Analysis Report On The Application And Technological Innovation Of Heating Vests in Semiconductor Manufacturing Exhaust Treatment Systems

Analysis Report on the Application and Technological Innovation of Heating Vests in Semiconductor Manufacturing Exhaust Treatment Systems

1. Technical Requirements and Background
Process exhaust gases generated during semiconductor manufacturing pose a complex environmental pollution challenge. In key processes such as plasma dry etching and chemical vapor deposition, the exhaust gas mixture from the reaction chamber contains a variety of highly hazardous compounds. For example, in a typical etching process, raw gas streams such as Cl₂, CF₄, SF₆, and BCl₃ react to produce byproducts such as TiClₓ, AlClₓ, MoClₓ, MoFₓ, and SiO₂. These substances readily crystallize at room temperature. When they adhere to the inner wall of the exhaust pipe, they can not only cause pipe blockage but also potentially lead to corrosion and leakage, resulting in incomplete exhaust treatment and production interruptions. In actual semiconductor fab operations, exhaust gas treatment systems face two core challenges: first, crystallization blockage, particularly in the pumping line and pump exhaust pipes. Solid deposits gradually accumulate, reducing pipe diameters and increasing system backpressure.

 

2. equipment maintenance costs.

Traditional solutions require frequent downtime for pipe cleaning (short PM cycles), significantly reducing equipment utilization. Heated vest technology uses precise temperature control and heating to alter the working environment of the exhaust pipes, ensuring that compounds remain in a gaseous state as they are transported to the treatment terminal, fundamentally addressing the crystallization blockage problem. Compared to traditional chemical inhibitor injection or mechanical cleaning solutions, active heating technology offers advantages such as low maintenance costs, no chemical pollution, and simple system modifications. 2 Technical Principles and System Components of the Heated Vest

2.1 Technical Implementation Principle
The core technical principle of the heated vest system is based on physical state control and thermal energy balance management:

Phase change inhibition mechanism: By maintaining the pipe temperature above the freezing point of the exhaust gas components (typically 20-50°C higher), the transformation of gaseous substances into solid forms is prevented. For example, during the etching process, when the freezing point of MoF₆ is 89°C, the system maintains the temperature at 120°C to ensure it remains in a gaseous state throughout the process.

Viscosity Control Mechanism: Appropriately increasing the temperature can significantly reduce the viscosity of the gas mixture. For example, the viscosity of ClF₃ at 100°C is 40% lower than at room temperature, significantly reducing pipeline resistance losses.

Thermal Compensation Design: The system calculates heat loss from the pipe wall in real time and dynamically adjusts the heating power to ensure temperature uniformity within ±5°C across all sections of the pipe, preventing the formation of localized undercooling zones.

 

2.2 Core System Components
A complete heating system consists of three functional modules working together:

Heating Unit: A nickel-chromium alloy resistance wire is used as the core heating element, typically designed for 0.1-0.3W/cm². Excessively high designation indicates weak design capabilities and a "big push" approach to achieve the desired effect, converting electrical energy into heat through the Joule effect. Depending on the operating environment, heating element wrapping materials are categorized as follows:

Silicone rubber base material: Suitable for operating temperatures below 120°C, offering excellent flexibility and waterproof properties (preferred for the ETCH process). This solution is being phased out by the plant operations department.

Teflon-coated glass cloth: Heat-resistant up to 400°C, meeting the high-temperature requirements of PVD (150-180°C).

Quartz glass cloth: Suitable for use in extreme environments (700°C) and with corrosive gases.

Temperature control unit: Utilizes a dual closed-loop control system: The primary control is a PID temperature regulator with real-time feedback from a K-type thermocouple sensor; the secondary protection is a mechanical temperature limiter (normally closed bimetallic strip), which forcibly disconnects the circuit if the primary control fails. The system features an automatic alarm for abnormal temperatures (±15% of the set value) to prevent the risk of sustained overheating.

