The role of PECVD in solar cells

PECVD (plasma enhanced chemical vapor deposition) is one of the core processes in photovoltaic cell manufacturing. It is mainly used to deposit key functional films (such as silicon nitride-SiNx) on the surface of silicon wafers to achieve anti-reflection and surface passivation functions. The PECVD tray plays a key role in this process, ensuring the uniformity of film deposition, the good stability of silicon wafers and the efficient operation of the equipment. It can efficiently generate dense films at lower temperatures (300–400°C) by activating chemical reactions through plasma, significantly improving the photoelectric conversion efficiency of the battery.

What is the workflow of PECVD in photovoltaic cells?

1.Silicon wafer pretreatment

After the diffusion process, the silicon wafer forms a PN junction, and after etching to remove the edge doping layer, it enters the PECVD stage. Surface contaminants (such as organic residues and metal ions) need to be thoroughly cleaned to ensure film adhesion.

2.Loading and vacuum environment establishment

The silicon wafers are evenly placed on the PECVD boat and sent into the reaction chamber by a robotic arm. The chamber is evacuated to 10⁻²–10⁻³ Torr to exclude interference from oxygen and moisture.

3.Plasma activation and thin film deposition

Gas introduction: Silane (SiH₄) and ammonia (NH₃) are mixed in proportion and introduced into the reaction chamber.

RF power source excites plasma: The high-frequency electric field (such as 13.56 MHz) ionizes the gas to generate highly active free radicals such as SiH₃⁻ and NH₂⁺.

Surface reaction: Free radicals react on the surface of the silicon wafer to generate amorphous silicon nitride (a-SiNx:H), and the thickness is controlled at 70–80 nm to optimize light absorption (refractive index ~2.0).

4.Annealing and passivation effect enhancement

After deposition, infrared annealing (300–450°C) is used to release film stress, and hydrogen atoms diffuse to the defects on the silicon surface to achieve chemical passivation (reducing the surface recombination rate).

5.Cooling and removal

The PECVD boat moves out of the chamber with the conveyor system, and the silicon wafer enters the next step (such as screen printing) after cooling to room temperature.

What are the practical uses of PECVD Boat?

PECVD boats (or PECVD graphite boats) are mainly used in the photovoltaic field to carry solar cell substrates into the PECVD reaction chamber. These boats are usually made of other high-temperature resistant materials such as graphite or quartz, and can withstand the high temperature environment in the PECVD process. PECVD Boat directly affects the deposition uniformity and fragmentation rate.

· Carrying substrates: The main function of the PECVD boat is to place the solar cell substrate in the PECVD reaction chamber for thin film deposition.

· Uniform heating: By evenly distributing heat, ensure that the substrate maintains a consistent temperature throughout the process, thereby improving the quality and uniformity of the film.

· Corrosion resistance: Since the PECVD process involves various chemical gases, the PECVD boat needs to have good corrosion resistance to ensure its integrity during long-term use.

What are the design points of PECVD Boat?

Its design needs to meet the following requirements:

Material is resistant to high temperature and corrosion:

Quartz or silicon carbide coated graphite is usually used to withstand plasma erosion and high temperature environment (graphite boats need to be replaced regularly to avoid particle contamination).

Structural optimization:

Tilted slot design: ensure uniform spacing between silicon wafers (5-10 mm) and avoid fluctuations in film thickness (target uniformity <5%).

Edge guide groove: optimize the distribution of reactive airflow and reduce the film thickness difference caused by edge effect.

Adaptation for large-scale production:

Compatible with large-size silicon wafers (such as M10/G12), the capacity of a single boat can reach 200-300 pieces, and the production capacity is improved (such as a single device can process 4000 pieces per hour).

Integrated automatic transmission interface, cooperate with AGV/robotic arm to realize unmanned operation.

Cost and maintenance:

The life of the graphite boat is about 6-8 months, and it needs to be regularly pickled (such as HF solution) to remove sediment residues.

Quartz boats are expensive but have low pollution risk, and are suitable for large-scale mass production of TOPCon/HJT technology.

Element for Quartz

Why choose Semixlab?

Semixlab is a leading PECVD boat manufacturer and supplier in China. Our PECVD boat products include PECVD graphite boats, PECVD quartz boats, etc.

We can provide customized products and technical services according to your actual production needs. In fact, with the continuous development of the photovoltaic industry, the continuous optimization of PECVD technology and equipment will further promote the improvement of photovoltaic cell performance and the expansion of production scale. Semixlab is willing to work with you to contribute more to the photovoltaic cell industry.