detecting and preventing measurement errors

IN THE DEVELOPMENT of new VLSI circuits,

engineers commonly use e-beam probing

to measure signals on a circuit’s internal

nodes. The waveforms obtained this way

help to verify design simulations and detect

errors in design and fabrication. As a result

of recent improvements in e-beam probing

systems, many engineers now routinely use

them as conveniently as if they were oscil-

loscopes (see box). Naturally, while these

users are interested in the design and test of

circuits, they are not generally versed in the

specialized topics of electron microscopy

and electron detection. Instrument manu-

facturers have intentionally designed e-

beam probers to require little or no

awareness of the scanning electron micro-

scope (SEM) within the instrument.

Unfortunately, this can lead to a blind re-

liance on the e-beam prober.

In fact, measurements made with e-beam

probers can be misleading or even erro-

neous; if you use an e-beam prober, you

need to be aware of its limitations. In many

cases, knowing the kinds of problems you

may encounter will help you prepare cir-

cuits—at the time of design—to give the

best e-beam prober results.1

The physical principles responsible for e-

beam prober measurement errors chiefly in-

volve the fact that the prober derives the

measurement signal from a few low-energy

electrons emitted from the circuit. Rather than

discuss the physics in detail, however, in this

article I classify measurement errors by their

consequences: apparent crosstalk, amplitude

errors, noise, and bandwidth limitations.

CrosstalkWaveform crosstalk may occur when you

make measurements on closely spaced cir-

cuit lines, as illustrated in Figure 1. Figure 2

shows an example of waveforms exhibiting

crosstalk. The waveform of Figure 2a shows

the signal measured when I applied a sim-

ple voltage step to a 3-µm circuit line (line X

in Figure 1) while I held all nearby lines at a

constant voltage. When I applied the signal

in Figure 2c to line Y, 2 µm away, I measured

the waveform of Figure 2b on line X. The

original signal has acquired a crosstalk com-

ponent from the signal on the adjacent line.

In fact, the converse is also true, and some of

the waveform of Figure 2a appears in Figure

2c. Clearly the unwanted component of

Figure 2b is an error, and if not recognized as

such, could mislead the circuit designer.

Crosstalk may result from one or more of

several possible conditions. The most com-

mon of these is the local field effect.

Voltages on circuit lines near the signal line

create electric fields. These fields modulate

the number of secondary electrons, which

were emitted from the signal line, arriving

Detecting and PreventingMeasurement Errors

E-BEAM PROBER

78 0740-7475/97/$10.00 © 1997 IEEE IEEE DESIGN & TEST OF COMPUTERS

Modern e-beam probersmay be as convenient touse as oscilloscopes, buttheir measurements canbe misleading or evenerroneous. The author

warns of potentialproblems and suggestsways to prevent andcure faulty readings.

KEITH A. JENKINSIBM T.J. Watson Research

Center

.

OCTOBER–DECEMBER 1997 79

at the electron detector. As this number of electrons is the

basis of the voltage measurement, crosstalk results.

Instrument manufacturers have studied the local field ef-

fect for years; consequently, they have designed modern e-

beam probers to minimize the effect. However, you should

still be aware of the possibility of such errors. The amount

of crosstalk in your measurements depends on the sec-

ondary electron detector, so in some cases you can reduce

it by adjusting the parameters of the detector. In all instru-

ments, the crosstalk due to the local field effect becomes

greater as the circuit lines become narrower and the adja-

cent lines get closer.

To learn the extent to which crosstalk occurs in your mea-

.

E-beam probers, formerly called e-beam testers, arevaluable tools for studying the very small conductors thatform the wiring networks of VLSI circuits. Each prober con-tains a scanning electron microscope (SEM) and uses theSEM voltage contrast mechanism to make oscilloscope-likewaveforms of voltages. Because the e-beam prober usesan electron beam as the voltage probe, it can make mea-surements on circuit lines as small as one micron. Theprober makes no mechanical contact with the lines itprobes, so it cannot damage them. (Feuerbaum,1

Richardson,2 and Thong3 explain the principles of e-beamprobers in greater detail.)

