Electrochemically deposited thin film alloys for ULSI and MEMS applications

Thin metal films can be electro-deposited for interconnect metallization and packaging. Electro-forming offers unique properties, such as excellent filling of high aspect ratio structures, unique compositions, low temperature processing and low stress films. Electroless forming offers also high selectivity. Binary and ternary metallic alloys, such as Ni, Co and Cu, alloyed with iron, phosphorous, boron and refractory metals have been demonstrated to form conducting layers, barriers, and corrosion protection layers. High quality very thin films, with thickness varied between 5 nm and 1 μm, have been demonstrated with good composition control. After reviewing the basic deposition mechanisms we focus on Co and Ni alloys with refractory metals (e.g., tungsten and molybdenum) and with phosphorous and/or boron. We present results of electroless deposition of CoWP as examples for an electrochemical process compatible with silicon technology. Finally we present a process outline for alloy deposition on silicon, or SiO₂, for MEMS applications.