 

Thermal insulation unit: Constructed of three functional layers:

• Inner layer: Woven inner fabric
• Middle layer: Flame-retardant insulation cotton
• Outer layer: PTFE-coated fabric

 

Table: Performance comparison of different heated vest materials:

Material Type	Temperature resistance limit	Applicable process	flexibility	Corrosion resistance	Cost Index
Silicone rubber base	200℃	ETCH, CVD	★★★★★	★★★☆	★★★ ☆
Teflon glass cloth	400℃	PVD, EPI	★★★☆☆	★★★★★	★★☆
Quartz glass cloth	700℃	特殊腐蚀性气体	★☆☆☆☆	★★★★★	★★★★☆
Fiber cloth (PTFE)	260℃	DIFF	★★★★☆	★★★★☆	★★★☆

 

2.3 Differences from Traditional Specialty Gas Heating

Although specialty gas delivery systems (such as low-vapor-pressure gases like BCl₃ and WF₆) in the semiconductor front end also utilize heating technology, there are fundamental differences between this and exhaust gas heating:

 

Temperature Range Differences: Specialty gas heating is a low-temperature application (35-65°C) and only needs to prevent the gas from liquefying; exhaust gas treatment requires a high-temperature environment (80-180°C) to change the phase of the material.

Control Accuracy Requirements: Specialty gas systems require temperature control accuracy of ±1°C to prevent changes in gas properties; exhaust gas systems can tolerate fluctuations of ±15°C.

 

Safety Design Differences: Specialty gas heating requires explosion-proof certification (such as ATEX) and grounding monitoring; exhaust gas systems focus more on fire protection levels and abnormal power outage management.

 

3 Application Scenarios and Temperature Requirements Analysis
3.1 Core Application Scenarios

• The heated vest system plays an irreplaceable role in four key processes in semiconductor manufacturing:
• DIFF diffusion zone: Treatment of hydride exhaust gases such as phosphine (PH₃) and arsine (AsH₃) requires maintaining a temperature of 80-120°C to prevent the deposition of solid arsenic/phosphorus compounds.
• ETCH etching zone: Halides produced by metal etching (such as TiCl₄ and AlCl₃) are highly susceptible to moisture absorption and crystallization below 90°C, requiring a temperature of 120±10°C.
• CVD deposition zone: Silane (SiH₄) byproducts easily form powdered SiO₂, requiring pipelines to be maintained at 100-150°C.
• PVD sputtering zone: High-melting-point metal fluorides (MoF₆ and WF₆) require a high temperature environment (150-180°C), with particular attention paid to preventing blockage at bends.

 

3.2 Temperature Setting Basis
Temperature parameter settings are based on dual validation from scientific measurements and engineering practice:

Physical Property Data Benchmark: Exhaust gas composition is analyzed by gas chromatography-mass spectrometry, and the freezing point curves of various substances are determined. For example, the freezing point of TiCl₄ is shown to be -24°C, but the actual deposition temperature rises to 85°C due to the frequent formation of tetramers (TiCl₄).

 

Pipeline Structural Factors:

At elbows, the recommended upper temperature limit is increased by 10°C+.

In standard FABs, 90-degree elbows are strictly prohibited in PUMP-#CH.

• Safety Margin Design: The actual set temperature is 20-30°C higher than the measured freezing point to accommodate fluctuations in operating conditions.
• Material Tolerance Limits: Silicone rubber accelerates aging above 200°C and has therefore been eliminated by the factory management. Teflon allows for PVD at higher temperatures.

