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Waveform Measurement by Auger Microscopy

IP.com Disclosure Number: IPCOM000119304D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Halbout, JM: AUTHOR [+2]

Abstract

A technique is described for reducing waveform distortion in high-speed SEM voltage contrast measurements due to transit time effects. Electron beam testing techniques can be used to directly measure voltage waveforms of a circuit. As circuits become faster, the time resolution needed becomes correspondingly shorter and requires a shorter electron pulse. However, the accuracy of the measured waveform decreases when resolutions of less than about 50 psec are sought, due to the transit time of the secondary electrons (*).

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Waveform Measurement by Auger Microscopy

      A technique is described for reducing waveform distortion
in high-speed SEM voltage contrast measurements due to transit time
effects.  Electron beam testing techniques can be used to directly
measure voltage waveforms of a circuit.  As circuits become faster,
the time resolution needed becomes correspondingly shorter and
requires a shorter electron pulse.  However, the accuracy of the
measured waveform decreases when resolutions of less than about 50
psec are sought, due to the transit time of the secondary electrons
(*).

      The effect arises when the circuit voltage changes while the
secondary electrons are close enough to feel the change, as illus
trated in Fig. 1.  Secondary electrons leave the specimen with their
characteristic energy spectrum shifted by the voltage of the
specimen.  This is the source of voltage contrast.  If, however, the
specimen voltage changes before the electrons are far away, their
energy will change while they are in transit, and the measured
voltage at the detector will be wrong.  This causes an error in the
waveform measurement.  The waveform distortion due to changing
electrode voltage and transit time effects is illustrated in Fig. 2.
The error is systematic, and depends on the risetime, and the
geometry of the specimen electrodes.  The conventional technique uses
an extraction grid above the electron, but the field thus generated
is not strong enough to prevent the transit time effect.  The problem
can be substantially reduced by using more energetic electrons.  The
transit time is inversely proportional to the square root of the
electron's initial energy.  Secondary electrons h...