Graphite Boat Silicon Carbide Coating for PERC Solar Cell Scratches
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Solution Overview
Problem
The existing tubular PECVD technology for producing PERC solar cells faces issues with poor appearance quality and low electroluminescence (EL) yield due to scratching of silicon wafers during the coating process, which affects the pass rate and electrical performance of the cells, and requires time-consuming pre-processing steps that consume silicon wafers and increase costs.
Innovation Solution
A coating device and method that simplifies the pre-processing of the graphite boat by baking and coating it with a silicon carbide film, reducing the need for silicon wafer insertion and minimizing scratches, with optimized pin slot dimensions and automatic wafer inserter adjustments to reduce friction and gas exposure, and shortening silicon nitride deposition time to enhance uniformity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the silicon wafer is inserted into the graphite boat with a narrow pin slot (0.25mm) to ensure tight contact with the graphite boat wall for uniform coating, then the coating uniformity is improved, but the silicon wafer surface is scratched during insertion
Solution Approach 1:
The graphite boat surface is pre-coated with silicon nitride film before wafer insertion. This preliminary coating creates a protective layer that reduces friction and prevents scratching during wafer insertion, while still allowing the wafer to maintain tight contact with the boat wall for uniform coating deposition.
Solution Approach 2:
A silicon nitride coating layer is introduced as an intermediary between the graphite boat wall and the silicon wafer. This intermediate layer acts as a lubricant and protective barrier, reducing direct contact friction and preventing wafer surface damage while maintaining the necessary contact pressure for uniform coating.
2Manufacturing precision
If the conventional pre-processing method is used (baking, coating boat with inserted wafer, coating empty boat), then the coating quality is improved, but the process time and silicon wafer consumption increase
Solution Approach 1:
The invention extracts and removes the unnecessary step of inserting a silicon wafer into the graphite boat for pre-coating. Instead, the boat is coated directly without wafer insertion, eliminating time consumption and silicon wafer usage while still achieving the required coating quality through optimized process parameters.
Solution Approach 2:
The graphite boat undergoes preliminary baking treatment before coating to prepare the surface for optimal coating adhesion and quality. This preliminary thermal treatment ensures the boat surface is at the appropriate temperature and condition for high-quality coating deposition without requiring additional wafer-based pre-processing steps.
3Strength
If the silicon wafer is in contact with the graphite boat wall during insertion, then the wafer is fixed securely, but the p-n junctions at the front surface are scratched affecting EL yield
Solution Approach 1:
The silicon nitride coating serves as an intermediary layer between the graphite boat wall and the silicon wafer surface. This intermediate coating reduces the coefficient of friction and prevents direct mechanical contact that would cause scratching of the p-n junctions, while still providing sufficient friction for secure wafer fixation during the coating process.
Solution Approach 2:
The invention changes the surface properties of the graphite boat by coating it with silicon nitride, which alters the friction characteristics and surface energy. This parameter change allows the wafer to be securely fixed during insertion and coating while minimizing mechanical damage to the sensitive p-n junction regions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces silicon wafer scratches, increases EL yield, saves silicon wafer consumption, and enhances production efficiency by streamlining pre-processing steps and improving coating uniformity, thereby improving the overall cost-effectiveness and quality of PERC solar cells.
Implementation Method 1
the graphite boat should be pre-processed before use or after several coating, the pre-processing including baking the graphite boat
Implementation Method 2
coating at least one layer of silicon carbide film on a surface of the baked graphite boat
Implementation Method 3
tubular PECVD technology to deposit a composite film on the rear surface of a silicon wafer
Data Source
Figure 1~2
Figure 3
AI summary
A coating device for a tube-type PERC solar cell comprises a wafer loading area (1), a furnace body (2), a gas cabinet (3), a vacuum system (4), a heating system (7), a control system (5) and a graphite boat (6), wherein the gas cabinet (3) is provided with a first gas line for feeding silane, a second gas line for feeding ammonia, a third gas line for feeding trimethylaluminum, a fourth gas line for feeding nitrous oxide and a fifth gas line for feeding methane. The graphite boat (6) is employed for loading and unloading a silicon wafer. Pre-processing is performed to the graphite boat (6) before use or after several coating, wherein the pre-processing includes: baking the graphite boat (6) and coating at least one layer of silicon carbide film on a surface of the baked graphite boat (6). The present application also discloses a coating method for a tube-type PERC solar cell. Such method simplifies the pre-processing steps of the graphite boat, reduces consumption of silicon wafers, avoids scratches on the silicon wafer and boosts the EL yield of the cell.