Failure mechanism

The initiating physical process which creates the failure mechanism.

A failure mechanism in semiconductor devices. Corrosion failures can occur when ULSI devices are exposed to moisture and contaminants. Corrosion failures are usually classified as one of two broad groups: bonding pad corrosion or internal chip corrosion. Bonding pad corrosion is usually more common simply because the die passivation does not cover the metallization in the bonding pad locations. Internal chip corrosion (internal to the chip, away from the bonding pads) can also occur if some weakness or damage exists in the die passivation, which would permit the moisture and contaminants (e.g., chlorine ions) to reach the metallization. (Reference JEP122F)

A failure mechanism in semiconductor devices. Due to momentum exchange between the current-carrying electrons and the host metal lattice, aluminum ions can drift in the direction of the electron current. In the presence of flux divergent sites, this drift induces a stress gradient that at steady state is proportional to the current density. In sufficiently long conductors and at high current densities, the stress will increase to the point where voids will form in regions of tensile stress that subsequently grow to the point of failure. It is also possible that at locations of high compressive stress extrusions and hillocks can form that can cause failure of the protective passivation or induce short circuits. (Reference JEP122F)

A failure mechanism in semiconductor devices. As in the case of aluminum (Al), momentum exchange between current-carrying electrons and copper (Cu) ions in a Cu line cause Cu ions to drift in the direction of the electron current. In the presence of flux divergence sites where the flux of Cu atoms into the site is unequal to the flux leaving the site, a stress gradient is induced that is proportional to the current density, and can be tensile or compressive, depending on the sign of the divergence. In sufficiently long conductors with sufficiently high current densities, the tensile stress at a negative divergence site will increase to the point where voids will form due to vacancy coalescence, and will grow until they are large enough to cause failure. Compressive stress at sites of positive divergence will cause the formation of extrusions and hillocks that can cause cracking in the protective passivation, and short circuiting of neighboring conductors due to extruded Cu. (Reference JEP122F)

A failure mechanism in semiconductor devices. Due to the combination of different materials and process temperatures used in chip fabrication, the Cu lines in advanced Cu technologies exist in a state of tensile stress. When geometric configurations produce local peaks in stress and when such a peak exists at a location of marginal adhesion or at a pre-existing process-induced void, large stress gradients are created. The term stress migration (stress-induced voiding, or simply stress voiding) refers to the movement of metal atoms under the influence of such a mechanical stress gradient. Little metal movement (migration) occurs until the stress exceeds the yield-point of the metallization. Then atoms diffuse from sites of low stress into regions of high stress and contribute to void growth, and when the void is large enough, the void can cause an electrical open or sufficient resistance increase to interfere with chip functionality. (Reference JEP122F)