Etching Solution Composition for Stable Silicon Oxide Processing
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Solution Overview
Problem
Existing etching solutions for silicon oxide films, such as buffered hydrofluoric acid, experience composition changes due to evaporation, leading to inconsistent etch rates and frequent solution replacement, which is inefficient and affects processing accuracy in semiconductor and liquid crystal processes.
Innovation Solution
An etching solution comprising hydrofluoric acid, ammonium fluoride, and a salt formed between hydrogen fluoride and a base with a boiling point higher than ammonia, where the ammonium fluoride concentration is not higher than 8.2 mol/kg and the total concentration of ammonium fluoride and the salt is not less than 9.5 mol/kg, stabilizing the etch rate and maintaining processing dimensional accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If buffered hydrofluoric acid with high ammonium fluoride concentration (greater than 30 mass %) is used, then the etch rate of silicon oxide film increases, but the chemical composition changes due to evaporation, making the solution unusable
Solution Approach 1:
The patent changes the chemical parameters by replacing part of the ammonium fluoride with a fluoride salt of a base having a higher boiling point than ammonia. This substitution maintains the etch rate while preventing composition changes due to evaporation, as the higher boiling point base does not evaporate under process conditions.
Solution Approach 2:
The patent creates a composite chemical solution by combining hydrofluoric acid, ammonium fluoride, and a fluoride salt of a base with higher boiling point. This composite formulation leverages the etching capability of HF and the buffering capacity of fluoride salts while using the higher boiling point base to prevent evaporation-induced composition changes.
2Duration of action of stationary object
If buffered hydrofluoric acid is left to stand for extended periods, then the chemical composition changes due to evaporation of ammonia, but the solution can be restored by adding composition-adjusting chemical solution
Solution Approach 1:
The patent creates a chemical solution designed to maintain stable composition throughout its intended lifespan without requiring restoration. While the solution may eventually need replacement, it eliminates the complexity of monitoring and adjusting composition during use, effectively making it a reliable disposable solution that maintains performance until replacement is needed.
3Stability of the object's composition
If the chemical solution composition is controlled by controlling the environment, then the change in chemical composition is reduced, but the solution itself is not improved
Solution Approach 1:
The patent extracts the environmental dependency from the system by incorporating a base with higher boiling point than ammonia into the chemical formulation. This removes the vulnerability to environmental evaporation conditions, making the solution inherently stable regardless of ambient temperature and humidity variations.
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 solution minimizes composition changes and etch rate variations over time, reducing the frequency of solution replacement and ensuring uniform etching of silicon oxide films, thereby enhancing processing efficiency and accuracy.
Implementation Method 1
The dissociation of ammonium fluoride, ammonium ion, and hydrofluoric acid in buffered hydrofluoric acid is expressed by the following Formulae (1) to (4). NH4F→NH4++F−
Implementation Method 2
NH4+⇄NH3+H+(pKa=9.24)
Implementation Method 3
HF⇄H++F−(pKa=3.17)
Implementation Method 4
HF+F−⇄HF2−
Implementation Method 5
ammonia evaporates according to Formula (2)
Data Source
AI summary
An etching solution, a process of producing the same, and an etching process using the same, in which the etching solution includes hydrofluoric acid (a), ammonium fluoride (b), and salt (c) formed between hydrogen fluoride and a base having a boiling point higher than that of ammonia; the concentration of ammonium fluoride (b) is not higher than 8.2 mol/kg, and the total amount of ammonium fluoride (b) and salt (c) formed between hydrogen fluoride and a base having a boiling point higher than that of ammonia is not less than 9.5 mol/kg.