Two-step hydrogen plasma treatment on low dielectric constant (low-k) fluorinated amorphous carbon films (a-C:F) was conducted to improve their thermal stability and reduce the damage caused by the patterning processes. First, hydrogen plasma treatment repairs imperfect bonds of as-deposited a-C:F films, stabilizing their chemical structures and increasing their resistance against elevated thermal stresses. After this passivation process, an additional hydrogen plasma treatment was applied to a-C:F films that had been etched using a mixture of N2+O2+CHF3, enabling sub-130 nm damascene trenches to be patterned and repairing the chemical structures destroyed by the etching plasma.
Fluorinated amorphous carbon films (a-C:F) deposited by plasma enhanced chemical vapor deposition with low dielectric constant (K∼2.3), thermal stability (higher than 400 °C) and acceptable adhesion to a cap layer such as SiOF or SiO2 were obtained by varying the range of content ratios between carbon and fluorine, the rf power, the process pressure and the base temperature. Standard x-ray photoelectron spectroscopy and thermal desorption spectroscopy metrologies were employed to characterize the deposited a-C:F films. The damascene pattern with 0.15 μm and an etching selectivity of more than 50 (a-C:F/SiOF, SiO2) was implemented by a mixture of etching gases of N2+O2. The bias power, rf power and gas flows were incorporated to optimize the etching recipe for achieving a damascene profile with a high aspect ratio. The scanning electron microscope results showed that a better etch profile can be obtained at higher bias power. In our damascene architecture, the etching stop layer or hard mask of both SiOF and SiO2 was studied. The SiOF, providing a lower dielectric constant than SiO2, would especially reduce the entire effective dielectric constant. Furthermore, we integrated electroplated copper into trenches or vias as small as 0.15 μm, with aspect ratio of 6.
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