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Testing Semiconductor Devices by Voltage Polarity Coding

IP.com Disclosure Number: IPCOM000082623D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

DeStefeno, JJ: AUTHOR [+3]

Abstract

This concerns contactless, nondestructive testing for failure analysis or for diagnosis of the causes of low yield in manufacturing of integrated circuits.

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Testing Semiconductor Devices by Voltage Polarity Coding

This concerns contactless, nondestructive testing for failure analysis or for diagnosis of the causes of low yield in manufacturing of integrated circuits.

The method depends on the phenomenon of voltage contrast in scanning electron microscopy (SEM) using secondary electron emission. In this mode of SEM operation, negative specimen potentials result in increased secondary electron signals and positive specimen potentials result in decreased signals. The voltage contrast can be enhanced by using a sensitive detector as described in the article by DeStafeno et al entitled: Display of Voltage Distributions on Microcircuits, IBM Technical Disclosure Bulletin, Vol. 15, No. 8, January 1973, pages 2547-48.

In its simplest form, the method consists of applying a polarity coded input signal to the device under test, while observing the voltage-contrast image with an SEM. The polarity-coded signal consists of a train of pulses of alternate polarity in which the alternate-polarity pulses may be separated by intervals, if desired. The pulse durations and repetition rates are not critical, but must be chosen within ranges such that they are translated by the scanning process into observable spatial frequencies in the image.

Consider, for example, a "go/no-go" test of a diode, using a train of square- wave pulses of alternate polarity. If the diode is open, the pulses in the polarity- coded signal corresponding to the forward bias of the diode will not pass the diode; and the spatial equivalent of these pulses will be visible only on the side of the diode at which the signal is applied.

The other polarity pulses, i.e., those corresponding to reverse bias of the diode, are adjusted in amplitude to match the specified minimum reverse breakdown voltage. If the diode's reverse breakdown voltage is above this specification, this portion of the polarity-coded signal will be visible only on the input side of the diode; otherwise this portion of the signal will be visible on both sides, indicating a weak reverse breakdown. Thus, simple inspection of the SEM voltage contrast image can show either open or weak diodes.

The two polarities in the polarity-coded signal are easily distinguished by their corresponding contrast, but they can be coded by their pulse widths...