Dopant diffusion and activation induced by sub-melt laser anneal within the co-implanted p+ polycrystalline silicon gate used in CMOS technologies

Abstract

Due to the continuous CMOS transistor scaling requirements, highly doped shallow junctions with improved activation have been widely investigated in recent CMOS technologies. In this scope, sub-melt millisecond laser annealing has been introduced in the integration flows to enhance dopant activation, without any additional detrimental diffusion. This MSA step impacts not only the transistor junction properties, but also the polysilicon gate depletion. This paper is devoted to the study of the MSA influence on boron and germanium co-implanted polysilicon films. A sensitive boron diffusion occurring during the laser anneal step, with or without an initial spike annealing step, has been observed. The activation energy of the boron diffusivity extracted from SIMS profiles in the laser only sequence has been found equal to 4.05 eV. In addition, it was shown that either a high temperature laser anneal sequence or a spike anneal followed by a laser anneal sequence can reach the same activation levels.