Sapphire Substrate
Single-crystal sapphire (Al₂O₃) substrates are the cornerstone for GaN-based LEDs, RF filters, MEMS and next-generation optoelectronics. This page gives you a deep technical overview of sapphire substrates — orientations, surface specs, patterning, suppliers, and pricing — plus case examples from actual production environments.
- Material: α-Al₂O₃, hexagonal crystal, Mohs hardness 9
- Orientations: c-plane (0001), a-plane (11-20), m-plane (10-10), r-plane (1-102)
- Diameters: 2″, 3″, 4″, 6″, 8″ wafer-scale single-crystal monolayers
- Surface finishes: As-sliced, lapped, single-side or double-side polished, epi-ready
Optional processes: Patterned sapphire substrate (PSS), annealing sapphire substrate to reduce dislocations, AFM characterization of sapphire (0001) for RMS <0.2 nm
Crystal Growth & Orientation
Sapphire substrates are grown by Kyropoulos, Czochralski or Heat-Exchanger Method (HEM). Each growth method affects dislocation density, bow/warp, and crystal uniformity.
c-plane sapphire substrate (0001) is the dominant orientation for GaN epitaxy because its lattice mismatch is manageable and its symmetry supports uniform film growth.
a-plane sapphire substrate (11-20) eliminates polarization effects in certain optoelectronic devices.
m-plane and r-plane are used for specialized optical applications where birefringence or polarization needs to be controlled.
Properties of Al₂O₃ Sapphire Substrate
| Property | Typical Value |
|---|---|
| Lattice constant (a) | 4.758 Å |
| Lattice constant (c) | 12.991 Å |
| Thermal conductivity | 35 W/m·K at 25 °C |
| Dielectric constant | 9.3 |
| Transmission range | 200 nm–5 µm |
| Mohs hardness | 9 |
These properties make sapphire an ideal substrate for high-temperature and high-frequency devices where silicon cannot perform.
We also provide customized sapphire substrate services tailored to your specific requirements — please contact us for full technical support and pricing information.
Faqs:
1. What is a sapphire substrate?
A sapphire substrate is a thin, flat piece of sapphire (a crystalline form of aluminum oxide, \(\text{Al}_2\text{O}_3\)) used as a base or platform in various technological applications, especially in the semiconductor and optoelectronics industries. It provides a stable, high-quality surface for growing other semiconductor materials or for fabricating devices like LEDs, laser diodes, and power electronics components.
2. What material is sapphire made of?
Sapphire is made of aluminum oxide Al2O3. It is a single crystal form of aluminum oxide, renowned for its exceptional hardness, thermal stability, and optical properties.
3. Is sapphire Al2O3?
Yes, sapphire is indeed aluminum oxide Al2O3. It is the crystalline form of Al2O3, which gives it its unique physical and chemical characteristics.
4. What substance gives sapphire its color?
The color of sapphire is primarily caused by trace impurities. For example, blue sapphires get their color from small amounts of titanium and iron impurities. Other colors, such as yellow (due to iron), pink or orange (due to chromium), and green (due to a combination of iron and titanium), are also the result of different trace elements present in the crystal structure.
5. Sapphire substrate uses
6. Is sapphire substrate polar or non - polar?
Sapphire is a non – polar crystal. However, different planes of sapphire (such as c – plane, a – plane, r – plane, m – plane) have distinct characteristics. For instance, the c – axis of GaN grown on c – plane sapphire is the polar axis of GaN, but the sapphire itself in terms of its crystal symmetry (space – group type r – 3 c) is non – polar.
7. How is a sapphire substrate manufactured?
Sapphire substrates can be produced through several methods. Bulk sapphire crystals can be grown using techniques like the Kyropoulos method or the Czochralski method. After crystal growth, the sapphire is cut into wafers of the desired thickness and orientation. These wafers are then polished, typically using chemical – mechanical polishing (CMP) to achieve a smooth surface suitable for epitaxial growth or other applications.
8. What factors affect the quality of a sapphire substrate?
- Crystal defects: Such as dislocations, twins, and inclusions can reduce the quality. Fewer defects lead to better performance when used as a substrate for epitaxial growth.
- Surface roughness: A rough surface can affect the growth of epitaxial layers. High – quality substrates usually have a surface roughness (Ra) of less than 0.3 nm after CMP.
- Orientation accuracy: The crystal orientation of the substrate, for example, c – plane, a – plane, etc., needs to be precise. Deviations from the desired orientation can impact the properties of the materials grown on it.
- Purity: Higher purity of the starting material () results in better – quality substrates. Impurities can introduce unwanted effects in the subsequent applications.
