A metrological atomic force microscope with a tip-tilting mechanism (tilting-mAFM) has been developed to expand the capabilities of 3D nanometrology, particularly for highresolution topography measurements at the surfaces of vertical sidewalls and for traceable measurements of nanodevice linewidth. In the tilting-mAFM, the probe tip is tilted from vertical to 16° at maximum such that the probe tip can touch and trace the vertical sidewall of a nanometer-scale structure; the probe of a conventional atomic force microscope cannot reach the vertical surface because of its finite cone angle. Probe displacement is monitored in three axes by using high-resolution laser interferometry, which is traceable to the SI unit of length. A central-symmetric 3D scanner with a parallel spring structure allows probe scanning with extremely low interaxial crosstalk. A unique technique for scanning vertical sidewalls was also developed and applied. The experimental results indicated high repeatability in the scanned profiles and sidewall angle measurements. Moreover, the 3D measurement of a line pattern was demonstrated, and the data from both sidewalls were successfully stitched together with subnanometer accuracy. Finally, the critical dimension of the line pattern was obtained.

Line edge roughness (LER) measurement is one of the metrology challenges for three-dimensional device structures, and LER reference metrology is important for reliable LER measurements. For the purpose of LER reference metrology, we developed an LER measurement technique that can analyze LER distribution along the height of a line pattern, with high resolution and repeatability. A high-resolution atomic force microscopy (AFM) image of a vertical sidewall of a line pattern was obtained using a metrological tilting-AFM, which offers SI-traceable dimensional measurements. The tilting-tip was controlled with an inclined servo axis, and it scans the vertical sidewall along a line pattern with a high sampling density to enable an analysis of the LER height distribution at the sidewall. A horizontal cross-section of the sidewall shows sidewall roughness with sub-nm resolution. Power spectral density (PSD) analysis of the sidewall profile showed that the PSD noise in the high-frequency region was several orders of magnitude lower than the noise of typical scanning electron microscopy methods. AFM measurements were sequentially repeated three times to evaluate the repeatability of the LER measurement; results indicated a high repeatability of 0.07 nm evaluated as a standard deviation of LER at each height. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Self‐catalyzed GaAs nanowires (NWs) were grown on a Si(111) substrate via molecular beam epitaxy (MBE) using a vapor‐liquid‐solid mechanism under an alternating supply of Ga and As. Compared to GaAs NWs grown using the conventional MBE method, the length and diameter of the GaAs NWs grown with an alternating supply of Ga and As were longer and narrower. In addition, the formation of polycrystals on the substrate was decreased, and it was possible to grow the GaAs NWs at a lower temperature using the alternating method. Furthermore, an increase in the formation of twin boundaries (TBs) in the GaAs NWs was observed. The effect of using an alternating supply of Ga and As on the shape and formation of TBs is also discussed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A known fundamental issue with atomic force microscopy (AFM) is that drift occurs during an AFM measurement, distorting the AFM image. In this study, a method for correcting this nonlinear drift in two dimensions (the vertical axis and one of the two horizontal axes) is proposed and demonstrated. A normal AFM measurement is accomplished with many fast-scan profiles, using the raster scan method. In the proposed drift-correction method, the first-scanned profile is set as the reference profile, and the scan at the first-scanned location is inserted periodically during the normal profile scans. The normal scanned profiles are used to construct a normal AFM image, which is distorted by the drift. The time-dependent drift distance can be estimated by a series of the scanned reference profiles, and the distorted AFM image is corrected using this estimated distance. It is shown, experimentally, that the drift correction in two dimensions has both high resolution and repeatability at the sub-nanometer scale.