Technical Analysis and Solutions for Carrier Lifetime Reduction Caused by Quartz Tubes (Part 1 of 10)

Case Background

The customer is a top-level committee in Turkey. They purchased customized quartz tubes from another supplier. After using the new quartz tubes in their experimental process and completing subsequent measurements, they observed a decrease in the carrier lifetime value of their products. The customer sincerely requested us to provide technical advice and the measures that should be taken.

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Reply

Thank you for contacting us regarding the issue of carrier lifetime reduction after using new quartz tubes. We fully understand the critical impact of this parameter on the performance of your products, and we have conducted a detailed analysis of the problem. Below, we present our technical insights, potential cause analysis, and targeted solutions.

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I. Application Scenario Assumptions

Based on your mention of carrier lifetime measurement and quartz tube usage, we speculate that your process may involve:

• High-temperature semiconductor manufacturing (such as diffusion, annealing, or epitaxial growth of Si/SiC devices)
• Photovoltaic cell production (such as PERC/TOPCon solar cell passivation or sintering processes)
• Advanced materials research (such as GaN and other wide-bandgap semiconductors)

To provide more accurate recommendations, please confirm the following information:

• Process temperature range and gas environment (e.g., O₂, N₂, H₂)
• Type of samples being processed (e.g., silicon wafers, epitaxial layers, etc.)

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II. Analysis of Causes for Carrier Lifetime Reduction

After analysis, the problem may stem from the interaction between the quartz tube, flange components, and process conditions.

1. Impact of the Quartz Tube

(1) Material Purity and Impurities

• Metal impurities (Fe, Cu, Na, etc.):
  Metallic ions in quartz tubes may diffuse into silicon wafers or epitaxial layers at high temperatures, becoming carrier recombination centers and significantly reducing lifetime.
  Key indicator: Metal impurity content should be controlled (e.g., ≤1 ppm; ultra-high-purity quartz tubes require ≤0.1 ppm).
• Hydroxyl (OH⁻) content:
  Hydroxyl groups can absorb energy in the ultraviolet range, potentially affecting photo-generated carrier generation, especially in photovoltaic or UV sensor applications.
  Recommendation: Choose low-hydroxyl quartz tubes (e.g., synthetic quartz, OH⁻ < 5 ppm).

(2) Structural Defects and Thermal Stability

• Microcracks or devitrification:
  At high temperatures, quartz tubes may devitrify (e.g., forming cristobalite) or develop thermal stress cracks, releasing particles that contaminate the process environment.
  Relation to carrier lifetime: Particles attaching to the wafer surface increase interface recombination rate.

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2. Impact of the Flange and Sealing Components

(1) Material Compatibility

• Metal flange contamination:
  Stainless steel or nickel-based flanges may release metallic vapors (e.g., Cr, Ni) at high temperatures, which can be transferred via gas phase to contaminate the quartz tube inner wall or the sample.
  Example: In SiC epitaxial growth, metal contamination can increase interface state density and reduce carrier lifetime.
  Alternative: Use ceramic flanges (e.g., Al₂O₃) or metal flanges with a platinum coating.

(2) Sealing Performance

• Leaks causing oxidation/contamination:
  Poor sealing between the flange and quartz tube can introduce oxygen or moisture, which at high temperature reacts with silicon to form a defective SiO₂ layer, increasing surface recombination.
  Detection method: Use a helium mass spectrometer leak detector to verify sealing (leak rate < 1×10⁻⁹ mbar·L/s).

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3. System-Level Interactions

(1) Quartz Tube–Flange Interface

• Coefficient of thermal expansion (CTE) mismatch:
  Quartz (CTE ~0.55×10⁻⁶/°C) and metal flanges (e.g., stainless steel, CTE ~16×10⁻⁶/°C) may undergo stress deformation at high temperatures, potentially causing micro-leaks or particle shedding.
  Design improvement: Use a gradient sealing structure (e.g., graphite gasket transition) or elastic sealing materials (e.g., Viton, heat-resistant <200°C).

(2) Gas Flow Disturbances

• Turbulence caused by flange structure:
  Improper flange inner diameter or sharp edges can disrupt process gas flow, creating local temperature non-uniformity in the quartz tube and affecting doping uniformity, which indirectly impacts carrier lifetime.

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III. Recommended Solutions

Основна причина	Improvement Measures
Quartz tube metal contamination	Switch to ultra-high-purity synthetic quartz tubes (metal impurities <0.1 ppm).
Metal vapor from flange	Replace with ceramic flanges or platinum-coated metal flanges.
Sealing leaks	Use double O-rings + helium leak test, or adopt metal seals (e.g., copper gaskets for UHV).
Thermal stress devitrification	Select high-purity quartz tubes or Ti-doped quartz tubes, and control heating/cooling rates (≤5°C/min).

Summary:
The reduction in carrier lifetime may be the combined result of quartz tube impurities, flange contamination, and system design defects. Optimization must be coordinated in three areas—material purity, sealing reliability, and thermal matching—to fundamentally solve the problem. We recommend that the customer provide more detailed process data (such as temperature profiles and gas types) to enable precise component recommendations.

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IV. Customer Diagnostic Suggestions

• Quartz tube batch testing:
  Require suppliers to provide ICP-MS (metal impurities) and FTIR (hydroxyl content) reports.
• Flange and seal inspection:
  Confirm flange material, sealing ring temperature resistance, and check for high-temperature discoloration (signs of metal vapor).
• Process parameter review:
  • Temperature control program: Limit heating/cooling rates to ≤5°C/min.
  • Pre-treatment plan: Pre-bake or acid clean quartz tubes before experiments to remove surface contaminants.
  • Process control: Compare whether the reduction in carrier lifetime coincides with changes in quartz tube/flange batches or process temperature adjustments.

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V. Warranty Policy

We provide the following assurance:
Due to the fragile nature of quartz products and the complexity of application environments, we do not offer formal quality guarantee clauses. However, we commit to actively assisting in root cause analysis when issues arise. If the customer finds any abnormal situation, we can assist in judgment and conduct internal evaluation based on specific information. We may request the following for analysis:

• Photos or videos of the problem area
• Brief description of process conditions during use (e.g., temperature, atmosphere)
• Other descriptions helpful for diagnosis

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VI. Additional Warranty Measures for This Case

• Pressure leak test before shipment: Connect the quartz tube to a flange (we can also provide flanges), pressurize to the rated value (or customer-specified value), and hold pressure for over 2 hours to ensure no leakage (we can share the test process).
• Thermal resistance test before shipment: After production, each quartz tube will undergo a 24-hour annealing process at 1000±50°C to ensure thermal resistance (continuous service temperature 1000°C, short-term up to 1200°C).
• Customization service: Customize quartz tube/flange specifications according to the reaction chamber structure.
• Technical service: If temperature curves and gas ratios are provided, we can precisely match the experimental plan.

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We look forward to working with you to resolve this issue. Please let us know a convenient time for further communication.

Sincerely,
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