Effect of Abrasive in Cu-CMP Slurry on Global Planarization
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Effect of Abrasive in Cu-CMP Slurry on Global Planarization Yutaka Nomura, Hiroshi Ono, Hiroki Terazaki*, Yasuo Kamigata, and Masato Yoshida Research & Development Center, Hitachi Chemical Co., Ltd. *Semiconductor Materials Div., Yamazaki Works, Hitachi Chemical Co., Ltd. 13-1, Higashi-cho 4-chome, Hitachi-shi, Ibaraki-ken 317-8555, Japan ABSTRACT We investigated the mechanical effect of an abrasive in an abrasive-free-like (AFL) slurry using CMP evaluation and ζ potential evaluation. The amount of abrasive strongly influenced CMP performance. We found out the optimum amount of abrasive for optimal CMP performance. The ζ potential of the abrasive was positive, and those of the Cu and barrier metal were negative. We discussed a planarization model of the AFL slurry in detail based on the ζ potential results obtained. INTRODUCTION Recently, Cu interconnects have been introduced to reduce the RC signal delay in high-performance logic LSIs [1]. The conventional dry etching method is not applicable to Cu wiring and, therefore, a damascene process is generally adopted to remove Cu and barrier layers, except for the wiring division using a chemical mechanical polishing (CMP) method [2]. We investigated the reaction layer on a Cu surface during CMP, which could be easily removed with a polishing pad and without any abrasive. We have developed an abrasive-free-polishing (AFP) solution based on these results [3-5]. Afterward, a low dielectric constant (low k) dielectric was introduced to improve the signal speed in next generation devices [6]. The down force in the CMP process should be weak for a low k dielectric with low mechanical strength. We tried to improve the conventional AFP slurry to match the low k/Cu interconnects, and we have developed a new AFL slurry [7]. To date, we have intensively studied the chemical effect of AFP slurry on CMP performance. In the present study, we investigate the mechanical effect of an abrasive in AFL slurry on CMP performance, i.e. Cu removal rate and planarity. In particular, the selective adsorption of the abrasive on both Cu and barrier metal was investigated in detail using ζ potential evaluation, and finally a planarization model was discussed on the basis of the results.
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EXPERIMENT DETAILS AFL slurry An AFL slurry containing a silica abrasive was used in this study. The amount of abrasive used was varied to meet a number of purposes. In this study, hydrogen peroxide solution was used as an oxidizer. Polishing characteristics Eight-inch Si substrates were used to evaluate CMP characteristics. Substrates were polished with the AFL slurry using a rotary-type polisher. The polishing down force was 14 kPa, and a conventional pad was used. The removal rate of the Cu layer was evaluated using a blanket wafer (a silicon wafer with a conformal layer). The planarity for the AFL slurry was evaluated using a SEMATECH 854 patterned wafer. The step-height of the line width/space of 100 µm/100 µm after the CMP process was measured using stylus profilers (Veeco DEKTAK) and cross-
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