In-situ measurements of internal stresses in copper thin films during thermal cycling using synchrotron X-rays

Using synchrotron X-rays at SPring-8, the internal stress in Cu thin films was measured in vacuum at various temperatures during heating and cooling cycle between room temperature and high temperature of 300 or 500°C. Cu films with the thickness of 600 nm was sputtered on top of the under coating of TiN on Si wafer substrate. Cu thin films had a strong fiber texture with the fiber axis <111> perpendicular to the film surface. The 311 diffraction was used for stress measurement. In the heating process, the tensile stress was decreased from 217 MPa to -115 MPa at 180°C and then stress relaxation took place at higher temperatures. The stress diminished in the film at 500°C. In the cooling process, the tensile stress was built up with decreasing temperature. After one heat cycle, the residual stress was increased from 217 to 367 MPa. The experimental results were compared with the theoretical prediction based on the method proposed by Thouless et al. A good agreement was obtained between experimental and theoretical results.