Browse Prior Art Database

Contactless Electrical Isolation Detector

IP.com Disclosure Number: IPCOM000049341D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Saleem, SM: AUTHOR [+2]

Abstract

This article describes a method for detecting defective electrical isolation between subcollector elements in bipolar devices or between source/drain elements in field-effect devices. The method features irradiating a wafer with a beam of pulsed infrared light and monitoring the propagation of the photovoltage induced by the beam.

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Contactless Electrical Isolation Detector

This article describes a method for detecting defective electrical isolation between subcollector elements in bipolar devices or between source/drain elements in field-effect devices. The method features irradiating a wafer with a beam of pulsed infrared light and monitoring the propagation of the photovoltage induced by the beam.

In the method, a beam of infrared light pulses is caused to impinge on a wafer resting on a grounded wafer chuck, as shown in the figure. If the device P- N junctions are electrically isolated, the pulses of photovoltage resulting when the pulsed light strikes the P-N junctions remain localized at the light beam spot. If the P-N junctions are not electrically isolated, for example, due to insufficient isolation diffusion and/or a thicker than normal epitaxial layer or other reasons, the photovoltage is propagated laterally through the resistive path provided by the continuous N type epitaxy layer. A pickup plate which is capacitively coupled to the wafer is thereafter used to monitor the presence or absence of a laterally propagated photovoltage. The pickup plate is located concentric to and laterally positioned from the perimeter of the light beam spot.

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