Control wet etching chemistry with a traceable measurement plan
Etching performance is sensitive to solution composition, temperature, loading and contamination. Online ultrasonic concentration measurement can provide frequent trend information for an identified chemical system, but it must be configured for the actual formulation and operating range. The project should connect the analyser signal to a sampling method, control rule and change-management process.
Measurement matched to chemistry
Rhosonics describes chemical concentration measurement using speed of sound and temperature, with conductivity available for multi-component duties. The selected model must represent the etchant mixture and the variables that change during production.
Compatibility is a design input
HF and other aggressive etchants require a formal wetted-material review. The analyser, seals, pipework, valves, sample system and cleaning method must all be assessed against the real process conditions.
See the measurement in its process context
Application planning includes the surrounding process, safe access, representative sampling and verification—not only the analyser itself. PMA reviews these conditions together before recommending a measurement arrangement.
Define the etching duty before choosing hardware
A clear measurement definition reduces ambiguous data and unsafe assumptions.
Etchant and range
Document every principal component, normal and excursion ranges, temperature, replenishment chemicals and expected by-products. State whether the process is batch, recirculating or once-through.
Reference method
Identify the laboratory or at-line method used as the reference, its sampling frequency and uncertainty, and how samples will be matched in time to the online reading.
Signal purpose
Decide whether the signal is for trending, alarm, replenishment support or closed-loop control. Higher-consequence actions require stronger validation and independent safeguards.
Wet etching concentration measurement pathway
- Describe the process. Map the bath, recirculation, dosing and drain paths.
- Define the measurands. Confirm the chemical components and reporting units.
- Screen compatibility. Review wetted materials, pressure, temperature and cleaning exposure.
- Select a representative location. Avoid gas pockets, stagnant legs and unrepresentative dilution points.
- Validate with paired samples. Cover fresh bath, normal loading and planned replenishment states.
- Set governance. Document alarms, permissions, verification and calibration review.
Evidence to collect
Retain the online value, temperature, conductivity where used, bath age, wafer or substrate loading, additions and paired laboratory result. Investigate deviations before changing the calibration. Trend evidence is more useful when operational events are time-aligned.
Limits, compatibility and safety
An ultrasonic model does not identify every contaminant or reaction product. Cross-sensitivity can occur when more than one constituent changes. Chemical safety systems, ventilation, segregation, containment, emergency response and approved operating procedures remain independent of the analyser.
Frequently asked questions
Can ultrasonic measurement work with wet etchants?
It can be applied to defined chemical concentration duties, including chemicals used in semiconductor production, provided the formulation, range, temperature and materials are suitable and validated.
Can it distinguish several changing chemicals?
A one-component model cannot independently resolve several unknown changes. A multi-parameter analyser may resolve a defined two-component system, but the calibration basis must be confirmed.
How is the analyser checked?
Use representative paired samples analysed by the approved reference method. Review agreement across the operating range rather than relying on one commissioning point.
Can the signal directly control replenishment?
Only after the measurement and control response have been validated for that duty. Independent interlocks and process-safety controls should not be removed.
Sources and engineering review scope
PMA will review the etchant formulation, target variables, material compatibility, operating range, reference method and proposed control action. This page is application guidance, not a substitute for a site survey, chemical compatibility review, risk assessment or manufacturer-approved configuration.
Related analyser range
The 8500 Series supports defined one-component concentration duties; ask PMA whether a multi-component analyser is needed.
View the relevant analyser range.
Review your wet etching measurement point
Provide the chemical system, operating range, materials specification, temperature and current sampling method so PMA can assess the duty.