Surface Topographic Measurement Using a Piezo-PVDF Film Stylus

カテゴリ: 部門大会

論文No: GS3-1

グループ名: 【C】平成14年電気学会電子・情報・システム部門大会講演論文集

発行日: 2002/09/02

タイトル(英語): Surface Topographic Measurement Using a Piezo-PVDF Film Stylus

著者名: Qiangxian Huang(Tokyo Institute of Technology)

著者名(英語): Qiangxian Huang(Tokyo Institute of Technology)

キーワード: PVDF|tapping stylus|SPM|profilometry

要約(日本語): A piezo-PVDF film stylus (polyvinilidene Fluoride) has been developed to measure the surface topography for non-destructive and high-step measurement. During measuring, the stylus touches the surface periodically to reduce scratching force and enables non-destructive measurement.

The working mechanism of the piezo-PVDF film stylus is similar to that of SPM. The sensing stylus constitutes a tungsten tip, a piece of PVDF film and a piezo-actuator. The tungsten tip is adhered to the center of PVDF film and used to tap sample surface. The piece of piezo-PVDF film is bended and adhered to both ends of Piezo-actuator. Driven by the piezo-actuator, the PVDF vibrates near its resonant frequency. Therefore, the same frequent piezo-electric signal is obtain from PVDF film, and the tungsten tip can tap sample surface periodically. While the tip approaches sample surface, the amplitude of piezoelectric signal from PVDF decreases. The decrement of the amplitude is the function of the approaching of the tip to the surface. This relation curve can be used to as a rule control the stylus near and apart from the surface, and the topography can be recorded while the stylus scans the sample surface along x-y direction.

The structure of this stylus is very simple. Instead of silicon cantilever often used in SPMs, a piece of piezo-PVDF film is adopted to form the cantilever here. Because PVDF film has piezoelectric character, the vibration of cantilever can be changed into electrical signal directly instead of that of interferometers in SPMs, which is used to measure the vibration of cantilever. The length, width and thickness of the PVDF film cantilever are about 12.8mm, 2mm and 40µm respectively, and far larger than cantilever used in SPM. Therefore, the stylus is easy to manufacture.

The parameters of the stylus are determined experimentally. By experiment, the optimal dimensions of PVDF cantilever are determined, and the relation curve of PVDF electric output and the approaching of tip to surface are obtained. From the experimental curve, the sensitivity of about 1.5V/ µm is obtained. Due to flexibility of the PVDF film, the resonant frequency and quality factor are low, with about 800Hz and 40 respectively. The time constant of system is about several tens of millisecond and faster speed may be realized.

Using the piezo-PVDF stylus, the silicon wafers are scanned, and the system has been proved to be effective. According to the obtained data, the main errors are piezo hysterics and temperature drift that is caused by thermal expansion and temperature character of PVDF film. If those errors can be corrected, the accuracy of several nanometers can be realized.

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