Cation Mass Spectrometer Research Articles

New neutral cesium evaporation chamber and UHV suitcase

AbstractIt is well known that the use of Cs+ primary ions results in an important increase of the negative ionization probability during SIMS analyses. Moreover, Cs+ bombardment allows working in the MCsx+ mode, which is a widely used technique to reduce the matrix effect. A major drawback of Cs+ primary ion bombardment is that the Cs+ beam serves both for the incorporation of Cs and for the sputtering of the surface. Therefore, the sputtering yield, and consequently the cesium surface concentration, are constricted by the primary bombardment conditions.To overcome this problem, the Cation Mass Spectrometer (CMS), equipped with an evaporator delivering a collimated and adjustable stream of neutral Cs onto the sample, has been developed at the SAM department. By continuous Cs0 deposition during the SIMS analysis, optimal Cs surface concentrations, and thus optimal ionization probabilities are obtained.1In order to make the Cs0 deposition technique available for other analysis instruments, a standalone UHV instrument for Cs evaporation prior to SIMS analyses has been developed. Furthermore, a suitcase for the transfer under UHV conditions of the samples in‐between the Cs0 evaporation chamber and the analysis instruments has been designed, to avoid any contaminations. In this work, we present this new Cs0 evaporation chamber, as well as our new UHV suitcase in terms of their characteristics and handling. Copyright © 2010 John Wiley & Sons, Ltd.

Biased sample holder for complete correction of SIMS transmission losses with tilted samples

For investigation of fundamental aspects of secondary ion mass spectrometry (SIMS) such as secondary ion distributions, roughness formation or simply for optimisation of a particular analysis, the ability to tilt a sample is vital. However many instruments suffer transmission losses when the sample is tilted. This phenomenon has been investigated for the Cation Mass Spectrometer (CMS) instrument using Monte Carlo simulations and the cause determined to be modification of the extraction field arising from the sample tilt. A new sample holder incorporating biasing electrodes has been developed to eliminate transmission losses during SIMS analysis when using tilted samples. Simulations and experimental result confirm complete elimination of transmission losses for sample tilts of up to 20°.

ELECTRA: Electrostatic lens calculation tool with real time adjustment. A virtual optics bench for rapid determination of optical parameters using pre-characterized lenses

A software for dynamically displaying basic optical parameters of a system of pre-characterized lenses (ELECTRA) has been written. The lens characterization may be carried out with any charged particle optics program. In this study the pre-characterization was carried out using SIMION versions 7.0.5 and 8.0. The ELECTRA software has been benchmarked against SIMION using a well known lens (the 3 cylinder Einzel lens) and used to determine the configuration of new transfer optics for the cation mass spectrometer. Good agreement has been achieved between the ELECTRA software and SIMION for basic optical parameters.

Important increase of negative secondary ion sensitivity during SIMS analysis by neutral cesium deposition

The Cation Mass Spectrometer (CMS) is a SIMS prototype developed in our laboratory in order to perform quantitative analysis with optimal sensitivity and high depth and lateral resolution in the MCs x + and M − modes. For this aim, a patented neutral Cs evaporator for varying the Cs surface concentration over the whole range has been developed. The sputtering and the Cs introduction have been decoupled successfully by applying simultaneously X y+ bombardment and neutral Cs deposition. X stands for any element except Cs. Currently the CMS is equipped with a Cs + and a Ga + gun. These guns are used for studying the useful yield variations of negative secondary ions (Si −, Al −, Ni −, In −, P −) with respect to the Cs surface concentration. Furthermore, the observed variations of the useful yield were linked to work function shifts. Qualitative agreement with the predictions of the electron tunnelling model are obtained. Several applications give further evidence of successful optimization of the useful yield for elements with high electron affinity.

SIMS analysis with neutral cesium deposition: Negative secondary ion sensitivity increase and quantification aspects

To overcome the SIMS matrix effect in the negative secondary ion mode, analyses can be performed on the Cation Mass Spectrometer using neutral cesium deposition with simultaneous primary ion bombardment. This paper discusses the advantages of this technique by applying it on several samples. The useful yields of various elements detected as negative secondary ions are calculated and discussed in terms of work function and electron affinity. The additional Cs deposition allows a significant increase of the useful yields of negative secondary ions and thus of the analysis sensitivity compared to traditional Cs + primary ion bombardment. At maximal cesium surface concentrations, quantitative analyses become possible for elements with high electron affinities. For other elements a significant increase of the analysis sensitivity is achieved.

