Structural Analysis of Pore Seal Layer Fabricated by Wet-process on Porous Low- k Films
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Structural Analysis of Pore Seal Layer Fabricated by Wet-process on Porous Low-k Films Shoko S. Ono, Yasuhisa Kayaba, Tsuneji Suzuki, Kazuo Kohmura, and Hirofumi Tanaka R&D Center, Mitsui Chemicals, Inc., Japan ABSTRACT Pore sealing has become a critical issue for the implementation of porous low-k dielectrics and for realizing acceptable reliability performance of the interconnect. This study focuses on fabrication of ultra-thin, conformal and plasma resistant pore seal layer and on understanding parameters playing a role in sealing the surfaces of porous low-k films. It was found that 2.5 nm-thick pore seal layer shows a perfect toluene seal property for the porous lowk film whose pore radius is 1.48 nm. The pore seal layer still show a good toluene seal property after irradiation of He plasma at 250℃ for 10 sec. The increments of dielectric constant by applying the pore seal layer and by the He plasma irradiation for 10 sec are 0.04 and 0.03, respectively. Interestingly, all of toluene seal property, refractive index of the bottom part of the film and dielectric constant started to deteriorate after irradiation of He plasma for 20 sec. It was suggested that when toluene seal property degrades, plasma would start diffusing into pores and both refractive index of the bottom part of the film and k value start to increase. INTRODUCTION LSI devices for 22 nm node and beyond needs ultra-low-k films having k-value below 2.1. One approach is to lower the dielectric constant by creating voids or pores in the low-k materials.[1] The pore diameter is in general in the 1.5 nm to 3 nm range. [2] Porous low-k film is sensitive to process-induced stimuli caused by plasma and metallization process, because such plasma or metals may diffuse into open pores of film. Therefore, the pores must be sealed to prevent diffusion of those species. For pore seal layer, “ultra-thin” is an important requirement because thinner layer would minimize the increment of k value of dielectric. In addition, as device pitches continue to shrink, new metal deposition technologies are developed such as plasma enhanced CVD or plasma enhanced ALD in order to form conformal metal layers and to meet the geometrical requirement. Therefore, plasma resistance became one of the important requirements. Considerable efforts have been devoted to the development of ultra-thin, conformal and plasma resistant pore seal layer. So far, ultra-thin films possessing Cu diffusion barrier effect have been reported. For example, 10 Å of ALD-TaN, [3] 0.6 nm of PEALD-TaNx, [4] carboxylic acid-, thiol-, and aminoterminated self assembled monolayers [5-9] and molecular layer deposition (MLD). [10-11] However, in those methods, when dielectric has pores whose size id 1.5 to 3 nm, the precursors may diffuse into pores of low-k film. Minimal PVD-TaN sealing thickness on the porous dielectric films was investigated in detail. [12] It was reported that 20 nm-thick PVD-Ta(N) shows a perfect seal but 10 nm-thick film shows “pin-hole” for dielectric films whose open porosity is 35 %, k
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