Test structure and method for yield improvement of double poly bipolar device
First Claim
1. A method of detecting crystal lattice defects in semiconductor manufacturing wherein a plurality of double-poly NPN transistors are formed in each of a plurality of spaced dies on a semiconductor wafer having a P-type substrate, comprising:
- forming a test circuit on the wafer, the test circuit comprising a plurality of semiconductor structures having an N-type emitter structure overlaying a P-type base structure overlaying P-type material integrated with the wafer substrate;
charging the test circuit with an electron beam;
detecting secondary electrons emitted from the N-type emitter of the transistor structures; and
identifying test circuits exhibiting crystal lattice detects as a function of secondary electron emission.
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Abstract
A method and apparatus for identifying crystal defects in emitter-base junctions of NPN bipolar transistors uses a test structure having an NP junction that can be inspected using passive voltage contrast. The test structure eliminates the collector of the transistor and simulates only the emitter and base. Eliminating the collector removes an NP junction between collector and substrate of a wafer allowing charge to flow from the substrate to emitter if the emitter-base junction is defective since only one NP junction exists in the test structure. In one embodiment, the test structures are located between dies on a wafer and may be formed in groups of several thousand.
12 Citations
7 Claims
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1. A method of detecting crystal lattice defects in semiconductor manufacturing wherein a plurality of double-poly NPN transistors are formed in each of a plurality of spaced dies on a semiconductor wafer having a P-type substrate, comprising:
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forming a test circuit on the wafer, the test circuit comprising a plurality of semiconductor structures having an N-type emitter structure overlaying a P-type base structure overlaying P-type material integrated with the wafer substrate;
charging the test circuit with an electron beam;
detecting secondary electrons emitted from the N-type emitter of the transistor structures; and
identifying test circuits exhibiting crystal lattice detects as a function of secondary electron emission. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A system for detecting crystal lattice defects in NPN bipolar transistor structures formed on a wafer having a substrate of P-type material, comprising:
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a plurality of test circuits formed on the wafer, each test circuit comprising a first N-type material layer over a second P-type material layer, the first and second layers having structural characteristics of an NPN transistor emitter and base, respectively;
a P-type material under the second layer and continuing into the substrate of the wafer; and
a PVC system arranged to examine the test circuits and for providing data indicative of electron leakage from the wafer substrate to the first N-type material layer caused by defects at the NP junction between the first and second layers.
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Specification