Influence of direct Au-bump formation on metal oxide semiconductor field effect transistor

Change in the electrical characteristic of a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) owing to direct Au bump formation on the MOSFET has been investigated. The investigation was carried out by correlating the spatial distribution of both dynamic strain and residual strain generated by Au bump formation with that of change in the electrical characteristic of the MOSFET. Strain was measured using chains of Si thin film gauges. The bump formation did not significantly affect threshold voltage V_th. However, some change was observed in the transconductance g_m of the MOSFET. The observed change in g_m was maximum at the center of the bump and its value was less than 3.5%. As the result of dynamic strain and residual strain measurements, it is found that residual strain causes the change in the transconductance g_m of MOSFETs, although dynamic strain generated during application of the ultrasonic vibration to the Au bump is much higher than residual strain. It is also found that the direction of g _m change (+ or -) is opposite for n-channel and p-channel and that the magnitude of g_m change is dependent on the crystallographic orientation.