Optimizing Pad Groove Design and Polishing Kinematics for Reduced Shear Force, Low Force Fluctuation and Optimum Removal
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1157-E01-01
Optimizing Pad Groove Design and Polishing Kinematics for Reduced Shear Force, Low Force Fluctuation and Optimum Removal Rate Attributes of Copper CMP Yasa Sampurno 1,2, Ara Philipossian 1,2, Sian Theng 1,2, Takenao Nemoto 3, Xun Gu 3, Yun Zhuang 1,2, Akinobu Teramoto 3 and Tadahiro Ohmi 3 1
Araca, Inc., 2550 East River Road, Suite 12204, Tucson, Arizona 85718 USA University of Arizona, 1133 James E. Rogers Way, Tucson, Arizona 85721 USA 3 Tohoku University, 6-6-10, Aza-Aoba, Aramaki, Aoba-ku, Sendai 90-8579 Japan 2
ABSTRACT The effect of polisher kinematics on average and standard deviation of shear force and removal rate in copper CMP is investigated. A ‘delamination factor’ consisting of average shear force, standard deviation of shear force, and required polishing time is defined and calculated based on the summation of normalized values of the above three components. In general, low values of the ‘delamination factor’ are preferred since it is believed that they minimize defects during polishing. In the first part of this study, 200-mm blanket copper wafers are polished at constant platen rotation of 25 RPM and polishing pressure of 1.5 PSI with different wafer rotation rates and slurry flow rates. Results indicate that at the slurry flow rate of 200 ml/min, ‘delamination factor’ is lower by 14 to 54 percent than at 400 ml/min. Increasing wafer rotation rate from 23 to 148 RPM reduces ‘delamination factor’ by approximately 50 percent and improves removal rate within-wafer-non-uniformity by appx. 2X. In the second part of this study, polishing is performed at the optimal slurry flow rate of 200 ml/min and wafer rotation rate of 148 RPM with different polishing pressures and platen rotation rates. Results indicate that ‘delamination factor’ is reduced significantly at the higher ratio of wafer to platen rotation rates. . INTRODUCTION During CMP, 2-body and 3-body interactions among the wafer, the slurry particles and the pad generate a wide range of shear forces. With IC devices shrinking further into nano-scale dimensions and low-k nano-porous materials becoming increasingly attractive, shearing needs to be re-visited vis-à-vis the mechanical integrity of the metal and underlying porous dielectric stack since high average shear force, in combination with its large fluctuating component and long polishing times (especially to clear the barrier) become major defect-causing problems. In this paper, the contributions of shear force, standard deviation of shear force and required polishing time are presented independently in a bar graph. The value of ‘delamination factor’ is calculated based the summation of normalized values of the above three components and normalized to illustrate the effect of polisher kinematics during copper CMP process. EXPERIMENTAL APPARATUS AND PROCEDURE All experiments were performed on an Araca APD-800 polisher and tribometer which is equipped with the unique ability to acquire shear force and down force in real-time.1 In this study, force acquisition rate was set at 1,000 H
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