High energy, low dose ion implantation monitoring and characterization using the C(V) technique

The threshold voltage is one of the most important parameters in DRAM, logic and analog designs that has to be controlled. Generally, it is determined by the oxide thickness, by ion implantation doping and by substrate doping. In the literature, much attention is paid to threshold voltage adjust implants but not to the influence of the well implantation on the threshold voltage. In this paper, the influence of the energy and dose variation of the well implantation on the threshold voltage of the buried channel PFET is shown. It was found that the accuracy of the energy is as important as that of the dose. For selecting the required ion energy the most widely used modern high energy implanter uses a calibrated magnetic field. After a calibration of the magnetic field it is very important to check the accuracy of the energy. For this, the capacitance-voltage (C(V)) technique is suitable. This method allows one to determine simultaneously the profile on several points on the wafer. It can only be used for low dose implants. Results are shown for implant energies between 130 to 1350 keV with a dose range from 5-10¹¹ to 2.7·10¹² implanted through 22 mm screen oxide. For selected energies the energy sensitivity was studied