Ultrashallow P+/N junctions using BCl2+ implantations for sub 0.1 μm CMOS devices

Abstract

Boron and more recently BF2 implantation are commonly used in production to achieve ultra shallow P+/N junctions. Very low energy implantation is needed for Boron and then specific ultra low energy implanters are necessary. Several studies have shown that Fluorine enhances Boron diffusion through the gate oxide and then BF2 is not so favorable. BCl2 implantation showed the interest of its high atomic mass to get shallow Boron as implanted profile, so that higher energy is needed to achieve the same depth. In this paper we show the implementation of the BCl2+ implantation process on a medium current implanter. BCl2 have been implanted with energies from 8 keV down to 3 keV with doses of 5e13 to 1e15 at/cm2. Such kind of implantation energy is equal to a 1.1 keV down to 400 eV Boron implant equivalent energy and p+/n junction can reach the 50nm ITRS node. SIMS characterizations combined with sheet resistance 4-point probe measurements shows very interesting result in terms of Xj vs. Rs criteria for the junction. Polysilicon gate implantation has also been done to look at the chlorine effect on Boron diffusion through the gate oxide. Defect in c-Si injected during implantation step is much higher with the high effective mass of this cluster ion, and amorphisation occurs with doses close to 2e14 at/cm2. Therefore the annealing step is regarded as a key point to restrict the Boron diffusion. Spike anneal activation as well as curing furnace anneal are also addressed here for BCl2.