Test wafer for diagnosing flaws in an integrated circuit fabrication process that cause A-C defects
First Claim
1. An integrated circuit test wafer, which detects flaws in any process by which the wafer is fabricated, comprising:
- a semiconductor substrate having a major surface;
multiple copies of a diagnostic circuit that are integrated over most of said surface;
each copy of said diagnostic circuit including-a plurality of ring oscillators which generate respective cyclic output signals;
an addressing circuit, coupled to said ring osciallators, that receives external input signals and in response selects an output signal from any particular ring oscillator of said plurality;
a timing circuit that generates a timing signal with a certain time period; and
,a counting circuit, coupled to said timing circuit and said addressing circuit, that counts the number of cycles that occur in the selected output signal during said time period and provides that number as an output.
5 Assignments
0 Petitions
Accused Products
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.
-
Citations
10 Claims
-
1. An integrated circuit test wafer, which detects flaws in any process by which the wafer is fabricated, comprising:
-
a semiconductor substrate having a major surface; multiple copies of a diagnostic circuit that are integrated over most of said surface;
each copy of said diagnostic circuit including-a plurality of ring oscillators which generate respective cyclic output signals; an addressing circuit, coupled to said ring osciallators, that receives external input signals and in response selects an output signal from any particular ring oscillator of said plurality; a timing circuit that generates a timing signal with a certain time period; and
,a counting circuit, coupled to said timing circuit and said addressing circuit, that counts the number of cycles that occur in the selected output signal during said time period and provides that number as an output. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
Specification