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A 100-femtosecond electron beam blanking system
Microelectronic Engineering 12 (1990) 221-226 Elsevier Science Publishers B.V.
221
A 100-FEMTOSECOND ELECTRON BEAM BLANKING SYSTEM J. FEHR, W. REINERS, L.J. BALK, E. KUBALEK, D. KOTHER, I. WOLFF Universit&t Duisburg Werkstoffe der Elektrotechnik und AIIgemeine und Theoretische Elektrotechnik Sonderforschungsbereich 254, KommandantenstraBe 60, D 4100 Duisburg 1, F.R.G. Conventional electron beam blanking systems show the drawbacks of a fixed electron energy, a fixed repetition rate or even unsuitability for repetition rates in the GHz region. This paper describes the development of an ultrafast electron beam blanking system, intended for testing microwave integrated circuits with very high temporal resolution. 100fs electron pulses can be generated with repetition. rates in the range from 8 to 18 GHz. 1. INTRODUCTION For optimization of design and for function and failure analysis of hybrid and monolithic integrated micro- and millimeterwave circuits (MMIC) a device-internal quantitative voltage measurement is required. Mechanical probes can not be used here because of their large size and capacitive load, thus only contactless measurement techniques are suitable. The electron beam test technique, already used for testing silicon high speed integrated circuits, offers high spatial-, voltage-, and time-resolution and may be a solution of this problem. The high time resolution is achieved by applying stroboscopic techniques, as being accessible by generating short primary electron (PE)-pulses which are usually generated by electron beam blanking systems (EBBS). The performance of existing EBBS, however, is not sufficient for measurements with very high temporal resolution on MMIC, as both PE-energy and pulse repetition rate must be adjustable in an arbitrary manner and independently from each other. Therefore a new EBBS has been developed which is optimized for electron beam testing of MMIC and is able to produce PE-pulses of less than l 0ors duration. It can be driven by a sinusoidal deflection voltage, by which phase-jitter between PE-pulse and signal can be avoided. 2. PREVIOUS METHODS FOR GENERATION OF SHORT PE-PULSES A short PE-pulse can either be generated indirectly from a continuous electron beam by an EBBS or directly by pulsed cathode emission. EBBS used for indirect generation are travelling wave structures and cavity resonators [1,2] and also blanking capacitors [3-11]. For these methods the same basic principle is applied: Electrons are deflected by an electric field perpendicular to their direction of propagation and can only pass an aperture when being deflected into a certain angle. However, travelling wave structures and cavity resonators can only be used at fixed PE-energies and repetition rates. In contrast to these, simple blanking capacitors do not show these drawbacks. A disadvantage is the difficulty in matching the capacitor plates to the impedance of the connecting line, especially at the high frequencies required for testing of MMIC [5,6]. The direct generation of short PE-pulses is either possible by illuminating a photocathode with short laser light pulses [12], where the repetition rate is fixed by that of the laser, or by a field emission cathode mounted within a cavity resonator [13], where the repetition rate is also fixed. So the blanking capacitor is the only concept, which is able to generate the short PE-pulses as required for testing MMIC and also allows to choose variable PE-energies and repetition rates. This paper presents design concepts and the realization of an EBBS which does not show the drawbacks of previous systems. 0167-9317/90/$3.50 © 1990, Elsevier Science Publishers B.V.
J. Fehr et al. / A lO0-femtosecond e-beam blanking system
222
3.