Work function shifts and variations of ionization probabilities occurring during SIMS analyses using an in situ deposition of Cs0

Abstract To optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, the Laboratoire d'Analyse des Materiaux (LAM) has developed the Cation Mass Spectrometer (CMS), a new instrument specially dedicated to performing this kind of analysis. To further enhance the potential of this instrument, we have developed a column that delivers a collimated and adjustable stream of neutral Cs atoms to be deposited on the surface of the sample while this one is being analyzed by SIMS. As this configuration permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs + ion bombardment, it becomes possible to optimize simultaneously the sensitivity of the analysis, by carefully adjusting the Cs concentration to its optimum value, and the depth resolution of the analysis, by choosing adequate primary bombardment conditions. For the present paper, we have performed in situ measurements of the produced variations of the sample's work function, which are a typical concomitant of alkali metal deposition, by recording successive energy distributions of secondary Cs + ions sputtered from three different samples (Al, Si, Ni). The work function shifts detected by using this method can subsequently be used to explain the variations of the ionization probability of secondary Cs found in a previous study of MCs x + cluster analysis based upon the described technique. In this respect, we find curves which are typical for what one would expect considering the electron-tunneling model and this theoretical prediction is thus corroborated by our experimental results.

Cation Mass Spectrometer (CMS): recent developments for quantitative analyses of positive and negative secondary ions

The Cation Mass Spectrometer (CMS) has been developed in our laboratory to perform quantitative measurements with an optimal sensitivity and excellent depth and lateral resolution. For positive secondary ions, the MCs x + mode has been used to circumvent the problems linked to the matrix effect by decoupling the Cs surface concentration from the sputtering conditions, so that an optimal Cs surface concentration is guaranteed and permits one to obtain high sensitivity. Similarly, flooding the sample surface with Cs lowers the work function and permits high useful yields for negative secondary ions. To obtain these performances, a patented neutral Cs deposition column is used for Cs surface concentration control in combination with a surface ionisation Cs + gun for the sputtering of depth profiles or a Ga + LMIS for imaging.

Optimization of SIMS analyses performed in the MC sx+ mode by using an in situ deposition of C s

In order to optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, we used the new Cs 0 column installed on the Cation Mass Spectrometer (CMS) and introduced an analysis technique consisting of an ion bombardment accompanied by a simultaneous deposition of Cs 0 at the surface of the sample. This experimental technique permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs + ion bombardment. In order to investigate numerous aspects of the mentioned analytical technique, analyses were performed on three different samples (Al, Si, Ni) using a Ga + ion bombardment. In this paper, we will present an overview of the obtained results. We will deal in particular with the Cs concentrations reached during the analyses and the behavior of the measured MCs x + signals. We show in this context that the values of the Cs concentration and of the useful yields only depend on the ratio between the erosion and deposition rates, but not on the individual values of these two rates.

Optimization of SIMS analyses performed in the MCs x+ mode by using an in situ deposition of neutral Cs

To optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, the Laboratoire d'Analyse des Matériaux (LAM) has developed the Cation Mass Spectrometer (CMS), a new instrument specially dedicated to perform this kind of analysis. To further enhance the potential of this instrument, we have developed a column that delivers a collimated and adjustable stream of neutral Cs atoms to be deposited on the surface of the sample while this one is being analyzed. Using this new column, it was possible to introduce an analysis technique consisting of an X y+ ion bombardment (where `X' stands for any element excepting Cs) accompanied by a simultaneous deposition of Cs 0 at the surface of the sample. This experimental technique permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs + ion bombardment. As a consequence, it becomes possible to optimize simultaneously the sensitivity of the analysis, by carefully adjusting the Cs concentration to its optimum value, and the depth resolution of the analysis, by choosing adequate primary bombardment conditions. In this paper, we investigate numerous aspects of the mentioned analytical technique by using a Ga + ion bombardment and by performing analyses on three different samples (Al, Si, Ni). We study in detail the behavior of the measured MCs x + signals as well as of the corresponding useful yields. In this context, the observed evolutions are discussed in terms of ionization probabilities, number of available atoms participating in the formation mechanisms and recombination probabilities. We show in particular that the useful yields only depend on the ratio between the erosion and deposition rates, but not on the individual values of these two rates.

