Materialien
Sapphire (Single-Crystal Al₂O₃)
Single-crystal aluminium oxide combining extreme hardness, chemical inertness, broadband optical transparency, and high-temperature stability — ideal for semiconductor viewports, windows, and wear components.
What Is Sapphire?
Sapphire is the single-crystal form of aluminium oxide (Al₂O₃), also known as corundum. Unlike polycrystalline alumina ceramics, single-crystal sapphire exhibits isotropic (or near-isotropic) optical properties, exceptional surface smoothness after polishing, and far superior chemical resistance.
Its combination of properties makes it the material of choice for:
- Optical windows requiring transmission from deep UV (0.14 μm) through mid-infrared (6 μm)
- High-temperature viewports in semiconductor process chambers
- Plasma-facing components where chemical attack resistance is critical
- Wear-resistant components where hardness approaches diamond (9 Mohs)
Key Material Properties
| Property | Value | Notes |
|---|---|---|
| Crystal Structure | Hexagonal (R3̄c) | Single crystal, Czochralski grown |
| Density | 3.98 g/cm³ | — |
| Hardness | 9 Mohs / ~2000 HV | Second only to diamond |
| Young’s Modulus | 335–400 GPa | Anisotropic; axis-dependent |
| Flexural Strength | 400–690 MPa | — |
| Max Use Temperature (air) | 1900°C | No phase transformation |
| Melting Point | 2053°C | — |
| Thermal Conductivity | 23–46 W/(m·K) | Axis-dependent |
| Thermal Expansion Coefficient | 5.0 (a-axis) / 5.6 (c-axis) × 10⁻⁶/°C | — |
| Refractive Index (589 nm) | nₒ = 1.768, nₑ = 1.760 | Birefringent |
| Optical Transmission Range | 0.14 – 6.0 μm | UV-VIS-NIR-MIR |
| Dielectric Constant | 9.3–11.5 | Frequency and axis dependent |
| Chemical Purity | > 99.99% Al₂O₃ | Czochralski-grown boule |
Optical Transmission
Sapphire transmits broadly across the ultraviolet, visible, near-infrared, and mid-infrared spectrum:
| Wavelength | Transmittance (2 mm) |
|---|---|
| 193 nm (ArF laser) | ~50% (surface loss limited) |
| 248 nm (KrF laser) | ~80% |
| 355–1064 nm (Nd:YAG) | > 85% |
| 2.9 μm (CO laser) | > 75% |
| 5.5 μm | > 50% |
This broad transmission window makes sapphire ideal for multi-wavelength process monitoring, pyrometry windows, and UV-process viewports.
Chemical Resistance
Sapphire is resistant to virtually all chemicals at room and elevated temperatures:
| Chemical | Resistance |
|---|---|
| HF (dilute) | Resistant at room temperature |
| HF (concentrated, hot) | Some attack above 80°C |
| H₂SO₄, HNO₃, HCl | Excellent resistance |
| NaOH, KOH (dilute) | Good resistance |
| NaOH, KOH (hot, concentrated) | Slight attack at prolonged exposure |
| Plasma (Cl₂, CF₄, O₂) | Excellent resistance |
| Water, steam | Excellent, up to 1000°C |
Crystal Orientation Options
We supply and machine sapphire in standard and custom crystal orientations:
| Orientation | Description | Common Applications |
|---|---|---|
| C-plane (0001) | Basal plane; zero birefringence in z-direction | LED substrates, general windows |
| A-plane (11-20) | — | Special optics, substrates |
| R-plane (10-12) | — | Heteroepitaxy substrates |
| M-plane (10-10) | — | Specialized semiconductor |
| Random / Custom | Off-axis cuts available | Customer-specified |
Machining Capabilities on Sapphire
Sapphire’s extreme hardness (9 Mohs) requires diamond tooling throughout. Tuguan Semiconductor’s machining capabilities include:
| Process | Achievable Specification |
|---|---|
| Core drilling (cylindrical blanks) | Diameter ±0.05 mm |
| Slicing (diamond wire) | Thickness ±0.02 mm, min 0.3 mm |
| Lapping | Flatness < 5 μm, parallelism < 5 μm |
| Optical polishing | Ra < 0.1 nm (Å-level), surface form λ/10 |
| Grinding (OD/ID) | Tolerance ±0.02 mm |
| Chamfering & edge grinding | As specified |
Typical Products
- Viewport windows — flanged or unmounted, for process chamber monitoring
- Optical flats & windows — UV-to-MIR transparent, single and double-side polished
- Laser windows — anti-reflection coated or bare, for 193/248/355/1064 nm
- Wear plates & bearing inserts — exploiting extreme hardness
- Custom shapes — discs, rectangles, prisms, rods — drawing-based fabrication
Quality & Documentation
- XRD crystal orientation verification (±0.5° standard)
- Surface roughness measurement (AFM or profilometer)
- Dimensional inspection report (CMM)
- Optical transmission test report available for optical-grade components