193nm immersion Lithography will be installed at 45nm and beyond. For severe CD control, BARC (Bottom Antireflective
Coating) has been used and this material must be used for immersion lithography.
So far, we have developed several BARCs with various advantages (fast etch rate, broad resist compatibility, high
adhesion, conformal...etc). Especially in an immersion process, development of BARC has to satisfy for the optical
control and defectivity.
The reflectivity control at Hyper NA is not same as the lower NA, because optical pass length in the BARC is not the
same between low NA and High NA. In order to achieve enough etch selectivity to the substrate, hard mask materials are
necessary. These under layers have absorption at 193nm. As a result of simulation, target optical parameters of next
BARC should be low k value (k = ~0.25) for multi BARC stack.
On the other hand, the defect issue must be decreased in the immersion process. However, the generation of many
kinds of defects is suspected in the immersion process (water mark, blob defect, sublimation defect...etc). Regarding the
BARC, there are also several specific defects in this process. Especially, after edge bead rinse, film peeling at edge area
is one of the concerns. We researched the root cause of edge peeling and a solution for this defect.
In this paper, we will discuss the detail of our BARC approach for litho performance, optical parameter, leaching,
sublimation, edge peel defects and etch selectivity, and introduce new BARC for 193nm immersion lithography.