The thermo-creep deformation of interconnects related to the residual stress, directly affects their performance and lifetime. In this paper, we proposed an optical method to measure the residual thermo-creep deformation of copper interconnects. This method takes advantages of grating fabrication and the phase-shifting scanning electron microscope (SEM) moiré method. The residual thermo-creep deformation can be acquired through deformation transformation. A one-way grating with frequency of 5000 lines/mm is fabricated on the surface of the copper line in a focused ion-beam (FIB) system. The principal direction of the grating is along the axis of the copper line. The sample is heated in a high temperature furnace under 90 °C for 70 min. The SEM moiré patterns before and after heating are recorded by a field emission SEM in low vacuum. Through the random phase-shifting algorithm, the residual thermo-creep deformation of the copper interconnect line is found to be 500 με. The cause of the tensile strain is analyzed. This work offers an effective technique for measuring the creep deformation of the film lines.
A study on the digital nano-moiré method and its phase shifting technique