EDX Analysis and WDX Analysis

EDX Analysis

EDX Analysis stands for Energy Dispersive X-ray analysis. It is sometimes referred to also as EDS or EDAX analysis. It is a technique used for identifying the elemental composition of the specimen, or an area of interest thereof. The EDX analysis system works as an integrated feature of a scanning electron microscope (SEM), and can not operate on its own without the latter.

During EDX Analysis, the specimen is bombarded with an electron beam inside the scanning electron microscope. The bombarding electrons collide with the specimen atoms' own electrons, knocking some of them off in the process. A position vacated by an ejected inner shell electron is eventually occupied by a higher-energy electron from an outer shell. To be able to do so, however, the transferring outer electron must give up some of its energy by emitting an X-ray.

The amount of energy released by the transferring electron depends on which shell it is transferring from, as well as which shell it is transferring to. Furthermore, the atom of every element releases X-rays with unique amounts of energy during the transferring process. Thus, by measuring the amounts of energy present in the X-rays being released by a specimen during electron beam bombardment, the identity of the atom from which the X-ray was emitted can be established.

The output of an EDX analysis is an EDX spectrum (see Figure 2 on Page 2). The EDX spectrum is just a plot of how frequently an X-ray is received for each energy level. An EDX spectrum normally displays peaks corresponding to the energy levels for which the most X-rays had been received. Each of these peaks are unique to an atom, and therefore corresponds to a single element. The higher a peak in a spectrum, the more concentrated the element is in the specimen.

An EDX spectrum plot not only identifies the element corresponding to each of its peaks, but the type of X-ray to which it corresponds as well. For example, a peak corresponding to the amount of energy possessed by X-rays emitted by an electron in the L-shell going down to the K-shell is identified as a K-Alpha peak. The peak corresponding to X-rays emitted by M-shell electrons going to the K-shell is identified as a K-Beta peak. See Figure 1.

Figure 1. Elements in an EDX spectrum are identified based on the energy content of the X-rays emitted by their electrons as these electrons transfer from a higher-energy shell to a lower-energy one

When performing EDX analysis, the following must be observed:

1) The probe current must be adjusted such that data collection is just between 10%-30% dead.

2) Spot Mode operation must be used for contaminants suspected to be concentrated in very small regions.

3) The EHT level used during the analysis must be higher than the energy peaks corresponding to the elements of interest.

Failure Mechanisms/Attributes Tested for by EDX Analysis: Inorganic Contamination, Elemental Composition

Figure 2. Example of an EDX Spectrum

WDX Analysis

WDX Analysis stands for Wavelength Dispersive X-ray analysis. It is sometimes referred to also as WDS analysis.

WDX analysis works in pretty much the same way as EDX analysis, except that its detector classifies and counts the impinging X-rays in terms of its characteristic wavelengths. The detector system uses an X-ray analyzing crystal that only allows the diffraction of desired wavelengths into the X-ray detector for counting.

Advantages of WDX analysis over EDX analysis include: 1) a much better energy resolution, preventing many peak overlap errors frequently encountered in EDX analysis; and 2) lower background noise allowing a more accurate quantitative analysis.

Its disadvantages include: 1) higher time consumption; 2) greater sample damage and chamber contamination because of the high beam currents required; and 3) high cost.

Failure Analysis; FA Techniques; Basic FA Flows; Package Failures; Die Failures

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