Total X-Ray Fluorescence

TXRF can be used to determine the contamination present on, in, and below the wafer surface (see Fig. 16). Changing the angle of incidence, while remaining below the critical angle of incidence, reveals the nature of the 

Illustration of metal contaminants on (particulate), in (plated), and below (bulk) a surface. 

A typical use of TXRF in CMP development is the study of post-W CMP surface metal contamination. Table III shows the surface metal residual atoms measured by TXRF after W CMP using different slurries (from vendors A, B, and C) and with or without an oxide buff process [17]. The control was a TEOS wafer without any CMP processing. We clearly see that slurry C has unacceptably high Fe contamination both with and without the buffer process. This probably is due to the fact that slurry C is Fe(N03)3 based while slurries A and B are not. 

Glancing angle dependence of relative fluorescence intensity of TXRF for each of the contamination situations. Here is the critical angle. (Courtesy of Charles Evans and Associates, Redwood City, CA.) 

TXRF Metal Surface Concentrations for Wafers Polished with Various Slurries, 

---

To measure a residence-time distribution, a pulse of tagged feed is inserted into a continuous mill and the effluent is sampled on a schedule. If it is a dry miU, a soluble tracer such as salt or dye may be used and the samples analyzed conductimetricaUy or colorimetricaUy. If it is a wet mill, the tracer must be a solid of similar density to the ore. Materials hke copper concentrate, chrome brick, or barites have been used as tracers and analyzed by X-ray fluorescence. To plot results in log-normal coordinates, the concentration data must first be normalized from the form of Fig. 20-15 to the form of cumulative percent discharged, as in Fig. 20-16. For this, one must either know the total amount of pulse fed or determine it by a simple numerical integration... 

In Total Reflection X-Ray Fluorescence Analysis (TXRF), the sutface of a solid specimen is exposed to an X-ray beam in grazing geometry. The angle of incidence is kept below the critical angle for total reflection, which is determined by the electron density in the specimen surface layer, and is on the order of mrad. With total reflection, only a few nm of the surface layer are penetrated by the X rays, and the surface is excited to emit characteristic X-ray fluorescence radiation. The energy spectrum recorded by the detector contains quantitative information about the elemental composition and, especially, the trace impurity content of the surface, e.g., semiconductor wafers. TXRF requires a specular surface of the specimen with regard to the primary X-ray light. 

Three techniques involving the use of X-ray emission to obtain quantitative elemental analysis of materials are described in this chapter. They are X-Ray Fluorescence, XRF, Total Reflection X-Ray Fluorescence, TXRF, and Particle-Induced X-Ray Emission, PIXE. XRF and TXRF use laboratory X-ray tubes to excite the emission. PIXE uses high-energy ions from a particle accelerator. 

XRF is closely related to the EPMA, energy-dispersive X-Ray Spectroscopy (EDS), and total reflection X-Ray Fluorescence (TRXF), which are described elsewhere in this encyclopedia. Brief comparisons between XRF and each of these three techniques are given below. 

Proceeding of the International Workshop on Total Ruction X-Ray Fluorescence. Vienna, 1990 (same as Reference 3). 

Since then, TXRE has become the standard tool for surface and subsurface microanalysis [4.7-4.11]. In 1983 Becker reported the angular dependence of X-ray fluorescence intensities in the range of total reflection [4.12]. Recent demands have set the pace of further development in the field of TXRE - improved detection limits [4.13] in combination with subtle surface preparation techniques [4.14, 4.15], analyte concentrations extended even to ultratraces (pg) of light elements, e. g. A1 [4.16], spe-dation of different chemical states [4.17], and novel optical arrangements [4.18] and X-ray sources [4.19, 4.20]. 

FCC feedstocks contain sulfur in the form of organic-sulfur compounds such as mercaptan, sulfide, and thiophenes. Frequently, as the residue content of crude oil increases, so does the sulfur content (Table 2-5). Total sulfur in FCC feed is determined by the wavelength dispersive x-ray fluorescence spectrometry method (ASTM D-2622), The results are expressed as elemental sulfur. 

Vol. 140. Total Reflection X-Ray Fluorescence Analysis. By Reinhold Klockenkamper... 

Method abbreviations D-AT-FAAS (derivative flame AAS with atom trapping), ETAAS (electrothermal AAS), GC (gas chromatography), HGAAS (hydride generation AAS), HR-ICP-MS (high resolution inductively coupled plasma mass spectrometry), ICP-AES (inductively coupled plasma atomic emission spectrometry), ICP-MS (inductively coupled plasma mass spectrometry), TXRF (total reflection X-ray fluorescence spectrometry), Q-ICP-MS (quadrapole inductively coupled plasma mass spectrometry)... 

XiE M, Von Bohlen A, Klockenkamper R, Jian X, Gunther K (1998) Multielement analysis of Chinese tea (Camellia sinensis) by total reflection X-ray fluorescence. Z Lebensm Unters Forsch 207A 3i-38. 

---