9. What is the typical cost of a sapphire substrate?
The cost of a sapphire substrate varies widely. Smaller, lower – grade substrates might cost tens of dollars. For example, a 2 – inch diameter c – plane sapphire substrate with basic quality could start at around 50−100. Larger, high – precision substrates used in advanced semiconductor manufacturing can cost several hundred to over a thousand dollars per substrate. Factors such as size, thickness, quality (crystal purity, surface finish), and quantity ordered all influence the price.
10. How to clean a sapphire substrate properly?
- Pre – rinse: First, rinse the substrate with deionized (DI) water to remove loose particles.
- Chemical cleaning: Soak it in a cleaning solution. For example, a mixture of sulfuric acid and hydrogen peroxide (piranha solution) can be used to remove organic contaminants. A combination of hydrochloric acid and hydrogen peroxide can be used to remove metal ions. Caution must be taken as piranha solution is highly corrosive.
- Rinse thoroughly: After chemical cleaning, rinse multiple times with DI water to remove any residual cleaning agents.
- Drying: Dry the substrate using a clean method, such as nitrogen blow – drying or spin – drying, to avoid leaving water spots or introducing new contaminants. In some ultra – clean applications, ultrasonic cleaning or plasma cleaning can also be employed.
11. What sizes of sapphire substrates are commonly available?
Commonly available sizes include 2 – inch diameter (50.8 mm), 4 – inch diameter (100 mm), and 6 – inch diameter (150 mm). Thicknesses for these diameters can be, for example, 0.43 mm for 2 – inch wafers, 0.65 mm for 4 – inch wafers, and 1.0 mm for 6 – inch wafers. However, other sizes and thicknesses can also be custom – made according to specific application requirements.
12. What are the advantages of using sapphire substrates in electronics?
- Thermal stability: It can withstand high temperatures during the manufacturing process and in operation, which is crucial for semiconductor and optoelectronic device fabrication.
- Mechanical strength: Sapphire has high mechanical strength, making it easy to handle and less likely to break during processing. It can also endure the stresses associated with device manufacturing steps like polishing and etching.
- Good lattice matching: For some semiconductor materials like GaN, sapphire provides a relatively good lattice match, allowing for the growth of high – quality epitaxial layers. Although there is still some lattice mismatch, it is manageable with proper techniques.
- Optical properties: In optoelectronic applications such as LEDs, its optical transparency in relevant wavelength ranges helps in light emission and extraction.
13. What are the limitations of sapphire substrates?
- Lattice and thermal mismatch: There is a significant lattice mismatch and thermal stress mismatch with some materials grown on it, like GaN. This can lead to the formation of defects in the epitaxial layer and cause difficulties in subsequent device processing.
- Insulating nature: Sapphire is an insulator, which makes it challenging to fabricate vertical – structure devices. It also requires additional processes to create electrical connections, increasing the complexity and cost of device manufacturing.
- Hardness: Its high hardness makes cutting and thinning processes difficult and expensive, as specialized equipment is needed.
- Cost: High – quality sapphire substrates can be relatively expensive, especially for large – size or high – precision requirements.
14. How do different crystal planes (c - plane, a - plane, r - plane, m - plane) of sapphire substrates affect their applications?
- C – plane: Widely used in GaN – based LED manufacturing as it has a relatively mature growth process and low cost. It provides a good base for growing GaN layers with a specific orientation.
- A – plane: Often used as a window material in military optoelectronic devices due to its non – polar nature, high transparency, and better light transmission performance compared to some other planes. It also has higher hardness and wear resistance in the a – plane atomic bonding direction.
- R – plane: Preferred for hetero – epitaxial deposition of silicon in microelectronic IC applications, enabling high – speed performance. After epitaxial silicon deposition, it is useful in high – speed IC and pressure transducer applications.
- M – plane: Competent in the ferromagnetic thin – film growth of materials like , making it suitable for applications such as solar – blind ultraviolet detection.
- M – plane: Competent in the ferromagnetic thin – film growth of materials like
15. What is a patterned sapphire substrate (PSS) and how does it work?
A patterned sapphire substrate (PSS) is a sapphire substrate on which nanoscale specific regular micro – structure patterns are created, usually through growth or etching methods. These patterns can reduce the lattice mismatch and thermal stress between the sapphire substrate and the epitaxial layer (such as GaN). They also scatter the light emitted from the active region of LEDs, increasing the light extraction efficiency. Additionally, PSS can reduce the differential defects during the growth of GaN on sapphire, thus improving the epitaxy quality and enhancing the internal quantum efficiency of LEDs.
16. Can sapphire substrates be reused?
In some cases, sapphire substrates can be reused. After the initial device fabrication process, if the substrate has not been severely damaged and the surface can be properly cleaned and re – polished to meet the required quality standards, it may be possible to use it for another round of epitaxial growth or other applications. However, the feasibility of reuse depends on factors such as the type of processing it has undergone, the level of contamination, and the specific requirements of the new application.
17. How does the thickness of a sapphire substrate affect its performance?
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