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Location of Lateral P/N Junction by Electron-Beam-Induced Current

IP.com Disclosure Number: IPCOM000038993D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Hsieh, CM: AUTHOR [+2]

Abstract

In order to properly model a transistor and correlate the electrical parameters with the physical structure, knowledge of the lateral junction shape must be used. This article proposes the use of a scanning electron microscope (SEM) in an electron-beam-induced current (EBIC) mode to determine the lateral distance and shape of P/N junctions on very shallow field-effect transistors (FETs). Correlation between the electrical properties of a transistor (beta, collector current, base current, B/C capacitance, etc.) and the physical structure of the device can be made with good precision only when the lateral edge of the diffusion, or implant, is characterized. In many applications, the vertical doping profile may be obtained by secondary ion mass spectroscopy (SIMS). However, this gives no information on the lateral out-diffusion.

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Location of Lateral P/N Junction by Electron-Beam-Induced Current

In order to properly model a transistor and correlate the electrical parameters with the physical structure, knowledge of the lateral junction shape must be used. This article proposes the use of a scanning electron microscope (SEM) in an electron-beam-induced current (EBIC) mode to determine the lateral distance and shape of P/N junctions on very shallow field-effect transistors (FETs). Correlation between the electrical properties of a transistor (beta, collector current, base current, B/C capacitance, etc.) and the physical structure of the device can be made with good precision only when the lateral edge of the diffusion, or implant, is characterized. In many applications, the vertical doping profile may be obtained by secondary ion mass spectroscopy (SIMS). However, this gives no information on the lateral out-diffusion. Knowledge of the lateral profile and lateral junction location and shape is necessary for precise correlations and modelling. The EBIC technique using high resolution electron beams does make it possible to locate the true electrical P/N junction and thereby determine the entire junction shape. The technique is carried out in an SEM and utilizes a high gain current amplifier whose output is used to drive the CRT of the SEM in either the brightness modulation mode or the Y-deflection mode. The transistor is sectioned at 90 degrees, preserving electrical contact to both sides of the junction of interest. It is mounted on a header, the contacts are wire bonded, and the

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sample is placed in the SEM. The device is positioned so that the electrical beam is perpendicular to the section face. This positioning is significant in order to obtain a good sharp clear definition. A line scan can then be made across the P/N junction being measured. For accurate location of the electrical junction, it is i...