In situ deposition of neutral Cs for Secondary Ion Mass Spectrometry

The Cation Mass Spectrometer (CMS) is a new instrument allowing to optimize the advantageous quantification technique consisting in analyzing MCsx+ clusters. To further enhance the potential of this instrument, we have developed a column that delivers a collimated and adjustable stream of neutral Cs atoms to be deposited on the surface of the sample while this one is being analyzed by Secondary Ion Mass Spectrometry (SIMS). Using this new column, it was possible to introduce an analysis technique consisting of a Xy+ ion bombardment (where X stands for any element except Cs) accompanied by a simultaneous deposition of Cs0 at the surface of the sample. This experimental technique permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs+ ion bombardment. As a consequence, it becomes possible to optimize simultaneously the sensitivity of the analysis, by carefully adjusting the Cs concentration to its optimum value, and the depth resolution of the analysis, by choosing adequate primary bombardment conditions. In this paper, we will first describe the new Cs0 column and outline its performances. In a second part, we will focus on the analytical aspect and study the ability to vary the Cs concentration over a complete and continuous range. Experiments using a Ga+ primary bombardment show in particular that the Cs concentration produced during analyses performed with the mentioned technique only depends on the characteristics of the analyzed material and the ratio between the erosion and deposition rates, but not on the individual values of these two rates.

Useful yields of MCs x+ clusters: a cesium concentration-dependent study on the Cation Mass Spectrometer (CMS)

To optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, the Laboratoire d’Analyse des Matériaux (LAM) has developed a new instrument specially dedicated to performing this kind of analysis. The Cation Mass Spectrometer (CMS) instrument leads to high MCs x + useful yields by allowing to reach an optimum value of the stationary Cs surface concentration, which is known to be a very critical parameter in MCs x + analysis due to its strong influence on the probability of secondary Cs + ionization. The present work focuses on the potential of the CMS instrument to vary the stationary Cs concentration over a large range and the benefits concerning the MCs x + useful yields resulting from this possibility. Analyses were performed on three different samples (Al, Si, Ni) while modifying the impact angle of the primary Cs + beam and in the Cs +–Ga + cobombardment mode. These techniques are shown to be complementary with respect to the covered ranges of cesium concentrations resulting in a complete range going from quasi 0 to some 30%. The observed variations of the useful yields are discussed in terms of the stationary Cs concentration produced during the analysis and the consequent variations of the Cs + ionization probability provoked by work function shifts which were determined by in-situ measurements. A comparison between the performances of the CMS and those of classic Cameca instruments shows, depending on the element, useful yield enhancements up to a factor 90 mainly due to work function conditions resulting in high Cs + ionization probabilities.

Cation Mass Spectrometer: towards an optimisation of MCs x+ cluster analysis

The Cation Mass Spectrometer (CMS) should lead to high MCs x + useful yields by allowing to reach an optimum value of the stationary Cs surface concentration, which is known to be a very critical parameter in MCs x + analysis due to its strong influence on the probability of secondary Cs + ionisation. For the present work, variations of the Cs concentration were obtained by modifying the impact angle of the primary Cs + beam and by bombarding the sample simultaneously with Cs + and Ga + beams. Results show that these techniques allow to cover a large and continuous range of Cs surface concentrations and to reach an optimisation of the MCs x + useful yields (enhancements up to a factor 100 compared to Cameca 4f and 6f instruments) mainly due to work function conditions resulting in high Cs + ionisation probabilities.

Useful yields of MCs + and MCs 2+ clusters: a comparative study between the Cameca IMS 4f and the Cation Mass Spectrometer

The useful yields of MCs + and MCs 2 + clusters strongly depend on the stationary cesium surface concentration c Cs incorporated in the specimen during the primary bombardment. The Cation Mass Spectrometer (CMS) has been designed to reach high MCs x + useful yields by allowing an optimization of c Cs in an instrument providing a high transmission via a high extraction field and a magnetic sector spectrometer. For this purpose the CMS instrument has been equipped by several newly developed features, among which figures a sample stage and adapted collection optics allowing variations of the impact angle of the primary beam on the specimen at a constant primary energy. These variations of the incidence angle imply changes of the sputtering yield Y, which determines the Cs surface concentration according to c Cs = 1/(1 + Y). In this paper, we will study the improvement of secondary yields obtained on the CMS, in comparison with a classical Cameca IMS 4f, by making use of precisely this possibility to vary the sputtering yield. On both machines, analyses were performed on six different elements (B, F, Mg, S, As, and In) implanted in silicon samples. The observed variations of the useful yields are discussed in terms of the stationary cesium surface concentration incorporated in the specimen during the primary bombardment. Depending on the element, useful yield enhancements ranging from a factor 7 to a factor 80 can be observed between the CMS and the Cameca IMS 4f. This finding can be explained by the fact that the CMS allows to reach lower stationary Cs surface concentrations, which are close to the optimum value for the investigated samples.