SET-UP AND DRIVING OF THE 100-FEMTOSECOND EBBS
The EBBS presented here shows a new concept [15]. The electron beam is deflected in the electromagnetic field of a coaxial transmission line (fig. 1) and is chopped by a pair of orthogonally arranged slit apertures. T--
/-
,J
/// // J
J
cut
AB electron
beam
J
,
-"
outer
conductor
FIGURE 1 Scheme of the coaxial transmission line based EBBS The electron beam enters the electromagnetic field through small holes in the outer conductor of the transmission line. These holes are made in such a way, that, on the one hand, emission of rf-power and perturbation of the electromagnetic field is prevented and that, on the other hand, the electrons pass regions of high electromagnetic field strength. Transmission lines filled with insulating materials have to be prepared. The dielectric has to be removed, so that there is no electric charging due to the electron beam. The transition from dielectrically to vacuum filled transmission line needs special design of the taper sections to minimize reflections at these dicontinuities. The termination of the transmission line can be positioned outside the vacuum and is connected by rf-vacuum-feedthroughs with the EBBS. The new EBBS shows the following advantages compared with previous developments : The repetition rate can be chosen freely. It is only limited by the monomode bandwidth of the transmission line used, and the rf-power supply. The PE-energy can be set independently on the required repetition rate and pulse duration. The electron beam is deflected by both the electric and the magnetic field inside the coaxial transmission line. The structure of the electric field is shown in fig. 1. By the electric field the electron is deflected towards or away from the inner conductor. When a sinewave is applied and the electromagnetic field is assumed to be transversal, the magnetic field is directed perpendicular to the electric field, thus the lines of magnetic flux are concentric circles around the inner conductor. So the deflection due to the magnetic field is in direction of the axis of the coaxial transmission line. Although the field distribution inside the transmission line changes while the electrons travel through it, the deflection of the electron beam is an ellipse. The amplitude of its semi-major and semi-minor axis depends on the amplitude and the frequency of the applied voltage. By using two slit apertures the elliptical deflection can be used to generate only one single PE-pulse per period of the sinewave. Each of the slit apertures consists of two plates, adjustable freely and independently of each other. Thus position and width of the slit can
J. Fehr et al. I A lO0-femtosecond e-beam blanking system
223
be set as required yielding corresponding values of pulse delay and duration, l#m slit width can be adjusted reproducibly without problems. The EBBS is a-matched with high quality, because the transmission line is not interrupted and its transversal structure is unchanged. Measurements with a network analyzer exhibit transmission and reflection values of the EBBS that are comparable to those of an unmodified transmission line (fig. 2). Whereas the transmission behaviour is almost unchanged, the reflection is somewhat different, but for practical points of view this change of the reflection factor is negligible as being below -15dB. Although one single PE-pulse of 100fs duration contains only 1/10 electron on an average when a typical beam current of lnA is assumed, the high repetition rate in the GHz-range provides an acceptable signal level. The duty cycle is in the order of 100-1000.
IS121
IS121
transmission --;~
t T f
-lO ; [ [ [ [ 8
13
GHz 18,
ISlll
8
13
'-d
:
GHz 18
ISlll
reflection
8 EBBS
13
GHz 18
8
13
GHz 1~5
unmodified Coaxialtransmission- line
FIGURE 2 Comparison between measured S-parameter magnitudes of the EBBS and an unmodified coaxial transmission line. Note: different scales for transmission and reflection. Control of the system (fig. 3) is exerted by a synthesized sweeper (HP 8341B, 0.01-20GHz) whose output power is amplified by a travelling wave tube (TWT) amplifier (LogiMetrics A500 I/J, amplification 50 dB, max. 150W output power, frequency range 8 - 18GHz). The required power level for deflecting the electron beam is about 10 - 20W. The TWT amplifier has a double ridged waveguide output (type WRD 750 D 24) which limits the frequency range from 8 to 18 GHz. Close to the scanning electron microscope (SEM) a transition from waveguide to coaxial transmission line (SMA-type) is made to match space requirements inside the SEM specimen chamber. The EBBS is connected by rf-vacuum-feedthroughs and semi-rigid cables inside the SEM. The termination of the line is realized by coaxial attenuators outside the vacuum. To achieve a constant output power of the TWT amplifier, from one of its sample ports a voltage proportional to the output power is generated by a crystal detector. This voltage controls the input power of the TWT amplifier within a feedback circuit. A second deflection unit can be mounted at the position of the sample as shown in fig. 3. This unit will be used to measure the duration of the generated PE-pulses by means of the streak technique. This technique transforms the temporal intensity distribution of the pulse into a spatial intensity distribution, which can be read out by a linear photodiode array.
224
J. Fehr et al. / A lO0-femtosecond e-beam blanking system
SEM col umn
double ridged wove
I
syntheslzed sweeper{HP8341E f:10MHz 20GHz P:10 mW
l
travelhng wave tube ompliher (LogiMetr ics A50C
terrn~nat~on
'i
magic I;
choppmg aperture
'5 W coaxial ransml£~an
1
I_
crystal detector for
]
photodlode
~__
array read out unit
photodiode array specimen chamber
FIGURE 3 Driving of the EBBS and streak-unit 4.
