X-Ray Fluorescence (XRF)

X-ray Fluorescence (XRF) is a non-destructive technique that is used to quantify the elemental compositions of materials and to measure film thickness and composition. X-rays are used to excite the sample, causing the emission of X-rays with energies characteristic of the elements present.

XRF is capable of detecting elements from B-U in concentrations from the ppm range to 100%.  Additionally, Be can be measured in copper.  Because X-rays are used to excite the sample, analysis depths from less than a nanometer to several millimeters can be achieved depending on the material. Through the use of appropriate reference standards, or fundamental parameters (FP) when standards aren’t available, XRF can accurately quantify the elemental composition of most materials.

Five XRF systems are available, four wavelength dispersive instrument (WDXRF) and an energy dispersive instrument (EDXRF) with the main difference being the way in which the X-rays are separated and measured. WDXRF has very good energy resolution which leads to fewer spectral overlaps and improved background intensities. EDXRF has higher signal throughput which enables small area analysis or mapping.

Ideal Uses
  • Measuring film thickness and composition from the angstrom range up to several micrometers
  • General elemental identification and quantitation in most materials, including glass, metals, ceramics, polymers, or residues
  • Identification of specific metal alloys or types of glass
  • Trace level analysis for contaminants in solid or liquid samples
  • Identifying and quantifying inorganic fillers in polymers
  • Nondestructive analysis of large sputter targets
  • Nondestructive analysis of thin films on wafers up to 300mm diameter
Technical Specifications

Signal Detected: X-rays
Elements Detected: B-U (WDXRF); Na-U (EDXRF)
Detection Limits: 1ppm-100ppm for most elements
Imaging/Mapping: Yes (up to 6x10cm area)
Lateral Resolution/Probe Size: 500µm, 1mm, 6mm, 10mm, 20mm, 26mm, 30 mm or 37mm (WDXRF); 30µm, 1mm, 2mm (EDXRF)

Strengths
  • Non-destructive
    • Whole wafer analysis (up to 300mm) as well as wafer pieces and small samples
    • EDXRF analysis of very large samples: 15cm x 15cm x 10cm (LxWxH)
    • WDXRF analysis of very large samples: 400mm diameter, 50mm thickness, 30kg mass
    • Thickness and composition of multilayer film stacks
  • Can analyze areas as small as ~30µm (EDXRF) or 500µm (WDXRF)
  • Can analyze any solid material and some liquids
  • Sampling depth ranging from less than a nanometer to several millimeters depending on the material
Limitations
  • Cannot detect elements lighter than Na using EDXRF
  • Cannot detect elements lighter than B using WDXRF
  • Highest accuracy measurements require reference standards similar in composition and/or thickness to the test sample

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