Etching of porous and solid SiO_2 in Ar/c-C_4F_8, O_2/c-C_4F_8 and Ar/O_2/c-C_4F_8 plasmas

摘要

C-C_4F_8-based plasmas are used for selective etching of high aspect ratio (HAR) trenches in SiO_2 and other dielectrics for microelectronics fabrication. Additives such as Ar and O_2 are often used to optimize the process. Understanding the fundamentals of these processes is critical to extending technologies developed for solid SiO_2 to porous SiO_2, as used in low-dielectric constant insulators. To investigate these issues, reaction mechanisms developed for etching of solid and porous SiO_2 in fluorocarbon plasmas and for etching of organic polymers in O_2 plasmas have been incorporated into a feature profile model capable of addressing two-phase porous materials. The reaction mechanism was validated by comparison to experiments for blanket etching of solid and porous SiO_2 in Ar/c-C_4F_8 and O_2/c-C_4F_8 plasmas using inductively coupled plasma reactors. We found that the blanket etch rates of both solid and porous SiO_2 had maxima as a function of Ar and O_2 addition to c-C_4F_8 at mole fractions corresponding to an optimum thickness of the overlying polymer layer. Larger Ar and O_2 additions were required to optimize the etch rate for porous SiO_2. Whereas etch stops occurred during etching of HAR features in solid and porous SiO_2 using pure c-C_4F_8 plasmas, Ar and O_2 addition facilitated etching by reducing the polymer thickness, though with some loss of critical dimensions. Mixtures of Ar/O_2/c-C_4F_8 can be used to manage this tradeoff.