Evaluation of Ultra-thin Layer Fabricated by Wet-process as a Pore-Seal for Porous Low-k Films
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Evaluation of Ultra-thin Layer Fabricated by Wet-process as a Pore-Seal for Porous Low-k Films Shoko Sugiyama Ono1, Kazuo Kohmura1, Hirofumi Tanaka1, Yasuhisa Kayaba2 and Takamaro Kikkawa2 1 R&D Center, Mitsui Chemicals, Inc., Japan 2 Research Institute for Nanodevice and Bio Systems, Hiroshima University, Japan ABSTRACT We focused on detailed evaluations of properties of the ultra-thin pore-seal layer (< 3 nmthick), such as Cu diffusion barrier property and thermal stability. Cu diffusion into dense thermal silica and porous silica low-k which are covered with the pore seal layer was evaluated using metal-insulator-semiconductor (MIS) capacitors under bias thermal stress (BTS). Triangular voltage sweep (TVS) measurement shows that the ultra-thin layer on dense thermal silica suppresses the drift of Cu ions. The Time-Dependent Dielectric Breakdown (TDDB) lifetime of porous silica low-k covered with the ultra-thin pore seal layer results in a drastic increase of the capacitor lifetime with respect to the no-pore-seal control system (stable at 125 °C at least for 10000 s). Thermal decomposition of bulk material of the pore sealant was measured by thermal gravity (TG) test in nitrogen. Bulk material did not decompose through around 350 °C. The amount of ultra-thin pore seal layer fabricated on silicon wafer after thermal cycle stress in vacuum was measured by x-ray photoelectron spectroscopy (XPS). Amount of pore sealant did not decrease even after 2 cycles of 20 min, at 250 °C. Those results show that the ultra-thin layer, which we propose here, has a potential as a pore seal layer for porous low-k films. INTRODUCTION Large scale integration technology for 32 nm node and beyond needs ultra-low-k films having k-value below 2.1. In order to reduce the dielectric constant, porous low-k film is indispensable and widely studied. However, porous low-k film is sensitive to process-induced stimuli caused by plasma and metallization process, because such plasma or metals may diffuse via open pores of film. Considerable efforts have been devoted to the development of barrier metal layer or pore seal layer which suppresses the diffusion of metals into porous low-k film. For both barrier metal layer and pore seal layer, “ultra-thin” is also an important requirement because thinner layer would minimize resistivity of Cu interconnect. Recently, ultra-thin layers possessing Cu diffusion barrier effect have been reported, for example, carboxylic acid-, thiol-, and amino-terminated self assembled monolayers [1-4] and molecular layer deposition (MLD) which allow us to grow very thin organic and organic/inorganic films [5-7]. However, in those methods, the precursors may diffuse into pores of low-k film. It is also proposed that precursor of Ti whose size is larger than the pore size of the porous SiOCH films in order to prevent the precursor from diffusing into pores. [8] To meet multiple requirements, ultra-thin layer which possesses Cu diffusion barrier effect and the precursor of the layer does not diffuse into pores, is still chall
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