analysis due to the rising voltage applied to the tip. In this paper we will discuss all four mechanisms show evidence of the causes of the breakdown and discuss options that allow avoiding tip failure. [Copyright &y& Elsevier]

Abstract: Accurate modeling of the enhancement of the ionization probabilities of secondary ions (positive and negative) by the presence of reactive species requires a precise determination of their concentration at the outermost surface and thus a fundamental understanding of their incorporation and release processes. In the present paper we discuss these processes for oxygen, cesium and cluster ion bombardment with a special emphasis on their importance at (very) low bombardment energies. At these energies the sputtering processes becomes very small and deposition instead of erosion is predicted while for some species such as oxygen and cesium, an additional process, i.e. desorption, becomes more important thereby enabling a stationary state without deposition. The desorption process is a property of the primary ion and element specific and can be predicted based on the sputter yields and heat of sublimation. For those species/conditions where desorption is not operational (such as for C60-beams), depth profiling at very low energies and with low sputter yields (<1) will not be possible and accumulation of the primary ion (thin film growth) is observed. The absence of deposition under oxygen, cesium and (SF5) n -bombardment and the positive impact of oxygen flooding on C60 bombardment can all be explained when the desorption mechanism is included in the balance equation. [Copyright &y& Elsevier]

Abstract: The application of secondary ion mass spectrometry in recent semiconductor applications has highlighted the need for extremely high depth resolution. The depth resolution limitations arise from the high dose, energetic interactions of the primary ion with the sample, leading to profile distortions due to the primary incorporation process and the collision cascades. Evolutionary and revolutionary approaches are presently proposed as potential solutions to achieve the ultimate in depth resolution. Evolutionary concepts are based on using extremely low bombardment energies (∼100eV) and/or cluster beams whereas revolutionary concepts such as zero-energy SIMS and the tomographic atomprobe remove the primary ion beam completely. [Copyright &y& Elsevier]

Abstract: Conductive atomic force microscopy (C-AFM) allows probing local phenomena such as trap assisted tunneling and oxide breakdown, which hamper meeting the high-k device requirements. In this work we present the improvement of Conductive AFM measurements in high vacuum (1e−5 torr) due to improved preservation of tip conductivity. Furthermore, we describe the gate removal process of real MOS devices, enabling standard macroscopic and microscopic measurements on the same gate dielectric. Using this procedure, we are able with C-AFM to locate the BD spots induced by standard macroscopic constant voltage stress. The C-AFM measured local current–voltage (I–V) characteristic of a single BD spot aligns well with the macroscopic post breakdown I–V trace. [Copyright &y& Elsevier]

Abstract: Conductive atomic force microscopy (C-AFM) and scanning capacitance microscopy (SCM) are used in this work to characterize trap creation and charge trapping in ultra-thin SiO2. It is found that C-AFM working at normal operational voltages causes severe damage and subsequent negative charge trapping in the oxide. Permanent hillocks are seen in the topography of stressed regions. The height of these features is determined rather by the applied voltage than the electric field. Electrostatic repulsion between tip and sample and Si epitaxy underneath the oxide are the two most probable causes of this feature. The immediate physical damage caused in the oxide during high field C-AFM measurements is a possible showstopper for use of the C-AFM to investigate differences in pristine interface states. SCM operates at lower voltages, yielding less oxide damage and is able to indicate the interface state density variations through hysteresis in the dC/dV vs. V curves. [Copyright &y& Elsevier]

Abstract: The use of an internal O18 implant to quantify the surface oxygen concentration, presented in Franzreb et al. [K. Franzreb, J. Lorincik, P. Williams, Surf. Sci. 573 (2) (2004) 291], is critically evaluated, in particular when applied for bombardment conditions leading to high depth resolution measurements. It is shown that this methodology gives no direct access to the surface composition, but only to the O/Si ratio in the total emission flux, ϕ O16/ϕ Si, which reflects the total amount of oxygen that passes through the surface. When applied under conditions relevant for high depth resolution studies (oxygen bombardment at low energies and small angles), extremely large ϕ O16/ϕ Si -ratios are observed (>50). These large values are interpreted in terms of the oxygen that leaves the surface by sputtering as well as by alternative processes such as by desorption. The latter is included in the total flux ratio ϕ O16/ϕ Si, but has little interaction with the sample surface and the departing Si-atoms. Therefore the use of these ϕ O16/ϕ Si ratios in ionization mechanism studies becomes inappropriate unless the desorbed oxygen fraction can be calculated quantitatively or is negligible. Based on the angular dependence of the useful ion yield of oxygen, we make a rough estimate of the desorbed oxygen fraction and show that this becomes a dominant fraction (up to 70%) in the emitted flux at low bombardment energies. [Copyright &y& Elsevier]

