Tungsten plug etchback and substrate damage measured by atomic force microscopy

Filling contact and vias holes with chemical vapor deposited (CVD) tungsten (W) eliminates the problems encountered with poor metal step coverage when using sputtered metals. Because of this advantage CVD W plugs have become widely used. The most common method of forming W plugs is to etchback a blanket layer of W leaving only the plugs intact. One major problem to overcome in this processing is the need for selectivity to the underlying barrier metal. This is especially true if the intent is to leave the barrier metal intact using it as the basis for the aluminum (Al) metallization. If this approach is taken, the effect of the W etchback process on the barrier metal and on any subsequent Al deposition is important. A blanket etchback process using a transformer coupled plasma (TCP) etcher was developed taking into account not only etch rate, selectivity, and plug loss, but also the effect of the structure of the barrier metal on the subsequent Al deposition. Surface damage of the underlying barrier metal...