If you use an e-beam prober, you are likely to encountersignificant measurement errors only when you need to studywaveforms in detail. When you are looking for design er-rors such as missing or mistimed signals in digital circuits,the logic state of a signal is often enough information. In

these circumstances, the e-beam measurements are quitereliable. E-beam probers can also be useful for image modevoltage contrast, but this mode does not involve quantita-tive measurements, so measurement errors should not oc-cur. It is in studying signals in detail, verifying design,measuring analog signals, or attacking subtle problems oftiming or amplitude that you need to watch out for mea-surement errors.

References1. H.P. Feuerbaum, “Electron Beam Testing: Methods and

Applications,” Scanning, Vol. 5, No 1., 1983, pp. 14–24.

2. N. Richardson, “E-Beam Probing for VLSI Circuit Debug,”

VLSI Systems Design, Aug. 1987, p. 24.

3. J.T.L. Thong, ed., Electron Beam Testing Technology,

Plenum, New York, 1993.

Electron-beam probers

X Y

Figure 1. Illustration of several neighboring circuit lines used toobserve crosstalk.

Volta

ge (1

V/d

iv)

Time (20 ns/div)(a)

Volta

ge (1

V/d

iv)

Time (20 ns/div)(b)

Volta

ge (1

V/d

iv)

Time (20 ns/div)(c)

Figure 2. E-beam prober waveforms measured on the struc-tures shown in Figure 1: the waveform measured on line X withall nearby lines held at a constant voltage (a), the waveformmeasured on line X showing crosstalk from line Y (b), the signalapplied to line Y (c).

E-BEAM PROBER

80 IEEE DESIGN & TEST OF COMPUTERS

surements, you should attempt to measure the magnitude

of the local field effect on your e-beam prober system. You

can do this by using a chip with lines of various dimensions

and spacings. If you notice crosstalk on a circuit under test,

repeat the measurement on a wider part of the line and at a

place where the nearest adjacent lines are farther away. If

the crosstalk is diminished or absent, you should discard the

first measurement. Always take waveform measurements on

the largest available portion of the node of interest, spaced

as far away from nearby circuit lines as possible. Even though

prober manufacturers acclaim the ability of the e-beam

prober to image submicron geometries, it is wise to make

measurements on points of at least a few microns in width.

A second cause of crosstalk is poor beam focus. As you

direct the electron beam at the signal line, if you do not di-

rect it entirely onto the line, some portion of it may land on

the neighboring circuit lines. The resulting measurement

will be a mixture of the true signal and the (unwanted) con-

tribution from neighbors. As a rule, the diameter of the elec-

tron beam must be less than about one-quarter the size of

the line you are measuring. This criterion implies that the

edges of the lines are clearly defined in the SEM image.

The waveforms of Figure 3 and the corresponding SEM im-

ages of Figure 4 demonstrate the effect of poor focus. I ap-

plied signals to the outer dark lines of Figure 4 while I ground-

ed the center line so that it had no signal. In Figure 3a, the

upper waveform is the measurement on an outer line, and

the lower waveform is the measurement on the inner line.

The appearance of a signal on the inner line is due to crosstalk

caused by the local field effect. For Figure 3b, I made the mea-

surements with the image slightly out of focus, as shown in

Figure 4b. The crosstalk is now significantly larger, since some

of the electron beam now samples the voltage on the active

outer line. In addition, the amplitude of the signal on the ac-

tive line appears reduced, since the sample now includes a

portion of the ground voltage of the center conductor.

Although it is possible to distinguish the lines in Figure 4b,

the blur of the image induces measurement error. As a rule,

if you cannot see the signal lines in the SEM image clearly,

you will not be able to make reliable waveform measure-

.

Volta

ge (2

V/d

iv)

Time (1 µs/div)(a)

Volta

ge (2

V/d

iv)

Time (1 µs/div)(b)

Figure 3. Waveforms measured with the prober image focusedas in Figure 4a (a), and as in Figure 4b (b). The upper andlower waves in each part correspond to measurements on theouter and inner circuit lines shown in Figure 4.

