Mechanism of abnormal dual-peak profiles in large tilt-angle ion implantation studied by SRIM analysis

Large-tilt angle (LTA) implantation has been employed in Si manufacturing processes in many applications, such as lightly-doped drain and Halo Implant. The depth profile of implant ions usually consists of only single peak at incident angle of zero degree with respect to the perpendicular of the silicon surface. However, an abnormal dual-peak profile was observed at LTA (>40 degree) for both boron and phosphorous. By using a Monte Carlo method (SRIM) to simulate the ion implant process, it was found that the projected range of the implant ions agrees with the formation of the first peak position which is shallower in depth. However, the cause for the second peak which corresponds to a depth much deeper in the Si substrate was unknown. During the simulation, it was also found that when the tilt angle was increased, the sputtering yields and Si displacements increased significantly, and this phenomenon indicated that during the LTA implantation, Si damage may not be negligible. The Si damage effect, which was due to either low Si density or transient Si displacement in the simulation, could have led to partial incident ions penetrating much deeper into the Si substrate and thus, caused the emergence of the second peak.