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

Abstract

Wafer level thin film residual stress is generally determined by a full-field optical method, which converts the measured curvatures into the stress 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 is measured by the full-field optical method. The residual stress of each film layer may then be obtained by the radii using the extended Stoney formula. By comparing the proposed method with the existing method using the traditional Stoney formula, it is shown that the proposed method is more simple and economical for practical applications. The extended Stoney formula was verified by Coventorware. Experiments show that the proposed method is simple and accurate for process monitoring.