Why abrasive free Cu slurry is promising?
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Why abrasive free Cu slurry is promising?
Yasuo Kamigata*, Yasushi Kurata*, Katsuyuki Masuda*, Jin Amanokura*, Masato Yoshida* and Masanobu Hanazono** *Hitachi Chemical Co., Ltd., Research and Development Center, Tsukuba, Japan **Hitachi Chemical Co., Ltd., Electronic Materials Operations Div., Tokyo, Japan ABSTRACT To develop high signal speed semiconductor LSIs, Cu interconnection is one of the most important requirements. In the fabrication of Cu interconnections using CMP method, minimized dishing, erosion and reduction in micro-scratches are large issues to be realized. We performed a research for superior properties of Cu CMP. Finally, we succeeded in developing Abrasive Free (AF) Cu slurry suitable for these requirements. We also developed slurry for barrier (TaN) with a high selectivity between TaN and SiO2 of 50 to reduce oxide (SiO2) loss. This reduced oxide loss is directly related to obtaining a controlled circuit resistivity. By applying these two kinds of slurries, ULSIs with multilevel Cu interconnects and excellent reliabilities were obtained. INTRODUCTION Since the first announcement of introducing Cu interconnection to high speed ULSIs in 1997 [1], many semiconductor manufacturers began to develop Cu interconnection by applying CMP method. [2,3] At the beginning of those researches, conventional Cu slurry was applied, and that introduced many problems to be overcome. An outline of the problems is summarized in the Figure 1. We surmised these problems should be solved from the viewpoint of both mechanical abrasions by abrasive powder and chemical reaction of a formation of Cu complex. In order to reduce microscratches and oxide loss, abrasion effects should be controlled, while a polishing pad deformation and Cu surface chemical reaction have to be controlled to reduce dishing. As for Cu damascene CMP process, one-step or two-step CMP process has been proposed, as shown in Figure 2. A one-step CMP process is the simplest, but it can control neither dishing nor erosion. A conventional two-step CMP process using abrasive containing slurries lessens the problems, but the degree of improvement is not sufficient due to rather uncontrollable removal rate selectivity of metals against oxide. In our development of two kinds of slurries, one for Cu and the other for TaN,
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Abrasive Free
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Micro
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Residue Oxide
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Loss
Resistivity Designed
Dishing
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Figure 1.
Problems of Cu CMP
we propose a highly selective CMP process as shown in Figure 2. For the first step Cu slurry, super high selectivity for Cu against TaN barrier is required to obtain a stop on barrier characteristic. For the second step TaN slurry, high removal selectivity of TaN against SiO2 is required to minimize an oxide loss. To realize the process, we succeeded in developing AF Cu CMP slurry with super high selectivity and high performances. For the consecutive TaN barrier CMP, we designed a slur
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