# US 12,604,691 B2 · Methods for wet atomic layer etching of molybdenum in aqueous solution

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- Number: US 12,604,691 B2
- Document ID: US12604691B2
- Status: Granted
- Kind: B2
- Application number: 18/636,818
- Filed: 2024-04-16
- Published: 2025-10-16
- Granted: 2026-04-14
- Earliest claimed: 2023-08-30
- Assignees: Tokyo Electron Limited
- Applicants: Tokyo Electron Limited
- Inventors: Tulashi Dahal
- Web page: https://patentgrep.com/patent/US12604691B2

## CPC

- H10P 50/667: {by liquid etching only}
- H10P 14/6314: {of a metallic layer}
- H10P 14/6939: {characterised by the metal}
- H10P 50/283: {by chemical means}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

Methods are provided for etching molybdenum in a wet ALE process. The methods disclosed herein use a wide variety of techniques and wet etch chemistries to oxidize a molybdenum surface and form a self-limiting, molybdenum oxide passivation layer in a surface modification step of the wet ALE process. In the wet ALE processes and methods disclosed herein, self-limiting behavior is provided in the oxidation step by adding a polydentate ligand to an aqueous oxidizing solution. The polydentate ligand reacts with and binds to the oxidized molybdenum surface to form a stable, ligand-molybdenum oxide complex, which is insoluble within the aqueous oxidizing solution. The insolubility of the ligand-molybdenum complex in the aqueous oxidizing solution provides self-limiting behavior in the oxidation step. After forming the molybdenum oxide passivation layer, the passivation layer is selectively removed in a dissolution step of the wet ALE process to etch the molybdenum surface.

## Claims

### Claim 1

A method of etching, the method comprising:
receiving a substrate having a molybdenum (Mo) layer formed thereon, wherein a molybdenum surface is exposed on a surface of the substrate;
exposing the surface of the substrate to a surface modification solution comprising an oxidizer and a polydentate ligand dissolved in an aqueous solvent, wherein the oxidizer reacts with the molybdenum surface to oxidize the molybdenum surface and form a molybdenum oxide passivation layer, and wherein the polydentate ligand binds to the molybdenum oxide passivation layer to form a surface species that is insoluble in the aqueous solvent;
removing the surface modification solution from the surface of the substrate subsequent to forming the molybdenum oxide passivation layer;
exposing the surface of the substrate to a dissolution solution to selectively remove the molybdenum oxide passivation layer, wherein the dissolution solution reacts with the molybdenum oxide passivation layer to form soluble species that are dissolved by the dissolution solution; and
removing the dissolution solution and the soluble species from the surface of the substrate to etch the molybdenum layer.

### Claim 2 (depends on 1)

The method of claim 1, further comprising repeating said exposing the surface of the substrate to the surface modification solution, removing the surface modification solution, exposing the surface of the substrate to the dissolution solution, and removing the dissolution solution and the soluble species a number of times until a predetermined amount of the molybdenum layer is removed from the substrate.

### Claim 3 (depends on 1)

The method of claim 1, wherein the polydentate ligand reacts with and binds to the molybdenum oxide passivation layer to change a surface chemistry of the molybdenum oxide passivation layer, and wherein changing the surface chemistry ensures that the molybdenum oxide passivation layer is self-limiting and insoluble in the aqueous solvent.

### Claim 4 (depends on 1)

The method of claim 1, wherein the polydentate ligand is a bidentate ligand, a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand.

### Claim 5 (depends on 1)

The method of claim 1, wherein the polydentate ligand is oxalic acid, acetic acid, ascorbic acid, mandelic acid, malic acid, maleic acid, fumaric acid, ethylenediamine, acetylacetonate ion, diethylenetriamine, terpyridine, diaminopyridine, pentamethyl diethylenetriamine, triethylenetetramine, nitrilotriacetate, tetraethylenepentamine, ethylenediaminetetraacetic acid (EDTA) or a diammonium salt of EDTA [(NH4)2EDTA].

### Claim 6 (depends on 1)

The method of claim 1, wherein the polydentate ligand reacts with and binds to the molybdenum oxide passivation layer to form a ligand-metal oxide complex that is insoluble in the aqueous solvent.

### Claim 7 (depends on 6)

The method of claim 6, wherein the polydentate ligand has more than two donor atoms to increase a stability of the ligand-metal oxide complex and render the molybdenum oxide passivation layer insoluble in the aqueous solvent.

### Claim 8 (depends on 6)

The method of claim 6, wherein the polydentate ligand is a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand.

### Claim 9 (depends on 6)

The method of claim 6, wherein the polydentate ligand is ethylenediamine, acetylacetonate ion, diethylenetriamine, terpyridine, diaminopyridine, pentamethyl diethylenetriamine, triethylenetetramine, nitrilotriacetate, tetraethylenepentamine, ethylenediaminetetraacetic acid (EDTA) or a diammonium salt of EDTA [(NH4)2EDTA].

