Diamond Electrolysis Viscosity Control for Persulfuric Acid
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Solution Overview
Problem
The persulfuric acid method for resist removal in semiconductor manufacturing faces electrode wear issues due to high viscosity and low ionic dissociation in sulfuric acid solutions, especially at high current densities, leading to reduced electrode life and increased chemical costs.
Innovation Solution
Adjusting the viscosity and temperature of the sulfuric acid solution by controlling electrolyte concentration to maintain a specific ion flux parameter (Pf ≥ 1.2 mol/(L·cP) at different current densities, using diamond electrodes to minimize electrode wear and enhance electrolysis efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high current density is used in electrolysis of sulfuric acid solution, then electrolysis efficiency is improved, but electrode wear increases due to insufficient ion supply
Solution Approach 1:
The patent changes the physical parameters of the electrolytic solution by controlling temperature and concentration to achieve optimal viscosity. By maintaining viscosity within 8-15 cP through temperature control (20-80°C) and sulfuric acid concentration adjustment (70-90 wt%), the patent ensures sufficient ion mobility to the electrode surface even at high current densities, preventing electrode wear while maintaining high electrolysis efficiency
Solution Approach 2:
The patent applies preliminary anti-action by pre-controlling the viscosity of the electrolytic solution before electrolysis begins. By adjusting temperature and concentration in advance to achieve the target viscosity range, the patent prevents the harmful effect of insufficient ion supply that would otherwise occur at high current densities, thereby protecting the electrode from wear before the electrolysis process starts
2Strength
If highly concentrated sulfuric acid solution is used, then oxidization power is improved, but viscosity increases reducing ion mobility
Solution Approach 1:
The patent applies parameter changes by controlling both concentration and temperature simultaneously. By maintaining sulfuric acid concentration between 70-90 wt% for high oxidization power while controlling temperature to keep viscosity within 8-15 cP, the patent achieves both high oxidization power and sufficient ion mobility. This dual parameter control resolves the contradiction between concentration and viscosity
3Reliability
If diamond electrode is used, then electrode stability is improved, but cost increases
Solution Approach 1:
The patent reduces diamond electrode wear by optimizing electrolyte viscosity through temperature and concentration control. By maintaining viscosity within 8-15 cP, the patent minimizes the extraction of carbon atoms from the diamond electrode surface, thereby extending electrode life and reducing replacement frequency. This indirectly reduces the overall cost despite the high initial electrode cost
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 approach allows for efficient electrolysis with reduced electrode wear, maintaining high current efficiency and preventing vaporization issues, thus extending electrode life and reducing operational costs.
Implementation Method 1
generates the persulfuric acid (peroxodisulfuric acid) by electrolyzing a sulfuric acid solution
Implementation Method 2
The persulfuric acid oxidizes and decomposes the resist into CO2 and H2O
Data Source
AI summary
A wear of an electrode is prevented as much as possible, thereby efficiently electrolyzing a sulfuric acid solution and the like. An electrolysis method includes: passing an electrolytic solution through an electrolysis cell including at least a pair of an anode and a cathode; and supplying the electrodes with an electric power, so as to electrolyze the electrolytic solution, wherein a viscosity of the electrolytic solution is set in a range in response to a current density upon the electric power supply to carry out the electrolysis. The viscosity of a sulfuric acid solution as the electrolytic solution is equal to or less than 10 cP when the current density is equal to or less than 50 A/dm2, the viscosity of the sulfuric acid solution is equal to or less than 8 cP when the current density is from more than 50 to 75 A/dm2, and the viscosity of the sulfuric acid solution is equal to or less than 6 cP when the current density is from more than 75 to 100 A/dm2. Particularly when a highly-concentrated sulfuric acid solution is electrolyzed at a high current density using diamond electrodes, the electrolysis process can be carried out highly efficiently while a wear of the electrode is reduced.