MOS TRANSISTOR AND FABRICATING METHOD THEREOF FOR PREVENTING LEAKAGE CURRENT AND IMPROVING RELIABILITY

摘要

PURPOSE: A MOS transistor and a fabricating method thereof are provided to prevent a leakage current and improve reliability by forming an LDD region with an ultra-low-density impurity region and a low-density impurity region. CONSTITUTION: A low-density impurity region(13) is formed by implanting low density impurities into a semiconductor substrate(11). An epitaxial layer(15) and a gate oxide layer(16) are formed on the semiconductor substrate except for the low-density impurity region. A gate(17) having a width smaller than a width of the epitaxial layer is formed on the gate oxide layer. An ultra-low-density impurity region(19) is formed by implanting ultra-low-density impurities into the epitaxial layer outside the gate. A sidewall(21) is formed on the gate and a lateral part of the epitaxial layer. A source/drain region(22) is formed by implanting high-density impurities into the semiconductor substrate outside the sidewall.