Laser-assisted deposition of Cu bumps for microelectronic packaging

Cu bump was transferred using a focused laser pulse for microelectronic packaging. An Nd:YAG laser pulse (maximum energy of 500 mJ; wavelength of 1064 nm; fluences of 0.4-2.1 kJ/cm2) was irradiated on a sacrificial absorption layer with copper coating. The focused laser beam induced plasma between the semi-transparent donor slide and the sacrificial layer, causing a shock wave. The shock wave pressure pushed the Cu layer and transferred material to deposit a bump on substrate. A beam-shaper was used to produce uniform pressure at the interface to reduce fragmentation of the transferred material on the substrate. The calculated shock wave pressure with respect to laser fluence was 1-3 GPa. A Cu bump of diameter of 200 μm was successfully deposited at laser fluence of 0.6 kJ/cm2. The pressure control at the sacrificial layer using a laser pulse was critical to produce a bump with less fragmentation. The technique can be applied to forming Cu bump for an interconnecting process in electronics.