### Claim 10 (depends on 1)

The method of claim 1, wherein the polydentate ligand is a hexadentate ligand.

### Claim 11 (depends on 1)

The method of claim 1, wherein the polydentate ligand is ethylenediaminetetraacetic acid (EDTA) or a diammonium salt of EDTA [(NH4)2EDTA].

### Claim 12 (depends on 1)

The method of claim 1, wherein the oxidizer comprises ammonium persulfate (APS), ferric chloride (FeCl3), an osmium tetroxide, a ruthenium tetroxide, a ruthenate, a manganate, a permanganate, a periodate, a metal nitrate, hydrogen peroxide (H2O2), or another peroxide.

### Claim 13 (depends on 1)

The method of claim 1, wherein the oxidizer comprises ammonium persulfate (APS), and wherein the polydentate ligand comprises ethylenediaminetetraacetic acid (EDTA) or a diammonium salt of EDTA [(NH4)2EDTA].

### Claim 14 (depends on 1)

The method of claim 1, wherein the dissolution solution is: (a) an aqueous acidic solution comprising hydrochloric acid (HCl), nitric acid or sulfuric acid, (b) an aqueous basic solution comprising ammonium hydroxide (NH4OH), tetramethylammonium hydroxide (TMAH), potassium hydroxide (KOH) or calcium hydroxide (Ca(OH)2), (c) a non-aqueous ligand solution comprising alpha-benzoin oxime in acetone, dimethyl sulfoxide (DMSO), methyl-ethyl ketone (MEK) or another ketone, or (d) an aqueous ligand solution comprising a base and a ligand.

### Claim 15 (depends on 1)

The method of claim 1, wherein the dissolution solution is an aqueous ligand solution comprising ammonium hydroxide (NH4OH) and a ligand.

### Claim 16 (depends on 15)

The method of claim 15, wherein the ligand is ascorbic acid, sodium ascorbate, calcium ascorbate, potassium ascorbate, oxalic acid, formic acid, acetic acid, ethylenediamine, ethylenediaminetetraacetic acid (EDTA) or iminodiacetic acid.

### Claim 17

A method of etching a substrate using a wet atomic layer etching (ALE) process, the method comprising:
receiving the substrate, the substrate having a molybdenum (Mo) layer formed thereon, wherein a molybdenum surface is exposed on a surface of the substrate; and
selectively etching the molybdenum layer by performing multiple cycles of the wet ALE process, wherein each cycle comprises:
exposing the molybdenum surface to a first etch solution comprising an oxidizer and a polydentate ligand dissolved in an aqueous solvent to form a chemically modified Mo surface layer that is self-limiting and insoluble in the aqueous solvent;
rinsing the substrate with a first purge solution to remove the first etch solution from the surface of the substrate;
exposing the chemically modified Mo surface layer to a second etch solution to dissolve the chemically modified Mo surface layer; and
rinsing the substrate with a second purge solution to remove the second etch solution from the surface of the substrate.

### Claim 18 (depends on 17)

The method of claim 17, wherein the oxidizer reacts with the molybdenum surface to oxidize the molybdenum surface and form the chemically modified Mo surface layer, wherein the polydentate ligand reacts with and binds to the chemically modified Mo surface layer to change a surface chemistry of the chemically modified Mo surface layer, and wherein changing the surface chemistry ensures that the chemically modified Mo surface layer is self-limiting and insoluble in the aqueous solvent.

### Claim 19 (depends on 17)

The method of claim 17, wherein the oxidizer comprises ammonium persulfate (APS), ferric chloride (FeCl3), an osmium tetroxide, a ruthenium tetroxide, a ruthenate, a manganate, a permanganate, a periodate, a metal nitrate, hydrogen peroxide (H2O2), or another peroxide.

### Claim 20 (depends on 17)

The method of claim 17, wherein the polydentate ligand is a bidentate ligand, a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand.

### Claim 21 (depends on 17)

The method of claim 17, wherein the polydentate ligand is oxalic acid, acetic acid, ascorbic acid, mandelic acid, malic acid, maleic acid, fumaric acid, ethylenediamine, acetylacetonate ion, diethylenetriamine, terpyridine, diaminopyridine, pentamethyl diethylenetriamine, triethylenetetramine, nitrilotriacetate, tetraethylenepentamine, ethylenediaminetetraacetic acid (EDTA) or a diammonium salt of EDTA [(NH4)2EDTA].

### Claim 22 (depends on 17)

The method of claim 17, wherein the first etch solution comprises ammonium persulfate (APS) and a hexadentate ligand dissolved in water.

### Claim 23 (depends on 17)

The method of claim 17, wherein the second etch solution is an aqueous ligand solution comprising ammonium hydroxide (NH4OH) and a ligand.

### Claim 24 (depends on 23)

The method of claim 23, wherein the ligand is ascorbic acid, sodium ascorbate, calcium ascorbate, potassium ascorbate, oxalic acid, formic acid, acetic acid, ethylenediamine, ethylenediaminetetraacetic acid (EDTA) or iminodiacetic acid.