Metal oxide semiconductor (MOS) controlled devices and methods of making the same
Metal-Oxide-Semiconductor (MOS) controlled semiconductor devices and methods of making the devices are provided. The devices include a gate which controls current flow through channel regions positioned between source/emitter and drain regions of the device. The devices include a gate oxide layer having a variable thickness. The thickness of the gate oxide layer under the edge of the gate and over the source/emitter regions is different than the thickness over the channel regions of the device. The oxide layer thickness near the edge of the gate can be greater than the oxide layer thickness over the channel regions. The source/emitter regions can be implanted to provide enhanced oxide growth during gate oxide formation. The source/emitter region can include regions that are implanted to provide enhanced oxide growth during gate oxide formation and regions which do not provide enhanced oxide growth during gate oxide formation. The devices can be SiC devices such as SiC MOSFETs and SiC IGBTs.
1. A semiconductor device comprising:
a drift layer of a semiconductor material of a first conductivity type comprising an upper surface and a lower surface;
a semiconductor substrate in direct or indirect contact with the lower surface of the drift layer;
an oxide layer on and in direct contact with the upper surface of the drift layer;
a gate electrode layer on the oxide layer opposite the drift layer; wherein the upper surface of the drift layer comprises:
one or more JFET regions of a semiconductor material of the first conductivity type; first and second channel regions of a semiconductor material of a second conductivity type different than the first conductivity type opposite and adjacent each of the one or more JFET regions; and
first and second source/emitter regions of a semiconductor material of the first conductivity type adjacent the first and second channel regions, respectively, opposite the JFET region;
wherein the oxide layer comprises a central region over the JFET region, first and second inner peripheral regions adjacent the central region and over the first and second channel regions and first and second outer peripheral regions adjacent the first and second inner peripheral regions and opposite the central region over the source/emitter regions;
wherein the gate electrode layer extends over the JFET region and the adjacent channel regions and wherein the gate electrode layer has a first edge on the first outer peripheral region of the oxide layer and a second edge on the second outer peripheral region of the oxide layer;
wherein the oxide layer has a first average thickness in the central region and a second average thickness in the first and second inner peripheral regions, wherein the first average thickness is different than the second average thickness by at least 25%; with the proviso that: the second average thickness is greater than the first average thickness;
the first average thickness is greater than the second average thickness and the oxide layer has a third average thickness in the first and second outer peripheral regions, wherein the third average thickness is greater than the second average thickness by at least 25%; or the oxide layer extends below the upper surface of the drift layer.
2. The semiconductor device of claim 1 , wherein the second average thickness is greater than the first average thickness.
3. The semiconductor device of claim 2 , wherein the source/emitter region comprises: an inner region contiguous with the channel region underlying the central region of the oxide layer and an outer region contiguous with the inner region opposite the channel region and underlying the first or second peripheral region of the oxide layer; wherein the inner region and the outer region have different implant species, different implant levels and/or different levels of implantation induced damage.
4. The semiconductor device of claim 1 , wherein the first average thickness is greater than the second average thickness and the oxide layer has a third average thickness in the first and second outer peripheral regions, wherein the third average thickness is greater than the second average thickness by at least 25%.
5. The semiconductor device of claim 1 , wherein: the first average thickness is different than the second average thickness by at least 50%; the first average thickness is different than the second average thickness by at least 100%; the first average thickness is different than the second average thickness by at least 200%; or the first average thickness is different than the second average thickness by at least 300%.
6. The semiconductor device of claim 1 , wherein the oxide layer extends below the upper surface of the drift layer.
7. The semiconductor device of claim 6 , wherein the first average thickness is greater than the second average thickness.
8. The semiconductor device of claim 7 , wherein the oxide layer has a third average thickness in the first and second outer peripheral regions, wherein the third average thickness is greater than the second average thickness by at least 25%.
9. The semiconductor device of claim 6 , wherein the second average thickness is greater than the first average thickness.
10. The semiconductor device of claim 1 , further comprising: a layer of semiconductor material of the second conductivity type between the drift layer and the substrate.
11. The semiconductor device of claim 1 , wherein the semiconductor material of the first conductivity type is an n-type material and the semiconductor material of the second conductivity type is a p-type material.
12. The semiconductor device of claim 1 , wherein the semiconductor material is a SiC semiconductor material.
13. The semiconductor device of claim 12 , wherein the source/emitter regions are SiC doped with a dopant species selected from the group consisting of Nitrogen, Phosphorus and combinations thereof.
14. The semiconductor device of claim 12 , wherein the source/emitter regions are SiC doped with phosphorus.
15. The semiconductor device of claim 12 , wherein SiC under the gate electrode layer has been implanted with an implant species selected from the group consisting of nitrogen, phosphorous, silicon, carbon, argon and combinations thereof.
16. The semiconductor device of claim 12 , wherein SiC under the gate electrode layer has been implanted with an electrically inactive species.
17. The semiconductor device of claim 1 , wherein the one or more JFET regions, the first and second channel regions, and the first and second source/emitter regions are elongate regions extending in an x direction in the drift layer and spaced apart from one another in a y-direction perpendicular to the x-direction.