Figure 4. SEM images (a) and (b) corresponding to thewaveforms shown in Figure 3.

(a)

(b)


ments. It is important to magnify the circuit enough to be able

to judge the quality of the focus. As in this example, you can

deliberately defocus the image slightly to study crosstalk in

the particular e-beam prober you are using.

Another source of crosstalk is misplacement of the e-beam

probe. The position of the probe in the SEM image is indi-

cated by a cursor or pointer. During the waveform measure-

ment, the prober should concentrate the beam of electrons

on that position, but due to the hysteresis of magnetic lenses,

the electron beam position may not correspond with the cur-

sor’s position. Thus, the electron beam may be partially off the

line of interest, or may even straddle two lines. You can some-

times determine the actual beam position by measuring a

waveform for a few minutes and then reexamining the SEM

image to look for a contamination spot. If the contamination

is offset from the cursor position, you need to correct the rel-

ative positions of the cursor and the electron beam. Both

good focus and good probe placement require high magni-

fication of the circuit. If you use a low magnification, a small

offset between the cursor and probe can cause serious mis-

placement of the electron beam. You can only place the e-

beam probe accurately if the magnification is high enough

to see the central portion of the signal line clearly. You should

avoid placing the electron beam on a topographic feature of

the circuit line, such as a via contact or a vertical step in a

conductor, as this can also lead to erroneous measurements.

Circuits contacted by wafer probes are susceptible to

crosstalk from signals on the probe needles. Figure 5 demon-

strates this effect. The bump indicated by the circle has the

appearance of power supply noise (see the section on noise)

but is actually the result of an input signal on a probe needle

400 µm away. It is rounded, not square like the previous ex-

amples, because the rise time of the probe needle’s signal

is greater than that of the internal signals being measured.

To verify that this crosstalk was due to the probe needle sig-

nal, I measured the internal node with no power applied to

the circuit, but with the inputs still operating. The result is

the gray line in Figure 5, in which a false signal is apparent.

To test for crosstalk due to signals on probe needles, measure

internal nodes with the power supplies turned off. Measuring

on wider nodes will not reduce this kind of crosstalk much,

since the probe needles are huge in comparison.

There is one source of apparent crosstalk that results not

from the positioning or focusing of the electron beam, but

from the nature of the circuit. If the circuit has a large num-

ber of conductors changing voltage simultaneously, it can

give rise to a global field effect. This can occur, for example,

when a read clock is activated and all the wordlines in a

random access memory change their voltages. Unlike the lo-

cal field effect, the presence of a voltage on a large area of

the chip actually has the effect of deflecting the primary

electron beam as it approaches the chip. The electron beam

may be well focused and may appear to be directed to the

center of the circuit line in a static state. As the clock switch-

es the circuit to another state, however, the beam may move

partially or completely off that line. If the electron beam

does not remain on the conductor of interest, the waveform

is certain to be in error.

You can often see the global field effect in the SEM image.

If you operate the chip at a low clock rate so that you can see

voltage changes in a live image, the global field effect will ap-

pear as a significant periodic shift of the image. The micro-

graph of Figure 6a (next page) shows an example of this

effect. The image shifts back and forth by about one micron

as the chip clock is toggled. This occurs even though the volt-

ages on the circuit lines in this image are not themselves

changing. The nature of the circuit and the design of the e-

beam prober detector determine the magnitude of the effect.

Since this effect is principally due to deflection of the pri-

mary electron beam as it approaches the chip, you can near-

ly eliminate it by putting a shielding grid near the chip.

Figure 7 shows a diagram of such an arrangement. Biasing

the grid a few volts above the circuit ground or prober

ground prevents deflection of the beam except in the small

gap between it and the circuit. Figure 6b shows the effect of

this grid: the global field effect has vanished. The closer the

grid is to the circuit under test, the smaller is the probe de-

flection due to the global field effect. You can also reduce

the global field effect by using a much higher e-beam en-

ergy, but this is not usually a practical option.

If you cannot use a grid, you need to either operate the

.

