Electrical, Mechanical, and Structural Properties of Fluoro-Containing Poly(silsesquioxanes) Based Porous Low k Thin Fil
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Electrical, Mechanical, and Structural Properties of Fluoro-Containing Poly(silsesquioxanes) Based Porous Low k Thin Films Jingyu Hyeon-Lee, Jihoon Rhee, Jungbae Kim, Jin-Heong Yim, Seok Chang Electronic Materials Laboratory, Samsung Advanced Institute of Technology, Suwon, 440-600, Korea ABSTRACT Low dielectric fluoro-containing poly(silsesquioxanes) (PSSQs) have been synthesized using trifluoropropyl trimethoxysilane (TFPTMS), methyl trimethoxysilane (MTMS), and 2, 4, 6, 8-tetramethyl-2, 4, 6, 8-tetra(trimethoxysilylethyl) cyclotetrasiloxane. The properties of fluorocontaining PSSQs based thin films were studied by electrical, mechanical, and structural characterization. Film was spun on a silicon substrate, baked at 150 oC and 250 oC for 1 minute, respectively, and cured in the furnace at 420 oC for 1 hour under vacuum condition. Thermally decomposable trifluoropropyl groups of the fluoro-containing PSSQ were served as a pore generator and partially contributed to lower a dielectric constant. β-cyclodextrin (CD) was also employed as a pore generator. The concentration of the pore generator in the film was varied from 0 to 30 %. The dielectric constants of the porous PSSQ films were found to be in the range of 2.7 – 1.9 (at 100 kHz). Hardness and Young’s modulus of the films were measured by nano-indentation. The elastic modulus and hardness of the porous films were well correlated with the concentration of the pore generators. Positronium Annihilation Lifetime Spectroscopy (PALS) was employed to characterize a pore size of the porous fluoro-containing PSSQ film. The pore size of the film was less than 2.2 nm. The nanoporous films showed quite promising properties for commercial application. INTRODUCTION New materials with low dielectric constants are demanded to solve the problem of RC delay in the integrated circuit as the minimum geometry of microelectronic devices continues to shrink [1, 2]. For last a couple of years, there have been significant advances in materials giving the dielectric constant of 2.2. However, the materials show some limitations in mechanical strength, moisture uptake, and thermal instability for practical uses. Poly(silsesquioxanes) (PSSQs) have been extensively studied because of their excellent thermal, mechanical, and electrical properties, and an easy application of the spin-on glass (SOG) process [3]. PSSQ containing methyl groups, polymethylsilsesquioxane (PMSSQ), is hydrophobic compared with silica and thus has minimal moisture absorption. Based on the PSSQ, siloxane unit in the polymer backbone is employed to improve toughness of the inorganic matrix. PSSQ has a dielectric constant of ca. 2.7-2.9. In order to reduce a dielectric constant,
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CD was chosen as a thermally labile pore generator (porogen). A trifluoropropyl group of th
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