- Email: [email protected]
Study of basic mechanisms of semiconductor devices using ion beam induced charge (IBIC) collection
CQs 1
--
__
Beam Interactions with Materials lk Atoms
~ ELSEVIER
Nuclear Instruments
and Methods in Physics Research 6 130 (1997) 528-533
Study of basic mechanisms of semiconductor devices using ion beam induced charge @3IC) collection T. Nishijima a**,H. Sekiguchi a, T. Hirao b, I. Nashiyama S. Matsuda ‘, N. Shiono d
b, N. Nemoto ‘,
” Electrotechnical Laborator?: Tsukuba-shi, Ibaraki. 305 Japan b Japan Atomic Energy Research Institute. Takasaki, Gunma, 3X-12 Jupun ’ National Space Deoelopment Agency of Japan, Tsukuba-shi, 305 Japan ’ Reliability Center for Electronic Components @Jupun. Chuoku. 103 Jupun
Abstract A change of wave form of current transients induced by a single heavy ion was investigated around a pn junction with 8 pm width and 10 pm length as a function of the ion incident position. Three pn junctions were made on a 3 hrn thick Si epilayer (1 x 10i6/cm3) grown on Si substrate and were in a line along an aluminum electrode with 10 pm spacing between the adjacent junctions. The elements of a pn junction array were irradiated with a I pm diameter 15 MeV C+ heavy ion microbeam spacing steps by 3 pm. At a bias voltage of - 10 V, 148, 91, and 54 fC were collected at the pn junction center, and at 3 pm and 4 pm from the edge of the electrode, respectively. Internal device structure was examined by IBIC (ion beam induced current) method by using a 2 MeV He + ion microbeam. From the IBIC spectrum and the IBIC image, the charge collected from the open space by the diffusion process was observed in addition to the charge collected from the depletion layer of the pn junction.
1. Introduction We have studied the basic mechanism of charge collection induced by high energy charged particles incident on semiconductor devices in order to obtain process-parameters to improve a resistance against a single event upset [l-4]. A change of the wave form of the current transient was investigated around a pn junction with 8 pm width and 10 urn length as a function of the ion incident position [5]. An element of pn junction array was irradiated wifh a 1 pm diameter 15 MeV C+ heavy ion microbeam spacing
Corresponding author. [email protected].
Fax:
+ 81
298
58
5695;
e-mail:
steps by 3 pm. At a bias voltage of - 10 V, 148, 91 and 54 fC were collected at the position of the pn junction, 3 pm and 4 pm apart from the edge of the electrode, respectively. The theoretically estimated value of the charge transient collected by the drift process is 50 fC from the depletion layer of the pn junction in this experimental condition [3]. Since there is no such a sensitive region for charge collection except pn junctions in this array, it is necessary to investigate another factor of a charge collection. Internal device structure was also examined by the IBIC method by using a 2 MeV He+ ion microbeam. In this paper test diode prep~ation, transient current induced by 15 MeV C+ ion measurement and IBIC measurement by 2 MeV He+ microbeam are described and discussed.
0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SO168-583X(97)00245-0
2. Experimental 2.1. Current surement
results and discussion
transient
thick Si epilayer (1 X 10r6/cm3) grown on a Si substrate and were in a line along an aluminum electrode with a 10 pm spacing between the adjacent junctions. A current transient induced by a single 15 MeV C’ ion was measured at several points by the wide bandwidth digitizing sampling oscilloscope described previously [2,3]. The C f ion beam was
induced by ion (CTII) mea-
Fig. 1 shows a schematic drawing of a Si three pn junction array prepared for this experiment. Three 8 pm X 10 pm pn junctions were made on a 3 pm
a)
, \
W
350,~~ m p>
Al Electrode 0.5 p m
Si02 lflm -\
Eh-Laver 3’pm N+ l~lO%-~,
\Back Contact Al 0.5 u m
Fig. 1. Circuit design of the Si pn junction
diode with three electrodes.
(a> Plane view; (b) cross sectional
view; t
X. ELECTRONICS
measurement
points.
