Process effects of copper film over a step etched with a plasma-based process

The additive gas effect of a new plasma-based process for etching the copper film over a dielectric step has been investigated. The addition of different gases, such as Ar, N₂, and CF₄, affected the copper vertical and lateral conversion rates, which are critical to the attack of the cusp region and the sidewall as well as the residue formation. This is due to changes of plasma phase chemistry and ion bombardment energy. Excessive attacks of the cusp region and the sidewall were observed when the chlorine radical concentration was high except for the short plasma exposure time or the sidewall passivation condition. When the slope angle of the dielectric step was small, the cusp structure of the copper film was barely visible; therefore, the excessive plasma attack of the cusp region was negligible. A two step etch process that minimizes excessive attacks of the cusp region and the sidewall as well as the residue formation has been developed. This new process is critical to the practical application of copper in microelectronic products.