Abstract
Sidewall roughness measurement is becoming increasingly important in the micro-electromechanical systems and nanoelectronics devices. Atomic force microscopy (AFM) is an emerging technique for sidewall scanning and roughness measurement due to its high resolution, three-dimensional imaging capability and high accuracy. We report an AFM sidewall imaging method with a quartz tuning fork (QTF) force sensor. A self sensing and actuating force sensor is fabricated by microassembling a commercial AFM cantilever (tip apex radius ≤10 nm) to a QTF. The attached lightweight cantilever allows high-sensitivity force detection (7.4% Q factor reduction) and sidewall imaging with high lateral resolution. Owing to its unique configuration, the tip of the sensor can detect sidewall surface orthogonally during imaging, which reduces lateral friction. In experiments, sidewalls of a micro-electro-mechanical system (MEMS) structure fabricated by deep reactive ion etching process and a standard step grating are scanned and the sidewall roughness, line edge roughness and sidewall angles are measured.
Highlights
Since its invention, the atomic force microscope has evolved into a versatile instrument with a wide spectrum of applications in the nano science and technology such as imaging of soft biological samples, atomic and subatomic level imaging, nano-manipulation and nano-metrology to name a few
We report a self-sensing and actuating quartz tuning fork (QTF) force sensor based Atomic force microscopy (AFM) method for non-destructive sidewall imaging with frequency modulation mode
We developed an atomic force microscopy sidewall imaging method with a quartz tuning fork force sensor, which is fabricated by attaching a commercial probe with a protruding tip
Summary
The atomic force microscope has evolved into a versatile instrument with a wide spectrum of applications in the nano science and technology such as imaging of soft biological samples, atomic and subatomic level imaging, nano-manipulation and nano-metrology to name a few. In the standard AFM, a sharp tip at the apex of a microcantilever scans over the sample surface with an orthogonal z-servo to obtain the surface topography and various properties of the sample, such as elastic modulus and adhesion This technique is limited in imaging sidewalls of the micro and nano structures for sidewall roughness (SWR) and critical dimension (CD) metrology. To enable AFM to access the sidewalls, shaped probes were used in the pioneering works [10,11] In this approach, probe is vibrated in vertical and horizontal directions to effectively detect the surface slope in order to image the horizontal surfaces (top or bottom) and sidewall. Sidewall imaging methods with the QTF force sensors are desired for flexible and high resolution sidewall scanning of micro/nano structures. Measurement principle and applications of the developed method for the sidewall roughness (SWR) and line edge roughness (LER) measurement are presented
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