AND PHOTONICS
moved in steps of 3 urn and five measuring points are illustrated in Fig. la. Points I, 2, 3, 4 and 5 correspond to 3 pm down from the central electrode edge, the electrode, 4 pm up from the central electrode (or 6 pm left from the upper electrode edge), 4 pm and 7 ym up from the upper electrode edge, respectively. In Fig, 2 three typical wave forms of the current transient selected from those measured at the abovementioned points are shown at bias voltage of - IO V. The wave form of the current transient measured at the electrode (point 2) has a rise time of 100 ps and a full width at half maximum (OHM) of 89 p.s. The pulse height of wave form 1 is one third of that of wave form 2. Its FWHM and decay time are 320 ps and 1200 ps, respectively. Wave form 3 is smaller than wave form 2 and its FWHM is 382 ps. Its decay time is longer than 1400 ps+ Current transients were measured to be 91, 148, 54 and 79 fC at points 1, 2, 3 and 4, respectively, by integra~ng the wave forms of transient currents from 0 to tSO0 ps and dividing by the specific system impedance of 50 0 [2,3], No current was observed at 7 pm up from the upper electrode ~m~asuring point 5).
Fig. 3 shows an IBXC!spectrum of the pn junction array measured with a 2 MeV He* microbeams [43. The microbeam diameter was measured to be 3.5 pm using a 100 pm diameter object slit. The microbeam scanning area was 80 pm X 80 pm. Beam intensity at the test diode was less than 2000 parti-
Fig. 2. Observed current transients induced by a 15 MeV C* ion for the pn junction diode with three electrodes. Bias voltage was - 10 V. (I) 3 pm down from the centnl electrode edge, (2) on the electrode and (3) 4 pm up from the central electrode
1000
ZQOO
Channels Fig. 3. Observed IBIC spectrumwith a 2.0
3000
4000
MeV He+ microbeam
for the pn junction diode with three electrodes.
cles,/s (0.3 fC> in consideration of the pile up of the pulse counting system and also of the radiation damage production during ion irradiation 161.The slit diameter used during this IBIC experiment was less than 20 pm. Bias voltage was - 10 V. Counts lower than 850 channel were discriminated by ADC to cut off electronic noise. In this experiment total counts for one fBIC spectrum were limited under 1OOOO (about IO counts/~m’}~ No radiation damage was, therefore, observed at this irradiation rate after several IBIC measurements on the same sample. The TBlC spectrum consists of a lower descending peak, a plateau, main peaks at the center, a plateau and a small peak, marked with A, B, C, D and E, respectively. Fig. 4 illustrates IBIC images drawn by IBIC spectrum of Fig, 3 coincide with a beam scanning signal, Figs. 4A, B, C, D and E correspond to windows A, B, C, D and E of the IBIC spectrum in Fig. 3 respectively. Fig. 4E shows that the three active regions are rectangular with a size of 7 pm X 10 pm each and with distances between two regions of 9.5 pm. These correspond quite well to the dimension of the pn junction electrode illustrated in Fig. la, This means that part E of the XBIC spectrum is the charge induced by the beam under the pn junction electrode and coltected from the depletion layer by a drift and a diffusion process. Fig. 4B shows three connected rings of 21.5 pm outer diameter and 17.5 pm inner diameter. In Fig. 4C, also, three rings with 17 pm outer diameter and 14.5 pm inner diameter are shown. Since the shapes of these rings did not change even if the bias voltage WAS changed from - 10 V to - 15 V, it is considered that
531
‘:
..
E Y
22
:-
I,-
B
A
t 4------
80um
A
182pm
-
:
t C
Fig. 5 Fig. 4. The IBIC images of the pn junction diode with three electrodes. Windows A, B, C, D and E correspond to regions A, B, C, D and E of Fig. 3, respectively. Beam scanning range was 80 pm X 80 pm. F is circuit design of the Si pn junction diode with three electrodes on the same scale as the IBIC images. Fig. 5. Measuring points (l)-(3) drawn by a whole IBIC current.
for the IBIC spectra and the IBIC image are put on the plane view of circuit design. The IBIC image is
X. ELECTRONICS
AND PHOTONICS
the charges induced outside the electrode were collected by a diffusion process. It seems that the observed ring shape instead of sharp rectangular electrode shape reflects the distribution of the potential of the electrode. In Fig. 4A one almost rectangular shape of area 57 pm X 22.5 pm was observed. Comparing Fig. 4A with Fig. 4B, it is seen that total area of the former expands slightly and the interior of the rectangular shape is filled with IBIC signals. An outer IBIC signal comes from the charge collected by the diffusion process. Distances between the electrodes and the boundary of the IBIC image show the maximum diffusion length of this sample. It seems that the middle of the IBIC image consists of charges detrapped from carrier traps. This phenomenon was also observed in the IBIC image of the GaAs Schottky diode made on the epilayer [4].
