# US 12,604,682 B2 · Methods for patterning a semiconductor substrate using metalate salt ionic liquid crystals

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- Number: US 12,604,682 B2
- Document ID: US12604682B2
- Status: Granted
- Kind: B2
- Application number: 18/388,222
- Filed: 2023-11-09
- Published: 2025-05-15
- Granted: 2026-04-14
- Earliest claimed: 2023-11-09
- Assignees: Tokyo Electron Limited
- Applicants: Tokyo Electron Limited
- Inventors: Kate Abel; Dipak Aryal
- Web page: https://patentgrep.com/patent/US12604682B2

## CPC

- H10P 14/6314: {of a metallic layer}
- H10P 14/6319: {Formation by plasma treatments, e.g. plasma oxidation of the substrate}
- H10P 14/6938: {the material containing at least one metal element, e.g. metal oxides, metal oxynitrides or metal oxycarbides}
- H10P 76/20: of masks comprising organic materials
- H10P 76/2041: {Photolithographic processes}
- H10P 76/405: {characterised by their composition, e.g. multilayer masks}
- H10P 76/4085: {characterised by the processes involved to create the masks}
- H10P 76/4088: {Processes for improving the resolution of the masks}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

Embodiments of improved process flows and methods are provided to pattern a semiconductor substrate using direct self-assembly (DSA) of metalate salt ionic liquid crystals (ILCs) having metalate anions. After self-assembly of the metalate salt ILCs into ordered structures, an oxidation process is used to remove the organic components of the ordered structures and convert the metalate anions into metal oxide patterns. In addition to providing a robust metal oxide pattern, which can be transferred to the underlying substrate, the process flows and methods disclosed herein enable ILCs to be used as pitch multipliers in advanced patterning techniques.

## Claims

### Claim 1

A method to pattern a semiconductor substrate, the method comprising:
producing a first pattern on an underlying layer of the semiconductor substrate, the first pattern comprising a plurality of features formed at a first pitch;
depositing an ionic liquid crystal (ILC) solution within each feature of the plurality of features, wherein the ILC solution comprises metalate salt ionic liquid crystals (ILCs) having cation head groups, alkyl tail groups, and metalate anions, and wherein the metalate salt ILCs deposited within the plurality of features self- assemble into layered structures having alternating layers of head group layers and tail group layers, with the metalate anions segregated to the head group layers;
exposing the semiconductor substrate to an oxidization process to remove the tail group layers from the layered structures and convert the head group layers of the layered structures into a metal oxide pattern having a second pitch, which is smaller than the first pitch; and
transferring the metal oxide pattern to the underlying layer of the semiconductor substrate.

### Claim 2 (depends on 1)

The method of claim 1, wherein said exposing the semiconductor substrate to the oxidization process comprises exposing the semiconductor substrate to an oxygen plasma ashing process, an ultra-violet (UV) ozone process, a gas phase oxidation process, or a solution phase oxidation process.

### Claim 3 (depends on 1)

The method of claim 1, wherein said exposing the semiconductor substrate to the oxidization process oxidizes the layered structures to:
convert the tail group layers into volatile carbon oxides, which are removed from the layered structures during the oxidation process; and
convert the metalate anions within the head group layers into non-volatile metal oxides, which remain after the oxidation process as the metal oxide pattern.

### Claim 4 (depends on 1)

The method of claim 1, wherein the cation head groups within the metalate salt ILCs comprise an imidazolium, pyrazolium, pyrrolidinium, pyridinium, piperidinium, morpholinium, ammonium, phosphonium, sulphonium, or cholinium based cation head group.

### Claim 5 (depends on 1)

The method of claim 1, wherein metalate salt ILCs comprise an imidazolium-based cation head group of the form: 1-R1-3-R2-imidazolium, where R1 is an alkyl chain with a chain length ranging from 8-18 carbons, and R2 is a hydrogen, a methyl group, an ethyl group, a propyl group, a butyl group, or a substituted or unsubstituted phenyl group.

### Claim 6 (depends on 5)

The method of claim 5, wherein the metalate anions within the metalate salt ILCs comprise chloroaluminate anions, chloroferrate anions, chlorostannate anions, chloroindate anions, or chlorozincate anions.

### Claim 7 (depends on 1)

The method of claim 1, wherein the metalate salt ILCs comprise 1-dodecyl-3-methylimidazolium tetrachloroaluminate or 1-dodecyl-3-methylimidazolium tetrachloroferrate.

