Semiconductor quartz crucibles hold molten silicon during Czochralski monocrystalline silicon growth. They require ultra-low trace metals (Al, Fe, Na, K, Ti, U, Th), low hydroxyl content, controlled bubble structure, high thermal stability, and minimal contamination release into molten silicon. The whole workflow includes ore selection, multi-stage purification, high-temperature chlorination, particle sizing, arc fusion molding, post-machining, cleaning and quality inspection.
1. Raw Ore Selection & Pre-Treatment
Select premium vein quartz ore with inherently low lattice impurities and low radioactive elements (U, Th). Reject ore with abundant fluid inclusions and heavy mineral intergrowths.
- Optical sorting: Remove stained rock and impurity-bearing mineral lumps.
- Calcination and water quenching: Heat quartz to 850–1000 °C then rapid quenching. Thermal shock creates microcracks, unlocking encapsulated impurities and improving later leaching efficiency.
- Zero-contamination crushing and sizing: Use quartz/ceramic-lined crushers to avoid iron contamination. Produce graded quartz sand with controlled particle size distribution for crucible raw material.
2. Multi-Stage Physical Purification
- Attrition scrubbing & desliming: Peel off surface iron oxide films and clay slimes; hydrocyclones separate fine impurity-rich slime.
- Multi-pass high-gradient magnetic separation: Remove weakly magnetic iron, titanium and chromium-bearing minerals.
- Reverse flotation: Selectively float feldspar, mica and aluminosilicates, which are major sources of Al and alkali metals.
- Repeated magnetic separation after flotation to catch newly liberated fine magnetic particles.
3. Deep Chemical Purification & Ultra-Pure Water Washing
- Mixed acid leaching (HCl + oxalic acid / diluted HF): Dissolve surface exposed metal oxides and soluble mineral inclusions. Use PTFE-lined reactors to prevent equipment contamination.
- Multi-stage countercurrent washing with ultra-pure DI water, until filtrate conductivity and metal ion residuals meet specs.
- Drying under clean, non-metallic equipment to avoid recontamination.
4. High-Temperature Chlorination (Core Purification Step)
This step differentiates semiconductor-grade quartz from ordinary high-purity silica.
- Heat purified quartz to 1000–1200 °C under chlorine or HCl gas atmosphere.
- Lattice-bound metal impurities react to form volatile metal chlorides, which are carried away by exhaust gas. This reduces Al, Fe, Ti and alkali metals to ppb levels and removes residual fluid inclusion contaminants.
- Strict corrosion protection and exhaust gas treatment are mandatory for safety.
5. Particle Grading & Layered Raw Material Preparation
Semiconductor crucibles adopt a two-layer structure:
- Inner layer: Ultra-high-purity chlorinated quartz sand, forming a transparent, low-bubble layer that contacts molten silicon directly.
- Outer layer: High-purity quartz sand with higher viscosity, forming a bubble-containing thermal insulation layer to improve mechanical strength and heat retention.
Accurate particle grading optimizes packing density and controls bubble formation during arc melting.
6. Arc Fusion Molding
Fill graded quartz sand into a rotating graphite mold. Apply arc heating above 2000 °C to melt quartz powder into fused silica glass.
- The centrifugal force distributes molten quartz along the mold wall.
- Control melting atmosphere and temperature gradient to form the dual-layer structure: transparent inner wall and insulated bubble outer layer.
- Slow cooling and annealing to release internal thermal stress and prevent microcracks.
7. Mechanical Machining & Surface Treatment
After demolding:
- CNC cutting, grinding and edge trimming to reach specified diameter, wall thickness and flatness.
- High-pressure pure water blasting to remove loose surface powder and carbon residues.
- Ultrasonic cleaning sequence with ultra-pure water and high-purity cleaning agents to eliminate surface particulate and metallic contaminants.
8. Final Inspection & Cleanroom Packaging
- Element analysis via ICP-MS for trace metals and radioactive U/Th testing.
- Visual and microscopic inspection for bubbles, cracks, inclusions and surface defects.
- Test hydroxyl content, thermal stability and devitrification resistance.
- Seal and package in cleanroom environment, nitrogen protection for long-term storage.
Critical Quality Control Points
- Contamination control: All contact surfaces must be quartz, PTFE or ceramic; graphite mold must be high-purity graphite to limit carbon pickup.
- Bubble control: Inner transparent layer must be nearly bubble-free; outer bubble layer is precisely tuned for thermal insulation.
- Low alkali metal: Na, K, Li must be strictly limited, as they diffuse into molten silicon and cause crystal defects.
- Devitrification resistance: Impurity enrichment will accelerate devitrification at high temperature, shortening crucible service life.
The complete production route: premium vein quartz selection → calcination-quenching and crushing → scrubbing, HGMS and reverse flotation → mixed acid leaching + ultra-pure water washing → high-temperature chlorination → particle grading → two-layer arc fusion melting → annealing, machining and ultrasonic cleaning → ppb-level quality testing and cleanroom packaging. Chlorination and dual-layer arc melting are the core technologies to produce qualified semiconductor monocrystalline quartz crucibles.
