AVS 53rd International Symposium
    Thin Film Monday Sessions
       Session TF-MoM

Paper TF-MoM12
Plasma Controlled Atomic Layer Deposition for Sealing Pores in Low-k Materials

Monday, November 13, 2006, 11:40 am, Room 2022

Session: ALD and Applications I
Presenter: J.L. Cecchi, University of New Mexico
Authors: Y.-B. Jiang, University of New Mexico
J.L. Cecchi, University of New Mexico
C.J. Brinker, Sandia National Laboratories
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On a porous substrate, atomic layer deposition (ALD) takes place not only on the top of the substrate, but also penetrates into the internal porosity. For sealing the pores of a nanoporous low-k materials, it is important to prevent any deposition in the internal pores, which would alter the material's dielectric constant. Consequently, an approach capable of confining ALD to the top surface of the porous substrate is needed. We have developed such a method by combining ALD with plasma processing. The ALD process is carried out such that deposition reaction will not take place unless triggered by a plasma. TEOS and O2 have been used as the precursors for SiO2 ALD in a plasma-ALD reactor. Although both precursors will be incident on all exposed surfaces, including the internal pores, they are not reactive to each other unless triggered by active plasma radicals. Since the radicals in the plasma do not penetrate into the nanoporous matrix, no ALD will take place in the internal pores. Another approach we have developed is an ALD process for which adsorption can not proceed unless the surface is activated by plasma. Using TMCS (trimethyl chlorosilane) and H2O vapor as SiO2 ALD precursors, ALD proceeds via the cycle of TMCS/Ar purge/O2-plasma/H2O vapor/Ar purge. After each TMCS exposure, the sample surfaces are passivated with -CH3 groups. Upon the following exposure of an O2 plasma, -CH3 groups on the top surface are removed, leaving the surface reactive to subsequent precursor adsorptions. But the internal pores remain passivated, since plasma cannot reach them. In this manner, ALD is also confined to the top surface of the porous substrate. We present transmission electron microscope (TEM) images that establish that the SiO2 ALD thus obtained was a several-nm-thick pore-sealing layer conformally on the top of patterned nanoporous silica without filling the internal pores.