Experimental investigation of the optimal laser-induced microbridges

Three new microbridge structures, which are able to form lateral-and-vertical links simultaneously in the metal layers of ICs for low resistance interline connections, are presented in order to solve the issue of undesirable links occurred after laser processing. Comprehensive laser processing experiments were performed to verify these designs. The results show that there exits different performance (electrical resistances) and laser energy windows for these structures. There is no perfect design so that one structure (S2) is selected as an optimal structure by considering of the production reality with respect to the highest yield first and then wider energy window, though it only presents the second low resistance. In addition, the same experiments were performed with the scaled-down structure sizes and two additive factors, relative process window and minimum resistance and its variation, are applied as the criteria to evaluate the scalability of these structures. The structure (S2) is selected as an optimal structure since it is the best design for scalability and it has a low resistance in the small scale. Therefore, structure 2 is determined to be the optimal microbridge design for all structures and scales due to the wide laser energy window, low resistance, high yield, and the best scalability. Moreover, it is able to achieve the fundamental requirements of low power consumption and current leakage for most applications of ASICs.