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As the world shifts toward renewable sources of energy, solar photovoltaic cells have become an essential part of the sustainable source of power. Among all renewable energies, photovoltaic benefits form many advantages such as unlimited renewable source of energy, increasingly cost competitive, environment friendly. Photovoltaic syster use cells to convert sunlight into electricity.
Home Products Photovoltaic Industry / PECVD Graphite Boat
As we all know, in the manufacturing of photovoltaic cells, there is a process called coating anti-reflection film. During this process, PECVD (plasma chemical vapor deposition) technology has the advantages of fast coating forming speed, light wrapping plating, and low cost.
Our graphite boat plays a crucial role in the PECVD coating process of photovoltaic cells. In a tube-style PECVD coating process, the graphite boat acts as a carrier for silicon wafers. The quality of the graphite boat directly affects the uniformity and color consistency of the coating on the surface of the wafer. With our high-quality graphite boat, the PECVD coating process can achieve better results in the solar cell performance.
A layer of silicon nitride anti-reflection film is deposited on the surface of the silicon wafer to increase the transmission of light incident on the silicon wafer and reduce reflection. Hydrogen atoms are doped in silicon nitride to add hydrogen passivation.
When light hits the surface of a silicon wafer, about one-third (about 35%) of the light is lost by reflection. If there are one or more layers of suitable thin films on the silicon surface, the reflection of light can be greatly reduced by using the principle of thin film interference. This kind of film is called ARC, antireflection coating of solar cells.
The heated thin gas is excited by pulsed radio frequency for glow discharge to form plasma, and the two corresponding graphite sheets are applied with opposite alternating voltage to accelerate the plasma to hit the gas between the plates and move to the surface of the silicon wafer to complete the coating process.
2-inch (50 mm) wafers
4-inch (100 mm) wafers
6-inch (150 mm) wafers
8-inch (200 mm) wafers
12-inch (300 mm) wafers (becoming more common)
Number of Substrates: Boat capacity ranges from single wafer to multiple wafer (batch processing) designs. Multiple wafer boats must ensure even gas distribution and plasma exposure to each substrate.
Temperature Requirements: The type and grade of graphite must be chosen to withstand the specific temperature range of the PECVD process. Different graphite grades have different thermal properties.
Precursor Gases: The compatibility of the graphite with the precursor gases is crucial. Some gases may react with graphite, leading to contamination or degradation of the boat. Consider surface treatments.
Chamber Compatibility: The boat must be designed to fit within the PECVD chamber without interfering with the plasma generation or gas flow.
Surface Finish: A smooth, clean surface finish is important to minimize particle contamination. Graphite dust can be a significant issue in cleanroom environments. Often, graphite boats undergo surface treatments to reduce dust and improve chemical inertness.
Electrical Properties: If electrical biasing is used, the boat's electrical conductivity and the design of the electrical contacts are critical.
Outgassing: The graphite should be baked out prior to use to remove adsorbed gases and moisture that could contaminate the deposited films.
Boat Cleaning: Develop a cleaning procedure to remove residual materials deposited on the boat during the PECVD process. This may involve solvents, etching, or thermal cleaning.
Isotropic Graphite: Offers uniform properties in all directions and is often used for general-purpose applications.
Anisotropic Graphite: Has different properties along different axes. Can be useful for specific thermal conductivity requirements.
Coated Graphite: Graphite can be coated with materials like silicon carbide (SiC) or pyrolytic carbon (PyC) to improve chemical resistance, reduce particle generation, and enhance thermal conductivity. Pyrolytic graphite is often used to seal the surface and reduce outgassing.
Design Considerations for Uniformity:
Gas Flow Management: The boat design must facilitate uniform gas flow across the substrates. This may involve incorporating gas distribution channels or baffles.
Plasma Uniformity: The boat's geometry can influence the plasma distribution. Careful design is needed to ensure uniform plasma exposure to all substrates.
Temperature Uniformity: Maintaining uniform temperature across all substrates is crucial for consistent film properties. The boat's thermal conductivity and heat transfer characteristics play a significant role.
Graphite purification: Removal of impurities from the graphite material.
Pyrolytic Carbon Coating: A thin, dense layer of pyrolytic carbon is deposited on the graphite surface to seal the pores and reduce outgassing.
Silicon Carbide (SiC) Coating: SiC coatings improve chemical resistance, hardness, and wear resistance.
Chemical Vapor Infiltration (CVI): A process where a coating material is infiltrated into the pores of the graphite to enhance its properties.
Surface Polishing: Smoothing the surface to reduce particle generation and improve cleanliness.
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