| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 88 === Shrinking the dimensions of devices beyond 0.25 mm or less to increase packing density impose greater demands on the planarization process. Among the newly developed planarization technologies for Ultra Large Scale Integration (ULSI) metallization, chemical-mechanical polishing (CMP) is the only way known to achieve the global planarization. In order to reduce RC delays of multilevel interconnect that connects individual devices of silicon ICs, the industry is currently making a transition to copper metallization and low dielectric constant insulators. Polymers have shown the great promise for using as inter-level dielectric (ILD) films because of their low stress and low dielectric constant. CMP of polymers for ILD applications is difficult owing to the chemical inertness and softness. In this thesis, the synthesis of ultrafine alumina powders and the CMP of oxide and low dielectric constant thin films are presented.
As the device line wide is gradually shrinking, the quality requirement of abrasive for CMP process is stricter. In this thesis, the study of synthesizing powder with using the method of hydrolyzing aluminum-tri-isopropoxide is preparing the nano-sized (< 150 nm) alumina powders and producing the different crystal phases or mixed-phase (a+q) alumina powders with various calcination conditions. Using these preparing alumina powders as abrasives for polishing oxide film, the results show that the higher removal rates of oxide films with the mixed-phase (a+q) alumina powders, prepared by calining at 1170℃ for 20 min. The mechanism of this CMP behavior is proposed and discussed in thesis.
The study of low dielectric constant (e: 2.5~2.9) thin films (HOSP、FLARETM 2.0 and Polyimide) for CMP polishing. First, the properties of these films are analyzing and presenting. Using FT-IR to analyze chemical bonding, the results show that the structure of HOSP film would be changing from cage-like to network with increasing temperature. From film stress to temperature analysis, the results show HOSP and FLARETM 2.0 films structure are stabilized after curing, however, the polyimide film start to deform plastically at ca. 230℃.
For polishing these three low-k thin film with using various types, crystal phases and particle sizes of commercial powders as abrasives. The results show that the higher removal rates and severe surface roughness with the larger abrasives. Therefore, the removal of these soft polymer films is mainly by mechanical abrasion. However, we could be improved surface roughness, caused from mechanical abrasion, by adding some chemical agents in slurry to increase chemical dissolution. For example, adding tetra-methyl-ammonium hydroxide in slurries for polishing HOSP and polyimide films; and adding hydrobromic acid in slurry for polishing FLARETM 2.0 film.
Taguchi Design of experiment of CMP polishing parameters for these low-k thin films is study in this thesis. The results show that the higher removal rate and lower standard deviation of removal rates with changing back-pressure and platen speed could be obtained at first polishing step and the removal rates followed the Preston's law that the higher removal rates with the higher speeds and pressures. At second polishing step, surface roughness was found to be independent upon down force and platen speed of CMP polishing parameters. Therefore, the properties of abrasives in slurry are mainly effect that causes the surface roughness of polished films.
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