Stress behavior of electrodeposited copper films as mechanical supporters for light emitting diodes
By Kim, Sunjung; Jang, Jun-Ho; Lee, Jeong-Soo & Duquette, David J.
Published in Electrochimica Acta
2007
Abstract
Thick copper films electrodeposited on vertically structured GaN-based LEDs play a critical role in supporting thin GaN multi-layers mechanically after laser lift-off (LLO) of the sapphire substrate. The intrinsic stress of electrodeposited copper was measured from the change in the substrate's curvature using a modified Stoney equation. 150-μm thick copper supporters showed very low intrinsic stress of 4–28 MPa (tensile stress), which developed during copper electrodeposition on Au seed. The stress generation was attributed to nuclei coalescence and formation of grain boundaries of which volume increased with the applied current density. The preferential texture plane of thick copper supporters was (2 2 0) at high current densities, while copper films thinner than 1 μm was strongly oriented along (1 1 1) plane. Various seed metals such as Cu, Ni, Au, Ag, and Al were employed to observe the influence of seed material on the stress of copper supporters. The effect of wetting agent on the stress of copper supporters was also monitored in the concentration range of 0.1–1.5 g/L of sodium lauryl sulfate (SLS).