PERFORMANCE TEST OF THE IO0-FEMTOSECOND EBBS
The frequency dependence of the electron beam deflection inside the time-dependent electromagnetic field was computed analytically. The results show elliptical movement of the position of the deflected electron beam in the plane of the chopping aperture depending on the phase of the driving voltage at which the electrons enter the EBBS. The amplitude (semi-major axis of the ellipse) changes slightly with the frequency. The deflection of the electron beam in the direction of the semi-major axis is due to the electric field, that in the direction of the semi-minor axis is due to the magnetic field of the coaxial transmission line. The theoretical results were confirmed by real measurements. The amplitude of deflection is of the same order as computed, also the frequency behaviour is the same. The recording of the electron beam deflection (fig. 4) is made by a phosphor positioned below the EBBS and by a silicon intensified target TV camera via a transfer optic.
FIGURE 4 Elliptical deflection of the electron beam
J. Fehr et al. / A lO0-femtosecond e-beam blanking system
225
Typical magnitudes of deflection are 240pro within the plane of the chopping apertures, for a PE-energy of 10keV, using a deflecting voltage of 64V peak to peak and a frequency of 12GHz. For an aperture slit of lprn as easily being adjusted, the duration of the PE-pulses can be determined to be in the order of 110fs. Current work is carried out in determining the full pulse shape by means of the streak technique as indicated in fig. 3. By this technique the temporal intensity shape of the electron pulse is converted into a spatial intensity shape on the photodiode array by means of a second deflection unit below the EBBS. 5.
POSITIONING OF THE EBBS WITHIN THE ELECTRON OPTICAL SYSTEM
Even if the generation of short PE-pulses is possible, transit time effects of the PE during their propagation from the EBBS to the device under test may lead to a pulse broadening. These transit time effects are caused by the non-monochromatism of the electron beam. For a tungsten hairpin cathode with an energy spread of AW=3eV and a field emission cathode with an energy spread of AW=0.5eV the pulse broadening has been computed (fig. 5). 1
I
psi aW=3eV
1
3 5 7 primery electron energy
g keY 11
1 ~W=0.5 eV
1
3 5 7 primary electron energy
9 keV 11
FIGURE 5 PE-pulse broadening dependent on the PE-energy shown for a tungsten cathode (AW=3eV) and a field emission cathode (AW=0.5eV) This leads to a pulse broadening of nearly 5ps/m when a tungsten filament and a PE-energy of 10keV are used. Therefore the new EBBS is positioned directly below the pole piece and inside the specimen chamber of the SEM. Consequently a poorer spatial resolution because of a greater working distance and also a reduced field of view have to be considered. 6. CONLUSIONS A new electron beam blanking system has been developed which allows the generation of PE-pulses of 100fs duration with a repetition rate in the range from 8 to 18GHz. The PE-energy can be chosen as required. Due to the elliptical deflection of the electron beam it is possible, to generate only one single pulse per period of the deflecting voltage. The EBBS has been tested on its rf-behaviour and was found to be perfectly if-matched. For driving the EBBS a rf-power supply of 20W is required. Transit-time effects of the PE require the build-in of the EBBS as near as possible to the device under test. This leads to a poorer spatial resolution and a reduced field of view. The next step will be to build up a complete high-frequency electron beam testing system which should allow the device internal test of MMIC, as being produced within the Sonderforschungsbereich 254.
