Double-Side Polished Sapphire Wafers are high-quality sapphire wafers that have undergone a polishing process on both sides, ensuring a smooth, flat, and uniform surface on each side of the wafer. This dual-polishing process is used to enhance the precision and performance of the wafer, making it ideal for a variety of advanced applications in the semiconductor, optoelectronic, and optical industries.
Key Characteristics of Double-Side Polished Sapphire Wafers:
Double-Side Polishing Process:
Double-side polishing involves polishing both the top and bottom surfaces of the sapphire wafer, ensuring that both sides are smooth, flat, and free from defects. This process improves the uniformity of the wafer's thickness and flatness, which is essential for applications requiring precise handling and uniform film deposition.
The polishing process significantly reduces surface roughness (Ra) and minimizes surface defects such as scratches or irregularities that could impact performance in device fabrication.
Material: Sapphire (Al₂O₃):
Sapphire is a crystalline form of aluminum oxide (Al₂O₃), known for its high mechanical strength, optical transparency, thermal conductivity, and chemical stability. These properties make sapphire an excellent choice for a range of high-performance applications in semiconductors, LEDs, optics, and MEMS devices.
Sapphire is particularly valuable because it can withstand extreme thermal conditions and is chemically inert, which is crucial for devices used in harsh environments or high-power applications.
Applications:
LEDs and Optoelectronics: Double-side polished sapphire wafers are commonly used as substrates for LEDs and other optoelectronic devices. The smooth, defect-free surfaces ensure uniform epitaxial growth of active layers in LED production. The precise control over surface flatness and thickness is critical for improving LED efficiency and reliability.
Semiconductor Devices: Sapphire wafers are also used for power devices and microwave devices. The dual polished surfaces ensure precise material deposition and high-quality device fabrication. Their excellent electrical insulation properties make them ideal for power electronics.
Optical Windows and Components: Double-side polished sapphire is often used in optical windows, lenses, and viewports due to its optical clarity and mechanical strength. It is commonly used in high-performance optical systems such as those in aerospace and military applications.
MEMS (Microelectromechanical Systems): The uniformity and smoothness of double-side polished sapphire wafers make them ideal for MEMS devices, such as sensors, actuators, and devices requiring high precision.
High-Temperature and Harsh Environments: Sapphire's thermal stability makes it ideal for use in environments where extreme temperatures, radiation, or chemical exposure are present, such as aerospace or high-energy physics applications.
Crystal Orientation:
Double-side polished sapphire wafers are typically oriented with the <0001> crystallographic plane (the c-plane), which is the most common orientation used for LED epitaxial growth and other device fabrication processes. The c-plane allows for optimal layer growth and electrical properties.
Other orientations like <1120> (a-plane) or <1102> (r-plane) may also be used depending on specific application needs, particularly in semiconductors or optical devices.
Surface Quality:
The polished surfaces of double-side polished sapphire wafers are critical for achieving high-quality device fabrication. The smooth, defect-free surfaces allow for precise thin-film deposition, lithography, and etching processes without the risk of defects that could affect the performance of the device.
These wafers have low surface roughness (Ra), ensuring better adhesion of materials during processes like epitaxial growth and thin-film deposition. This is especially important for high-performance devices like LEDs, laser diodes, and microsensors.
Mechanical and Thermal Properties:
High Strength: Sapphire is incredibly hard (9 on the Mohs scale), making it highly resistant to scratches and abrasion. This strength is beneficial for applications where mechanical durability is essential.
Thermal Conductivity: Sapphire has excellent thermal conductivity, which allows for better heat dissipation in high-power and high-performance electronics. This is particularly useful in devices like power LEDs, laser diodes, and semiconductor power components.
Thermal Expansion: Sapphire has a relatively low thermal expansion coefficient, which helps maintain structural stability and alignment in devices subjected to temperature variations.
Thickness and Diameter:
Diameter: Double-side polished sapphire wafers are available in a variety of diameters, with 2-inch, 4-inch, 6-inch, and 8-inch sizes being common. Larger wafers are used for more extensive production processes or applications requiring a larger substrate.
Thickness: The thickness of the wafer can vary, but it is generally consistent and highly uniform across both polished sides. Common thickness ranges are 200µm to several millimeters, depending on the requirements of the application.