Implementation of block copolymer based directed self-assembly for advanced lithography.

Optical lithography technology has been one of the key enablers for Moore’s Law for over four decades, allowing semiconductor devices to shrink down by approximately a factor of two every two years. This has brought astounding benefits to the industry, as transistors become cheaper, more powerful and faster as they grow smaller. However, current technology, 193 nm immersion lithography, has reached its fundamental resolution limit and, as such, manufacturers have resorted to expensive multiple patterning processes. This economic reality has spurred interest in alternative patterning technologies. Among these, directed self-assembly of block copolymers stands out due to its ability to generate well-controlled sub-20 nm features. Block copolymers are unique soft materials that can self-assemble through microphase separation into various periodic nanostructures such as lamellae, spheres and cylinders, driven by the incompatibility between the different blocks. Of these morphologies, the lamellar and cylindrical phases are of high interest for the lithographic community. Specifically, the cylindrical features, directed by a topographic pre-pattern through a grapho-epitaxy process, are suitable for patterning contacts and vias in integrated circuits. Before directed self-assembly can be employed as a via patterning approach in integrated circuit manufacturing, it needs to be demonstrated that these self-assembled patterns can be generated with a pattern quality adequate for device manufacturing. This dissertation focuses on an experimental investigation of the parameters that need to be controlled to achieve this. First, it is demonstrated that control over the interfacial energy between the pre-pattern template and the different blocks of the copolymer is required to properly direct the assembly. Several techniques for surface modification of the pre-pattern were developed for this purpose. Next, the influence of template fill, which is related to the circuit design, is addressed. Subsequently, it is shown that the pattern quality of specific features can be significantly improved by adding homopolymer of the right molecular weight to the block copolymer. Finally, the patterning of a representative 7 nm node logic via layout is demonstrated.