Novel End-point Detection Method by Monitoring Shear Force Oscillation Frequency for Barrier Metal Polishing in Advanced
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1157-E13-03
Novel End-point Detection Method by Monitoring Shear Force Oscillation Frequency for Barrier Metal Polishing in Advanced LSI Xun Gu 1, Takenao Nemoto 2, Yasa Sampurno 3,4, Jiang Cheng 3, Sian Nie Theng 3,4, Ara Philipossian 3,4, Yun Zhuang 3,4, Akinobu Teramoto 2, Takashi Ito 1, Shigetoshi Sugawa 1, and Tadahiro Ohmi 2,5 1
Graduate School of Engineering, Tohoku University, Aza-Aoba 6-6-5, Aramaki, Aoba-Ku, Sendai, Miyagi 980- 8579 Japan 2 New Industry Creation Hatchery Center, Tohoku University, Sendai, Miyagi 980-8579 Japan 3 University of Arizona, 1133 James E. Rogers Way, Tucson, AZ 85721 USA 4 Araca, Inc., 2550 East River Road, Suite 12204, Tucson, AZ 85718 USA 5 World Premier International Research Center, Tohoku University, Sendai, Miyagi 980-8579 Japan
ABSTRACT A novel end-point detection method based on a combination of shear force and its spectral amplitude was proposed for barrier metal polishing on copper damascene structures. Under some polishing conditions, the shear force changed significantly with polished substrate. On the other hand, the change in shear force was insignificant under certain polishing conditions. Therefore, a complementary end-point detection method by monitoring oscillation frequency of shear force was proposed. It was found that the shear force fluctuated in unique frequencies depending on polished substrates. Using Fast Fourier Transformation, the shear force data was converted from time domain to frequency domain. The amplitude of spectral frequencies corresponding to the rotational rate of wafer carrier and platen was monitored. Significant frequency amplitude changes were observed before, during and after the polished layer transition from barrier film to silicon dioxide film. The results indicated that a combination of shear force and its spectral amplitude analyses provided effective end-point detection for barrier CMP process. INTRODUCTION As technology node progresses, chemical mechanical planarization (CMP) becomes a crucial method in integrated circuit fabrication. It was reported that CMP reduces the total process steps involved in the device fabrication by as much as 25 percent.1 During CMP, a rotating wafer is pressed against a rotating polishing pad with a certain pressure. A real-time endpoint detection technique is required to ensure that the wafer is planarized properly and achieve constant yield.2 As part of the copper damascene process, Ta/TaN is deposited on patterned inter-layer dielectric (ILD) before copper deposition. The thin Ta/TaN layer acts as a liner to prevent copper from diffusing and also helps copper adhesion. During copper CMP, to remove the overburden Cu, Ta/TaN becomes a stopping layer to prevent over-polishing of copper lines. The optimal process time for Ta/TaN polishing is critical, especially when the Ta/TaN to ILD removal rate selectivity is low.3 While the end-point detection (EPD) methods based on motor current, optical detection, and shear force measurement are widely used in commercial CMP equipment, there are many difficu
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