Methods and Apparatus for Variable Selectivity Atomic Layer Etching

• US 20170338122A1
• Filed: 07/31/2017
• Published: 11/23/2017
• Est. Priority Date: 02/12/2015
• Status: Active Application

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Daulton, Jeffrey W.
• Application Number:
  US15/665,036
• Publication Number:
  US 20170338122A1
• Time in Patent Office: Days
• CPC Class Codes: H01J 2237/1825 Evacuating means
• CPC Class Codes: H01J 2237/2001 Maintaining constant desired temperature
• CPC Class Codes: H01J 2237/334 Etching
• CPC Class Codes: H01J 37/32357 Generation remote from the workpiece, e.g. down-stream
• CPC Class Codes: H01J 37/3244 Gas supply means
• CPC Class Codes: H01L 21/02241 III-V semiconductor
• CPC Class Codes: H01L 21/30621 Vapour phase etching
• CPC Class Codes: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 29/205 in different semiconductor regions , e.g. heterojunctions
• CPC Class Codes: H01L 29/42316 for field-effect transistors
• CPC Class Codes: H01L 29/66462 with a heterojunction interface channel or gate, e.g. HFET, HIGFET, SISFET, HJFET, HEMT
• CPC Class Codes: H01L 29/7786 with direct single heterostructure, i.e. with wide bandgap layer formed on top of active layer, e.g. direct single heterostructure MIS-like HEMT
• CPC Class Codes: H01L 29/7787 with wide bandgap charge-carrier supplying layer, e.g. direct single heterostructure MODFET

Abstract

A method of fabricating a microelectronic device, such as a high electron mobility transistors (HEMT), is disclosed. In some examples, the method comprises placing a masked semiconductor sample into a treatment chamber. An oxidizing gas is introduced into the treatment chamber and ionized by an inductively-coupled plasma (ICP)-only plasma source to form a first plasma that oxidizes an exposed region of the sample surface. The oxidizing gas is then evacuated from the treatment chamber, and a reducing gas is introduced into the treatment chamber. The reducing gas in the treatment chamber is ionized via the ICP-only plasma source to form a second plasma that reduces the exposed region of the sample surface. The sample may be heated to a temperature of at least about 100° C. (e.g., 200° C.), resulting in the etching/removal of a portion of the exposed region of the sample via chemical conversion and thermal desorption.

Claims

1. A method of fabricating a device, the method comprising:

receiving a sample in a treatment chamber, the sample including a surface with an etch mask disposed thereon, the etch mask defining an exposed region of the sample surface;

introducing an oxidizing gas into the treatment chamber;

ionizing the oxidizing gas, via a remote plasma source, thereby forming a first plasma to oxidize the exposed region of the sample surface;

evacuating the oxidizing gas from the treatment chamber;

introducing a reducing gas into the treatment chamber; and

ionizing the reducing gas, via the remote plasma source, thereby forming a second plasma to reduce the exposed region of the sample surface.

2. The method of claim 1, wherein the remote plasma source comprises at least one of an inductively-coupled plasma (ICP) source or a transformer coupled plasma (TCP) source.

3. The method of claim 1, further comprising introducing an inert gas into the treatment chamber to purge the treatment chamber prior to introducing the reducing gas into the treatment chamber.

4. The method of claim 1, wherein the method does not include applying an external bias to the sample.

5. The method of claim 1, further comprising heating the sample to a temperature of at least about 100°

C. to remove an Al-containing semiconductor from the sample.

6. The method of claim 5, further comprising removing reduced regions of the sample surface via thermal desorption.

7. The method of claim 1, wherein the oxidizing gas comprises at least one of oxygen (O₂), nitric oxide (NO), or nitrous oxide (N₂O).

8. The method of claim 1, wherein the reducing gas comprises at least one of boron trichloride (BCl₃), silicon tetrachloride (SiCl₄), carbon tetrachloride (CCl₄), other chlorocarbons (C_xCl_y), or hydrochlorocarbons (C_xH_yCl_z).