### Claim 8 (depends on 1)

The method of claim 1, wherein said producing the first pattern comprises:
depositing a neutral layer on the underlying layer of the semiconductor substrate;
depositing a hydrophilic layer on the neutral layer; and
using a photolithography process to produce the first pattern within the hydrophilic layer, such that the neutral layer is exposed at a bottom of each feature and the hydrophilic layer is exposed on sidewall surfaces of each feature.

### Claim 9 (depends on 8)

The method of claim 8, wherein the metalate salt ILCs deposited within the plurality of features self-assemble into vertically layered structures having alternating layers of head group layers and tail group layers, wherein the head group layers of the vertically layered structures are oriented towards the sidewall surfaces of the features.

### Claim 10 (depends on 9)

The method of claim 9, further comprising controlling a layer pitch between the alternating layers of the vertically layered structures by controlling a chain length of the alkyl tail groups.

### Claim 11 (depends on 9)

The method of claim 9, wherein a width of each feature is equivalent to an integer multiple of a layer pitch between the alternating layers of the vertically layered structures, and wherein the second pitch is equivalent to the layer pitch.

### Claim 12 (depends on 9)

The method of claim 9, wherein said using the photolithography process to produce the first pattern comprises:
using the photolithography process to form a plurality of trenches within the hydrophilic layer to form a pattern of hydrophilic lines on the neutral layer; and
wherein the ILC solution is deposited within each trench of the plurality of trenches.

### Claim 13 (depends on 9)

The method of claim 9, wherein said using the photolithography process to produce the first pattern comprises:
using the photolithography process to form a pattern of holes that extend through the hydrophilic layer to the neutral layer; and
wherein the ILC solution is deposited within each of the holes.

### Claim 14

A pitch multiplication method comprising:
producing a first pattern on a semiconductor substrate, the first pattern comprising a plurality of features formed at a first pitch; and
producing a second pattern within each feature of the plurality of features using direct self-assembly (DSA) of metalate salt ionic liquid crystals (ILCs) followed by oxidation to convert metalate anions included within the metalate salt ILCs into metal oxides, the second pattern comprising the metal oxides formed at a second pitch, which is less than the first pitch.

### Claim 15 (depends on 14)

The pitch multiplication method of claim 14, wherein said producing the second pattern comprises:
depositing an ionic liquid crystal (ILC) solution comprising the metalate salt ILCs within each feature of the plurality of features, wherein the metalate salt ILCs comprise cation head groups, alkyl tail groups, and the metalate anions, and wherein the metalate salt ILCs deposited within the plurality of features self-assemble into layered structures having alternating layers of head group layers and tail group layers, with the metalate anions segregated to the head group layers; and
exposing the semiconductor substrate to an oxidization process to remove the tail group layers from the layered structures and convert the metalate anions into the metal oxides.

### Claim 16 (depends on 15)

The pitch multiplication method of claim 15, wherein said exposing the semiconductor substrate to the oxidization process comprises exposing the semiconductor substrate to an oxygen plasma ashing process, an ultra-violet (UV) ozone process, a gas phase oxidation process, or a solution phase oxidation process.

### Claim 17 (depends on 15)

The pitch multiplication method of claim 15, wherein said exposing the semiconductor substrate to the oxidization process oxidizes the layered structures to:
convert the tail group layers into volatile carbon oxides, which are removed from the layered structures during the oxidation process; and
convert the metalate anions within the head group layers into non-volatile metal oxides, which remain after the oxidation process as the metal oxides.

### Claim 18 (depends on 15)

The pitch multiplication method of claim 15, wherein said producing the first pattern comprises:
depositing a neutral layer on the semiconductor substrate;
depositing a hydrophilic layer on the neutral layer; and
using a photolithography process to produce the first pattern within the hydrophilic layer, such that the neutral layer is exposed at a bottom of each feature and the hydrophilic layer is exposed on sidewall surfaces of each feature.

### Claim 19 (depends on 18)

The pitch multiplication method of claim 18, wherein the metalate salt ILCs deposited within the plurality of features self-assemble into vertically layered structures having alternating layers of head group layers and tail group layers, wherein the head group layers of the vertically layered structures are oriented towards the sidewall surfaces of the features.

### Claim 20 (depends on 19)

The pitch multiplication method of claim 19, further comprising controlling a layer pitch between the alternating layers of the vertically layered structures by controlling a chain length of the alkyl tail groups.

### Claim 21 (depends on 19)

The pitch multiplication method of claim 19, wherein a width of each feature is equivalent to an integer multiple of a layer pitch between the alternating layers of the vertically layered structures, and wherein the second pitch is equivalent to the layer pitch.