Semiconductor devices and methods of manufacturing the same

A method of manufacturing a semiconductor device, the method comprising:

• forming a gate insulation layer on a substrate including a first region and a second region;
• forming a first polysilicon layer and a second polysilicon layer on the gate insulation layer, the first polysilicon layer including atoms larger than silicon and being on a first portion of the gate insulation layer in the first region, and the second polysilicon layer including atoms smaller than silicon and being on a second portion of the gate insulation layer in the second region;
• forming a first hard mask and a second hard mask on the first and second polysilicon layers, respectively;
• patterning the first and second polysilicon layers and the first and second portions of the gate insulation layer to form first and second gate electrodes and first and second gate insulation layer patterns, respectively;
• forming n-type impurity regions by implanting n-type impurities at first upper portions of the substrate adjacent to the first gate electrode;
• and
• forming p-type impurity regions by implanting p-type impurities at second upper portions of the substrate adjacent to the second gate electrode.