Amorphous Silicon Encapsulation for PECVD Chamber Fluorine Protection
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Solution Overview
Problem
Residual fluorine contamination in plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films on solar cells leads to reduced solar cell efficiency due to blocked hydrogen diffusion, increased surface recombination, and lower refractive index, as fluorine residue accumulates in the process chamber, particularly at chamber corners and tray corners, requiring costly and time-consuming thick silicon nitride encapsulation.
Innovation Solution
A method involving the use of nitrogen trifluoride (NF3) to clean the process chamber, followed by silane (SiH4) to form an amorphous silicon encapsulating layer, which protects against fluorine contamination, and subsequent deposition of silicon nitride films using PECVD with silane, ammonia, and nitrogen, reducing fluorine residue accumulation and enhancing encapsulation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick silicon nitride encapsulation is used to protect against fluorine contamination, then protection effectiveness is improved, but manufacturing time and cost increase
Solution Approach 1:
The patent applies preliminary action by performing a chamber cleaning step with fluorine-containing gas before the silicon nitride deposition. This cleaning step removes residual fluorine contamination from the chamber walls and surfaces, preventing fluorine incorporation into the silicon nitride film. By addressing the contamination source beforehand, the patent achieves effective protection without requiring excessive film thickness, thus reducing manufacturing time while maintaining reliability.
Solution Approach 2:
The patent extracts the harmful fluorine residue from the system by implementing a dedicated cleaning step that removes fluorine-containing contaminants from the process chamber before deposition. This extraction of the harmful element prevents fluorine from being incorporated into the silicon nitride film, achieving effective protection without needing thick encapsulation layers, thereby reducing both material usage and processing time.
2Manufacturing precision
If chamber cleaning is performed to remove fluorine residue, then film purity is improved, but processing time increases
Solution Approach 1:
The patent performs chamber cleaning with fluorine-containing gas as a preliminary step before silicon nitride deposition. This cleaning action removes residual fluorine from chamber surfaces, ensuring high film purity by preventing fluorine incorporation. The cleaning step is optimized to be efficient, achieving the required purity level without excessive processing time, thus resolving the contradiction between film purity and processing time.
3Productivity
If PECVD deposition is used to form silicon nitride film, then deposition efficiency is improved, but fluorine contamination occurs
Solution Approach 1:
The patent applies preliminary anti-action by performing a fluorine-containing gas cleaning step before PECVD deposition. This cleaning step creates a fluorine-free environment on chamber surfaces, counteracting the potential for fluorine contamination during the subsequent PECVD process. By eliminating the contamination source beforehand, the patent maintains high deposition efficiency while preventing fluorine incorporation into the silicon nitride film.
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
This approach significantly improves solar cell efficiency and refractive index performance by reducing fluorine contamination, achieving comparable results to thick silicon nitride films while minimizing processing time and cost, with amorphous silicon encapsulation providing effective protection against residual dopant and metal contamination.
Implementation Method 1
flowing nitrogen triflouride (NF3) gas to clean a process chamber from excess silicon nitride
Implementation Method 2
flowing silane (SiH4) gas to coat the process chamber with amorphous silicon
Implementation Method 3
depositing a silicon nitride film on the substrate by plasma-enhanced chemical vapor deposition (PECVD)
Data Source
AI summary
A method for forming of a thin film on a substrate is disclosed. The method includes cleaning a process chamber by flowing a first gas having fluorine. The method also includes coating the process chamber with a first encapsulating layer including amorphous silicon (A-Si) by flowing a second gas for a first duration, where the first encapsulating layer protects against fluorine contamination. The method further includes loading a substrate into the process chamber, depositing a thin film on the substrate by flowing a third gas into the process chamber and unloading the substrate from the process chamber. The thin film can include silicon nitride (SiN), the first gas can include nitrogen triflouride (NF3) gas and second gas can include silane (SiH4) gas. The thin film can be formed using plasma-enhanced chemical vapor deposition. The substrate can be a solar cell or a liquid crystal display (LCD).