Volta

ge (2

V/d

iv)

Time (1 µs/div)

Figure 5. Effect of a signal on a probe needle on measuredinternal signals. The upper curve is the signal measured on aninternal point, showing a bump in the circled area. The graywave is the signal measured with the circuit power supplyvoltage off. The signal on a probe needle, shown in the lowercurve, causes the crosstalk.

E-BEAM PROBER


chip with fewer nodes switching in parallel or make mea-

surements on conductors that are larger than the image

shift. Otherwise, you will not produce accurate measure-

ments. If the simultaneous switching signals are very short

compared with the live SEM image scan rate (1/30 second),

there may be a significant global field effect that is too brief

to see. This can occur if the chip internal signals are return-

to-zero (RZ) or self-resetting. In this case, measurement er-

rors can occur with no visual clues.

Finally, if you suspect that the crosstalk you observe is

true electrical crosstalk due to capacitance between adja-

cent lines, you can test this theory by operating the circuit

at a variety of cycle times. The crosstalk artifacts described

earlier are all independent of cycle time, whereas crosstalk

due to capacitive coupling shows a characteristic expo-

nential scalloping at low frequencies, as shown in Figure 8.

Amplitude errorsOnce you are aware of it, you should easily recognize the

characteristic appearance of crosstalk in e-beam prober

waveforms. A less obvious type of measurement error is an

incorrect waveform amplitude. Amplitude errors can result

from several different factors, some of which are related to

crosstalk errors.

Poor focus and poor probe position can cause amplitude

errors if the nearby lines have DC voltages rather than time-

varying signals. As in crosstalk, if the e-beam probe samples the

voltage of neighboring lines, those static voltages will be mixed

in with the desired signal, resulting in a distortion of the sig-

nal. Because this type of crosstalk is not obvious in the wave-

form, errors are subtle. You should take the same precautions

against amplitude errors that you take against crosstalk.

One seldom-recognized source of amplitude errors is the

local field effect from nearby circuit lines that have DC volt-

.

≈ 1 mm ≈ 2 V

Ipe

Figure 7. Configuration of the suppression grid near the circuitunder test.

Signal

Crosstalk

Signal

Crosstalk

(a)

(b)

Figure 8. Showing the change of crosstalk expected for truecapacitive coupling between nearby circuit lines.

(a)

(b)

Figure 6. SEM image showing the global field effect caused bymultiple circuit elements switching simultaneously (a). The sameSEM image with a suppression grid near the chip (b).


ages. In the same way that a time-varying voltage of a neigh-

boring line induces a signal on the waveform being mea-

sured, a DC voltage can affect the amplitude of the measured

signal. Figure 9 shows an example of this effect. The signal

shown in black is the measurement with neighboring lines

grounded. The negative voltage of the neighboring lines de-

creases the amplitude of the measured signal, resulting in

the superimposed gray waveform. Again, to prevent the lo-

cal field effect from changing waveform amplitudes, you

should measure the signals on the widest possible circuit

lines and as far away from neighboring lines as possible.

A related problem is that of insulator charging. Under

close examination in an SEM, the insulating regions be-

tween the circuit conductors acquire a net charge. If enough

charge accumulates, a significant voltage can develop on

the insulator. This can affect the amplitude of the measured

signal on a conductor in the region in the same way DC volt-

ages on nearby conductors can. Both positive and negative

charging can occur; positive charging appears as black

patches in the SEM image, and negative charging appears

as white flare. Positive charging is self-limiting, and only a

few volts can develop. Negative charging, however, can re-

sult in tens or hundreds of volts. This leads to beam deflec-

tion and defocusing, in which case measurements may be

impossible. Figure 10 shows an example of the effect of mild

negative charging. I measured the waveform shown in black

before charging had occurred. After a negative charge ac-

cumulated, I measured the waveform shown in gray. The

amplitude is significantly changed, and the waveform is

noisier. Avoid negative charging of insulators between con-

ductors. You can minimize charging by using a magnifica-

tion no higher than necessary to focus and place the beam

correctly. The best way to prevent negative charging is to

use a lower primary beam energy. When you reduce the en-

ergy, you will quickly neutralize the white flare.

