On July 1st, Toshiba Corporation's Semiconductor Company and Storage Products Company consolidated to form Semiconductor & Storage Products Company.This page describes reliability information of semiconductor products.

Failure Mechanisms

[As of April, 2011]

Passivation

The role of passivation can be broadly divided as follows:

Stabilization of the Si surface
Creation of interlayer insulating film in multilayered wiring
Protection of the entire chip

Passivation often results in fatal defects such as unstable device operation caused by changes in film properties, instability, water permeability, permeability of movable ions such as Na, pinholes and cracks; and Al metal disconnection or corrosion due to degradation and stress. These factors are important having influence on device reliability. Device operation instability and degradation modes include V_th shift and field leakage in MOS transistors, decreased h_FE in bipolar transistors, and breakdown voltage degradation in PN junctions.
The device instability and degradation mode mechanisms which cause passivation are known to be caused by the following:

Ion contamination
Polarization
Parasitic MOS due to lateral extension of electrical charge
Corrosion of Al metal due to phosphorous in PSG, fluorine in plasma CVD film or moisture penetration
Pinholes and cracks
Stress
Degradation of device characteristics due to degassing^{Note 1}

Ion Contamination

Contamination from Na⁺ and other external ions introduced into passivation or into the interface during the manufacturing process greatly affects device reliability.
The Na⁺ ions introduced in the manufacturing process are deactivated by phosphorus gettering. However, an applied electrical field can cause them to move into the passivation oxide film and collect in the field region, gate region or near the PN junction, resulting in failures due to parasitic MOS, T_th change, breakdown voltage degradation, etc.
Breakdown voltage degradation is characterized by the fact that recovery is achieved by baking without bias, similar to breakdown voltage from the above-described crystalline defects. Factors which accelerate degradation due to ion contamination include the strength of the electrical field applied, temperature as well as humidity.
For ion contamination, a protective film with ion-blocking capability such as phosphorus silicate glass (PSG) is used. For external contamination, a film with an even superior ion-blocking effect such as a silicon nitride film is used for top passivation.

Polarization

PSG provides an ion gettering effect as previously mentioned. On the other hand, increased phosphorus content causes polarization, resulting in various types of instability and degradation.^{Note 2}

Parasitic MOS

As shown in Fig. 1, if the SiO₂ surface becomes conductive, the electrode potential extends in a lateral direction to the adjacent PN junction, forming parasitic MOS due to the inversion of the field region.
Although measures against this type of failure mechanism are implemented from aspects of the design and manufacturing process, there is still a small chance that the problem will occur, depending on the humidity and ionic contamination in the external operating environment.

This is [Figure 1 Extended Charge in Lateral Direction Model].

Figure 1 Extended Charge in Lateral Direction Model^{Note 3}

Pinholes and Cracks

If passivations include defects such as pinholes or cracks, interlayer shorts can occur in multilayered metallization. Also, moisture, Na⁺ ions and/or other contaminants can enter in top passivation via the said defects, causing device operation instability, degradation or Al metal corrosion as previously described. Cracks can be formed by thermal stress in the manufacturing process or by mold distortion. The effects of mold distortion cannot be ignored, particularly with the increasing level of miniaturization and scaling in integrated circuits.

Note 1: Bibliography. K. Harada, et al.; "ESR Study of MOSFET characteristics Degradation Mechanism by Water in Intermetal Oxide," IEICE Transactions on Electronics, (1994), p. 595

Note 2: Bibliography. J.M.Eldrige, R.B.Laibowitz and P.Balk; “Polarization of Thin Phosphosilicate Glass Films in MGOS Structures,” J.Appl. Phys., Vol. 40, (1969), p. 1922

Note 3: Bibliography. A.S. Grove, Physics and Technology of Semiconductor Devices, John Wiley & Sons Inc., 1987