A novel scalable low dielectric constant (low-k) film technology was developed by use of self-assembled porous silica. Non-periodic disordered porous silica film structure was formed on a Si wafer by spin-coating a precursor solution with micelles of surfactant and a silica oligomer. Polyoxyethylene-polyoxypropylene-polyoxyethylene (EOPOEO) triblock copolymers and tetraethyl orthosilicate (TEOS) were used as a surfactant and a silica oligomer, respectively. A novel tetramethylcyclotetrasiloxyane (TMCTS) vapor treatment process was developed to reinforce mechanical properties of the porous silica film and to recover process-induced damages. New copper (Cu) electroplating solution and post cleaning process of chemical mechanical polishing (CMP) were developed to improve leakage current characteristics and dielectric constant of the porous silica low-k film. Cu/porous silica low-k damascene structures were fabricated and their characteristics were investigated.
We have developed sol-gel self-assembly techniques to control the pore structure and diameter of ultra-low-k interlayer dielectric (ILD) films. Porous silica films have been fabricated using cationic and nonionic surfactants as templates, resulting in 2D-hexagonal and disordered pore structures, respectively. The disordered mesoporous silica film has a worm-hole like network of pore channels having a uniform diameter. Precursors of the mesoporous silica films were synthesized by use of tetraethyl-orthosilicate (TEOS), inorganic acid, water, ethanol and various surfactants. The surfactants used were cationic alkyltrimethyl-ammonium (ATMA) chloride surfactants for 2D-hexagonal pores and nonionic tri-block copolymer for disordered structures. Dimethyldiethoxysilane (DMDEOS) was added for forming the disordered mesoporous silica. The disordered cylindrical pore structure with a uniform pore size was fabricated by controlling the static electrical interaction between the surfactant and the silica oligomer with methyl group of DMDEOS.
Tetramethylcycrotetrasiloxane (TMCTS) vapor treatment was developed, which improved the mechanical strength of mesoporous silica films. The TMCTS polymer covered the pore wall surface and cross-linked to passivate the mechanical defects in the silica wall. Significant enhancement of mechanical strength was demonstrated by TMCTS vapor treatment. The porous silica film modified with a catalyst and a plasma treatment achieved higher mechanical strength and lower dielectric constant than conventional porous silica films because the TMCTS vapor treatment was more effective for mechanical reinforcement and hydrophobicity.
In order to develop ultra-low-k interlayer dielectric films for ULSIs in 45 nm technology generation, a self-assembly technology was introduced to form porous silica films. The precursor solution for the self-assembly contained cationic surfactant such as alkyltrimethylammonium chloride (ATMACl) and TEOS in ethanol diluted with water. It was spin-coated on a Si wafer so that 2-dimentional hexagonal configuration of self-assembled cylindrical micelles was
formed on the wafer, resulting in formation of the 2-dimensional hexagonal structure of the cylindrical tubes of silica after calcination. The pore diameter and the resulting dielectric constant can be controlled by the number of carbon atoms in the alkyl chain of ATMACl surfactant. A nonionic surfactant such as polyethylene oxide (PEO)-polypropylene oxide (PPO)-PEO triblock copolymer was also used to form disordered porous silica as well as periodic porous silica
films. The mechanical properties of the self-assembled porous silica film were reinforced without changing the dielectric constant by introducing tetramethyl-cyclo-tetra-siloxane (TMCTS) treatment. Significant enhancement of elastic modulus (E) and hardness (H) was achieved by TMCTS treatment at 350°C. The effect of TMCTS treatment on the reinforcement of disordered porous silica was demonstrated. Another important property of porous low-k film is adhesion. TMCTS treatment increased the adhesion of the porous low-k silica film at the Si interface significantly. High modulus porous silica films were formed and E of 8 GPa and k of 2.07 were achieved simultaneously. Cu/low-k damascene structure for 45-nm BEOL technology was demonstrated successfully.