Effect of stress on the evolution of mask-edge defects in ion-implanted silicon

Abstract

In an effort to extend the scaling of advanced complementary metal-oxide semiconductor devices, strain has been incorporated to enhance carrier mobility. In this study, the effect of strain on the solid-phase epitaxial regrowth process of patterned wafers was explored. Implants of 1×1015∕cm2 Si+ with an energy of 40keV were introduced into these patterned regions forming a continuous amorphous layer. After implantation, the oxide and nitride masks were removed and the wafers stressed uniaxially between 0 and 250MPa. The wafers were subsequently annealed under stress to crystallize the amorphous layer, which was monitored using transmission electron microscopy. It was found that without stress, defects formed at the mask edge where the vertical and lateral epitaxial regrowth fronts meet. These defects were threading dislocations which form at the amorphous-crystalline interface and propagate to the surface. Tensile stress levels of as little as 50MPa were found to begin to suppress the formation of mask-edge defects by altering the shape of the corner of the regrowing amorphous layer at the mask edge. Tensile stress appears to retard the lateral recrystallization velocity, creating the obtuse corner geometry necessary to prevent the occurrence of a pinch point at the corner and thereby suppressing defect formation. The evidence suggests that the half-loop threading dislocation nucleates at the corner. The role of varying the stress on the formation of mask-edge defects will be discussed.