Radical and ion compositions of BCl3/Cl-2 plasma and their relation to aluminum etch characteristics

Plasma compositions in BCL3/Cl-2 were calculated using a molecular orbital method and a plasma kinetic method. The key factors for plasma compositions and their relations to the etch characteristics of Al-based multilayers were investigated. The etch rate of Al seemed to be correlated with the Cl density rather than the Cl-2 density. The etch rates of TiN and the resist were also related to the Cl density and the ion density. Therefore the ion energy distribution (IED) impinging on the wafer was also calculated and the rf frequency dependence of the selectivity of the TiN/resist was evaluated using an etching model. Even if the rf frequency increased to 10 MHz, where the IED had a single peak, the predicted selectivity was slightly improved. A narrower IED was required.