Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene

We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration

Towards inline metrology of thin materials in semiconductor environment

This presentation will illustrate some of the metrological challenges I faced during the last 15 years in the semiconductor world, more precisely in the inline metrology group at CEA-Leti. After a brief introduction to the need for metrology (and not only characterization) to probe thin inorganic materials in semiconductor environment, I will present highlights related to some research topics :-the metrology of thickness and optical constants using inline optical techniques such as spectroscopic ellipsometry or M-line spectroscopy-the metrology of thickness and composition using X-ray techniques, with a strong focus on the quantitative analysis of high-Z, medium-Z and low-Z materials by X-ray fluorescence-the elemental-depth profiling in thin layered materials of thicknesses from nm to µm and with nm-like depth resolution, by means of X-ray photoemission, combination of X-ray fluorescence and reflectometry in grazing incidence, and plasma-profiling time-of-flight mass spectrometry-the metrology and characterization work required to support the development of innovative phase change materials for non-volatile memor

Determination of free carrier concentration of polar semiconductors using LOPC modes: an example of InP

International audienceFree carrier concentration is one of the important properties of semiconductor devices/materials that may directly affect the performance of several applications in microelectronic and optoelectronic fields such as photodetector, lasers and light-emitting diodes [1]. This property therefore needs to be precisely controlled and measured. Conventional techniques (Hall Effect measurements and C-V characterization) can provide accurate results but usually require a time-consuming and/or destructive sample preparation. In polar semiconductors such as GaN, GaAs, InP, SiC, etc., the coupling between the longitudinal-optical phonon mode (LO) and the collective oscillations of the free carrier systems (plasmons) results in the so-called LO phonon-plasmon coupled modes (LOPC) [2-4]. This spectral feature, which strongly depends on the free carrier concentration, makes Raman spectroscopy an alternative nondestructive and contactless technique for rapid determination of doping concentration and can be used upon process validation and/ormass production. It is to note that, depending on the nature of the material as well as the doping type (n- or p-type), the evolution of LOPC modes vary differently as varying free carrier concentration. The LOPC consist of two branches: L- and L+ at low and high frequency, respectively. In general, the free carrier concentration can be deduced from L+ peak position by fitting Raman spectral data to theoretical mathematic equations [2-4]. However, the doping concentration measured by different theoretical models existing in literature (and associated adjustable parameters) may present a significant variation (up to > 30%) [2]. Thus, establishing a calibration curve dedicated for an interesting concentration range is still needed to ensure the highest accuracy of quantitative measurement. The simplest way is correlating directly the spectral parameters measured at a given experimental configuration to the carrier concentrations obtained from a conventional method. Among the aforementioned semiconductors, the LOPC modes of InP is sensitive the most to the measurement conditions, especially the excitation wavelength and power due to the photogenerated carrier phenomenon [4]. Knowing the impact of different measurement parameters is primordial for accurate quantitative measurements. In this presentation, we present Raman analyses of n-doped bulk InP samples of various carrier concentrations performed with different configurations to illustrate their impact. The free carrier concentration deduced by Raman analyses is then compared to results of Hall Effect measurements. Finally, we present the calibration data linking directly the L+ peak position to the carrier concentration obtained from Hall Effect measurements

A step toward calculating the uncertainties in combined GIXRF-XRR

International audienceThe combination of XRR and GIXRF is used for the characterization of thin films and multilayered materials, since both techniques use similar measuring and data analysis procedures and combining them leads to more accurate characterization in terms of thickness, roughness, density and elemental composition. However, there is a major difficulty to determine the associated uncertainties, due to the large number of fitting parameters and more specifically, to the combination of the two methods with dramatically different dynamic ranges. In this paper, we propose a recursive method for the estimation of the uncertainties of the data from the GIXRF-XRR analysis, based on a Bootstrap statistical method. We applied this method on a one layer chalcogenide GST thin film with a carbon caping layer for which we found small uncertainties on the model parameters. We propose also a method for calculating the uncertainty on the solid angle of the detector based on Monte Carlo simulation

Méthodes avancées en XPS et HAXPES pour la détermination des épaisseurs des matériaux high-k

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Improvement of Capacitive Behavior on Gradient-Free PZT Thin Films

International audiencePbZr0,52Ti0,48O3 thin films were synthetized by sol-gel techniques on large scale Pt(111)/TiOx/SiO2/Si substrates (200 mm in diameter). The Zr/Ti ratio gradient – that appears through the thickness of the layer with standard processing – can be reduced using an optimized “gradient-compensated” approach. Capacitance measurements revealed an augmentation of the effective permittivity from 5 to 15% using “gradient-free” PZT (reaching 1700 for 2μm). Large scale breakdown voltage analysis revealed an increase of 20% for the breakdown field for low thicknesses (1.25MV/cm for 240 nm-thick layer) suitable for capacitor integration

Rapid, semi-quantitative elemental depth profiling using plasma profiling time-of-flight mass spectrometry

International audiencePlasma Profiling Time-Of-Flight Mass Spectrometry (PP-TOFMS) is a novel elemental depth profiling technique developed by Horiba Scientific. It couples an argon plasma source for sample sputtering and ionization with an orthogonal time-of-flight mass spectrometer. The technique delivers nanometer-scale depth profiles with high sensitivity and is capable of providing calibration-free semi-quantitative results. Moreover, the operation of the instrument is simpler and faster compared to typical SIMS instruments requiring only a few minutes including sample introduction and pumping.The instrument is installed in a cleanroom at CEA-Leti in close proximity to process tools allowing fast feedback for materials development. The potential of this technique will be illustrated by several examples

Assessing advanced methods in XPS and HAXPES for determining the thicknesses of high-k oxide materials: From ultra-thin layers to deeply buried interfaces

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Characterizing Critical Buried Interfaces by Inelastic Background Analysis using Lab-Scale Hard X-ray Spectroscopy

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Reference-free grazing incidence x-ray fluorescence and reflectometry as a methodology for independent validation of x-ray reflectometry on ultrathin layer stacks and a depth-dependent characterization

International audienceNanolayer stacks are technologically very relevant for current and future applications in many fields of research. A nondestructive characterization of such systems is often performed using x-ray reflectometry (XRR). For complex stacks of multiple layers, low electron density contrast materials, or very thin layers without any pronounced angular minima, this requires a full modeling of the XRR data. As such a modeling is using the thicknesses, the densities, and the roughnesses of each layer as parameters, this approach quickly results in a large number of free parameters. In consequence, cross correlation effects or interparameter dependencies can falsify the modeling results. Here, the authors present a route for validation of such modeling results which is based on the reference-free grazing incidence x-ray fluorescence (GIXRF) methodology. In conjunction with the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt, the method allows for reference-free quantification of the elemental mass depositions. In addition, a modeling approach of reference-free GIXRF-XRR data is presented, which takes advantage of the quantifiable elemental mass depositions by distributing them depth dependently. This approach allows for a reduction of the free model parameters. Both the validation capabilities and the combined reference-free GIXRF-XRR modeling are demonstrated using several nanoscale layer stacks consisting of HfO 2 and Al 2 O 3 layers