Method for manufacturing synchronous DRAM device

A method for manufacturing a synchronous dynamic random access memory (SDRAM), comprising the steps of:

• a) preparing a semiconductor substrate on which a gate insulating layer, a stacked gate having a polysilicon layer and a metal layer containing tungsten, and an insulating layer are formed;
• b) forming a first oxide layer on the semiconductor substrate and sidewalls of the polysilicon layer, whereby a resulting structure is formed;
• c) forming a first nitride layer on the resulting structure;
• d) forming first nitride spacers on sidewalls of the metal layer, on the first oxide layer and on the gate insulating layer by applying a blanket etching process to the first nitride layer;
• e) injecting dopants into the semiconductor substrate exposed at both sides of the first nitride layer spacers;
• f) forming source/drain regions by activating the dopants through a thermal treatment in an O2 atmosphere and simultaneously forming a second oxide layer on a surface of the substrate;
• and
• g) forming second nitride layer spacers on sidewalls of the first nitride layer and on the second oxide layer, wherein the second oxide layer is a buffer layer to decrease stress caused by the second nitride layer.