Achievement of Ultralow Contact Resistivity of Metal/n+-Ge Contacts with Zr-N-Ge Amorphous Interlayer

A bottleneck for achieving Ge-CMOS is the Fermi-level pinning (FLP) phenomenon, which causes high electron barrier height (Phi(BN)) for metal/Ge contacts, resulting in an increase in contact resistivity (rho(C)) between metal and n(+)-source/drain for n-MOSFET. We have found that the low Phi(BN) can be realized by directly sputtered TiN/Ge and ZrN/Ge contacts, which is induced by amorphous interlayer (alpha-IL) formed during the sputter deposition. In this paper, we present that the alpha-IL in the ZrN/Ge contact can be retained on Ge surface, which enables us to fabricate metal/alpha-IL/Ge contacts with different metals. We investigated the electrical properties of metal/alpha-IL/Ge and metal/alpha-IL/n(+)-Ge contacts and showed that the alpha-IL remarkably modulate the Phi(BN) and rho(C). As a result, we succeeded in ultralow rho(C) for Ag/alpha-IL/n(+)-Ge with post metallization annealing at 400 degrees C, which was an average rho(C) value of 2 x 10(-7)Omega.cm(2) .