As a promising way to scale down semiconductor devices, 193-nm immersion exposure lithography is being developed
at a rapid pace and is nearing application to mass production. This technology allows the design of projection lens with
higher numerical aperture (NA) by filling the space between the projection lens and the silicon wafer with a liquid
(de-ionized water). However, direct contact between the resist film and water during exposure creates a number of
process risks. There are still many unresolved issues and many problems to be solved concerning defects that arise in
193-nm immersion lithography.
The use of de-ionized water during the exposure process in 193-nm immersion lithography can lead to a variety of
problems. For example, the trapping of microscopic air bubbles can degrade resolution, and residual water droplets left
on the wafer surface after immersion exposure can affect resolution in the regions under those droplets. It has also been
reported that the immersion of resist film in de-ionized water during exposure can cause moisture to penetrate the resist
film and dissolve resist components, and that immersion can affect critical dimensions as well as generate defects.
The use of a top coat is viewed as one possible way to prevent adverse effects from the immersion of resist in water, but
it has been reported that the same problems may occur even with a top coat and that additional problems may be
generated, such as the creation of development residues due to the mixing of top coat and resist. To make 193-nm
immersion lithography technology practical for mass production, it is essential that the above defect problems be solved.
Importance must be attached to understanding the conditions that give rise to residual defects and their transference in
the steps between lithography and the etching/cleaning processes.
In this paper, we use 193-nm immersion lithography equipment to examine the transference (traceability) of defects that
appear in actual device manufacturing. It will be shown that defect transfer to the etching process can be significantly
reduced by the appropriate use of defect-reduction techniques.