Silicon Etching Liquid Stabilization via Carbonate Ions
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Solution Overview
Problem
Hydroxylamine-containing etching liquids used for silicon etching suffer from decomposition during storage, leading to a decrease in etching rate over time, especially when kept warm, requiring frequent monitoring and complicating deep pore etching processes.
Innovation Solution
An alkaline aqueous solution containing alkali metal hydroxide, hydroxylamine, and an inorganic carbonate compound with a pH of 12 or more, which suppresses hydroxylamine decomposition and maintains a high etching rate by stabilizing carbonate ions, preventing bicarbonate formation and thus maintaining etching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hydroxylamine is added to accelerate etching rate, then etching speed increases, but hydroxylamine decomposes during storage causing rate reduction over time
Solution Approach 1:
The patent introduces carbonate ions as an intermediary substance that mediates between hydroxylamine and the etching process. The carbonate ions suppress hydroxylamine decomposition by providing an alternative chemical pathway, thereby maintaining hydroxylamine concentration stability while preserving high etching rates. This mediator approach resolves the contradiction by preventing the harmful decomposition reaction without interfering with the beneficial etching action.
Solution Approach 2:
The patent changes the chemical composition parameters of the etching liquid by adding carbonate compounds (such as potassium carbonate or sodium carbonate) to the hydroxylamine-containing solution. This parameter change - the addition of carbonate ions - fundamentally alters the chemical environment to suppress hydroxylamine decomposition, thereby stabilizing the hydroxylamine concentration over time while maintaining the high etching rate.
2Productivity
If hydroxylamine-containing etching liquid is kept in warmed state, then etching efficiency improves, but hydroxylamine decomposition accelerates causing rate reduction
Solution Approach 1:
The patent applies preliminary anti-action by adding carbonate ions to the etching liquid before use, which pre-establishes a protective chemical environment that counteracts the decomposition tendency of hydroxylamine. This preliminary protective measure ensures that even when the solution is warmed to improve etching efficiency, the hydroxylamine decomposition is suppressed from the outset, maintaining stable etching rates over extended periods.
3Length of moving object
If deep pore etching is performed using hydroxylamine-containing liquid, then etching depth increases, but frequent monitoring is required due to decomposition
Solution Approach 1:
By introducing carbonate ions as a mediator, the patent stabilizes hydroxylamine concentration throughout the etching process, enabling deep pore etching without the need for frequent monitoring. The carbonate ions continuously suppress decomposition reactions, ensuring consistent etching rates even during extended processing times required for deep structures.
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 solution allows for anisotropic etching of monocrystalline silicon with a high and stable etching rate, simplifying operations and extending the life of the etching liquid by preventing significant rate reduction over time.
Implementation Method 1
an alkaline aqueous solution containing (A) an alkali metal hydroxide, (B) hydroxylamine and (C) an inorganic carbonate compound and having a pH of 12 or more
Implementation Method 2
etching of monocrystalline silicon proceeds while keeping anisotropy. This is based on the fact that there is a difference in a dissolution rate of silicon in every crystal face orientation of silicon
Implementation Method 3
silicon is dissolved as a silicate ion by a hydroxy anion in the liquid
Data Source
AI summary
In etching processing of silicon, in particular anisotropic etching processing of silicon in a manufacturing step of MEMS parts, an etching liquid having a long life of etching liquid and an etching method are provided by suppressing a lowering of an etching rate at the time of warming which is characteristic of a hydroxylamine-containing etching liquid.A silicon etching liquid which is an alkaline aqueous solution containing an alkali metal hydroxide, hydroxylamine and an inorganic carbonate compound and having a pH of 12 or more and which is able to anisotropically dissolve monocrystalline silicon therein, and an etching method of silicon using this etching liquid are provided.