Flow monitoring in semiconductor production: why precision and safety are inseparable
A silicon wafer leaving the production facility has gone through hundreds of process steps. At every step, precise quantities of ultra-pure chemicals, gases and slurries are involved. A single deviating flow can ruin an entire batch. And a defective line without protection can do so without anyone noticing.
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The technical challenge: flow as a critical process parameter
In the semiconductor industry, flow is not a side issue but a critical process parameter that directly determines the quality of the end product. Modern chips consist of structures of just a few nanometres, smaller than the wavelength of visible light. At that scale, the quantity and uniformity of a chemical medium on the wafer surface helps determine whether a transistor works or not.
Flow management in a wafer fab involves two fundamentally different challenges. The first is precision: delivering the right amount of the right medium at the right time, repeatably over thousands of runs and over a production period of months. The second is safety: preventing a line break, a leak or an unexpected peak flow from damaging equipment, product or personnel.
Both challenges place demands on component selection that go far beyond what is common in most other industries. Ultra-high purity of materials, resistance to corrosive chemicals, minimal contamination of the process medium and reliability over years of service without maintenance are not wishes but hard requirements.
What is at stake?
A modern wafer fab processes substrates worth hundreds of euros each, in batches of dozens of wafers at a time. Failure due to process deviations costs not only the material itself but also machine capacity, chemicals and cycle time. At advanced nodes, the scrap value of a single failed batch can run into tens of thousands of euros.
The process steps and their flow risks
A wafer passes through roughly four categories of process steps in which flow management is crucial. Each has its own risk profile.
Wet cleaning and etching
High risk
Ultra-pure acids such as HF, H₂SO₄ and H₂O₂ are mixed in precise ratios and passed over the wafer surface. Too high a flow increases the etch depth and the risk of undercutting structures. Too low a flow results in incomplete cleaning. In the event of a line break, corrosive liquids are released into the process area.
Dry etching and deposition (CVD, PVD, ALD)
High risk
Process gases such as Cl₂, HBr, SiH₄ and NH₃ are fed into the process chamber at precisely controlled flow rates. Deviations in gas flow directly affect layer thicknesses, etch profiles and uniformity across the wafer surface. Many of these gases are also toxic or flammable.
CMP (chemical mechanical polishing)
Medium risk
A slurry of abrasive particles in a chemical solution is applied to the wafer surface. The flow rate of the slurry determines the polishing rate and the layer thickness that is removed. Blockage or pulsating flow leads to non-uniform polishing and wafer defects.
Ultra-pure water (UPW) distribution
Medium risk
A slurry of abrasive particles in a chemical solution is applied to the wafer surface. The flow rate of the slurry determines the polishing rate and the layer thickness that is removed. Blockage or pulsating flow leads to non-uniform polishing and wafer defects.
The two levels of flow management
Flow management in semiconductor production works on two levels that complement but do not replace each other.
Level 1: flow measurement and monitoring
Flow measurement measures the flow of a medium and returns it as a signal to the process system. Flow monitoring adds a supervisory function: the flow monitor gives an alarm or switching signal as soon as the measured flow falls outside a set window. This is the active monitoring of the process window. Too little flow can indicate a blockage. Too much flow can indicate a leaking connection, a defective valve or an unintended opening elsewhere in the system.
Unlike a mass flow controller, which actively controls and corrects, a flow monitor is a guard that alerts the operator or the system. In a well-designed wafer fab, a flow monitor sits downstream of the controller, as independent monitoring that also checks the controller itself.
Level 2: excess flow protection
An excess flow valve (EFV) works on a fundamentally different principle from a flow monitor. Where a monitor measures and signals, the EFV intervenes mechanically. As soon as the flow exceeds a set threshold, the valve closes automatically and blocks the flow.
How an excess flow valve works
Normal operation
The medium flows through the valve. A magnetic piston or spring is held in place by the pressure differential created by the flowing liquid or gas. The valve remains open.
Line break or peak flow
With a sudden increase in flow, the pressure differential across the valve changes. The piston or springless element moves and closes the port. The flow stops almost immediately. After pressure equalisation, the valve can be reset manually or automatically.
An EFV does not protect against gradual leaks or small deviations; the flow monitor is the right tool for that. The EFV protects against sudden, major events: a completely broken line, a fitting coming loose or a valve being opened at the end of a line. In an environment with corrosive or hazardous media, this is the last line of defence.
Why both flow monitoring and an EFV are needed
A flow monitor without an EFV gives an alarm in the event of a line break but does not stop the flow automatically. An EFV without flow monitoring only responds to major events and misses gradual deviations that undermine product quality. A well-protected system uses both layers: monitoring for process integrity, a safety valve for emergencies.
ChemTec solutions for flow monitoring and protection
Since 1968, ChemTec has developed a range of flow monitors, flow meters and excess flow valves specifically for applications requiring low flows, high purity and reliability over a long service life. The range is available via Inacom for the Dutch market.
Adjustable flow monitors and flow switches
The adjustable series (including the FAV, LCA and CCM) monitor the flow of gases and liquids and provide a switching output in the event of a deviation. The setpoint can be adjusted without tools, making them suitable for use in multiple process windows. Available in versions made of inert materials for aggressive media. The CCM series is specially designed for use with gas analysis systems and corrosive gases, with minimal pressure drop across the sensor.
Non-adjustable flow monitors for ultra-high purity
The LPH UHP series has been developed for ultra-pure applications in the semiconductor industry. No metals in contact with the process medium, fully inert design. The switching threshold is factory-set to the desired flow value. Ideal for in-line monitoring of UPW systems and ultra-pure chemical distribution where contamination is absolutely unacceptable.
Excess flow valves (EFV) for emergency shut-off
The EFV series closes automatically in the event of a peak flow indicating a line break or rupture. Available as an adjustable model for customised activation thresholds and as the HPEFV version for high-pressure gas applications up to 6,000 psig, including hydrogen. The magnetic piston principle ensures an almost instantaneous response without external energy or a control signal. After activation, the valve is reset by pressure equalisation.
| Process step | Medium | Primary need | ChemTec solution |
| Wet cleaning | HF, H₂SO₄, H₂O₂ | Flow monitoring + emergency shut-off in the event of a leak | Flow monitor + EFV |
| CVD / ALD gas supply | SiH₄, NH₃, Cl₂ | Process window monitoring + safety shut-off | Flow monitor + EFV |
| CMP slurry supply | Abrasive slurry | Monitoring of continuity and flow rate | Flow monitor + flow meter |
| UPW distribution | Ultra-pure water | Leak detection, cooling water monitoring | LPH UHP monitor |
| Chemical distribution | Various acids and solvents | Protection in the event of a line break | EFV |
| Process equipment cooling | Cooling water, DI water | Alarm in the event of low cooling flow | Flow monitor |
Custom solutions for specific applications
ChemTec has no minimum order for custom products. Specific connections, non-standard materials, customised activation thresholds or compact OEM formats are developed on request. ChemTec designs, manufactures and tests all products in-house, which enables short lead times for custom work. Contact Inacom for application advice and a quotation.
