Process for NiFe fluxgate device

Patent metadata

Field	Value
Publication number	US-10266950-B2
Application number	US-201715809143-A
Country	US
Kind code	B2
Filing date	Nov 10, 2017
Priority date	Dec 2, 2014
Publication date	Apr 23, 2019
Grant date	Apr 23, 2019

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.

First claim

What is claimed is:

1. A method of forming an integrated circuit, comprising the steps: forming a first dielectric layer on a semiconductor wafer;
forming an etch stop layer on the first dielectric layer;
forming a first stress relief material layer on the etch stop layer;
forming a stack of magnetic core material composed of alternating layers of NiFe permalloy and AlN dielectric on the first stress relief material layer;
forming a first pattern on the stack of magnetic core material and etching the stack with a wet etchant to remove the magnetic core material where exposed by the first pattern to form a magnetic core wherein the wet etchant is comprised of phosphoric acid, acetic acid, nitric acid and deionized water;
overetching the magnetic core material so that the first pattern extends laterally beyond the magnetic core;
removing the first 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 second pattern on the second stress relief material wherein the second pattern extends beyond the bottom of the magnetic core;
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 second pattern.

2. The method 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 method of claim 1 , 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.

4. The method of claim 1 , 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.

5. The method of claim 1 , 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.

6. The method of claim 1 , wherein the first and second stress relief layers are selected from the group consisting of Ti, TiN, Ta, TaN, Ru, and Pt.

7. The method of claim 1 , 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.

8. The method of claim 1 , 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 deionized water rinse until the magnetic material is removed from the exposed areas.

9. The method of claim 1 , 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 deionized water rinse until the magnetic material is removed from the exposed areas.

10. The method of claim 1 , 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.

11. The method of claim 1 , wherein the second pattern extends lateral beyond the magnetic core by at least 1.5 μm and wherein the second pattern has the same dimensions as the first pattern.

12. A method of forming an integrated circuit, comprising the steps:
forming a first dielectric layer on a semiconductor wafer;
forming a silicon nitride layer on the first dielectric layer;
forming a first titanium layer on the silicon nitride layer;
forming a stack of magnetic core material composed of alternating layers of NiFe permalloy and AlN dielectric on the first titanium layer;
forming a first pattern on the stack of magnetic core material and etching the stack with a wet etchant to remove the magnetic core material where exposed by the first pattern to form a magnetic core wherein the wet etchant is comprised of phosphoric acid, acetic acid, nitric acid and deionized water;
overetching the magnetic core material so that the first pattern extends laterally beyond the magnetic core by at least 1.5 μm;
removing the first pattern;
forming a second titanium layer on the first titanium layer and on the top and sides of the magnetic core;
forming a second pattern on the second titanium layer wherein the second pattern extends beyond the bottom of the magnetic core by at least 1.5 μm;
etching the first and the second titanium layers using a plasma etch with a fluorine containing gas, wherein the plasma etch stops on the silicon nitride layer; and
removing the second pattern.

13. The method of claim 12 , 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%.

14. The method of claim 12 , 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.

15. The method of claim 12 , 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 deionized water rinse until the magnetic material is removed from the exposed areas.

16. The method of claim 12 , 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 deionized water rinse until the magnetic material is removed from the exposed areas.

17. The method of claim 12 , wherein the silicon nitride layer is formed by PECVD using silane, ammonia, and nitrogen gases and has a thickness between 35 nm and 150 nm.

Assignees

• Texas Instruments Inc

Inventors

• Eissa Mona M
• Zhang Yousong
• Jenson Mark

Classifications

• H10P14/60

  of insulating materials · CPC title

• G03F7/0005

  Production of optical devices or components in so far as characterised by the lithographic processes or materials used therefor · CPC title

• C23F1/28 Primary

  for etching iron group metals · CPC title

• C23F1/02

  Local etching · CPC title

• G01R33/04

  using the flux-gate principle · CPC title