Improvement of Contact Resistance with Molecular Ion Implantation

Basic characteristics of ClusterBoronTM (B18H22) implantation were investigated for improving contact resistance in DRAM devices. Generally, 49BF2 has been widely used for contact implant application in DRAM manufacturing because of its higher productivity compared to monomer boron (11B). However, because of limited activation in a low thermal budget (~800 deg C) anneal, the sheet resistance was saturated for doses over 5X1015 ions/cm2. Although many investigations have been reported, such as 30BF implant mixed implant with monomer boron etc., no practical solution has been found for dramatic improvement of contact resistance in a productive manner. B18H22 was developed to overcome the productivity limitations encountered in low energy, high dose boron implantation and the limited activation of 49BF2 due to co-implanted fluorine. In this study, basic characterization of the B18H22 contact implant was performed through sheet resistance, SIMS (Secondary Ion Mass Spectrometry) and XTEM (cross-sectional transmission electron microscopy). The B18H22 implants showed lower sheet resistance than conventional 49BF2 for 5X1015 ions/cm2 on bare wafer tests. Through XTEM study, we found the activation behavior of both B18H22 and 49BF2 were directly related with the amorphous layer thickness and residual defects from low thermal budget anneal. PMOS contact resistance in the sub-70 nm device by B18H22 implantation showed considerable improvement (about 30%), showing B18H22 could replace the BF2 for contact implant in contact resistance implant.