Preliminary study on laser annealed NP junction in phosphorus implanted germanium

Abstract

One option in enhancing metal-oxide-semiconductor transistor devices is by replacing silicon with high-mobility material of germanium. However, fabrication of Ge np junction faces low dopant activation problem due to the interaction between dopant and defect that was originated from ion implantation, during thermal annealing process results in dopant deactivation. Eventually, series resistance of np junction between source and drain regions will increase and affect the device drive current. Therefore, minimizing junction resistance remains an important issue to be solved. In this work, ultrafast/high temperature excimer laser of KrF was adopted for post-implantation annealing process in order to achieve high activation level. Laser energy fluences and shot numbers were varied between 100-2000 mJ/cm2 and 1-1000 shots, respectively to investigate the influence of laser parameter to the np junction resistance value, surface morphology and recrystallization. It is found that resistance lower than 300 Ω can be obtained when annealing the substrate between 500-1000 mJ/cm2 with shot number up to two. Taking into consideration on the morphological and structural analyses leads to the conclusion that an optimum parameter for LTA in the sample implanted with phosphorus at higher energy/dose concentration of 40 keV/6.0×1014 cm-2 is 700 mJ/cm2, with shot number of two.