Rapid low-resistance interconnects by selective tungsten deposition on laser-direct-written polysilicon

Polysilicon interconnections were locally deposited on oxide-covered silicon wafers by pyrolysis of silane using a scanned Ar+-laser spot. The 2-µm-wide interconnects, written at scan speeds of 2.5 mm/s, have a 500-µΩ.cm resistivity and exhibit low contact resistance to underlying Al and Al/Si structures. These films were subsequently reacted with WF6vapor to form a tungsten-silicon composite interconnect by the silicon reduction of WF6. Electrical tests show that the conductivity of 0.4-µm-thick conductors is enhanced up to 20-fold, by formation of a surface metallic layer having conductivity characteristic of pure thin-film tungsten. Auger and Rutherford backscattering spectra (RBS) confirm the purity and selectivity of the surface tungsten layer formed at temperatures compatible with preexisting aluminum metallization. The tungsten-polysilicon composite interconnects have applications as rapidly written discretionary metallization for prototyping and in situ analysis of integrated circuits.