Ni-based metallization of GeSn layers: A review and recent advances

Abstract

In this paper, we review the last 10 years studies related to Ni-based metallization of GeSn layers. We also introduce the recent achievements obtained at CEA-Leti.First, we present and discuss the solid-state reaction between a Ni thin film and GeSn layers. At low temperature, a Ni-rich phase, namely the hexagonal ∊-Ni5(GeSn)3 metastable phase, is obtained. This phase is then consumed to the benefit of the mono-stanogermanide phase Ni(GeSn). The Ni/GeSn system exhibits a poor thermal stability mainly governed by 2 phenomena: Ni(GeSn) agglomeration and Sn segregation.We then describe the behavior of Sn during the solid-state reaction and its subsequent impact. Sn tends to segregate first around grain boundaries (GBs) and then toward the sample surface. The presence of Sn around GBs can hamper diffusion paths and impact the solid-state reaction.The last part of this study is dedicated to the technological solutions implemented to overcome the low thermal stability of this system. We review literature solutions and present two options: pre-amorphization by implantation (PAI) prior to metallization and the addition of an alloying element in Ni-based metallization. These solutions enable to extent the thermal stability of the Ni/GeSn system by delaying the Ni(GeSn) agglomeration and Sn segregation phenomena.