PROCESS FOR NiFe FLUXGATE DEVICE

• US 20160155935A1
• Filed: 12/02/2014
• Published: 06/02/2016
• Est. Priority Date: 12/02/2014
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Eissa, Mona M., ZHANG, Yousong, Jenson, Mark
• Granted Patent: US 9,840,781 B2
• Time in Patent Office: Days
• CPC Class Codes: C09K 13/06 with organic material
• CPC Class Codes: C23F 1/02 Local etching
• CPC Class Codes: C23F 1/28 for etching iron group metals
• CPC Class Codes: G01R 33/04 using the flux-gate principle
• CPC Class Codes: G03F 7/0005 Production of optical devices or components in so far as characterised by the lithographic processes or materials used therefor
• CPC Class Codes: H01L 21/02107 Forming insulating materials on a substrate

Abstract

An etchant for simultaneously etching NiFe and AlN with approximately equal etch rates that comprises phosphoric acid, acetic acid, nitric acid and deionized water. Alternating layers of NiFe and AlN may be used to form a magnetic core of a fluxgate magnetometer in an integrated circuit. The wet etch provides a good etch rate of the alternating layers with good dimensional control and with a good resulting magnetic core profile. The alternating layers of NiFe and AlN may be encapsulated with a stress relief layer. A resist pattern may be used to define the magnetic core geometry. The overetch time of the wet etch may be controlled so that the magnetic core pattern extends at least 1.5 um beyond the base of the magnetic core post etch. The photo mask used to form the resist pattern may also be used to form a stress relief etch pattern.

Claims

1. An etchant for the simultaneous etching of NiFe and AlN comprising:

phosphoric acid;

acetic acid;

nitric acid; and

distilled water;

2. The etchant of claim 1, wherein the phosphoric acid is concentrated phosphoric acid with a weight percent between 10% and 40%, the acetic acid is concentrated acetic acid with a weight percent between 1% and 10%, and the nitric acid is concentrated nitric acid with a weight percent between 0.1% and 3%.

3. The etchant of claim 2, wherein the weight percent of concentrated phosphoric acid is 30%, the weight percent of concentrated acetic acid is 4%, and the weight percent of concentrated nitric acid is 0.45%.

4. A method of forming an integrated circuit, comprising the steps:

forming a first dielectric layer on a wafer of the integrated circuit;

forming a layer of magnetic core material composed of alternating layers of NiFe permalloy and AlN dielectric on the first dielectric layer;

forming a magnetic core pattern on the magnetic core material which exposes areas outside a magnetic core;

etching with a wet etchant to remove the magnetic core material where exposed by the magnetic core pattern to form the magnetic core wherein the wet etchant is comprised of phosphoric acid, acetic acid, nitric acid and distilled water; and

removing the magnetic core pattern.

5. The method of claim 4, wherein the phosphoric acid is concentrated phosphoric acid with a weight percent between 10% and 40%, the acetic acid is concentrated acetic acid with a weight percent between 1% and 10%, and the nitric acid is concentrated nitric acid with a weight percent between 0.1% and 3%.

6. The method of claim 4, wherein each layer of NiFe permalloy has a thickness between 225 nm and 425 nm and where each layer of AlN has a thickness between 5 nm and 15 nm and where there are between 3 and 10 layers each of NiFe permalloy and AlN.

7. The method of claim 4 wherein each layer of NiFe permalloy has a thickness of 325 nm and each layer of AlN has a thickness of 10 nm.

8. The method of claim 4, wherein the step of etching with the wet etchant comprises repeated cycles of etching the magnetic core material with the wet etchant followed by a distilled water rinse until the magnetic material is removed from the exposed areas.

9. The method of claim 4, wherein the step of etching with a wet etch comprises repeated cycles of etching the magnetic core material with the wet etchant for a time less than 6 minutes followed by a distilled water rinse until the magnetic material is removed from the exposed areas.

10. The method of claim 4, wherein the wet etchant is comprised of 30% by weight concentrated phosphoric acid, 4% by weight concentrated acetic acid, 0.45% by weight concentrated nitride acid, and distilled water.

11. A method of forming an integrated circuit, comprising the steps:

forming a first dielectric layer on a wafer of the integrated circuit;

forming an etch stop layer on the first dielectric layer wherein the etch stop layer is silicon nitride;

forming a first stress relief material layer on the etch stop layer;

forming a layer of magnetic core material composed of alternating layers of NiFe permalloy and AN dielectric on the stress relief material layer;

forming a magnetic core pattern on the magnetic core material which exposes areas outside a magnetic core and where the magnetic core pattern is formed using a photomask;

etching with a wet etchant to remove the magnetic core material where exposed by the magnetic core pattern to form the magnetic core wherein the wet etchant is comprised of phosphoric acid, acetic acid, nitric acid and distilled water;

overetching the magnetic core material so that the magnetic core pattern extends beyond the bottom of the magnetic core by at least 1.5 um;

removing the magnetic core pattern.

forming a second stress relief material layer on the first stress relief material layer and on the top and sides of the magnetic core;

forming a stress relief material etch pattern on the second stress relief material wherein the stress relief material etch pattern extends beyond the bottom of the magnetic core by at least 1.5 um and wherein the stress relief material etch pattern is formed using the same photomask that is used to form the magnetic core pattern;

etching the first and the second stress relief material layers using a plasma etch with a fluorine containing gas wherein the plasma etch stops on the etch stop layer; and

removing the stress relief material etch pattern.

12. The method of claim 11, wherein the phosphoric acid is concentrated phosphoric acid with a weight percent between 10% and 40%, the acetic acid is concentrated acetic acid with a weight percent between 1% and 10%, and the nitric acid is concentrated nitric acid with a weight percent between 0.1% and 3%.

13. The method of claim 11, wherein the wet etchant comprises 30% by weight concentrated phosphoric acid, 4% by weight concentrated acetic acid, 0.45% concentrated nitric acid, and DI water.

14. The method of claim 11, wherein the first stress relief material has a thickness of between 30 nm and 50 nm and where the second stress relief layer has a thickness between 90 nm and 300 nm.

15. The method of claim 11, wherein each layer of NiFe permalloy has a thickness between 225 nm and 425 nm and where each layer of AlN has a thickness between 5 nm and 15 nm and where there are between 3 and 10 layers each of NiFe permalloy and AlN.

16. The method of claim 11, wherein the first and second stress relief layers are selected from the group consisting of Ti, TiN, Ta, TaN, Ru, and Pt.

17. The method of claim 11, wherein the first stress relief layer is titanium with a thickness between 30 nm and 50 nm and wherein the second stress relief layer is titanium with a thickness between 90 nm and 300 nm.

18. The method of claim 11, wherein the step of etching with the wet etchant comprises repeated cycles of etching the magnetic core material with the wet etchant followed by a distilled water rinse until the magnetic material is removed from the exposed areas.

19. The method of claim 11, wherein the step of etching with a wet etch comprises repeated cycles of etching the magnetic core material with the wet etchant for a time less than 6 minutes followed by a distilled water rinse until the magnetic material is removed from the exposed areas.

20. The method of claim 11, wherein the etch stop layer is silicon nitride formed by PECVD using silane, ammonia, and nitrogen gases with a thickness between 35 nm and 150 nm.