To confirm the above assignment of the diffusion process as the main charge collection mode of outer electrode, IBIC spectra of a Si pn junction diode were measured at the typical points of the pn junction diode. Fig. 5 shows a plane view of Si pn junction diode with three measuring points. A 2 pm X 20 pm Al electrode connected to a 50 pm diameter Al electrode was evaporated onto a 3 pm thick Si epilayer (4.85 X iO’5/cm3) grown on Si substrate (0.01 fi cm>. Fig. 6 shows IBIC spectra marked by I, 2 and 3 measured at the center of the electrode, 9 pm and 18 pm apart from the edge, respectively. I .X MeV He+ beam was scanned around 3 pm x 3 brn in order to reduce the radiation
damage. Channel numbers at the peaks of the spectra decreases with increasing distance from the electrode. Assuming the channel numbers of IBIC spectra are proportional to the numbers of electron-hole pairs created by incident ions and collected by the electrode, a diffusion length L = 20 pm is obtained from this experiment by a calculation on the basis of the diffusion equation [7,8].
3. Conclusion From the IBIC images corresponding to the IBIC spectra of the pn junction diode array, the collection process of the transient charge induced by high energy C’ ions are clearly assigned to either drift at the electrode or diffusion near the electrode. Using the IBIC spectra of Fig. 6, the carrier diffusion length was obtained to be L = 20 pm for the Si epilayer of minority carrier density 4.85 X 10”/cm3. On the contrary, both the transient current wave form and the IBIC spectrum were not observed at 7 pm up from the edge of the upper electrode (measuring point 5) of the pn junction diode array made on the Si epilayer (1 x 10”/cm3). Since the diffusion length of the epilayer is estimated to be less than 7 pm, this suggests that the minority carrier density exceeds 1 X 10”/cm3 during the pn junction fabrication procedure. The collected charge induced by high energy C+ ions at the middle of two electrodes (measuring point 3) was less than that measured at 4 Frn up from the upper electrode (measuring point 4). We cannot clearly understand the reason for this, but we add that we have measured the same tendency in preliminary measurements of the transient current induced by high energy O+ and Si+ ion beams.
References
2000
3000
4000
Channels Fig. 6. Observed IBIC spectrum for the Si pn junction diode.
with a 1.8 MeV He*
microbeam
[l] I. Nashiyama, T. Nishijima, H. Sekiguchi, Y. Shimano and T. Goka, Nucl. Instr. and Meth. B 54 (1991) 407. [2] I. Nashiyama, T. Hirao, T. Kamiya. H. Yutoh, T. Nishijima and H. Sekiguchi. IEEE Trans. Nucl. Sci. NS 40 (1993) 1935. [3] T. Nishijima, H. Sekiguchi, S. Matsuda, M. Takeuchi. N. Shiono, H. Anayama and A. Mario, Nucl. Instr. and Meth. B 104 (1995) 528.
[4] T. Nishijima, H. Sekiguchi, S. Matsuda and N. Shiono, these proceedings (ICN~TA-9~), Nucl. Instr. and Meth. B 130 0997) 557. [S] T. Hirao, T. Kamiya, T. Suds, I. Nashiyama, T. Nishijima, I. Naito, S. Matsuda, N. Shiono and M. Takeuchi, these proceedings (ICNMTA-96). Nucl. Instr. and Meth. B 130 (1997) 486.
(61 M.B.H. Breese, G.W. Grime and M. Dellith, Nucl. Instr. and Meth. B 77 (19931 332. [7] M.B.H. Breese, G.W. Grime and F. Watt, Nucl. Instr. and Meth. B 77 (1993) 301. [s] M.B.H. Breese, J. Appl. Phys. 74 (19931 3789.
