Halo doping is done near the source and drain junction in MOSFETs to create a shallow, lightly doped region between the heavily doped source and drain regions. This helps to reduce the electric field at the drain junction and improve device performance.
Halo doping helps to reduce the leakage current and improve the subthreshold slope of MOSFETs. It also helps to reduce the short channel effect and improve the breakdown voltage of the device.
While halo doping is typically done near the source and drain junction, it can also be done at other locations such as the channel region or the gate region. However, doping near the source and drain junction has been found to be the most effective in improving device performance.
Halo doping is achieved through the use of ion implantation, where dopant atoms are implanted into the silicon substrate near the source and drain junction. The dopant atoms used are typically boron or phosphorus, which are commonly used dopants in semiconductor devices.
One potential disadvantage of halo doping is the increase in junction capacitance, which can limit the switching speed of the MOSFET. Additionally, if not properly controlled, halo doping can also lead to increased leakage current and decreased breakdown voltage. Therefore, careful optimization and control of the halo doping process is necessary to avoid these potential drawbacks.