Method for reducing and homogenizing the thickness of a semiconductor layer which lies on the surface of an electrically insulating material
To reduce and homogenize the thickness of a semiconductor layer which lies on the surface of an electrically insulating material, the surface of the semiconductor layer is exposed to the action of an etchant whose redox potential is adjusted as a function of the material and the desired final thickness of the semiconductor layer, so that the material erosion per unit time on the surface of the semiconductor layer due to the etchant becomes less as the thickness of the semiconductor layer decreases, and is only from 0 to 10% of the thickness per second when the desired thickness is reached. The method is carried out without the action of light or the application of an external electrical voltage.
1. A method for homogenizing the thickness of a semiconductor layer which lies on the surface of an electrically insulating material comprising selecting a target thickness, and reducing the thickness of the semiconductor layer to a reduced target thickness by contacting the surface of the semiconductor layer with an etchant whose redox potential is adjusted as a function of both the material of the semiconductor layer and the target thickness of the semiconductor layer and etching the semiconductor layer, so that the erosion of the surface of the semiconductor layer per unit time by the etchant becomes less as the thickness of the semiconductor layer decreases and is only from 0 to 10% of the final thickness per second when the target thickness is reached, and wherein the method is carried out without the action of light or the application of an external electrical voltage.
2. The method of claim 1 , wherein the semiconductor layer comprises one or more of silicon, germanium, silicon carbide, III/V compound semiconductors, and II/VI compound semiconductors.
3. The method of claim 1 , wherein the redox potential of the etchant is adjusted via the composition of the etchant.
4. The method of claim 3 , wherein the redox potential of the etchant is adjusted via the choice of the constituents of the etchant.
5. The method of claim 3 , wherein the redox potential of the etchant is adjusted via the concentrations of the constituents of the etchant.
6. The method of claim 5 , wherein the redox potential of the etchant is determined essentially by its pH, and wherein the concentrations of the constituents of the etchant are selected so that a suitable pH is obtained.
7. The method of claim 3 , wherein the redox potential is additionally adjusted via a selection of an etching temperature.
8. The method of claim 3 , wherein the semiconductor layer comprises silicon and the etchant comprises one or more fluorine compounds.
9. The method of claim 8 , wherein the etchant comprises hydrogen fluoride and a fluoride salt.
10. The method as claimed in claim 9 , wherein at least one fluoride salt is ammonium fluoride.
11. The method of claim 1 , wherein the semiconductor layer comprises p-doped silicon.
12. The method of claim 1 , wherein the semiconductor layer is the functional layer of an SOI wafer.
13. The method of claim 1 , wherein material erosion per unit time on the surface of the semiconductor layer due to the etchant is from 0 to 1 nm when the desired final thickness is reached.