Source/drain engineering for parasitic resistance reduction for germanium p-MOSFETs

A reduction of parasitic resistance is presented with incorporation of preamorphization implantation (PAI) and self-aligned CU3Ge in the source/drain region for germanium p-MOSFETs. Full activation of boron in the amorphous layer can be obtained during solid-phase epitaxial growth, and a concentration as high as 4 x 10(20)/cm(3), is achieved. This non-thermal equilibrium concentration is maintained during the subsequent CU3Ge formation. Cu3Ge is adopted as a contact metal in germanium p-MOSFETs for the first time, due to its superior electrical properties (6.8 mu ohm center dot ern for resistivity and similar to 1 x 10(-7) ohm center dot cm(2) on p-type germanium for specific contact resistance). The fabricated p(+)/n diode yields a five order of magnitude between forward and reverse currents, which can be attributed to the reduction in parasitic resistance. The low reverse current mitigates concerns of possible deep-level traps introduced by copper. It also confirms the nonexistence of extended defects created by PAI as a result of the unique role of vacancies in germanium. With high dopant concentrations achieved by PAI and low resistance Of Cu3Ge, excellent MOSFET characteristics are demonstrated in self-aligned CU3Ge p-MOSFETs. A 15% mobility enhancement over Si universal mobility and a 60% parasitic resistance reduction are achieved.