Kanarov V, Siegfried D, Sferlazzo P, Hayes A, Yevtukhov R
Veeco Instruments, Inc., Terminal Drive, Plainview, New York 11803, USA.
Rev Sci Instrum. 2008 Sep;79(9):093304. doi: 10.1063/1.2972175.
Characterization of the ion energy distribution function (IEDF) of low energy high current density ion beams by conventional retarding field and deflection type energy analyzers is limited due to finite ion beam emittance and beam space charge spreading inside the analyzer. These deficiencies are, to a large extent, overcome with the recent development of the variable-focusing retarding field energy analyzer (RFEA), which has a cylindrical focusing electrode preceding the planar retarding grid. The principal concept of this analyzer is conversion of a divergent charged particle beam into a quasiparallel beam before analyzing it by the planar retarding field. This allows analysis of the beam particle total kinetic energy distribution with greatly improved energy resolution. Whereas this concept was first applied to analyze 5-10 keV pulsed electron beams, the present authors have adapted it to analyze the energy distribution of a low energy (<or=1 KeV) broad ion beam. In this paper we describe the RFEA design, which was modified from the original, mainly as required by the specifics of broad ion beam energy analysis, and the device experimental characterization and modeling results. Among the modifications, an orifice electrode placed in front of the RFEA provides better spatial resolution of the broad ion beam ion optics emission region and reduces the beam plasma density in the vicinity of analyzer entry. An electron repeller grid placed in front of the RFEA collector was found critical for suppressing secondary electrons, both those incoming to the collector and those released from its surface, and improved energy spectrum measurement repeatability and accuracy. The use of finer mesh single- and double-grid retarding structures reduces the retarding grid lens effect and improves the analyzer energy resolution and accuracy of the measured spectrum mean energy. However, additional analyzer component and configuration improvements did not further change the analyzed IEDF shape or mean energy value. This led us to conclude that the optimized analyzer construction provides an energy resolution considerably narrower than the investigated ion beam energy spectrum full width at half maximum, and the derived energy spectrum is an objective and accurate representation of the analyzed broad ion beam energy distribution characteristics. A quantitative study of the focusing voltage and retarding grid field effects based on the experimental data and modeling results have supported this conclusion.
由于有限的离子束发射度以及分析仪内部束流空间电荷扩展的影响，采用传统的减速场和偏转型能量分析仪来表征低能高电流密度离子束的离子能量分布函数（IEDF）存在局限性。随着可变聚焦减速场能量分析仪（RFEA）的最新发展，这些不足在很大程度上得到了克服，该分析仪在平面减速栅之前有一个圆柱形聚焦电极。这种分析仪的主要概念是在通过平面减速场对发散的带电粒子束进行分析之前，将其转换为准平行束。这使得能够以大大提高的能量分辨率分析束流粒子的总动能分布。尽管这一概念最初应用于分析5 - 10 keV的脉冲电子束，但本文作者已将其应用于分析低能（≤1 keV）宽离子束的能量分布。在本文中，我们描述了RFEA的设计，该设计主要根据宽离子束能量分析的具体要求对原始设计进行了修改，以及该装置的实验表征和建模结果。在这些修改中，放置在RFEA前面的孔电极提高了宽离子束离子光学发射区域的空间分辨率，并降低了分析仪入口附近的束流等离子体密度。发现放置在RFEA收集器前面的电子排斥栅对于抑制进入收集器的二次电子以及从其表面释放的二次电子至关重要，并提高了能谱测量的重复性和准确性。使用更细网格的单栅和双栅减速结构减少了减速栅透镜效应，并提高了分析仪的能量分辨率和测量谱平均能量的准确性。然而，分析仪其他组件和配置的改进并未进一步改变所分析的IEDF形状或平均能量值。这使我们得出结论，优化后的分析仪结构提供的能量分辨率比所研究的离子束能量谱半高宽窄得多，并且导出的能谱是所分析的宽离子束能量分布特性的客观准确表示。基于实验数据和建模结果对聚焦电压和减速栅场效应的定量研究支持了这一结论。
