Crystallographic orientation of Ta/TaN bilayer and its effect on seed and bulk Cu 〈111〉 formation

Abstract

The effect of nitrogen flow rate on the phase formation of TaN formation through ionized physical vapor deposition (IPVD) as well as its effect on the subsequent deposition of Cu seed and the bulk Cu layer has been investigated. The objective is to understand the barrier characteristics and its effect, if any, on the formation of Cu〈111〉 phases. The four main phases of Orthorhombic, Hexagonal, BCC and FCC were found to be present in the film, with BCC and Orthorhombic phases being the major constituents across different flow rates of nitrogen. A summary of the different crystallographic orientations has been recorded. At 20sccm nitrogen flow rate, the bulk of the film consists of Orthorhombic structure with a smaller mixture of BCC and FCC phases. This Orthorhombic phase in the film tends to form in an inversely proportional manner to the BCC phase. As the nitrogen flow rate increases to 40sccm, the bulk trend changes to more BCC phase and lesser Orthorhombic. The small percentage of FCC phases also tends to decline with the rising nitrogen flow rate. At 60sccm, the BCC phase has reached a maximum while the Orthorhombic reaches its minimum. The presence of a high percentage of BCC TaN substrate was found to increase the formation of Ta 〈110〉. Contrary to former reports [8], it was found that the presence of Ta〈110〉 does not facilitate the growth of Cu〈111〉 seed layer. Thicker electroplated Cu was found to be independent of the Cu seed orientation and the underlying Ta or TaN based diffusion barrier. © 2005 Materials Research Society.