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Use of Surface Charge Gradient Produced by SEM for Localization of Leakage Paths

IP.com Disclosure Number: IPCOM000089295D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Related People

Leighton, WW: AUTHOR

Abstract

Vertical leakage through the dielectric surface of a substrate can be detected through the use of surface charge gradients produced by a scanning electron microscope (SEM). The specimen is rastered by the SEM beam. No secondary electron discriminator electrode or specimen current amplifier is used. Instead, the SEM is operated at minimum acceleration potential and minimum beam current. This results in a negative charge being distributed over the specimen surface.

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Use of Surface Charge Gradient Produced by SEM for Localization of Leakage Paths

Vertical leakage through the dielectric surface of a substrate can be detected through the use of surface charge gradients produced by a scanning electron microscope (SEM). The specimen is rastered by the SEM beam. No secondary electron discriminator electrode or specimen current amplifier is used. Instead, the SEM is operated at minimum acceleration potential and minimum beam current. This results in a negative charge being distributed over the specimen surface.

If a leakage path exists from the surface to the substrate and ground, incident electrons from the primary beam will be absorbed at the site and not be repelled. This produces a voltage gradient pattern for the SEM CRT display, usually appearing as a darkened false depression over the leakage site (Figs. 1, 2). Low beam currents and voltages must be used, for large discharge surges can damage the specimen and alter the defect structure. The technique is particularly useful in applications in which the leakage path is under metallurgy, with microsection confirmation (Figs. 3, 4).

Fig. 1, a photograph taken at 50X magnification, shows two leakage sites. The upper site is at a probe scratch. The lower site is at a substrate defect. Fig. 2, taken at 500X magnification, is a closeup of the probe scratch leakage site. Figs. 3 and 4, both taken at 2000X magnification under sodium light, are micro- sections of the substrate defect a...