J. Fehr et al. / A lO0-femtosecond e-beam blanking ©'stem
226
ACKNOWLEDGEMENTS This work was supported by the Deutsche Forschungsgemeinschaft
REFERENCES
[1] [2] [3]
[4] [5] [6] [7]
[8] [9] [10] [11] [12] [13]
[14] [15]
Gopinath, A. and Hill, M.S., SEM Stroboscopy At 9 GHz, Scanning Electron Microscopy, Part I (1973) pp. 197-204. Hosokawa, T., Fujioka, H and Ura, K., Generation and measurement of subpicosecond electron beam pulses, Rev. Sci. Instrum., Vol. 49, No. 5 (1978) pp. 624-628. Menzel, E., Elektronenstrahltestsystem for die Funktionskontrolle und Fehleranalyse h0chstintegrierter Schaltkreise, Dissertation, Universit&t Duisburg, Fachgebiet "Werkstoffe der Elektrotechnik" (1981). Menzel, E., Kubalek, E., Elektronenstrahlaustastsysteme, BEDO, Vol. 11 (1978) pp. 47-66. Sadorf, H. and Kratz, H. A., Plug-in fast electron beam chopping system, Rev. Sci. Instrum., Vol. 56, No. 4 (1985) pp. 567-571. Kratz, H. and Sadorf, H., ps-Elektronenstrahlaustasteinheit, application for a patent, reference P 33 39 811.9 (march 11, 1983) Winkler, D., Schmitt, R., Brunner, M. and Lischke, B., Pulstastsystem for die ElektronenstrahlmeStechnik im Pikosekundenbereich, Optik, Vol. 78, No. 4 (1988) pp. 165-172. Thong, J. T. L., Garth, S. C. J., Breton, B. C. and Nixon, W. C., Ultra high speed electron beam testing system, Microelectronic Engineering Vol. 6 (1987) pp. 683-688. Thong, J. T. L., Garth, S. C. J., Nixon, W. C. and Broers, A. N., Ultrahigh speed electron beam pulsing systems for electron beam testing, SPIE, Vol. 795 (1987) pp. 178-187. Todokoro, H., Yoneda, S., Seitou, S. and Hosoki, S., Electron Beam Tester with 10 ps Time Resolution, 1986 International Test Conference, Paper 16B.2. Fujioka, H. and Ura, K., Electron Beam Blanking Systems, Scanning, Vol. 5 (1983) pp. 3-13. May, P. G., Halbout, J.-M. and Chiu, G. L.-T., Noncontact High-Speed Waveform Measurements with the Picosecond Photoelectron Scanning Electron Microscope, IEEE J. Quant. Electronics, Vol. 24, No. 2 (1988) pp. 234-239. HObner, H., R6hm, E., Generating pico-second electron pulses with microwave field emission, Optik, Vol. 78, No. 4 (1988) pp. 173-182. Fujioka, H., Nakamae, K. and Ura, K., Analysis of the transit time effect on the stroboscopic voltage contrast in the scanning electron microscope, J. Phys. D: Appl. Phys. 18 (1985) pp. 1019 - 1027. Balk, L. J., Fehr, J. and Reiners, W., Subpikosekunden - Elektronenstrahlaustastsystem, application for a patent, reference P 39 04 280.4 (feb. 14, 1989).
221
A 100-FEMTOSECOND ELECTRON BEAM BLANKING SYSTEM J. FEHR, W. REINERS, L.J. BALK, E. KUBALEK, D. KOTHER, I. WOLFF Universit&t Duisburg Werkstoffe der Elektrotechnik und AIIgemeine und Theoretische Elektrotechnik Sonderforschungsbereich 254, KommandantenstraBe 60, D 4100 Duisburg 1, F.R.G. Conventional electron beam blanking systems show the drawbacks of a fixed electron energy, a fixed repetition rate or even unsuitability for repetition rates in the GHz region. This paper describes the development of an ultrafast electron beam blanking system, intended for testing microwave integrated circuits with very high temporal resolution. 100fs electron pulses can be generated with repetition. rates in the range from 8 to 18 GHz. 1. INTRODUCTION For optimization of design and for function and failure analysis of hybrid and monolithic integrated micro- and millimeterwave circuits (MMIC) a device-internal quantitative voltage measurement is required. Mechanical probes can not be used here because of their large size and capacitive load, thus only contactless measurement techniques are suitable. The electron beam test technique, already used for testing silicon high speed integrated circuits, offers high spatial-, voltage-, and time-resolution and may be a solution of this problem. The high time resolution is achieved by applying stroboscopic techniques, as being accessible by generating short primary electron (PE)-pulses which are usually generated by electron beam blanking systems (EBBS). The performance of existing EBBS, however, is not sufficient for measurements with very high temporal resolution on MMIC, as both PE-energy and pulse repetition rate must be adjustable in an arbitrary manner and independently from each other. Therefore a new EBBS has been developed which is optimized for electron beam testing of MMIC and is able to produce PE-pulses of less than l 0ors duration. It can be driven by a sinusoidal deflection voltage, by which phase-jitter between PE-pulse and signal can be avoided. 2. PREVIOUS METHODS FOR GENERATION OF SHORT PE-PULSES A short PE-pulse can either be generated indirectly from a continuous electron beam by an EBBS or directly by pulsed cathode emission. EBBS used for indirect generation are travelling wave structures and cavity resonators [1,2] and also blanking capacitors [3-11]. For these methods the same basic principle is applied: Electrons are deflected by an electric field perpendicular to their direction of propagation and can only pass an aperture when being deflected into a certain angle. However, travelling wave structures and cavity resonators can only be used at fixed PE-energies and repetition rates. In contrast to these, simple blanking capacitors do not show these drawbacks. A disadvantage is the difficulty in matching the capacitor plates to the impedance of the connecting line, especially at the high frequencies required for testing of MMIC [5,6]. The direct generation of short PE-pulses is either possible by illuminating a photocathode with short laser light pulses [12], where the repetition rate is fixed by that of the laser, or by a field emission cathode mounted within a cavity resonator [13], where the repetition rate is also fixed. So the blanking capacitor is the only concept, which is able to generate the short PE-pulses as required for testing MMIC and also allows to choose variable PE-energies and repetition rates. This paper presents design concepts and the realization of an EBBS which does not show the drawbacks of previous systems. 0167-9317/90/$3.50 © 1990, Elsevier Science Publishers B.V.