 

 

Table: Heating parameter configuration for typical semiconductor manufacturing processes

Process Department	Main components of exhaust gas	Crystallization critical point	Set temperature	Pipe diameter adaptation	Elbow compensation
PVD	MoF₆, TiF₄	110-130℃	150-180℃	4-6inch	+10℃/Elbow
ETCH	TiCl₄, AlCl₃	80-95℃	100-120℃	2-4inch	+5℃/Elbow
CVD	SiH₂Cl₂, NH₃	70-85℃	90-110℃	3-5inch	+8℃/Elbow
DIFF	AsH₃, PH₃	-	80-100℃	2-3inch	-

 

4 Key Issues and Technical Challenges

4.1 Scientific Basis for Temperature Setting
There are many questions within the industry regarding temperature settings, but there is rigorous scientific logic behind them:

The selection of 120°C is based on calculations of the equilibrium constant for halide hydrolysis. When the temperature exceeds 115°C, the reaction rate of TiCl₄ + 2H₂O → TiO₂ + 4HCl decreases to a negligible level, effectively preventing TiO₂ deposition and blockage. While 90°C is above the melting point of TiCl₄ (-24°C), it does not inhibit its hydrolysis.

PVD High-Temperature Requirements: Because MoF₆ sublimates at 138°C, the actual temperature must be maintained above 150°C to ensure molecular free path. Furthermore, the O-ring must be made of perfluoroelastomer (FFKM), which has a temperature resistance rating of over 300°C.

The 200°C solution is not recommended because overheating will accelerate the aging of silicone rubber (at 150°C, the lifespan reduction rate can reach up to 30% per year) and may trigger side reactions that produce hazardous substances such as ClF₃. Therefore, FFKM is generally used above 150°C.

 

4.2 Power Supply and Risk Management
The power configuration of the heating system must balance safety and cost:

UPS is not recommended: Based on crystallization kinetics research, halide deposition requires over 48 hours to reach a critical thickness (for example, the TiCl₄ deposition rate is 0.8 mm/h). In practice, a 72-hour emergency repair window is sufficient, so adding a UPS is not recommended.

Dual Power Supply: Not recommended.

Emergency Management Procedure: After a power outage, a nitrogen purge (GN2 purge) can be performed to remove residual reaction gases from the tube and slow the crystallization process. Not recommended.

 

4.3 Overtemperature Protection Mechanism
To address the risk of temperature runaway, the system has a three-layer protection mechanism:

Master Control Layer: The PLC scans the thermocouple feedback value every 0.5 seconds, and the PID algorithm dynamically adjusts the SSR. As far as we know, the only domestic manufacturers that independently design PLCs and PID controllers specifically for semiconductor heating systems are Moore Electromechanical and Xinhuilong. Xinhuilong's products haven't been updated in ten years, so whether they can adapt to rapidly evolving needs remains to be seen.

Hardware: Independent bimetallic temperature limiter (normally closed), forced power off at 230°C (50°C above the set point).

Monitoring: Temperature differential alarm module (triggered when ΔT > 15°C) and heating rate alarm (triggered when > 5°C/min).

To date, no sustained overheating incidents have been reported in semiconductor factories worldwide, thanks to the effectiveness of this protection system. 4.4 Exhaust System Optimization Design
The exhaust system behind the scrubber typically does not require heating, based on three considerations:

Economic Factor: Full heating of main pipe diameters (typically >24 inches) is costly (approximately $500/meter), resulting in a low return on investment.

Technical Necessity: After wet scrubbing, the gas moisture content is <100 ppm, significantly reducing the risk of crystallization.

Alternative: Using a large inclination angle design (>30°) and wall thickness monitoring (ultrasonic thickness gauge) for physical blockage prevention is more economical.

 

5 Industry Practices and Optimization Directions
5.1 Cost Control Strategies
Leading domestic wafer fabs have significantly reduced system costs through innovative designs:

Zone Temperature Strategy: A fab in Xiamen implemented three temperature control zones on a 160-meter ETCH pipeline: the reaction chamber interface (120°C), the middle section (100°C), and the scrubber front section (80°C). This reduced overall energy consumption by 35%. This practice has not been certified in the semiconductor industry, and whether it is just a rumor spread by the heating manufacturer remains to be confirmed.

Modular Design: A Singapore FAB utilizes a modular design, facilitating procurement and design, and shortening the construction cycle.

