Alain Boudou

Laser Programmable Vias For Reconfiguration Of Integrated Circuits

The post process reconfiguration of 2 metal layers integrated VLSI circuits, achieved by via formation in intermetal oxide, was studied with doubled frequency YAG laser (532 nm). The creation of vias is experimented on test patterns placed within 3 circuits of different technology. Vias thus formed are created by thermal effect with mechanism of fusion and by mechanical explosion in the insulating layers. No damage was verified by electrical measurements and SEM cross section studies. For metallizations containing refractory metals, the via yields reached 100 % for patterns of 2.6 μm x 4.7 μm. The feasibility of this process has been established for recovering area of 3 μm x 3 μm. Via resistance was measured to be a few Ohms without resorting to post process annealing and the minimum breakdown current was found to be 150 mA. A via is creatable in a metallic line without damaging others lines as close as 1.5 μm. Reliability test of vias at 125°C and 5 mA showedno failure after 1000 hours. Consequently, creation of vias by laser has been shown to be achievable in a metal interconnection environment conforming to VLSI minimum design rules of 1.2 μm.