Apply multiple target for advanced gate ADI critical dimension measurement by scatterometry technology Wei-Jhe Tzaia; Howard Chena; Yu-Hao Huanga; Chun-Chi Yua; Ching-Hung Bert Linb; Shi-Ming Jeremy Weib; Zhi-Qing James Xub; Sungchul Yoob; Chien-Jen Eros Huangb; Chao-Yu Harvey Chengb; Juli Chengb; Lanny Mihardjab; Houssam Chouaibb a
b
United Microelectronics Corp. (UMC); Tainan, Taiwan, R.O.C. KLA-Tencor Corporation; one Technology drive, Milpitas, CA 95035, U.S.A. ABSTRACT
Scatterometry-based metrology measurements for advanced gate after-develop inspection (ADI) and after-etch inspection (AEI) structures have been well proven1. This paper discusses the metrology challenges encountered in implementing a production-worthy methodology for accurately measuring gate ADI middle CD (MCD) and sidewall angle (SWA) to monitor focus and exposure dose. A Multi-Target Measurement (MTM) methodology on KLA-Tencor’s SpectraShape 8810 was evaluated on its ability to characterize and measure FEM (Focus Exposure Matrix) and EM (Exposure Matrix) wafers. The correlation of MCD and SWA to the focus and exposure dose was explored. CD-SEM measurements were used as a reference to compare the accuracy of scatterometry MCD measurements. While there was no reference tool available to compare scatterometry SWA measurements, the SWA and focus tracking on the FEM wafer were verified. In addition to the MTM methodology evaluation, a fleet of four SpectraShape 8810 tools was evaluated to measure the fleet’s capability for in-line monitoring in high volume manufacturing. The final results confirmed that the Multi-Target Measurement approach on SpectraShape 8810 is an effective solution for gate ADI metrology and the robust fleet matching performance would enable in-line monitoring use. Keywords: Scatterometry, MTM, Multi-Target Measurement, Sensitivity, FEM, Focus Exposure Matrix, EM, Gate ADI, Parameter Correlation
1. INTRODUCTION Scatterometry Critical Dimension (SCD) technology has been widely adopted as a CD and shape process control solution for today’s advanced design nodes. In this study, SCD applications for front end of line (FEOL) 28nm gate ADI FEM and EM wafers were explored. One of the currently existing SCD methods to measure and monitor gate ADI is to separately measure MCD on the dense grating target to monitor the exposure modulation, and to perform another measurement for SWA on the isolated grating target to monitor the focus modulation. Simultaneous MCD and SWA measurement usually yields inaccurate results due to the limited sensitivity of and the high parameter correlation between the parameters of interest. In this paper we first evaluated the Multi-Target Measurement (MTM) method available on the SpectraShape 8810 to address the challenges associated with simultaneous MCD and SWA measurements. Our data analyses provided solid evidence that this method is highly effective in breaking the strong parameter correlation and in providing the unique sensitivity needed for gate ADI applications. Secondly, we verified the accuracy of the MTM results with CD-SEM reference data. The analysis showed that the SCD result has high correlation to CD-SEM reference data and less error in the measurement data than CD-SEM. Finally, tool fleet performance was evaluated to assess SpectraShape 8810 fleet capability for gate ADI in-line monitoring. The data showed that MTM and superior tool-to-tool matching performance provides the robustness needed in high volume manufacturing.
Metrology, Inspection, and Process Control for Microlithography XXVI, edited by Alexander Starikov, Proc. of SPIE Vol. 8324, 832420 · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.916234
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