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B3.4.1

Determining Pore Structure and Growth Mechanisms in Templated Nanoporous Low-k Films Hua-Gen Peng, Richard S. Vallery, Ming Liu, William E. Frieze, David W. Gidley, 1JinHeong Yim, 2Hyun-Dam Jeong and 2Jongmin Kim Physics Department, University of Michigan, Ann Arbor, MI 48109-1040 1 Division of Advanced Materials Engineering, Kongju National University, 182, Sinkwan-dong, Kongju City, Chungnam, 314-701, Korea 2 Materials Lab., Samsung Advanced Institute of Technology (SAIT), San 14-1, Nongseori, Kiheung-eup, Yongin-shi, Kyungki-do, 449-712, Korea ABSTRACT Templating is one of the most popular methods for generating nanocomposite and nanoporous films and the resultant pore size and pore interconnection length depend strongly on porogen concentration/porosity among other factors. Positronium Annihilation Lifetime Spectroscopy (PALS) analysis has been performed on a series of films produced using increasing concentrations of a type of cyclodextrin (CD) porogen in a modified silsesquioxane host matrix. PALS reveals the relationship between the resulting pore structure (both size and interconnection length) and porosity, which can be used to deduce pore shape. At low porogen concentration, isolated pores are resolved, but the pore size is consistent with a cluster of two or three CD molecules, rather than an individual one. As the porosity increases, the aggregation of the porogen domains appears to be more 3-dimensional (pseudo-random) with gradual increase in pore size. Computer simulations using a random pore growth model show consistent trends for pore size growth, but the agreement is poor for interconnection length. It is a key demonstration of the usefulness of PALS in untangling the fundamental pore structure and its evolution in porosity. PALS characterization of porosity provides novel feedback in the understanding and design of nanoporous materials. INTRODUCTION The ever-increasing speed of computer chips requires the implementation of nanoporous ultra-low dielectric constant (low-k) films as the interlayer dielectric in future generations of microprocessors [1]. A common pore generation scheme in spin-on dielectrics involves spin-coating a solution of the low-k matrix precursor and an unstable pore generator (porogen) such as an organic compound. The film thus formed is then cured (thermal, e-beam or UV) to vitrify the matrix and decompose the porogen to leave pores behind [2]. Introducing porosity into the low-k films will reduce the line-to-line resistance-capacitance delay. However, the processing vulnerability of a porous structure has presented a great challenge for integration of such materials [3], and thus tremendous efforts are being made to create a desirable pore structure that is compatible with the microchip fabrication process. To this end, the fundamental mechanism of the pore formation process needs to be understood, e.g. how the pore size, distribution and interconnectivity are determined from film preparation.

B3.4.2

Studying the pore structure evolution with increasing porogen co