Pore Seal Property of Ultra-thin Layer for Porous Low- k Films revealed by Ellipsometric Porosimetry
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Pore Seal Property of Ultra-thin Layer for Porous Low-k Films revealed by Ellipsometric Porosimetry Shoko Sugiyama Ono, Yasuhisa Kayaba, Tsuneji Suzuki, Hirofumi Tanaka and Kazuo Kohmura R&D Center, Mitsui Chemicals, Inc., 580-32, Nagaura, Sodegaura, Chiba, 299-0265, Japan ABSTRACT It was found for the first time that the control of the size of pore sealant is important to prevent diffusions of pore sealant into pores of porous low-k films and to achieve a good toluene seal property. Two pore sealants (PS-A, B) were prepared and the seal property and porous structure were studied using toluene based ellipsometric porosimetry (EP) measurements. It was revealed that small pore sealant (PS-B) diffuses into pores of porous low-k (PLK) films and did not show any seal property, while large pore sealant (PS-A) does not diffuse into pores of porous low-k films and shows a good toluene seal property. Ellipsometry shows that PS-A forms conformal layer only on the vicinity of surface of porous low-k films, but porous structure of porous low-k films at the bottom part is kept, according the fact that the refractive index did not increase. Furthermore, we developed a new pore seal material (PS-C) to form ultra-thin conformal layer by a single pass, which shows a good toluene seal property. The dielectric constant increased from 2.10 to 2.25 by covering with PS-C. The obtained layer also shows the effect as the protect layer of porous low-k films from plasma damages. INTRODUCTION Large scale integration technology for 22 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. In addition, new metal deposition technologies are developed such as metal CVD or ALD in order to form conformal metal layers on the wall in trenches or vias whose aspect ratio is large. Considerable efforts have been devoted to the development of barrier metal layer or pore seal layer which suppresses the diffusion of plasma or metals into porous low-k film. For both barrier metal layer and pore seal layer, “ultra-thin” is 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 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] On the contrary, a new approach, pores are completely filled with various polymers in order to improve plasma resistance of porous l
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