Recrystallization, redistribution, and electrical activation of strained-silicon/Si0.7Ge0.3 heterostructures with implanted arsenic

For strained-silicon metal-oxide-semiconductor field-effect-transistors (MOSFETs), the formation of a low-resistance source and drain region is as important in terms of enhanced performance as optimizing the strain-induced increase in inversion-carrier mobility. The crystallographic, compositional, and electrical properties of an arsenic-ion implanted strained silicon/Si0.7Ge0.3 heterostructure were investigated in order to acquire basic information for fabricating low-resistance source and drain region of the n-channel strained-silicon MOSFET. The strained-silicon layer is completely recrystallized by rapid thermal annealing after arsenic implantation, but misfit dislocations were formed by annealing (at 1000 degreesC) in the case thickness of the strained-silicon layer exceeding the critical thickness. Arsenic diffusivity in strained silicon was identical to that in silicon, whereas that in SiGe was higher than that in silicon. Germanium recoil and enhanced diffusion caused by arsenic implantation to the SiGe layer was observed. This phenomenon can degrade the abruptness of the strained-silicon/SiGe interface during the formation of a shallow source and drain region. Solubility limit of arsenic in strained silicon was 2x10(20) cm(-3) and identical to that in silicon, on the other hand, the solubility limit in Si0.7Ge0.3 reduced by half. Electron mobility in strained silicon was by about 20%-30% higher than that in silicon, and that in Si0.7Ge0.3 was by about 20%-30% lower than those in silicon. In order to reduce parasitic resistance in the shallow source and drain region, thicker strained silicon layer is thus desirable, however, it should be very careful to control the strained-silicon thickness below the critical value. (C) 2004 American Institute of Physics.