More Failure Analysis Techniques

SEM Voltage Contrast Analysis

Voltage Contrast is a failure analysis technique performed using a Scanning Electron Microscope (SEM) to detect open conductor lines, open junctions, or reverse-biased junctions.  It operates on the basic principle that the emission of secondary electrons by a sample bombarded with the primary electron beam of a SEM is restricted or enhanced by the presence of local electric fields within the circuit.

Since these secondary electron emissions are the basis for forming the SEM images, localized fields can result in image contrast differences (darker or brighter areas than normal, depending on the voltage polarity) that visually indicate circuit anomalies. For instance, applying a small positive voltage to a metal line will make it appear darker during SEM inspection than when it is grounded.  Thus, if there's a discontinuity or a non-conducting junction along that line, one section of the line will appear dark (the one connected to the voltage) while the other section will appear bright.

X-ray Fluorescence (XRF) Analysis

XRF Analysis is a failure analysis technique that employs a primary beam of x-ray to excite a sample into emitting x-rays that are collected and analyzed to identify the composition of the sample, similar to how EDX and WDX analyses are done.  The advantage of XRF over EDX/WDX analysis is that it can be used to analyze layers that would otherwise charge or decompose with electron bombardment, since it uses x-rays for sample bombardment. Sample charging or decomposition is a common issue with EDX/WDX analysis, which bombard the sample with electrons. However, the large diameter of XRF primary beam limits its spatial resolution.

Neutron Activation Analysis (NAA)

Neutron Activation Analysis (NAA) is a failure analysis technique that is useful for detecting very small concentrations of certain elements in a sample. Elements such as arsenic, copper, gold, sodium and tungsten can be detected by NAA down to concentration levels of 10¹¹-10¹² atoms per cm³. NAA irradiate silicon samples with a flux of thermal neutrons, creating radioisotopes of all elements in the sample. The elements present in a sample are identified through the half-lives exhibited by the various silicon radioisotopes, particularly the longer-lived ones.

See Also:  Failure Analysis;  All FA Techniques; FA Lab Equipment; 

Basic FA Flows;  Package Failures;  Die Failures