Novel Reducing Chemistry for Supercritical Fluid Deposition of Copper
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0914-F09-20
Novel Reducing Chemistry for Supercritical Fluid Deposition of Copper Takeshi Momose1, Tomohiro Ohkubo1, Masakazu Sugiyama2, and Yukihiro Shimogaki1 1 Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Tokyo, 113-8656, Japan 2 Department of Electronic Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Tokyo, 113-8656, Japan
ABSTRACT We study new deposition chemistry in Cu-SCFD (supercritical fluid deposition), especially effect of acetone is investigated as reducing agent and additives into H2 reducing CuSCFD. Acetone reduction yields Cu film deposition onto Ru coated Si substrate, because Ru has catalytic effect to generate reducing agent from acetone. When acetone is added into H2 reducing chemistry, the solubility of precursor is enhanced approximately 50 %, which is socalled “entrainer effect”. Ethanol can enhance the deposition of Cu in H2 reduction chemistry, which is a solvent effect. Two effects of entrainer effect by acetone and solvent effect by ethanol works independently, without interfering each other.
INTRODUCTION Cu is employed for a current ULSI interconnects material largely due to its low electrical resistivity. Interconnects are assembled via the so-called "damascene process", which involves Cu seed-layer formation by sputtering followed by gap-filling by electro plating into high aspect ratio features [1]. The poor step coverage by sputtering is unacceptable for features with high aspect ratio of over 5. Cu thin film depositions which enable conformal deposition onto highly complex features are getting significant attention. Supercritical fluid deposition (SCFD), which is the reduction of metal organic compounds with hydrogen in supercritical carbon dioxide, may be a promising technology for ULSI Cu metallization [2, 3]. The benefit of SCFD is inherent in the superior properties of supercritical fluid. Gas-like diffusivity of scCO2 enables excellent gap filling, and liquid-like solubility of scCO2 enables high precursor concentration and wide range of applicable precursor. In addition to these characteristics, optimal control of its chemistry enabled by large solubility of scCO2 has a potential to realize novel and desirable process performance. For example, SCFD generally employs H2 as a reducing agent and it may be a drawback of this process, but we may have a chance to use new liquid reducing agent to eliminate the risk of using high pressure H2 [4]. Besides, due to promotion of solvation, certain liquids might also exhibit an entrainer effect, i.e., enhance the solubility of metal organics into scCO2 [5, 6], and/or a solvent effect, i.e., decrease the deposition temperature [6, 7]. In fact, we investigated the reducing agent and additives into Cu-SCFD, and found that adding ethanol to Cu-SCFD using Cu(tmhd)2 and H2 can promote deposition, whereas the reduction only by ethanol could not get any Cu deposits [8]. These results strongly suggest that the possibility of novel SCFD process development for ULSI metallization l
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