Although you can obtain a waveform from a node buried

under an insulator, the resulting amplitude will always be in-

correct. It is usually easy to tell when a line is buried, but

occasionally a very thin layer of insulator can cover the line

and lead to error. For example, if you etch away the inter-

level dielectric for e-beam probing, an incomplete etch may

leave a very thin layer. If you then operate the circuit, the

covered circuit lines will be visible, but because of the di-

electric, the waveform amplitudes will be incorrect. To

check for the presence of an insulating layer, look at the

lines in the prober image when the circuit is operating and

when it is not operating. Covered lines will be less distinct

when the circuit is not operating; they will be the same gray

as the background, and show only topographic contrast. If

you cannot clearly distinguish circuit lines from the back-

ground insulator when the circuit is quiescent, a thin insu-

lating material may be covering them.

Finally, the prober electron detector itself can introduce

amplitude errors even if you avoid all the previous prob-

lems. This is because the prober measures voltage by at-

tempting to linearize the integration of a complicated

secondary electron spectrum. It achieves this by setting a

filter grid voltage (or loop gain) to an optimum point on the

spectrum. Because the linearization is only approximate,

the amplitude of the measured signal may vary by 10 to 20

percent if this filter grid voltage changes. For accurate am-

plitude measurement, you should determine the best op-

erating value of this parameter. You can do this by

.

Volta

ge (0

.5 V

/div

)

Time (5 ns/div)

Figure 9. Effect of nearby DC voltage levels on waveform ampli-tude. I measured the black wave with nearby lines grounded andthe gray wave when the nearest lines were at −2 V.

Volta

ge (1

V/d

iv)

Time (5 ns/div)

Figure 10. Effect on waveforms of negative charge on theinsulator between circuit lines. The black (upper) wave is thenormal result, while the gray (lower) wave resulted when anegative charge had accumulated on the insulator.

E-BEAM PROBER


measuring a waveform on a circuit or test structure for

which you are confident that you know the voltage.

NoiseSignals measured with an e-beam prober will exhibit volt-

age noise. This term can refer to several different types of de-

viations from a steady voltage value. Noise can be random

or systematic. Random noise, or shot noise, results from the

random nature of the secondary electron signal. Random

noise will be very apparent to the first-time user of an e-beam

prober. The amplitude of the noise is independent of the sig-

nal level, so for a 5-V CMOS circuit it may be unimportant, but

it may be a very significant portion of a 1-V ECL circuit sig-

nal. Systematic noise can result from e-beam prober elec-

tronics, in which case it is instrumental noise. In addition,

switching transients on the circuit under test can give the ap-

pearance of noise. You will want to measure the noise from

switching transients because it is part of the true signal.

Random and instrumental noise are undesirable.

Figure 11 shows examples of random and circuit-switch-

ing noise. The enlargement of the first 5 ns of this waveform

shows the random noise inherent in all e-beam probers.

However, the longer fluctuations, such as the two bumps

before the low-to-high transition, and the large dip at about

32 ns, are part of the true circuit signal. They are caused by

ground bounce and capacitive coupling from a line passing

below the one measured.

The presence of noise on a fast transition can sometimes

create the appearance of a step on the signal. Looking care-

fully, you can see that steps or glitches on transitions can be

artifacts of the same random noise that is evident on the rest

of the waveform. First-time users of e-beam probers often mis-

take noise pulses on their waveforms for true circuit activity.

Unfortunately, all e-beam probers use a recursive aver-

aging method to accumulate waveforms. This can mean

that a large noise pulse at the start of waveform acquisition

can remain for a long time before averaging removes it.

Although experience is a useful guide in understanding

waveform noise, there are several tests you can perform to de-

termine if the fluctuations you see on a measured waveform

are noise or a true signal. To check for random noise, you can

examine the characteristic time scale of the noise. If the wave-

form noise time scale is substantially less than the e-beam

pulse width, it cannot be true signal. For example, in Figure 11

the small fluctuations occur with typically a 0.125-ns period,

whereas the beam pulse width for this measurement was 1 ns.

