PFA (Physical Failure Analysis)

Notes

There is only one sample, so the plan is agreed before the first cut and every step is documented photographically.

Overview

PFA (physical failure analysis) is the stage of failure analysis in which the suspected defect site on a chip is physically exposed and examined, using decapsulation, delayering, cross-sectioning and electron or ion beam microscopy. It normally follows electrical failure analysis, which locates the fault without destroying the part. Because most PFA steps cannot be undone, analysts plan the sequence carefully so that the one failing sample yields a root cause.

How it works

PFA starts from a location. Electrical fault isolation, such as lock-in thermography, optical or e-beam probing and nanoprobing, narrows the failure to a region, a net or a single transistor. The analyst then removes whatever hides it. Decapsulation strips the package, for example by etching the mould compound with acid, by laser or mechanically, so the die can be seen. Delayering removes metal and dielectric layers until the suspect level is reached, often with a focused ion beam (FIB) or plasma FIB.

Imaging and analysis follow. A scanning electron microscope (SEM) shows surfaces and cross-sections. A FIB can cut a precise section through the defect and prepare a thin slice for transmission electron microscopy (TEM), which resolves nanometre-scale structures and, with energy-dispersive X-ray spectroscopy, shows which elements are present.

Advanced nodes and packages make this harder. A logic defect may be only nanometres wide and hidden among three-dimensional gate structures, while a packaging defect such as a crack may lie anywhere across millimetres. Labs therefore combine large cross-sections with high-resolution imaging, and postpone destructive steps for as long as possible on expensive packages.

Examples

• A FIB cross-section through a via chain that reveals a void left by incomplete metal fill.
• A TEM lamella from a failing transistor showing a defect in the gate stack of a gate-all-around device.
• Acid decapsulation of a returned automotive part to inspect the die surface for burn damage.
• Cross-sectioning an advanced package to find a cracked solder bump after thermal imaging pointed to it.

Why it matters

PFA is what turns a failing part into an explanation: a particle, a void, a missing silicide, a cracked bump. Failure analysis engineers and sample preparation technicians carry it out, and the result goes to process, yield, reliability and customer quality teams who must fix the cause or answer a customer return.

Related terms

• EFA
• Decapsulation
• SEM
• FIB

Where it appears on the Hub

Used on 6 pages of the Hub. In each group, the pages that mention it most come first.