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Detection of Exposed Thin Oxide by Scanning Electron Microscope

IP.com Disclosure Number: IPCOM000079232D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Schick, JD: AUTHOR

Abstract

A recurring cause for failure of field-effect transistor (FET) devices has been exposed thin oxide. This results when the aluminum gate does not completely cover the thin (about 500 Angstroms) gate oxide, so that during overlay sputtering the gate oxide may be contaminated, leading to a shifted threshold voltage and possibly a gate short.

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Detection of Exposed Thin Oxide by Scanning Electron Microscope

A recurring cause for failure of field-effect transistor (FET) devices has been exposed thin oxide. This results when the aluminum gate does not completely cover the thin (about 500 Angstroms) gate oxide, so that during overlay sputtering the gate oxide may be contaminated, leading to a shifted threshold voltage and possibly a gate short.

By connecting the ground pad (n-type) and the substrate pad (p-type) to a current amplifier when the device is under scanning electron microscope observation, a nondestructive determination of this exposed thin oxide may be made. The current amplifier output is connected to a cathode-ray tube in the Y- modulation mode. As the electron beam passes an area where exposed thin oxide exists, a larger current signal is observed due to increased beam penetration. This appears as a peak in the area of exposed thin oxide.

This technique may also be applied to other devices, such as bipolar transistors, where missing metal can be detected since a larger beam induced current results from increased electron beam penetration.

Fig. 1A shows an FET structure where the aluminum gate completely covers the thin oxide, and Fig. 1B shows the resulting beam induced current. Fig. 2A shows an FET structure where the aluminum gate does not adequately cover the thin oxide, and Fig. 2B shows the resulting beam induced current having a large peak.

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