Generation mechanism of surface roughness in resists - Free volume effect on surface roughness

To clarify the origin of the roughness generated on resist surface, we investigated the effects of molecular weight of resist, exposure dose, and developer molecular size on surface roughness by atomic force microscope observations of surface morphology of electron-beam exposed surface after development. Surface roughness is strongly influenced by the polymer aggregates appearing on the exposed resist surface after exposure and development. As the molecular weight becomes higher, surface roughness becomes larger because the aggregate size increases. On the other hand, at higher exposure doses, surface roughness gradually decreases because the number of aggregates on the surface decreases. This indicates that appearance of the aggregates due to aggregate extraction development is suppressed at higher doses. As the developer molecules become smaller, fewer aggregates appear on the surface and the surface roughness becomes small. This also indicates that the aggregate extraction development can be suppressed with small developer molecules. These results can be explained by considering the relationship between the size of free volume holes in the aggregates and the developer molecular size.