Fused Silica Glass
Help you choose the right material for your semiconductor process, from ppb-grade purity synthetic fused silica to single crystal sapphire
What Is Fused Silica Glass?
Fused silica glass-also known as fused silica-is the amorphous (non-crystalline) form of silicon dioxide (SiO₂), made by melting high-purity quartz crystals or synthetic silicon compounds at high temperatures in excess of 1700°C. Unlike borosilicate glass, fused silica contains almost no metal oxides and has a unique combination of properties:
Extremely high thermal stability-softening point above 1683°C
Very low thermal expansion-the coefficient of thermal expansion is only 0.55 × 10 +/°C, which is about 1/15 of that of stainless steel
Excellent UV transmission -150 nm to 3500 nm
Excellent chemical stability-resistance to attack by almost all acids except hydrofluoric acid and hot phosphoric acid
Ultra-Low Metal Contamination-Critical for Preventing Wafer Contamination in Semiconductor Processes
Available Material Grade
Picture Crown Semiconductor stocks and processes three main fused silica grades, each for different purity and performance requirements:
Grade I-Natural Fused Quartz
| Performance Index | Value |
|---|---|
| SiO₂ Purity | ≥ 99.99% |
| OH content | < 30 ppm |
| Total Metal Impurities | < 20 ppm |
| maximum use temperature | 1150°C continuous/1400°C short term |
| coefficient of thermal expansion | 0.55 × 10 over/°C |
| softening point | 1683°C |
| annealing point | 1120°C |
| Efraction (589 nm) | 1.4585 |
| density | 2.20 g/cm³ |
applicable scenarios:standard diffusion tube, furnace tube lining, 1150°C below the process boat. Equivalent to Momentive GE-124 / Heraeus F300 / Tosoh ES grades.
Grade II-Synthetic Fused Silica (High Purity)
| Performance Index | Value |
|---|---|
| SiO₂ Purity | ≥ 99.9999% |
| OH content | 800-1200 ppm (standard wet)/ < 1 ppm (dry) |
| Total Metal Impurities | < 50 ppb |
| maximum use temperature | 1200°C continuous |
| heat | ultra-low trace metal contamination |
Applicable Scenarios:CVD chambers, wet-etched parts, wash tanks, and any application with zero tolerance for trace metals at ppb levels. Equivalent to Momentive HPFS 7980 / Heraeus Suprasil grades.
Grade III-Opaque (Opal) Fused Quartz
| Performance Index | Value |
|---|---|
| SiO₂ Purity | ≥ 99.9% |
| Appearance | Translucent/Creamy |
| infrared reflectivity | > 90% |
| maximum use temperature | 1100°C |
Applicable ScenariosApplicable Scenarios:heat shields, crystal boat supports, and insulation parts that require high infrared reflectivity rather than optical transparency.
Physical And Optical Properties
| Performance Index | Value | Test Standard |
|---|---|---|
| density | 2.20 g/cm³ | ISO 61183 |
| Vickers hardness | ~600 HV | ISO 6507 |
| modulus of elasticity | 73 GPa | - |
| Poisson's ratio | 0.17 | - |
| thermal conductivity | 1.38 W/(m·K)(20°C) | - |
| dielectric constant | 3.75(1 MHz) | - |
| ultraviolet transmittance | (200 nm) | - |
| birefringence | < 5 nm/cm (after annealing) | - |
Choose Fused Silica For Semiconductor Manufacturing?
Semiconductor wafer manufacturing puts stringent requirements on process components:
Thermal cycle resistance-the diffusion furnace is repeatedly raised from room temperature to 1000-1200°C; the ultra-low thermal expansion coefficient of quartz prevents thermal shock cracking.
Metal Purity-Even ppb-level contamination of the process tube material can introduce complex traps in the silicon, resulting in reduced device lifetime. Natural fused silica reaches <20 ppm total metal; synthetic silica reaches <50 ppb.
Chemically inert-Process gases (O₂, N₂, Cl₂, HCl) and cleaning chemicals (HF, H₂ SO₂, HCl) do not react with SiO under normal process conditions.
Dimensional stability-At 1000°C, the dimensional stability of quartz is much better than that of metal or polymer materials.
Processing Capability Of Fused Silica
Semiconductor applies the following processes to fused silica bar and tube stock:
| Process | Up To Specification |
|---|---|
| CNC External/Internal Grinding | tolerance ± 0.01mm |
| Surface Grinding and Lapping | flatness <0.002mm |
| precision cutting (diamond wire cutting) | thickness ± 0.02mm |
| CNC Drilling | aperture ± 0.01mm, position ± 0.02mm |
| optical polishing | Ra < 0.05 μm, surface accuracy & lambda;/4 |
| fusion welding | helium leakage rate <1 × 10 to mbar · L/s |
| Flame Elbow/Flaring | wall thickness uniformity ± 10% |
| annealing treatment | birefringence <5 nm |
Fused Silica Typical Processed Products
Diffusion pipe and furnace pipe lining-straight pipe, flange pipe or bell pipe
wafer boat-horizontal and vertical, compatible with 4-inch to 12-inch wafers
focus ring and etch ring-tight tolerance plasma decent parts
bell jar and dome-CVD and epitaxial reaction chamber enclosure
viewing windows and windows-optically polished flat or curved surfaces
cleaning tank-compatible with HF/SC-1/SC-2 wet cleaning tank body
gas injector and showerhead-precision porous gas distribution device
Certification and Documentation
Each batch of fused silica parts comes:
material certificate (including XRF/ICP-OES purity data)
Dimensional Inspection Report (Traceable to Calibrated CMM)
Surface Condition Report (Roughness Cleanliness)
ISO 9001, RoHS, REACH declarations of conformity are available on demand.
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