X. ~ECT~ONICS
AND PHOT~NICS
--
__
Beam Interactions with Materials lk Atoms
~ ELSEVIER
Nuclear Instruments
and Methods in Physics Research 6 130 (1997) 528-533
Study of basic mechanisms of semiconductor devices using ion beam induced charge @3IC) collection T. Nishijima a**,H. Sekiguchi a, T. Hirao b, I. Nashiyama S. Matsuda ‘, N. Shiono d
b, N. Nemoto ‘,
” Electrotechnical Laborator?: Tsukuba-shi, Ibaraki. 305 Japan b Japan Atomic Energy Research Institute. Takasaki, Gunma, 3X-12 Jupun ’ National Space Deoelopment Agency of Japan, Tsukuba-shi, 305 Japan ’ Reliability Center for Electronic Components @Jupun. Chuoku. 103 Jupun
Abstract A change of wave form of current transients induced by a single heavy ion was investigated around a pn junction with 8 pm width and 10 pm length as a function of the ion incident position. Three pn junctions were made on a 3 hrn thick Si epilayer (1 x 10i6/cm3) grown on Si substrate and were in a line along an aluminum electrode with 10 pm spacing between the adjacent junctions. The elements of a pn junction array were irradiated with a I pm diameter 15 MeV C+ heavy ion microbeam spacing steps by 3 pm. At a bias voltage of - 10 V, 148, 91, and 54 fC were collected at the pn junction center, and at 3 pm and 4 pm from the edge of the electrode, respectively. Internal device structure was examined by IBIC (ion beam induced current) method by using a 2 MeV He + ion microbeam. From the IBIC spectrum and the IBIC image, the charge collected from the open space by the diffusion process was observed in addition to the charge collected from the depletion layer of the pn junction.
1. Introduction We have studied the basic mechanism of charge collection induced by high energy charged particles incident on semiconductor devices in order to obtain process-parameters to improve a resistance against a single event upset [l-4]. A change of the wave form of the current transient was investigated around a pn junction with 8 pm width and 10 urn length as a function of the ion incident position [5]. An element of pn junction array was irradiated wifh a 1 pm diameter 15 MeV C+ heavy ion microbeam spacing
Corresponding author. [email protected].
Fax:
+ 81
298
58
5695;
e-mail:
steps by 3 pm. At a bias voltage of - 10 V, 148, 91 and 54 fC were collected at the position of the pn junction, 3 pm and 4 pm apart from the edge of the electrode, respectively. The theoretically estimated value of the charge transient collected by the drift process is 50 fC from the depletion layer of the pn junction in this experimental condition [3]. Since there is no such a sensitive region for charge collection except pn junctions in this array, it is necessary to investigate another factor of a charge collection. Internal device structure was also examined by the IBIC method by using a 2 MeV He+ ion microbeam. In this paper test diode prep~ation, transient current induced by 15 MeV C+ ion measurement and IBIC measurement by 2 MeV He+ microbeam are described and discussed.
0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SO168-583X(97)00245-0
2. Experimental 2.1. Current surement
results and discussion
transient
thick Si epilayer (1 X 10r6/cm3) grown on a Si substrate and were in a line along an aluminum electrode with a 10 pm spacing between the adjacent junctions. A current transient induced by a single 15 MeV C’ ion was measured at several points by the wide bandwidth digitizing sampling oscilloscope described previously [2,3]. The C f ion beam was
induced by ion (CTII) mea-
Fig. 1 shows a schematic drawing of a Si three pn junction array prepared for this experiment. Three 8 pm X 10 pm pn junctions were made on a 3 pm
a)
, \
W
350,~~ m p>
Al Electrode 0.5 p m
Si02 lflm -\
Eh-Laver 3’pm N+ l~lO%-~,
\Back Contact Al 0.5 u m
Fig. 1. Circuit design of the Si pn junction
diode with three electrodes.
(a> Plane view; (b) cross sectional
view; t
X. ELECTRONICS
measurement
points.
