Plasma Profiling Time Of Flight Mass Spectrometry Research Articles

Accelerating the development of phase‐change random access memory with in‐fab plasma profiling time‐of‐flight mass spectrometry

We demonstrate the potential of using plasma profiling time‐of‐flight mass spectrometry (PP‐TOFMS) to accelerate process developments for phase‐change random access memory (PCRAM) applications, which require advanced materials with composition‐driven properties. We assess the performances of PP‐TOFMS for the chemical depth‐profiling of GeSbTe phase change materials, first after deposition steps to investigate the top surface layer and the incorporation of silicon into the amorphous matrix, then after the thermal annealing step to refine in situ capping strategies, and finally in close loop with etching process steps. Comparison of reference‐free semiquantitative PP‐TOFMS analysis based on ion beam ratio with Rutherford backscattering spectrometry shows remarkable agreement (~10% relative). PP‐TOFMS proves to be a fast screening tool, which allows process monitoring and selection of samples that indeed need more complex analysis.

Plasma profiling time-of-flight mass spectrometry for fast elemental analysis of semiconductor structures with depth resolution in the nanometer range

Plasma profiling time of flight mass spectrometry (PP-TOFMS) has recently gained interest as it enables the elemental profiling of semiconductor structures with high depth resolution in short acquisition times. As recently shown by Tempez et al PP-TOFMS can be used to obtain the composition within structures of modern field effect transistors []. There, the results were compared to conventional SIMS measurements. In the present study, we compare PP-TOFMS measurements of an Al-/In-/GaN quantum well multi stack to established micro- and nanoanalysis techniques like cathodoluminescence (CL), scanning transmission electron microscopy (STEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD). We show that PP-TOFMS is able to resolve the layer structure of the sample even more than 500 nm deep into the sample and allows the determination of a relative elemental composition with an accuracy of about 10 rel%. Therefore, it is an extremely rapid alternative method to obtain semiconductor elemental depth profiles without the expensive and time consuming sample preparation required for TEM. Besides, PP-TOFMS offers better depth resolution and more elemental information than, for example, electrochemical capacitance–voltage (ECV) evaluations, since all elements are detected in parallel and not only electrically (ECV) or optically (CL) active elements are observed.

Multitechnique elemental depth profiling of InAlGaN and InAlN films

This work shows the capabilities of the plasma profiling time of flight mass spectrometry (PP-TOFMS) for the determination of elemental composition and distribution in InAlGaN thin films used for high electron mobility transistors. The PP-TOFMS results have been compared with wavelength dispersive x-ray fluorescence analyses for the elemental composition determination and with x-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry (TOF-SIMS) for elemental distributions. Relative sensitivity factors have been developed for the comparison of PP-TOFMS with TOF-SIMS results. The PP-TOFMS was able to determine the relative composition of In and Al in the thin films with an accuracy of 10 rel. % without calibration. Depth profiles acquired from the PP-TOFMS technique were obtained within a few minutes and exhibited very similar In, Al, and Ga distributions to TOF-SIMS measurements, and thus PP-TOFMS has been shown to be a valuable addition to TOF-SIMS analysis for a fast process development.

Advanced characterizations of fluorine-free tungsten film and its application as low resistance liner for PCRAM

Using a metal-organic tungsten based precursor, a fluorine-free tungsten thin film has been obtained. The process deposition recipe includes a plasma-enhanced CVD (PECVD) step and atomic layer deposition (ALD) cycles. A set of physicochemical characterizations including X-ray reflectivity (XRR), in-plane X-ray diffraction (XRD), wavelength dispersive X-ray fluorescence (WDXRF), plasma profiling time of flight mass spectrometry (PPTOFMS) and microscope observations has been realized in order to study the W thin film structure and properties. The film is perfectly conformal whatever the structure size investigated (from tens of nanometers to micrometers wide). It was also highlighted that the F-free W film exhibits the lowest electrical resistivity phase (α-W) but is not pure. Indeed, in addition to a top surface oxidation, a layer located at the W film / substrate interface is present. This interface layer (IL) contains impurities, including carbon and oxygen, due to ligand decomposition. This IL might be deposited during the soak step or during the PECVD step.The W liner with thicknesses ranging from 3 to 4nm has been implemented on PCRAM structures in order to evaluate its impact on contact plug resistivity. First electrical results are promising and demonstrate the interest of using a F-free low resistance W liner. At the aspect ratio studied, the gain in terms of contact plug resistivity is about 20% compared to the process of reference using a TiN liner. Modeling shows that this benefit is mainly due to the reduction of interface resistances.

High quality boron-doped epitaxial layers grown at 200°C from SiF4/H2/Ar gas mixtures for emitter formation in crystalline silicon solar cells

Controlling the doping profile in solar cells emitter and front/back surface field is mandatory to reach high efficiencies. In the current state of the art, these doped layers are made by dopant diffusion at around 900°C, which implies potential temperature induced damages in the c-Si absorber and for which a precise control of doping is difficult. An alternative solution based on boron-doped epitaxial silicon layers grown by plasma-enhanced chemical vapor deposition (PECVD) from 200°C using SiF4/H2/Ar/B2H6 chemistry is reported. The structural properties of the doped and undoped epitaxial layers were assessed by spectroscopic ellipsometry (SE), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The incorporation of boron has been studied via plasma profiling time of flight mass spectrometry (PP-TOFMS) and secondary ion mass spectrometry (SIMS) measurements. The boron-doped epitaxial layers revealed excellent structural and electrical properties even for high carrier concentrations (>1019cm-3). Sheet resistances between 100 and 130 Ω/sq can been obtained depending on the thickness and the doping concentration, which is within the range of targeted values for emitters in c-Si solar cells. Electrochemical capacitance voltage (ECV) revealed a uniform doping profile around 3.1019 cm-3 and by comparing with SIMS measurement a doping efficiency around 50% has been found.

