Determination of precise crystallographic directions on Si{111} wafers using self-aligning pre-etched pattern

Abstract

Silicon wet anisotropic etching based bulk micromachining technique is widely used for the fabrication of microelectromechanical systems components. In this technique of microfabrication, alignment of mask edges with crystallographic directions plays a crucial role to avoid unwanted undercutting to control the dimensions of fabricated structures. Various kinds of pre-etched designs have been reported to identify the crystallographic directions (e.g. 〈110〉 and 〈100〉) on Si{100} and Si{110} wafer surfaces. To the best of our knowledge, no pre-etched design has been reported to identify crystal directions on Si{111} wafer. In this work, a self-aligning technique based on pre-etched patterns has been investigated to precisely determine the 〈110〉 direction on Si{111} wafer surface. In this technique, a set of circular shape mask patterns close to wafer edge are etched for the identification of 〈110〉 direction. On wet anisotropic etching these patterns transform to hexagonal shapes. The notches of hexagonal patterns align precisely along a straight line only when they lie on exact 〈110〉 direction. The self-aligned notches can easily be identified by visual inspection using an optical microscope. The major advantages of this technique are simplicity, precision, and self-alignment. In addition, the pre-etched patterns at the wafer periphery occupy very less place.