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• Lam engineers collaborated with a customer to cut NF₃ gas consumption 
• Results demonstrate the potentially large benefits of small optimizations 

The semiconductor industry is always seeking ways to use fewer resources in the manufacturing process, which can help improve overall sustainability.  

Recently, we collaborated with our customer ST Microelectronics to develop an in-situ plasma clean technique that uses less nitrogen trifluoride (NF₃) gas in the etch chamber cleaning process without impacting overall throughput. 

We realized that we don’t need to re-invent the wheel for more sustainable practices. Reducing gas flows in a widely used process like chamber plasma clean is just one way to improve and optimize what’s already available.  

Leveraging feedback from the Lam Research Fremont Lab and using Lam Equipment Intelligence^® in-house software (including a greenhouse gas calculator), we found that our solution have the potential to deliver: 

• 33% lower NF₃ consumption thanks to reduced gas flows; 
• 8% faster clean times through clean process time optimization; and  
• 32% lower CO₂e emissions. 

The Role of NF₃ in Chamber Cleaning 

Plasma chamber clean is a well-known process used in the semiconductor industry, particularly in etch chambers, to ensure repeatable wall conditions for every wafer and to enhance wafer particle performance.  

NF₃ gas is used to remove precoat and silicon byproducts from etch chamber walls. NF₃ is known to have a high global warming potential (GWP), but it also has a relatively good dissociation rate (85%), meaning it can be easily broken down into smaller components that often have lower GWP values. The main byproduct of NF₃ dissociation is silicon tetrafluoride (SiF₄), which has a very low GWP (<1). 

By reducing NF₃ gas flows while maintaining overall throughput, our research team was able to reduce CO₂e emissions 32% after abatement.  

In our study, we found NF₃ use could be reduced successfully during the in-situ plasma chamber clean step (Step 3).  

Our Study on Optimizing NF₃ Gas Usage  

We worked with ST to develop a short-term solution that reduces the use of high GWP gases like NF₃ that is also relatively easy to implement and doesn’t jeopardize the quality of the production.  

The amount of NF₃ gas needed depends on the process recipe itself, which influences the amount of precoat (made of SiOCl) applied in the chamber. Harsher process chemistries will chemically attack the precoat layer on the chamber walls. Therefore, thickness of the precoat determines how much NF₃ is needed to remove it.   

We applied our modified in situ plasma clean during the waferless autoclean step, during which the chamber is cleaned of all remaining materials (precoat, etch residuals, carbon contaminants, etc.)  

The authors Luigi Mascarello (left) and Maximilien Nebois (right) at Semicon Europa 2024 present their study with ST Microelectronics’ Cyril Villieu (center) on reducing carbon emissions during the etch cleaning process.  

We conducted several experiments using blanket wafers and found that NF₃ in most cases could easily be reduced by 300 sccm with very little effect on throughput. We realized the current waferless autoclean time was overly long and not optimized for specific process recipes. Shortening the residence time helped reduce overall NF₃ consumption and the carbon footprint induced by those cleans.      

These promising results represent a step in the right direction toward a more sustainable and efficient etch and clean process on a significant portion of the ST Microelectronics installed base.  

Luigi Mascarello is a senior engineer of technical program management and Maximilien Nebois is a field process engineer at Lam Research. 

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