| 摘要 |
PURPOSE: A method for fabricating a transistor of a semiconductor device is provided to improve the characteristic of a metal oxide semiconductor field effect transistor(MOSFET) by forming an insulation layer under a source/drain region where a depletion layer is generated. CONSTITUTION: A gate electrode(17) is patterned on a semiconductor substrate(11) including a trench-type isolation layer while a trench having a depth of a source/drain region is formed by over-etching. An oxide layer(21) and a nitride layer are stacked on the resultant structure including the trench. The nitride layer is anisotropically etched to form a nitride layer spacer on the sidewall of the trench by using a difference of etch selectivity of the nitride layer and the oxide layer while the nitride layer spacer having a predetermined height from the bottom of the trench is left by over-etching. Only the oxide layer exposed to the upper portion of the nitride layer spacer is removed by a wet process. The nitride layer spacer is eliminated to leave the oxide layer in the bottom of the trench and in the lower portion of the sidewall of the trench. The trench is filled with a polysilicon layer(25) doped with low density impurities. An insulation layer spacer(27) is formed on the sidewall of the gate electrode. High density impurity ions are implanted into the polysilicon layer by using the gate electrode and the insulation layer spacer on the sidewall of the gate electrode as a mask.
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