Improvement of sawtooth shape generated by anisotropic etching process of single-crystal silicon for microparts feeding using horizontal and symmetric vibrations

Abstract

Etching process is a fabrication technology to generate a pattern on a single crystal silicon wafer. The etching process can generate stable and precise periodic pattern on the silicon wafer with a pitch of smaller than 100 µm order according to the etching mask on the surface and characteristics of surface plane orientation. Using a silicon wafer with a plain orientation of [221], an asymmetric periodic structure is generated on its surface because the etching speed is different between forward and backward of the crystal face. We previously showed that microparts can be fed along an asymmetric microfabricated surface using simple planar symmetric vibrations. Microparts move in one direction because they adhere to the microfabricated surface asymmetrically. We developed sawtoothed surfaces with an elevation angle of 20 deg and various pitches of from 10 to 100 micrometer on the surface of silicon wafer material using a dicing saw with a bevel type blade. Then we found fabrication errors and cracks on the top of teeth, and they caused contact probability among fed microparts and feeder surfaces, which affected the feeding stability of microparts. In the present work, we applied the asymmetry etched surface of the [221] oriented single crystal silicon wafer to develop higher accurate and uniform asymmetric fabricated surfaces. The section geometry, the tribology characteristics, and the feeding stability were evaluated among four types of the asymmetry etched silicon wafer pieces we developed in this work. We finally evaluated the stability of micropart feeding on each surface by the particle tracking velocimetry (PTV) method.