Copper Deposition Technology for Thru Silicon Via Formation Using Supercritical Carbon Dioxide Fluids Using a Flow Type
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Copper Deposition Technology for Thru Silicon Via Formation Using Supercritical Carbon Dioxide Fluids in a Flow-Type Reaction System Masahiro Matsubara and Eiichi Kondoh Graduate School of Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu-city, Yamanashi 400-8511, Japan. ABSTRACT A supercritical fluid is a high-pressure medium that possesses both high diffusivity and solvent capabilities. Metal thin films can be deposited in supercritical fluids from an organometallic compound (precursor) through thermochemical reactions. In the present study, we used a technique, aimed at applying to the fabrication of through-silicon vias (TSVs), where copper thin films were deposited in silicon microholes 10 µm in diameter and 350 µm in depth. The temperature and pressure were varied from 180°C to 280°C and 1 MPa to 20 MPa, respectively. The maximum coating depth decreased with deposition temperature, whereas a peak maximum of the depth was observed at around 10 MPa. The temperature and pressure dependences on the coating depth were numerically studied. On the basis of the analysis, a deposition program was modified as to elongate the coating depth. Keywords: through-silicon via, supercritical carbon dioxide, copper thin film, diffusion constant
INTRODUCTION Three-dimensional (3D) die stacking technology offers many potential advantages compared to traditional packaging technologies. For example, the distance between circuits can be significantly reduced, and use of through silicon via (TSV) can increase chip interconnection density compared to that of traditional wire-bonding interconnection. Wafer processing can be simplified to having differently functioned chips such as processors or memory, instead of adding process steps for heterogeneous function, in a conventional two-dimensional (2D) chip. This new 3D silicon technology is emerging at a time when Moore’s Law for semiconductor chip scaling seems to be slowing or reaching an end [1]. 3D IC applications may require only millions of TSV, in the near future, so that TSVs should have a very high aspect ratio depending on silicon thinning technology. In the TSV fabrication process, vias etched with deep silicon etching are filled with copper. Existing deposition technologies, such as sputtering and electroplating, have limitations in forming a uniform liner and filling TSVs with conductor metal. We have been investigating Cu thin film deposition technology using supercritical carbon dioxide (scCO2) in order to fill/coat a very high aspect ratio of vias. In this technology vehicle, wherein an organometal complex is dissolved in scCO2, it is reduced to a thin film. Deposition of variety of noble and near-noble metals has been reported from Cu to Pd, Au, Ni, Pt, Rh, and to alloys.[2-6] ScCO2 possesses not only its density and solvent capability as high as liquid, but also has high diffusivity and low viscosity as a gas and has zero-surface tension, which allows scCO2 to penetrated into very small features. These properties make scCO2 an ideal medium fo
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