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Proceedings Paper

AFM method for sidewall measurement through CNT probe deformation correction and its accuracy evaluation
Author(s): Masahiro Watanabe; Shuichi Baba; Toshihiko Nakata; Hiroshi Itoh; Takafumi Morimoto; Satoshi Sekino
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Paper Abstract

To use atomic force microscope (AFM) to measure dense patterns of 32-nm node structures, there is a difficulty in providing flared probes that go into narrow vertical features. Using carbon nanotube (CNT) probes is a possible alternative. However, even with its extremely high stiffness, van der Waals attractive force from steep sidewalls bends CNT probes. This probe deflection effect causes deformation (or "swelling") of the measured profile. When measuring 100-nm-high vertical sidewalls with a 24-nm-diameter and 220-nm-long CNT probe, the probe deflection can cause a bottom CD bias of 13.5 nm. This phenomenon is inevitable when using long, thin probes whichever scanning method is used. We proposed a method to deconvolve this probe deflection effect. By detecting torsional motion of the base cantilever for the CNT probe, it is possible to estimate the amount of CNT probe deflection. Using this information, we have developed a technique for deconvolving the probe deformation effect from measured profiles. This technique, in combination with deconvolution of the probe shape effect, enables vertical sidewall profile measurement. We have quantitatively evaluated the performance of the proposed method using an improved version of a "tip characterizers" developed at the National Institute of Advanced Industrial Science and Technology (AIST), which has a well-defined high-aspect-ratio line and space structure with a variety of widths ranging from 10 to 60 nm. The critical dimension (CD) values of the line features measured with the proposed AFM method showed good matches to TEMcalibrated CD values. The biases were within a range of ±1.7 nm for combinations of three different probes, five different patterns, and two different threshold heights, which is a remarkable improvement from the bias range of ±4.7 nm with the conventional probe tip shape deconvolution method. The static repeatability was 0.54 nm (3σ), compared to 1.1 nm with the conventional method. Using a 330-nm-deep tip characterizer, we also proved that a 36-nm-narrow groove could be clearly imaged.

Paper Details

Date Published: 23 March 2009
PDF: 12 pages
Proc. SPIE 7272, Metrology, Inspection, and Process Control for Microlithography XXIII, 72721P (23 March 2009); doi: 10.1117/12.813375
Show Author Affiliations
Masahiro Watanabe, Hitachi, Ltd. (Japan)
Shuichi Baba, Hitachi, Ltd. (Japan)
Toshihiko Nakata, Hitachi, Ltd. (Japan)
Hiroshi Itoh, National Institute of Advanced Industrial Science and Technology (Japan)
Takafumi Morimoto, Hitachi Construction Machinery Co., Ltd. (Japan)
Satoshi Sekino, Hitachi Construction Machinery Co., Ltd. (Japan)

Published in SPIE Proceedings Vol. 7272:
Metrology, Inspection, and Process Control for Microlithography XXIII
John A. Allgair; Christopher J. Raymond, Editor(s)

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