E-Mail:sales@czgraphite.com
Tel:+86 15533739372
Graphite susceptors are widely used in semiconductor production, particularly in chemical vapor deposition (CVD) and epitaxial processes. These components serve as carriers or heating elements that ensure uniform temperature distribution, enhancing the quality of semiconductor wafers.
Home Products Semiconductor Industry / Graphite Susceptors for Silicon and SiC Epitaxy
Graphite susceptors are critical components in epitaxial growth systems for both silicon (Si) and silicon carbide (SiC) wafers. They serve as the support and heating platform for the wafers during the high-temperature deposition process. Their material properties and design significantly impact the quality, uniformity, and cost-effectiveness of the epitaxial layer. This introduction will cover the fundamental roles, requirements, and considerations for graphite susceptors used in silicon and SiC epitaxy.
Before diving into graphite susceptors, it's crucial to understand the context of epitaxy. Epitaxy (from the Greek epi meaning "upon" and taxis meaning "arrangement") is a process of growing a thin, crystalline film on a substrate such that the crystalline structure of the film aligns with the crystalline structure of the substrate. This technique allows for the creation of highly controlled layers with specific electrical and optical properties.
Silicon Epitaxy: Primarily used for fabricating power devices, bipolar transistors, and integrated circuits. It allows for the creation of lightly doped layers on heavily doped substrates, improving device performance.
Silicon Carbide (SiC) Epitaxy: Essential for high-power, high-frequency, and high-temperature electronic devices. SiC's wide bandgap and superior material properties necessitate highly precise and controlled epitaxial growth.
The graphite susceptor plays a multifaceted role in both Si and SiC epitaxy:
Wafer Support: Provides a stable and level platform to hold the silicon or SiC wafers during the high-temperature growth process.
Heating: Efficiently absorbs energy (typically RF induction or resistance heating) and transfers it to the wafer, maintaining the necessary temperature for epitaxial deposition.
Temperature Uniformity: Ensures a uniform temperature distribution across the wafer surface. This is vital for achieving uniform growth rates and layer thickness across the entire wafer.
Gas Flow Management: The susceptor's geometry can influence gas flow patterns around the wafer, impacting the deposition process and uniformity.
Outgassing Control: Graphite susceptors can be treated to minimize outgassing of impurities at high temperatures, preventing contamination of the epitaxial layer.
Stress Management: The design and material properties of the susceptor can influence the stress induced in the growing epitaxial layer, especially important for SiC epitaxy.
To effectively fulfill its roles, graphite susceptors must meet a stringent set of requirements:
High Purity: Low levels of impurities (e.g., metals, sulfur, halogens) are crucial to prevent contamination of the epitaxial layer and ensure desired electrical properties. High-purity graphite is typically used.
High Thermal Conductivity: Efficiently transfers heat to the wafer and promotes temperature uniformity.
High Temperature Stability: Maintains its structural integrity and properties at the elevated temperatures required for epitaxy (typically 1000-1200°C for Si and 1500-1700°C for SiC).
Low Thermal Expansion Coefficient (CTE): Matching the CTE of the silicon or SiC wafer minimizes stress during heating and cooling cycles, reducing wafer warpage and defect formation. CTE matching is more critical for SiC epitaxy due to the higher process temperatures.
Excellent Machinability: Allows for the creation of complex geometries needed for optimal gas flow and temperature uniformity.
Chemical Inertness: Resistant to reaction with the source gases used in the epitaxial process (e.g., silane, dichlorosilane for Si; silane, propane for SiC).
Minimal Outgassing: Low vapor pressure at high temperatures minimizes the release of contaminants that can degrade the epitaxial layer quality.
Electrical Conductivity: Required for RF induction heating.
Surface Finish: A smooth surface finish promotes uniform contact with the wafer and minimizes particle generation.
Long Lifespan: Resistance to degradation over repeated heating and cooling cycles reduces operational costs.
Isostatic Graphite: The most common type used for susceptors due to its high purity, homogeneity, and isotropic properties (uniform properties in all directions). It is produced by compressing graphite powder in all directions simultaneously.
Fine-Grained Graphite: Provides a smoother surface finish and is often preferred for applications requiring tight tolerances.
Graphite susceptors are often coated with various materials to enhance their performance:
Silicon Carbide (SiC) Coating: Commonly used to provide a chemically inert and stable surface that prevents carbon diffusion into the epitaxial layer, especially for SiC epitaxy. It also improves resistance to oxidation.
Pyrolytic Graphite (PG) Coating: Provides a highly oriented graphite layer with excellent thermal conductivity and low outgassing.
Pyrolytic Boron Nitride (PBN) Coating: Offers exceptional chemical inertness and resistance to oxidation at high temperatures.
Other Coatings: Depending on the specific application, other coatings like refractory metals (e.g., tungsten) or ceramics may be used.
The design of the susceptor is critical for optimizing temperature uniformity and gas flow. Factors to consider include:
Shape and Geometry: Susceptor shape (e.g., flat, recessed, grooved) and the presence of features like slots or channels influence gas flow patterns and temperature distribution.
Wafer Pocket Design: The design of the pocket that holds the wafer affects the thermal contact between the wafer and the susceptor.
Heating Configuration: The method of heating (e.g., RF induction, resistance heating) and the placement of heating elements influence the temperature profile of the susceptor.
Susceptor Material Properties: Thermal conductivity, CTE, and other material properties influence the overall performance of the susceptor.
Achieving Higher Uniformity: Meeting the increasingly stringent uniformity requirements for large-diameter wafers presents a significant challenge.
Reducing Defects: Minimizing defect density in the epitaxial layer requires careful control of all aspects of the epitaxy process, including the susceptor design and material quality.
Cost Reduction: Improving the lifespan and performance of susceptors can help to reduce overall production costs.
Advanced Coatings: Research into new and improved coatings is ongoing to further enhance the performance and durability of graphite susceptors.
Simulation and Modeling: Computational fluid dynamics (CFD) and finite element analysis (FEA) are increasingly used to optimize susceptor design and predict its performance.
Russian