JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Heavy-ion Induced Current in SOI p + n Junction Diode
Y. Takahashi a) , A. Ohwaki a) , H. Takeyasu a) ,
T. Hirao b) , S. Onoda b) and T. Ohshima b)
a) Nihon University, b) Environment and Industrial Materials Research Division, QuBS, JAEA
One of the most detrimental effects on semiconductor
devices in radiation environments is the single-event effect
(SEE). Recently, silicon-on-insulator (SOI) technology
has been developed to reduce SEE, because it was believed
that the charge collection is suppressed by the existence of a
buried oxide (BOX) layer 1) . However, anomalous charge
2)
collection through the BOX layer was also reported . So
it is important to clarify the charge collection mechanism
through the oxide layer. In the present work, we have
investigated the heavy-ion induced transient gate currents in
MOS structures and we concluded that the transient current
through an oxide layer is dominated by a displacement
current 3) . In this study, the heavy-ion induced transient
current in SOI p + n junction diode was investigated, in order
to discuss the features of transient current in SOI devices.
The Al gate p + n junction diodes with the junction area of
100 µm in diameter were fabricated on a SOI substrate as
shown in Fig. 1. The donor concentration of each silicon
layer is about 10 15 cm -3 and the thicknesses of active SOI
layer and BOX layer are 1.5 µm and 0.3 µm, respectively.
The transient currents in diodes induced by 15 MeV
Oxygen ions were measured. The LETs and project range
of the ions are 6.5 MeV/(mg/cm 2 ) and 12.3 µm, respectively.
Heavy-ion irradiation tests were carried out using the Single
Ion hit (SIH) system in JAEA and the transient current
caused by the single ion was measured by Transient Ion
Beam Induced Current (TIBIC) measurement system.
Figure 2 shows the transient current and the total
collected charge, the integration value along a time after
irradiation, of each electrode in the device, in which the
reverse bias of 10 V is applied during irradiation test. The
peak height of the current signal of p + electrode, anode
electrode, is 24 µA and the maximum collected charge is
230 fC. These values correspond to 1/20 and 1/3 of the
4)
diode fabricated on bulk Si substrate, respectively . These
results indicate that the SEE effects can be reduced using
the SOI devices. On the other hand, the current of n +
electrode, cathode electrode, is almost 0 and the amount of
collected charge of back electrode is almost the same as that
of anode electrode. These results show that the charges
collected by anode electrode were mostly caused by the
radiation induced generated charges in handle Si substrate
and these charges were collected through the BOX layer as
a displacement current. So it is important to reduce the
displacement current in order to suppress the SEE effects of
SOI device.
It is considered that the displacement current can be
reduced by decrease the width of depletion layer at the
surface of handle Si substrate. We evaluated the heavy-ion
JAEA-Review 2010-065
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induced current in SOI p + n diodes using device simulation.
By the results of simulation, it was found that the width of
depletion layer was changed by the impurity concentration
of the handle Si substrate and the collected charge could be
reduced using the handle Si substrate with low resistivity.
References
1) O. Musseau, IEEE Trans. Nucl. Sci., NS-43, 2 (1996)
603-613.
2) T. Hirao et al., Nucl. Instrum. Meth. Phys. Res., B-206
(2003) 457-461.
3) Y. Takahashi et al., Nucl. Instrum. Meth. Phys. Res., B-
260 (2007) 309-313.
4) Y. Takahashi, Abst. 4th Takasaki Adv. Radiat. Res.
Symp. (2009) 41.
Fig. 1 Device structure of SOI p + n junction diode.
Fig. 2 Transient current and total collected charge
in a SOI p + n junction diode. Solid lines show
the current and dashed lines show the amount of
collected charges.