The inset shows an enlarged view of a portion of this wave-

form in which this small structure is apparent. True signal

changes of less than 1 ns would not be resolved. As you in-

crease the averaging period, you should see random noise

decrease with the square root of the time during which the

averaging occurs. You can also reduce random noise by

smoothing with a low-pass filter—easily accomplished by av-

eraging adjacent points—providing this does not degrade the

time resolution needed. Another way to check is to make a

second measurement to compare with the first. Random noise

will be different in the two measurements.

These tests will not detect instrumental noise introduced

by the imperfections of the prober electronics. Typical in-

strumental errors are short voltage spikes and curvature of

a supposedly flat voltage level. Two tests for such errors ex-

ist. The first test involves repeating the measurement with

the trigger signal slightly delayed (by inserting a length of

coaxial cable). When you compare the two measurements

by overlaying, the true signal will be shifted in time, but in-

strumental noise will not. The second test involves mea-

suring a node with no power or signal active on the chip,

and with all inputs and outputs grounded. Averaging the

waveform for the longest time possible should result in a

completely flat waveform, except for random noise. If the

waveform is not flat, you can attribute the noise to the e-

beam prober electronics.

Time resolution limitationsThe effective bandwidth of the e-beam pulse can limit the

measured transition times of signals. Careful design verifi-

cation often requires study of transition times; this is neces-

sary, for example, to test if a device is strong enough to drive

its load. Naturally, too coarse a time resolution renders such

a study useless. At a simpler level, reduction of measured

transition time can limit the accuracy of critical delay mea-

surements, which often yield the most important informa-

tion for performance verification. With today’s CMOS

technologies and circuits, transition times are often less than

.

Ampl

itude

(V)

Volts

Time (ns)

5

4

3

0.200.100.00

−0.10−0.20

0 1 2 3Time (ns)

4 52

1

0

−10 10 20 30 40 50

Figure 11. Waveform showing random and circuit-switchingnoise.


200 picoseconds, and total delays through a circuit can be

as little as a few nanoseconds. The use of e-beam probers

under these circumstances demands a continuing effort to

understand and improve their measurement resolution.

When you need to determine if the beam pulse band-

width has degraded a measured signal edge, you will need

to measure this limitation. Although you can do this by

putting a known very fast pulse onto a test structure and

measuring the pulse with the e-beam prober, it is sometimes

advantageous to use sine waves of various frequencies to

determine the bandwidth directly.

It is easy to apply a sine wave to a circuit in the e-beam

prober or onto a special test structure. Figure 12 shows an

example of the resulting measurements. For these mea-

surements, I made all connections to the test chip through

a 50-ohm coaxial cable, and I set the e-beam pulse width at

2 ns. At low frequencies, the amplitude of the measured sig-

nal is about constant, but at several hundred MHz the am-

plitude starts to drop, indicating that the e-beam prober

limits the frequency of signals that can be measured.

Figure 13 shows the corresponding amplitude of the mea-

sured signal as a function of frequency, corrected for sine

wave amplitude levelness and connection bandwidth (mea-

sured by high-frequency oscilloscope). The bandwidth of

the e-beam prober clearly degrades the signal by about 250

MHz, although it does not follow a particularly simple form.

If necessary, you can determine the effect of the band-

width on a measured signal by Fourier analysis. For the mea-

surements shown here, Figure 14 shows an ideal and a

bandwidth-limited step function. I used the data from Figure

13 for the Fourier coefficients. In this example, the beam

pulse bandwidth degraded the ideal step function to some-

what less than 2 ns (10- to 90-percent levels). Thus, a nomi-

nal 2-ns beam pulse results in a rise time of the same amount.

If the actual signals of the waveform being measured have

edges that are shorter than this beam pulse width, their rise

times cannot be measured. In principle, it is possible to ob-

tain the true signal rise time using this type of analysis and de-

convolution, but this requires very careful measurements.2

Today’s conventional e-beam probers have a practical min-

.

