Bipolar punch-through semiconductor device and method for manufacturing such a semiconductor device

1. A method for manufacturing a bipolar punch-through semiconductor device having at least a two-layer structure with layers of a first and a second conductivity type, which second conductivity type is different from the first conductivity type, the method comprising:

providing a wafer which comprises a first side and a second side, a wafer thickness and a high-doped layer of the first conductivity type at the first side, wherein the high-doped layer has a constant high doping concentration;

forming a low-doped layer of the first conductivity type on top of the high-doped layer by epitaxial growth on the first side;

performing a diffusion step, to form a diffused inter-space region, which comprises a portion of the high-doped layer and a portion of the low-doped layer, wherein the portions are arranged adjacent to each other, wherein the diffused inter-space region has a doping concentration higher than the doping concentration of the low-doped layer and lower than the doping concentration of the high-doped layer, wherein the remaining part of the low-doped layer forms a drift layer;

forming at least one layer of the second conductivity type on top of the drift layer on the first side; and

reducing the wafer thickness on the second side within the high-doped layer to form a buffer layer comprising both the inter-space region and the remaining portion of the high-doped layer, wherein the remaining portion of the high-doped layer forms a high-doped region, wherein the doping profile of the buffer layer decreases steadily from the doping concentration of the high-doped region to the doping concentration of the drift layer.

2. The method according to claim 1 , wherein the wafer is completely made of the first conductivity type and constantly doped with a high doping concentration from 5×10 14 to 5×10 16 cm −3 .

3. The method according to claim 1 , comprising:

removing a mounting layer from the second side of the wafer during the step of reducing the wafer thickness on the second side.

4. The method according to claim 1 , comprising:

reducing the thickness of the wafer such that the buffer layer has a thickness of about 20 μm to 40 μm.

5. The method according to claim 1 , comprising:

forming the inter-space region such that the inter-space region has a thickness of about 10 μm to 30 μm.

6. The method according to claim 1 , wherein the high-doped layer has a doping concentration of about 5×10 14 to 5×10 16 cm −3 .

7. The method according to claim 1 , comprising:

performing the diffusion step at a temperature of at least 1200° C.

8. The method according to claim 1 , comprising:

performing the diffusion step during a time period of at least 180 min.

9. The method according to claim 1 , comprising:

forming the low-doped layer with a doping concentration of about 3×10 13 cm −3 to 2×10 14 cm −3 .

10. The method according to claim 1 , comprising:

performing the diffusion step after the step of forming the low-doped layer of the first conductivity type.

11. The method according to claim 10 , comprising:

performing the step of forming the at least one layer of the second conductivity type on the first side after the diffusion step.

12. The method according to claim 11 , comprising:

performing the step of reducing the wafer thickness on the second side after the step of forming the at least one layer of the second conductivity type on the first side.

13. The method according to claim 1 , wherein the device is an insulated gate bipolar transistor.

14. The method according to claim 1 , wherein the device is a diode.

15. A bipolar punch-through semiconductor device in form of an insulated gate bipolar transistor having a four-layer structure with layers of a first and a second conductivity type, which second conductivity type is different from the first conductivity type, between a first main side and a second main side, the semiconductor device comprising:

a drift layer of the first conductivity type, which is constantly low-doped with a doping concentration of about 3×10 13 cm −3 to 2×10 14 cm −3 ;

a buffer layer of the first conductivity type, which is arranged on the drift layer towards the second main side and which has a higher doping concentration than the drift layer, wherein the buffer layer has a thickness of about 20 μm to 40 μm, wherein the buffer layer comprises towards the second main side a high-doped region, which is constantly high-doped with a doping concentration of about 5×10 14 to 5×10 16 cm −3 and between the high-doped region and the drift layer an inter-space region, which is a diffused region and which has a doping concentration, which decreases steadily from the doping concentration of the high-doped region to the low doping concentration of the drift layer, wherein the inter-space region has a thickness of about 10 μm to 30 μm; and

a layer of the second conductivity type in form of a base layer on the first main side.

16. The semiconductor device according to claim 15 , wherein the doping concentration of the inter-space region decreases by a Gaussian function.

17. The semiconductor device according to claim 15 , wherein the drift layer has a doping concentration of doping concentration of about 3×10 13 to 2×10 14 cm −3 .