METHOD FOR FABRICATING SEMICONDUCTOR DEVICE

摘要

PURPOSE: A method for fabricating a semiconductor device is provided to prevent a gate and a bitline from being electrically short-circuited by a polysilicon layer left in a moat by controlling the doping density of the impurities of a polysilicon layer as a gate material and by oxidizing all of the polysilicon layer left in the moat by a thermal oxide process after the gate is formed. CONSTITUTION: An STI(shallow trench isolation) process is performed on a field region of a silicon substrate(21) to form a trench-type isolation layer(26) having a moat of a dual profile at its upper edge. A gate oxide layer(27) is formed on the entire region of the substrate including the isolation layer having the moat of the dual profile. The first polysilicon layer doped with phosphor of a density designating a sufficient oxidation rate is deposited on the gate oxide layer. The second polysilicon layer doped with phosphor of a relatively low density is deposited on the first polysilicon layer. The third undoped polysilicon layer is deposited on the second polysilicon layer. A tungsten silicide layer(29) is deposited on the third polysilicon layer. The tungsten silicide layer, the third, second and first polysilicon layers and the gate oxide layer are etched to form a gate. A heat oxide process is performed on the resultant structure to recover etch damage and the first polysilicon layer remaining at the moat of the isolation layer is oxidized.