J. Fehr et al. / A lO0-femtosecond e-beam blanking system
222
3.
SET-UP AND DRIVING OF THE 100-FEMTOSECOND EBBS
The EBBS presented here shows a new concept [15]. The electron beam is deflected in the electromagnetic field of a coaxial transmission line (fig. 1) and is chopped by a pair of orthogonally arranged slit apertures. T--
/-
,J
/// // J
J
cut
AB electron
beam
J
,
-"
outer
conductor
FIGURE 1 Scheme of the coaxial transmission line based EBBS The electron beam enters the electromagnetic field through small holes in the outer conductor of the transmission line. These holes are made in such a way, that, on the one hand, emission of rf-power and perturbation of the electromagnetic field is prevented and that, on the other hand, the electrons pass regions of high electromagnetic field strength. Transmission lines filled with insulating materials have to be prepared. The dielectric has to be removed, so that there is no electric charging due to the electron beam. The transition from dielectrically to vacuum filled transmission line needs special design of the taper sections to minimize reflections at these dicontinuities. The termination of the transmission line can be positioned outside the vacuum and is connected by rf-vacuum-feedthroughs with the EBBS. The new EBBS shows the following advantages compared with previous developments : The repetition rate can be chosen freely. It is only limited by the monomode bandwidth of the transmission line used, and the rf-power supply. The PE-energy can be set independently on the required repetition rate and pulse duration. The electron beam is deflected by both the electric and the magnetic field inside the coaxial transmission line. The structure of the electric field is shown in fig. 1. By the electric field the electron is deflected towards or away from the inner conductor. When a sinewave is applied and the electromagnetic field is assumed to be transversal, the magnetic field is directed perpendicular to the electric field, thus the lines of magnetic flux are concentric circles around the inner conductor. So the deflection due to the magnetic field is in direction of the axis of the coaxial transmission line. Although the field distribution inside the transmission line changes while the electrons travel through it, the deflection of the electron beam is an ellipse. The amplitude of its semi-major and semi-minor axis depends on the amplitude and the frequency of the applied voltage. By using two slit apertures the elliptical deflection can be used to generate only one single PE-pulse per period of the sinewave. Each of the slit apertures consists of two plates, adjustable freely and independently of each other. Thus position and width of the slit can
J. Fehr et al. I A lO0-femtosecond e-beam blanking system
223
be set as required yielding corresponding values of pulse delay and duration, l#m slit width can be adjusted reproducibly without problems. The EBBS is a-matched with high quality, because the transmission line is not interrupted and its transversal structure is unchanged. Measurements with a network analyzer exhibit transmission and reflection values of the EBBS that are comparable to those of an unmodified transmission line (fig. 2). Whereas the transmission behaviour is almost unchanged, the reflection is somewhat different, but for practical points of view this change of the reflection factor is negligible as being below -15dB. Although one single PE-pulse of 100fs duration contains only 1/10 electron on an average when a typical beam current of lnA is assumed, the high repetition rate in the GHz-range provides an acceptable signal level. The duty cycle is in the order of 100-1000.
