Epitaxial Coating of Silicon 

What Silicon Wafer Should Be Used for Epitaxial Silicon Coating?

High-purity, high-resistivity float-zone silicon wafers are often preferred as substrates for epitaxial silicon deposition. Their low impurity concentration helps reduce background signals during the characterization of thin epitaxial layers.

The following wafer specification has been used by researchers depositing silicon epitaxial layers from silane-based process gases:

150 mm Prime-Grade FZ Silicon, N-Type Phosphorus, <100> Orientation, >5,000 Ω·cm, 425 ±15 µm, SSP, TTV <10 µm, Bow <30 µm, Warp <30 µm

High-Purity Silicon Substrates for Epitaxial Deposition

These silicon wafers are used as substrates for depositing epitaxial silicon from process gases such as silane, disilane, and dichlorosilane. After deposition, the epitaxial coatings can be analyzed using Fourier transform photoluminescence (FTPL) spectroscopy.

FTPL analysis can be used to detect and quantify electrically active impurities in silicon, including donor and acceptor elements. Depending on the process, these may include:

• Phosphorus
• Boron
• Arsenic
• Aluminum
• Gallium

These Group III and Group V elements modify the electrical properties of silicon by creating P-type or N-type conductivity. Because the goal of the analysis is to measure very low impurity concentrations in the deposited epitaxial layer, the underlying substrate must contribute as little background contamination as possible.

Why Float-Zone Silicon Purity Matters

Ultra-trace FTPL measurements may be performed at very low concentration levels. For this reason, substrate purity is critical. If the starting wafer contains measurable concentrations of phosphorus, boron, arsenic, aluminum, or other electrically active impurities, those elements may contribute to the measured spectrum.

This is especially important when analyzing relatively thin epitaxial silicon layers. The excitation and optical response may extend into the substrate, allowing the substrate signal to appear alongside the signal from the deposited layer.

A doped or insufficiently pure substrate can therefore make the epitaxial coating appear more contaminated than it actually is. High-resistivity float-zone silicon helps minimize this interference and improves the reliability of donor and acceptor measurements.

FTPL Analysis of Silicon Process Gases

In this application, epitaxial silicon layers are deposited from silicon precursor gases and then measured to determine the concentrations of donor and acceptor impurities. The resulting FTPL data may be used to certify impurity levels reported on product certificates of analysis (COAs).

The silicon substrate must therefore support both successful epitaxial growth and sensitive optical characterization. Important substrate characteristics may include:

• Float-zone crystal growth
• Very high resistivity
• Low concentrations of donor and acceptor impurities
• Prime-grade surface quality
• Controlled crystal orientation
• Low total thickness variation
• Low bow and warp
• Single-side-polished or custom surface finishes

Alternative Dopants for Reducing Spectral Interference

Some researchers have considered silicon substrates doped with bismuth or indium as a possible method for reducing interference from the strong silicon two-phonon band in FTPL spectra.

In principle, an appropriately selected dopant could suppress or alter the substrate-related spectral response without overlapping the impurity peaks being measured in the epitaxial layer. However, bismuth- and indium-doped silicon wafers are specialized materials and may be difficult to source.

Gallium-doped silicon may also be considered for some experiments, although the gallium-related signal can occur closer to the spectral regions used to quantify phosphorus, arsenic, and aluminum. The suitability of any doped substrate should therefore be evaluated against the specific FTPL measurement range and detection limits.

Recommended Information for a Quote

When requesting silicon wafers for epitaxial coating and FTPL analysis, include the following information:

• Wafer diameter
• Crystal growth method, such as float-zone
• Crystal orientation
• Conductivity type
• Required resistivity
• Acceptable dopant and impurity limits
• Wafer thickness
• Surface finish
• Total thickness variation
• Bow and warp limits
• Epitaxial deposition gas
• Target epitaxial layer thickness
• FTPL detection requirements
• Quantity

Silicon Wafers for Epitaxial Coating Research

UniversityWafer supplies high-resistivity float-zone silicon wafers for epitaxial silicon growth, semiconductor impurity analysis, process-gas qualification, photoluminescence characterization, and advanced materials research.

Submit your wafer specifications, purity requirements, analytical method, and quantity to request pricing and availability.

Related Silicon Epitaxy Resources

• Silicon Epitaxial Wafers
• 150 mm Silicon Wafers
• Float-Zone (FZ) Silicon Wafers
• High-Resistivity Silicon Wafers
• Silicon Wafers
• Doped Silicon Wafers
• Carrier Concentration
• Carrier Mobility
• Thermal Oxide Silicon Wafers
• Silicon-on-Insulator (SOI) Wafers
• Semiconductor Wafers
• Research Substrates