A novel AFM method for sidewall measurement of high-aspect ratio patterns

Masahiro Watanabe; Shuichi Baba; Toshihiko Nakata; Takafumi Morimoto; Satoshi Sekino

doi:10.1117/12.772712

22 March 2008 A novel AFM method for sidewall measurement of high-aspect ratio patterns

Masahiro Watanabe, Shuichi Baba, Toshihiko Nakata, Takafumi Morimoto, Satoshi Sekino

Proceedings Volume 6922, Metrology, Inspection, and Process Control for Microlithography XXII; 69220J (2008) https://doi.org/10.1117/12.772712
Event: SPIE Advanced Lithography, 2008, San Jose, California, United States

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 have developed a method of deconvolving this probe deflection effect that is well suited to our AFM scanning mode, Advanced Step-in^TM mode. In this scanning mode, the probe is not dragged on the sample surface but approaches the sample surface vertically at each measurement point. The CNT probe deformation is stable because we do not use cantilever oscillation that can cause instability, but we detect static flexure of the cantilever. Consequently, it is possible to estimate the amount of CNT probe deflection by detecting the degree of cantilever torsion. 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 makes vertical sidewall profile measurement possible.

Citation Download Citation

Masahiro Watanabe, Shuichi Baba, Toshihiko Nakata, Takafumi Morimoto, and Satoshi Sekino "A novel AFM method for sidewall measurement of high-aspect ratio patterns", Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 69220J (22 March 2008); https://doi.org/10.1117/12.772712

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