IS121
IS121
transmission --;~
t T f
-lO ; [ [ [ [ 8
13
GHz 18,
ISlll
8
13
'-d
:
GHz 18
ISlll
reflection
8 EBBS
13
GHz 18
8
13
GHz 1~5
unmodified Coaxialtransmission- line
FIGURE 2 Comparison between measured S-parameter magnitudes of the EBBS and an unmodified coaxial transmission line. Note: different scales for transmission and reflection. Control of the system (fig. 3) is exerted by a synthesized sweeper (HP 8341B, 0.01-20GHz) whose output power is amplified by a travelling wave tube (TWT) amplifier (LogiMetrics A500 I/J, amplification 50 dB, max. 150W output power, frequency range 8 - 18GHz). The required power level for deflecting the electron beam is about 10 - 20W. The TWT amplifier has a double ridged waveguide output (type WRD 750 D 24) which limits the frequency range from 8 to 18 GHz. Close to the scanning electron microscope (SEM) a transition from waveguide to coaxial transmission line (SMA-type) is made to match space requirements inside the SEM specimen chamber. The EBBS is connected by rf-vacuum-feedthroughs and semi-rigid cables inside the SEM. The termination of the line is realized by coaxial attenuators outside the vacuum. To achieve a constant output power of the TWT amplifier, from one of its sample ports a voltage proportional to the output power is generated by a crystal detector. This voltage controls the input power of the TWT amplifier within a feedback circuit. A second deflection unit can be mounted at the position of the sample as shown in fig. 3. This unit will be used to measure the duration of the generated PE-pulses by means of the streak technique. This technique transforms the temporal intensity distribution of the pulse into a spatial intensity distribution, which can be read out by a linear photodiode array.
224
J. Fehr et al. / A lO0-femtosecond e-beam blanking system
SEM col umn
double ridged wove
I
syntheslzed sweeper{HP8341E f:10MHz 20GHz P:10 mW
l
travelhng wave tube ompliher (LogiMetr ics A50C
terrn~nat~on
'i
magic I;
choppmg aperture
'5 W coaxial ransml£~an
1
I_
crystal detector for
]
photodlode
~__
array read out unit
photodiode array specimen chamber
FIGURE 3 Driving of the EBBS and streak-unit 4.
PERFORMANCE TEST OF THE IO0-FEMTOSECOND EBBS
The frequency dependence of the electron beam deflection inside the time-dependent electromagnetic field was computed analytically. The results show elliptical movement of the position of the deflected electron beam in the plane of the chopping aperture depending on the phase of the driving voltage at which the electrons enter the EBBS. The amplitude (semi-major axis of the ellipse) changes slightly with the frequency. The deflection of the electron beam in the direction of the semi-major axis is due to the electric field, that in the direction of the semi-minor axis is due to the magnetic field of the coaxial transmission line. The theoretical results were confirmed by real measurements. The amplitude of deflection is of the same order as computed, also the frequency behaviour is the same. The recording of the electron beam deflection (fig. 4) is made by a phosphor positioned below the EBBS and by a silicon intensified target TV camera via a transfer optic.
FIGURE 4 Elliptical deflection of the electron beam
J. Fehr et al. / A lO0-femtosecond e-beam blanking system
225
Typical magnitudes of deflection are 240pro within the plane of the chopping apertures, for a PE-energy of 10keV, using a deflecting voltage of 64V peak to peak and a frequency of 12GHz. For an aperture slit of lprn as easily being adjusted, the duration of the PE-pulses can be determined to be in the order of 110fs. Current work is carried out in determining the full pulse shape by means of the streak technique as indicated in fig. 3. By this technique the temporal intensity shape of the electron pulse is converted into a spatial intensity shape on the photodiode array by means of a second deflection unit below the EBBS. 5.
