Practical Electron Microscopy and Database

In integrated circuits (ICs), conductive lines provide electrical interconnection among different parts of the ICs, devices, and the outside. The main applications of metallization are classified by gate, contact, and interconnection. Polysilicon and silicides are commonly applied as gates and interconnects in MOS devices. Aluminum, copper, tungsten, silver, titanium, platinum, gold, and palladium are used as these types of contacts, connections, and/or interconnection to external components. The requirements of the metals for the ICs normally involve:
       1) Low resistivity;
       2) Easy to deposit;
       3) Good etchability for clean pattern generation;
       4) Minimal need for post planarization;
       5) High melting point;
       6) Stable in oxidation environments;
       7) High electromigration resistance;
       8) Mechanical stability, good adherence to interlayer dielectrics and other  materials on the chip, and low stress;
       9) Substrate matched coefficient of thermal expansion;
       10) High resistance throughout processing, including corrosion, high temperature sinter, dry or wet oxidation, gettering, phosphorus glass passivation, and metallization;
       11) Does not contaminate devices, wafers, or working apparatus;
       12) Compatible with surrounding materials and their processing
       13) Good device characteristics and lifetimes;
       14) Low contact resistance, minimal junction penetration if used for window contacts;
       15) Low cost.

Note that practically no metal can satisfy all the desired characteristics above.

Metallization processing includes i) PVD, CVD, or electroplating, ii) damascene process, and iii) chemical mechanical polishing.