As the critical dimension of metal oxide semiconductor field effect transistor (MOSFET) devices continues to shrink, the short channel effect becomes more problematic. Fin field effect transistor (FinFET) devices have better control capability of gates than planar MOSFET devices to effectively suppress the short channel effect. Gate-all-around (GAA) devices have even better control ability than FinFET devices to more effectively suppress the short channel effect. An example of a GAA device is a nanowire vertical transistor.
In the manufacturing process of a FinFET or nanowire vertical transistor device, the device's threshold voltage (Vt) is generally adjusted by doping the fin or the nanowire. However, as the critical dimension of the device decreases, the size of the fin and the nanowire is getting smaller and smaller, adjusting the device's threshold voltage by doping is not ideal. For devices with different threshold voltages, there is a need for different doping levels of the fin or nanowire, but because the size of the fin and nanowire is getting smaller and smaller, the total amount of dopants that can be implanted in the fin or nanowire is limited. Therefore, the range of the threshold voltages through doping the fin or the nanowire is also limited. In addition, adjusting the threshold voltages by doping will inevitably cause damage to the fin or the nanowire. Further, implantation of dopants into the fin or the nanowire may result in mobility degradation in the channel due to dopant scattering.