Semiconductor device and method for fabricating the same

1. A method for fabricating a semiconductor device comprising a memory section formed in a semiconductor region and including a first transistor having a first gate dielectric that can store charges and a first isolation region for isolating the first transistor, and a logic section including a second transistor having a second gate dielectric and a second isolation region for isolating the second transistor, said method comprising the steps of:

(a) forming the first isolation region and the second isolation region in a memory formation area and a logic formation area of the semiconductor region, respectively;

(b) making the height of the first isolation region from the top surface of the semiconductor region smaller than that of the second isolation region from the top surface of the semiconductor region;

(c) after the step (b), forming the first gate dielectric on all the surfaces of the memory formation area and the logic formation area of the semiconductor region, the first isolation region and the second isolation region;

(d) removing a part of the first gate dielectric covering the logic formation area;

(e) forming the second gate dielectric on the logic formation area of the semiconductor region;

(f) forming a gate electrode of the first transistor on the first gate dielectric in the memory formation area and forming a gate electrode of the second transistor on the second gate dielectric in the logic formation area;

(g) forming sidewalls on respective at least one sides of the gate electrodes of the first and second transistors; and

(h) forming source/drain diffusion layers of the first transistor in the memory formation area of the semiconductor region and source/drain diffusion layers of the second transistor in the logic formation area of the semiconductor region, wherein the height

of the first isolation region from the top surface of the semiconductor region is smaller than the height of the second isolation region from the top surface of the semiconductor region.

2. The method of claim 1 , wherein

the first gate dielectric is a multilayer film of silicon nitride and silicon oxide.

3. The method of claim 1 , wherein

the first gate dielectric is an ONO film (a multilayer film obtained by successively stacking a silicon oxide film, a silicon nitride film and a silicon oxide film).

4. The method of claim 1 , wherein

the first and second isolation regions are trench isolation regions obtained by forming trenches in the upper part of the semiconductor region and filling the formed trenches with an insulator.

5. The method of claim 1 , wherein

the step (b) comprises the steps of:

forming a mask pattern having an opening corresponding to the memory formation area; and

selectively removing the upper part of the first isolation region by etching using the formed mask pattern.

6. The method of claim 1 , further comprising the step of forming metal silicide layers on the source/drain diffusion layers of the first transistor and the source/drain diffusion layers of the second transistor, respectively.