Silicon Etchant Composition for High Aspect Ratio Substrates

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Solution Overview

Problem

The reduction in tetramethylammonium hydroxide levels due to occupational safety regulations in Taiwan limits the silicon etching rate, and conventional strong alkalis are unsuitable for miniaturization in microelectronic devices, while the addition of surfactants to enhance permeability significantly reduces the silicon etching rate.

Innovation Solution

A silicon etchant comprising a combination of tetramethylammonium hydroxide, a strongly basic amine such as polyamine or alkanolamine, and an anionic surfactant, which maintains a high etching rate with low surface tension and contact angle, suitable for substrates with high aspect ratios.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the amount of tetramethylammonium hydroxide is reduced to meet legal standards (2.38% by weight or less), then health hazards are prevented, but the etching ability becomes insufficient

Engineering Contradiction:

Improvehealth hazards from chemical inhalationVSAvoidsilicon etching rate

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The patent combines tetramethylammonium hydroxide with strongly basic amines (polyamines or alkanolamines) to create a synergistic etching system. This merging allows the formulation to achieve high etching rates while keeping tetramethylammonium hydroxide content at or below the legal limit of 2.38% by weight, thus preventing health hazards while maintaining productivity

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the chemical composition parameters by introducing specific strongly basic amines (polyamines with 2-6 carbon atoms or alkanolamines with 2-6 carbon atoms) to replace part of the tetramethylammonium hydroxide function. This parameter change allows the system to maintain high etching ability while reducing the concentration of the regulated substance

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If a surfactant is added to increase etchant permeability in narrow high aspect ratio spaces, then permeability is improved, but the silicon etching rate is drastically reduced

Engineering Contradiction:

Improveetchant permeabilityVSAvoidsilicon etching rate

Core Design Contradiction:

Quantity of substanceVSProductivity

Solution Approach 1:

The patent changes the chemical parameters by selecting specific strongly basic amines with appropriate molecular weights and basicities that inherently provide good permeability in narrow spaces without requiring surfactant addition. This parameter optimization maintains high etching rates while achieving the necessary permeability for high aspect ratio structures

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses the strongly basic amines as alternative etching agents that can be applied and quickly removed, providing sufficient permeability enhancement without the need for persistent surfactant coatings that would reduce etching rates. The system achieves permeability through the chemical properties of the amine components themselves

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

The combination achieves a high silicon etching rate with low surface tension and contact angle, effectively addressing the limitations of reduced tetramethylammonium hydroxide levels and conventional alkali concerns, enabling efficient etching of substrates with high aspect ratios.

Implementation Method 1

a silicon etchant containing a quaternary ammonium hydroxide and a strongly basic amine... achieves a high silicon etching rate

Methodology Applied

Scientific EffectChemical etching: Chemical Bonding

Implementation Method 2

having a low surface tension and a small contact angle with respect to a substrate... the addition of the surfactant also drastically reduces the silicon etching rate

Methodology Applied

Scientific EffectSurface tension reduction: Surfactant