Reliability engineers have long recognized an inherent characteristic in many types of equipment to exhibit a decreasing failure rate during their early operating life. Intuitively, a relatively high early failure rate, that decreases with time until it eventually levels off, can be explained by the inherent variability of any production process.
Table 1.1 [1] lists the possible failure mechanisms which are unique to each process step involved in manufacturing a microelectronic device. A failure mechanism will be eventually exhibited as a failure because the device will fail to meet its specified performance characteristics. Common microcircuit failures can be classified with respect to failure as follows:
Degradation of performance characteristics.
Shorts.
Opens.
Intermittents.
| Process step | Failure mechanism introduced as a reliability influencing variable |
| Slice preparation | Dislocations and stacking faults. Nonuniform resistivity. Irregular surfaces. Cracks, chips, scratches (general handling damage). Contamination. |
| Passivation | Cracks and pin holes. Nonuuiform thickness. |
| Masking | Scratches, nicks, blemishes in the photomask. Misalignment. Irregularities in photoresist pattern (line widths, spaces, pinholes). |
| Etching | Improper removal of oxide. Undercutting. Spotting (etch splash). Contamination (photoresist, chemical residue). |
| Diffusions | Improper control of doping profiles. |
| Final seal | Poor hermetic seal. Incorrect atmosphere sealed in package. Broken or bent external leads. Cracks, voids in kovar-to-glass seals. Electrolytic growth of metals or metallic compounds across glass seals between leads and metal case. Loose conducting particles in packages. Improper marking. |
| Process step | Failure mechanism introduced as a reliability influencing variable |
| Metalization |
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