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Materials characterization (SEM, TEM, XRD, XPS)

In semiconductor failure analysis, which technique is best suited to measuring the depth profile of dopant concentration with sensitivity at the ppm to ppb level?

  1. ASIMS (secondary ion mass spectrometry)
  2. BEDS (energy-dispersive X-ray spectroscopy)
  3. CXRD (X-ray diffraction)
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Answer: A. SIMS (secondary ion mass spectrometry)

SIMS sputters the specimen surface with primary ions such as O₂⁺ or Cs⁺ and mass-analyzes the ejected secondary ions. It can measure many elements with ppm to ppb sensitivity and a depth resolution of a few nanometers, and it is the standard method for measuring profiles of boron, phosphorus and arsenic in silicon. It is destructive, since it removes material, and accurate quantification requires reference standards of the same matrix. The detection limit of EDS is roughly 0.1 wt%, not sensitive enough to measure dopant concentrations. XRD examines crystal structure and lattice parameters and cannot measure concentration profiles of trace elements.

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