A novel energy saving process for PFAS-free ArF immersion lithography

Evolving global trends in the semiconductor industry require prioritization of social responsibility and regulatory compliance. Consumers demand eco-friendly practices to put emphasis on their environmental benefits and positive impact on brand reputation. Elimination of forever chemicals, such as perfluorinated alkylated substances (PFAS) became a key focus. As a result, using sustainable materials and processes are becoming increasingly vital in our industry. Our cross-industry team has been working on PFAS-free materials and process solutions to lower energy consumption in lithography processes, more specifically by replacing the conventional thermal crosslinking approach of spin-on carbon (SOG) and spin-on glass (SOG) layers with a photo-crosslinking process using PFAS-free materials. While thermal baking processes are very effective and have been used as the standard in lithography tracks, the hot plates must stay at the right temperature to maintain thermal stability and throughput. By changing the crosslinking mechanism of the spin-on layers to optical crosslinking, similar level of material performance should be achieved with more energy efficiency since optical curing is only accessed on demand. Another added benefit is that the time to perform optical curing is much shorter than for thermal crosslinking, resulting in increased throughput. In this work, we will show the feasibility of the proposed approach using ArF immersion (ArFi). Lithographic performance obtained with PFAS-free, light-curable underlayers will be compared with traditional PFAS-containing thermal crosslinking processes. The results show that significant dose reduction is achieved for the positive tone line/space (L/S) process by using the optical crosslinking approach. For the negative tone contact hole (CH) process we observed a positive impact on the exposure latitude (EL).