Semiconductor device and method for fabricating the same

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

forming a first well and a second well having a different impurity doping concentration on a substrate;

etching the substrate to form a trench in a boundary region in which the first well and the second well are in contact with each other such that a first side of the trench is disposed in the first well and a second side of the trench is disposed in the second well;

forming a sacrificial pattern to cover the first side of the trench without covering the second side of the trench;

etching an exposed bottom surface of the second side of the trench by using the sacrificial pattern as an etch barrier;

removing the sacrificial pattern; and

filling the trench with an insulation material to form an isolation layer having two different depths with respect to a top surface of the substrate.

2. The method of claim 1 , wherein the substrate has a low-voltage region and a high-voltage region, the first well is disposed in the low-voltage region, and the second well is disposed in the high-voltage region.

3. The method of claim 1 , wherein the impurity doping concentration of the first well is higher than the impurity doping concentration of the second well.

4. The method of claim 1 , wherein the isolation layer has a first bottom surface and a second bottom surface lower than the first bottom surface, and an interface in which the first bottom surface and the second bottom surface are in contact with each other is aligned with an interface in which the first well and the second well are in contact with each other.

5. A method for fabricating a semiconductor device, comprising:

forming a first well and a second well having a different impurity doping concentration on a substrate;

selectively etching the substrate to form a first trench and a second trench in the first well and the second well, respectively, and form a third trench in a boundary region in which the first well and the second well are in contact with each other;

forming a sacrificial pattern filling the first trench and covering a portion of the bottom surface of the third trench;

etching the bottom surface of the second trench and an exposed portion of the bottom surface of the third trench by using the sacrificial pattern as an etch barrier;

removing the sacrificial pattern; and

filling the first trench, the second trench, and the third trench with an insulation material to form a first isolation layer and a second isolation layer in the first well and the second well, respectively, and form a third isolation layer in the boundary region in which the first well and the second well are in contact with each other, the third isolation layer having two different depths with respect to a top surface of the substrate.

6. The method of claim 5 , wherein the substrate has a low-voltage region and a high-voltage region, the first well is disposed in the low-voltage region, and the second well is disposed in the high-voltage region.

7. The method of claim 5 , wherein the impurity doping concentration of the first well is higher than the impurity doping concentration of the second well.

8. The method of claim 5 , wherein the third isolation layer has a first bottom surface having a height substantially equal to a height of the bottom surface of the first isolation layer, and a second bottom surface having a height substantially equal to a height of the bottom surface of the second isolation layer.

9. The method of claim 8 , wherein an interface in which the first bottom surface and the second bottom surface are in contact with each other is aligned with an interface in which the first well and the second well are in contact with each other.

10. The method of claim 5 , further comprising, after forming the first well and the second well, forming a hard mask pattern on the substrate in order to form the first trench, the second trench, and the third trench.

11. The method of claim 10 , wherein the hard mask pattern has a structure in which a first oxide layer, a nitride layer, and a second oxide layer are sequentially stacked.

12. A method for fabricating a semiconductor device, comprising:

sequentially depositing a first insulation layer, a second insulation layer, and a third insulation layer on a substrate, and forming a hard mask pattern by etching the first insulation layer, the second insulation layer, and the third insulation layer until the substrate is exposed;

forming a trench by etching the substrate using the hard mask pattern as an etch barrier;

forming a sacrificial pattern covering a portion of the bottom surface of the trench and one side of the trench;

etching an exposed portion of the bottom surface of the trench using the sacrificial pattern as an etch barrier;

removing the sacrificial pattern; and

filling the trench with an insulation material to form an isolation layer having two different depths with respect to a top surface of the substrate.