Semiconductor device having field-effect structures with different gate materials, and method for manufacturing thereof

1. A method for manufacturing a semiconductor device, the method comprising:

providing a semiconductor substrate having a first side;

forming, at the first side of the semiconductor substrate, a first trench in the semiconductor substrate for a first field-effect structure, the first trench having a first width in a lateral direction and the second trench having a second width in the lateral direction, which is larger than the first width;

forming a first gate dielectric at least in the first trench;

depositing a polycrystalline layer of a polycrystalline semiconductor material in the first and second trench;

isotropic etching the polycrystalline layer to remove the polycrystalline layer from the second trench while leaving the polycrystalline layer in the first trench, the polycrystalline layer remaining in the first trench forming a first gate electrode;

forming a second gate dielectric at least in the second trench; and

depositing a metallic material comprising at least one of a metal, a metal alloy, a metal layer stack, a metal alloy layer stack and any combination thereof into the second trench to form a second gate electrode.

2. The method of claim 1 , wherein the first gate dielectric has a first thickness and the second gate dielectric has a second thickness, wherein the second thickness is larger than the first thickness.

3. The method of claim 1 , wherein the first gate dielectric is formed by a thermal oxidation process which is different to a thermal oxidation process used to form the second gate dielectric.

4. The method of claim 1 , wherein the polycrystalline layer has a thickness which is larger than half of the first width of the first trench and which is less than half of the second width of the second trench.

5. The method of claim 1 , wherein the first gate dielectric is formed in the first and second trench prior to depositing the polycrystalline layer, the method further comprising:

removing the first gate dielectric from the second trench after isotropic etching the polycrystalline layer and before forming the second gate dielectric.

6. The method of claim 1 , further comprising:

forming a respective p-doped body region in the semiconductor substrate for each of the first and second field-effect structures; and

forming a respective n-doped source region in the semiconductor substrate for each of the first and second field-effect structures.

7. The method of claim 6 , further comprising:

forming an electrical connection between the first gate electrode and the n-doped source region of the first field-effect structure.

8. A method for manufacturing a semiconductor device, the method comprising:

providing a semiconductor substrate having a first side;

forming a first gate dielectric on the first side of the semiconductor substrate;

depositing a polycrystalline layer of a polycrystalline semiconductor material on the first gate dielectric;

forming a mask on the polycrystalline layer to cover a portion of the polycrystalline layer;

etching the polycrystalline layer using the mask as etching mask to remove the polycrystalline layer from regions which are not covered by the mask, the portion of the polycrystalline layer remaining on the first gate dielectric forming a first gate electrode;

forming a second gate dielectric on the first side of the semiconductor substrate;

depositing a metal-containing layer on the second gate dielectric, the metal-containing layer comprising one of a metal, a metal alloy, a metal layer stack, a metal alloy layer stack and any combination thereof

forming a mask on the metal-containing layer; and

etching the metal-containing layer using the mask as etching mask to form a second gate electrode.

9. A method for manufacturing a semiconductor device, the method comprising:

providing a semiconductor substrate having a first side;

forming, at the first side of the semiconductor substrate, a first trench in the semiconductor substrate for a first field-effect structure and a second trench in the semiconductor substrate for a second field-effect structure;

forming a first gate dielectric at least in the first trench;

depositing a polycrystalline layer of a polycrystalline semiconductor material at least in the first and second trench;

forming a mask on the polycrystalline layer to cover the polycrystalline layer in the first trench while leaving the polycrystalline layer in the second trench uncovered;

etching the polycrystalline layer using the mask as etching mask to remove the polycrystalline layer from the second trench, the portion of the polycrystalline layer remaining in the first trench forming a first gate electrode;

forming a second gate dielectric at least in the second trench; and

depositing a metallic material comprising one of a metal, a metal alloy, a metal layer stack, a metal alloy layer stack and any combination thereof into the second trench to form a second gate electrode.

10. The method of claim 9 , wherein the first gate dielectric is formed in the first and second trench prior to depositing the polycrystalline layer, the method further comprising:

removing the first gate dielectric using at least one of the mask and the etched polycrystalline layer as etching mask after anisotropic etching the polycrystalline layer and before forming the second gate dielectric.

11. The method of claim 9 , further comprising:

forming a respective p-doped body region in the semiconductor substrate for each of the first and second field-effect structures; and

forming a respective n-doped source region in the semiconductor substrate for each of the first and second field-effect structures.

12. The method of claim 11 , further comprising:

forming an electrical connection between the first gate electrode and the n-doped source region of the first field-effect structure.