Buried oxide layers formed by low-dose oxygen implantation
- PDF / 493,661 Bytes
- 3 Pages / 612 x 828 pts Page_size
- 78 Downloads / 198 Views
The structure of buried oxide layers formed by low-dose 16 O + implantation of 0.4 and 0.7 x 1018 cm"2 at 180 keV and by subsequent annealing in the temperature range of 1150 to 1350 °C has been investigated using cross-sectional transmission electron microscopy (XTEM). At a dose of 0.4 x 1018 cm"2, an 80-nm continuous uniform buried oxide layer having a breakdown voltage of approximately 40 V is formed after annealing at 1350 °C. At a dose of 0.7 x 1018 cm"2, multiple buried oxide layers having Si islands between them are formed at an anneal temperature of 1150 °C. The number of multiple layers is reduced as the annealing temperature increases, but the Si islands do not dissolve even after annealing at 1350 °C. The existence of the Si islands causes the breakdown voltage to fall to 0 V despite the higher dose.
SIMOX1 has come to be regarded as one of the most promising silicon-on-insulator technologies.2 SIMOX wafers generally have dislocation densities of 10 8 -10 9 cm"2 for standard oxygen doses of 1.8-2.0 x 1018 cm"2. The high dislocation density is considered a significant issue for ULSI applications of SIMOX technology. Recently, the authors have reported high-quality SIMOX wafers with an extremely low dislocation density on the order of 102 cm"2 by relatively low-dose implantation (£1.2 x 1018 cm"2) and hightemperature annealing (>1300 °C). 3 In the relatively low-dose region, the breakdown voltage of the buried oxide layers for 1350 °C-annealed wafers is found to show an unexpected dose-dependence.3 In this paper, the relationship between the structure of SIMOX wafers and the annealing temperature is investigated. The unexpected dose-dependence of the breakdown voltage is found to derive from the buried oxide layer formation mechanism during post-implantation annealing. Oxygen ions (16O+) were implanted into 100 mm (100) Si wafers at an acceleration energy of 180 keV with doses of 0.4 and 0.7 x 1018 cm"2. The wafer temperature during implantation was kept at 550 °C to promote self-annealing.4'5 The implanted wafers were annealed in the temperature range of 1150 to 1350 °C in an A r - O 2 gas mixture. The annealing time was fixed at 4 h to clarify the effect of annealing temperature on the structure of the SIMOX wafers. The structure of the SIMOX wafers was investigated using XTEM. Figure 1 shows the relationship between the breakdown voltage of the buried oxide layer and the oxygen dose.3 Annealing was performed at 1350 °C. For wafers implanted with doses lower than 0.2 x 1018 cm"2, the breakdown voltage is 0 V because no buried oxide layer is formed. The breakdown voltage of the buried 788
http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 4, Apr 1992
Downloaded: 18 Mar 2015
oxide layer is approximately 40 V with a dose of 0.4 x 1018 cm"2, and falls to 0 V despite a higher dose range of 0.5 to 0.7 x 1018 cm"2. With doses higher than
1.0 l6 +
0
2.0 l8
2
dose (xio cnf )
FIG. 1. Relationship between the breakdown voltage of the buried oxide layer and the oxygen dose. Oxygen ions were implant
Data Loading...
