Study of electromigration in thin tin film using edge displacement method

Abstract

Threshold current density and other electromigration parameters of pure. Sri films were measured using edge displacement method. Sn film with a thickness of 5000 A was evaporated on a 1200-angstrom-thick Ti film on a Si substrate. Electromigration behavior was investigated under the current densities of 2.5 X 10(4)-1.5 X 10(5) A/cm(2) at room temperature (RT 27-32 degrees C), 50, 75, and 100 degrees C. Both needle-type and hillock-type whiskers grew in the anode end when the films were stressed at RT and 50 degrees C, but only hillock-type whiskers were observed when they were stressed at 75 and 100 degrees C. The electromigration rate increased linearly with the applied current density for the four stressing temperatures. The threshold current density (J(c)) was measured to be 1.93 X 10(4) 9.65 X 10(3), 9.57 X 10(3), and 7.93 X 10(3) A/cm(2) for RT, 50, 75, and 100 degrees C, respectively. The measured activation energy was 0.32 eV. In addition, the measured critical length of the Sn film was 18 mu m at RT and the products of DZ* were 1.95 X 10(-10), 4.84 X 10(-10), 1.27 X 10(-9), and 1.99 X 10(-9) cm(2)/s for RT, 50, 75, and 100 degrees C, respectively. These results are fundamental to electromigration in Pb-free solders, since most of their matrices consist of almost pure Sri. 0 2005 American Institute of Physics.