Abstract: Understanding dopant diffusion and activation mechanisms is a key issue for future sub-45-nm CMOS technologies. This understanding requires the availability of accurate chemical and electrically active dopant profiles. In this work we will focus on the accurate and reliable characterization of carrier depth profiles for ultra-shallow (USJ) structures. Typically conventional means such as spreading resistance probe (SRP), which uses two high-pressure probes (10GPa) with a contact radius of about 1μm and a separation of 30μm, are running out of steam in the sub-30-nm depth regime. This is mainly due to the need to apply for multi-layer structures quite large Laplace-based deconvolution correction factors (>1000) on the raw data causing excessive noise amplification. These correction factors can be circumvented by performing a series of microscopic four-point probe (M4PP) measurements along a beveled sample with a small enough angle (few minutes). In M4PP, the probe tips make an elastic (non-penetrating) contact with a 1.5μm pitch leading to an enhanced dynamic range because of the reduced sampling size and penetration. Subsequently, the underlying resistivity and carrier depth profiles can be easily extracted by the simple calculation of the differential sheet resistance for each of the sub-layers. [Copyright &y& Elsevier]

Abstract: The electrical quality of ultra-thin (∼1nm) Plasma and Thermal nitrided silicon oxide layers was investigated with Conductive AFM and a macroscopic I-V measurement setup. PN layers were found to be superior to TN layers. A longer nitridation time resulted in a better quality of the layer. Annealing in N2 was not beneficial and re-oxidation resulted in a lower leakage due to a significant increase in the physical thickness. A trap-assisted kind of tunneling was observed in these layers. The exact role of nitrogen herein is not yet well understood. [Copyright &y& Elsevier]

Abstract: The interpretation of the conductive atomic force microscopy (C-AFM) results is discussed in the framework of the characterization of the high-k layers as gate oxide. Because the high-k layer is deposited on an interfacial layer, at high gate voltage, the C-AFM current maps do not reflect the high-k properties but rather the interface. Moreover, in the point contact mode, the surface of the equivalent capacitor as well as the voltage and current ranges used with the C-AFM are different from the one used in common IV. The interpretation of macroscopic measurements can therefore not be transposed to the C-AFM results. More specifically, the shift towards lower voltage of the backward curve is ascribed to the creation of a conducting path at high voltage. [Copyright &y& Elsevier]

This paper investigates the effect of thickness, composition and anneal temperature in N2 on the band gap of the mixed oxide layer and the band offset with the Si substrate for layers grown by atomic layer deposition. For 1:1 (Al/Zr or Al/Hf) mixed oxides, the band gap reaches the bulk value for a thickness larger than 2 nm. In both cases (AlxZryOz and AlxHfyOz), the bulk values of the band gap show a linear dependence on the Al2O3 mol%, going from 5.6 (5) eV for pure ZrO2 (HfO2) to 6.7 eV for pure Al2O3. The effect of a post-deposition anneal on the band gap and the valence band alignment is also studied. Here, AlxHfyOz and AlxZryOz seem to act differently: while the annealing temperature does not have any influence on the band gap of AlxZryOz mixed oxide, the annealing in N2 at temperature from 900 °C generates an increase in the band gap value measured by XPS for AlxHfyOz. [Copyright &y& Elsevier]

To get an insight in the diffusion behavior of dopants such as arsenic and boron after annealing and in particular their segregation characteristics towards the interface in oxide structures on silicon, it is necessary to probe the dopant profile with very high accuracy and depth resolution. Sputter depth profiling as employed in secondary ion mass spectrometry (SIMS) is frequently used as the most suited tool for dopant profiling in view of its sensitivity and depth resolution. However in order to determine the segregated arsenic/boron peak, sub-nanometer depth resolution is required and artifacts such as beam induced broadening effects, potential ionization yield changes at interfaces, transient sputter yields need to be considered in detail. When reducing the primary beam energy the depth resolution can be improved and sub-nanometer depth sensitivity can be demonstrated. However comparisons with high resolution elastic recoil detection analysis demonstrate that it is at present impossible to obtain a reliable depth profile in the first nanometer near the surface nor even in the oxide part of the profile, where no ionization nor sputter yield transients are expected. Enhanced beam induced migration of boron during the initial phase of the bombardment needs to be invoked to explain the results. The latter appears to be enhanced under conditions (∼normal incidence) where full oxidation occurs. [Copyright &y& Elsevier]

