Cohesive fracture measurement technique for free-hanging thin films using highly stressed superlayer

Abstract

• Development of thin film cohesive fracture test method using highly stressed superlayer. • Test method does not require expensive test equipment or external fixtures or loads. • Test method uses standard fabrication processes that create representative films. • Cohesive fracture toughness of thin film silicon dioxide measured to be 8.9-14 J/m 2 . The cohesive fracture of thin films is a concern for the reliability of many devices in microelectronics, nano-electromechanical systems/micro-electromechanical systems, photovoltaics, and other applications. In microelectronics, cohesive fracture toughness has become a concern with new dielectric materials currently being used. To design against such cohesive cracking, it is necessary to experimentally measure the cohesive fracture properties of these thin films. Many of the current tests to measure the cohesive fracture toughness of thin films are based on methods developed for larger scale specimens. Here, a fixtureless method to measure the critical total energy release rate of thin films has been developed that utilizes photolithography fabrication processes and a thin film superlayer. The superlayer has a high intrinsic stress and is used to drive cohesive fracture in the test material that it is deposited on top of. This test method has been used here to measure the cohesive critical total energy release rate of a dielectric thin film of silicon dioxide with experimental samples of thicknesses ranging from ∼100 to 400 nm to be between 8.9 and 14 J/m 2 .