In lithography, a pattern is imaged onto a wafer covered with a photosensitive layer. The incident light changes the material’s chemical properties and so effectively writes a pattern in the resist. This is used in further processing steps.
EUV photons have very high energies. When these photons hit the resist molecules, they create multiple charged particles. These in turn decay into other particles. All of these particles can engage in chemical reactions within the resist, which creates the required change in the material’s properties. Some of the problems with current resists are poor sensitivity and the so-called line edge roughness: the edges of the lines written are too wobbly, leading to an undesired variation in line width. A fundamental understanding of the interaction between resist and EUV light should lead to solutions for these problems.
ARCNL has considerable expertise in photochemistry and time-resolved spectroscopy and uses this to study what happens inside the photoresist at different timescales. Which charged particles and molecules are formed? What are their concentrations at any given time? How do they move through the layer? What chemical reactions take place? And what aspects of the resist should be changed to optimise the final image?