Combining plasma profiling TOFMS with TOF-SIMS depth profiling for microelectronic applications

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is routinely used for depth profiling of microelectronic materials but interpretation of results can sometimes be hampered by artifacts such as matrix effects. Plasma profiling time-of-flight mass spectrometry (PP-TOFMS) provides direct measurement of the elemental composition of materials as a function of depth, with nanometer resolution and higher sputter rates than for TOF-SIMS. Here, the two techniques are compared on a range of multilayers used for microelectronic applications. Although depth resolution and sensitivity are less in the PP-TOFMS profiles, both techniques were able to determine the composition, detect contamination, and characterize diffusion as a function of annealing. Indeed, the use of both techniques on the same sample is complementary: (1) the PP-TOFMS profiles can be in most cases easily semiquantified using the ion beam ratio, whereas standards are required for the SIMS analysis and (2) simpler PP-TOFMS mass spectra with low contributions from molecular adducts allow for spontaneous detection of unexpected contaminants.

PECVD BSG Diffusion Sources for Simplified High-Efficiency N-PERT BJ and BJBC Solar Cells

We investigate boron silicate glasses (BSG) deposited by plasma-enhanced chemical vapor deposition (PECVD) as a boron diffusion source on n-type wafers for the simplified fabrication of crystalline Si solar cells by the codiffusion processes. By varying the SiH4/B2H6 gas flow ratio and the layer thickness of the PECVD BSG layers, we obtain sheet resistivities in a wide range from 30 to 500 Ω/□ after thermal B drive-in. Emitter saturation current densities as low as $J_{{\rm 0e}} = 4$ fA/cm2 (for $R_{{\rm sheet}} = 236$ Ω/□) are demonstrated using PECVD BSG layers as diffusion sources. A boron concentration in the PECVD BSG of up to 6.4 × 1021 cm−3 is measured by plasma profiling time-of-flight mass spectrometry (PP-TOFMS). A process simulation model of the B diffusion from the PECVD BSG into the Si substrate reproduces the experimental B concentration profile in the Si, measured both by PP-TOFMS and electrochemical capacitance–voltage (ECV) measurements. We fabricate industrial-type passivated emitter and rear totally diffused back-junction (PERT BJ) solar cells, as well as back-junction back-contact cells on n-type wafers. Applying codiffusion from PECVD BSG layers and thus a lean process flow including only one high-temperature step, we demonstrate n-PERT BJ cells with conversion efficiencies of up to 19.85%.

Concentration determination and activation of rare earth dopants in zinc oxide thin films

AbstractIn this paper, we will present the development of rare‐earth (RE) doped zinc oxide (ZnO) films for white light emitting diodes (LED). We will present the structural changes of these films as well as their optical properties and associated photoluminescence before and after rapid thermal treatments. We will report depth profile results from plasma profiling time of flight mass spectrometry (PP‐TOFMS) giving the distributions and concentrations of the different elements in the films. We will correlate depth profile and luminescence data to understand the RE emission mechanisms in ZnO matrix. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Depth profile analysis by plasma profiling time of flight mass spectrometry

Plasma profiling time of flight mass spectrometry (PP-TOFMS) provides direct measurement of the chemical composition of materials as a function of depth, with nanometre resolution and the capability to measure both thin and thick layers. It consists in a pulsed radio frequency (RF) glow discharge plasma source fed with pure Ar and created under a pulsed RF potential coupled to a time of flight mass spectrometer (TOFMS). There is a perfect fit between the fast erosion rate of the high density and low energy plasma and the ultra-fast detection and quasi-simultaneous acquisition of all mass ions of the TOFMS. Furthermore the separation between sputtering and ionisation processes makes this technique much less matrix dependent compared to SIMS. The orthogonal TOFMS configuration allows extraction of temporal plasma source characterisation. This is all the more important as signals are largely enhanced in the plasma extinction phase (once RF is turned off) in the so called afterglow region. Sample ion signals are then created through ionisation by Ar metastables called Penning Ionisation (Arm+M→M++e−+Ar0).Various applications will be presented ranging from thin film analysis for composition, contamination detection, surface area measurements and doping level to characterisation of diffusion mechanisms. Aspects of analytical performance with regards to sensitivity, quantification, repeatability and sample throughput will be discussed.

18O distributions in porous anodic alumina by plasma profiling time‐of‐flight mass spectrometry and nuclear reaction analysis

A comparison is made between plasma profiling time‐of‐flight mass spectrometry (PP‐TOFMS) and nuclear reaction analysis (NRA) for depth profiling of 18O tracer in porous anodic oxide films on aluminum. The films were formed galvanostatically, for a range of times, using phosphoric acid electrolytes that were either enriched in 18O or of the natural isotopic concentration. The morphologies of the films were determined by electron microscopy. The findings from PP‐TOFMS and NRA reveal a partitioning of the tracer between the surface regions and buried layers of the films. However, a relatively high background of 16O in PP‐TOFMS prevents a reliable quantification of the concentration of 18O. Copyright © 2012 John Wiley & Sons, Ltd.