Influence of He implantation conditions on strain relaxation and threading dislocation density in Si 0.8 Ge 0.2 virtual
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B8.2.1
Influence of He implantation conditions on strain relaxation and threading dislocation density in Si0.8Ge0.2 virtual substrates J. Caia, P. M. Mooneya, S. H. Christiansena*, H. Chenb, J. O. Chua, and J. A. Otta IBM Research and Development Center, a T. J. Watson Research Center, Yorktown Heights, NY, USA b Microelectronics Division, Hopewell Junction, NY, USA *Present address: MPI-Mikrostrukturphysik, Halle, Germany. ABSTRACT The strain relaxation and threading dislocation density of He-implanted and annealed SiGe/Si heterostructures have been studied. For He doses above a threshold of 8x1015 cm-2, the degree of strain relaxation depends primarily on the SiGe layer thickness; a similar degree of strain relaxation is obtained when the He dose and energy are varied over a relatively wide range. In contrast, the threading dislocation density is strongly influenced by the implantation depth. There is a strong correlation between the parameter He(SiGe), the He dose in the SiGe layer calculated from He profiles simulated using the program Stopping and Range of Ions in Matter (SRIM), and the threading dislocation density. We find that to achieve a low threading dislocation density, 70%) is achieved only when the SiGe thickness is >200 nm. The scatter in the data is due to a variation of the SiGe layer thickness across the wafer. The degree of strain relaxation was found to be the same for annealing at both 800 and 850 oC and for times of 12-60 minutes. Comparing with pieces of the wafer that were not implanted but were annealed under the same conditions, He implantation before annealing greatly enhances the strain relaxation, even for the thickest SiGe layers. Clearly the degree of strain relaxation is the same for samples grown by both methods. For doses of 8x1015 cm-2 and higher, the degree of strain relaxation was found to depend primarily on the SiGe layer thickness and was relatively insensitive to the implantation dose or the energy.
% Strain Relaxation
100
UHVCVD-200 (■□) RTCVD -200 (●○) RTCVD-300 (▲ ∆)
80 60 40 20 0 0
100
200
300
400
SiGe Layer Thickness (nm)
500
Figure 1. Strain relaxation of Si0.8Ge0.2 layers grown in three different reactors. Open symbols are areas of the wafer that were not implanted. Solid symbols are areas that were implanted with 1x1016 cm-2 He at a depth of 140-200 nm below the SiGe/Si interface.
B8.2.3
We have also studied the effect of layer thickness and implantation conditions on the threading dislocation density in SiGe layers. In order to compare results from layers with different thickness and implantation conditions, we introduce here a composite parameter, the amount of He in the SiGe layer, He(SiGe), defined as the integral of the He profile over the SiGe t layer thickness, i.e., ∫ [ He]dx . Fig. 2 shows the threading dislocation density plotted against 0
-2
Threads density (cm )
He(SiGe) for both UHVCVD-and RTCVD-grown Si0.8Ge0.2 layers. The threading dislocation density increases strongly with He(SiGe). When the value of He(SiGe) increases by one order o
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