XRF—See X-Ray fluorescence

Electron Beam Techniques. One of the most powerful tools in VLSI technology is the scanning electron microscope (sem) (see Microscopy). A sem is typically used in three modes secondary electron detection, back-scattered electron detection, and x-ray fluorescence (xrf). AH three techniques can be used for nondestmctive analysis of a VLSI wafer, where the sample does not have to be destroyed for sample preparation or by analysis, if the sem is equipped to accept large wafer-sized samples and the electron beam is used at low (ca 1 keV) energy to preserve the functional integrity of the circuitry. Samples that do not diffuse the charge produced by the electron beam, such as insulators, require special sample preparation. 

Exposure of elements to a broad spectrum of X-rays results in the ejection of electrons from their inner shells. Electrons from outer shells falling into these vacancies emit radiation of specific wavelengths (see Figure 14.13). Analysis of this radiation, referred to as X-ray fluorescence (XRF), allows for the identification of the element from which the photon is emitted. Instruments for carrying out this analysis can be either laboratory sized or can be handheld... 

The most frequently applied analytical methods used for characterizing bulk and layered systems (wafers and layers for microelectronics see the example in the schematic on the right-hand side) are summarized in Figure 9.4. Besides mass spectrometric techniques there are a multitude of alternative powerful analytical techniques for characterizing such multi-layered systems. The analytical methods used for determining trace and ultratrace elements in, for example, high purity materials for microelectronic applications include AAS (atomic absorption spectrometry), XRF (X-ray fluorescence analysis), ICP-OES (optical emission spectroscopy with inductively coupled plasma), NAA (neutron activation analysis) and others. For the characterization of layered systems or for the determination of surface contamination, XPS (X-ray photon electron spectroscopy), SEM-EDX (secondary electron microscopy combined with energy disperse X-ray analysis) and... 

In the technique of X-ray fluorescence (XRF) characteristic X-ray wavelengths are produced from a solid sample, and may be used to identify elements present (see Topic A4). The method is less accurate than those based on the atomic spectra of gases, but is useful for solid samples, especially minerals that may contain many elements. X-rays may be excited by the electron beam in an electron microscope, and the resulting energy dispersive X-ray analysis (EDAX) can be used to give approximate atomic analyses of individual grains of a powdered solid and to estimate the chemical homogeneity of a sample. 

Analysis for metals in solids can be carried out by two different approaches, namely direct analysis of the solid, or after decomposition of the matrix to liberate the metal. Samples can be analysed directly for metals by using, for example, X-ray fluorescence (XRF) spectroscopy (see Chapter 11). This present chapter principally focuses on methods of decomposition of the matrix to liberate its metal content. In addition, selective methods of metal extraction are considered, together with appropriate methods of analysis. 

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