The Role of Pore Characterization in the Challenge to Integrate Porous low-k Dielectrics
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The Role of Pore Characterization in the Challenge to Integrate Porous low-k Dielectrics David W. Gidley, Richard S. Vallery, and Ming Liu Physics, University of Michigan, Ann Arbor, MI, 48109-1040 Beam-based positron annihilation lifetime spectroscopy (PALS) is a powerful porosimetry technique with broad applicability in characterizing nanoporous thin film dielectrics. Pore sizes and distributions in the 0.3 ñ 30 nm range are non-destructively determined with only the implantation of low energy positrons from a table-top beam. The implantation of positrons to capture an electron to form positronium (Ps), its trapping and subsequent annihilation is depicted in figure 1. The lifetime(s) of Ps determines pore size and distribution. Diffusion of Ps through a network of pores is related to the pore interconnection length. Depth-profiling with PALS (by controlling the positron implantation energy) has proven to be an ideal way to measure the interconnection length of pores, search for depth-dependent inhomogeneities or damage in the pore structure, and to explore porosity hidden Figure 1. Schematic view of Ps beneath dense layers or diffusion barriers. References [1] and trapping in closed and open pores [2] provide recent reviews of using PALS to probe porous thin films. As the need for ultra-low k dielectrics (k
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