Ozone Treatment on Nanoporous Ultralow Dielectric Materials to Optimize their Mechanical and Dielectrical Properties
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Ozone Treatment on Nanoporous Ultralow Dielectric Materials to Optimize their Mechanical and Dielectrical Properties
Il-Yong Kang, Bo-Ra Shin and Hee-Woo Rhee*
Department of Chemical & Biomolecular Engineering, Sogang University, South Korea ABSTRACT The continual miniaturization of microprocessors has resulted in increased RC delay and cross talk noise. To solve these problems ultralow nanoporous dielectric materials are required but have not developed yet. To develop ultralow dielectric materials with required mechanical and dielectrical properties for next generation semiconductors, it is essential to control the pore size in nm range and its morphology by preventing porogen aggregation. Thus we have used ozone treatment during thermal curing process of the nanoporous dielectrics in order to increase the reactivity between the matrix and reactive porogens and to possibly induced changes in Si bond structures. Ozone treatment was quite effective in enhancing the reactivity of the low-k matrix and the reactive porogen, which converted effectively the alkoxy or alkyl groups into Si-OH groups, which mostly converted to the formation of Si-O-Si network structures. Therefore, ozone treatment greatly increased modulus up to 11.25 GPa at the same porogen loading (60 vol%). The modulus increased by more than 23% compared with non-treated samples (9.1 GPa). The porosity of the ozone-treated sample reduced to 19.3 vol% at the same porogen loading. Solid state Si-NMR showed that less porosity was related to the breakage of methyl groups in the matrix by ozone irradiation, which also resulted in a little sacrificed dielectric constant. In general, the mechanical properties of nanoporous dielectrics deteriorate sharply above certain high porosity ca. 15 ~20 vol% due to non-uniform distribution of nanopores, their aggregation and resultant open pores. Therefore, this result may suggest the possibility of increasing mechanical properties of nanoporous dielectrics. However, we need to experimentally control processing variables such as irradiation time, intensity, temperature and so forth in order to optimize both mechanical and dielectrical properties. INTRODUCTION Low dielectric materials (low-k) have been used as interlayer dielectrics in Cu microprocessors over the years. However, the delayed development of ultralow dielectrics has forced to modify the ITRS roadmap for the dielectrics every year. The main problem with nanoporous ultralow dielectrics is due to their low mechanical properties by the introduction of pores into low-k materials. Therefore, it is very important to find ways to increase the mechanical properties without sacrifice of dielectrical properties. In order to optimize both properties we use ozone during thermal curing of ultralow dielectrics. Since the ozone was quite effective to produce Si-OH groups from alkoxy or alkyl groups in the organosilicates, which will improve the compatibility between matrices and
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porogen (pore-generating material). The improved compatibility will help to uniformly dist
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