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

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Evaluation of Soft Error Rates in SOI SRAM with
a Technology Node of 90 nm Using Oxygen Ion Probe
S. Abo a) , N. Masuda a) , F. Wakaya a) , S. Onoda b) , T. Makino b) , T. Hirao b) ,
T. Ohshima b) , T. Iwamatsu c) , H. Oda c) and M. Takai a)
a) Center for Quantum Science and Technology under Extreme Conditions, Osaka University,
b) Environment and Industrial Materials Research Division, QuBS, JAEA,
c) Advanced Device Development Department, Renesas Technology Corporation
A soft error or bitstate upset due to the excess charge
carriers generated by high energy incident particles becomes
a serious problem in advanced semiconductor devices. A
silicon-on-insulator (SOI) device has an advantage over the
conventional bulk device for the soft error, in which a
device region is insulated from the silicon substrate by a
buried oxide (BOX) layer and the excess charge carriers in
the silicon substrate are not accumulated to the drain
electrode. However, the generated excess carriers in a SOI
body are kept at the channel region in the SOI body or
accumulated to the drain and source electrodes. The
generated holes in the channel region of an n-channel SOI
metal oxide semiconductor field effect transistor (MOSFET)
increase the SOI body potential, which results in a floating
body effect and the soft error. The floating body effect can
be suppressed by a body-tie structure, in which the SOI
body regions are connected to the source electrode. The
body electrode subtracts the generated excess carriers from
the channel region and suppresses the floating body effect.
In this study, the difference in soft error rates (SERs) of
SOI SRAM with a technology node of 90 nm was
investigated by oxygen ion probes with energies ranging
from 9.0 to 18.0 MeV. The memory cell included 4
n-MOSFETs sand 2 p-MOSFETs. The memory cell size,
the memory capacity and the critical charge of SOI SRAM
were 1.25 m 2 , 8 Mbits and 1.8 fC, respectively. The
thicknesses of the SOI body and the BOX layer were 75 and
145 nm. The over-layers were 4 copper metal and
polyimide passivation layers without top plastic mould.
The body-tie structure was used for suppressing the floating
body effect. The amount of soft error in SRAM was
monitored after oxygen ion probe irradiation. The dose
Normalized SER
2.0
1.5
1.0
0.5
0.0
8 10 12 14 16 18
Energy (MeV)
Fig. 1 SERs as a function of oxygen ion energy for the
SOI SRAMs. The values of SER were normalized to
the error bits by 12 MeV oxygen ion irradiation.
JAEA-Review 2010-065
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rates of oxygen probes for each of the energies were
monitored by a solid state detector before irradiation. The
minimum and maximum dose rates were 50 and 930 cps.
The beam spot sizes were less than 1 m. The scanned
areas were calculated from secondary electron images.
The minimum and maximum scanned areas were 220 ×
187 m 2 and 327 × 275 m 2 , respectively. The irradiation
time was adjusted for less than 1 oxygen ion hit to 1 SRAM
cell from the dose rate and the scanned area.
Figure 1 shows SERs as a function of oxygen ion energy
in SOI SRAM. The values of SER were normalized to the
error bits for those by 12 MeV oxygen ion irradiation. No
soft error occurred in SOI SRAM with oxygen ion energies
of less than 10.0 MeV. This indicates that the oxygen ions
with energies of less than 10.0 MeV were shielded by the
over-layers of MOSFET. Soft error rates started to
increase at 10.5 MeV and gradually saturated with energies
above 13.5 MeV. Figure 2 shows the generated charge in
the SOI body in SOI SRAM as a function of oxygen ion
energy simulated by SRIM code. The energy loss through
the over-layers was corrected by the designed thickness.
The oxygen ions with energies less than 12.5 MeV
generated less excess charge carriers than the critical charge.
Therefore the soft error in SOI SRAM by oxygen ion
irradiation with energies at end below 12.5 MeV shown in
Fig. 1 occurred by the floating body effect due to the
generated excess charge carriers in the channel regions.
The oxygen ions with energies at end above 13.0 MeV
generated more excess charge carriers than the critical
charge, in which the soft error was induced by both the
floating body effect and these excess carriers at the storage
nodes.
Generated Charge in SOI Body (fC)
6
5
4
3
2
1
0
8 10 12 14 16 18
Energy (MeV)
Fig. 2 Generated charge in the SOI body as a function
of oxygen ion energy in the SOI SRAM.