Investigation and Modeling of Fluorine Co-Implantation Effects on Dopant Redistribution
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D6.15.1
Investigation and modeling of fluorine co-implantation effects on dopant redistribution M. Diebel1,2 , S. Chakravarthi2 , S.T. Dunham3 , C.F. Machala2 , S. Ekbote2 , A. Jain2 Department of Physics, Univ. of Washington, Seattle, WA 98195-1560, USA 2 Silicon Technology Development, Texas Instruments, Dallas, TX 75243, USA 3 Department of Electrical Engineering, Univ. of Washington, Seattle, WA 98195-2500, USA 1
ABSTRACT A comprehensive model is developed from ab-initio calculations to understand the effects of co-implanted fluorine (F) on boron (B) and phosphorus (P) under sub-amorphizing and amorphizing conditions. The depth of the amorphous-crystalline interface and the implant depth of F are the key parameters to understand the interactions. Under sub-amorphizing conditions, B and P diffusion are enhanced, in contrast to amorphized regions where the model predicts retarded diffusion. This analysis predicts the F effect on B and P to be entirely due to interactions of F with point-defects. INTRODUCTION As ULSI devices enter the nanoscale, ultra-shallow junctions become necessary. Reduction in transient enhanced diffusion (TED) and enhanced dopant activation are desired. Experimentally, co-implanted F has been shown to reduce B and P TED [2, 3, 4, 5, 6] as well as enhance B activation [2, 3]. However, to utilize these benefits effectively, a fundamental understanding of the F behavior is necessary, particularly since implanted F has been observed to behave unusually in silicon, manifesting an apparent uphill diffusion [1]. Also we find that depending on the implant conditions F can actually enhance B diffusion (see Fig. 4 (right)). This paper focuses on the effects of co-implanted F on dopant redistribution. Previously reported ab-initio calculation results [7] were used to develop a comprehensive model to analyze and explain the effects of co-implanted F on B and P redistribution under various implant conditions. MODEL Theoretically, F can affect B and P diffusion in at least two distinct ways. A direct interaction could explain the reported F effects if there is a large binding energy between dopant and F atoms. The second possibility is an indirect interaction. If F interacts strongly with point-defects, it alters the local point-defect concentrations, changing the point-defect mediated diffusion behavior of B and P. Ab-initio calculations find only about 1eV binding for dopant-fluorine complexes (B-F and P-F), which is insufficient to significantly influence diffusion behavior [8]. In contrast, strongly bound fluorine vacancy clusters (Fn Vm ) were identified [7]. This suggests that the effects of F on B and P are primarily due to fluorine point-defect interactions. In this case, it is expected that once the anomalous F diffusion is understood, the same model should also explain the effects on B and P.
D6.15.2
Retardation
FV FV2 F2V F3V F6V2
0.8
Enhancement
Concentration
Fluorine in FnVm/Total Fluorine
1
0.6
0.4
B or P
I 0.2
F3V a/c
0 -1 10
10
0
1
10 Time [s]
10
2
10
3
Depth
Figure 1: Left: Simulated fluorine d
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