In order to increase performance in advanced MOS devices, alternative gate insulators with high electrical permittivity are investigated to replace SiO2. Recent developments include the presence of nitrogen in or around the HfO2 stack. It is thus important to be able to acquire knowledge of the depth distribution of the nitrogen in the layers with enough accuracy. This remains a real challenge for SIMS due to varying matrices in which the nitrogen is distributed.We first present results obtained with Xe and Cs profiling. We determined the “best to use” clusters in order to retrieve the maximum information of the data.In the second part, we investigate some less standard operational mode of SIMS profiling. For instance, it has also long been considered that the detection of MCs+ clusters suffers from less matrix effect and could thus be advantageous for this kind of analysis, where the Cs surface concentration is reduced by the use of Xe–Cs co-sputtering. We also introduce a new method in order to increase the sensitivity to nitrogen by using a “carbon-based” flooding and using the CN- cluster detection. [Copyright &y& Elsevier]

Measuring HfO2/Si stacks-by secondary ion mass spectroscopy (SIMS) has become a common task in the semiconductor industry. Although the reliability of the SIMS-profiles from multilayer structures can be influenced by sputter yield and ionization yield variations in the interface region, the part of the dopant profile located beyond the interface can normally be obtained with excellent SIMS-characteristics.By comparing the SIMS-profiles from B-profiles in Si, measured with and without a HfO2-cap layer, it becomes clear that the high k film has a strong impact on the resulting dopant profiles. With the high k film present, a significant distortion of the depth and intensity scale can be observed and the B-profile (which is, in principle, fully contained in the Si) appears almost twice as deep when profiling through the HfO2-layer as compared to the uncapped sample. Normalizing the depth and concentration scale with the variations of the SiO-signals, seems to lead to an acceptable B-profile. The distortion results from a strong reduction in sputter yield due to the presence of (even small) amounts of Hf. Apparently, Hf segregates towards the surface forming a (fractional) layer, which shields the Si-atoms from sputtering. The sputter yield of this Hf-layer on the other hand is very low leading to a drastic reduction in average erosion rate. For conditions where normally no full oxidation is obtained (high energy, non-normal incidence beams on Si and Ge-substrates), this reduction leads to a temporary enhancement of the oxygen incorporation and the ionization probability. [Copyright &y& Elsevier]

The effect of thermal annealing on the electrical properties of thin HfO2 layers was studied by conductive atomic force microscopy. Based on high resolution (10 nm) current maps it is possible to observe the transition from a homogeneous current distribution for the non-annealed case towards the presence of electrical weak spots in the annealed samples. Although the current density in the weak spots can reach 20 A/cm2, local I–V curves indicate that not all of them are acting as a real breakdown spot. The weak spots density observed is around 1010–1011/cm2, which represents 5–10% of the scanned area. [Copyright &y& Elsevier]

For deep submicron technologies it is of crucial importance to grow ultra-thin (<3–4 nm) dielectrica with extreme quality and uniformity. It has been shown that the growth mode of these films (layer by layer versus island like) has a dramatic impact on the further integration with polysilicon and the electrical performance of the high k stack. Since a large number of process parameters need to be investigated, a rapid diagnostic tool for determining the growth mode is required. We show, based on a comparison between LEIS, XPS, and TOF-SIMS that TOF-SIMS surface spectra can be used to probe the layer structure (in particular for the detection of island growth). For this purpose, we have examined ZrO2/Si stacks grown by ALCVD for which it has already been reported that ZrO2 grows on HF-etched Si surfaces in an island growth mode. We have studied the possible matrix effects which could hamper the TOF-SIMS data interpretation and show that it is (fairly easily) possible to distinguish between different growth modes for ZrO2. [Copyright &y& Elsevier]

