Semiconductor device
A semiconductor device includes a semiconductor layer made of SiC. A transistor element having an impurity region is formed in a front surface portion of the semiconductor layer. A first contact wiring is formed on a back surface portion of the semiconductor layer, and defines one electrode electrically connected to the transistor element. The first contact wiring has a first wiring layer forming an ohmic contact with the semiconductor layer without a silicide contact and a second wiring layer formed on the first wiring layer and having a resistivity lower than that of the first wiring layer.
1. A method of manufacturing a semiconductor device which includes a first conductivity type SiC semiconductor layer having a front surface and a rear surface, and a MOSFET having a gate trench formed at a front surface side of the SiC semiconductor layer and a first conductivity drain region formed at a rear surface side of the SiC semiconductor layer, the method of manufacturing the semiconductor device, comprising:
a first step of forming a carbon layer conformal to the front surface of the SiC semiconductor layer and an inner surface of the gate trench from which a part of a source forming region and a part of a body forming region are exposed, the source forming region containing first conductivity type ions selectively implanted into a surface portion of the body forming region, and the body forming region containing second conductivity type ions selectively implanted into a surface portion of the SiC semiconductor layer;
a second step of forming a second conductivity type body region at the surface portion of the SiC semiconductor layer, of forming a first conductivity type source region at the surface portion of the second conductivity type body region, by annealing the SiC semiconductor layer on which the carbon layer is formed, and activating ions inside the body forming region and the source forming region;
a third step of removing the carbon layer and forming a gate insulating film on the inner surface of the gate trench; and
a fourth step of embedding a polysilicon into the gate trench, wherein
the first step includes a step of holding at a first temperature at a first predetermined time, and
the second step includes a step of holding at a second temperature higher than the first temperature for a second predetermined time.
2. The method of manufacturing a semiconductor device according to claim 1 , wherein the third step includes a step of forming the gate insulating film thinner than the carbon layer.
3. The method of manufacturing a semiconductor device according to claim 1 , wherein the first step includes a step of forming the carbon layer having an upper surface positioned below the front surface of the SiC semiconductor layer at a center part of the gate trench which is away from a side surface of the gate trench.
4. The method of manufacturing a semiconductor device according to claim 1 , the third step includes a step of forming the gate insulating film such that a ratio (a first thickness/a second thickness) of a first thickness of a portion located on a bottom surface of the gate trench to a second thickness of a portion located on a side surface of the gate trench is 0.3 to 1.0.
5. The method of manufacturing a semiconductor device according to claim 1 , further comprising a step of performing an etchback to the polysilicon until an etchback surface of the polysilicon is flush with the front surface of the SiC semiconductor layer.
6. The method of manufacturing a semiconductor device according to claim 1 , wherein a transition from the first temperature to the second temperature takes at least 30 minutes.
7. The method of manufacturing a semiconductor device according to claim 1 , wherein the gate insulating film is formed in gas containing at least one of NO and N 2 O.
8. The method of manufacturing a semiconductor device according to claim 1 , wherein the first step includes a step of forming an organic material layer on the front surface of the SiC semiconductor layer and altering the organic material layer into the carbon layer by heating the organic material layer up to the first temperature.
9. The method of manufacturing a semiconductor device according to claim 8 , wherein a polyimide is used as the organic material layer.
10. The method of manufacturing a semiconductor device according to claim 1 , further comprising a step of forming a source contact wiring so as to form an ohmic contact with the source region, wherein
the step of forming the source contact wiring includes a step of forming a polysilicon layer at a contact portion between the source region and the source contact wiring.
11. The method of manufacturing a semiconductor device according to claim 10 , further comprising a step of forming a source trench so as to penetrate the source forming region and the body forming region from the front surface of the SiC semiconductor layer before the first step.
12. The method of manufacturing a semiconductor device according to claim 11 , wherein the step of forming the source contact wiring includes a step of embedding the polysilicon layer into the source trench.
13. The method of manufacturing a semiconductor device according to claim 10 , further comprising a step of implanting at least one of a first conductivity type impurities or a second conductivity impurities into the polysilicon layer.
14. The method of manufacturing a semiconductor device according to claim 1 , wherein the third step includes a step of forming the gate insulating film such that a nitrogen content in the gate insulating film is 0.1 to 10%.
15. The method of manufacturing a semiconductor device according to claim 1 , wherein the third step includes a step of oxidizing and removing the carbon layer by introducing oxygen-containing gas and forming the gate insulating film by oxidizing the SiC semiconductor layer, and
the first step, the second step and the third step are continuously performed in a single resistance heating furnace without removing the SiC semiconductor layer from the heating furnace.