Method for manufacturing semiconductor device
A semiconductor device of the present invention includes a substrate having a drift layer, metal wiring formed on an upper surface of the substrate, and an electrode formed on a back surface of the substrate, wherein the lifetime of carriers in the drift layer satisfies the following expression 1: [Expression 1] τ≥1.5×10 −5 exp(5.4×10 3 t N− ) expression 1 τ: the lifetime of carriers in the drift layer t N− : the layer thickness of the drift layer.
1. A method of manufacturing a semiconductor device, comprising performing, in this order:
a manufacturing step of forming a first diffusion layer on an upper surface side of a substrate having a drift layer, performing film forming and performing etching;
a gettering layer forming step of forming a gettering layer on a lower surface side of the drift layer exposed at a lower surface of the substrate;
an annealing step of heating the substrate to capture by the gettering layer a metal impurity, contaminant atoms and damage introduced in the drift layer in the manufacturing step;
a removal step of removing the gettering layer after the annealing step;
a step of forming a second diffusion layer on the lower surface side of the drift layer after the removal step; and
a step of forming an electrode so that the electrode contacts the second diffusion layer, wherein
the gettering layer forming step includes:
a step of forming doped polysilicon doped with an impurity so that the doped polysilicon contacts the drift layer exposed at the lower surface of the substrate; and
a preprocessing annealing step of heating the substrate to diffuse the impurity to the lower surface side of the drift layer so that a gettering layer having crystal defects and the impurity is formed on the lower surface side of the drift layer, and
wherein the doped polysilicon is also removed in the removal step.
2. The method of manufacturing a semiconductor device according to claim 1 , wherein the temperature of the substrate in the preprocessing annealing step is in a range from 900 to 1000[° C.].
3. The method of manufacturing a semiconductor device according to claim 2 , wherein the density of the impurity in the doped polysilicon is equal to or higher than 1×10 19 [cm −3 ].
4. The method of manufacturing a semiconductor device according to claim 1 , wherein the layer thickness of the doped polysilicon is equal to or larger than 500 nm.
5. The method of manufacturing a semiconductor device according to claim 1 further comprising a step of forming, on the upper surface side of the substrate, after the annealing step, a contact hole through which a portion of the first diffusion layer is exposed to the outside, and forming metal wiring electrically connected to the first diffusion layer.
6. The method of manufacturing a semiconductor device according to claim 1 , wherein, in the manufacturing step, an emitter, a base and a trench constituting a surface structure of an IGBT are formed.
7. The method of manufacturing a semiconductor device according to claim 1 , wherein, in the manufacturing step, an anode layer and an insulating film constituting a surface structure of a diode are formed.
8. The method of manufacturing a semiconductor device according to claim 1 , wherein, in the annealing step, the temperature of the substrate is maintained at a point in a range from 600 to 700[° C.] for a time period equal to or longer than four hours.
9. The method of manufacturing a semiconductor device according to claim 1 , wherein, in the removal step, a portion of the drift layer in contact with the gettering layer is removed by a desired thickness.
10. The method of manufacturing a semiconductor device according to claim 1 , wherein the substrate is a wafer formed by an FZ method.
11. The method of manufacturing a semiconductor device according to claim 1 , wherein the substrate is formed of a wide-bandgap semiconductor.
12. The method of manufacturing a semiconductor device according to claim 11 , wherein the wide-bandgap semiconductor is silicon carbide, a gallium nitride-based material or diamond.
13. The method of manufacturing a semiconductor device according to claim 1 , wherein
the gettering layer forming step of forming a gettering layer is performed directly after the manufacturing step of forming the first diffusion layer, without any intervening steps.
14. The method of manufacturing a semiconductor device according to claim 1 , wherein
the annealing step of heating the substrate is performed directly after the gettering layer forming step of forming a gettering layer, without any intervening steps.
15. A method of manufacturing a semiconductor device, comprising performing, in this order:
a manufacturing step of forming a first diffusion layer on an upper surface side of a substrate having a drift layer, performing film forming and performing etching;
a gettering layer forming step of forming a gettering layer on a lower surface side of the drift layer exposed at a lower surface of the substrate;
an annealing step of heating the substrate to capture by the gettering layer a metal impurity, contaminant atoms and damage introduced in the drift layer in the manufacturing step;
a removal step of removing the gettering layer after the annealing step;
a step of forming a second diffusion layer on the lower surface side of the drift layer after the removal step; and
a step of forming an electrode so that the electrode contacts the second diffusion layer, wherein, in the gettering layer forming step, the drift layer exposed at the lower surface of the substrate is heated so that the gettering layer having crystal defects is formed on the lower surface side of the drift layer.
16. The method of manufacturing a semiconductor device according to claim 15 , wherein the gettering layer is formed by heating the lower surface of the drift layer with laser light.
17. The method of manufacturing a semiconductor device according to claim 16 , wherein the power of the laser light is equal to or higher than 4.0 [J/cm 2 ].
18. The method of manufacturing a semiconductor device according to claim 15 , wherein
the gettering layer forming step of forming a gettering layer is performed directly after the manufacturing step of forming the first diffusion layer, without any intervening steps.
19. The method of manufacturing a semiconductor device according to claim 15 , wherein
the annealing step of heating the substrate is performed directly after the gettering layer forming step of forming a gettering layer, without any intervening steps.