Filling of materials in trenches and holes is important for fabrication of three dimensional structures such as ULSI interconnects, quantum dots and wires, micro-electrochemical systems, and system in package. Recently, we have realized anisotropic deposition of Cu, for which Cu is filled preferentially from the bottom of trenches without being deposited on their sidewall, using H-assisted plasma chemical vapor deposition [1, 2]. The anisotropic deposition is useful for fabricating nano-scale interconnects, because it has two interesting features. One is the fact that the narrower the width of trench is, the faster the deposition rate on its bottom becomes. The other is the self-limiting deposition, that is, the deposition in the trench stops automatically just after filling it completely. Such type of deposition has a potential to overcome common problems associated with conformal filling: namely, small crystal grain size below half of the trench width, and formation of a seam with residual impurities of relatively high concentration. Ion irradiation on the surfaces of interest is the key to realizing the anisotropic deposition, since the deposition rate on the bottom surface of trenches increases with the flux and kinetic energy of ions impinging on the surface. Moreover, irradiation of H atom on the surface removes impurities in films and enhances deposition rate. Hence, we optimized the deposition condition by measuring Hα emission intensity as a parameter of discharge power, gas mixture ratio, and pressure. In the presentation, we will show the features of anisotropic deposition and discuss the deposition mechanism. We will also show anisotropic deposition of other materials, which suggests wide applicability of the deposition method.
[1] K. Takenaka, M. Shiratani, M. Takeshita, M. Kita, K. Koga, and Y. Watanabe, Pure Appl. Chem. 77, 391 (2005).
[2] K. Takenaka, M. Kita, T. Kinoshita, K. Koga, M. Shiratani, and Y. Watanabe, J. Vac. Sci. Technol. A22, 1903 (2004). |