熱サイクルを受けた多結晶Cu薄膜の残留応力と微視的損傷

抄録

Copper thin films with a thickness of 600nm were coated on the undercoating by sputtering. The top layer of the undercoating was TiN with the thickness of 50nm sputtered on SiO₂ layer on Si wafers. Films were subjected to heat cycling to various temperatures ranging from 50 to 500°C. The surface topography was examined by atomic force microscopy and scanning electron microscopy, The X-ray diffraction method was used to measure the residual stress and the intensity ratio of 222 to 200 diffraction. Heating cycles to temperatures below 200°C did not induce any remarkable change in the microstructure and topography. By heating to 500°C, the crystalline size increased from 0.5μm to 1.1μm. The volume fraction of hillocks increased after heating cycles above 250°C. At the same time, the intensity ratio of 222 to 200 diffraction increased, while the half-value breadth decreased. The residual stress at room temperature was equi-biaxial tension. The residual stress increased from 270MPa before heating to 350MPa after heating cycle to 500°C. The variation of the measured residual stress with heating temperature does not agree with the prediction based on the model proposed by Thouless et al.