JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構
JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構
JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構
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1-03<br />
Evaluation of Soft Error Rates in SOI SRAM with<br />
a Technology Node of 90 nm Using Oxygen Ion Probe<br />
S. Abo a) , N. Masuda a) , F. Wakaya a) , S. Onoda b) , T. Makino b) , T. Hirao b) ,<br />
T. Ohshima b) , T. Iwamatsu c) , H. Oda c) and M. Takai a)<br />
a) Center for Quantum Science and Technology under Extreme Conditions, Osaka University,<br />
b) Environment and Industrial Materials Research Division, QuBS, <strong>JAEA</strong>,<br />
c) Advanced Device Development Department, Renesas Technology Corporation<br />
A soft error or bitstate upset due to the excess charge<br />
carriers generated by high energy incident particles becomes<br />
a serious problem in advanced semiconductor devices. A<br />
silicon-on-insulator (SOI) device has an advantage over the<br />
conventional bulk device for the soft error, in which a<br />
device region is insulated from the silicon substrate by a<br />
buried oxide (BOX) layer and the excess charge carriers in<br />
the silicon substrate are not accumulated to the drain<br />
electrode. However, the generated excess carriers in a SOI<br />
body are kept at the channel region in the SOI body or<br />
accumulated to the drain and source electrodes. The<br />
generated holes in the channel region of an n-channel SOI<br />
metal oxide semiconductor field effect transistor (MOSFET)<br />
increase the SOI body potential, which results in a floating<br />
body effect and the soft error. The floating body effect can<br />
be suppressed by a body-tie structure, in which the SOI<br />
body regions are connected to the source electrode. The<br />
body electrode subtracts the generated excess carriers from<br />
the channel region and suppresses the floating body effect.<br />
In this study, the difference in soft error rates (SERs) of<br />
SOI SRAM with a technology node of 90 nm was<br />
investigated by oxygen ion probes with energies ranging<br />
from 9.0 to 18.0 MeV. The memory cell included 4<br />
n-MOSFETs sand 2 p-MOSFETs. The memory cell size,<br />
the memory capacity and the critical charge of SOI SRAM<br />
were 1.25 m 2 , 8 Mbits and 1.8 fC, respectively. The<br />
thicknesses of the SOI body and the BOX layer were 75 and<br />
145 nm. The over-layers were 4 copper metal and<br />
polyimide passivation layers without top plastic mould.<br />
The body-tie structure was used for suppressing the floating<br />
body effect. The amount of soft error in SRAM was<br />
monitored after oxygen ion probe irradiation. The dose<br />
Normalized SER<br />
2.0<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
8 10 12 14 16 18<br />
Energy (MeV)<br />
Fig. 1 SERs as a function of oxygen ion energy for the<br />
SOI SRAMs. The values of SER were normalized to<br />
the error bits by 12 MeV oxygen ion irradiation.<br />
<strong>JAEA</strong>-<strong>Review</strong> <strong>2010</strong>-065<br />
- 7 -<br />
rates of oxygen probes for each of the energies were<br />
monitored by a solid state detector before irradiation. The<br />
minimum and maximum dose rates were 50 and 930 cps.<br />
The beam spot sizes were less than 1 m. The scanned<br />
areas were calculated from secondary electron images.<br />
The minimum and maximum scanned areas were 220 ×<br />
187 m 2 and 327 × 275 m 2 , respectively. The irradiation<br />
time was adjusted for less than 1 oxygen ion hit to 1 SRAM<br />
cell from the dose rate and the scanned area.<br />
Figure 1 shows SERs as a function of oxygen ion energy<br />
in SOI SRAM. The values of SER were normalized to the<br />
error bits for those by 12 MeV oxygen ion irradiation. No<br />
soft error occurred in SOI SRAM with oxygen ion energies<br />
of less than 10.0 MeV. This indicates that the oxygen ions<br />
with energies of less than 10.0 MeV were shielded by the<br />
over-layers of MOSFET. Soft error rates started to<br />
increase at 10.5 MeV and gradually saturated with energies<br />
above 13.5 MeV. Figure 2 shows the generated charge in<br />
the SOI body in SOI SRAM as a function of oxygen ion<br />
energy simulated by SRIM code. The energy loss through<br />
the over-layers was corrected by the designed thickness.<br />
The oxygen ions with energies less than 12.5 MeV<br />
generated less excess charge carriers than the critical charge.<br />
Therefore the soft error in SOI SRAM by oxygen ion<br />
irradiation with energies at end below 12.5 MeV shown in<br />
Fig. 1 occurred by the floating body effect due to the<br />
generated excess charge carriers in the channel regions.<br />
The oxygen ions with energies at end above 13.0 MeV<br />
generated more excess charge carriers than the critical<br />
charge, in which the soft error was induced by both the<br />
floating body effect and these excess carriers at the storage<br />
nodes.<br />
Generated Charge in SOI Body (fC)<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
0<br />
8 10 12 14 16 18<br />
Energy (MeV)<br />
Fig. 2 Generated charge in the SOI body as a function<br />
of oxygen ion energy in the SOI SRAM.