What is Aluminum Oxide?

Aluminum oxide, also known as alumina, is a chemical compound made up of aluminum and oxygen. It has the chemical formula $Al_2O_3$ and is the most commonly occurring oxide of aluminum.

In nature, it is found as the mineral corundum (the second hardest mineral after diamond) and is a primary component of bauxite. Due to its hardness, high melting point, and chemical stability, it is used extensively as an abrasive, refractory material, catalyst, and protective coating.

Aluminum Oxide in Semiconductor Fabrication

Aluminum oxide is a critical semiconductor fabrication material acting as a dielectric. In Integrated Circuit (IC) manufacturing, thin layers of aluminum oxide act as insulators between conductive layers.

Deposition Methods

The layer is typically formed via:

  • Chemical Vapor Deposition (CVD)
  • Atomic Layer Deposition (ALD): A gas containing aluminum and oxygen reacts on the wafer surface to deposit a precise thin layer.

This layer is patterned using lithography and etching. Engineers prefer Aluminum Oxide for its high dielectric constant, low leakage current, and thermal stability.

Common Substrates for Aluminum Oxide

Aluminum oxide serves as a dielectric material on various substrates:

  1. Silicon: The standard for acting as an insulating layer in ICs.
  2. Gallium Arsenide (GaAs): Used in high-speed electronics; aluminum oxide acts as a passivation layer to protect the GaAs surface.
  3. Sapphire: Often used as a substrate for Gallium Nitride (GaN) thin films. Aluminum oxide provides insulation on top of the GaN layer.
  4. Glass: Used in flat panel displays and touchscreens. Aluminum oxide acts as a barrier layer preventing ion diffusion.

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