Semiconductor device and method of forming a semiconductor device
A high voltage/power semiconductor device has a semiconductor layer having a high voltage terminal end and a low voltage terminal end. A drift region extends between the high and low voltage terminal ends. A dielectric layer is provided above the drift region. An electrical conductor extends across at least a part of the dielectric layer above the drift region, the electrical conductor being connected or connectable to the high voltage terminal end. The drift region has plural trenches positioned below the electrical conductor. The trenches extend laterally across at least a part of the drift region in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer, each trench containing a dielectric material. The trenches improve the distribution of electric field in the device in the presence of the electrical conductor.
1. A high voltage/power semiconductor device, the device comprising:
a semiconductor layer;
the semiconductor layer having a high voltage terminal end for connection to a high voltage terminal;
the semiconductor layer having a low voltage terminal end for connection to a low voltage terminal;
the semiconductor layer having a drift region between the high and low voltage terminal ends of the semiconductor layer;
a dielectric layer above the drift region; and,
an electrical conductor that extends across at least a part of the dielectric layer above the drift region, the electrical conductor being connected or connectable to the high voltage terminal end;
the drift region having plural trenches therein positioned below the electrical conductor, the trenches extending laterally across at least a part of the drift region in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer, the trenches being longitudinally spaced apart from each other in the direction between the high and low voltage terminal ends of the semiconductor layer, each trench containing a dielectric material.
2. A device according to claim 1 , wherein the width of at least some of said trenches in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer is greater than the width of the electrical conductor in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer.
3. A device according to claim 1 , wherein the semiconductor layer is provided on a dielectric layer that is provided on a semiconductor substrate.
4. A device according to claim 1 , wherein the semiconductor layer is provided on a dielectric layer, there being no semiconductor substrate below at least a portion of the drift region.
5. A device according to claim 1 , wherein the trenches are equally spaced from each other in the direction between the high and low voltage terminal ends of the semiconductor layer.
6. A device according to claim 1 , wherein the length of each trench in the direction between the high and low voltage terminal ends of the semiconductor layer is the same.
7. A device according to claim 1 , wherein the length of each trench in the direction between the high and low voltage terminal ends of the semiconductor layer increases from the low voltage terminal end to the high voltage terminal end.
8. A device according to claim 1 , wherein the spacing of the trenches from each other in the direction between the high and low voltage terminal ends of the semiconductor layer is non-uniform.
9. A device according to claim 8 , wherein the spacing of the trenches from each other in the direction between the high and low voltage terminal ends of the semiconductor layer increases from the low voltage terminal end to the high voltage terminal end.
10. A device according to claim 8 , wherein the length of each trench in the direction between the high and low voltage terminal ends of the semiconductor layer is the same.
11. A device according to claim 8 , wherein the length of each trench in the direction between the high and low voltage terminal ends of the semiconductor layer increases from the low voltage terminal end to the high voltage terminal end.
12. A device according to claim 1 , comprising a respective relatively highly doped region at the surface of the drift region between at least some of the trenches, each of said relatively highly doped regions having a doping polarity that is opposite that of the drift region.
13. A device according to claim 1 , comprising one or more field plates in a dielectric layer above the drift region, the one or more field plates being positioned above one or more of said trenches.
14. A device according to claim 1 , wherein at least some of the trenches have a non-linear shape in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer.
15. A method of forming a high voltage/power semiconductor device having a semiconductor layer, the semiconductor layer having a high voltage terminal end for connection to a high voltage terminal, the semiconductor layer having a low voltage terminal end for connection to a low voltage terminal, the semiconductor layer having a drift region between the high and low voltage terminal ends of the semiconductor layer, the semiconductor layer having a dielectric layer above the drift region, and the semiconductor layer having an electrical conductor that extends across at least a part of the dielectric layer above the drift region, the electrical conductor being connected or connectable to the high voltage terminal end; the method comprising:
forming plural trenches in the drift region below the electrical conductor such that the trenches extend laterally across at least a part of the drift region in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer and such that the trenches are longitudinally spaced apart from each other in the direction between the high and low voltage terminal ends of the semiconductor layer; and,
filling each trench with a dielectric material.
16. A method according to claim 15 , wherein the width of at least some of said trenches in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer is greater than the width of the electrical conductor in the direction transverse the direction between the high and low voltage terminal ends of the semiconductor layer.
17. A method according to claim 15 , comprising forming a respective relatively highly doped region at the surface of the drift region between at least some of the trenches, each of said relatively highly doped regions having a doping polarity that is opposite that of the drift region.
18. A method according to claim 17 , wherein said relatively highly doped regions are formed in the same process step as other CMOS regions of the device.
19. A method according to claim 15 , comprising providing one or more field plates in a dielectric layer above the drift region, the one or more field plates being positioned above one or more of said trenches.