Epitaxial Wafer Service

For epitaxial layer deposition, it is important to determine what type EPI layer the application requires before determining how to deposit it. Homoepitaxy is when a crystalline film is grown with the same material as the substrate. Heteroepitaxy is more common, and grows a crystalline film made of a different material than the substrate. Depending on the type EPI layer, there are three different ways that they can be deposited.

Liquid Phase Epitaxy (LPE)

Liquid phase epitaxy is common in compound semiconductor device fabrication. This method usually deposits heteroepitaxial films, so it is important to be sure that both the substrate and the film have similar coefficients of expansion to prevent any damage.

This process takes place in an oxygen free environment to prevent any oxide film growth, so the wafers are either under vacuum or in a furnace with hydrogen and nitrogen gases. The process starts by making a melt, which will be used to create the epitaxial film. The melt consists of molecules for the film and any dopants mixed in a low melting point (lower than 500°C) solvent metal. The heat from the melt partially dissolves the surface of the wafer, removing any defects, then the entire system heats up. After heating the wafers to about 1200 K, they are cooled very slowly. The cooling rate determines the film quality and characteristics, so it is important that this is precisely controlled. This is best for depositing doped films, because it is easy to control the concentration.

Molecular Beam Epitaxy (MBE)

Molecular beam epitaxy is a thin film deposition method that prints epitaxial layers on substrates one atomic layer at a time. MBE can deposit both homoepitaxial and heteroepitaxial layers, so it is more popular in very thin film applications.

The process begins by placing wafers in an ultra high vacuum, then heating them to between 500°C – 600°C for silicon substrates and 900°C – 1100°C for gallium arsenide (GaAs) substrates. After being heated, multiple beams shoot molecules from effusion cells towards the target wafer. Each effusion cell can only shoot one molecule, so each system needs multiple beams to create the correct film composition. As the beam hits the wafer, the molecules mix and spread evenly, depositing the film one atomic layer at a time.

Vapor Phase Epitaxy (VPE)

Vapor phase epitaxy uses chemical vapor deposition with silane (SiH₄) and propane (C₃H₈) as precursor gases to create heterostructures on substrates. VPE was developed specifically for depositing layers of silicon on gallium arsenide wafers using metalorganic chemical vapor deposition. The process takes place in a furnace heated to between 1500°C – 1650°C. Due to its repeatability and simplicity, this is the most common epitaxial growth method for opto- and microelectronics.

SVM’s Epitaxial Wafer Services Specifications:

• Diameters: 100mm, 125mm, 150mm, 200mm, and 300mm*
• Wafer Orientation: <100>, <111>, <110>
• EPI Thickness: 1µm to 150μm
• Dopants: Arsenic, Phosphorus, Boron
• Typical Resistivity Ranges
  • 0.01 – 1,200 ohm-cm
  • 3000 – 5,000 ohm-cm (intrinsic layers)