Germanium MOSFET Devices: Advances in Materials Understanding, Process Development, and Electrical Performance

Abstract

Germanium possesses higher electron and hole mobilities than silicon. There is a big leap, however, between these basic material parameters and implementation for high-performance microelectronics. Here we discuss some of the major issues for Ge metal oxide semiconductor field effect transistors (MOSFETs). Substrate options are overviewed. A dislocation reduction anneal decreases threading dislocation densities for Ge-on-Si wafers 10-fold to ; however, only a 2 times reduction in junction leakage is observed and no benefit is seen in on-state current. Ge wet etch rates are reported in a variety of acidic, basic, oxidizing, and organic solutions, and modifications of the RCA clean suitable for Ge are discussed. Thin, strained epi-Si is examined as a passivation of the Ge/gate dielectric interface, with an optimized thickness found at monolayers. Dopant species are overviewed. P and As halos are compared, with better short channel control observed for As. Area leakage currents are presented for p+/n diodes, with the n-doping level varied over the range relevant for pMOS. Germanide options are discussed, with NiGe showing the most promise. A defect mode for NiGe is reported, along with a fix involving two anneal steps. Finally, the benefit of an end-of-process anneal for device performance is shown.