A novel method for determining Young’s modulus of thin films by micro-strain gauges

Abstract

This work presents a novel method for in-situ determining Young's modulus of thin films at the wafer level by using a set of compact micromachined test structures and without any extra load applied to test such structures. The test structures comprise of a pair of microstrain gauges with known Young's modulus and a cantilever beam made of the measured film. The method utilizes inexpensive and available optical measuring equipment. An analytical model is derived to extract the Young's modulus of the measured film. A conventional surface-sacrificial layer micromachining technique is used to fabricate the structures. The micro strain gauges employed in the measurement are made of low-pressure chemical-vapor deposition (LPCVD) undoped polycrystalline silicon films produced by Semiconductor Research Center (SRC) and the measured film is made of PECVD silicon nitride for demonstration. The average value of the obtained Young's modulus of PECVD silicon nitride SiN x is 170 ± 3 GPa by using strain gauges with a residual stress of 211 ± 10 MPa.