In-Situ Synchrotron Measurement of Thermal Stress in Textured Copper Thin Films during Thermal Cycling
Keisuke TANAKA, Toshimasa ITO, Yoshiaki AKINIWA and Hiroyuki OHTA
Abstract:Copper thin films with a thickness of 600nm were sputtered on the undercoating. The top layer of the undercoating was TiN with a thickness of 50nm sputtered on SiO2 layer with the thickness of 300nm on the Si wafer. Films were subjected to heating upto 500[C in vacuum followed by cooling. During heat cycling, the in-situ measurement of the X-ray profiles and the stress of the film was conducted by using X-rays from a synchrotron radiation source of Spring-8. The stress was determined from the measured strains using the two-point version of the sin 2 method assuming the equi-biaxial stress state. The half-value breadth of the diffraction profiles decreased during heating and then increased during cooling. This behavior of the half-value breadth corresponded to the decrease and increase of the lattice defects during heat cycling. The lattice constant measured by X-rays was a linear function of the temperature. With respect to the stress, the heating process upto 180[C decreased the stress from about 200MPa to about -100MPa, and then, at higher temperatures, the compressive stress was relaxed by creep. The stress in the film was almost zero above 400[C. In the cooling process, the tensile stress was built up with decreasing temperature. After heat cycling, the residual stress was increased to about 350MPa. The experimental data was compared with the prediction based on the model proposed by Thouless et al. The model was based on the stress relaxation by various creep mechanisms. The predicted variation of the stress during heat cycling agreed well with the experimental results. Key Words:X-ray stress analysis, Residual stress, Copper thin film, Heat cycling, Thermal stress, Stress relaxation