Double-sided vertical semiconductor device with thinned substrate
A vertical semiconductor device is formed in a semiconductor layer having a first surface, a second surface and background doping. A first doped region, doped to a conductivity type opposite that of the background, is formed at the second surface of the semiconductor layer. A second doped region of the same conductivity type as the background is formed at the second surface of the semiconductor layer, inside the first doped region. A portion of the semiconductor layer is removed at the first surface, exposing a new third surface. A third doped region is formed inside the semiconductor layer at the third surface. Electrical contact is made at least to the second doped region (via the second surface) and the third doped region (via the new third surface). In this way, vertical DMOS, IGBT, bipolar transistors, thyristors, and other types of devices can be fabricated in thinned semiconductor, or SOI layers.
1. A method of forming a semiconductor device, the method comprising:
providing a semiconductor layer doped to a first conductivity type, the semiconductor having a first surface and a second surface;
forming, in the semiconductor layer and adjacent to the second surface, a first doped region of a second conductivity type opposite the first conductivity type;
forming, inside the first doped region, a second doped region of the first conductivity type;
forming a first external electrical contact to the second doped region at the second surface of the semiconductor layer;
removing a portion of the semiconductor layer from the first surface to expose a third surface of the semiconductor layer;
forming a third doped region inside the semiconductor layer adjacent to the third surface;
forming a second external electrical contact to the third doped region at the third surface of the semiconductor layer; and
forming a physical contact to the first doped region at the third surface of the semiconductor layer, the physical contact creating a third external electrical contact to the first doped region,
wherein forming the physical contact comprises:
forming, in the semiconductor layer and extending from the first doped region to the third surface, a diffused region of the first conductivity type; and
forming the physical contact to the diffused region at the third surface of the semiconductor layer.
2. The method of claim 1 , wherein the third doped region has the first conductivity type.
3. The method of claim 1 , wherein the semiconductor layer is doped uniformly to a first doping concentration, and wherein the third doped region has a peak doping concentration greater than 10 times the first doping concentration.
4. The method of claim 1 , wherein the third doped region has the second conductivity type.
5. The method of claim 1 , wherein the third doped region has a doping concentration greater than 10 18 cm −3 .
6. The method of claim 1 , wherein the step of forming the third doped region inside the semiconductor layer comprises heating the semiconductor layer to a temperature greater than 800° C. for a time longer than 5 seconds.
7. The method of claim 1 , wherein the step of forming the third doped region inside the semiconductor layer occurs after the step of removing the portion of the semiconductor layer.
8. The method of claim 1 , wherein the step of forming the first external electrical contact to the second doped region comprises electrically connecting the first doped region and the second doped region.
9. The method of claim 1 , further comprising, before the step of removing the portion of the semiconductor layer, coupling a handle layer to the second surface of the semiconductor layer.
10. The method of claim 1 , wherein the semiconductor layer comprises:
an insulator layer having a first surface and a second surface,
a semiconductor-on-insulator layer having a first surface and a second surface, the first surface contacting the first surface of the insulator layer; and
a substrate contacting the second surface of the insulator layer;
wherein the step of removing the portion of the semiconductor layer comprises:
removing a portion of the substrate layer to expose a portion of the second surface of the insulator layer; and
removing a portion of the insulating layer to expose a portion of the first surface of the semiconductor-on-insulator layer.
11. The method of claim 10 , wherein the step of removing the portion of the substrate layer comprises removing the entire substrate layer.
12. The method of claim 1 , wherein the step of forming the first external electrical contact to the second doped region at the second surface of the semiconductor layer comprises using a refractory metal to contact the second doped region at the second surface of the semiconductor layer.
13. The method of claim 12 , wherein the refractory metal comprises tungsten.