Nano-scale Observation of Si Trench Sidewall Surface Morphology by AFM Technology
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1025-B07-11
Nano-scale Observation of Si Trench Sidewall Surface Morphology by AFM Technology Reiko Hiruta1, Hitoshi Kuribayashi1, and Ryosuke Shimizu2 1 Electron Device Laboratory, Fuji Electric Device Technology Co., Ltd., 4-18-1, Tsukama, Matsumoto, 390-0821, Japan 2 Material and Science Laboratory, Fuji Electric Advanced Technology Co., Ltd., 1, Fujimachi, Hino, 191-8502, Japan ABSTRACT We have developed an atomic force microscopy (AFM) observation technique with which Si trench sidewall surface can be scanned with the tip of cantilever to investigate its nano-scale morphologies. By developing a new technique of cleaving the substrate at the center of a micron-sized trench along its longitudinal direction [011], the sidewall nano-scale morphology of the trench could be observed with the AFM technique. By comparing of cross sections of the images, we also investigated the difference between Si and carbon nanotube (CNT) tips for the AFM observations. According to the results, the CNT tip proved to show a superior signal-to-noise (S/N) ratio compared with the Si tip. The CNT tip enables us to observe the step patterns of the sidewalls of micron-sized trench structures in the various phases of hydrogen annealing. INTRODUCTION Controllability of the shape and surface morphology of microstructures is the essential issue for the development of a wide range of devices, such as semiconductor devices, micro electro-mechanical systems (MEMS), photonic crystals, and various kinds of nano-devices. Especially in three-dimensional Si devices, such as trench metal-oxide-semiconductor field-effect-transistor (MOSFET) [1], fin-FET [2] and Si-MEMS [3], atomic-level flatness is strongly required for their constituent surfaces for the progressive downscaling of the devices structures. Recently, in the context of development of trench MOSFET, the effect of high temperature hydrogen annealing on the nano-scale surface morphology of micron-sized trench sidewalls has been investigated on Si (100) substrates by AFM [4-6]. In this process, it is necessary to make the tip of cantilever scan the trench sidewall to observe the micro-structures of its surface by AFM. The cross-sectional sizes of the trenches being 0.7 µm wide and 3.0 µm deep, we could not touch the tip of cantilever directly to the surface. In order to solve this issue, we developed a technical method to cleave the Si substrate along the longitudinal direction of the trenches, which was chosen to be parallel to the [011] direction, with the trench sidewall surfaces being formed on {011} plane. With this newly developed method we could obtain samples with the trench sidewall surface as the outer surface, which allowed us be able to make AFM observations. Meanwhile, using cross section images we investigated the differences between Si and CNT tips from the AFM observations. Combination of both technologies mentioned above enables us to investigate the nano-scale morphology and the step patterns on the trench sidewall
surface. And it also enables us to observe the morphologic
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