AND PHOTONICS
moved in steps of 3 urn and five measuring points are illustrated in Fig. la. Points I, 2, 3, 4 and 5 correspond to 3 pm down from the central electrode edge, the electrode, 4 pm up from the central electrode (or 6 pm left from the upper electrode edge), 4 pm and 7 ym up from the upper electrode edge, respectively. In Fig, 2 three typical wave forms of the current transient selected from those measured at the abovementioned points are shown at bias voltage of - IO V. The wave form of the current transient measured at the electrode (point 2) has a rise time of 100 ps and a full width at half maximum (OHM) of 89 p.s. The pulse height of wave form 1 is one third of that of wave form 2. Its FWHM and decay time are 320 ps and 1200 ps, respectively. Wave form 3 is smaller than wave form 2 and its FWHM is 382 ps. Its decay time is longer than 1400 ps+ Current transients were measured to be 91, 148, 54 and 79 fC at points 1, 2, 3 and 4, respectively, by integra~ng the wave forms of transient currents from 0 to tSO0 ps and dividing by the specific system impedance of 50 0 [2,3], No current was observed at 7 pm up from the upper electrode ~m~asuring point 5).
Fig. 3 shows an IBXC!spectrum of the pn junction array measured with a 2 MeV He* microbeams [43. The microbeam diameter was measured to be 3.5 pm using a 100 pm diameter object slit. The microbeam scanning area was 80 pm X 80 pm. Beam intensity at the test diode was less than 2000 parti-
Fig. 2. Observed current transients induced by a 15 MeV C* ion for the pn junction diode with three electrodes. Bias voltage was - 10 V. (I) 3 pm down from the centnl electrode edge, (2) on the electrode and (3) 4 pm up from the central electrode
1000
ZQOO
Channels Fig. 3. Observed IBIC spectrumwith a 2.0
3000
4000
MeV He+ microbeam
for the pn junction diode with three electrodes.
cles,/s (0.3 fC> in consideration of the pile up of the pulse counting system and also of the radiation damage production during ion irradiation 161.The slit diameter used during this IBIC experiment was less than 20 pm. Bias voltage was - 10 V. Counts lower than 850 channel were discriminated by ADC to cut off electronic noise. In this experiment total counts for one fBIC spectrum were limited under 1OOOO (about IO counts/~m’}~ No radiation damage was, therefore, observed at this irradiation rate after several IBIC measurements on the same sample. The TBlC spectrum consists of a lower descending peak, a plateau, main peaks at the center, a plateau and a small peak, marked with A, B, C, D and E, respectively. Fig. 4 illustrates IBIC images drawn by IBIC spectrum of Fig, 3 coincide with a beam scanning signal, Figs. 4A, B, C, D and E correspond to windows A, B, C, D and E of the IBIC spectrum in Fig. 3 respectively. Fig. 4E shows that the three active regions are rectangular with a size of 7 pm X 10 pm each and with distances between two regions of 9.5 pm. These correspond quite well to the dimension of the pn junction electrode illustrated in Fig. la, This means that part E of the XBIC spectrum is the charge induced by the beam under the pn junction electrode and coltected from the depletion layer by a drift and a diffusion process. Fig. 4B shows three connected rings of 21.5 pm outer diameter and 17.5 pm inner diameter. In Fig. 4C, also, three rings with 17 pm outer diameter and 14.5 pm inner diameter are shown. Since the shapes of these rings did not change even if the bias voltage WAS changed from - 10 V to - 15 V, it is considered that
531
‘:
..
E Y
22
:-
I,-
B
A
t 4------
80um
A
182pm
-
:
t C
Fig. 5 Fig. 4. The IBIC images of the pn junction diode with three electrodes. Windows A, B, C, D and E correspond to regions A, B, C, D and E of Fig. 3, respectively. Beam scanning range was 80 pm X 80 pm. F is circuit design of the Si pn junction diode with three electrodes on the same scale as the IBIC images. Fig. 5. Measuring points (l)-(3) drawn by a whole IBIC current.
for the IBIC spectra and the IBIC image are put on the plane view of circuit design. The IBIC image is
X. ELECTRONICS
AND PHOTONICS
the charges induced outside the electrode were collected by a diffusion process. It seems that the observed ring shape instead of sharp rectangular electrode shape reflects the distribution of the potential of the electrode. In Fig. 4A one almost rectangular shape of area 57 pm X 22.5 pm was observed. Comparing Fig. 4A with Fig. 4B, it is seen that total area of the former expands slightly and the interior of the rectangular shape is filled with IBIC signals. An outer IBIC signal comes from the charge collected by the diffusion process. Distances between the electrodes and the boundary of the IBIC image show the maximum diffusion length of this sample. It seems that the middle of the IBIC image consists of charges detrapped from carrier traps. This phenomenon was also observed in the IBIC image of the GaAs Schottky diode made on the epilayer [4].
