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Contactless Testing and Measuring Junction Characteristics

IP.com Disclosure Number: IPCOM000051207D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Abstract

This article describes improved techniques for testing and measuring electrical characteristics of junctions without physical contact.

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Contactless Testing and Measuring Junction Characteristics

This article describes improved techniques for testing and measuring electrical characteristics of junctions without physical contact.

In the first technique to be described, secondary electron threshold monitoring is used to determine the voltage level of a junction for rapid contactless diode testing.

Measuring the low energy threshold of the secondary electron distribution of a tesr point on a chip provides an accurate, contactless measure of the voltage level of that point (1). This is conveniently accomplished in a scanning Auger microprobe, for example. At the same time, current (reverse or forward) through a junction can be produced by the incident electron beam with the chip suitably biased (2).

Greater testing speed can be expected by monitoring the secondary electron current at only a single point in the secondary electron distribution, namely, the threshold (lowest energy secondaries). Consider as an example the case of a Schottky contact on n-Si. With reverse currents just sufficient to drive the junction to saturation and toward breakdown for a barrier height 0(1), the voltage level of the metal overlayer contact of the junction will become more negative by the avalanche breakdown voltage of the diode, while for a smaller barrier height 0(s) the reverse current will not reach saturation and the voltage level will not change substantially.

When viewing secondary electron pictures of such diodes on a chip with the energy analyzer set to threshold, the 0(s) diodes will give appreciable secondary electron intensities; at the same time the 0(1) diodes will yield essentially no secondary intensity because their threshold shifted appreciably to higher energy. Such a secondary electron threshold picture of a chip could be used to distinguish diodes with 0 greater than 0 from those with 0 less than 0 .

Alternatively, with proper biasing of the chip a corresponding image could be obtained in forward bias. If feedback stabilization of the forward current were employed (e.g., by changing the incident beam current or chip bias), the threshold voltage measurement could be used to distinguish between diodes of different barrier height.

A technique to determine the electrical properties, such as the current- voltage characteristic of a junction without low resistance Ohmic back contact to the substrate side of the junction, will next be described.

Characterizing the current-voltage characteristic of a junction is usually done using a circuit arrangement like that shown in Figs. 1 and 2 (which depict a Schottky barrier contact on n-Si as an example). The current I through the junction is straightforwardly determined. However, in...