Tungsten Film Deposition Suppressing Base Etching

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Solution Overview

Problem

The formation of tungsten films using tungsten chloride gas in ALD methods often results in etching of Ti-based base films, leading to thinner films than required due to the reactivity of tungsten chloride with Ti-based materials, and fluorine-containing gases can deteriorate gate insulating films, affecting electrical properties.

Innovation Solution

A film forming method involving alternately supplying a metal chloride gas and a reducing gas to a substrate, with a gradual increase in the flow rate of the metal chloride gas to minimize etching of the base film, and using a depressurization step to control the internal pressure of the buffer tank, thereby suppressing etching and ensuring proper film adhesion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If tungsten chloride gas is supplied at a high flow rate to form a tungsten film, then film formation speed is improved, but etching of the Ti-based base film worsens

Engineering Contradiction:

Improvefilm formation speedVSAvoidetching of base film

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent applies dynamics by gradually increasing the flow rate of tungsten chloride gas over time rather than maintaining a constant high flow rate. The gas flow rate transitions from an initial low rate to a final high rate, allowing the system to adapt dynamically. This resolves the contradiction by enabling high productivity at the end of the process while preventing base film etching during the initial stage when the tungsten film thickness is insufficient.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies preliminary action by first supplying tungsten chloride gas at a low flow rate to form an initial protective tungsten film layer on the base film. This preliminary film acts as a barrier that prevents subsequent etching of the base film. Only after this protective layer is formed does the gas flow rate increase to achieve high-speed film formation, thus preventing harmful etching effects before they can occur.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If fluorine-containing gas is used to form tungsten film, then film formation is improved, but gate insulating film deterioration worsens

Engineering Contradiction:

Improvefilm formation capabilityVSAvoidgate insulating film deterioration

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies the taking out principle by removing fluorine from the tungsten chloride gas formula, using WCl6 instead of WF6 as the tungsten source. This extraction of the harmful fluorine element eliminates the etching of gate insulating films while maintaining the ability to form tungsten films through chloride-based chemistry, thus resolving the contradiction between film formation capability and insulating film protection.

Inventive Principle:

Principle #2Taking out (Extraction)

3Strength

If Ti-based material film is used as base film to improve adhesion, then adhesion is improved, but etching susceptibility worsens

Engineering Contradiction:

Improvefilm adhesionVSAvoidetching of base film

Core Design Contradiction:

StrengthVSObject-generated harmful factors

Solution Approach 1:

The patent maintains the Ti-based base film for adhesion purposes but applies dynamic control to the tungsten chloride gas flow rate. The gradual increase in gas flow rate allows the system to benefit from the strong adhesion of Ti-based films while preventing their etching through controlled timing of high chloride exposure.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses preliminary action by first forming a protective tungsten layer on the Ti-based base film before exposing it to high concentrations of tungsten chloride gas. This preliminary tungsten coating serves as a protective barrier that preserves the adhesion benefits of the Ti-based film while preventing chloride-induced etching during subsequent high-rate deposition.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method effectively suppresses etching of the base film, ensures proper adhesion, and maintains electrical properties by gradually increasing the flow rate of the metal chloride gas and controlling the internal pressure, resulting in a tungsten film with desired thickness and step coverage.

Implementation Method 1

a reducing gas for reducing the metal chloride gas

Methodology Applied

Scientific EffectChemical reduction: Reduction

Implementation Method 2

the alternately supplying the metal chloride gas and the reducing gas includes a period of time during which a flow rate of the metal chloride gas gradually increases

Methodology Applied

Scientific EffectEtching suppression through controlled deposition:

Data Source

PatentUS10829854B2Film forming method

Publication Date: 2020.11.10 TOKYO ELECTRON LTD

AI summary

There is provided a film forming method of forming a metal film, which includes: alternately supplying a metal chloride gas and a reducing gas for reducing the metal chloride gas to a substrate arranged inside a processing vessel a plurality of times, wherein the alternately supplying the metal chloride gas and the reducing gas includes a period of time during which a flow rate of the metal chloride gas gradually increases.