The study of stress relaxation mechanisms in copper thin films

• Main Authors: Chi-Tse Li, 李奇澤
• Other Authors: Cho-Jen Tsai
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/86052052537628526905

碩士 === 國立清華大學 === 材料科學工程學系 === 90 === Mechanical stresses in thin films are often significantly higher than those supported by the same material in bulk form. The thermomechanical behavior of metallic thin films on stiff substrates is relevant for thin film devices, but its mechanisms are not yet fully understood. In this investigation, the stress behaviors of copper thin films with different thickness on diffusion-barrier (TaN) coated Si substrates are studied using a laser scanning method for in-situ curvature measurements. The heat treatments of the samples include isochronal (from room temperature to 500℃ and 700℃) and isothermal (200℃, 300℃, 400℃) annealing in vacuum. The film properties of Cu were analyzed by Auger electron spectroscopy (AES), X-ray diffraction (XRD), and four-point probe measurement. The stress relaxation data obtained during isothermal annealing were curve-fitted with different strain-rate equations with appropriate parameters for bulk copper and the plausible mechanisms for the relaxation were determined. The results show that copper thin films on different dielectric materials have different thermomechanical behavior. At temperatures above 650℃, the grain growth of Ta2N was observed which affects the thermomechanical of the copper films. The biaxial modulus of copper thin films decreases with increasing thickness. According to the results of curve-fitting for plastic deformation, high temperature creep appears to be the dominate stress relaxation mechanism for copper thin films in TaN/Cu/TaN structure at 300℃and 400℃. At 200℃, no existing models for relaxation mechanism could describe the relaxation behavior properly.