Platinum Germanosilicide Contacts Formed on Strained and Relaxed $\hbox {Si}_{1 - x}\hbox {Ge}_{x}$ Layers

Contact resistivity is a key contributor to the parasitic series resistance of nanoscale MOSFETs. Since the contact resistivity is an exponential function of the Schottky barrier height, new contact materials that can provide smaller barrier heights to source-drain junctions are needed. Platinum germanosilicide (PtSi_1-xGe_x) is of interest as a contact material to the recessed Si_1-xGe_x junctions of p-channel MOSFETs due to the large work function of platinum silicide (PtSi). In this paper, we explore the impact of in-plane biaxial compressive strain in Si_1-xGe_x layers on PtSi_1-xGe_x formation and the impact of the PtSi_1-xGe_x on the strain in Si_1-xGe_x. The parameters considered in this paper include the Ge content, the thickness of the Si_1-xGe_x epitaxial layer, and the PtSi_1-xGe_x thickness. The results show that the resistance, surface morphology, and the crystalline structure of the PtSi_1-xGe_x films are independent of the strain in the original Si_1-xGe_x layer. The results also indicate that PtSi_1-xGe_x does not influence the strain in the Si_1-xGe_x layer. The barrier-height measurements suggest the presence of Fermi-level pinning, and the pinning position is independent of the strain in the alloy, and it is primarily determined by the Ge concentration. As a result of Fermi-level pinning, hole Schottky barrier height of PtSi_1-xGe_x-Si_1-xGe_x contacts is 0.1-0.2 eV higher than that of the PtSi-Si contacts.