Die-related Failure Mechanisms and Attributes (Page 2 of 3)

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Electrical Overstress (EOS)

Electrical Overstress, or EOS, refers to the destruction of the circuit because of excessive voltage, current, or power. EOS damage is usually very obvious. Metal lines are discolored, burnt, or melted (see photo on the right and article on metal burn-out). Thin-film resistors are severed, with the severing usually showing up as straight, whitish lines. Transistors and diodes exhibit metal migration from one terminal to another. The glassivation may even show mechanical damage.

EOS is usually caused by improper application of excitation to the device, whether it's still being tested in the manufacturing line or it is already in the field. Simple socketting violations such as device misorientation and shifting can cause EOS damage, especially if the voltages intended for the power supply pins will be applied to stress-sensitive or power-limited pins. Improper excitation settings or voltage spikes in the excitation source are also common causes of EOS damage.

EOS damage is not always obvious though. Some EOS events leave no apparent physical manifestation on the die surface at all. Such EOS events can still render the affected component non-functional, even if no physical anomalies are observable. Weak EOS events may also occur, simply shifting the parametric performance of the affected component, but nonetheless affecting the over-all performance of the device.

Latch-up and Electrostatic Discharge (ESD) are special cases of EOS, and are discussed in more detail as separate failure mechanisms in this reference.

See also separate article on EOS/ESD Failures.

Electromigration

Electromigration refers to the gradual displacement or mass transport of the metal atoms of a conductor as a result of current flowing through that conductor. It can lead to formation of voids or hillocks in the metal line, which may cause open and short circuits, respectively.

See separate article on electromigration.

Electrostatic Discharge (ESD)

Electrostatic Discharge, or ESD, is a single-event, rapid transfer of electrostatic charge between two objects, usually resulting when two objects at different potentials come into direct contact with each other. ESD can also occur when a high electrostatic field develops between two objects in close proximity. An ESD event can damage a device in many ways, e.g., conductor fusing, metal-resistor severing, junction damage, dielectric/oxide ruptures, etc.

There are three (3) ESD models that are widely accepted in the industry today. These are the Human Body Model (HBM), the Charged Device Model (CDM), and the Machine Model (MM). The HBM simulates the electrostatic discharge of a person touching an IC at a different potential. The CDM simulates the discharge of a device charged to either a positive or negative potential when it touches a conductive surface that is at another potential. The MM simulates the discharge of a machine or a tool when it comes into contact with a device at a different potential.

See also separate articles on ESD and EOS/ESD Failures.

Gate Oxide Breakdown

In a MOS transistor, the electrical characteristics of the channel through which the carriers flow are controlled by a gate. This gate is isolated from the channel by a thin layer of oxide. Gate oxide breakdown is therefore simply the destruction of this dielectric layer. Gate oxide breakdown is also sometimes referred to as gate oxide rupture, and often manifests as a short or leakage path from the gate to the channel or substrate.

Gate oxide breakdowns are usually caused by electrical overstress (EOS) or electrostatic discharge (ESD), although imperfections or defects in the gate oxide layer can also lead to its early life or time-dependent breakdown. These defects may be in the form of mobile ions, stray particles, or insufficient coverage.

See also Oxide Breakdown and Dielectric Breakdown.

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