Xafs as a Direct Local Structural Probe in Revealing the Effects of C Presence in B Diffusion in Sige Layers
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XAFS AS A DIRECT LOCAL STRUCTURAL PROBE IN REVEALING THE EFFECTS OF C PRESENCE IN B DIFFUSION IN SiGe LAYERS M. Alper Sahiner1, Parviz Ansari1, Malcolm S. Carroll2, Charles W. Magee3, Steven W. Novak3, Joseph C. Woicik4 1
Seton Hall University, Physics Department, South Orange, New Jersey 07079 Sandia National Laboratories, Albuquerque, New Mexico 87185 3 Evans East, East Windsor, New Jersey 08520 4 National Institute of Standards and Technology, Gaithersburg, Maryland 20899 2
ABSTRACT The local structural information around the germanium atom in boron doped SiGe alloys is important in understanding the dopant diffusion mechanisms. Epitaxial SiGe test structures with B and C markers were grown on Si substrates by using rapid thermal chemical vapor deposition (RTCVD). The local structure around the Ge atom was probed using Ge K-edge x-ray absorption fine structure spectroscopy (XAFS) to determine the effects of the B and C on the Ge sites. The concentration profiles obtained from secondary ion mass spectroscopy are correlated with the Ge XAFS results. The modifications on the local structure around the Ge atoms are revealed from the multiple scattering analyses on the Ge near-neighbors. First and second shell XAFS fits to the B doped SiGe samples indicate a direct evidence of the Ge trapping of the B atoms whereas the C is randomly distributed to the Si lattice sites. INTRODUCTION As the semiconductor device dimensions continue to shrink, the ultra narrow boron doped regions are needed for SiGe electronic devices. The goal is to keep the dopants within the SiGe layers. The transient enhanced diffusion (TED) of boron in SiGe samples is one of the most important challenges the semiconductor industry is currently facing in accomplishing this. Previously, it was shown that one of the effective methods to decrease boron diffusion is to incorporate carbon into the SiGe layers [1,2,3]. The observed decrease in the TED of boron in the presence of carbon has been explained as the undersaturation of the silicon self interstitials under carbon presence [4]. In order to understand the mechanisms that are important in B diffusion in SiGe layers, the local structural information is critical. In the presence of such atomic scale knowledge on the local structures, the attempts to reduce the boron diffusion will be much more directed and effective. One effective experimental tool capable of providing local structural information is XAFS. By tuning to the absorption edge of any specific atom in a cluster of atoms near-neighbor distances, coordination numbers, and the bond angles can be extracted and the structure of the cluster can be probed. XAFS analysis on the precipitates and clusters of ion implanted Si wafers led to specific and quantitative information on the type of the electrically inactive structures [5,6,7,8,9]. In Si1-xGex alloys also, XAFS proved to be a reliable quantitative tool in describing the local structure [10,11] and studying the strain introduced by the 4% lattice mismatch between the Si and the Ge [12,13].
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