Method of porosifying part of a semiconductor wafer

Patent metadata

Field	Value
Publication number	US-11810779-B2
Application number	US-202217841781-A
Country	US
Kind code	B2
Filing date	Jun 16, 2022
Priority date	Nov 23, 2018
Publication date	Nov 7, 2023
Grant date	Nov 7, 2023

Abstract

A method includes: in a semiconductor wafer having a first semiconductor layer and a second semiconductor layer adjoining the first semiconductor layer, forming a porous region extending from a front surface into the first semiconductor layer; and removing the porous region by an etching process, wherein a doping concentration of the second semiconductor layer is less than 10 −2 times a doping concentration of the first semiconductor layer and/or a doping type of the second semiconductor layer is complementary to a doping type of the first semiconductor layer, wherein forming the porous region comprises bringing in contact a porosifying agent with the front surface of the first semiconductor layer and applying a voltage between the first semiconductor layer and a first electrode that is in contact with the porosifying agent, wherein applying the voltage comprises applying the voltage between the first electrode and an edge region of the first semiconductor layer.

First claim

What is claimed is:

1. A method, comprising:
in a semiconductor wafer comprising a first semiconductor layer and a second semiconductor layer adjoining the first semiconductor layer, forming a porous region extending from a front surface into the first semiconductor layer; and
removing the porous region by an etching process,
wherein a doping concentration of the second semiconductor layer is less than 10 −2 times a doping concentration of the first semiconductor layer and/or a doping type of the second semiconductor layer is complementary to a doping type of the first semiconductor layer,
wherein forming the porous region comprises bringing in contact a porosifying agent with the front surface of the first semiconductor layer and applying a voltage between the first semiconductor layer and a first electrode that is in contact with the porosifying agent,
wherein applying the voltage comprises applying the voltage between the first electrode and an edge region of the first semiconductor layer,
wherein the edge region of the first semiconductor layer does not get in contact with the porosifying agent and remains non-porous.

2. The method of claim 1 , wherein each of the first semiconductor layer and the second semiconductor layer is a monocrystalline semiconductor layer, and wherein the semiconductor wafer is a monocrystalline semiconductor wafer.

3. The method of claim 1 , wherein applying the voltage comprises:
immerging the first electrode into the porosifying agent;
contacting the first semiconductor layer with a second electrode; and
applying the voltage between the first electrode and the second electrode.

4. The method of claim 3 , wherein the voltage is a DC voltage in a range of between 1V and 12V and a current flows between the first electrode and second electrode via the porosifying agent and the first semiconductor layer, wherein an energy associated with the current causes the porosifying agent to porosify the first semiconductor layer in each region that is in contact with the porosifying agent, wherein the current flowing between the first electrode and the second electrode is associated with a current density at the front surface of the first semiconductor layer, and wherein the current density in a certain region of the front surface is given by the current flowing into that region divided by an area of that region.

5. The method of claim 3 , further comprising:
connecting a current source between the first electrode and the second electrode such that a current flows between the first electrode and second electrode via the porosifying agent and the first semiconductor layer,
wherein an energy associated with the current causes the porosifying agent to porosify the first semiconductor layer in each region that is in contact with the porosifying agent,
wherein the current flowing between the first electrode and the second electrode is associated with a current density at the front surface of the first semiconductor layer,
wherein the current density in a certain region of the front surface is given by the current flowing into that region divided by an area of that region.

6. The method of claim 3 , wherein a polarity of the voltage is such that an electrical potential of the first electrode is more negative than an electrical potential of the second electrode.

7. The method of claim 1 , wherein the porosifying agent includes hydrofluoric acid.

8. The method of claim 1 , wherein an aqueous solution including hydrofluoric acid is used as the porosifying agent.

9. The method of claim 1 , wherein the porosifying agent includes hydrofluoric acid and ethanol.

10. The method of claim 1 , wherein the porosifying agent includes an aqueous solution including hydrofluoric acid and ethanol.

11. The method of claim 10 , wherein a concentration of the hydrofluoric acid in the aqueous solution is in a range between 20% and 25%.

12. The method of claim 1 , wherein the porosifying agent is a liquid, and wherein bringing in contact the porosifying agent with the front surface of the first semiconductor layer comprises:
forming a reservoir by the front surface of the first semiconductor layer and a tubular element; and
at least partially filling the reservoir with the porosifying agent,
wherein the tubular element is in contact with the front surface of the first semiconductor layer and forms sidewalls of the reservoir and the front surface forms a bottom of the reservoir.

13. The method of claim 12 , wherein a horizontal dimension of the porous region is given by a horizontal dimension of the tubular element, the horizontal dimension being parallel to the front surface of the first semiconductor layer.

14. The method of claim 1 , wherein porosification starts at the front surface of the first semiconductor layer such that the porous region is formed at the front surface, and wherein the porosifying agent, at first, is in contact with the first semiconductor layer and then penetrates the porous region, so that the porous region further extends into the first semiconductor layer.

15. The method of claim 1 , wherein the porous region, in a vertical direction, extends from the front surface of the first semiconductor layer through the first semiconductor layer down to the second semiconductor layer.

16. The method of claim 15 , wherein the porous region extends to the second semiconductor layer but not into the second semiconductor layer, such that the second semiconductor layer remains unaffected by the porosifying agent.

17. The method of claim 1 , wherein the porous region covers at least 80% of a volume of the first semiconductor layer.

18. The method of claim 1 , wherein the first semiconductor layer is a p-type layer and the second semiconductor layer is an n-type layer.

19. The method of claim 1 , wherein the doping concentration of the second semiconductor layer is less than 10 −2 times the doping concentration of the first semiconductor layer and the doping type of the second semiconductor layer is complementary to the doping type of the first semiconductor layer.

20. The method of claim 1 , wherein the semiconductor wafer is comprised of silicon, silicon carbide, gallium arsenide, or gallium nitride.

21. A method, comprising:
in a semiconductor wafer comprising a first semiconductor layer and a second semiconductor layer adjoining the first semiconductor layer, forming a porous region extending from a front surface into the first semiconductor layer; and
removing the porous region by an etching process,
wherein a doping concentration of the second semiconductor layer is less than 10 −2 times a doping concentration of the first semiconductor layer and/or a doping type of the second semiconductor layer is complementary to a doping type of the first semiconductor layer,
wherein forming the porous region comprises bringing in contact a porosifying agent with the front surface of the first semiconductor layer and applying a voltage between the first semiconductor layer and a first electrode that is in contact with the porosifying agent,
wherein applying the voltage comprises applying the voltage between the first electrode and an edge region of the first semiconductor layer,
wherein the porosifying agent is a liquid, and wherein bringing in contact the porosifying agent with the front surface of the first semiconductor layer comprises:
forming a reservoir by the front surface of the first semiconductor layer and a tubular element; and
at least partially filling the reservoir

Assignees

• Infineon Technologies Ag

Inventors

• Friedler Sophia
• Goller Bernhard
• Moder Iris
• Muri Ingo

Classifications

• H10P95/70

  Chemical treatments · CPC title

• H10P90/126

  by chemical etching · CPC title

• H10P52/00

  Grinding, lapping or polishing of wafers, substrates or parts of devices · CPC title

• H10P50/20

  Dry etching; Plasma etching; Reactive-ion etching · CPC title

• H10P90/15 Primary

  by making porous regions on the surface · CPC title