Improvement of Contact Resistance with Molecular Ion Implantation Available to Purchase

Basic characteristics of ClusterBoron™ $(B18H22)$ 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 $(∼800 °C)$ anneal, the sheet resistance was saturated for doses over $5×1015 ions/cm2.$ 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 $5×1015 ions/cm2$ 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.