Deposition of low stress silicon nitride thin film and its application in surface micromachining device structures

Abstract

Surface machining processes are responsible for creating microstructures that reside near the surfaces of a substrate and are characterized by the fabrication of micromechanical structures from deposited thin films. These films can be selectively removed to build three-dimensional structures whose functionality typically requires that they should be freed from the planar substrate. Silicon nitride thin film is one of these important materials. In this paper, by adjusting the SiHlNHgaseous ratio, low stress silicon nitride (LS SiN) is deposited by the low pressure chemical vapor deposition (LPCVD) process. The internal stress generally in 135 MPa has been detected using an FLX-2320 film stress tester. Based on the wide application in surface micromachining devices, the mechanical properties of LS SiN are measured by nanoindentation, giving the value of Young's modulus of 224 GPa and the hardness of 22.5 GPa, respectively. Dry etching and wet etching are utilized to fabricate the LS SiN thin film for structural layers. The etching rate compared with normal Sifilm by LPCVD is demonstrated for silicon chip manufacture. © 2013 Beirong Zheng et al.