Measurement of residual stress in multilayered thin films by a full-field optical method

Wafer level thin film residual stress measurement is crucial for the structural reliability of many semiconductor and MEMS devices. The curvature measurement scheme is usually the most widely used method. Film stress is determined by converting the measured curvatures using Stoney formula. During the fabrication of the IC and MEMS devices, however, multilayered thin films are often generated on both sides of the wafer simultaneously. By extending the Stoney formula, this paper presents a method for measuring residual stress in the multilayered films on the wafer. In the method, only the back film layers of the wafer need to be etched in turn and corresponding curvature radii need to be measured by a full-field optical method. The residual stress of each film layer may then be obtained by the radii using the extended Stoney formula. The extended Stoney formula was verified by Coventorware. Experiments show that the proposed method is simple and accurate for process monitoring.