500

300

250

200

160

80

20

Ampl

itude

(5 V

/div

)

Amplitude (20 ns/div)

MHz

Figure 12. Measurement of sinusoidal signals to determine e-beam prober bandwidth.

Ampl

itude

10−1

101 102

100

2-ns beam pulse

Frequency (MHz)

Figure 13. Amplitude of signals in Figure 12.

Ampl

itude

(arb

itrar

y un

its)

Time (1 ns/div)

Figure 14. Fourier analysis of step function to determinetransition time resolution from bandwidth measurement. Thegray line is the ideal step function; I obtained the black line byapplying the measured amplitudes shown in Figure 13.

E-BEAM PROBER


imum pulse width of about 200 ps, although some systems

have been built with much better resolution.3,4

There is an additional benefit in using a sine wave for

bandwidth measurement: you will automatically obtain a

time-base calibration as a by-product. In the signals with fre-

quencies of 160 MHz and above, the first cycle or two of the

wave has a different period from the rest. This indicates a

nonlinearity of the time base, which would also be present

on a digital signal. It requires that you either repair the e-

beam prober or correct the data.

E-BEAM PROBERS HAVE BECOME STANDARD equipment

in development laboratories, but many circuit designers fail

to recognize the limitations of these complex tools. By tak-

ing the following precautions, you can ensure the greatest

possible accuracy in your e-beam prober measurements:

■ Minimize amplitude errors and crosstalk by measuring

the widest possible circuit lines.

■ Use a suppression grid to reduce errors caused by the

simultaneous switching of large portions of the circuit.

■ Reduce random noise by using very long measurement

times.

■ Study waveforms carefully to avoid interpreting ran-

dom noise as true circuit voltages.

■ Measure the bandwidth of the prober, if necessary, to

determine if the pulse width of the electron beam limits

the measurable rise and fall times of circuit signals.

References1. W.T. Lee, “Engineering a Device for Electron-Beam Probing,”

IEEE Design & Test of Computers, Vol. 6, No. 3, June 1989, pp.

36–49.

2. E. Plies and M. Chweizer, “Testing for Different Methods of De-

convolution for Electron Beam Measured Waveforms,” Mi-

croelectronic Engineering, Vol. 7, No. 2-4, 1987, pp. 183–193.

3. R. Schmitt, et al., “Electron Beam Sampling of IC-Internal GHz

Signals,” Electronics Letters, Vol. 24, Feb., 1987, pp. 235–236.

4. A.J. Fixl et al., “Laser Stimulated Electron-Beam Prober for 15ps

Resolution Internal Waveform Measurements of a 5 Gb/s ECL

Circuit,” Proc. 1993 Int’l Reliability Physics Symp., IEEE, Pis-

cataway, N.J., pp. 190–203.

Keith A. Jenkins is a senior engineer in the

VLSI Systems Department of the IBM T.J. Wat-

son Research Center. He has worked in a va-

riety of device and circuit subjects, including

high-frequency measurement techniques, e-

beam circuit testing, passive voltage contrast

defect detection, radiation-device interac-

tions, and low-temperature electronics. His current activities in-

clude evaluation of integrated silicon RF circuits and applications

of high-bandwidth e-beam measurement techniques. Jenkins re-

ceived his PhD in physics from Columbia University.

Send correspondence about this article to Keith A. Jenkins,

Thomas J. Watson Research Center, M/S 14-254, Yorktown Heights,

NY 10598; [email protected].

.

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the field of design and test for publication in upcoming

1998 issues.

Tutorials, case studies, summaries of work in progress,

and descriptions of recently completed works are most

welcome. Readers particularly look for practical articles

that help them on the job.

Interested authors should submit a 150-word abstract

or an outline to Editor-in-Chief Yervant Zorian at the ad-

dress below. Include your full contact information (au-

thor(s) name(s), postal address, e-mail address, and

phone and fax numbers). D&T does not accept papers un-

der consideration elsewhere. Check D&T’s home page at

http://computer.org/dt for author guidelines.

detecting and preventing measurement errors

Documents