AVS 49th International Symposium
    Plasma Science Wednesday Sessions
       Session PS+NT-WeM

Paper PS+NT-WeM1
Plasma Enhanced Chemical Vapor Deposition of a Dense SiO@sub 2@ Cap Layer on Low-k Nanostructured Porous Silica

Wednesday, November 6, 2002, 8:20 am, Room C-103

Session: Plasma Science and Technology for Nanostructures
Presenter: Y.B. Jiang, University of New Mexico
Authors: Y.B. Jiang, University of New Mexico
N. Liu, University of New Mexico
C.J. Brinker, University of New Mexico
J.L. Cecchi, University of New Mexico
Correspondent: Click to Email
Surfactant-templated self-assembled nanostructured porous silica is a promising material for low-k interlevel dielectrics (ILDs) in integrated circuits. With mono-dispersed pore sizes as small as 2 nm and an ordered pore structure, nanoporous silica has excellent mechanical and thermal properties, even at porosities high enough for k values of 2 and below. For ILD applications, the pores must be capped to prevent adsorption on pore surfaces during subsequent processing, such as the deposition of a copper diffusion barrier. In this work, we report on a process for capping nanoporous silica with a dense-but-thin SiO@sub 2@ layer that acts as a diffusion barrier without significantly increasing the overall dielectric constant of the ILD. Nanoporous silica was deposited on a silicon wafer by spin coating with a sol-gel solution. After spin coating, the films were solidified by heating. The pore surfaces were rendered hydrophobic by soaking the films in a 6% HMDS solution, which terminated the pore surfaces with methyl groups. An SiO@sub 2@ cap layer was deposited by plasma-enhanced chemical vapor deposition (PECVD) in an inductively-coupled plasma reactor, using a SiH@sub 4@/O@sub 2@/Ar gas feed mixture. RF power, total pressure, gas composition, and flow rate were varied systematically to produce a high-density film with low surface roughness. The corresponding deposition rate resulted in 50 nm-thick films in approximately 15 minutes. N@sub 2@ absorption measurements performed with a surface acoustic wave (SAW) technique indicate a reduction of more 10 between the capped and the uncapped nanoporous film. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements both confirm that the pore structure in the nanoporous silica is unchanged by the capping process. Fourier transform infrared (FTIR) detection of methyl groups shows that the hydrophobicity of the nanoporous silica remains after the dense SiO@sub 2@ cap layer is deposited.