Current evolution of electrodeposited copper bumps with photoresist angle

We report the current distribution of copper bumps with photoresist sidewall angles. The role of outer diffusion, vortices, and penetration flow within the cavity is discussed, with numerical fluid dynamics computed in order to prevent side bumping. The current distributions were calculated at the diffusion controlled overpotential. The mass transfer-limited current distribution showed that a zero or negative angle reduced diffusion from the outer surroundings and enhanced vortex formation at the cathode corners. Reduction in the diffusion and enhancement in vortices reduced current at the cathode corners and prevented side bumping.