Redundancy Repair is a process step almost exclusively used for memory chips. The best way to think of this is via the analogy of the spare wheel in a car. The spare is a redundant fifth wheel carried and used in the event a defect occurs in one of the other four. Similarly, a memory is designed with redundant rows and columns (spares) which can be logically replaced for rows or columns which may contain defective memory cells. The replacement is made by special precision tools which take the wafer probe failure data, locate the failed element, and use a laser beam to perform micro-surgery on links to remove the defective element and connect in a replacement.

Carrying "spares" on a die adds cost overhead, but when one sees that yields can be improved through repair by as much as tens of percent, the overhead cost is well justified.

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