Methyl-doped silicon oxide film for inter-layer dielectric applications in copper interconnect technology.

摘要

As integrated circuits (IC) features scale down, performance limitations and reliability issues associated with conventional interconnect technology using aluminum (Al) and silicon dioxide (SiO₂) necessitate the employment of interconnect metals with lower resistivity and low-dielectric-constant (low-κ) inter-layer dielectrics (ILD). Copper (Cu) interconnects with low-κ ILD has been accepted as the next-generation interconnect technology. This thesis explores the material properties of a methyl-doped silicon oxide film for ILD applications and investigates some process integration issues of this film implementation with copper metallization.; Methyl-doped silicon oxide films studied in this thesis were deposited using Low-κ Flowfill™ chemical vapor deposition (CVD) technique. This low-κ film has a dielectric constant as low as 2.7 and a composition of form SiO_X(CH₃)_YH_Z with X = ∼1.5, Y = ∼0.6 and Z = 0.2–0.4. Methyl groups are incorporated into the oxide network and bonded to silicon atoms. The film is thermally stable up to 500°C and has excellent resistance to moisture absorption because of the large amount of methyl groups. The film has a tensile stress of about 6.8 × 108 dyne/cm2 and a hardness of 2.4 GPa (measured using nanoindentation technique). The hysteresis in stress at 50°C after a heating and cooling cycle (25°C–500°C–50°C) is about 6.7 × 10 dyne/cm2.; The chemical mechanical polishing (CMP) characteristics were studied and fundamental removal mechanism investigated. CMP removal rates using both copper and oxide CMP slurries were found to decrease with increase in film methyl content. Water absorption onto the film during CMP appears to be the removal rate-limiting step.; Film stability under different plasma environments was examined. The film can be damaged by O₂ and N₂O plasmas, while remaining stable under H₂ and N₂ plasmas. While exposure to O ₂ plasma during processing should be minimized, either H₂ or N₂ plasmas can be used to remove photo-resist (PR).; A major part of this thesis is devoted to the studies of electrical properties and their relationship to integration with Cu interconnects. Current-voltage characteristics at room temperature show low leakage current density of 7.9 × 10−11 A/cm2 at 1.0 MV/cm and 1.8 × 10−10 A/cm2 at 2.0 MV/cm. Breakdown voltage was found to be greater than 3.0 MV/cm. Ohmic conduction dominates at room temperature and low temperatures, while Frenkel-Poole conduction dominates at high temperature and high electric field.; Cu ion (Cu) drift in this film was investigated using bias temperature stressing/capacitance-voltage (BTS/C-V), current-voltage (I-V) and time dependent dielectric breakdown (TDDB) techniques. Cu+ ions readily drift into the film; an activation energy of 0.76eV was extracted with a 1 MV/cm electric field. Therefore, diffusion barrier layers are required to prevent Cu drift into this low-κ film. Studies on carrier transport with the presence of Cu ions indicate that transport of Cu+ ions in the film probably follow an ionic conduction process.