First, work is ongoing on optical lithography where we try to squeeze everything we can out of immersion lithography by both enhancing resolution and controlling variability.Resolution enhancement for immersion is being achieved through both an increasing degree of multiple patterning and by leveraging the unique properties of novel materials such as in directed self-assembly (DSA). In DSA, sub-resolution patterns are created by the micro-phase separation of specially engineered polymer chains called block copolymers, which are directed in specific orientations by lithographically generated guide patterns. Minimising the impact of variability is done by first developing techniques to measure, optimise and control the patterning process window, as then by the employment of clever patterning tricks to neutralise any remaining variability. Examples of such tricks, or the co-optimisation of multiple unit process steps (litho, etch, deposition, etc.), are the variety of self-aligned integration schemes that are being developed.
But, of course, all eyes are on EUV lithography as it appears a necessity for the continuation of cost-effective physical scaling. Research institutes are helping industry to understand when and how to insert this technology. Certainly the performance of the tool - or more specifically the ramp in stable power of the light source - is a prerequisite for EUV insertion. ASML has realised some very promising results in this field this past year. However, there is a whole ecosystem involved with EUV lithography, such as materials, masks, understanding the imaging fundamentals , and development of computational techniques – and it is that ecosystem that imec is focused on.
EUV resolution is currently material-limited, as a result imec has set up a strong program to work with materials suppliers to develop novel photoresist platforms, and now serves as the centerpiece for such work in the industry. There is also work ongoing on various aspects of the photomask. Our strong collaboration with the Japanese consortium EIDEC is aimed at understanding the capabilities of new mask inspection systems and to link this with printing performance. Additionally, imec launched a very successful pellicle program in 2015, where the pellicle is a very thin free-standing film designed to protect the mask surface from particles. We are now exploring various novel films and have set up a testing facility for characterisation of samples developed around the world. Finally, various efforts are focused on understanding the complex interactions between the light source, mask, lens system, and photoresist and to employ computational techniques to optimise the resulting pattern.
With all these technical issues in mind, it becomes clear that collaboration is key to continue the path of lithography. Many parties are involved that all have to work together and contribute their piece of the puzzle. It’s imec’s role to bring all these parties together and understand how all the pieces fit together. This is done in our core CMOS program where all the main chip manufacturers, tool and material suppliers are gathered. But also the supplier hub that imec set up a few years ago, has evolved as a very important aspect of the collaboration platform. Tool and material suppliers can evaluate their products in an early phase of technology development and get valuable feedback on how to further optimise them. In the collaboration process, they bring in not only state-of-the-art tools and materials, but also valuable insights and experiences that help fuel imec’s developments and thus strengthen the core CMOS program.
In 2015, various supplier interactions ramped up and have definitely started to pay off.
Greg McIntyre is director of the advanced patterning department at imec and is responsible for areas related to advanced lithography equipment and process development, patterning process control, computational lithography, and exploratory patterning materials.
