Plasma doping method and method for fabricating semiconductor device using the same

A method for fabricating a semiconductor device, the method comprising:

• forming a gate insulation layer over a substrate;
• forming a polysilicon layer over the gate insulation layer;
• doping the polysilicon layer with impurities by performing a plasma doping method, wherein the plasma doping method is performed while applying a bias voltage to the substrate, the bias voltage being changed from a lower range, through a medium range to a higher range and the dosage of the impurities in the medium range is higher than those in the lower range and higher range;
• annealing the substrate such that an impurity profile of the doped polysilicon layer resembles a Gaussian distribution with respect to a doping depth;
• and
• forming a conductive layer including a metal-based material over the doped polysilicon layer.

A plasma doping method comprising:

• providing a plasma doping source over a substrate, the plasma doping source having dopants that are to be injected into a target layer formed over the substrate;
• injecting the dopants from the plasma doping source into the target layer while applying a bias voltage to the substrate, the bias voltage being changed from a higher range, through a medium range to a lower range and the dosage of the dopants in the medium range is higher than those in the lower range and higher range;
• and
• annealing the substrate such that an impurity profile of the dopants resembles a Gaussian distribution with respect to a doping depth.