To get an insight in the diffusion behavior of boron after annealing and in particular its segregation characteristics towards the interface in oxide structures on silicon, it is necessary to probe the boron profile with very high accuracy and depth resolution. Sputter depth profiling as employed in secondary ion mass spectrometry (SIMS) is frequently used as the most suited tool for dopant profiling in view of its sensitivity and depth resolution. However, in order to determine the segregated boron peak, sub-nm depth resolution is required and artifacts such as beam induced broadening effects, potential ionization yield changes at interfaces, transient sputter yields need to be considered in detail. When reducing the primary beam energy the depth resolution can be improved and sub-nm depth sensitivity can be demonstrated. However, comparisons with high-resolution elastic recoil detection analysis demonstrate that even under those conditions no reliable depth profile can be obtained in the first nm near the surface nor even in the oxide part of the profile, where no ionization nor sputter yield transients are expected. Enhanced beam induced migration of boron during the initial phase of the bombardment needs to be invoked to explain the results. [Copyright &y& Elsevier]

This letter reports on the Ge segregation mechanism occurring during ultrathin (few monolayers) Si cap growth on Ge substrates by reduced pressure chemical vapor deposition. Thanks to extremely low energy secondary ion mass spectroscopy, we have highlighted that Ge segregation in Si-covered Ge does not depend on the growth temperature (in the 350–500 °C range) or on the carrier gas (H2,N2) used during Si growth. Solely the Si precursor used, i.e., the Si incorporation mechanism, impacts the Ge segregation rate. A multi-Ge segregation model is proposed, considering probabilities of sites exchanges in between all Si–Ge stacked atoms within the first nanometer of the layers. [ABSTRACT FROM AUTHOR]

We investigate the influence of thermal conditions during solid phase epitaxial regrowth (SPER) on the electrical activation level of boron in preamorphized silicon, both with respect to heating ramp rates and the use of low temperature preanneals. Enhancement of electrically active boron concentration by 36% is observed for activation with the fastest ramp rate (487 °C/s) compared to the slowest one (1 °C/s). An important clustering pathway occurs within the amorphous silicon phase (during low temperature preanneal) prior to completion of the SPER process. In these junctions boron deactivation during isochronal post-annealing is almost independent on the maximum boron activation level. [ABSTRACT FROM AUTHOR]

The formation of a thin strained Si layer on top of a strain-relaxed SiGe buffer is a recent approach to improve the drive current of complementary metal-oxide-semiconductor devices by inducing strain within the transistor channel. At the same time, advanced process technologies require junction formation processes with minimal diffusion and very high dopant activation. Solid-phase epitaxial regrowth is a low temperature process based on preamorphization and subsequent regrowth leading to highly activated and shallow junctions. In this letter, we investigate the stability of the thin strained Si layer, during solid-phase epitaxial regrowth process by monitoring the Ge redistribution/strain after the preamorphization step (without any anneal) and after the thermal regrowth process. [ABSTRACT FROM AUTHOR]

A quantitative comparison is made of the junction depths determined by spreading resistance (SR) and secondary-ion mass spectrometry (SIMS) for submicron abrupt pn junctions (grown by molecular beam epitaxy) and Gaussian implants. The discrepancies between SR and SIMS are explained in terms of carrier spilling. From the comparison with a theoretical model, general trends can be adequately explained. In order to overcome the uncertainties imposed by the boundary conditions in this model, experimental diagrams are derived which can be used in routine analysis to assess the importance of carrier spilling effects in SR. [ABSTRACT FROM AUTHOR]

The use of an I+2 and I+ primary ion beam in secondary-ion mass spectrometry measurements was studied to investigate its depth profiling properties. A comparison with the results of a Cs+, O+2, and O+ primary beam was made. Experiments were performed with low impact energy (down to 1.7 keV) and glancing angle of incidence on molecular beam epitaxy AlGaAs-GaAs multilayer structures. The best obtainable decay length of the Al+ signal with an iodine primary beam is 1.1 nm. At low impact energies, no mass dependence on the depth resolution is observed. In these conditions, a useful yield for Al+ of approximately 5×10-5 was obtained with the Cs+ beam and 10-2 with the iodine and oxygen beams. [ABSTRACT FROM AUTHOR]

