Materials characterization for multilayer electron beam lithography
Successful implementation of multilayer lithography to fabricate three-dimensional structures involves depositing multiple layers of radiation sensitive materials with necessary dose and tone contrast. Resists are radiation sensitive materials (usually polymers dissolved in solvents) used in micro- and nanolithography. Currently, they are deposited on wafers using the spin coating process. Solvent incompatibilities between different resist systems can cause unwanted dissolution and intermixing of adjacent layers. Here, the authors show the use of Hansen solubility parameters to identify compatible solvents and developers. Multiple solubility models have been proposed, and Hansen solubility parameters are the most widely accepted. The Hansen solubility parameters are used to form a three dimensional space in which polymers and their solubility in different solvents can be represented as spheres. This representation makes it convenient to select compatible solvents and developers. It can also provide necessary guidance to synthesize compatible polymer systems for enhancing the lithographic technique.