The IC fabrication process contains several testing stages. Because of the high cost of packaging, the testing stage prior to aging, called wafer probe, is key in reducing the overall manufacturing cost. Typically in this stage, specification tests are performed. Even though specification tests can certainly distinguish a good circuit from all faulty ones, they are expensive, and many types of faulty behavior can be detected by simpler tests. The construction of a set of measurements that detects many faulty circuits before specification testing is described. Bounds on these measurements are specified, and an algorithm for test selection is presented. An example of a possible simple test is a test of DC voltages (i.e., parametric tests). This type of test is defined rigorously, and its effectiveness in detecting faulty circuits is evaluated.
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