The Preparation And Properties Of Low Dielectric Constant-nanoporous Silica Films Based On POSS

With the rapid development of the ultra-large-scale integration(ULSI). continuing increase in device density has markedly made the feature size of integrated circuit(IC) device continue to decrease. As feature size approach beyond submicron, the resistance-capacity (RC) delay, cross-talking and power dissipation of the interconnect structure become limiting factors for the overall performance of integrated system. In order to improve circuit performance, new materials with low dielectric constant and excellent properties are required to replace the traditional silicon dioxide(k=4.0) as interlayer dielectrics. According to the International Technology Roadmap for Semiconductors(ITRS 2005), nano-electronic times with 32 nm of wiring dimension may appear in 2013. Ultra-low-dielectric-constant materials (k<2.0) should be achieved for the insulator between interconnect. However, ultra-(?)-k materials which satisfy the requirement of ULSI fabrication have not emerged so far. Therefore, ultra-low-k materials are extremely important in the current microelectronic industry. This dissertation is devoted to the exploration and investigation of the design and preparation of novel ultra-low-k materials. The major contents are as follows:(1) The recent development of low-k materials was systematically reviewed. Based on the existing problems in research and application, the contents of our research were put forward.(2) A POSS molecule (T8H8) with multiple functional groups and three diene monomers which contain different structures with olefin bond in the molecular end were designed and synthesized. Their structures were characterized by FT-IR. 'H-NMR and 13C-NMR. The thermodynamic properties and liquid crystalline characters of three diene monomers were analyzed by DSC and POM. The results showed that two of them exhibited nematic phase with high thermal stability. But the other one showed us nothing because of the effect of alkyl chain. This work paves the way for designing new functional liquid crystalline polymers. (3) Three organic-inorganic hybrid polymers based on POSS were prepared via hydrosilylative addition reaction between octahydridosilsesquioxane (T8H8) and linear dienes with rigid liquid crystalline mesogenic unit, and the synthetic conditions were optimized and their structures were characterized by FTIR,29Si-NMR. The results confirmed that the hybrid polymers with POSS cages uniformly dispersed in the networks were successfully synthesized.(4) The TGA results showed that three hybrid polymers have good thermal stability. The Tds increase with increasing the rigidity of linking chains between POSS cages, and the thermal properties are affected by molecular cross-linking density.(5) AFM and SEM observation shows that the surfaces of the hybrid polymer films are smooth and free of cracks or flaws at multiple magnifying scale, indicating that the synthesized hybrids have good film formability. No crystalline peaks appearing on the XRD spectra showed that POSS cages were well dispersed in the polymeric matrix and no POSS aggregation occurred.(6) The mechanical properties of the hybrid polymer films were measured using a nanoindenter (Hysitron Tribolndenter) with a Berkowich diamond tip. All the three films show good mechanical properties with their hardness around 0.13-0.20 GPa and elastic modulus in the range of 5.37～8.08 GPa. Both hardness and elastic modulus increase with increasing the rigidity of linking chains between POSS cages.(7) Nanoporous silica films based on POSS were prepared via oxidation-decomposition process. HRTEM observation and BET characterization show that porous silica films had evenly dispersed nanopores with 23～88 nm in pore diameter, 307-612m2/g of surface area and 0.03～0.37 cm3/g of pore volume.By changing the length and rigidity of organic linking chain in the hybrids, porous silica films with various porosities can be achieved.(8) The contact angle tests showed that three hybrid polymer films had contact angles bigger than 100°, standing for considerable hydrophobic property. The moisture adsorption of films decreases with increasing the rigidity of linking chains between POSS cages.(9) The electrical properties of nanoporous films were analyzed by variable-angle spectroscopic ellipsometry. The results show that porous films had low dielectric constant values around 1.69-2.10.The porosity of films had much influence on dielectric constants, which showed an obvious decreasing trend with increasing porosities.