Combined Physical and Chemical Etch to Reduce Magnetic Tunnel Junction (MTJ) Sidewall Damage

• US 20180331279A1
• Filed: 05/15/2017
• Published: 11/15/2018
• Est. Priority Date: 05/15/2017
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Shen, Dongna, Wang, Yu-Jen, Tong, Ru-Ying, Sundar, Vignesh, Patel, Sahil
• Granted Patent: US 10,522,749 B2
• Time in Patent Office: Days
• CPC Class Codes: B81C 1/00111 Tips, pillars, i.e. raised structures microneedles A61M37/0015
• CPC Class Codes: B81C 1/00523 Etching material
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: H01L 21/30604 Chemical etching
• CPC Class Codes: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H10N 50/01 Manufacture or treatment

Abstract

A process flow for forming magnetic tunnel junction (MTJ) nanopillars with minimal sidewall residue and minimal sidewall damage is disclosed wherein a pattern is first formed in a hard mask that is an uppermost MTJ layer. Thereafter, the hard mask sidewall is etch transferred through the remaining MTJ layers including a reference layer, free layer, and tunnel barrier between the free layer and reference layer. The etch transfer may be completed in a single RIE step that features a physical component involving inert gas ions or plasma, and a chemical component comprised of ions or plasma generated from one or more of methanol, ethanol, ammonia, and CO. In other embodiments, a chemical treatment with one of the aforementioned chemicals, and a volatilization at 50° C. to 450° C. may follow an etch transfer through the MTJ stack with an ion beam etch or plasma etch involving inert gas ions.

Claims

1. A method of etching a magnetic tunnel junction (MTJ) stack of layers, comprising:

(a) providing a MTJ stack of layers on a first electrode wherein the MTJ stack of layers includes an uppermost hard mask layer, and a first stack of layers comprising a reference layer, a free layer, and a tunnel barrier layer between the reference layer and free layer;

(b) forming a pattern in the hard mask layer with a first etch step that is an ion beam etch (IBE) with inert gas, or a reactive ion etch (RIE) with a fluorocarbon or chlorocarbon, wherein the pattern has a sidewall that extends from a hard mask top surface to a top surface of the first stack of layers; and

(c) forming a pattern in the first stack of layers with a sidewall that forms a continuous surface with the sidewall in the hard mask layer, and that extends to a top surface of the first electrode, wherein the pattern in the first stack of layers is produced by a second etch step that combines a physical component in the form of noble gas ions or plasma, and a chemical component in the form of ions or plasma of one or more chemicals selected from methanol, ethanol, ammonia, N₂O, H₂O₂, H₂O, and carbon monoxide.

2. The method of claim 1 further comprised of a volatilization step to remove volatile residue on the first stack sidewall after the second etch step.

3. The method of claim 2 wherein the volatilization step is an IBE or plasma sputter etch comprised of an inert gas and a RF or DC power.

4. The method of claim 3 wherein the IBE or plasma sputter etch during the volatilization step generates inert gas ions or plasma that are directed with a certain penetration angle between 0°

and 90°

for IBE, or orthogonal with respect to a top surface of the first electrode for plasma sputter etching.

5. The method of claim 2 wherein the volatilization step is a thermal treatment comprised of a temperature between about 50°

C. and 450°

C.

6. The method of claim 1 wherein the one or more chemicals in the second etch step further includes oxygen.

7. The method of claim 1 wherein a direction of ions and plasma in the second etch step is essentially orthogonal to the top surface of the first electrode.

8. The method of claim 1 wherein the ions and plasma in the second etch step are generated with a RF power in the range of 600 to 3000 Watts.

9. The method of claim 5 wherein the volatilization step is further comprised of a flow rate of an inert gas, or a flow rate of oxygen and an inert gas.

10. A method of etching a magnetic tunnel junction (MTJ) stack of layers, comprising:

(a) providing a MTJ stack of layers on a first electrode wherein the MTJ stack of layers includes an uppermost hard mask layer, and a first stack of layers comprising a reference layer, a free layer, and a tunnel barrier layer between the reference layer and free layer;

(b) forming a pattern in the hard mask layer with a first etch step that is an ion beam etch (IBE) with inert gas, or a reactive ion etch (RIE) with a fluorocarbon or chlorocarbon, wherein the pattern has a sidewall that extends from a hard mask top surface to a top surface of the first stack of layers; and

(c) forming a pattern in the first stack of layers with a sidewall that forms a continuous surface with the sidewall in the hard mask layer, and that extends to a top surface of the first electrode, wherein the pattern in the first stack of layers is produced by a process sequence, comprising;

(1) a first step that is an IBE with an inert gas; and

(2) a second step that is a chemical treatment to convert a non-volatile residue that is formed on the continuous surface during the first step to a volatile residue.

11. The method of claim 10 further comprised of performing a volatilization step to remove the volatile residue on the continuous surface after the chemical treatment.

12. The method of claim 11 wherein the volatilization step comprises a second IBE or plasma sputter etch step with an inert gas and a RF power less than 100 Watts.

13. The method of claim 11 wherein the volatilization step comprises one or both of a thermal treatment at a temperature between about 50°

C. and 450°

C., and introduction of oxygen into the chamber.

14. The method of claim 10 wherein the chemical treatment comprises one or more of methanol, ethanol, NH₃, and CO.

15. The method of claim 14 wherein the chemical treatment further comprises oxygen.

16. The method of claim 10 wherein the second step further comprises the addition of an inert gas and a temperature in the range of 25°

C. to 150°

C. to remove the volatile residue.

17. The method of claim 14 wherein the chemical treatment further comprises RIE conditions with a RF power from about 100 to 800 Watts that generates a plasma.

18. A method of etching a magnetic tunnel junction (MTJ) stack of layers, comprising:

(a) providing a MTJ stack of layers on a first electrode wherein the MTJ stack of layers includes an uppermost hard mask layer, and a first stack of layers comprising a reference layer, a free layer, and a tunnel barrier layer between the reference layer and free layer;

(b) forming a pattern in the hard mask layer with a first etch step that is an ion beam etch (IBE) with inert gas, or a reactive ion etch (RIE) with a fluorocarbon or chlorocarbon, wherein the pattern has a sidewall that extends from a hard mask top surface to a top surface of the first stack of layers; and

(c) forming a pattern in the first stack of layers with a sidewall that forms a continuous surface with the sidewall in the hard mask layer, and that extends to a top surface of the first electrode, wherein the pattern in the first stack of layers is produced by a second etch step comprising RIE conditions with one or more chemicals selected from methanol, ethanol, N₂O, H₂O₂, H₂O, ammonia, and carbon monoxide.

19. The method of claim 18 further comprised of performing a volatilization step to remove volatile residue on the first stack sidewall after the second etch step wherein the volatilization step comprises an IBE or plasma sputter etching with an inert gas.

20. The method of claim 18 further comprised of performing a volatilization step after the second etch step wherein the volatilization step comprises a temperature in the range of 50°

C. to 450°

C.

21. The method of claim 19 wherein the IBE or plasma sputter etching further comprises introducing a flow of oxygen with the inert gas.

22. The method of claim 20 wherein the volatilization step further comprises introducing a flow of oxygen.