Properties of liquid-phase-deposited SiO₂ films for interlayer dielectrics in ultralarge-scale integrated circuit multilevel interconnections

Properties of a new fluorinated SiO₂ film for interlayer dielectrics in multilevel interconnections of ultralarge-scale integrated circuits (ULSIs) are investigated. The fluorinated SiO₂ films are formed at 35 °C by a liquid phase deposition (LPD) technique using a supersaturated hydrofluosilicic acid (H₂SiF₆) aqueous solution. The LPD SiO₂ film surface profiles on polysilicon and aluminum wirings are flat enough, indicating that the LPD technique has good capability for the surface planarization of interlayer dielectric films. The compositions of as-deposited LPD SiO₂ films and those annealed at 400 and 900 °C are SiO_1.85F_0.15, SiO_1.85F_0.15 and SiO_1.90F_0.10 respectively. The LPD SiO₂ film deposition mechanism is explained as follows: (i) fluorosilanols [F_nSi(OH)_4-n] formation; (ii) fluorosilanol oligomer formation by a catalytic reaction in the solution; (iii) oligomer adsorption onto the substrate surface; (iv) oligomer polymerization by a catalytic reaction. The absorption peak position, full width at half-maximum (FWHM) and absorption coefficient for the Si-O bond in the Fourier transform infrared spectra for the as-deposited LPD SiO₂ films are 9.17 micrometer, 0.83 micrometer and 1.19 × 10⁶ m^-1, respectively, indicating that the films are formed by tightly bonded Si-O networks. The as-deposited LPD SiO₂ films have a refractive index of 1.433, a density of 2.19 × 10³ kg m^-3, an etching rate (measured using 1:30 buffered hydrofluoric acid (HF) solution) of 83 nm min^-1, and a residual stress of 20 MPa (tensile). The film shrinkages after annealing at 400 and 900 °C are 0.8% and 2.0% respectively. Although these properties are changed by annealing at 400 and 900 °C, these values are still better than those of SiO₂ films deposited by chemical vapor deposition (CVD) at 400 °C for use as interlayer dielectric films. The LPD SiO₂ films have better electrical properties, such as lower leakage current, higher dielectric breakdown strength (> 6.3 × 10⁸ V m^-1) and lower dielectric constant (< 3.9 at 1 MHz), than the CVD SiO₂ films.