Insulation Optimization: The Hefei project is testing the use of nano-aerogel (thermal conductivity 0.02 W/m·K). It's reported that aerogel powder may remain on the pipes during PM removal and installation, but long-term testing is needed to confirm the PA (pa) issue. Currently, only GORE's GTI material globally can meet the various working conditions.

 

5.2 Material Iteration Trends
Next-generation material systems are being promoted:

Composite-reinforced silicone: Adding silicon carbide nanowires (for enhanced thermal conductivity) and aramid fibers (for tear resistance) extends the lifespan to 7 years. Domestically produced materials cannot solve the PA (pa) issue.

Smart Fabrics: Phase Change Thermostatic Material (PCM) under development can release latent heat during power outages, maintaining pipe temperature for >2 hours.

Self-healing Coating: Microencapsulated silicone automatically repairs surface cracks upon rupture at 200°C. Whether this rumor is true remains to be verified.

 

5.3 Maintenance Standard Upgrade
Based on the five-year lifespan requirement, the maintenance system is continuously evolving:

Daily Inspection: Use an infrared thermal imager to scan the temperature distribution weekly, and issue an alert if the temperature difference exceeds 15%.

Preventive Maintenance: Insulation testing (>20MΩ/1000VDC) and mechanical strength testing are performed every six months.

End of Life Determination: Replacement is required when three characteristics appear: elasticity loss >30%, surface crack depth >0.5mm, and cold resistance change >15%.

 

6 Technological Development and Future Outlook
6.1 Intelligent Upgrade
The next-generation heating system is moving towards intelligent IoT:

Digital Twin System: A leading manufacturer has built a three-dimensional model of the pipeline temperature field, simulating heat distribution in real time and automatically optimizing parameter settings. Currently, there is no actual evidence to prove the effectiveness of this solution. The author holds a PhD in semiconductor thermal simulation and is not known to have worked for any domestic manufacturer.

Predictive maintenance: Analyzing current fluctuations (±5%) predicts heating ribbon aging, providing up to 30 days of warning for faults.

Dynamic temperature control technology: Based on the MES system, process recipes are automatically matched to the optimal temperature profile (e.g., Al etching is set to 115°C, W etching is set to 125°C).

6.2 Breakthroughs in New Material Systems
Material innovation will continuously enhance system performance:

Graphene composite film: Laboratory-stage products achieve a thermal conductivity of 530 W/m·K, two orders of magnitude higher than traditional materials.

Variable emissivity coating: Intelligently adjusts thermal radiation efficiency (adjustable from ε = 0.1 to 0.9), improving environmental adaptability.

Ultra-flexible conductor: Stretchable up to 300% while maintaining conductivity, adapting to thermal expansion and contraction.

 

6.3 Modularity and Standardization
The industry is promoting unified design specifications:

Quick-connect interface standards: SEMI is developing a draft specification for quick-connect interfaces for heating jackets (SEMI-HJ210).

Performance grading certification: A related certification system is planned.

Environmentally friendly material requirements: The EU will restrict the use of PFAS materials starting in 2026, promoting the development of fluorine-free coatings.

 

 

Conclusion
Heated jackets, a key technology for semiconductor exhaust treatment, address the industry's persistent problem of process exhaust crystallization and blockage through precise temperature control. Current technology has developed two mature systems: silicone rubber (which has been phased out of factory operations) for medium and low temperatures and Teflon glass cloth for high temperatures. Combined with intelligent temperature control strategies, these systems effectively support the stable operation of core processes such as PVD, ETCH, and CVD. With the application of new materials and intelligent upgrades, the next five years will see comprehensive improvements in energy efficiency (expected to increase by 40%), lifespan (targeted to extend to 8 years), and maintenance costs (reduced by 30%). Manufacturers are advised to comprehensively consider process adaptability (temperature/tube diameter/bend angle), lifecycle costs, and intelligent compatibility when selecting a suitable system. Prioritize modular systems with SEMI certification to allow for future technology upgrades.