1. Technical Field
The inventive concept relates to semiconductor devices and methods of fabricating the same. More particularly, the inventive concept relates to metal-oxide-semiconductor (MOS) transistors and methods of fabricating the same.
2. Description of Related Art
There is an ever increasing demand for more highly integrated and higher performance semiconductor devices. In this respect, metal-oxide-semiconductor (MOS) transistors constituting semiconductor devices are continuously being scaled down. For example, the thickness of gate insulation layers of MOS transistors and the channel length of the MOS transistors are being minimized in an attempt to maximize the density of integration and performance of semiconductor devices. In particular, reducing the thickness of the gate insulation layers of the MOS transistors and the channel length of the MOS transistors results in an increase in the mobility of carriers (e.g., electrons or holes) of the MOS transistors and thus, an increase in the operating speed of the semiconductor devices. However, small channel lengths of the MOS transistors sometimes give rise to a so-called short channel effect, and thin gate insulation layers may allow for excessive gate leakage current. To suppress such a short channel effect, the channel of a MOS transistor may be formed with a high concentration of impurities. However, in this case, the carrier mobility in the channel region is compromised by the impurities in the channel region because the greater the concentration of the impurities the lower the carrier mobility. Therefore, the switching speed of the MOS transistors is impeded even though the channel length is kept to a minimum.