Laser programmed vias for restructurable VLSI

A technique has been developed which uses a laser to form selectively connecting vias between two levels of aluminum wiring on a silicon wafer. The same laser can remove metal thus providing a capability of either adding or deleting connections in fully fabricated devices. Experiments have been performed with a commercial IC mask trimmer using a 100 nsec pulse width neodymium YAG laser. Single pulses provide low resistivity connections with no thermal annealing required. The inter-metal insulating layer is formed by sputtering 2600 Å of amorphous silicon. Chains containing forty 6.3 µm × 6.3µm vias between first and second level metal were successfully connected with low resistances and high current capability. At a thickness of 4400 Å of thermal oxide breakthrough to the substrate limits the operating margins on laser power to only 10% above the power for 100% via contacts; at one micron breakthrough is eliminated entirely.