Intrinsic Mechanical Properties of Free-Standing SiNx Thin Films Depending on PECVD Conditions for Controlling Residual Stress

Abstract

Silicon nitride (SiNx) thin films are crucial in electronic devices and are used as gate dielectrics and diffusion barriers for thin-film transistors (TFTs). Plasma-enhanced chemical vapor deposition (PECVD) has been used for the deposition of SiNx thin films because it allows the tuning of the properties of SiNx thin films by changing the deposition conditions depending on their usage. However, the intrinsic mechanical properties of SiNx thin films depending on the PECVD conditions have rarely been studied because of extreme brittleness and inherent residual stress of SiNx thin films. In this study, the intrinsic mechanical properties of PECVD SiNx thin films are measured from free-standing tensile tests. For the test, 130-150 nm-thick SiNx thin films are prepared using three types of PECVD conditions to induce tensile (T-SiNx), neutral (N-SiNx), and compressive (C-SiNx) residual stress. Compared with the T-SiNx thin films (77 GPa, 0.10%, and 83 MPa, respectively), the C-SiNx thin films shows an approximately 45% increase in Young's modulus (112 GPa), a twofold enhancement of the elongation (0.21%), and a threefold improvement in the fracture strength (226 MPa). The improved intrinsic mechanical properties of C-SiNx thin films compared with those of the T-SiNx and N-SiNx thin films are attributed to increased film density (2.42-2.64 g/cm(3)) and reduced dangling H of the N-H bonding, which are induced by their deposition conditions of higher RF power, lower chamber pressure, and lower NH3 feed ratios. We anticipate that the mechanism of changing the mechanical properties can be extended to fabricate mechanically robust SiNx thin films as dielectric layers for flexible devices.