Test wafer for diagnosing flaws in an integrated circuit fabrica

Details Test wafer for diagnosing flaws in an integrated circuit fabrica Test wafer for diagnosing flaws in an integrated circuit fabrica

1992-06-26

1993-11-30

Nguyen, Vinh

Electricity: measuring and testing

Measuring, testing, or sensing electricity, per se

With rotor

324 731, 371 225, G01R 3100

Patent

active

052668908

ABSTRACT:
An integrated circuit test wafer quickly detects A-C defects in any process by which the wafer is fabricated. This test wafer includes a semiconductor substrate having a major surface, and a diagnostic circuit that is repeatedly integrated over most of the wafer's surface. Each diagnostic circuit includes: a) a plurality of ring oscillators which generate respective cyclic output signals; b) an addressing circuit that receives external input signals and in response selects an output signal from any particular ring oscillator of the plurality; c) a timing circuit that generates a timing signal with a certain time period; and, d) a counting circuit that counts the number of cycles that occur in the selected output signal during the time period and provides that number as an output. By comparing the relative or absolute speeds of all of the ring oscillators, a ring oscillator with an A-C defect is detected; and, a defective ring oscillator can then be analyzed under an E-beam microscope to determine the defects cause. Preferably, the ring oscillators occupy at least 90% of the test wafers surface so that A-C defects are detected even when they are sparsely distributed on the test wafer.

REFERENCES:
patent: 4243937 (1981-01-01), Maltani et al.
patent: 4486705 (1984-12-01), Stopper
patent: 4855253 (1989-08-01), Weber
patent: 4956602 (1990-09-01), Parrish
patent: 5053700 (1991-10-01), Parrish
patent: 5059899 (1991-10-01), Farnworth et al.
patent: 5095267 (1992-03-01), Merrill et al.

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