To confirm the above assignment of the diffusion process as the main charge collection mode of outer electrode, IBIC spectra of a Si pn junction diode were measured at the typical points of the pn junction diode. Fig. 5 shows a plane view of Si pn junction diode with three measuring points. A 2 pm X 20 pm Al electrode connected to a 50 pm diameter Al electrode was evaporated onto a 3 pm thick Si epilayer (4.85 X iO’5/cm3) grown on Si substrate (0.01 fi cm>. Fig. 6 shows IBIC spectra marked by I, 2 and 3 measured at the center of the electrode, 9 pm and 18 pm apart from the edge, respectively. I .X MeV He+ beam was scanned around 3 pm x 3 brn in order to reduce the radiation
damage. Channel numbers at the peaks of the spectra decreases with increasing distance from the electrode. Assuming the channel numbers of IBIC spectra are proportional to the numbers of electron-hole pairs created by incident ions and collected by the electrode, a diffusion length L = 20 pm is obtained from this experiment by a calculation on the basis of the diffusion equation [7,8].
3. Conclusion From the IBIC images corresponding to the IBIC spectra of the pn junction diode array, the collection process of the transient charge induced by high energy C’ ions are clearly assigned to either drift at the electrode or diffusion near the electrode. Using the IBIC spectra of Fig. 6, the carrier diffusion length was obtained to be L = 20 pm for the Si epilayer of minority carrier density 4.85 X 10”/cm3. On the contrary, both the transient current wave form and the IBIC spectrum were not observed at 7 pm up from the edge of the upper electrode (measuring point 5) of the pn junction diode array made on the Si epilayer (1 x 10”/cm3). Since the diffusion length of the epilayer is estimated to be less than 7 pm, this suggests that the minority carrier density exceeds 1 X 10”/cm3 during the pn junction fabrication procedure. The collected charge induced by high energy C+ ions at the middle of two electrodes (measuring point 3) was less than that measured at 4 Frn up from the upper electrode (measuring point 4). We cannot clearly understand the reason for this, but we add that we have measured the same tendency in preliminary measurements of the transient current induced by high energy O+ and Si+ ion beams.
References
2000
3000
4000
Channels Fig. 6. Observed IBIC spectrum for the Si pn junction diode.
with a 1.8 MeV He*
microbeam
[l] I. Nashiyama, T. Nishijima, H. Sekiguchi, Y. Shimano and T. Goka, Nucl. Instr. and Meth. B 54 (1991) 407. [2] I. Nashiyama, T. Hirao, T. Kamiya. H. Yutoh, T. Nishijima and H. Sekiguchi. IEEE Trans. Nucl. Sci. NS 40 (1993) 1935. [3] T. Nishijima, H. Sekiguchi, S. Matsuda, M. Takeuchi. N. Shiono, H. Anayama and A. Mario, Nucl. Instr. and Meth. B 104 (1995) 528.
[4] T. Nishijima, H. Sekiguchi, S. Matsuda and N. Shiono, these proceedings (ICN~TA-9~), Nucl. Instr. and Meth. B 130 0997) 557. [S] T. Hirao, T. Kamiya, T. Suds, I. Nashiyama, T. Nishijima, I. Naito, S. Matsuda, N. Shiono and M. Takeuchi, these proceedings (ICNMTA-96). Nucl. Instr. and Meth. B 130 (1997) 486.
(61 M.B.H. Breese, G.W. Grime and M. Dellith, Nucl. Instr. and Meth. B 77 (19931 332. [7] M.B.H. Breese, G.W. Grime and F. Watt, Nucl. Instr. and Meth. B 77 (1993) 301. [s] M.B.H. Breese, J. Appl. Phys. 74 (19931 3789.
X. ~ECT~ONICS
AND PHOT~NICS