Contact resistance of focused ion beam deposited platinum and tungsten films to silicon

Focused ion beam (FIB) techniques are currently being used in industry for circuit repair and rewiring in the prototyping stage. The ability to deposit a conductor directly onto silicon with a good electrical contact using the FIB methods would increase the utility of this technique in repair and circuit function diagnosis. In addition, FIB made contacts may be encountered in microelectromechanical devices (MEMS), and, when combined with FIB direct implantation, may permit local fabrication of transistors [e.g., bipolars and junction field-effect transistors (JFETs)] without conventional, planar techniques. The contact resistance of FIB-deposited platinum and tungsten onto variously doped silicon was investigated. FIB-metal contact to n(+) and p(+) Si was found to be ohmic after a sintering at 400 degreesC for 20 min in H2N2 forming gas. Individual contacts were found to vary widely in contact resistance, likely due to nonuniformity in the deposition process. Contacts to lightly doped Si were nonohmic. The contact resistance for Pt contacts to heavily doped Si was found to be on the order of 10(-2) Omega cm(2), and the contact resistance for W contacts on the order of 10(-3) Omega cm(2). It is believed that the sintering leads to formation Of Pt2Si and PtSi silicides, which may interfere with the metal/semiconductor tunneling contact. Platinum silicides form around 300 degreesC, at the metal to silicon interface for the platinum contacts. Tungsten silicide, WSi2, forms at 650 degreesC and is not believed to play a part in the tungsten contact dynamics. (C) 2001 American Vacuum Society.