The Si[sup +] and O[sup +] signals, as obtained in secondary ion mass spectrometry (SIMS) analysis of silicon when using oxygen as the primary species, pass through an initial transient region before reaching the stationary state. We simulate this transient zone to check a phenomenological model for the secondary ionization of sputtered atoms. The simulation is split into two parts: the sputtering of neutrals obtained from implantation, sputtering, relocation/replacement, and diffusion, simulations and their subsequent ionization. The ionization phenomena are also described by some ad hoc fitting functions with which the SIMS measurements are better approached than with the model. The fitting functions and the model outputs are verified with experimental secondary ionization data. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Monolayer-thin WS2 with (0002) texture grows by chemical vapor deposition (CVD) from gas-phase precursors WF6 and H2S at a deposition temperature of 450 °C on 300 mm Si wafers covered with an amorphous Al2O3 starting surface. We investigate the growth and nucleation mechanism during the CVD process by analyzing the morphology of the WS2 crystals. The CVD process consists of two distinct growth regimes. During (i) the initial growth regime, a fast and self-limiting reaction of the CVD precursors with the Al2O3 starting surface forms predominantly monolayer-thin WS2 crystals and AlF3 crystals that completely cover the starting surface. During (ii) the steady-state growth regime, a much slower, anisotropic reaction on the bottom, first WS2 layer proceeds with the next WS2 layer growing preferentially in the lateral dimensions. We propose that the precursor adsorption reaction rate strongly diminishes when the precursors have no more access to the Al2O3 surface as soon as the WS2 layer completely covers the Al2O3 surface and that the WS2 crystal basal planes and AlF3 crystals have a low reactivity for WF6 adsorption at 450 °C. Nonetheless, a second layer of WS2 starts to form before the first WS2 layer completely covers the starting surface, albeit the surface coverage of the second layer is low (<20%, after 25 min of CVD reaction). During the steady-state growth regime, predominantly the WS2 crystals in the second monolayer continue to grow in lateral dimensions up to ∼40 nm. These crystals reach larger lateral dimensions compared to the crystals in the bottom, first layer due to low reactivity for WF6 adsorption on the WS2 basal plane compared to Al2O3. Presumably, they grow laterally by precursor species that adsorb on and diffuse across the WS2 surface, before being incorporated at the more reactive edges of the WS2 crystals in the second layer. Such a process proceeds slowly with only up to 40% surface coverage of the second WS2 layer after 150 min of CVD reaction. The CVD reaction is mediated by the starting surface: WF6 precursor preferentially adsorbs on Al2O3, whereas adsorption is not observed on SiO2. Nevertheless, WS2 grows on SiO2 in close proximity to Al2O3 in 90 nm pitch Al2O3/SiO2 line patterns. Hence, functionalization of the starting surface (e.g., SiO2 with Al2O3) can provide opportunities to grow monolayer-thin WS2 crystals at predetermined locations by selective, lateral growth with tunable crystal size, even at low deposition temperatures. [ABSTRACT FROM AUTHOR]

Evaluating the thermal processes occurring inside an illuminated nanoscale semiconducting tip is of utmost importance for the physical understanding of laser assisted atom probe tomography (L-APT). In this paper, we present a methodology to evaluate the temperature at the apex of the tip using L-APT. The method is based on the known exponential dependence of the probability for field evaporation on the temperature and the electric field at the apex. We use this method to gain insights into the effect of tip shape, doping, and laser power on the peak temperature reached at the apex of an illuminated Si tip. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are of great interest for applications in nano-electronic devices. Their incorporation requires the deposition of nm-thin and continuous high-k dielectric layers on the 2D TMDs. Atomic layer deposition (ALD) of high-k dielectric layers is well established on Si surfaces: the importance of a high nucleation density for rapid layer closure is well known and the nucleation mechanisms have been thoroughly investigated. In contrast, the nucleation of ALD on 2D TMD surfaces is less well understood and a quantitative analysis of the deposition process is lacking. Therefore, in this work, we investigate the growth of Al2O3 (using Al(CH3)3/H2O ALD) on MoS2 whereby we attempt to provide a complete insight into the use of several complementary characterization techniques, including X-ray photo-electron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. To reveal the inherent reactivity of MoS2, we exclude the impact of surface contamination from a transfer process by direct Al2O3 deposition on synthetic MoS2 layers obtained by a high temperature sulfurization process. It is shown that Al2O3 ALD on the MoS2surface is strongly inhibited at temperatures between 125°C and 300°C, with no growth occurring on MoS2 crystal basal planes and selective nucleation only at line defects or grain boundaries at MoS2 top surface. During further deposition, the as-formed Al2O3 nano-ribbons grow in both vertical and lateral directions. Eventually, a continuous Al2O3 film is obtained by lateral growth over the MoS2crystal basal plane, with the point of layer closure determined by the grain size at the MoS2 top surface and the lateral growth rate. The created Al2O3/MoS2interface consists mainly of van der Waals interactions. The nucleation is improved by contributions of reversible adsorption on the MoS2 basal planes by using low deposition temperature in combination with short purge times. While this results in a more two-dimensional growth, additional H and C impurities are incorporated in the Al2O3 layers. To conclude, our growth study reveals that the inherent reactivity of the MoS2 basal plane for ALD is extremely low, and this confirms the need for functionalization methods of the TMD surface to enable ALD nucleation. [ABSTRACT FROM AUTHOR]

