Semiconductor structure and method for fabricating semiconductor structure

1. A method for fabricating a semiconductor structure, comprising:

forming a gate oxide layer;

forming a gate structure on the gate oxide layer;

forming a source region and a drain region on two sides of the gate structure; and

forming a conductive plug at a corresponding location of the source region and a corresponding location of the drain region, respectively;

wherein the gate structure comprises a conductive layer having a recessed side surface facing toward the conductive plug;

wherein the forming a gate structure on the gate oxide layer comprises:

forming a first conductive layer on the gate oxide layer;

forming a second conductive layer on the first conductive layer, the second conductive layer comprising a plurality of metal layers stacked;

repeatedly performing following steps until the first conductive layer is exposed: if a current layer exposed in a first region is a predetermined metal layer, performing non-identical isotropic etching on the predetermined metal layer in the first region until a next metal layer is exposed, or etching the predetermined metal layer in the first region for a first time until a next metal layer is exposed and then etching the predetermined metal layer for a second time, such that the predetermined metal layer has a recessed side surface facing toward the source region and the drain region; and if the current layer exposed in the first region is not the predetermined metal layer, etching down the current layer in the first region until a next metal layer is exposed, wherein the first region is a region other than a region between the source region and the drain region; and

etching down the first conductive layer in the first region until the gate oxide layer is exposed to form the gate structure.

2. A method for fabricating a semiconductor structure, comprising:

forming a gate oxide layer;

forming a gate structure on the gate oxide layer;

forming a source region and a drain region on two sides of the gate structure; and

forming a conductive plug at a corresponding location of the source region and a corresponding location of the drain region, respectively;

wherein the gate structure comprises a conductive layer having a recessed side surface facing toward the conductive plug;

wherein the forming a gate structure on the gate oxide layer comprises:

forming a first dielectric layer on the gate oxide layer;

forming a third conductive layer on the first dielectric layer, the third conductive layer being a metal layer;

performing a non-identical isotropic etching on the third conductive layer in a first region until the first dielectric layer is exposed, such that the third conductive layer has a recessed side surface facing toward the source region and the drain region, wherein the first region is a region other than a region between the source region and the drain region; and

etching down the first dielectric layer in the first region until the gate oxide layer is exposed to form the gate structure.

3. A method for fabricating a semiconductor structure, comprising:

forming a gate oxide layer;

forming a gate structure on the gate oxide layer;

forming a source region and a drain region on two sides of the gate structure; and

forming a conductive plug at a corresponding location of the source region and a corresponding location of the drain region, respectively;

wherein the gate structure comprises a conductive layer having a recessed side surface facing toward the conductive plug;

wherein the forming a gate structure on the gate oxide layer comprises:

forming a first dielectric layer on the gate oxide layer;

forming a third conductive layer on the first dielectric layer, the third conductive layer being a metal layer;

etching the third conductive layer in a first region for a first time until the first dielectric layer is exposed;

etching the third conductive layer for a second time, such that the third conductive layer has a recessed side surface facing toward the source region and the drain region; and

etching down the first dielectric layer in the first region until the gate oxide layer is exposed to form the gate structure.

4. The method according to claim 1 , wherein the forming a conductive plug at a corresponding location of the source region and a corresponding location of the drain region comprises:

forming a second dielectric layer on a substrate and the gate structure;

forming a patterned etch protection layer on the second dielectric layer, the etch protection layer covering a surface of a dielectric layer except a partial region corresponding to the source region and a partial region corresponding to the drain region;

etching down from an exposed surface of the second dielectric layer until a surface of the source region and a surface of the drain region are exposed, and over-etching the surface of the source region and the surface of the drain region to form a contact hole with a shallow trench structure at a bottom thereof, the shallow trench structure being positioned in the corresponding source region and the drain region; and

forming a barrier layer on an inner wall of the contact hole, and filling a metal in the contact hole covered with the barrier layer to form the conductive plug.

5. The method according to claim 4 , wherein before the barrier layer is formed on the inner wall of the contact hole, the method further comprises:

forming a metal silicide on an inner wall of the shallow trench structure at the bottom of the contact hole.

6. The method according to claim 1 , wherein the forming a gate structure on the gate oxide layer comprises:

forming a gate structure on the gate oxide layer, wherein a top layer of the gate structure is a protection layer.

7. The method according to claim 1 , wherein after the gate structure is formed on the gate oxide layer, the method further comprises:

forming a side isolation structure on two side surfaces of the gate structure facing toward the source region and the drain region.

8. The method according to claim 7 , wherein the forming a side isolation structure on two side surfaces of the gate structure facing toward the source region and the drain region comprises:

forming a first isolation sidewall on the two side surfaces of the gate structure facing toward the source region and the drain region;

covering a spacer medium on an outer wall of the first isolation sidewall; and

forming a second isolation sidewall on the outer wall of the spacer medium, and a top of the second isolation sidewall extending to a top of the first isolation sidewall to form an enclosed space surrounding the spacer medium.

9. The method according to claim 7 , wherein the forming a side isolation structure on two side surfaces of the gate structure facing toward the source region and the drain region comprises:

forming a third isolation sidewall on two side surfaces of the gate structure facing toward the source region and the drain region;

covering a third dielectric layer on an outer wall of the third isolation sidewall;

forming a fourth isolation sidewall on an outer wall of the third dielectric layer, and a top of the fourth isolation sidewall extending to a top of the third isolation sidewall to form an enclosed space surrounding the third dielectric layer;

etching the top of the fourth isolation sidewall until a surface of the third dielectric layer is exposed to form an etching hole;

etching the third dielectric layer through the etching hole until reaching a surface of the gate oxide layer; and

enclosing the etching hole between the top of the fourth isolation sidewall and the top of the third isolation sidewall by means of a rapid deposition process to form an enclosed space filled with air.