POSITIONING OF THE EBBS WITHIN THE ELECTRON OPTICAL SYSTEM
Even if the generation of short PE-pulses is possible, transit time effects of the PE during their propagation from the EBBS to the device under test may lead to a pulse broadening. These transit time effects are caused by the non-monochromatism of the electron beam. For a tungsten hairpin cathode with an energy spread of AW=3eV and a field emission cathode with an energy spread of AW=0.5eV the pulse broadening has been computed (fig. 5). 1
I
psi aW=3eV
1
3 5 7 primery electron energy
g keY 11
1 ~W=0.5 eV
1
3 5 7 primary electron energy
9 keV 11
FIGURE 5 PE-pulse broadening dependent on the PE-energy shown for a tungsten cathode (AW=3eV) and a field emission cathode (AW=0.5eV) This leads to a pulse broadening of nearly 5ps/m when a tungsten filament and a PE-energy of 10keV are used. Therefore the new EBBS is positioned directly below the pole piece and inside the specimen chamber of the SEM. Consequently a poorer spatial resolution because of a greater working distance and also a reduced field of view have to be considered. 6. CONLUSIONS A new electron beam blanking system has been developed which allows the generation of PE-pulses of 100fs duration with a repetition rate in the range from 8 to 18GHz. The PE-energy can be chosen as required. Due to the elliptical deflection of the electron beam it is possible, to generate only one single pulse per period of the deflecting voltage. The EBBS has been tested on its rf-behaviour and was found to be perfectly if-matched. For driving the EBBS a rf-power supply of 20W is required. Transit-time effects of the PE require the build-in of the EBBS as near as possible to the device under test. This leads to a poorer spatial resolution and a reduced field of view. The next step will be to build up a complete high-frequency electron beam testing system which should allow the device internal test of MMIC, as being produced within the Sonderforschungsbereich 254.
J. Fehr et al. / A lO0-femtosecond e-beam blanking ©'stem
226
ACKNOWLEDGEMENTS This work was supported by the Deutsche Forschungsgemeinschaft
REFERENCES
[1] [2] [3]
[4] [5] [6] [7]
[8] [9] [10] [11] [12] [13]
[14] [15]
Gopinath, A. and Hill, M.S., SEM Stroboscopy At 9 GHz, Scanning Electron Microscopy, Part I (1973) pp. 197-204. Hosokawa, T., Fujioka, H and Ura, K., Generation and measurement of subpicosecond electron beam pulses, Rev. Sci. Instrum., Vol. 49, No. 5 (1978) pp. 624-628. Menzel, E., Elektronenstrahltestsystem for die Funktionskontrolle und Fehleranalyse h0chstintegrierter Schaltkreise, Dissertation, Universit&t Duisburg, Fachgebiet "Werkstoffe der Elektrotechnik" (1981). Menzel, E., Kubalek, E., Elektronenstrahlaustastsysteme, BEDO, Vol. 11 (1978) pp. 47-66. Sadorf, H. and Kratz, H. A., Plug-in fast electron beam chopping system, Rev. Sci. Instrum., Vol. 56, No. 4 (1985) pp. 567-571. Kratz, H. and Sadorf, H., ps-Elektronenstrahlaustasteinheit, application for a patent, reference P 33 39 811.9 (march 11, 1983) Winkler, D., Schmitt, R., Brunner, M. and Lischke, B., Pulstastsystem for die ElektronenstrahlmeStechnik im Pikosekundenbereich, Optik, Vol. 78, No. 4 (1988) pp. 165-172. Thong, J. T. L., Garth, S. C. J., Breton, B. C. and Nixon, W. C., Ultra high speed electron beam testing system, Microelectronic Engineering Vol. 6 (1987) pp. 683-688. Thong, J. T. L., Garth, S. C. J., Nixon, W. C. and Broers, A. N., Ultrahigh speed electron beam pulsing systems for electron beam testing, SPIE, Vol. 795 (1987) pp. 178-187. Todokoro, H., Yoneda, S., Seitou, S. and Hosoki, S., Electron Beam Tester with 10 ps Time Resolution, 1986 International Test Conference, Paper 16B.2. Fujioka, H. and Ura, K., Electron Beam Blanking Systems, Scanning, Vol. 5 (1983) pp. 3-13. May, P. G., Halbout, J.-M. and Chiu, G. L.-T., Noncontact High-Speed Waveform Measurements with the Picosecond Photoelectron Scanning Electron Microscope, IEEE J. Quant. Electronics, Vol. 24, No. 2 (1988) pp. 234-239. HObner, H., R6hm, E., Generating pico-second electron pulses with microwave field emission, Optik, Vol. 78, No. 4 (1988) pp. 173-182. Fujioka, H., Nakamae, K. and Ura, K., Analysis of the transit time effect on the stroboscopic voltage contrast in the scanning electron microscope, J. Phys. D: Appl. Phys. 18 (1985) pp. 1019 - 1027. Balk, L. J., Fehr, J. and Reiners, W., Subpikosekunden - Elektronenstrahlaustastsystem, application for a patent, reference P 39 04 280.4 (feb. 14, 1989).