Structures and Properties of an Ultra-Low- k Material: Classical-molecular-dynamics and First-principles Calculations
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0914-F03-02
Structures and Properties of an Ultra-Low-k Material: Classical-molecular-dynamics and First-principles Calculations Jiro Ushio1, Tomoyuki Hamada2, Takahisa Ohno1,2, Shin-Ichi Nakao3, Katsumi Yoneda3, Manabu Kato3, and Nobuyoshi Kobayashi3 1
Computational Materials Science Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan 2
Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505, Japan 3
Semiconductor Leading Edge Technologies, Inc., 16-1 Onogawa, Tsukuba, Ibaraki, 305-8569, Japan ABSTRACT We determined the most probable atomistic structure of an ultra-low-k material (k≅ 2.5) by computer simulations. Among the trial structures generated by a molecular-dynamics calculation, the most probable one that reproduces the observed properties was selected using a first-principles density-functional-theory calculation. The trial structures consisted of Si-O-Si network with some silicon atoms, each of which had a CH3 group or a hydrogen atom bonded. The experimental properties were reproduced well by the structure with CH3 groups but no hydrogen atom. This structure was then used to investigate the behaviors of the material irradiated with ultraviolet light. INTRODUCTION A use of low-k dielectric materials with copper interconnects has recently been required for manufacturing high-performance system-on-a-chip (SoC) devices. Continuous advance in device performance necessitates a material with even lower dielectric constant, while chemical mechanical polishing (CMP) in the device fabrication process requires a certain mechanical strength [1]. To meet these demands, the trade-off between lower dielectric constant and higher mechanical strength must be resolved [2]. Information on the atomistic structure of the material is useful for addressing the issue. Such information is, however, difficult to obtain because the material is amorphous. There is no experimental technique to determine the total structure of an amorphous material. We can only obtain fragmentary information about the structure through, for example, Rutherford back scattering (RBS), infrared (IR) absorption, and nuclear magnetic resonance. The aim of this study is to make it possible to design low-k dielectrics by clarifying the relation between structure and property of low-k dielectrics by means of computer simulations. In the present simulation, we obtained, for the first time, the atomistic structure of an ultra-low-k material called porous carbon-doped oxide (p-SiOC; k=2.55), which has been intensively developed for SoC applications. Utilizing the obtained structure, we investigated a mechanism for improving the mechanical and dielectric properties of p-SiOC film by ultraviolet (UV) irradiation.
CALCULATION DETAILS To perform a classical-molecular-dynamics (MD) calculation, a three-dimensional periodic structure of p-SiOC was assumed. The method we adopted was basically that reported by Tajima et al. [3]. The MD calculations were performed with the program
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