|
The development of next-generation exposure equipment in the field of lithography is now underway as the demand
increases for faster and more highly integrated semiconductor devices. At the same time, proposals are being made for
lithography processes that can achieve finer pattern dimensions while using existing state-of-the-art ArF exposure
equipment.
Immersion exposure technology can use a high-refraction lens by filling the space between the exposed substrate and the
projection lens of the exposure equipment with a liquid having a high refractive index. At present, the development of
193-nm immersion exposure technology is proceeding at a rapid pace and approaching the realm of mass production.
However, the immersion of resist film in de-ionized water in 193-nm immersion exposure technology raises several
concerns, the most worrisome being the penetration of moisture into the resist film, the leaching of resist components
into the water, and the formation of residual moisture affecting post-processing. To mitigate the effects of directly
immersing resist in de-ionized water, the adoption of a top coat is considered to be beneficial, but the possibility is high
that the same concerns will rise even with a top coat.
It has been reported that immersion-specific defects in 193-nm immersion exposure lithography include "slimming,"
"large bridge," "swell," "micro-bridge," and "line pitch expansion," while defects generated by dry lithography can be
summarized as "residue," "substrate induced," "discoloration," and "pattern collapse." Nevertheless, there are still many
unexplained areas on the adverse effects of water seeping into a top coat or resist. It is vitally important that the
mechanisms behind this water penetration be understood to reduce the occurrence of these immersion-induced defects.
In this paper, we use top coats and resist materials used in immersion lithography to analyze the penetration and
diffusion of water. It is found that the water-blocking performance of protective-film materials used in immersion
lithography may not be sufficient at the molecular level. We discuss the diffusion of water in a top coat and its effects.
|