9. The method of claim 1, further comprising:

introducing an inert gas into the treatment chamber to aid ionization of the oxidizing gas and/or the reducing gas.

10. The method of claim 9, wherein introducing the inert gas comprises admitting at least one of argon, helium, neon, or nitrogen into the treatment chamber.

11. The method of claim 1, wherein the sample comprises a semiconductor material.

12. The method of claim 11, wherein the semiconductor material comprises at least one of a III-Nitride (III-N) material or a III-Arsenide (III-As) material.

13. The method of claim 11, wherein the semiconductor material comprises at least one of aluminum gallium nitride (AlGaN) or aluminum nitride (AlN).

14. The method of claim 1, wherein the second plasma reduces the exposed region of the sample surface to yield an etch rate of the exposed region of the sample surface of about 1 Angstrom per second.

15. A product produced according to the method of claim 1.

16. An apparatus for remote plasma microfabrication of a sample, the apparatus comprising:

a process chamber to process a surface of the sample received therein;

a power supply, coupled to the process chamber, to power a remote plasma source so as to deliver a remote plasma to the surface of the sample to alternately oxidize and reduce the surface of the sample; and

a heater, disposed in the process chamber, to heat the sample to a temperature sufficient to thermally desorb components of the surface of the sample.

17. The apparatus of claim 16, wherein the remote plasma is an inductively coupled plasma (ICP).

18. The apparatus of claim 16, further comprising:

a vacuum pump, in fluid communication with the process chamber, to evacuate the process chamber between oxidizing and reducing the surface of the sample.

19. The apparatus of claim 18, further comprising:

a gas inlet, in fluid communication with the process chamber, to receive an inert gas to purge the process chamber before and/or after evacuating the process chamber between oxidizing and reducing the surface of the sample.

20. A method of patterning a III-N semiconductor substrate, the method comprising:

(A) placing the III-N semiconductor substrate in a vacuum chamber;

(B) evacuating the vacuum chamber;

(C) heating the III-N semiconductor substrate to a temperature of at least about 100°

C.;

(D) introducing an oxidizing gas into the vacuum chamber;

(E) ionizing the oxidizing gas, via an inductively-coupled plasma (ICP) source, so as to oxidize at least a portion of a surface of the III-N semiconductor substrate;

(F) evacuating the oxidizing gas from the vacuum chamber;

(G) introducing a reducing gas into the vacuum chamber after the oxidizing gas has been evacuated from the vacuum chamber;

(H) ionizing the reducing gas, via the ICP source, so as to reduce the exposed region of the at least a portion of the surface of III-N semiconductor substrate; and

(I) evacuating the reducing gas from the vacuum chamber.

21. The method of claim 20, further comprising:

repeating steps (E) through (I) at least once before removing the III-N semiconductor substrate from the vacuum chamber.

22. The method of claim 20, further comprising:

introducing an inert gas into the vacuum chamber to purge the vacuum chamber after step (G) and removing the inert gas prior to step (H).

23. The method of claim 20, wherein the oxidizing gas comprises at least one of oxygen (O₂), nitric oxide (NO), or nitrous oxide (N₂O).

24. The method of claim 20, wherein the reducing gas comprises at least one of boron trichloride (BCl₃), silicon tetrachloride (SiCl₄), carbon tetrachloride (CCl₄), other chlorocarbons (C_xCl_y), or hydrochlorocarbons (C_xH_yCl_z).

25. The method of claim 20, further comprising:

introducing an inert gas into the treatment chamber to aid ionization of the oxidizing gas and/or the reducing gas.

26. The method of claim 25, wherein introducing the inert gas comprises admitting at least one of argon, helium, neon, or nitrogen into the treatment chamber.

27. The method of claim 20, wherein no bias is applied to the III-N semiconductor substrate.

28. A product produced according to the method of claim 20.