A Novel Organic Low-k Film Deposited by Plasma-Enhanced Co-Polymerization
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A Novel Organic Low-k Film Deposited by Plasma-Enhanced Co-Polymerization Nobutaka Kunimi1, Jun Kawahara1,2, Keizo Kinoshita1,2, Akinori Nakano1, Masashi Komatsu1 and Takamaro Kikkawa3,4 1
MIRAI-ASET, Tsukuba, Japan
2
Graduate School of Advanced Sciences and Matter, Hiroshima Univ., Higashi-Hiroshima, Japan
3
MIRAI-ASRC-AIST, Tsukuba, Japan
4
RCNS, Hiroshima Univ., Higashi-Hiroshima, Japan
ABSTRACT A new organic precursor was designed and synthesized in order to form polymer films having low dielectric constants by a plasma-enhanced co-polymerization (PCP) technology. The organic monomer features a large aliphatic hydrocarbon structure, tricyclodecane (TCD) group. Optimized polymer films deposited from the monomer had dielectric constants less than 2.5. A solid 13C-NMR spectrum showed that the TCD moiety in the precursor was included in the polymer without changing the structure. The effect of the deposition temperature on the film structure was studied by analyzing Raman spectra. It was revealed that the dielectric constant is strongly associated with sp2 carbon content in the TCD-based polymer films. INTRODUCTION A variety of low-dielectric constant (low-k) materials has been proposed for a solution to meet the requirements for high-performance ULSIs. There are two types of the developed low-k materials, such as inorganic films and organic polymer films. While the silica-based inorganic material has been widely investigated from the standpoint of introducing micro pores in films to reduce a dielectric constant [1, 2], few works on reducing dielectric constants of the organic materials have not been reported. We have developed a plasma-enhanced co-polymerization (PCP) technology for organic low-k materials [3]. Divinylsiloxane bisbenzocyclobutene (BCB) has ever been used as a skeleton monomer, whose polymer film has the dielectric constant of 2.8 [4]. In this study, we will focus on a development of a novel organic skeleton monomer and the polymer films deposited from the monomer by the PCP technology. The developed monomer has a large aliphatic hydrocarbon such as tricyclodecane (TCD) group. The calculated dielectric constant of the TCD structure is expected to be lower than that of BCB [5].
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EXPERIMENTAL An alcohol derivative of TCD was treated with dimethylvinylchlorosilane to synthesize the new TCD monomer. The chemical reaction is well-known as “alkyl silyl ether formation reaction”, which features a high conversion yield [6]. The new monomer had a sufficient saturated vapor pressure to be applicable to the vapor phase deposition as shown in Figure 1, which also includes the chemical structure. Figure 2 shows a schematic diagram of the PCP apparatus based on a plasma-CVD system for a 300mm wafer mass production process [7]. The monomer was vaporized through a heated vaporizer with helium carrier gas and then introduced into a plasma chamber via a shower plate at the top of the chamber. In order to increase the deposition rate, acetylene gas (C2H2) could also be supplied simultaneously.
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