Extended drain metal oxide semiconductor transistor and manufacturing method thereof

1. A metal-oxide-semiconductor transistor having an extended drain structure comprising:

a semiconductor substrate having a well of a first conductivity type;

a gate insulating layer formed on the substrate;

a gate electrode formed on the gate insulating layer;

a source region formed in a first portion of the well in the substrate, which is near to one side of the gate insulating layer and the gate electrode;

a drain region formed in a second portion of the well in the substrate, which is near to another side of the gate insulating layer and the gate electrode, said second portion being recessed from the surface of the substrate by a predetermined depth; and

an insulating layer formed on the source region,

wherein the gate insulating layer is located higher than the insulating layer formed on the source region.

2. The transistor of claim 1 further comprising a pair of insulating sidewall spacers formed at both sides of the gate electrode, to which the source and drain regions are aligned.

3. The transistor of claim 2 further comprising lightly doped source and drain regions.

4. The transistor of claim 1 further comprising a protective layer on the gate electrode.

5. The transistor of claim 4 , wherein the semiconductor substrate is a silicon substrate, the gate electrode is made of polysilicon, and the protective layer includes a silicon oxide layer formed on the polysilicon gate electrode and a silicon nitride layer formed on the silicon oxide layer.

6. The transistor of claim 1 , wherein the insulating layer formed on the source region is also formed on sidewalls of the gate electrode.

7. A method for fabricating a metal-oxide-semiconductor transistor having an extended drain structure, comprising the steps of:

(A) forming a well of a first conductivity type in a semiconductor substrate;

(B) sequentially depositing a gate insulating layer and a gate conducting layer on the substrate;

(C) forming a gate stack by patterning the gate insulating layer and the gate conducting layer;

(D) forming a photoresist pattern, which covers the surface of the substrate and opens a portion of the substrate at one side of the gate stack;

(E) etching the portion of the substrate, which is opened by the photoresist pattern, to a predetermined depth to form a recessed region in the substrate;

(F) forming an insulating layer on the source region, the insulating layer being located lower than the gate insulating layer; and

(G) injecting dopants of a second conductivity type into the well of the substrate to form a drain region in the recessed region of the substrate at said one side of the gate stack and to form a source region in a surface region of the substrate at another side of the gate stack.

8. The method of claim 7 , wherein a protective layer is formed on the gate conducting layer in step (B) and the protective layer is etched during step (C).

9. The method of claim 8 , wherein the semiconductor substrate is a silicon substrate, the gate conducting layer is made of polysilicon, the protective layer includes a first silicon oxide layer and a first silicon nitride layer, and said first silicon oxide layer is formed on the gate conducting layer and said first silicon nitride layer is formed on the first silicon oxide layer.

10. The method of claim 7 , wherein step (G) comprises the steps of:

injecting dopants of the second conductivity type into the substrate at both side of the gate stack to form lightly doped source and drain regions;

forming a pair of insulating sidewall spacers at sidewalls of the gate stack; and

injecting dopants of the second conductivity type into the substrate with the pair of insulating sidewall spacers and gate stack as a mask to form highly doped source and drain regions.

11. The method of claim 7 , wherein the insulating layer formed in step (F) also formed on the on sidewalls of the gate electrode.

12. The method of claim 11 , wherein the insulating layer formed in step (F) is formed by a thermal oxidation process.