Abstract: Ultra thin Si cap growth by Reduced Pressure Chemical Vapor Deposition on relaxed Ge substrates is detailed in this paper for Ge pMOSFET (Metal Oxide Semiconductor Field Effect Transistors) passivation purposes. A cross calibration of different measurement techniques is first proposed to perfectly monitor Si monolayers thickness deposited on Ge substrates. Different characteristics, impacting Ge pMOSFETs device performances, are next detailed for various Si cap growth processes using different Si precursors: DiChloroSilane (DCS), silane and trisilane. The critical Si thickness of plastic relaxation has been determined at 12 monolayers. Presence of point defects has been identified for very low growth temperature as 350°C. Ge–Si intermixing, caused by a Ge segregation mechanism, is strongly reduced by the use of trisilane as Si precursor at low temperatures. [Copyright &y& Elsevier]

Abstract: Dichlorosilane (DCS), silane and trisilane have been investigated as Si precursors for low temperature (<700°C) Si reduced pressure chemical vapor deposition. DCS and silane are limited to growth temperatures higher than 600–650 and 500°C, respectively. At lower temperatures, absence of either Cl or H desorption from the surface impedes Si growth with acceptable growth rate (>5Å/min). Trisilane permits the growth of Si at lower temperatures below 350°C due to a specific growth mechanism enhancing H desorption. Layers grown at temperatures lower than 500°C are defective, irrespective of the carrier gas, pressure and precursor flow used. [ABSTRACT FROM AUTHOR]

Abstract: Single and polycrystalline Si1−x Ge x samples have been bombarded using low energy oxygen ions to study the change in their surface morphologies and ripple formation. Both strained, relaxed and polycrystalline Si1−x Ge x samples grown on Si(001) were used to study the effect of crystallinity on ripple formation. Bombardment by 1keV oxygen ions shows completely different morphologies for the different samples under identical experimental conditions. Ripples on Si1−x Ge x samples appear much earlier than in Si. Moreover, the nature of the ripples for the polycrystalline sample is markedly different from those of the single crystals. The ripples on relaxed samples are greatly influenced by the location of the dislocation lines on the sample surface. The observations clearly show that rippling is affected not only by the layer constituents but also by its crystallinity and presence of regular structures that favour rippling in a specific direction. [Copyright &y& Elsevier]

Abstract: Nowadays, fundamental SIMS physics limits the quantitative compositional analysis of new semiconductor structures with high depth resolution and high spatial resolution. Therefore, a new concept (Zero-energy SIMS) is introduced which is based on electron beam inducted etching (EBIE) of the substrate surface and subsequent post-ionization of the volatile species by short high-power laser pulses. Silicon electron beam induced etching with SF6 as precursor species with an etching yield of 0.003 Si atoms/electron is demonstrated. Zero-energy SIMS experiments in a magnetic sector instrument with SF6 in positive mode show both electron-induced processes (ESD of fluorine) and collision-induced removal of Si atoms. These sputter events are caused by the impact of accelerated SF6 fragment anions which are formed by an electron-attachment process in the gas phase. In negative mode, a large contribution of cluster ions is observed due to the high flux of incoming polyatomic cations, formed by electron-impact ionization of SF6 molecules in the gas phase. The kinetic energy distributions of these particles are in agreement with the recombination model for cluster emission. [Copyright &y& Elsevier]

Abstract: In the first part of this work, the fabrication of silicon germanium-on-insulator substrates (SGOI) by the Ge condensation technique was studied. Ge atomic fractions as high as 93% have been obtained while maintaining nice structural properties of the films. We show that these layers exhibit a large compressive strain and that the strain can be lowered by introducing some annealing steps in argon ambient during the condensation. SGOI substrates with a Ge atomic fraction of 75% were subsequently used as template for the growth of strained epitaxial Ge layers. Because of the important strain in the SGOI, the temperature for the in-situ bake prior to the growth has to be carefully selected in order to avoid relaxation. Ge layers with compressive strain up to −1% and thicknesses up to 40 nm have been obtained. The crystal quality, roughness and thermal stability of the strained Ge layers were finally evaluated. [Copyright &y& Elsevier]