KOH Etching Concentration Measurement Correction

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Solution Overview

Problem

Current methods for measuring active KOH concentration in KOH etching processes are impractical due to high costs and inaccuracy, especially when multiple batches are processed without solution replacement, as they fail to accurately account for the cumulative errors introduced by reaction products.

Innovation Solution

The method involves using a refractometer to measure the total KOH concentration and correcting the result with estimated K2H2SiO4 concentration, leveraging the distinct refractive index behavior of KOH and K2H2SiO4 to achieve accurate in-line measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If refractive index measurement is used to measure KOH concentration, then initial concentration can be measured with sufficient accuracy, but reaction products introduce error into the measurement

Engineering Contradiction:

ImproveKOH concentration measurement accuracyVSAvoidmeasurement accuracy with reaction products

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The measurement process is segmented into two distinct steps: first measuring the total concentration using refractive index, then separately estimating the silicon complex concentration based on process parameters. This segmentation allows each measurement to target specific components, improving overall accuracy by addressing the interference problem systematically.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system implements feedback by using the measured total concentration and estimated silicon complex concentration to calculate the active KOH concentration. This feedback loop continuously monitors and adjusts the concentration measurement, compensating for errors introduced by reaction products and maintaining measurement reliability throughout the etching process.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If indirect measurement by measuring silicon concentration and subtracting from total concentration is used, then active KOH concentration can be determined, but two independent measurements are required

Engineering Contradiction:

Improveactive KOH concentration determinationVSAvoidnumber of measurement systems

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The refractometer is designed to serve multiple functions: it measures both the total concentration of the etching solution and, through correlation with process parameters, the silicon complex concentration. This multi-functionality eliminates the need for separate measurement systems, reducing device complexity while maintaining measurement precision.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses process parameters (etching time, temperature, initial concentration) as intermediaries to estimate silicon complex concentration without direct measurement. This intermediary approach allows the single refractometer to provide information that would otherwise require multiple independent measurement systems, simplifying the overall measurement device.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Quantity of substance

If KOH solution is reused for multiple batches, then cost is reduced, but cumulative error from reaction products makes measurement unacceptable

Engineering Contradiction:

ImproveKOH solution reuseVSAvoidconcentration measurement accuracy

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The system performs preliminary estimation of silicon complex concentration based on process parameters before the actual concentration measurement. This preliminary action allows the system to compensate for cumulative errors from reaction products in advance, maintaining measurement precision even when KOH solution is reused for multiple batches.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The measurement approach changes parameters from directly measuring only KOH concentration to measuring total concentration and estimating silicon complex concentration separately. This parameter change enables the system to account for cumulative reaction products, allowing KOH solution reuse without sacrificing measurement accuracy.

Inventive Principle:

Principle #35Parameter changes

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 provides a simple, reliable, and accurate method for measuring active KOH concentration, reducing costs and maintaining precision across multiple batches by minimizing the impact of cumulative errors, while ensuring the measurement system is cost-effective and requires minimal maintenance.

Implementation Method 1

refractive index measurement, capable of measuring the initial concentration of KOH in water with sufficient accuracy

Methodology Applied

Scientific EffectRefractive index measurement: Refraction

Data Source

PatentUS8628678B2Method for measuring the active KOH concentration in a KOH etching process

Publication Date: 2014.01.14 JANESKO

AI summary

The invention relates to a method for in-line measuring the active KOH concentration in a KOH etching process in which process silicon hydroxide is produced by a reduction reaction according to the formula: 2K+ (aq.)+2OH− (aq.)+2H2O+Si→2K+ (aq.)+H2SiO42− (aq.)+2H2 (g). The total concentration of KOH bath is measured by using a refractometer and the measurement result is corrected by the estimated K2H2SiO4 concentration.